Review of literature quantifying ecological
responses to low flows
R. Rolls1, N. Marsh2 and F. Sheldon1
1. Australian Rivers Institute, Griffith University
2. Yorb Pty Ltd
Low flows report series – June 2012
Low flows report series
This paper is part of a series of works commissioned by the National Water Commission on key water
issues. This work was undertaken by the Australian Rivers Institute, Griffith University and Yorb Pty
Ltd on behalf of the National Water Commission.
NATIONAL WATER COMMISSION — Low flows report series
iii
© Commonwealth of Australia 2012
This work is copyright.
Apart from any use as permitted under the Copyright Act 1968, no part may be reproduced by any
process without prior written permission.
Requests and enquiries concerning reproduction and rights should be addressed to the
Communications Director, National Water Commission, 95 Northbourne Avenue, Canberra ACT 2600
or email bookshop@nwc.gov.au.
Online/print: ISBN: 978-1-921853-82-1
Published by the National Water Commission
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Tel: 02 6102 6000
Email: enquiries@nwc.gov.au
Date of publication: June 2012
An appropriate citation for this report is:
Rolls R, Marsh N and Sheldon F 2012, Review of literature quantifying ecological responses to low
flows, National Water Commission, Canberra.
Disclaimer
This paper is presented by the National Water Commission and does not necessarily reflect the views
or opinions of the Commission.
NATIONAL WATER COMMISSION — Low flows report series
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Contents
Contents ................................................................................................................................................ v
Executive summary ............................................................................................................................. vii
Report context ...................................................................................................................................... ix
1.
Introduction ................................................................................................................................ 1
1.1.
Introductory concepts ..................................................................................................... 1
2.
Quantifying the effect of low flow on stream ecology ................................................................ 6
2.1.
Implications of multiple environmental stressors associated with low flows ................ 12
2.2.
Quantifying recovery from low flow .............................................................................. 12
3.
Key principles and conceptual models of low-flow processes ................................................. 15
3.1.
Low-low principles ........................................................................................................ 15
3.2.
Temporal considerations of low-flow impact and recovery .......................................... 20
4.
Informing case study analyses ................................................................................................ 26
4.1.
Datasets available ........................................................................................................ 26
4.2.
Preferred method – traits approach.............................................................................. 28
5.
Conclusions ............................................................................................................................. 31
Shortened forms ................................................................................................................................... 0
Glossary ............................................................................................................................................... 1
References ........................................................................................................................................... 5
Tables
Table 1: Summary of selected literature to elucidate key ecological responses to different
low-flow scenarios (a more detailed account of ecological responses to low flow and
drought is given by Lake (2011) .................................................................................................... 8
Table 2: Summary of examples of ecological recovery trajectories following low-flow
conditions ..................................................................................................................................... 14
Table 3: Summary of known biological traits associated with high and low resistance and
resilience to low flows. Sources: Bonada et al. 2007; Díaz et al. 2008; Haxton &
Finlay 2008; Rose et al. 2008; Finn et al. 2009; Brooks et al. 2011; Walters 2011. .................... 29
Figures
Figure S1: Context of reports produced for the National Water Commission's Low Flow
Ecological Response and Recovery Project. The circles represent the location of
individual case studies and the size of each circle represents the spatial extent of
each case study. ........................................................................................................................... ix
Figure 1: Assessing impact and recovery is highly dependent on the sensitivity of the
taxa and their response to declining aquatic habitat and water quality: (a) represents
a succession of processes after the onset of low flow in a perennial stream, whereas
(b) represents the same processes in a naturally intermittent stream. ......................................... 4
Figure 2: Conceptual representation of temporal scale of hydrology from individual flow
events, or pulses, to longer flow regimes (modified from Walker et al. 1995) .............................. 5
Figure 3: Conceptual model of fish response to a cease-to-flow event ............................................. 11
Figure 4: Four principles outline the broad mechanistic links between low flow and
processes and patterns in riverine ecosystems. These links do not operate in
isolation, and many ecological pathways that are affected by low flows are likely to
occur simultaneously, potentially resulting in similar or synergistic and complex
consequences ............................................................................................................................. 16
Figure 5: Expected response based on habitat changes. Dashed lines along the temporal
axis indicate timelines for inducing ecological response to low flows vary significantly
(based on regime, antecedent conditions and other environmental stressor effects). ............... 17
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Acknowledgements
We thank the National Water Commission for funding and support and the helpful comments of
reviewers. We would also like to thank the project advisory group, jurisdictional agency staff and
review workshop participants for their input and useful comments throughout the project.
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Executive summary
This report summarises literature quantifying the ecological response to, and recovery from, low-flow
events in streams and rivers. The review focuses on the low-flow responses of macroinvertebrates
and fish, and has particularly sought to identify potential ecological indicators and thresholds useful
for low-flow planning and management. It provides a context for related National Water Commission
low flows reports, and especially informs a series of case studies attempting to develop quantitative
relationships between low flow and ecosystem responses (Marsh et al. 2012), and a monitoring
approach for low flows (Sheldon et al. 2012).
Research interest in the effects of natural low-flow events, drought and water diversion or extraction,
on aquatic ecology is predominantly driven by a need to understand the ecological consequences of
reduced water due to human demands and/or to support water-dependent biodiversity in the context
of climate variation. Most literature examines patterns in stream ecosystem structure and function
over cycles of low-flow events or by comparing the ecology of streams with contrasting flow regimes.
Such studies indicate that low flows initially increase density and diversity of biota due to habitat
contraction, followed by a progressive decline in the density or presence of biota unable to persist in
the progressively harsher conditions. Over time, this results in reduced richness and biodiversity of
stream biota as species become locally extinct. Recently, manipulative experimental water extraction
studies have provided further information of the effects of low flows. In particular, such experimental
studies increase confidence in identifying the duration and frequency of particular low-flow events
required before changes in ecosystem structure and function are detected.
It is difficult or impossible to use the available literature to identify thresholds of low-flow stress (e.g. a
duration of time below a particular flow magnitude before an impact) that can be generalised across
geographic regions such as Australia. This is due to differences in climate, land use and both
antecedent flow regime and water quality conditions. Research indicates that the ecological effect of
reduced flow depends on the interaction with the antecedent flow history and the antecedent water
quality conditions that are driven by climate, flow regime and the surrounding landscape. These
details, particularly details of antecedent flow conditions, are infrequently included in the assessment
of ecological effects of low flows, which further hinders the ability to produce quantitative relationships
with enough certainty to allow extrapolation to rivers with little or no information on their ecology.
Based on Australian and international literature, we present four key principles linking low-flow
hydrology and ecological responses in surface water ecosystems. These principles focus on the
mechanistic drivers of change in ecosystem structure and function due to reduced stream discharge.
Specifically, low flows control the extent and arrangement of physical aquatic habitat, therefore
influencing ecological patterns and processes (e.g. the composition and diversity of biota, along with
trophic structure and carrying capacity) (principle 1). Secondly, low flows influence physical and
biological conditions in remaining aquatic habitat, which in turn drive changes in ecological patterns
and processes (e.g. the distribution and recruitment of biota) (principle 2). Thirdly, low flows affect the
sources and exchange of energy in riverine ecosystems, affecting ecosystem production and biotic
composition (principle 3). Finally, low flow restricts dispersal, increasing the importance of refugia and
affecting multi-scale ecological patterns and processes (principle 4). These principles (along with
accompanying temporal considerations) can be used to inform water planning and management, as
well as guide ongoing research interest into the ecological consequences of low flows – facilitating the
development of a cause/effect framework. We note that addressing low-flow impact is potentially
more straightforward than assessing recovery from low flows, which needs to include concepts of
resistance and resilience.
This literature review shows that biological traits are increasingly being used to improve knowledge of
the ecological consequences of low flow, by way of predicting specific taxa, or groups of taxa, that are
either vulnerable or resistant to changes in low-flow hydrology. For example, biota that are able to
rapidly disperse appear more resistant to reduced flow when compared with poor dispersers because
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they are able to avoid predators and declining habitat quality and move to more suitable habitats.
However, poor knowledge of the basic ecology and biology of many groups of biota in large regions of
Australia, combined with high variation in traits among taxa that are taxonomically similar, is likely to
hinder the broadscale assessment of ecological responses to low flows. A national traits database
may help in this regard.
This report concludes by describing an approach and data available for analysis via case study
analyses. For a more detailed understanding of low-flow impacts and recovery, both case studies and
broader meta-analysis are necessary since increasing pressure for water, climate variability and other
stressors simultaneously affect stream ecosystems. A thorough literature review focusing on drought
can be found in Lake (2011).
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Report context
This report is part of a larger series of reports produced for the National Water Commission’s Low
Flow Ecological Response and Recovery Project (Figure S1). It reviews selected Australian and
international literature where attempts have been made to quantify the ecological effects of low flows.
Guidance on ecological response and hydrological modelling for low -flow
water planning
Low-flow hydrological classification of Australia
Review of literature quantifying ecological responses to low flows
Early warning, compliance and diagnostic monitoring of ecological
responses to low flows
Synthesis of case studies quantifying ecological responses to low flows
Figure S1: Context of reports produced for the Low Flow Ecological Response and Recovery Project.
Each circle represents the location of individual case studies and the size of each circle represents
the spatial extent of each case study.
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1. Introduction
This report reviews scientific literature quantifying ecological responses to low flows (both natural and
experimental studies) to determine whether detectable ecological effects and thresholds for low-flow
events are likely to exist, and the types of ecological indicators used to date. It identifies the response
and recovery of ecosystems following low-flow events and the potential confounding factors
influencing responses to low flows, focusing on macroinvertebrates and fish. The review presents
conceptual models of response to low-flow conditions in the form of four principles and provides an
analysis approach for 11 case studies investigating the relationships between patterns in biological
data and a range of low-flow characteristics (Marsh et al. 2012). It also provides a basis for the
monitoring guidelines report (Sheldon et al. 2011). The review can be used to inform water planning
and management and an associated report, “Guidance on ecological responses and hydrological
modelling for low-flow water planning” (Marsh et al. 2012b), places the key points in this report into a
water planning framework.
The review is organised into three parts. The first presents introductory concepts for considering the
effects of low flow on aquatic biota and ecological processes, such as the difference between impact
and recovery, and resilience. The second part presents the bulk of the literature proper; it identifies
general response principles and then discusses temporal complexities. The last section of the report
translates the review of literature into an analysis approach, which has been used to inform the 11
case studies (see Marsh et al. 2012).
1.1. Introductory concepts
1.1.1. Why are low flows important?
The natural flow regime is the fundamental driver of the structural and functional attributes of surface
water ecosystems worldwide (Poff et al. 1997). Specific flow events, such as floods, droughts and
flow pulses, are key hydrological disturbances that influence ecological processes supporting aquatic
and terrestrial biota at population, species and assemblage levels (Resh et al. 1988; Lake 2000). The
abundance and diversity of aquatic biota in rivers and streams are influenced indirectly by the spatial
and temporal effects of flow regime on habitat structure and availability, and directly through the
influence of flow regime on life-history strategies and the establishment of alien species. Therefore,
impacts on the natural flow regime threaten aquatic biodiversity (Bunn & Arthington 2002). In the
context of the entire flow regime, impacts on the low-flow regime (e.g. drought or extended periods of
low flow as a result of water resource development) have significant effects on aquatic ecosystems,
including the multi-scale persistence of biota (e.g. Lake 2003) from species persistence at an
individual site to broader regional persistence, or to localised extinction.
1.1.2. Impact versus recovery
In considering a low-flow event and how water resource management may affect the ecological
outcomes, there are two related elements. Firstly, we need the ability to predict the likely ecological
effect of the low-flow event with particular attention to any critical thresholds that may limit recovery.
Secondly, we need an ability to predict the recovery trajectory (if any) from the low-flow event, which
combines both the severity of the event (described as the ecological condition at the start of the
recovery period) with the prevailing abiotic conditions for the recovery period within the context of the
resilience of the ecosystem or biota. For example, in a perennial stream the general pattern following
the onset of low flows is an initial reduction in available aquatic habitat as velocity decreases and
water levels decline: this is followed by declining water quality. As water quality declines and the lowflow event continues there will be a gradual shift in the assemblage composition of a range of biota
from taxa that are sensitive to changes in their environment (habitat availability, flow velocity or water
quality), such as macroinvertebrates that prefer flowing conditions (rheophiles), to those more tolerant
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of a broad range of conditions (Figure 1a). If low flows continue there will be an increasing loss of
aquatic habitat and continued decline in water quality, along with a shift in the assemblage to one
dominated by tolerant generalists. These community shifts are equally applicable to algal biofilms as
well as macroinvertebrates, fish and even waterbirds. Following the return of flow to the system there
will be a process of ‘recovery’ where habitat availability will increase, water quality will return to more
suitable conditions and eventually the more ‘sensitive’ taxa will return to the community. A similar
process can be seen in a hypothetical naturally intermittent site (Figure 1b). In this second example,
the assemblage will be naturally dominated by tolerant and generalist taxa, with those taxa that have
more specific habitat requirements (e.g. rheophiles) potentially making up smaller percentages of the
assemblage abundance. Therefore, this conceptual succession must always be considered in relation
to the spatial context of the site (whether the stream is naturally perennial or naturally ephemeral), the
length of the low-flow event and the recent low-flow history (Figure 2). Through this project, we are
looking to develop or describe methods that quantitatively measure both response and recovery
potential to inform water resource planning. Ideas relating to this conceptual understanding of impact
and recovery from low flows will be explored further in this review.
1.1.3. Thresholds, resistance and resilience
Concepts of ecological thresholds, lag effects, resilience and resistance are applicable to identifying
the ecological effects of low flows. Resistance (capacity to withstand a disturbance) and resilience
(ability to recover from a disturbance) (Holling 1973; Lake 2000) are relevant to low flows as many
biota can either persist during low-flow disturbances or recover rapidly afterwards. Ecological
thresholds are particularly useful for determining how ‘stressed’ an ecosystem can be before sharp
changes are detected associated with relatively small changes in an environmental driver (Huggett
2005; Groffman et al. 2006; Dodds et al. 2010). Lag effects are also important to recognise. For some
biota (e.g. some aquatic macroinvertebrates), responses to a low-flow disturbance may only be
evident after the disturbance has ceased and the loss of recruitment may be detected after flows
return (e.g. Boulton 2003). Multiple analytical approaches exist to identify ecological thresholds in
response to disturbances (e.g. Andersen et al. 2009; Dodds et al. 2010), but few studies have tested
whether the concept of ecological thresholds holds in the context of low-flow stress.
1.1.4. Indicators of low flow
Indicators that highlight a change in ecosystem structure or function as the result of a low-flow event
and in response to flow recovery are necessary. This is to understand the impacts of low-flow
disturbances on aquatic and riparian ecosystems and to assess the ecological responses to the
management actions evoked to reduce or negate the negative effects of low flows. Indicators
illustrating the effects of low flows vary in their sensitivity and temporal response (e.g. Dewson et al.
2007a; Death et al. 2009; Benejam et al. 2010) because mechanisms differ in the time taken to
produce an ecological change that can be detected over naturally high background variability. Two
key aspects when defining ecological indicators are: firstly, what each indicator demonstrates
(Lindenmayer & Likens 2010) and, secondly, that multiple indicators are necessary to identify the
response and recovery of disturbances (Kelly & Harwell 1990). As low flows affect aquatic
ecosystems via multiple interacting mechanisms, a suite of ecological indicators is therefore
necessary to obtain a complete perspective of the impacts and recovery of low flows.
Ecological indicators can be grouped into ‘early warning’, ‘compliance’ and ‘diagnostic’ indicators
(Cairns & McCormick 1992 cited in Boulton 1999; Dale & Beyeler 2001). Early-warning indicators
highlight potential changes in ecosystem structure and function associated with a low-flow impact;
compliance indicators reveal changes from acceptable or guideline limits; and diagnostic indicators
identify the cause of changes in ecosystem condition. For example, in the context of low flows,
increases in the density of riffle macroinvertebrates due to habitat contraction could be an early
warning indicator of the impending loss of macroinvertebrate diversity (which would perhaps be a
compliance indicator). Increased diel variation in temperature and dissolved oxygen could be a
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potential diagnostic indicator of the loss of macroinvertebrate taxa sensitive to altered water quality.
Identification and validation of early warning, compliance and diagnostic indicators are necessary to
determine when aquatic ecosystems are at risk of future change and establish when an ecosystem
has either permanently shifted to a new state or has recovered to the conditions preceding low flow.
More information is contained in Early warning, compliance and diagnostic monitoring of ecological
responses to low flows (Sheldon et al. 2012).
1.1.5. Generalising low-flow effects
Classification of river flow regimes across large spatial ranges (e.g. entire continents, Kennard et al.
2010) has the potential to help management decisions by illustrating broadscale variations in flow
regime. It also helps inform to what extent limited ecological information can be applied across rivers
with varying flow regimes. As it is often logistically unfeasible to gather ecological data over large
spatial scales at the temporal frequency necessary to determine thresholds of ecosystem response to
low flows, it is necessary to determine how consistent the ecological responses to low flows among
regions with similar low-flow regimes are. This is important because although many regions around
the globe are likely to experience considerable changes to low-flow hydrology caused by human
demands for water, land use changes and climate change, we have little or no information to identify
the potential impacts on aquatic ecosystems and to inform management decisions. Mackay et al.
(2012) have developed a low-flow classification of Australia as part of this low flows report series.
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High
Diagnostic
indicators
Low
Relative assemblage proportion of tolerant & generalist taxa
High
Relative assemblage
proportion of rheophilic taxa
Low
High
Low
Good
Compliance
and/or
Diagnostic
indicators
Water quality
Poor
High
Low
Available aquatic habitat
High
Low
Velocity
Discharge
Early
warning
indicator
Relative assemblage proportion of
water quality sensitive taxa
Time
(a)
High
Relative assemblage proportion of tolerant & generalist taxa
Low
Diagnostic
indicators
High
Low
Relative assemblage proportion of rheophilictaxa
High
Relative assemblage proportion of water quality sensitive taxa
Low
Good
Compliance
and/or
Diagnostic
indicators
Water quality
Poor
High
Low
Available aquatic habitat
High
Low
Velocity
Discharge
Early
warning
indicator
Time
(b)
Figure 1: Assessing impact and recovery is highly dependent on the sensitivity of the taxa and their
response to declining aquatic habitat and water quality: (a) represents a succession of processes
after the onset of low flow in a perennial stream, whereas (b) represents the same processes in a
naturally intermittent stream.
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Flow
Flow
Flow
Hours or Days
Flood Pulse
Months or Years
Flow History
Years
Flow Regime
Figure 2: Conceptual representation of temporal scale of hydrology from individual flow events, or
pulses, to longer flow regimes (modified from Walker et al. 1995)
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2. Quantifying the effect of low flow on
stream ecology
The increasing frequency of drought events, particularly in temperate regions, has stimulated
research into the ecological effects of low flows and droughts (Table 1; Lake 2011). This research is
generally focused on examining the effects of droughts and stream-channel drying on patterns in the
composition of aquatic biota (predominantly macroinvertebrates and fish); physical-chemical water
quality parameters and the structure and transport of energy in stream foodwebs (comparing
perennial and intermittently flowing rivers); and assessing the ecological effects of water extraction.
Results are used to ascertain the ecological consequences of increased frequencies of drought, of
changing flow regimes from perennial to intermittent flow, and of increasing water extraction to
support human demands – particularly in mid-latitude regions that are likely to experience greater
frequencies and durations of low-flow events due to climate change (Boulton & Lake 2008; Table 1).
Table 1 summarises key findings from this research. While the experimental designs and hypotheses
vary across studies, there is a consistent finding that as the flow permanence decreases, so too does
the presence of taxa with limited tolerance to high temperatures and poor water quality, which
generally translates into a decline in diversity. While Table 1 summarises the key findings of selected
literature to provide a context for the case studies, it is not a complete meta-analysis of the literature
on low flows or studies that have examined impacts of low flows and drought. Such a task would be
an interesting and potentially useful exercise, and Lake (2011) contains a much more detailed
analysis of this topic.
Patterns in the distribution and composition of benthic macroinvertebrates and fish assemblages are
predominantly used to assess the ecological consequences of low flows. Far fewer studies examine
the consequences of changes in the flow regime on amphibians, birds and ecosystem processes
(Poff & Zimmerman 2010). However, there are numerous studies exploring the impacts of flow
change on aquatic plants and algae. Aquatic algae, particularly diatoms, are known as good
indicators of water quality (see McCormick & Cairns 1994; Biggs 1996; Biggs & Smith 2002; Bella et
al. 2007; Ponader et al. 2007); and, as water quality is known to decline and change with the onset of
reduced flow, diatoms are likely a very useful indicator of low-flow effect. As low flows reflect changes
in both water level and velocity, benthic algal communities have been found to respond significantly to
both velocity (Peterson & Stevenson 1992; Biggs & Stockseth 1996; Uehlinger et al. 1996; Jowett &
Biggs 1997; Saravia et al. 1998; Matthaei et al. 2003; Ryder 2006; Villeneuve et al. 2010) and water
level variations (Burns & Walker 2000; Robertson et al. 2001; Batten et al. 2003; Ryder 2004;
Villeneuve et al. 2011), with desiccated biofilm able to respond rapidly to the return of flow in
intermittent streams (Robson 2000; Robson et al. 2004). In lowland rivers, or places in intermittent
streams where remnant or refugial pools form, phytoplanktonic algal communities have been shown
to respond to longitudinal connection (Istvanovics et al. 2010) and water depth and velocity (Leland
2003), along with aspects of water quality (Rudek et al. 1991; Schemel et al. 2004). In dryland rivers
(that spend long periods of time essentially under a low flow), where the river is confined to a series of
disconnected waterholes, benthic algae have been shown to be the primary source of carbon
dominating the foodweb (Bunn et al. 2003; Bunn et al. 2006) and driving productivity (Fellows et al.
2009). Aquatic macrophytes are also known to be influenced by reduced flow conditions: different life
stages are often impacted differentially (Franklin et al. 2008), with frequency, seasonality, duration of
inundation and drying, water depth, flow velocity, and flow variability all shown to influence
macrophytes across different life stages (Roberts & Marston 2000). Drought was shown to lead to the
decline in macrophyte cover due to increased silting in the United Kingdom (Wright & Berrie 1987),
whereas macrophyte assemblages in temperate Australian rivers showed little response to water
abstraction of up to 20 per cent (Chessman et al. 2008). Like macroinvertebrates and fish, the
composition of aquatic plants such as benthic algal assemblages become increasingly dominated by
desiccation-resistant taxa as the natural frequency and duration of reduced flows increases (e.g.
Ledger et al. 2008).
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During flow reductions, macroinvertebrate assemblages typically increase in taxa richness and
density due to habitat contraction. For example, benthic macroinvertebrates increased in density
during both natural stream drying in Sapin, Spain (Acuña et al. 2005) and experimental flow
diversions in New Zealand (Dewson et al. 2007b). Macroinvertebrate taxa that favour habitats with
flowing water and are intolerant of the poorer water quality conditions typically associated with low
flows and droughts usually become uncommon or extinct with an increasing duration of low flows and
aquatic habitat disconnection. In streams in Victoria, Australia, assemblages of benthic
macroinvertebrates in riffle habitats shifted from a dominance by rheophilic (‘flow-loving’) taxa
sensitive to deteriorating water quality to an assemblage dominated by tolerant lentic (standing water)
taxa during drought (Rose et al. 2008). During low flows, macroinvertebrate assemblages become
increasingly dominated by predators and algal scrapers, with declines in the proportions of
detritivorous collector-gatherers and filter-feeders (e.g. Miller et al. 2007). With increasing duration of
low flows, macroinvertebrates may move to the hyporheic zone (the saturated sediments below the
streambed) which may function as a source of aquatic recolonists following the return of higher flows
(e.g. Wood et al. 2010); or in streams where hyporheic regions are limited or absent, they must find
other refuges (e.g. moist zones under rocks or aquatic vegetation) (Boulton & Lake 1992b; Boulton
2003) or disperse to other more suitable habitats (Sheldon et al. 2010).
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Table 1: Summary of selected literature to elucidate key ecological responses to different low-flow scenarios (a more detailed account of ecological responses
to low flow and drought is given by Lake (2011)
Drought, stream drying
Natural flow permanence
gradient
Experimental water extraction or
diversion
Actual water extraction or
diversion
Regions
Australia (Victoria), United
Kingdom, New Zealand, Spain,
United States
Zimbabwe, New Zealand,
Spain, United States, United
Kingdom
New Zealand, Australia,
Canada, United Kingdom,
Sweden
Australia (NSW), United States
Time span of studies
Single sample – 22 years
Single sample – 2.5 years
Three days – 2 years
Single sample – 6 years
Increased densities, diversity
and dispersal (drift) during initial
habitat contraction
Reduced abundances of
macroinvertebrates in refuge
pools, particularly with fish
present
Increased densities, diversity
and dispersal (drift) during initial
habitat contraction
Taxa with preference for flowing
habitats and taxa with limited
swimming abilities show
greatest effect of extraction
Loss of sensitive taxa
susceptible to desiccation
leading to decline in species
richness, density and biomass
Reduced taxa richness in
ephemeral reaches when
compared with intermittently or
perennially flowing reaches
Loss of sensitive taxa such as
Ephemeroptera, Plecoptera,
Trichoptera (EPT) families with
increasing extraction
Prolonged abstraction results in
low-flow assemblage dominated
by tolerant species
Increased dominance of lowflow-tolerant taxa with increased
duration of reduced flow
Desiccation-resistant and highly
mobile taxa dominate sites with
increasing duration of low flow
Reduced taxa richness,
abundance and biomass with
increasing duration of extraction
Altered trophic organisation with
increasing dominance of
predators, scrapers
Reduced dispersal (drift)
Increased proportion of
predatory species
Interaction between water
quality and flow regime
indicates biota in pristine
reaches less resistant and
resilient to low flows
Magnitude of assemblage
change depends on magnitude
of water extracted
Increased use of hyporheic
refuges with increasing low-flow
duration and magnitude
Intermittent sites characterised
by high diversity but low
abundance, smaller-bodied taxa
Increased drift dispersal during
major change to flow (e.g. 75%
extraction)
Reduced drift distance
Indicator groups
Macroinvertebrates
Increasing proportion and
density of predators, reduced
proportion of collectorgatherers, filterers, scrapers
Fish
Distribution mediated by
temperature and drought
resistance
Low fish density at intermittent
sites when compared with
perennial sites
Increased movement and
dispersal during low flows
Negative relationship between
increasing water extraction and
proportion of fluvial species
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Drought, stream drying
Natural flow permanence
gradient
Experimental water extraction or
diversion
Actual water extraction or
diversion
Regions
Australia (Victoria), United
Kingdom, New Zealand, Spain,
United States
Zimbabwe, New Zealand,
Spain, United States, United
Kingdom
New Zealand, Australia,
Canada, United Kingdom,
Sweden
Australia (NSW), United States
Time span of studies
Single sample – 22 years
Single sample – 2.5 years
Three days – 2 years
Single sample – 6 years
Increased mortality and poorer
condition of drought-intolerant
taxa with increasing duration of
low flow
Increased proportion of habitatgeneralist taxa in intermittent or
ephemeral sites
Increased mortality with
decreasing flow
Increasing proportion of habitatgeneralist taxa in flow-extracted
sites
Reduced body size and
condition
Reduced total densities at flowextracted sites
Altered composition between
dry and wet years depending on
low-flow tolerance
Increased total abundances of
fish with increasing flow
permanence
Macrophytes/periphyton
composition/plants
Decline in intolerant taxa at
flow-extracted sites
Reduced cover of macrophytes
Altered composition towards
desiccation-resistant taxa
Little effect on richness or
composition when low
proportions of water extracted
Encroachment of terrestrial
plants with increasing duration
Water quality
Significant decrease in
dissolved oxygen and increase
in conductivity and temperature
Increased diel temperature
variation
Increases in temperature,
potentially confounded by
seasonal changes
Functional indicators
(primary production,
detritus retention, detritus
breakdown, energy flow)
Reduced energy flow between
energy sources and consumers
Increased retention of course
particulate organic material
(CPOM)
Reduced energy flow between
energy sources and consumers
Increased sedimentation and
retention of detritus with
increased duration
Increasing primary production
with increasing duration of
extraction
Increasing primary production
with increasing duration of
extraction
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Drought, stream drying
Natural flow permanence
gradient
Experimental water extraction or
diversion
Actual water extraction or
diversion
Regions
Australia (Victoria), United
Kingdom, New Zealand, Spain,
United States
Zimbabwe, New Zealand,
Spain, United States, United
Kingdom
New Zealand, Australia,
Canada, United Kingdom,
Sweden
Australia (NSW), United States
Time span of studies
Single sample – 22 years
Single sample – 2.5 years
Three days – 2 years
Single sample – 6 years
Supporting examples
Reduced quality of benthic
organic matter to support
microbial activity
Reduced trophic complexity due
to loss of biota
Larimore et al. 1959
Chessman & Robinson 1987
Wright & Berrie 1987
Closs 1994
Closs & Lake 1994
Clinton et al.1996
Closs & Lake 1996
Wood & Petts 1999
Caruso 2002
Boulton 2003
Suren et al. 2003
Hakala & Hartman 2004
Wood & Armitage 2004
Acuña et al. 2005
Bonada et al. 2006
Sotiropoulos et al. 2006
Westwood et al. 2006
Bêche & Resh 2007
Davey & Kelly 2007
Magalhães et al. 2007
Rose et al. 2008
Bêche et al. 2009
Stubbington et al. 2009
Wood et al. 2010
Ylla et al. 2010
Sponseller et al. 2010
Reduced leaf breakdown with
increasing low-flow stress
No change in food chain length
over three months
Feminella et al.1996
Miller & Golladay 1996
Fowler 2004
Wood et al.2005
Datry et al. 2007
Larned et al. 2007
Chakona et al. 2008
Nhiwatiwa et al. 2009
Bonada et al. 2007
Datry et al. 2010
Arscott et al. 2010
Mas-Marti et al. 2010
Robson 2000
McKay & King 2006
Dewson et al. 2007a
Dewson et al. 2007b
Dewson et al. 2007d
Ledger et al. 2008
Walters & Post 2008
James et al. 2008b
Leberfinger et al. 2008
James et al. 2009
James & Suren 2009
Riley et al. 2009
Walters & Post 2011
Rader & Belish 1999,
Freeman & Marcinek 2006
Miller et al. 2007
Chessman et al. 2008
Finn et al. 2009
Kanno & Vokourn 2010
Benejam et al. 2010
Brooks et al. 2011
Chessman et al. 2011
NATIONAL WATER COMMISSION — Low flows report series
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Low flows generally result in greater mortality of fish, leading to reduced densities and altered
assemblage composition because of a decline in the proportion of fluvial/rheophilic species. The
spatial distribution of fish during low flows depends on species-specific tolerances to loss of habitat
and increasing harshness of environmental conditions (e.g. Closs & Lake 1996; Davey & Kelly 2007).
Species that have broad habitat requirements are generally able to resist low flows or flow cessation
for much longer than fluvial species (e.g. Mas-Marti et al. 2010). As well as reduced population
viability (e.g. densities), individual fish size and condition has been found to decline during
experimentally reduced flows. For example, fish in stream reaches where water was experimentally
extracted for three months were significantly smaller than in undiverted reaches (Walters & Post
2008). This suggests that measures of individual fish condition and size may have application for
predicting declines in population size with increasing low-flow stress (Figure 3).
Figure 3: Conceptual model of fish response to a cease-to-flow event
Most low-flow studies compare either:

ecological patterns and processes through time, such as drought assessments (e.g. Rose et al.
2008; Baptista et al. 2010)

perennial versus intermittently flowing streams, or

treatment versus control reaches when assessing the impacts of water extraction (e.g. Benejam
et al. 2010).
Based on our knowledge of the ecological impacts of low flows (Table 1), it appears there is a
relationship between the cumulative duration (i.e. including the interaction between frequency of
events and duration of individual events) and ecological response to low flows across all ecosystems.
The specific magnitude of discharge that constitutes a low-flow event depends on the natural flow
regime experienced by individual rivers. This means it is difficult to define a ‘low flow’ broadly across
geographic and climatic regions (Smahktin 2001; Dewson et al. 2007; Larned et al. 2010; Suren &
Riis 2010). Frequently ‘low flow’ is defined in hydrologic contexts based on flow exceedence
probabilities (e.g. 95 per cent exceedence flow) or deviations from baseflow (e.g. Suren & Riis 2010).
For the purpose of this project we have defined low flow as the volume (i.e. magnitude) of water that
occurs over a given frequency and duration that is responsible for a mechanistic change in the
processes and structure of aquatic ecosystems (including surface water, groundwater and estuaries),
NATIONAL WATER COMMISSION — Low flows report series
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relative to the average or median discharge for an individual river (or river reach). We emphasise that
this implies that ecologically relevant definitions of low flow will never be universally applicable given
spatial variation in river-flow regimes and also the temporal scale at which ‘low flow’ events are
quantified (sensu Biggs et al. 2005). The relationship between low-flow response and background
hydrological variation was highlighted by Finn et al. (2009) who found that the macroinvertebrate
assemblage composition patterns of two rivers in temperate Australia with differing water extraction
during low flows were significantly associated with the long-term (365-day) antecedent flow
characteristics, such as the cumulative duration of low flow variables (Finn et al. 2009). Patterns in
ecosystem structure and function among river reaches with differences in flow permanence (e.g.
perennially flowing reaches versus intermittent reaches) indicate that ecological responses are
primarily structured along a gradient of flow permanence (Table 1).
2.1. Implications of multiple environmental stressors
associated with low flows
Low flows are almost always associated with changes in other variables of importance to stream
ecosystem structure and function. Low flows, particularly in temperate regions, are associated with
higher air temperatures and, consequently, increased water temperatures (e.g. Chessman &
Robinson 1987). To effectively manage the consequences of low flows, the causal mechanisms of
low-flow ecological responses must be understood (Downes 2010). For example, many benthic
macroinvertebrates are particularly sensitive to temperature, dissolved oxygen and conductivity
(Chessman 2003): three water quality measures that are known to be affected by low flows.
Separating the impact of seasonal variations in water quality (e.g. temperature) from the effects of low
flows is difficult, meaning that without experimental evidence, the direct effect of low flows cannot be
determined with certainty.
Nutrient enrichment, sedimentation and increased pressure from higher-order consumers on prey
(e.g. macroinvertebrates) are examples of multiple stressors on aquatic ecosystems that often occur
simultaneously with low flows. These multiple stressors mean that, in many cases, accurately
predicting the effects of low flows is difficult because interactions with other variables are inconsistent
during low flows. For example, patterns in benthic macroinvertebrate assemblage composition
associated with low flows in New Zealand rivers depended on the level of nutrient enrichment among
rivers (Suren et al. 2003b). Densities of macroinvertebrates in intermittent rivers in Zimbabwe have
been reduced by the effect of predatory fish (Nhiwatiwa et al. 2009), implying that the effect of low
flows on macroinvertebrates may be caused by increased predation pressure by consumers rather
than loss of habitat, although it may have been the loss of habitat that increased predation pressure.
Also, effects of sedimentation and nutrient enrichment on benthic macroinvertebrates intensify during
reduced flow conditions (Matthaei et al. 2010). These consistent responses to low flows suggest
some underlying principles.
2.2. Quantifying recovery from low flow
Floods and drought are natural phenomena in river ecosystems. To make informed management
decisions, understanding ecosystem recovery (i.e. resilience) is necessary to determine how
modifying low-flow hydrology (e.g. altering frequency, duration, timing etc.) can threaten the long-term
resilience of aquatic ecosystems. Very few studies of the ecological impact of water extraction or
drought determine the response of biota and ecosystem processes during flow recovery (e.g. Dewson
et al. 2007a; James et al. 2008a; McKay & King 2006; Stubbington et al. 2009) – a period that is
especially critical to determining the long-term persistence of stream biota.
Ecosystem recovery trajectories generally follow the same pattern for indicators during the return of
higher-flow conditions (Table 2). Water quality rapidly returns to pre-drought conditions (e.g.
Chessman & Robinson 1987), and the quality of organic matter increases to support greater biomass
NATIONAL WATER COMMISSION — Low flows report series
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of macroinvertebrates (e.g. Ylla et al. 2010). Over time, foodwebs become more complex with
increasing richness of biota (e.g. macroinvertebrates, fish, birds). Initial recovery is usually rapid for
macrophytes, algae, macroinvertebrates and fish, particularly for species tolerant of low flow. Refugia
are critical to the recovery of biota following drought and facilitate rapid recovery (Magoulick & Kobza
2003). Those species that are particularly sensitive to low-flow conditions either become extinct over
time (with repeated low-flow events) or show prolonged recovery times (e.g. Boulton 2003; Lake
2011).
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Table 2: Summary of examples of ecological recovery trajectories following low-flow conditions
Ecological indicator group
Recovery trajectories
Examples
Water quality
Rapid (<1 month) return to pre-drought conditions
Chessman & Robinson 1987
Foodwebs
Quality of organic matter supporting foodweb
increased with flow recovery
Ylla et al. 2010
Increased trophic complexity; initial recovery of
foodwebs dependent on order of return of consumers;
long-term recovery trajectories converge over time
Closs & Lake 1994
Murdock et al. 2010
Macrophytes/algae
Rapid recovery from short-term drought (<1 year)
Wright & Berrie 1987
Holmes et al. 1999
Robson & Matthews 2004
Macroinvertebrates
Rapid recovery of desiccation-resistant and mobile
taxa following low flows; recruitment of sensitive taxa
may be affected for multiple generations after
disturbance
Larimore et al. 1959
Boulton & Lake 1992b
Miller & Golladay 1996
Rader & Belish 1999
Pires et al. 2000
Boulton 2003
Bêche et al. 2009
Assemblage recovery following low flow does not
occur until water quality conditions have returned to
levels within tolerances of biota
Miller et al. 2007
Complete loss of sensitive taxa after prolonged
drought followed by prolonged recovery increases
composition similarity
Feminella 1996
Miller & Golladay 1996
Wood & Armitage 1999
Wood et al. 1999
Fowler 2004
Wood & Armitage 1994
Acuña et al. 2005
Rapid recovery once flow and water quality conditions
allow; delayed recovery of sensitive taxa
Larimore et al. 1959
Closs & Lake 1996
Hakala & Hartman 2004
Increased species richness and proportion of fluvial
specialist species
Travnichek et al.1995
Recovery dependent on refugia and dispersal
characteristics
Davey & Kelly 2007
Bêche et al. 2009
Fish
NATIONAL WATER COMMISSION — Low flows report series
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3. Key principles and conceptual models
of low-flow processes
The literature reviewed to quantify the ecological response to, and recovery from, low-flow events is
consistent in either detecting significant relationships or hypothesising significant processes.
However, from a water resource management perspective, it is important to not only know that low
flows have specific ecological impacts, but also to be able to both quantify and predict these impacts
and recovery potentials. This project’s 11 case studies and accompanying synthesis report (Marsh et
al. 2012) undertook such an analysis by using existing biological datasets to test the robustness of
hydro-ecological relationships for predictive modelling and planning applications. Because we wanted
a systematic approach from which to interpret results, and draw conclusions and generalisations
useful for water resource planning, we first set out to identify some key low-flow principles that we
could test via the case studies.
3.1. Low-low principles
There are two general predictions that relate to the role of low-flow history and ecological response:
(i) the magnitude of ecological response to a low-flow event will be a function of past exposure
manifested as the condition of the biological community at the onset of the low-flow period
and the sensitivity (species traits) of the assemblage
(ii) the ecological response will be driven by changes in physical habitat and perhaps the
resulting increase in intensity of biological interactions, and these responses will vary with
past exposure.
To help interpret the impacts of low-flow hydrology on aquatic ecosystems, we have translated these
two predictions into four guiding principles (Figure 4). These principles build on the concepts
presented in Bunn and Arthington (2002) in which aquatic ecosystem responses to altered flow
regimes are outlined. Ecological principles, and their underlying conceptual models, are useful for the
managers of aquatic environments because they highlight (a) the mechanisms through which various
stressors can impact ecosystems, and (b) the processes that influence the recovery of ecosystems
from disturbances (Lake et al. 2007). Our principles describe the effects of low flow on aquatic
ecology and can be used to predict ecosystem responses – both as a result of altered flow regimes
and naturally through the onset of drought – and include recognition of the response with the initial
onset of low flows, along with longer-term effects and the process of recovery (Figure 5). The
principles are:

Ecological low-flow principle 1: Low flows control the physical extent and arrangement of
aquatic habitat, therefore influencing ecological patterns and processes.

Ecological low-flow principle 2: Low flows influence physical and biological conditions in
remaining aquatic habitats, which drives changes in ecosystem patterns and processes.

Ecological low-flow principle 3: Low flows affect the sources and exchange of energy in aquatic
ecosystems, altering ecosystem production and biotic composition.

Ecological low-flow principle 4: Low flows restrict dispersal, influencing multi-scale ecological
patterns and processes and increasing the importance of refugia to sustain biota.
NATIONAL WATER COMMISSION — Low flows report series
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Figure 4: Four principles outline the broad mechanistic links between low flow and processes and
patterns in riverine ecosystems. These links do not operate in isolation, and many ecological
pathways that are affected by low flows are likely to occur simultaneously, potentially resulting in
similar or synergistic and complex consequences
NATIONAL WATER COMMISSION — Low flows report series
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Timeframe
Initial response
Medium-long term response
Recovery
Proportional shifts in assemblage
composition
Reduced
habitat
availability and
quality
(Principle 2)
Habitat
space
(Principle 1)
? streamlined
? drifting
? erosional
? armoured
Changes in energy
flow
(Principle 3)
Change in the spatial
connectivity of habitat
(Principle 4)
? sensitive taxa
? resistant taxa
? trophicgeneralist
taxa
? desiccation
resistant taxa
? habitat generalist
taxa
? Tegument
? Pollution sensitive
? Gilled breathers
? Sedentary (low mobility)
? Long adult life span
? Semi or univoltine
? Seasonal taxa
? Slow seasonal development
? Consumer production
? Dietary specialisation (e.g. Filter feeders,
herbivores)
? Fast seasonal development
? Inter & intra species
competition
?Assemblage
homogenisation
?Diversity (Alpha, beta,
gamma)
? Air breather (plastron)
? Mobile taxa
? Multivoltine
? Small bodied
? Pool -dwelling biota
? Niche generalist
Dashed lines along temporal axis indicate timelines for inducing ecological response to low flows vary significantly (based on regime,
antecedent conditions and other environmental stressor effects).
Figure 5: Expected response based on habitat changes. Dashed lines along the temporal axis
indicate timelines for inducing ecological response to low flows vary significantly (based on regime,
antecedent conditions and other environmental stressor effects).
3.1.1. Ecological low-flow principle 1: Low flows control the
physical extent and arrangement of aquatic habitat, therefore
influencing ecological patterns and processes
Low flows obviously result in considerable physical changes to aquatic habitats. These physical
changes typically result in reduced wetted area, habitat volume, depth and instantaneous flow velocity
(i.e. shear stress). Effects of flows on aquatic habitat depend on the local-scale (i.e. patches and
reaches) interaction between hydrology and geomorphology, resulting in effects of low flows mediated
by changes in specific hydraulic conditions. Consequently, habitats with little geomorphological
gradient, such as pools, experience little change in area, depth and volume during significant
reductions in flow when compared with habitats that have steeper gradients (e.g. riffles) (e.g. Hakala
& Hartman 2004). In floodplain habitats, low flows typically result in disconnection between floodplain
and river-channel habitats.
Low flows typically result in short-term increases in density and diversity (taxa richness) of aquatic
biota in rivers and streams, primarily due to habitat contraction. Riffle and other fast-flowing hydraulic
habitats shrink in depth and area, resulting in the concentration of benthic macroinvertebrates (e.g.
Boulton 2003; Dewson et al. 2007a; Finn et al. 2009). Reduced shear stress (instantaneous flow
velocity) and loss of flow disturbances also result in increased biomass of benthic algae and
macrophytes (e.g. Ryder et al. 2006). Densities of benthic macroinvertebrates are often greatest
immediately before flow cessation in riffles (e.g. Acuña et al. 2005), then show significant declines in
richness and density of species that favour flowing-water habitats (rheophilic macroinvertebrates) and
those taxa intolerant to increased variation in habitat conditions (see ecological low-flow principle 2).
NATIONAL WATER COMMISSION — Low flows report series
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Prolonged low flows are associated with reduced densities and loss of rheophilic taxa (Haxton &
Findlay 2008). Biota that have low dispersal abilities show the greatest effects of low flows (e.g. Miller
et al. 2010; Walters 2011), whereas desiccation-resistant taxa or those taxa that can recruit during
low flows dominate during low flows (e.g. Bonada et al. 2007; Ledger et al. 2008). Low flows are also
associated with an altered population structure of species due to loss of cohorts susceptible to
changes in rearing habitat (e.g. Riley et al. 2009) or reduced energy sources required to sustain
higher concentrations (i.e. biomass) of larger adult predators such as fish (e.g. Elliott et al. 1997).
Prolonged low flows leading to increased densities of consumers and reduced flood disturbances also
increase competition for energy sources. Increased competition during low flows has two key
ecological outcomes. Firstly, increased competition contributes to loss of species and reduced
abundance in the medium to long term. Secondly, altered densities of consumers can produce trophic
cascades in the short to medium term, resulting in a loss of trophic complexity (e.g. Closs & Lake
1994) or increased biomass of primary energy sources (e.g. autochthonous benthic algae) as a result
of reduced grazing pressure from herbivorous macroinvertebrates that become subject to increased
predation pressure by higher-level consumers (e.g. Power et al. 1985).
Potential early warning indicators of low flows associated with loss of habitat include increases in the
richness, density and dispersal (i.e. drift) of biota such as benthic macroinvertebrates. These
increases suggest an impending loss of biota and species intolerant of prolonged low flows. Changes
to the diversity and density of specific biota would therefore have potential application as a
compliance indicator, particularly if a proportion of species in the local species pool is expected to be
affected by prolonged low flows. Coupled with biological information, data on the hydraulic habitat
conditions (e.g. changes in area, volume, velocity) or knowledge of life-history patterns may serve as
diagnostic indicators by illustrating the underlying mechanisms causing changes in biota (Figure 1;
also see Sheldon et al. 2011 for a detailed discussion of monitoring approaches and indicators for low
flows).
Aspects of low-flow hydrology that may indicate changes in ecosystem structure due to changes in
physical habitat include the rate of reduction in flow (drawdown) and its timing, magnitude and
duration. Prolonged droughts can result in loss of biotic resilience. For example, fish and
macroinvertebrates showed persistent effects over 10 years after a five-year drought in Californian
streams (Bêche et al. 2009), and the effects of low flows are often only detected after low-flow
conditions have started to occur (e.g. Dewson et al. 2007a). The magnitude of low flows can have
variable impacts on stream biota: benthic macroinvertebrates occupying pools and the hyporheic
zone often show little response to extreme low-flow drawdown (e.g. around 90 per cent of flow from a
mean discharge of 56–275 ls-1), yet benthic riffle macroinvertebrates showed significant increases in
population densities (Dewson et al. 2007a; James et al. 2008b). Rapid changes in flows, such as
rapid flow drawdown, can strand fish and macroinvertebrates in residual pools (e.g. Bradford 1997).
Similar responses are likely to be seen for other physical habitats in streams and rivers, such as
exposed wood, rocky substrates, littoral macrophytes and edge habitat.
3.1.2. Ecological low-flow principle 2: Low flows influence physical
and biological conditions in remaining aquatic habitats, which
drives changes in ecosystem patterns and processes
Reduced flows affect the physical and chemical conditions within remaining aquatic habitats. Low
flows typically alter water quality conditions, decreasing dissolved oxygen and increasing conductivity
and diel variation in temperature and dissolved oxygen. Low flows often coincide with the warmest air
temperatures (i.e. during summer), therefore increasing evaporation and water temperatures.
Increased sedimentation of benthic habitats is also often associated with low flows (e.g. Dewson et al.
2007c). Reduced turbulence of the remaining water, due to reduced velocity, also increases
stratification of temperature and dissolved oxygen in residual pools and waterholes.
NATIONAL WATER COMMISSION — Low flows report series
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The ecological consequences of altered habitat conditions during low flows are reflected in the
distribution and abundance of biota according to thresholds of water quality tolerances. For example,
increased water temperatures during summer significantly reduce survival of brook trout (Salvelinus
fontinalis) in streams in North America (Xu et al. 2010). Low flows can result in hypoxic (deprived of
oxygen) conditions, thereby restricting species that can either tolerate or adapt to low dissolved
oxygen levels (e.g. Chessman 2003; McNeil & Closs 2007). Increased sedimentation of benthic
habitats drives changes in the composition of benthic and hyporheic biota, producing homogenous
assemblages that reflect similarities in substrate (Boulton 2007).
Measuring indicators of changes to low-flow-habitat conditions includes quantifying changes in
substrate composition and physical and chemical water quality attributes during flow recession. Water
quality attributes could include both surface and hyporheic water quality conditions, and those water
quality indicators that are likely to become critical for sensitive biota as flow and water levels decline
(pH, salinity, dissolved oxygen, temperature, dissolved organic carbon). Biological indicators could
include patterns in the composition of biota associated with patterns in water quality to detect both
relationship and threshold responses. For example, a measurement of overall diversity (number of
taxa) may not detect critical threshold changes occurring within a low-flow stressed system as
sensitive taxa are lost but perhaps replaced with tolerant taxa, so the overall number of taxa does not
change. More specific indicators that focus on the proportion of taxa with specific traits (e.g.
percentage of rheophilic taxa in the assemblage – requirement of flow) may better detect threshold
responses.
Low-flow hydrological attributes that have ecological relevance by inducing change in ecosystem
structure and function include timing, duration and magnitude of low flows. River discharge interacts
with seasonal variations to drive ecologically significant changes in water quality (e.g. Sheldon &
Fellows 2010), to the extent that reduced flows in different seasons have markedly different ecological
responses. For example, the 24-hour minimum dissolved oxygen concentration experienced by a
remnant waterbody during winter, when water temperatures are cooler, may not reach critical
thresholds for biota compared with the same remnant waterbody in summer, when higher water
temperatures cause a reduction in the solubility of oxygen leading to greatly reduced oxygen
saturation. Likewise, the increased evaporation potential during a summer low-flow event may act to
reduce available aquatic habitat faster than the same low-flow event in winter. The magnitude of diel
variation in water quality varies with the size of remaining habitats (a function of the interaction of flow
magnitude and habitat-scale topography): with smaller, shallow habitats experiencing greater diel
variation when compared with larger, deeper and more complex habitats. Low-flow duration and
magnitude interact.
3.1.3. Ecological low-flow principle 3: Low flows affect the sources
and exchange of energy in aquatic ecosystems, altering ecosystem
production and biotic composition
Low flows reduce the lateral connections between river channels, riparian zones and floodplains.
Longitudinal water-borne transport of energy is disrupted due to increased disconnection between
habitat patches at the reach scale. This results in increased retention of large volumes of organic
detritus, such as terrestrial plant matter (e.g. Boulton & Lake 1992a). Despite this increase in detritus,
leaf breakdown rates can decline due to limited physical breakdown and microbial conditioning (e.g.
Leberfinger et al. 2010; Ylla et al. 2010), resulting in altered foodweb structure due to reduced inputs
of allochthonous energy. However, this pattern varies among flow regimes (e.g. Reid et al. 2008).
Filter-feeding macroinvertebrates experience reduced densities due to the decline in longitudinal
transport of energy and loss of flowing-water habitats (e.g. Walters & Post 2011). Benthic invertebrate
drift also declines (e.g. Sotiropoulos et al. 2006), resulting in decreased production of drift-feeding
consumers such as fish (e.g. Harvey et al. 2006) or forcing prey-switching to terrestrial energy
sources such as insects (e.g. Sotiropoulos et al. 2006). The impact of low flows on productivity is
most consistent in estuarine ecosystems, with reduced discharge associated with reduced production
NATIONAL WATER COMMISSION — Low flows report series
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of fish (e.g. Loneragan & Bunn 1999; Vorwerk et al. 2009); however, similar insights into river systems
have been shown in dryland rivers where Bunn et al. (2003) estimated that one day’s production on
the floodplain of the flooded Cooper Creek (i.e. over an area of 14 000 km2) was equivalent to about
80 years of waterhole production during low or zero flow (Bunn et al. 2006a).
Changes to the duration and magnitude of low flows, particularly over seasonal or annual time scales,
are relevant to predicting and assessing patterns in ecosystem production, particularly at higher
trophic levels such as fish or waterbirds. Altered sources of energy can be assessed at finer temporal
scales, such as weeks to months (e.g. Acuña et al. 2005), indicating that short-term periods of low
flows can be used to predict long-term changes to ecosystem production with prolonged low flows
(see Bunn et al. 2006b). Reduced transport and production at intermediate levels of the food chain
are often detected over periods of weeks to seasons (e.g. Harvey et al. 2006; Death et al. 2009).
3.1.4. Ecological low-flow principle 4: Low flows restrict dispersal,
influencing multi-scale ecological patterns and processes and
increasing the importance of refugia to sustain biota
Low flows restrict movement of biota between habitats, river reaches and throughout river networks.
During declining flows, refuge habitats become increasingly important for sustaining diversity,
particularly throughout river networks. Reduced flows may also trigger biota to seek out refuge
habitats (Magoulick & Kobza 2003), yet often simultaneously restrict movement. Species vary in their
ability to access and persist in low-flow refuge habitats (e.g. Crook et al. 2010), resulting in sequential
changes to biodiversity, particularly at reach and catchment scales.
Provision of refugia increases biotic resilience during and following low flows by providing habitat for
source populations when higher-flow conditions return. Low-flow water extraction in rivers in Austria
has been shown to increase habitat fragmentation and reduce movement and persistence of bullhead
(Cottus gobio) (Fischer & Kummer 2000). Therefore, loss of refugia is likely to have widespread
consequences for biodiversity at the catchment scale (e.g. Robson & Mathews 2004; Rayner et al.
2009; Leigh et al. 2010).
Patterns in measures of biodiversity can be used to assess the effects of prolonged low flows and
loss of refuge habitats and/or complete drying of river reaches. During low flows and flow recession,
reach- and catchment-scale variability in population density and assemblage structure (i.e. beta
diversity) increase over time as local-scale factors (e.g. predation) structure biotic composition.
Increased duration of low flows results in a loss of sensitive taxa, consequently reducing assemblage
variability (e.g. Magalhães et al. 2002). As beta diversity declines, large-scale biodiversity (i.e. gamma
diversity) declines as flow-dependent biota and taxa intolerant to poor water quality become extinct.
Frequency and duration of low flows are especially important for large-scale biodiversity, as it is
predicted that separate low-flow events act as a biological ‘filter’, removing biota intolerant of low
flows from the reach or regional species pool (e.g. Bonada et al. 2007).
3.2. Temporal considerations of low-flow impact and
recovery
The impact of, and subsequent recovery from, low-flow events will vary spatially depending on
background hydrological conditions. For example, upland perennial streams will likely have different
responses to, and recovery trajectories from, a low-flow event when compared with a semi-arid river.
The spatial context of low flows has been explored in the low-flow classification report (Mackay et al.
2012) and to some extent reflects the hydro-ecological classification undertaken by Kennard et al.
(2010). Within the spatial classification of low-flow classes of streams (Mackay et al. 2012) there will
also be a temporal signal, whereby the responses to any one low-flow event are a reflection of the
NATIONAL WATER COMMISSION — Low flows report series
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temporal history of low flows over both short (weeks to months) and long (years to decades) time
scales.
It is therefore important to consider specific hydrological conditions before, during and after a low-flow
event to inform interpretations of the broad principles, and four key considerations are identified
below. For example, the extent of aquatic habitat (principle 1) at the onset of a low flow will be a
function of prior hydrological conditions (consideration 1) – is the low flow coming right after a series
of very high flows (where soil etc. will be saturated and perhaps baseflow high) or is it coming during
a relatively dry time where the same hydrological low-flow event (as above) may be more severe?
3.2.1. Consideration 1: Hydrological conditions before low-flow
events provide the context for subsequent biotic responses, and
post-event hydrology affects ecological recovery
Antecedent conditions constitute the hydrological characteristics to which aquatic biota and their
habitats are exposed before each hydrological disturbance event. These conditions affect the
response and recovery of the biota and ecosystems to low flows. For example, long-term antecedent
conditions in intermittent prairie streams in Kansas, United States, were the driving factor behind
invertebrate responses to low flows and drought, having a stronger effect than low-flow duration and
frequency and distance to refugia (Fritz & Dodds 2005). This suggests that historical factors influence
evolutionary adaptations of aquatic biota to low flows, especially when low-flow periods are more
extreme than those experienced on average. Indeed, antecedent flow permanence was critical in
determining the invertebrate community response to supra-seasonal low flows in Derbyshire streams,
United Kingdom (Stubbington et al. 2009). Compared with flood responses, however, our
understanding of in-stream ecological responses to long supra-seasonal droughts in perennial rivers
is incomplete (Wood & Armitage 2004).
Following low-flow periods, recovery of aquatic biota will depend on several factors. Unless aquatic
organisms have developed adaptations such as long dormant phases, rapid development and prolific
reproduction, the ecological impacts of drought can be more long-lasting than the effects of floods
(Gordon 2004). For example, the recovery of invertebrates within a groundwater-dependent river
(Canterbury, United Kingdom) following a supra-seasonal drought took two years, which
corresponded with the recovery of groundwater inputs (Wood & Armitage 2004). Experimental
inundation of sediment samples taken from an ephemeral reach of the Selwyn River (New Zealand)
with 1–592 days preceding dry periods found that macroinvertebrate taxa richness, sediment
respiration and microbial activity decreased linearly with length of the dry period (Larned et al. 2007).
These authors suggested long-term data were required to assess ecological recovery from low-flow
and drought events. This area of study is particularly lacking in low-flow ecohydrological research
(e.g. Dewson et al. 2007a).
Confounding our lack of understanding of recovery, taxa may experience differential lag periods
following low-flow events, due to different levels of tolerance and adaptations to antecedent conditions
and low flows (e.g. macroinvertebrates, Boulton 2003). For example, rapid recovery of invertebrates
after extreme low-flow events in New Zealand streams (Caruso 2002) suggests different taxa and
trophic levels may have different levels of resilience to low-flow hydrology. Recovery following lowflow and drought events will also depend on event duration, timing, frequency, and magnitude as well
as source populations (Lake 2003, 2011) (see below). Similar patterns of recovery of algal
communities after the cessation or low flow, or drying events, have been observed (Robson 2000).
NATIONAL WATER COMMISSION — Low flows report series
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3.2.2. Consideration 2: Duration of low-flow events affects species
diversity, survival and life-history strategies
Aquatic biota have evolved life-history strategies in response to natural flow regimes, which include
low-flow events (Bunn & Arthington 2002). In terms of low-flow duration, however, we lack any
detailed understanding of these responses. This may result from the focus of many studies on only
short low-flow events (i.e. weeks to months), which has generally resulted in undetectable responses
(e.g. Dare et al. 2002; Magalhaes et al. 2007; Miller et al. 2007; James & Suren 2009). Despite this,
and the fact that past ecohydrological assessments rarely considered the duration of low flows
(Jowett 1997), several studies have reported specific ecological responses as detailed below.
In Australia, studies have demonstrated that taxa exhibit different life-history responses to the
duration of low-flow events, and in different geographical locations. For example, Milton and
Arthington (1983, 1984, 1985) reported that a range of unrelated fish species concentrate
reproduction during the dry season in south-east Queensland when the risk of high-flow events that
may reduce larval and juvenile survival is low. Similarly, melanotaeniid rainbowfishes in tropical
stream systems also recruit most strongly during predictable periods of low flow (Pusey et al. 2000).
Humphries et al. (1999) developed the ‘low-flow recruitment hypothesis’ to explain why some fish
species in the Murray-Darling Basin spawn and recruit within in-channel habitats during the warmest
months and lowest flow events. The hypothesis predicts that some fish species take advantage of the
extended low-flow periods that occur in certain regions of the river system and lead to the
concentration of appropriate-sized prey such as zooplankton, the biomass of which was shown to
positively correlate with water residence time and temperature and negatively correlate with flow. In
addition, golden perch (Macquaria ambigua) and silver perch (Bidyanus bidyanus) are well-suited to
the semi-arid and temperate hydrology of the Murray-Darling river system by their longevity and
opportunistic method of growth (Mallen-Cooper & Stuart 2003). Both species have exhibited strong
recruitment in non-flood years compared with poor recruitment in flood years. However, the duration
of low-flow events does not have a consistent effect on all taxa in all regions.
In general, reduction in habitat availability and size of refugia during extended low-flow periods is
likely to increase competitive interactions among taxa due to limited resources (food and habitat)
(Pusey & Bradshaw 1996; Bond et al. 2008). Reduction of flow magnitude may exacerbate this
phenomenon, as feeding success (gut fullness) of fish has been shown to decline as flows reduce
(Sotiropoulus et al. 2006). Increased competition and reduced feeding on invertebrate drift has been
found consistently under low-flow conditions (e.g. Closs 1994; Pires et al. 1999), and a combination of
duration and magnitude has been identified as the most important hydrological determinant for fish
abundances in a gravel-bed New Zealand river (Jowett et al. 2005). As low-flow periods extend and
habitat quality declines or becomes unstable, physically tolerant taxa are likely to dominate,
particularly carnivores (Gasith & Resh 1999; Puckridge et al. 1998; Pires et al. 1999). Starvation and
death may occur even in these species (Burford et al. 2008). In addition, extended low flows may
increase the retention of organic matter in streams and refugia, which in turn causes declines in
dissolved oxygen and habitat suitability (Lake 2003). The influence of periodic resource limitation and
the physical challenge posed by continued periods of low flow has been shown to reduce the regional
biodiversity of stream fishes (Oberdorff et al. 1995).
The increased competition for food and habitat, and the interacting impacts of low flows on the
biomass and production of both energy sources and consumers (e.g. algae, macroinvertebrates and
fish), may eventually lead to trophic cascades (Lake et al. 2007), as shown in streams in Portugal and
the United States (Pires et al. 1999; Sotiropoulos et al. 2006). This may also manifest as a result of
successional processes in algal and invertebrate communities due to low flows and their duration. For
example, Suren et al. (2003a) detected changes in invertebrate communities during summer low
flows in New Zealand streams in association with increases in filamentous algae, which correlated
with number of days at low flow. Time between freshes (i.e. the low-flow duration between pulses)
NATIONAL WATER COMMISSION — Low flows report series
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has been identified as the most important limiting factor for algal growth in New Zealand rivers
(Caruso 2001).
3.2.3. Consideration 3: Magnitude and duration of low-flow events
affect the availability and quality of habitat and the structure,
diversity, persistence and recovery of biotic assemblages
Few studies explicitly separate the effects of low-flow magnitude and duration on stream ecosystems.
For example, trophic interactions and ecosystem production are strongly associated with the duration
and magnitude of flow reduction in flowing waters, extending downstream into estuaries (Glaister
1978; Livingston et al. 1997; Loneragan & Bunn 1999). However, the interactions and their effects will
vary depending on functional feeding mode and the energy requirements of individual taxa. For
macroinvertebrates, abundances of shredders and predators rose during low-flow periods when
compared with normal conditions in Colorado, United States, whereas collector-gatherers reduced in
abundance (Canton et al. 1984). It has been hypothesised that these effects are due to a higher
biomass of shredders being supported by the increased retention of detritus, and reduced habitat and
increasing predation pressure on collector-gatherers (Canton et al. 1984).
One of the most apparent effects of reduced magnitude and extended duration on aquatic biota is
loss and fragmentation of habitat: low flows limit the size and availability of in-stream habitats (see
Duration section above). Many studies predict that the most significant ecological changes to stream
ecosystems during low-flow events will occur in flowing riffle habitats (e.g. Dewson et al. 2007a; Finn
et al. 2009; Poff et al. 2010). This habitat is consistently shown to be the most altered by low flows
(Hakula & Hartman 2004). The vulnerability of riffle habitats to change during periods of low flow has
consequences for biota dependent on this habitat type. For example, the highly diverse endemic
freshwater fish fauna of Queensland’s Wet Tropics region (second only to Western Australia’s
Kimberley region in terms of endemic species richness (Unmack 2001)) is composed largely of riffledwelling species, particularly gobies (Pusey et al. 2008). The development of endemic specialist riffledwellers suggests that riffle habitats in this region have not experienced prolonged or spatially
extensive low flows over a long period and highlights the potential impacts of artificially induced low
flows in perennial streams.
As riffles contract and dry, slow-flowing and deeper habitats (e.g. pools) become more important as
refugia for fish, macroinvertebrates and algae. Many studies show that wetted width, depth and flow
velocity all decrease in response to reduced low flows (e.g. Harvey et al. 2006; Sotiropoulos et al.
2006; Hay 2009). For macroinvertebrates, these habitat changes first tend to be associated with
increased faunal densities due to concentration within the contracting habitats (e.g. Boulton & Lake
1992), followed by declines as the low-flow period extends (e.g. Cowx et al. 1984; Outridge 1988;
Stubbington et al. 2009). However, in systems where riffle and refugia habitats (e.g. pools) are closely
arranged, broadscale changes in biotic assemblages may not be detected. Indeed, many studies
detect only subtle effects of experimental low flows on riffle assemblages (e.g. Dewson et al. 2003,
2007b) because source biota in nearby refugia are able to replenish riffle habitat assemblages.
Under low-flow conditions, differences in abundance and assemblage composition of
macroinvertebrates between pool and riffle habitats also become more subtle as flowing and nonflowing habitats become more homogenous. For example, during low-flow periods, macroinvertebrate
assemblages were more variable when compared between reaches than between riffle and pool
habitats, whereas during higher flows, habitat differences were greater than reach-scale differences
(Lind et al. 2006). In contrast, experimental manipulations of stream fishes mimicking the effects of
droughts reveal that chance alone has a substantial role in determining the overall trajectory of fish
assemblage structure in time (Matthews & Marsh-Matthews 2006) and helps explain spatial variation
in natural stream communities’ responses to drought. As habitat contracts and fish are concentrated
in a decreasing volume of habitat space, the chance presence of individual species greatly affects the
outcome of the low-flow event (WJ Matthews, personal communication). Large-scale river health
NATIONAL WATER COMMISSION — Low flows report series
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assessments have shown that during drought, riffle-habitat macroinvertebrate assemblages resemble
those of pool and edge habitats due to the conversion of lotic habitats to lentic ones, and that the
detection of drought impacts are confined to pool-edge habitats (Rose et al. 2008). This highlights that
understanding source-sink population dynamics is critical in the management of low flows (Lake et al.
2007).
Comparative studies examining the patterns in biotic assemblages in flowing (e.g. riffle) and slowflowing (pool and run) habitats are also useful for predicting the habitat guilds of biota (e.g. riffledwelling fish and rheophilic invertebrates) that are most susceptible to low flows, and their strategies
for dealing with low flows. In a lowland gravel-bed river in New Zealand, changes in the abundances
of fast- and slow-flow dwelling fish were consistent with the amount of habitat available. High-flow
preference species showed the greatest loss whereas the abundances of low-flow species increased
(Jowett et al. 2005). Differences in refuge use among biota also determine spatial and temporal
variability in assemblage composition. For example, in New Zealand streams under experimental low
flows, Canterbury galaxias (Galaxias vulgaris) preferred to burrow into riffle substrate, whereas
upland bullies (Gobiomorphus breviceps) moved into deeper run sections during slow-flow
recessions; but under rapid-flow recessions, burrowing and surface stranding of fish increased (Davey
et al. 2006). Therefore, the impact of low-flow events is contingent on species-specific strategies of
refuge use and the interaction with refuge availability and the rate of change in flow magnitude (Davey
et al. 2006). Impacts are also probably contingent on organism size. For example, many species of
northern Australian freshwater fishes are dependent on riffle habitats as juveniles, presumably
because invertebrate production is high and predation pressure low because shallow water depths
preclude access for larger fish and reptilian predators (Pusey et al. 2004). Adjacent pools do not
provide a high-quality refuge for such species during periods of low flow. Persistence of low-flow
events for periods approaching or exceeding the generational time of such species is therefore likely
to have long-term negative consequences for freshwater biodiversity.
Two studies have demonstrated the effects of changes in low-flow magnitude and duration on postevent ecosystem production. Experimental surface water extraction in Connecticut streams, United
States, reduced fish body size (and therefore ecosystem production) by up to 40 per cent (Walters &
Post 2008). Harvey et al. (2006) experimentally reduced dry-season flows in small north-west
Californian streams by 75 to 80 per cent for six weeks such that flow diversion decreased flow velocity
in riffle-pool transition areas but did not alter habitat volume or temperature. Growth in fish in
impacted reaches was 8.5 times slower than fish in control reaches, even though survival was not
affected, and invertebrate drift was significantly reduced.
Ecological changes associated with the magnitude of low-flow events also occur at the bottom of the
foodweb. In the Darling River in New South Wales, Australia, extreme low-flow magnitudes, high
nutrient conditions and temperatures all contributed to a major cyanobacterial bloom in 1991 (Bowling
& Baker 1996). High algal biomass can cause large diel fluctuations in oxygen concentration, which
directly affects oxygen-dependent taxa at higher trophic levels (Matthews 1998). These changes can
interact with the duration of low-flow events to determine event severity and therefore the ecological
response and recovery of aquatic biota, which may or may not become confounded by trophic
cascades (see above).
3.2.4. Consideration 4: Frequency and predictability of low-flow
events affect long-term species diversity, life-history strategies,
and the timing and extent of recovery from low-flow events
Although the frequency, timing or predictability of flow events are ecologically relevant (Colwell 1974;
Townsend et al. 1997; Puckridge et al. 1998), there is little information available on specific ecological
responses to the components of low-flow events (cf. Konrad et al. 2008; Leigh & Sheldon 2008;
Bertrand et al. 2009). One study on the effects of water extraction on microinvertebrate assemblages
in the Murray-Darling Basin, Australia, has shown, however, that less-frequent flooding and increased
NATIONAL WATER COMMISSION — Low flows report series
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frequency of drying reduces microinvertebrate richness, potentially resulting in adverse repercussions
for waterbird and fish breeding (Jenkins & Boulton 2007). More generally, the frequency and timing of
low-flow events are considered to affect long-term species diversity, life-history strategies, and the
timing and extent of recovery (for biota and ecosystems). In subtropical and tropical regions, stable
(predictable) baseflows are important for fish spawning and recruitment during low-flow periods (Bunn
& Arthington 2002; Pusey et al. 2004). Conversely, the predictable absence of baseflows during the
dry season in rivers within regions with a Mediterranean climate, such as those of south-western
Australia (Kennard et al. 2010), present an inimical environment for small fishes such that their
reproduction is restricted to the winter wet season (Pusey & Bradshaw 1996). In contrast, high
variability and lack of predictability of flow events, of low or high magnitude, is a defining feature of
many Australian rivers, both tropical and dryland, to which the native aquatic biota are adapted
(Puckridge et al. 1998; Leigh & Sheldon 2008). Fish taxa may respond to this variation in the
frequency, timing and duration of low flows by employing brief and/or flexible breeding systems (e.g.
‘bet-hedging’) and life-history characteristics (see Puckridge et al. 1998; Humphries et al. 1999). Most
Australian macroinvertebrates are well-adapted to the high levels of flow variability that exist in
Australian river systems (e.g. Sheldon & Thoms 2006) (although this may not be the case in regulated
systems where natural levels of flow variability have been lost). Consequently, any responses to
subtle changes in the frequency and timing of low-flow events may be difficult to detect. However,
measures of production (changes in biomass and body condition) may be more sensitive than
abundance or assemblage measures to these aspects of the low-flow regime. This suggests that
studies of low-flow impact and recovery need to be undertaken and interpreted in the context of
general regional hydrology (see Kennard et al. 2010).
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4. Informing case study analyses
One of the aims of this literature review was to inform a series of case studies analysing relationships
between low-flow and ecological responses using available datasets (Marsh et al. 2012). Ideally, a
similar analytical approach would have been designed and undertaken for all of these case studies.
However, each dataset used was unique and dataset-specific analysis was required. Although the
analytical approach actually used could not be prescriptive, all studies:

tested the four principles described in this report

considered a traits-based approach (as described below)

adopted a similar philosophy in describing hydrology; that is, the hydrologic metrics used
represented those components of the hydrograph previously described and covered the shortand medium-term hydrologic conditions leading up the biological sampling time, as well as a
regime-level metric.
Example flow metrics used in the hydro-ecological studies are:

short term: mean daily flow for 30 days preceding sample

medium term: number of zero flow days in previous 12 months

regime: inter-annual variability in the number of cease-to-flow days.
4.1. Datasets available
In testing low-flow hypotheses, one ideally requires long datasets of high temporal and spatial
frequency that cover a gradient of conditions. The most suitable candidate datasets currently
available are those used by state jurisdictions as indicators of river health. Assessment of river
ecosystem condition (or ‘health’) in Australia has grown rapidly since the early 1990s, and a number
of large-scale river health monitoring programs have been initiated such as the Murray-Darling Basin
Sustainable Rivers Audit (MDB SRA) and South East Queensland Ecosystem Health and Monitoring
Program (EHMP) (Bunn et al. 2010; Davies et al. 2010). These river health monitoring programs are
used to detect both the current status of ecosystem health and track changes over time with
alterations to disturbances (e.g. climate, human impacts) or assess ecological response to
environmental restoration (e.g. riparian restoration). Many of these monitoring programs, as well as
smaller-scale ecological experiments, use indicators or metrics designed to reflect changes in
ecological condition associated with environmental stress. However, many of these indicators of river
health have not been selected to detect effects of low flows and drought. Nonetheless, given that
large-scale river health monitoring programs now have extensive datasets, there is the potential that
some widely used indicators can be used to detect ecological responses to low flows.
The Australian Rivers Assessment System (AUSRIVAS) is an Australia-wide rapid assessment
system used to monitor and assess the ecological health of Australian rivers. It operates under the
Australian National River Health Program, and uses a standardised and rapid approach to assess
river ecosystem health. The AUSRIVAS scheme is based on a reference condition approach,
whereby the current condition of a sampling site is compared with the predicted natural undisturbed
condition. In Victoria, the utility of AUSRIVAS to detect anthropogenic impacts on benthic
macroinvertebrate assemblages has been investigated, and indicates that change in edge-habitat
assemblage composition can indicate either an effect of reduced flow or anthropogenic impacts (Rose
et al. 2008). In contrast, macroinvertebrates sampled in riffles did not reveal the effects of reduced
flows, partly as samples were only taken during sufficient flows (Rose et al. 2008). Use of similar rapid
biological assessment techniques for monitoring the effects of flow extraction on macroinvertebrates
indicates that such techniques may lack sensitivity to reduced flows or in dryland river ecosystems
(Chessman et al. 2010; Chessman et al. 2011).
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Stream Invertebrate Grade Number-Average Level (SIGNAL) (Chessman 2003) is a method whereby
benthic macroinvertebrate families are assigned a tolerance score, with the average score indicating
the site’s condition. SIGNAL was developed primarily to detect river condition in relation to the effect
of wastewater and discharge from sewage water treatment plants on river condition in temperate
Australia (Growns et al. 1995). It is currently included in the assessment of river health in the MDB
SRA, SEQ EHMP and the Victorian Index of Stream Condition, as well as many smaller-scale
projects. SIGNAL scores are based on sensitivity to water quality conditions that are influenced by low
flows (Chessman 2003), such as temperature, dissolved oxygen and conductivity. During a long-term
drought in Victoria, Australia, SIGNAL scores declined, indicating that river health was affected (Rose
et al. 2008). However, SIGNAL scores for many macroinvertebrate families also appear to reflect
tolerance for low flows (Boulton & Lake 2008), suggesting that SIGNAL scoring may be used to detect
ecological consequences and (potentially) recovery from low flows. However, the valid use of SIGNAL
in arid-zone rivers has been questioned (Sheldon 2005) and it may require modification for different
flow regimes to include spatial differences in low-flow regimes. Potential modifications include
incorporating antecedent hydrology before sampling (Chessman et al. 2010), although selecting the
appropriate time period may be challenging because taxa would likely respond to flow based on their
life-history and metapopulation dynamics.
Ephemeroptera, Plecoptera and Trichoptera (EPT) are three orders of macroinvertebrates that are
particularly sensitive to declines in water quality, and are often used in the assessment of river
ecosystem condition. The number of families in the EPT orders and the proportion of both individuals
and taxa of EPT have been used to assess ecological responses to low flows. For example, the
percentage of EPT individuals declined in a pristine river during experimental water extraction over 12
months when compared with upstream control reaches (Dewson et al. 2007a). However, much
shorter-term low-flow events (e.g. one to two months) do not typically result in changes to EPT (e.g.
McKay & King 2006; Dewson et al. 2007b). Changes in EPT taxa, therefore, appear not to reflect
short-term changes in low flows, and are also likely to depend on the long-term environmental
conditions.
The Index of Biotic Integrity (IBI) was developed in the United States and assesses the ecological
condition of rivers using fish assemblages (Karr 1981). The IBI includes the number of fish species
sampled, the composition of fish according to trophic and meso-habitat guilds, and the proportions of
native species and native individuals (e.g. Harris 1995). The IBI has been used to assess the effects
of water extraction and dams in the United States. Increasing rate of water withdrawal increased the
probability that a site’s IBI score would fall below a threshold indicating poor biological condition as
reflected in a low IBI (Freeman & Marcinek 2006). Streams with high rates of water withdrawal are
generally characterised by reduced proportions of fluvial species and benthic invertivores (Kanno &
Vokourn 2010), most likely reflecting the impact of low flows on habitat and the availability of energy
sources. The IBI has had relatively little use in Australia (e.g. Harris & Silveira 1999), yet may have
potential for detecting ecological responses to low flows given the inclusion of flow-habitat guilds.
The sampling frequency of many large-scale river health monitoring programs typically varies from
seasons to years (e.g. SEQ EHMP – six-monthly sampling, MDB SRA – sampling every three years);
hence the use of these monitoring programs to detect changes due to low flows may be limited. This
is particularly so for early warning indicators where, in some cases, almost continual monitoring over
days or weeks is likely to be necessary to detect initial changes in ecosystem structure and function.
Large-scale monitoring programs may have the potential to assess ecological responses to low flows,
particularly in the use of diagnostic indicators and/or coupled with more frequent monitoring at
selected reaches vulnerable to reduced flows. Although current river health monitoring programs (e.g.
MDB SRA, EHMP) may not use ecological indicators designed to assess low-flow responses, raw
data are often available if such metrics or analytical approaches are developed (e.g. Brooks et al.
2011).
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4.2. Preferred method – traits approach
Due to spatial differences in the composition of aquatic fauna across Australia, taxonomic-based
approaches are limited in their ability to help determine whether the effects of low flows are consistent
between hydrologically variable regions (e.g. Kennard et al. 2010; Mackay et al. 2012). An alternative
approach is to analyse the effects of low flows using biological characteristics or species traits, where
different taxa are predicted to show similarities in their trait responses to environmental disturbance
(e.g. McGill et al. 2006).
Species traits (biological characteristics) are increasingly being used to predict and analyse the
ecological effects of anthropogenic and natural disturbances on aquatic ecosystems (Menezes et al.
2010). The use of biological traits has an advantage over taxonomic groupings (particularly coarse
groupings such as family) because taxonomically similar biota often vary considerably in their
tolerances and responses to environmental stressors (Downes 2010). The proportion of specific traits
occurring within an assemblage reflects the natural environmental drivers (hydrology, habitat
availability, water quality and biological interactions) present in a system (Verberk et al. 2008).
Mechanistic effects of environmental stressors can be used to improve predictions of the ecological
consequences of environmental change (Statzner & Bêche 2010), and biological traits are used to
predict the effects of river-flow regimes on patterns in biodiversity and species dynamics (Lytle & Poff
2004).
Species traits have also been used to assess ecological consequences or predict the risk and
magnitude of future environmental impacts such as climate change (e.g. Chessman 2009; Brooks et
al. 2011; Walters 2011). Due to the interest in assessing and predicting the effects of water extraction
and hydrological alteration as a consequence of both climate change and human demands, the use of
traits-based approaches is increasing because the effects of flow manipulation can be difficult to
detect when unimpacted control sites do not exist. For example, species trait analysis was found to be
more sensitive than taxonomic-based measures to assess the impacts of water extraction in the
United States (Miller et al. 2010). Species traits have been used to describe taxa most susceptible to
reduced flows both in Australia (Brooks et al. 2011) and the United States (Walters et al. 2011).
Traits have been used to assess the ecological responses to low flows in surface-flowing ecosystems
and to identify particular species that are capable of resisting low flows and those with high resilience
(Table 3). Conversely, traits can identify particular species that are especially vulnerable to change in
low flows. For example, rivers that frequently experience low flows (either due to regular water
extraction or their being naturally intermittent) typically favour habitat-generalist species at the
expense of rheophilic taxa (e.g. Haxton & Finlay 2008; Rose et al. 2008; Finn et al. 2009; Brooks et
al. 2011). Habitat-generalist taxa are generally resistant to low flows, as they are less sensitive than
rheophilic taxa to changes in flowing habitats. Many predacious macroinvertebrates with armoured
bodies and a high crawling rate (i.e. ability to disperse during rapid low flows) also have high
resistance to low flows, particularly to rapid drawdown events (Miller et al. 2010; Walters 2011).
In contrast to resistance traits, biological characteristics that allow for rapid recolonisation and
recovery from low flows can be used to predict particular biota able to persist in flow regimes with high
frequency and long duration of low flow. Short-lived multivoltine (i.e. breed and recruit multiple times
during a typical breeding season) species with dormant/resting egg phases are traits conferring high
resilience to low flows (Table 3). For example, the Selwyn River, New Zealand, has four distinct
hydrological reaches: perennial-losing, ephemeral, intermittent and perennial-gaining. Benthic
macroinvertebrate assemblages show distinct patterns according to hydrological conditions (Arscott et
al. 2010) – the proportion of short-lived, smaller-bodied multivoltine species with low individual
fecundities increased with decreasing flow permanence and flow duration. These traits are consistent
across streams in semi-arid climates, such as Spain (Bonada et al. 2007; Díaz et al. 2008), and
indicate that longer-lived, larger-bodied univoltine taxa have low resilience to low flows.
NATIONAL WATER COMMISSION — Low flows report series
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Species traits have been shown to be more sensitive than structural indices (e.g. taxonomic grouping)
at detecting the effects of low flows (e.g. Miller et al. 2010). However, many species also exhibit trait
plasticity, whereby biological characteristics in response to low flows vary in association with other
factors. For example, size at sexual maturity of brown trout (Salmo trutta) is linked with mean annual
discharge. Individuals become sexually mature at shorter body sizes in streams with lower flows when
compared with fish from streams with greater discharges (Jonsson et al. 2001). Knowledge of the
biological traits associated with resistance and resilience to low flows is relatively poor, particularly for
fish, algae, macrophytes and birds, yet research into macroinvertebrate traits is increasing (e.g. Miller
et al. 2010; Walters 2011; Brooks et al. 2011). Some of the traits described above are likely to have
consistent responses to low flows across taxonomic groups (e.g. fish and macroinvertebrates).
However, research is still needed to determine which taxa can be grouped according to their similar
responses to low-flow hydrological stressors. Due to the high variability of traits within taxonomically
similar groups (e.g. families, genera), identifying the traits that are a compromise between sensitivity
to environmental stressors (low-flow sensitivity in this case) and different taxonomic levels is
necessary (Downes 2010). Responses of taxonomically similar biota to flow regime and flow regime
change are largely inconsistent globally (Poff & Zimmerman 2010). Therefore, traits-based
approaches to assessing the ecological consequences of low flows are likely to improve predictions
and identify whether consistent or distinct responses to low flows exist across large geographic
regions. Some traits may be strongly correlated with common sensitivity grade measures of
ecosystem condition (e.g. SIGNAL, Chessman 2003; Boulton & Lake 2008; Boulton & Lake
unpublished data), and these indices may reflect particular biological characteristics that are directly
or indirectly associated with low-flow conditions (e.g. water quality; Chessman 2003). But for largescale (e.g. continental) analysis, major impediments to using a traits-based approach include the
limited availability of data from large spatial scales, a lack of basic biological and ecological
information to group taxa into ecologically similar classes (Pyron et al. 2011) and, in Australia, the
lack of an adequate traits database.
Table 3: Summary of known biological traits associated with high and low resistance and resilience to
low flows. Sources: Bonada et al. 2007; Díaz et al. 2008; Haxton & Finlay 2008; Rose et al. 2008;
Finn et al. 2009; Brooks et al. 2011; Walters 2011.
Attribute
Key biological traits
High resistance
Rapid crawling rate, armoured bodies, tolerance to
high water temperature, pollution-tolerant, preference
for lentic habitat, habitat-generalist, predatory
High resilience
Aerial dispersal, small body size, multivoltine,
ovoviviparity, low fecundity, short lifespan
Low resistance/resilience
Rheophilic, clinging preference, shredder/detritivore,
slow seasonal development, poor swimming ability,
high fecundity
4.2.1. Macroinvertebrate traits database
When undertaking broad comparisons across large areas of Australia, relatively few taxa occur
across all regions – making large-scale comparisons difficult. Those taxa that are widespread are
generally tolerant of widespread environmental conditions (at least partially explaining their
widespread distribution). One possible solution is to increase the number of taxa with biological
information available by modifying existing traits databases, such as those developed by Brooks et al.
(2011) and Schafer et al. (2011), to apply to low-flow stresses.
Schafer et al. (2011) have developed a traits-based database of 171 macroinvertebrate taxa (mostly
to family) to inform ecological risk assessment of salinity and pesticides in south-eastern Australia.
Based on the synthesis of the ecological consequences of low flows on physical conditions,
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ecosystem processes and aquatic biota, many of the traits identified by Schafer et al. (2011) have
potential application for assessing the impacts of low flows (Table 4).
Brooks et al. (2011) used biological traits to determine the likelihood of impact from water extraction
on macroinvertebrate taxa in rivers of New South Wales, Australia. The information available for 29
biological traits was limited and only available for 32 families (highlighting the deficit of this information
for many Australian macroinvertebrate families). In addition, because many macroinvertebrate taxa
that occur in New South Wales are not found in other hydrologically distinct regions (e.g. semi-arid,
tropical), the ability to use the assessed traits and taxa in other regions of Australia is limited.
An attempt was made to develop a database of traits that could be applied across most of Australia
by collating traits from Brooks et al. (2011), Schafer et al. (2011) and others. This attempt remains
incomplete and the establishment of a national traits database is seen as a priority.
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5. Conclusions
Periods of low flow are a natural part of every river’s flow regime (Poff et al. 1997) and, similar to
floods, they can act as ‘disturbance phenomena’ in resetting ecological processes and maintaining
ecological diversity (Lake 2000). Low-flow impact in streams and rivers may occur naturally under the
extremes of climatic variability and is often referred to as ‘drought’ (Lake 2011); however, more
commonly low-flow impact is caused by anthropogenic influences on rivers and streams. The
frequency, magnitude and duration of low flows can be increased through water extraction and flow
regulation, resulting in a shift from streams that may be naturally perennial to systems that may
hydrologically resemble more ephemeral streams. Such hydrological shifts can result in reduced
ecological diversity and changed ecosystem function. Flow regulation through dams and weirs can
also decrease the natural frequency, magnitude and duration of low flows through continual water
releases, with consequences for the stream or river similar to an increase in low flow.
This review has highlighted that although there is a large and rapidly growing research interest into
the ecological consequences of low flows, a key issue remains apparent: although it is necessary to
understand the impacts of low flows while they occur, it is equally important to identify how
ecosystems recover after they occur. Most research has focused on ecological patterns during lowflow and drought events, but monitoring often ceases when higher flow periods return (Boulton & Lake
2008; Lake 2011). From a management perspective, this results in a mismatch between
understanding and management information needs. This review has summarised the impacts of low
flow on streams and rivers into four guiding principles that can be used to select indicators and
construct monitoring programs for assessing the impact of and recovery from low flows; namely, low
flows influencing habitat availability (principle 1), habitat quality (principle 2), energy transfers
(principle 3) and the connectivity of habitats influencing dispersal (principle 4).
The guiding principles in this review have been used to inform the recommendation of a range of
indicators that could be used to assess the impact of, and recovery from, low-flow events. However,
the assessment of the ecological responses to low flows needs to ensure that the spatial and
temporal scales of monitoring are ecologically relevant according to the predicted mechanism of lowflow stress. Streams and rivers across Australia have now been classified based on a range of broad
hydrological metrics (Kennard et al. 2010), as well as a suite of low-flow specific metrics (Mackay et
al. 2012). This provides a mechanism for the spatial comparison of sites across broad geographic
areas. This review suggests that different potential indicators of low-flow impact respond to low flows
over different temporal and spatial scales; for example, a macroinvertebrate indicator that reflects the
proportion of rheophilic taxa in an assemblage would be more applicable for assessing low-flow
impact in perennial streams, where low flows may cause a decrease in the proportion of rheophilic
taxa. Such an indicator would be less relevant or useful in a naturally intermittent river where the
proportion of rheophilic taxa is either very low naturally, or rheophilic taxa do not naturally occur. In
this latter situation indicators more relevant to ephemeral streams would need to be used. Indicators
of low-flow stress are likely to be harder to define as the frequency, magnitude and duration of natural
low-flow stress increases and the biota are naturally adapted to cope.
Addressing low-flow impacts is potentially more straightforward than assessing low-flow recovery,
which needs to include concepts of resistance and resilience. For example, if ecosystems display low
resistance but high resilience to natural low flows, then this indicates that the resident biota have traits
that allow them to persist during low-flow periods (e.g. rapid dispersal to/from refugia) and their
recovery from a low-flow impact will be rapid. However, if an ecosystem displays low resilience to lowflow events, then the recovery from a low-flow event may be protracted. Management actions
therefore need to be informed by examining post-low-flow events to enable prediction of ecological
thresholds to altered low-flow regimes.
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Shortened forms
ANZECC
Australia New Zealand Environment Conservation Council
BFI
Baseflow index
CV
coefficient of variation
EM
Expectation-maximisation
EPT
Ephemeroptera (mayfly), Plecoptera (stonefly) and Trichoptera (caddisfly)
IBI
Index of Biotic Integrity
MDB SRA
Murray-Darling Basin Sustainable Rivers Audit
NDVI
Normalised Difference Vegetation Index
NWI
National Water Initiative
SEQ EHMP
South East Queensland Environmental Health Monitoring Program
SIGNAL
Stream Invertebrate Grade Number-Average Level
SPEAR
Species at Risk
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Glossary
Abundance: frequency of occurrence. A species present in great numbers is abundant.
Aerophily: pertaining to air or oxygen. Aerophilic species have a preference for well-oxygenated
waters.
Alien species: a species that would not have occurred at a location without anthropogenic input.
Allochthonous: pertaining to substances, materials or organisms originating outside the stream.
Usual context is to refer to the source of carbon or nutrients from terrestrial sources that are washed
into the stream.
ANZECC guidelines: Australia New Zealand Environment Conservation Council water quality
guideline values which are frequently used to assess water quality.
Australian drainage divisions: regions of broadly similar hydrology, originally defined by the
Australian Water Resources Commission on the basis of climate and topography.
Autochthonous: pertaining to substances, materials or organisms originating within the stream.
Usual context is to refer to the source of carbon or nutrients as derived from the stream (as opposed
to terrestrial inputs – see Allochthonous)
Benthic: bottom. Refers to organisms that live on the stream bed (as opposed to those that live in the
water column).
Baseflow index: the proportion of a stream’s discharge due to baseflow or groundwater.
Community diversity: a community is a collection of organisms within a specified area. The number
of different taxa represents the diversity of the community.
Coefficient of variation: mean divided by the standard deviation of a dataset. A unitless measure of
the distribution of a dataset.
Decomposition: the process by which organic matter is broken down into simpler forms of matter.
Diatom: a major group of algae and one of the most common types of phytoplankton.
Disturbance (ecological): a change in environmental condition(s) that produce or cause a response
in an aspect (either structural or functional) of an ecosystem (see, for example, Resh et al. 1988; Lake
2000).
Drainage division: the major hydrologic drainage areas of Australia are divided into 12 drainage
divisions (e.g. Murray-Darling Division, Tasmanian Division).
Drought: difficult to define (Humphries & Baldwin 2003) due to significant variability in flow regimes
(Kennard et al. 2010). A period of significantly lower water availability (flow) when compared with
long-term central (median) or average conditions for a particular geographic region.
Ecosystem recovery trajectories: explains the path that an ecosystem takes as it recovers from a
disturbance (see Disturbance).
Ephemeral: Streams and rivers that discharge water during and immediately after rainfall. These
streams do not have significant baseflow, meaning that such streams are generally dry (apart from
isolated waterholes) when not flowing.
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Ephemeroptera (mayfly), Plecoptera (stonefly) and Trichoptera (caddisfly): these taxa are
sensitive to low dissolved oxygen, high salinity and high water temperatures and scores of their
collective relative abundance are often used to demonstrate the prevailing stream conditions.
Expectation-maximisation: algorithm: an iterative method for estimating the parameters of a
statistical model.
Family richness: the number of different taxonomic families in a sample. A site of high family
richness has many different families of species present. A site of high species richness has many
different species, but these may be from only a few families. Macroinvertebrate datasets are
frequently only identified to family level.
Flow regime: the long-term (tens of years) combination of the magnitude, timing, duration, frequency,
and rate of change of streamflow that characterises the hydrology for a stream.
Fluvial: pertaining to water (fluvial geomorphology is the study of landforms created by water such as
river channels).
Fulton’s Condition Factor (K): a commonly used indicator of fish health which is computed as a
fish’s body mass divided by the cube of its length.
GIS: Geographic Information System.
Higher-order consumers: a ‘first order consumer’ is any organism that feeds on a plant. Higherorder consumers feed on first order consumers.
Hydraulic conditions/hydraulic habitat: the characteristic habitat features created by water (e.g.
velocity, depth, shear stress).
Hyporheic zone: the wetted interstitial zone within the sediments below and alongside rivers. This
zone often contains invertebrates specialised for a hypogean existence.
Impact (pressure): a disturbance (see definition of Disturbance) either natural or anthropogenic that
creates a resultant affect. Usually considered in the context of a pressure (such as water extraction)
resulting in an effect such as water quality decline.
Index of Biotic Integrity: the IBI was initially developed as a multi-metric index reflecting fish health
(based on 12 metrics including species richness, composition and abundance). Many alternative
region-specific IBI approaches are now used, and the term generally means a multi-metric index.
Intermittent: streams and rivers that have seasonally predictable flow that occurs between a few
months to multiple years depending on climate conditions. These streams are placed in the middle of
a continuum from ephemeral to permanent.
Lag effect: a delayed response to an impact or disturbance (see definition of Disturbance and
Impact).
Low-flow regime: ecologically, the hydrological definition of ‘low flow’ will depend on the spatial
extent and temporal aspect of a river’s hydrograph and the varying flow requirements of waterdependent biota and ecological processes (Smakhtin 2001).
Low flow (working definition): difficult to define broadly across geographic and climatic regions
(Smahktin 2001), hence the likely reason why the term ‘low flow’ is often not defined in the
ecohydrological literature, although this lack of a clear definition is generally acknowledged (e.g.
Dewson et al. 2007; Larned et al. 2010; Suren & Riis 2010). Frequently ‘low flow’ is defined in
hydrologic contexts based on flow exceedence probabilities (e.g. 95 per cent exceedence flow) or
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deviations from baseflow (see, for example, Suren & Riis 2010). For the purpose of this work, we
define low flow as the volume (i.e. magnitude) of water that occurs over a given frequency and
duration that is responsible for a mechanistic change in the processes and structure of aquatic
ecosystems (including surface water, groundwater and estuaries), relative to the average or median
discharge for an individual river (or river reach). We emphasise that this implies that definitions of low
flow that are ecologically relevant will never be universally applicable given spatial variation in river
flow regimes and also the temporal scale at which ‘low flow’ events are quantified (sensu Biggs et al.
2005)
Low-flow spell/low-flow event: a continuous period where low-flow conditions continuously prevail.
In tropical Australia the low-flow spell typically coincides with the dry season and is a period of
continuous drying or decrease in streamflow.
Macroinvertebrate indicators:
–
predators: a functional feeding group that consumes other animals
–
scrapers: a functional feeding group that feeds by scraping algae from surfaces
–
collector-gatherers: a functional feeding group that feeds on fine organic matter by brushing it
off surfaces or from by burrowing in soft sediments
–
filter-feeders: a functional feeding group that filter-feeds on fine organic matter.
Multi-metric classification: pertaining to a classification or reporting method whereby more than one
measurement is combined to give a single score.
Normalised Difference Vegetation Index: a satellite-derived vegetation vigour index (2003).
NDVI anomaly: this is a measure of the deviation in vegetation vigour from the long-term vegetation
vigour. The NDVI Anomaly can be used to compare the relative changes in vegetation vigour between
regions (e.g. compare relative drought severity in different locations) that otherwise have different
long-term NDVI scores.
Num. zero days: number of consecutive days where there is no measured streamflow.
National Water Initiative: the Intergovernmental Agreement on a National Water Initiative was
signed at the 25 June 2004 Council of Australian Governments meeting. The Tasmanian Government
joined the Agreement in June 2005 and the Western Australian Government joined in April 2006. The
NWI represents a shared commitment by governments to increase the efficiency of Australia's water
use, leading to greater certainty for investment and productivity, for rural and urban communities, and
for the environment (http://www.nwc.gov.au/reform/nwi).
Nutrient cycling: movement and exchange of organic and inorganic matter back into the production
of living matter, and through this process the transformation of nutrients to different compound forms
which are more or less bioavailable (e.g. ammonium, nitrites, nitrates, nitrogen).
Perennial: streams and rivers that consistently discharge water sourced from runoff and groundwater
in all but extreme drought periods where groundwater availability is so low that connection to the main
channel of the stream is lost.
Population metrics: the combined range of measures used to describe the dynamics of a
population, such as fecundity and survivorship.
P90: 90th percentile flow. This is the flow value, below which 90 per cent of flow values fall (i.e. a high
flow-value). The 90th percentile exceedence is the flow which is exceeded by 90 per cent of flow
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values (i.e. a low flow). 90th percentile = 10th percentile exceedence; 10th percentile = 90th
percentile exceedence.
Recruitment: a reproductive opportunity that results in the production of juveniles. A fish may lay
eggs that hatch (i.e. reproduce), but this is not considered recruitment until the larvae reach a juvenile
stage.
Refuges/refugia: habitat remnants that provide refuge for species during periods of environmental
stress. In the context of these reports, refuges are pools where animals retreat during extended dry
periods.
Resistance: the capacity to tolerate or withstand a disturbance. That is, to show little or no change in
response to a disturbance (see Lake 2000).
Resilience: the ability to recover from a disturbance (see Disturbance definition and Lake 2000).
Response (ecological): the ecological effect of a disturbance (see Disturbance definition and Lake
2000). Response can be measured using a range of different indicators (e.g. species richness,
decomposition etc.).
Rheophilic: having a preference for running water; for example, filter-feeding macroinvertebrates
have a preference for flowing waters.
Sensitive taxa: taxa sensitive to periods of stress (in this case from low flow).
Short-term flow conditions: those prevailing during the 90 days before sampling).
Stream Invertebrate Grade Number – Average Level: an indication of water quality based on the
presence and abundance of different macroinvertebrates. Streams with high SIGNAL scores are likely
to have low levels of salinity, turbidity, and nutrients such as nitrogen and phosphorus and are likely to
be high in dissolved oxygen.
SPEAR (Species at Risk): a response indicator used to measure impact of a stressor (in this case
low flow).
Specific mean annual min: the mean of the minimum flow values for each year of the record.
Temporary: often used interchangeably between ephemeral and intermittent flow regimes (see
Larned et al. 2010).
Thermophily: being able to tolerate a large temperature range. This particularly applies to
macroinvertebrates that can tolerate higher temperatures that occur in shallow pools.
Tolerant taxa: taxa able to withstand periods of stress (in this case from low flow).
Traits: characteristics or properties of an organism. Rheophily (preference for flowing water) is an
example of a trait.
Trophic relationships: also called feeding relationships. Can be presented as a foodweb or a food
chain representing links between different trophic levels (producers, consumers, decomposers).
Water quality: the chemical and physical characteristics of the water. In the context of these reports,
the principal water quality components are temperature, dissolved oxygen, salinity (reported as
conductivity) and water clarity (often reported as turbidity).
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Reports in the low flows series
Balcombe SR & Sternberg D 2012, Fish responses to low flows in dryland rivers of western
Queensland, National Water Commission, Canberra.
Barma D & Lowe L 2012, Low-flow hydrological monitoring and modelling gaps, National Water
Commission, Canberra.
Barmah D & Varley I 2012a, Hydrologic modelling practices for estimating low flows – stocktake,
review and case studies, National Water Commission, Canberra.
Barmah D & Varley I 2012b, Hydrologic modelling practices for estimating low flows – guidelines,
National Water Commission, Canberra.
Bond N 2012, Fish responses to low flows in lowland streams: a summary of findings from the Granite
Creeks system, Victoria, National Water Commission, Canberra.
Bond N, Thomson J & Reich P 2012, Macroinvertebrate responses to antecedent flow, long-term flow
regime characteristics and landscape context in Victorian rivers, National Water Commission,
Canberra.
Chessman B, Haeusler T & Brooks A 2012, Macroinvertebrate responses to low-flow conditions in
New South Wales rivers, National Water Commission, Canberra.
Deane D 2012, Macroinvertebrate and fish responses to low flows in South Australian rivers, National
Water Commission, Canberra.
Dostine PL & Humphrey CL 2012, Macroinvertebrate responses to reduced baseflow in a stream in
the monsoonal tropics of northern Australia, National Water Commission, Canberra.
Hardie, SA, Bobbi, CJ & Barmuta, LA 2012, Macroinvertebrate and water quality responses to low
flows in Tasmanian rivers, National Water Commission, Canberra.
Kitsios A, Galvin L, Leigh C & Storer T 2012, Fish and invertebrate responses to dry season and
antecedent flow in south-west Western Australian streams, National Water Commission,
Canberra.
Leigh, C 2012, Macroinvertebrate responses to dry season and antecedent flow in highly seasonal
streams and rivers of the wet-dry tropics, Northern Territory, National Water Commission,
Canberra.
Mackay S, Marsh N, Sheldon F & Kennard M 2012, Low-flow hydrological classification of Australia,
National Water Commission, Canberra.
Marsh N, Sheldon F & Rolls R 2012, Synthesis of case studies quantifying ecological responses to
low flows, National Water Commission, Canberra.
Marsh N, Sheldon F, Wettin P, Taylor C & Barma D 2012, Guidance on ecological responses and
hydrological modelling for low-flow water planning, National Water Commission, Canberra.
Rolls R, Marsh N & Sheldon F 2012, Review of literature quantifying ecological responses to low
flows, National Water Commission, Canberra.
Rolls R, Sheldon F & Marsh N 2012, Macroinvertebrate responses to prolonged low flow in subtropical Australia, National Water Commission, Canberra.
Sheldon F, Marsh N & Rolls R 2012, Early warning, compliance and diagnostic monitoring of
ecological responses to low flows, National Water Commission, Canberra.
Smythe-McGuiness Y. Lobegeiger J, Marshall J, Prasad R, Steward A, Negus P, McGregor G & Choy
S 2012, Macroinvertebrate responses to altered low-flow hydrology in Queensland rivers,
National Water Commission, Canberra.
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