PLANKTON COMMUNITIES OF ARTIFICIAL
LAKES CREATED ON IRISH CUTAWAY
PEATLANDS
Tara Higgins, Henry Kenny and Emer Colleran
ABSTRACT
Lake creation represents a major post-harvesting land-use option for industrial cutaway peatlands in
Ireland, yet little is currently understood about the ecology of cutaway water-bodies, particularly at
the microbiota level. The current paper describes for the first time the littoral zooplankton
community in three contrasting artificial cutaway lakes and one natural bog lake. The study lakes,
which were sampled on five occasions in 2003, contrasted strongly in their physico-chemical
characteristics, nutrient states and trophic classifications. These trends reflected variations between
sites in sediment types, water supply sources and catchment land uses. In the absence of fish,
invertebrate predation by cyclopoid copepods (Tropocyclops prasinus ) and cladocerans (Polyphemus
pediculus) appeared to play an elevated role in structuring the zooplankton communities in the study
lakes, in terms of abundance, species composition and size structure.
Tara Higgins
(corresponding
author, e-mail: tara.
higgins@nuigalway.
ie), Department of
Zoology, National
University of Ireland,
Galway; Ireland;
Henry Kenny and
Emer Colleran
Environmental
Microbiology
Research Unit,
Department of
Microbiology,
National University of
Ireland, Galway.
Received 26 May
2006. Accepted 15
March 2007.
Published 20 July
2007.
BIOLOGY
AND
INTRODUCTION
Of the 80,000 hectares of peatlands coming out of
commercial production in Ireland by 2030, Bord na
Móna, the Irish Peat Board, envisages that more
than 50% will be designated as semi-natural
wilderness areas for conservation and recreation
uses (Egan 1999). This will include an estimated
20,000 hectares of shallow lakes and wetlands. The
scale of the proposals is vast, representing one of the
largest wildlife habitat creation opportunities to
emerge in Europe in modern times.
An initial series of experimental lakes has been
created within a 2000ha cutaway raised bog site in
the Irish midlands, in a pilot rehabilitation project
called the Lough Boora Parklands. Smaller-scale
lake creation trials are also being conducted at Bord
na Móna’s Oweniny Atlantic blanket bog complex
near Bellacorick in County Mayo. Approaches used
when developing lakes on industrial cutaway
peatlands have varied enormously in terms of the
degree of peat removal, basin construction,
hydrological manipulation and post-flooding
management. Cutaway lakes, as a consequence,
differ markedly in their water chemistry
characteristics and trophic statuses, ranging from
alkaline, oligotrophic angling lakes with inorganic
sediments to highly acidic, hypertrophic waterbodies underlain exclusively by peat (Higgins and
Colleran 2004; 2006). Because cutaway lakes are
new and highly complex systems, very little is
understood about their ecology as yet, particularly
at the level of the microbiota, and there are at
present no methods for predicting development
ENVIRONMENT: PROCEEDINGS
OF THE
that are based on experience. As part of a wider
investigation into the potential conservation value
of cutaway lakes (Higgins and Colleran 2006), the
current research provides the first ever assessment of
the littoral zooplankton communities of three
contrasting cutaway lake types and a natural,
intact bog lake. The primary factors governing
zooplankton distribution in cutaway lakes are elucidated in this paper, and the wider significance of
these findings for cutaway lake ecology is assessed.
METHODS
STUDY SITES AND FIELD SAMPLING
Three artificial cutaway peatland lakes and one
natural blanket bog lake were selected for this
study. The study lakes differed in terms of their
location, age, type of underlying sediments and
littoral vegetation cover (Table 1). Two of the
cutaway lakes, Turraun (Fig. 1c) and Clongawny
(Fig. 1a), were located on cutaway raised bog in
mid-west County Offaly (for detailed descriptions,
see Higgins and Colleran (2006)). The third
cutaway lake, Bellacorick cutaway lake, was
located on cutaway blanket bog at Bellacorick in
north-west County Mayo. The fourth study site,
regarded as a reference bog lake, was situated on
intact Atlantic (lowland) blanket bog at Bellacorick,
Co. Mayo.
Samples for zooplankton analysis were
collected on a monthly basis between June and
October 2003. Samples were collected from the
two Bellacorick lakes on 25 June, 24 July, 20
ROYAL IRISH ACADEMY, VOL. 107B, NO. 2, 77 85 (2007).
#
ROYAL IRISH ACADEMY
77
BIOLOGY
AND
ENVIRONMENT
August, 25 September and 30 October, while
samples from the midland lakes were collected on
23 June, 22 August, 19 August, 23 September
and 29 October. Six-litre surface water samples
(0.2m) were collected from between eight and
ten different sampling stations along the littoral
zone of each lake. Samples were screened though
a 90mm mesh in a filtering cone, to give a single
composite sample for each lake. Composite samples
were gently washed with 100% ethanol into 500ml
wide-mouth plastic storage bottles. PH and
conductivity were determined on site using a field
kit (WTW P4 Multiline). Composite 2l water
samples for physico-chemical, nutrient and phytoplankton analysis were also collected from each
lake.
WATER CHEMISTRY ANALYSIS
Dissolved colour was read spectrophotometrically
at 465nm on samples filtered through GF/C filters,
while alkalinity was calculated using a standard
H2SO4 titration method (APHA 1998). Soluble
inorganic carbon was measured on filtered samples
using a Shimadzu TOC-5000A analyser (APHA
1998), and silicate was determined on filtered
samples using a low-range heteropoly blue
method (Hach 2001). Soluble reactive phosphorus
(SRP) and total phosphorus (TP) were analysed
using the ascorbic acid reduction method (Murphy
and Riley 1962), involving persulphate digestion of
unfiltered samples for TP. Ammonium, nitrate and
nitrate were determined spectrophotometrically on
filtered samples using low-range indophenol blue
(Chaney and Morbach 1962), cadmium reduction
and diazotisation methods, respectively (Hach
2001). The sum of nitrate, nitrite and ammonium
is reported as dissolved inorganic nitrogen (DIN).
Table 1
*
ZOOPLANKTON AND PHYTOPLANKTON
ANALYSIS
Zooplankton subsamples were enumerated in a
custom-made, mechanically rotating, circular
counting
tray
and
binocular
dissecting
microscope. At least 100 individuals of the more
common species were counted. Identifications of
zooplankton to the genus or species level, where
possible, were based on standard identification keys,
with expert verification where necessary (M.
Holmes and E. De Eyto, pers. comm.). Size
determinations were made using a micrometer
fitted in one of the microscope eyepieces;
biovolumes were calculated by comparing
individual species to geometric shapes and
applying the relevant geometric formula. Size
measurements were taken of at least five
individuals of each species from every sample
counted. Species richness (S ) was estimated as the
total number of species recorded (MacIntosh 1967).
Species diversity was assessed using Simpson’s index
(D) (Simpson 1949), which ranks samples on a scale
of 0 (a community comprised of a single species) to
1 (all species in a community are present in equal
proportion).
Phytoplankton cells were preserved in Lugol’s
iodine and were identified, measured and counted
Characteristics of the four study lakes, Turraun cutaway lake, Clongawny cutaway
lake, Bellacorick natural lake and Bellacorick cutaway lake.
Location
Year constructed
Size (ha)
Mean depth (m)
Lake sediments
Littoral vegetation
biomass (kg m 2)
Dominant littoral
vegetation
78
Samples for chlorophyll a analysis were filtered
immediately on return to the laboratory through
GF/C filters, extracted using a mixture of 90%
acetone and dimethly sulfoxide (1:1 v/v) (Burnison
1980) and measured spectrophotometrically with
correction for phaeopigments. All water chemistry
analyses were performed in triplicate; data presented
are overall means for each lake9the standard error
of the mean (SEM).
Turraun
cutaway lake
Clongawny
cutaway lake
Bellacorick
natural lake
Bellacorick
cutaway lake
07844?W 53815?N
1991
55
0.5
Phragmites peat,
shell marl
38
07853?W 53810?N
2001
12
1.0
Sphagnum peat,
woody fen peat
0.6
54806?N 9834?W
n/a
10
1.5
Cyperaceous peat
35
54807?N 9835?W
1995
6
0.8
Highly humified
cyperaceous peat
18
Typha
Phragmites
Juncus
Phragmites
Juncus
Schoenus
Molinia
Calluna
Juncus
Eriophorum
Carex
PLANKTON
COMMUNITIES OF CUTAWAY PEATLAND LAKES
*
Fig. 1 (a) Clongawny cutaway lake, showing the paucity of recolonising vegetation and the bare, unconsolidated nature
of the peaty sediments at the site; (b) the industrial peatland landscape, pre-flooding; (c) flooded cutaway peatland at
Turraun, showing the success and extent of revegetation at this site.
with an inverted microscope. Biovolumes were
calculated by comparing individual cells to simple
geometric shapes and applying relevant standard
formulae (Rott 1981). Phytoplankton species
diversity was assessed using Simpson’s index of
diversity (Simpson 1949).
RESULTS
A number of distinct trends are evident from the
physico-chemical and biological data for the four
study lakes presented in Table 2. Turraun was an
alkaline, largely clear water, mesotrophic eutrophic
lake, with a moderately diverse phytoplankton
assemblage comprising a mixture of chlorophytes,
cyanophytes and diatoms. Clongawny was an
acidic, highly stained, eutrophic hypereutrophic
lake in which minute, unicellular chlorophytes
were overwhelmingly dominant. Bellacorick
natural lake was an acidic, highly stained,
mesotrophic lake in which flagellated unicellular
chlorophytes characterised the phytoplankton
community. Bellacorick cutaway lake was a
neutral, very highly stained, mesotrophic lake
with a diverse phytoplankton community consisting of diatoms and chlorophytes.
The study sites also contrasted strongly in
zooplankton abundances. Zooplankton densities
were highest in Clongawny, particularly in
September, when a peak of 1237 organisms l 1
was recorded (Fig. 2a). Bellacorick natural lake
records showed the second greatest abundance
of zooplankton (13 141 organisms l 1) (Fig. 2d),
while zooplankton numbers were consistently low
in Bellacorick cutaway lake (1 12 organisms l 1)
(Fig. 2c) and Turraun (0.04 7 organisms l 1)
(Fig. 2b).
Species richness and diversity levels were
highest in Bellacorick natural lake (18 species,
D 0.613), lowest in Turraun (nine species, D
0.395) and intermediate in Clongawny (twelve
species, D 0.431) and Bellacorick cutaway
lake (twelve species, D 0.520) (Table 3). The
zooplankton community in Clongawny was
dominated by chydorids, chiefly Chydorus
sphaericus , in June, July and October (Fig. 2a and
Table 3). Cyclopoid copepods, represented mainly
by Tropocyclops prasinus , were recorded in
Clongawny in high numbers during August (347
organisms l 1) and September (108 organisms l 1).
These high densities of Tropocyclops prasinus
corresponded with reduced rotifer densities in the
79
BIOLOGY
AND
ENVIRONMENT
lake, while the reverse was true in October when
rotifer densities increased to 1087 organisms l1
(72% of total zooplankton biovolume) and
cyclopoid copepod densities declined (Fig. 3a).
In Turraun, the Bosminidae was the only
family consistently present. Rotifers, and to a
lesser extent bosminids, accounted for the higher
zooplankton abundance observed in Turraun in
June (7 organisms l1) (Fig. 2b). The calanoid
copepod Diaptomus gracilis was notably present in
the lake in August and September, while the
macrothricid species Ilyocryptus sordides was
significant in October (Fig. 2b and Table 3).
The zooplankton fauna in Bellacorick natural
lake was dominated by cladocerans. Dominant
cladoceran species in Bellacorick natural lake
included the large predatory polyphemid species
Table 2
*
Polyphemus pediculus in June, July and August,
bosminids in June and July, chydorids in June,
July and October, daphnids such as Ceriodaphnia
setosa and Scapholeberis mucronata in July, August and
September, and the large-bodied macrothricid
Acantholeberis curvirostris in August and September.
The cyclopoid copepod Eucyclops serrulatus was
significant in Bellacorick natural lake in October
(Fig. 2c and Table 3). An inverse relationship was
discernable between densities of Polyphemus
pediculus and small cladocerans in Bellacorick
natural lake over the course of sampling, with
peaks in the density of P. pediculus in June (28
organisms l1) and August (22 organisms l1)
corresponding to low numbers of cladocerans, with
the reverse being true in July, September and
October (Fig. 3b).
Nutrient status and phytoplankton characteristics of the Turraun cutaway lake, Clongawny cutaway lake,
Bellacorick natural lake and Bellacorick cutaway lake. Values shown are the mean of five monthly samples
collected between June and October 2003, 9SEM.
Turraun
cutaway lake
PH
Conductivity (mS cm 1)
Colour (mg Pt. Co. l 1)
Alkalinity (mg CaCO3 l1)
Silica (mg l1)
Dissolved inorganic N (mg l1)
Soluble reactive P (mg l1)
Total P (mg l 1)
Chlorophyll a (mg l1)
Trophic status1
Phytoplankton biovolume
(mm3 l1)
Phytoplankton composition (%)2
Bellacorick
natural lake
Bellacorick
cutaway lake
4.590.09
7792
14495
0.990.4
0.0790.02
1.291.0
5.492.0
66.198.0
126.795.8
Eutrophic hypertrophic
77,60096,642
4.490.06
9697
16697
2.090.6
0.0690.02
6.491.6
6.190.5
13.191.2
3.991.2
Mesotrophic
903988
7.190.04
119917
18499
30.594.1
0.2590.15
11.396.8
6.091.4
14.591.2
2.990.8
Mesotrophic
1,0019329
30% Cyanophyta
30% Chlorophyta
27% Bacillariophyta
5% Dinophyta,
5% Chrysophyta
Dominant phytoplankton groups Chlorococcaleans
Naviculoid diatoms
Coelosphaerium
90% Chlorophyta
5% Dinophyta
2% Cryptophyta
48% Bacillariophyta
34% Chlorophyta
9% Chrysophyta
4% Dinophyta
Phytoplankton diversity (D )3
0.256
60% Chlorophyta
18% Dinophyta
6% Chrysophyta
4% Bacillariophyta
Chlamydomonas
Dunaliella
Pteromonas
Gymnodinium
Mallomonas
Dinobryon
0.473
1
8.390.05
261912
4593
114.797.7
0.4290.25
9.297.0
3.090.6
27.394.1
10.192.6
Mesotrophic eutrophic
4,40091,049
Clongawny
cutaway lake
0.501
Cosmarium pygmaeum
Chlorella ; Peridinium
Based on total phosphorus and chlorophyll a concentrations (OECD 1982).
Based on mean (n 5) percentage contribution of phytoplankton groups to total phytoplankton biovolume.
3
Values are Simpson Diversity Indices.
2
80
Cyclotella
Tabellaria
Achnanthes
Chlorella
Kirchnerialla
Dinobryon
0.705
PLANKTON
COMMUNITIES OF CUTAWAY PEATLAND LAKES
*
Fig. 2 Composition of zooplankton in the four study lakes between June and August 2003, in terms of density
(organisms l 1) and relative biovolume (%).
In Bellacorick cutaway lake, the polyphemid
Polyphemus pediculus dominated the zooplankton
between June and September (0.12 9 organisms
l1), while bosminids were significant in July and
September and the cyclopoid copepod Eucyclops
serrulatus was abundant in July, September and
October (Fig. 2d and Table 3). Despite the lower
densities of Polyphemus pediculus at this site
compared with Bellacorick natural lake, a similar
inverse relationship between small cladocerans and
P. pediculus abundance was apparent in Bellacorick
cutaway lake (Fig. 3c).
DISCUSSION
Differences in physico-chemical, nutrient and
trophic statuses among the four study lakes
corresponded with large variations in littoral
zooplankton density, composition and size
structure. Clongawny cutaway lake was an acidic,
highly stained lake, reflecting the presence of
unconsolidated Sphagnum and woody fen peat
sediments at this site and an absence of hard water
inflows. High phosphorus levels in Clongawny
supported extremely high phytoplankton growth
81
BIOLOGY
AND
ENVIRONMENT
rates, and the lake contained bloom quantities of
minute, unicellular Chlorophytes such as Chlorella
and Cosamarium pygmaeum . The eutrophication of
Clongawny has resulted from phosphorus leaching
Table 3
*
from adjacent commercial forestry plantations
(Higgins et al . 2006), highlighting the vulnerability of lakes created on unvegetated, bare
cutaway peatlands to nutrient runoff.
Presence and relative abundance of zooplankton species in the four study lakes.
Turraun
cutaway lake
CLADOCERA
Chydoridae
Chydorus sphaericus (Müller)
Chydorus piger (Sars)
Alona affinis (Leydig)
Alona rustica (Scott)
Alona costata (Sars)
Alonella exigua (Lilljeborg)
Alonella nana (Baird)
Alonopsis elongata (Sars)
Graptoleberis testudinaria (Fischer)
Bosminidae
Bosminia spp
Daphnidae
Daphnia spp
Ceriodaphnia setosa (Matile)
Scapholeberis mucronata (Müller)
Polyphemidae
Polyphemus pediculus (Linnaeus)
Macrothricidae
Acantholeberis curvirostris (Müller)
Drepanothrix dentate (Eurén)
Ilyocryptus sordides (Liénen)
Clongawny
cutaway lake
Bellacorick
natural lake
Bellacorick
cutaway lake
ROTIFERA
Keratella spp
Total species number
Simpson’s D
9
0. 395
12
0. 517
18
0.613
12
0.520
COPEPODIA
Cycloida
Eucyclops serrulatus (Fischer)
Tropocyclops prasinus* (Fischer)
Calanoida
Diaptomus gracilis (Sars)
Calanoid spp
Harpacticoida
Bryocamptus pygmaeus (Sars)
* rare species in Ireland (M. Holmes, pers. comm.)
55% of biovolume.
6 15% of biovolume.
16 50% of biovolume.
51% of biovolume.
82
PLANKTON
Org a ni sms l
400
Rotifera
Sml. cladocera
T. prasinus*
300
200
−1
1,000
800
600
400
200
0
Orga nisms l
−1
a 1,200
COMMUNITIES OF CUTAWAY PEATLAND LAKES
100
0
June
July
Aug
Sept
Oct
Clongawny cutaway lake
10
1.0
Polyphemus pediculus
0.8
Small Cladocera*
6
0.6
4
0.4
2
0.2
−1
O r g a ni sm s l
8
O rga ni sms l
−1
b
0.0
0
June
July
Aug
Sept
Oct
Bellacorick natural lake
c
O r ga ni s ms l
−1
100
80
Polyphemus pediculus
Small Cladocera
60
40
20
0
June
July
Aug
Sept
Oct
Bellacorick cutaway lake
*
Fig. 3 Distribution of dominant zooplankton groups in
Clongawny cutaway lake, Bellacorick natural lake and
Bellacorick cutaway lake between June and August 2003
(*series plotted on secondary y -axis).
Although Chydorus sphaericus was abundant in
Clongawny (1056 8842 organisms ml1), similar
to other productive Irish lakes (De Eyto et al. 2000;
De Eyto 2001; Irvine et al . 2001), it proved
ineffective
in
controlling
phytoplankton
production in Clongawny. Large numbers of the
predatory cyclopoid copepod Tropocyclops prasinus
also occurred in Clongawny. This species is rarely
recorded in Ireland (M. Holmes, pers comm.),
although it is widely reported in bog pools in the
US (Sanderson and Frost 1996) and Canada
(Masson and Pinel-Alloul 1998). The success of
predatory cyclopoid copepods in bog pool is caused
by an absence of fish predation, and it results in
zooplankton communities characterised by largebodied invertebrates, reduced overall foodweb
complexity and stronger interactions between
zooplankton and invertebrate predators (Arnott
and Vanni 1993; Gibbons 1998). The omnivorous
T. prasinus has the potential to selectively capture
a wide variety of suitably sized invertebrate
prey, particularly given enriched food availability;
studies have documented the effectiveness of
T. prasinus in reducing populations of small
cladocerans, (Melao and Rocha 2004) and rotifers
(Dieguez and Gilbert 2002; Lapesa et al. 2002).
Its abundance in Clongawny appeared to impact
on the populations of small cladocerans and rotifers
recorded in the lake, whose susceptibility to
predation by T. prasinus was likely to have been
enhanced by the lack of shielding macrophytes at
this bare, unvegetated site (Fig. 1a).
The structure and composition of the
zooplankton communities in Bellacorick Natural
and Bellacorick cutaway lakes, as in Clongawny,
reflected an elevated level of invertebrate predation
in these fishless systems. Despite strongly contrasting physico-chemical environments indicative
of contrasting peat sediment types, the zooplankton
community in Bellacorick cutaway lake was
broadly similar to that of the nearby indigenous
bog lake, Bellacorick natural lake. Both sites
contained large populations of the large-bodied
predatory cladoceran Polyphemus pediculus , a species
that feeds selectively on protozoans, rotifers and
small cladocerans across a wide range of pH
environments (Berzins and Bertilsson 1990;
Packard 2001). The three coloured lakes,
Bellacorick natural lake, Bellacorick cutaway lake
and Clongawny lake, all contained high densities of
detritivorous chydorids, as is characteristic of bog
pools (Crisp and Heal 1998; Irvine et al. 2001).
Chydorids are also successful pioneering species,
and were historically the characteristic fauna of
post-glacial lakes following the retreat of the ice
sheets (Harmsworth 1968; Duigan and Birks 2000).
In Turraun cutaway lake, zooplankton
densities were consistently low, despite of the
high food base in the form of an abundant and
edible phytoplankton population. The low zooplankton densities in Turraun, relative to the
rich food base, were probably symptomatic of
a rich macroinvertebrate population. Although
not quantitatively assessed in the current study,
the well-developed macroinvertebrate population
in Turraun has been previously described by
O’Connor (2000), O’Connor et al. (2000) and
Trodd (2003). Macroinvertebrate predation by
specialised grazer guilds is known to have
substantially greater effects on the dynamics and
structure of zooplankton communities in habitats
where vertebrate predators are scarce or absent
(Herwig and Schindler 1996; Wissel and Benndorf
1998; McNaught et al. 1999).
Age and subsequently colonisation time were
likely to have been major factors influencing the
proportionately greater role of macroinvertebrate
predation in Turraun, relative to the other
sites. Turraun, which was created in 1991, is the
longest established cutaway lake in Ireland, and it
contains extensive cover of submerged, emergent,
littoral and terrestrial macrophytes (Fig. 1c and
83
BIOLOGY
AND
Table 1). While studies have shown that populations of phytoplankton (Feehan and Donovan
1996), protozoans (Buttler et al. 1996), and microinvertebrates (Van Duinen et al . 2003) can establish
very quickly after cutaway peatlands are flooded,
macroinvertebrate populations take a considerable
length of time to develop (Van Duinen et al. 2004).
This is because macroinvertebrates have more
complex life cycles and make higher demands on
their environment (O’Connor 2000; Trodd 2003;
Van Duinen et al . 2003; 2004). Age increases both
the length of time over which colonisation can
proceed and also influences sediments, vegetation
cover and plant species richness. The paucity of
recolonising vegetation at Clongawny (Fig. 1a and
Table 1), in contrast to Turraun and Bellacorick
cutaway lake sites, reflects its more recent
establishment and related physical and biological
features, such as the propensity of bare,
unconsolidated peat sediments to desiccate and
the absence of viable seed banks (Curraun and
MacNaeidhe 1986), which collectively hamper
plant invasion. Given the considerable timescales
involved in ecosystem establishment and
stabilisation, further monitoring and in-depth
research is needed in order to assess long-term
successional trends in artificial cutaway peatland
lakes.
ACKNOWLEDGEMENTS
The authors wish to thank Bord na Móna for
funding this research. The assistance of Mark
Holmes (Natural History Division, Natural
History Museum, Dublin) and Elvira De Etyo
(Marine Institute, Furnace, Newport, Co. Mayo)
in confirming zooplankton identifications is also
appreciated.
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