Nearshore Coastal Water Quality
in Pegasus Bay, Canterbury
July 2013
Nearshore Coastal Water Quality
in Pegasus Bay, Canterbury
July 2013
Report prepared for Environment Canterbury by
Fiona Death
Dr Olivier Ausseil
Aquanet Consulting Limited
This report has been prepared for Environment Canterbury by Aquanet Consulting Limited. No liability is
accepted by this company or any employee or sub-consultant of this company with respect of its use by
any other parties.
EXECUTIVE SUMMARY
Context
Environment Canterbury is responsible for the coastal environment of Pegasus Bay (from mean high
water out to 12nM). A number of freshwater bodies including the Waipara, Kowai, Ashley, Kaiapoi,
Waimakariri, Styx, Avon and Heathcote Rivers and Saltwater Creek flow into Pegasus Bay at various
points along the coastline. Two wastewater outfalls from Waimakariri District Council and Christchurch
City Council also make point-source contributions to Pegasus Bay.
Water quality and river flow were monitored by Environment Canterbury at locations on each of the
above rivers. Water quality was also monitored at 10 beaches along Pegasus Bay, monthly between 1 July
2010 and 30 June 2011.
This report was commissioned by Environment Canterbury in order to provide up-to-date information
regarding the state of the water quality in coastal Pegasus Bay.
In particular, the aim was:

to analyse and summarise the state of water quality at nearshore and offshore water quality
sites in Pegasus Bay, as well as at river sites that feed into Pegasus Bay;
 to determine annual contaminant loadings from rivers and wastewater outfalls into nearshore
Pegasus Bay; and
 to quantify the contribution made by each river and wastewater outfall to the annual
contaminant loadings entering Pegasus Bay.
The above assessments were primarily focussed on nutrients (nitrogen and phosphorus).
Assessment undertaken
The state of each river and coastal site surveyed monthly from 2010-2011 is presented with descriptive
statistics, such as mean, median, distribution percentiles, standard error and confidence intervals, as well
as relevant guidelines used here as reference points to describe the state of the resource.
Principal Components Analysis (PCA) was used to compare all variables between the main stem rivers
and coastal sites sampled, while a Spearman Rank correlation was used to compare survey data with that
collected from the Regional Monitoring Programme to determine if survey results reflected a typical year.
Annual loads were calculated for the survey sites for the year 1 July 2010 -30 June 2011.
Inputs of total nitrogen, total phosphorus and total suspended solids from each of the rivers were
calculated as a daily load (kg/day) and as a percentage of the total from all rivers.
Results
 In terms of overall volumes, the Waimakariri River contributed 80% of the flow from all the
rivers surveyed between 2010 and 2011. The next highest flows came from the Ashley (7%), and
the Waipara (3%) with the remaining rivers and two outfalls contributing less than 1.5% each.
 Principal Components Analysis (PCA) showed coastal sites were similar to each other in their
overall nutrient composition regardless of where they are located in the Bay.
 PCA analysis also revealed that most river sites were similar in composition to each other and to
the coastal sites with a few exceptions.












The main drivers of the PCA patterns appear to be total nitrogen, total phosphorus and dissolved
reactive phosphorus for river sites and total phosphorus and total ammonia-nitrogen for coastal
sites.
All river sites except the Waipara, Ashley and Waimakariri had total nitrogen concentrations
which were above reference guidelines (ANZECC 2000).
Half of the rivers surveyed had average concentrations of total phosphorus which exceeded the
reference values (ANZECC 2000).
All rivers had ammonia-nitrogen concentrations that were within reference guidelines.
The Kaiapoi, Ohoka and Cust Rivers had DIN concentrations which were above reference values;
while the Heathcote River exceeded reference guidelines for DRP concentrations.
All coastal sites were within the Canterbury coastal water reference guidelines for total nitrogen
and total phosphorus.
The Christchurch City Council outfall contributes the highest annual loads of DRP, DIN, TN and
TP of all the sites sampled.
The Waimakariri River is the highest river contributor for annual loads of DRP, DIN, TP and TN.
The Waimakariri River contributes the highest annual load of TSS followed by the Waipara
River.
The Christchurch City Council outfall contributed the highest daily total nitrogen, total
phosphorus and suspended sediment loads followed by the Waimakariri River.
Excluding the Waimakariri and WDC and CCC outfalls from analysis revealed the Kaiapoi to
contribute the next highest loads of total nitrogen; the Heathcote and Avon Rivers contribute the
next highest loads of total phosphorus and most other rivers to be contributing similar daily loads
of suspended sediments.
The CCC and WDC outfalls combined contributed 49% of the daily total nitrogen and 66% of the
daily total phosphorus, compared with 51% of daily TN and 34% of daily TP from the rivers.
CONTENTS
Table of Contents
1
2
Context .................................................................................................................................................. 1
1.1
Introduction ................................................................................................................................... 1
1.2
Background ................................................................................................................................... 1
1.3
Aim and scope of the study ........................................................................................................... 4
Methods................................................................................................................................................. 4
2.1
Original dataset ............................................................................................................................. 4
2.2
Additional datasets ........................................................................................................................ 7
2.3
Water quality data preparation .................................................................................................... 10
2.4
Waimakariri River Sites .............................................................................................................. 10
2.5
Ashley River ............................................................................................................................... 11
2.6
Flow data..................................................................................................................................... 11
2.7
Data analysis ............................................................................................................................... 14
2.7.1
Descriptive and Exploratory Statistics ................................................................................ 14
2.7.2
Annual Contaminant loads .................................................................................................. 14
2.8
3
Water quality guidelines ............................................................................................................. 16
Water Quality State ............................................................................................................................. 17
3.1
Mean Annual Flows .................................................................................................................... 17
3.2
Nutrients...................................................................................................................................... 17
3.2.1
Total Nitrogen ..................................................................................................................... 18
3.2.2
Total Phosphorus................................................................................................................. 19
3.2.3
Total Ammonia-Nitrogen .................................................................................................... 21
3.2.4
Dissolved Inorganic Nitrogen ............................................................................................. 23
3.2.5
Dissolved Reactive Phosphorus .......................................................................................... 25
3.2.6
Total Suspended Solids ....................................................................................................... 27
3.3
Comparison between Survey and Regional Programme data ..................................................... 29
3.4
Comparison between River and Coastal sites - PCA Analysis ................................................... 30
3.5
Annual Loads .............................................................................................................................. 34
3.5.1
Total Nitrogen ..................................................................................................................... 34
3.5.2
Total Phosphorus................................................................................................................. 35
3.5.3
Dissolved Reactive Phosphorus .......................................................................................... 36
3.5.4
3.6
Dissolved Inorganic Nitrogen ............................................................................................. 37
Daily Nutrient Loads................................................................................................................... 38
3.6.1
Nitrogen .............................................................................................................................. 38
3.6.2
Phosphorus .......................................................................................................................... 41
3.6.3
Total Suspended Solids ....................................................................................................... 44
4
Conclusions ......................................................................................................................................... 47
5
Recommendations ............................................................................................................................... 48
5.1
Site selection ............................................................................................................................... 48
5.2
Eutrophication issues in Pegasus Bay ......................................................................................... 49
Figures
Figure 1: Pegasus Bay................................................................................................................................... 2
Figure 2: Water quality monitoring sites in Pegasus Bay, 1 July 2010 – 30 June 2011. .............................. 6
Figure 3: Map showing sites monitored monthly on the Waimakariri River from 1 July 2010 to 30 June
2011. ........................................................................................................................................................... 10
Figure 4: Average Annual flow (log scale) for rivers surveyed from 1 July 2010 to 30 June 2011. .......... 17
Figure 5: Total nitrogen concentrations for the rivers sampled in Pegasus Bay, 1 July 2010 – 30 June
2011. The dashed line represents the reference guideline value for total nitrogen concentrations (Table 4).
.................................................................................................................................................................... 18
Figure 6: Total nitrogen concentrations for the coastal sites sampled in Pegasus Bay, 1 July 2010 – 30
June 2011. The dashed line represents the recommended reference value for total nitrogen concentrations
in Canterbury coastal waters (Table 4). ...................................................................................................... 19
Figure 7: Total phosphorus concentrations for the rivers sampled in Pegasus Bay, 1 July 2010 – 30 June
2011. The dashed line represents the recommended reference guideline for total phosphorus (Table 4). . 20
Figure 8: Total phosphorus concentrations for the coastal sites sampled in Pegasus Bay, 1 July 2010 – 30
June 2011. The dashed line represents the recommended reference value for total phosphorus
concentrations (Table 4). ............................................................................................................................ 21
Figure 9: Total ammonia-nitrogen concentrations for the rivers sampled in Pegasus Bay, 1 July 2010 – 30
June 2011. The dashed line represents the reference guideline for ammonia-nitrogen concentrations
(Table 4). ..................................................................................................................................................... 22
Figure 10: Total ammonia-nitrogen concentrations for the coastal sites sampled in Pegasus Bay, 1 July
2010 – 30 June 2011. The dashed line represents the recommended reference value for ammonia-nitrogen
concentrations (Table 4). ............................................................................................................................ 22
Figure 11: Dissolved inorganic nitrogen (DIN) concentrations for the rivers sampled in Pegasus Bay, 1
July 2010 – 30 June 2011. The dashed lines represent reference guidelines for un-enriched (red), low level
of enrichment (orange), moderately enriched (green) and enriched (blue) river systems (Table 4). .......... 24
Figure 12: Dissolved inorganic nitrogen (DIN) concentrations for the coastal sites sampled in Pegasus
Bay, 1 July 2010 – 30 June 2011. ............................................................................................................... 24
Figure 13: Dissolved reactive phosphorus (DRP) concentrations for the rivers sampled in Pegasus Bay, 1
July 2010 – 30 June 2011. The dashed lines represent recommended guidelines (Table 4)....................... 26
Figure 14: Dissolved reactive phosphorus (DRP) concentrations for coastal sites sampled in Pegasus Bay,
1 July 2010 – 30 June 2011. The dashed line represents the recommended reference guideline for DRP
(Table 4). ..................................................................................................................................................... 26
Figure 15: Total suspended solid concentrations for the rivers sampled in Pegasus Bay, 1 July 2010 – 30
June 2011. ................................................................................................................................................... 28
Figure 16: Total suspended solid concentrations for coastal sites sampled in Pegasus Bay, 1 July 2010 –
30 June 2011. .............................................................................................................................................. 28
Figure 17: Box plots of total nitrogen and total phosphorus data collected at a selection of rivers during
Environment Canterbury’s Regional Monitoring (2000-2012). The red line represents the monthly total
nitrogen or total phosphorus concentration based on data collected monthly from 1 July 2010 to 30 June
2011. ........................................................................................................................................................... 29
Figure 18: Plot of Axis 1 against Axis 2 from a Principal Components Analysis for all river and coastal
sites sampled along Pegasus Bay in 2010-2011.......................................................................................... 30
Figure 19: Plot of Axis 1 against Axis 2 from a Principal Components Analysis for averages of all river
and coastal sites sampled along Pegasus Bay in 2010-2011 ....................................................................... 31
Figure 20: Cluster analysis for river and coastal sites sampled along Pegasus Bay in 2010-2011. ............ 32
Figure 21: Plot of axis 1 against axis 2 from a Principal Components Analysis for all coastal sites sampled
along Pegasus Bay in 2010-2011. ............................................................................................................... 33
Figure 22: Cluster analysis for coastal sites sampled along Pegasus Bay in 2010-2011. ........................... 33
Figure 23: Annual and Summer (November to April inclusive) loads (tonnes/year) of total nitrogen for
rivers and outfalls sampled throughout Pegasus Bay in 2010-2011. .......................................................... 34
Figure 24: Annual and Summer (November to April inclusive) loads (tonnes/year) of total phosphorus for
rivers and outfalls sampled throughout Pegasus Bay in 2010-2011. .......................................................... 35
Figure 25: Annual and Summer (November to April inclusive) loads (tonnes/year) of dissolved reactive
phosphorus for rivers and outfalls sampled throughout Pegasus Bay in 2010-2011. ................................. 36
Figure 26: Annual and Summer (November to April inclusive) loads (tonnes/year) of dissolved inorganic
nitrogen for rivers and outfalls sampled throughout Pegasus Bay in 2010-2011. ...................................... 37
Figure 27: Total nitrogen inputs (kg/day) in rivers and outfalls sampled in Pegasus Bay, 1 July 2010 – 30
June 2011. ................................................................................................................................................... 39
Figure 28: Total nitrogen inputs (as a percentage of the total) in rivers and outfalls sampled in Pegasus
Bay, 1 July 2010 – 30 June 2011. ............................................................................................................... 39
Figure 29: Total nitrogen inputs (kg/day) in rivers sampled in Pegasus Bay, 1 July 2010 – 30 June 2011
with the Waimakariri River, Waimakariri District Council and Christchurch City Council outfalls
excluded. .................................................................................................................................................... 40
Figure 30: Total nitrogen inputs (as a percentage of the total) in rivers sampled in Pegasus Bay, 1 July
2010 – 30 June 2011 with the Waimakariri River, Waimakariri District Council and Christchurch City
Council outfalls excluded. .......................................................................................................................... 40
Figure 31: Total phosphorus inputs (kg/day) in rivers and outfalls sampled in Pegasus Bay, 1 July 2010 –
30 June 2011. .............................................................................................................................................. 42
Figure 32: Total phosphorus inputs (as a percentage of the total) in rivers and outfalls sampled in Pegasus
Bay, 1 July 2010 – 30 June 2011. ............................................................................................................... 42
Figure 33: Total Phosphorus inputs (kg/day) in rivers sampled in Pegasus Bay, 1 July 2010 – 30 June
2011 with the Waimakariri River, Waimakariri District Council and Christchurch City Council outfalls
excluded. ..................................................................................................................................................... 43
Figure 34: Total phosphorus inputs (as a percentage of the total) in rivers sampled in Pegasus Bay, 1 July
2010 – 30 June 2011 with the Waimakariri River, Waimakariri District Council and Christchurch City
Council outfalls. .......................................................................................................................................... 43
Figure 35: Total suspended solid inputs (kg/day) in rivers and outfalls sampled in Pegasus Bay, 1 July
2010 – 30 June 2011. .................................................................................................................................. 45
Figure 36: Total suspended solid inputs (as a percentage of the total) in rivers and outfalls sampled in
Pegasus Bay, 1 July 2010 – 30 June 2011. ................................................................................................. 45
Figure 37: Total suspended solids inputs (kg/day) in rivers sampled in Pegasus Bay, 1 July 2010 – 30
June 2011 with the Waimakariri River and the Waimakariri District Council and Christchurch City
Council outfalls excluded. .......................................................................................................................... 46
Figure 38: Total suspended solid inputs (as a percentage of the total) in rivers sampled in Pegasus Bay, 1
July 2010 – 30 June 2011 with the Waimakariri River, the Waimakariri District Council and Christchurch
City Council outfalls excluded. ................................................................................................................... 46
Tables
Table 1: Pegasus Bay River and Coastal sites monitored monthly between 1 July 2010 and 30 June 2011.
...................................................................................................................................................................... 5
Table 2: Summary of the water quality and flow data used in the 2010-2011 study on Pegasus Bay.
Phys-Chem: Physico-chemical parameters (eg. temperature, pH, conductivity and dissolved oxygen).
Nutrients comprise nitrogens, phosphorus, dissolved reactive phosphorus (DRP). ..................................... 8
Table 3: Summary of the flow data accepted or rejected for use in the 2010-2011 study on Pegasus Bay.
.................................................................................................................................................................... 13
Table 4: Summary of the reference guidelines used in assessing the state of rivers and coastal sites
surveyed in Pegasus Bay from 1 July 2010 – 30 June 2011. ...................................................................... 16
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
1 Context
1.1 Introduction
Environment Canterbury is responsible for the coastal environment of Pegasus Bay (from mean high
water out to 12nM). A number of freshwater bodies including the Waipara, Kowai, Ashley, Kaiapoi,
Waimakariri, Styx, Avon and Heathcote Rivers and Saltwater Creek flow into Pegasus Bay at various
points along the coastline. Wastewater from both the Waimakariri District and Christchurch City also
enter the bay via ocean outfalls. Inputs of contaminants, in the form of nutrients, sediment, microorganisms from all of these sources have the potential to adversely affect the water quality of coastal
Pegasus Bay.
Environment Canterbury has monitored water quality and flow at locations on each of the above rivers (as
close to the coast as possible but without being affected by tidal influence); as well as at 10 beaches along
Pegasus Bay. These data were collected monthly between 1 July 2010 and 30 June 2011. Furthermore,
Consent conditions for the Waimakariri District Council (WDC) and Christchurch City Council (CCC)
wastewater discharges also require monitoring of water quality and flow.
This report was commissioned by Environment Canterbury in order to provide up-to-date information
regarding the state of the water quality in coastal Pegasus Bay.
1.2 Background
Pegasus Bay is a gently curved coastline some 50 km long (Figure 1). The bay runs essentially southnorth from Banks Peninsula to north of the Waipara River mouth. Banks Peninsula to the South and the
cliffs and shores of the Teviotdale Hills north of the Waipara River to the North, create the embayment.
The Pegasus Bay shoreline consists of sand and gravel beaches. The sediment making up the beaches
changes along the bay from sand and fine gravels in the north to medium and fine sands in the south.
Seaward of the intertidal beaches the seabed slopes to a depth of 5 m at a distance of around 700 m to 1.9
km from shore. The 10 m depth contour is 4 – 10 km from the shore (NZ chart 63).
1
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
Figure 1: Pegasus Bay
The nearshore Pegasus Bay is a high energy environment. Wind waves and ocean swells from the northeast, east and south east, generated over long fetches, average 1 m in height (range 0.3 – 2.6 m) and deep
water waves may potentially attain heights of 4.9 – 6.6 m (Fenwick, 1999). Wind waves are
predominantly from the north-east in summer and from the south-east in winter.
Water movement in Pegasus Bay is influenced by the large scale coastal circulation process of the
Southland Current in combination with the influence of tides, wind and waves (Miller et al., 2004). The
Southland Current flows northward along the east coast of the South Island. However, episodic eddies
2
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
from the Southland Current do occur in Pegasus Bay (Reynolds-Fleming and Fleming, 2005). Nearshore,
current flow is predominantly aligned with the shoreline and the majority of the time the current is a
uniform northward or southward flow. The tides play a major role in controlling current direction with the
current in the lower half of the water column reversing in phase with the tides (Cox and Hudson, 2003).
Wind influences the direction of surface water currents in Pegasus Bay. However, as the wind energy is
not equitably distributed in Pegasus Bay current variations do occur (Miller et al., 2004).
The water plume that leaves the Estuary of the Heathcote and Avon Rivers/Ihutaiu, as the tide is ebbing,
flows either north or south. Data collected by Environment Canterbury indicates that this plume
influences water quality at the waters’ edge and out to at least 300 m from shore (the length of the New
Brighton Pier) to at least 6.2 km north and 1.8 km south of the estuary mouth (Bolton-Ritchie, 2007).
The Waimakariri River flows from the mountains through a predominantly rural catchment to discharge
to the sea. In its lower reaches this river receives the water from the Kaiapoi River and Jockey Baker
Creek and until recently the discharge from the PPCS freezing works. Stormwater runoff from both
Rangiora and Kaiapoi also eventually ends up in the Lower Waimakariri River. The Waimakariri River
discharge plume is often visible because of the colour of the river water, with the plume being most
evident when the river is in flood and the river water laden with sediment. The plume of the Waimakariri
River is normally contained within Pegasus Bay and is more often in the northern than the southern part
of the Bay (Hadfield and Zeldis, 2012). For river flows up to the mean of 122 m3/s, the plume has a weak
influence on salinity some 10 km from shore (Stenton-Dozey, 2005). The outward extent of influence is
likely to be greater during flood events in the river.
Pegasus Bay has high environmental, cultural, social and economic values. The following is a very brief
evaluation of each value.
Environmental
The Banks Peninsula Marine Mammal Sanctuary extends into Pegasus Bay as far as the Waipara River
mouth and 12 nM out to sea from the coast. This sanctuary was established to protect the endangered
Hector’s dolphins/upokohue (Cephalorhynchus hectori). Other whale and dolphin species are transitory
as they migrate through the area. Pegasus Bay is habitat for a diversity and abundance of benthic and
pelagic flora and fauna including fish and shellfish species that are caught commercially.
Cultural
The following information has been obtained from the Mahaanui Iwi Management Plan 2013.
Nġai Tūāhuriri, of Nġai Tahu are the tāngata whenua of Pegasus Bay. There are wāhi tapu and wāhi
taonga sites along the coast. The coastal area between the Waipara and Kōwai Rivers is of immense
significance as one large mahinga kai resource. The coastal lowland region from the Waimakariri to the
Rakahuri/Ashley River is a cultural landscape of immense importance. Tuatua is an important kai moana
species that can be collected from the low shore of the sandy beaches. The discharge of treated human
wastewater into Pegasus Bay is culturally unacceptable. A consequence of the discharges in the mauri of
coastal waters is now degraded and tāngata whenua are highly unlikely to use the area for mahinga kai.
3
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
Social
The beaches of Pegasus Bay are popular for swimming, surfing, kite surfing and walking. Many people
fish recreationally for whitebait, salmon and other fish such as kahawai and mullet at the mouth of the
rivers. Tuatua, a bivalve mollusc and popular seafood item, are collected from the low shore area by
recreational gatherers.
Economic
There is commercial fishing for surf clams in the northern part of Pegasus Bay. The surf clam species are
Paphies donacina (tuatua), Spisula aequilateralis, Dosinia anus and a Mactra species. A commercial
company has resource consent for a 2,695 hectare mussel farm 10 km from shore within Pegasus Bay.
1.3 Aim and scope of the study
The aim of this study was to analyse water quality and flow data collected monthly by Environment
Canterbury, between 1 July 2010 and 30 June 2011, from rivers and coastal sites along Pegasus Bay. In
particular, the study aims at investigating the following points:
 To analyse and summarise the state of water quality at nearshore and offshore water quality sites
in Pegasus Bay, as well as at river sites that feed into Pegasus Bay;
 To determine annual contaminant loadings from rivers and wastewater outfalls into nearshore
Pegasus Bay;
 To quantify the contribution made by each river and wastewater outfall to the annual contaminant
loadings entering Pegasus Bay.
The assessment undertaken primarily focusses on nutrients (nitrogen and phosphorus) but data relative to
other water quality determinands such as suspended solids are also analysed and presented.
This report also makes recommendations for future water quality monitoring and management in Pegasus
Bay.
2 Methods
2.1 Original dataset
Water quality and quantity data were collected by Environment Canterbury from locations on fourteen
rivers which flow into Pegasus Bay (Table 1, Figure 2). Each monitoring site was chosen to be as close to
the coast as possible without being influenced by the tide. Two wastewater outfalls, the Waimakariri
District Council and Christchurch City Council, also enter the Bay and water quality data collected from
these sites (corresponding to the river sampling dates) have also been obtained from WDC and CCC and
included in this report for analysis.
Water quality data were also collected from ten coastal sites along the Bay (Table 1, Figure 2). Sampling
at these sites was undertaken a day after monitoring at the river sites by Environment Canterbury.
Water quality indicators monitored at both river and coastal sites included total ammonia-nitrogen,
dissolved reactive phosphorus, total nitrogen, total phosphorus, total suspended solids, volatile suspended
solids, turbidity, dissolved oxygen and water temperature.
4
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
All data were collected monthly between 1 July 2010 and 30 June 2011.
Table 1: Pegasus Bay River and Coastal sites monitored monthly between 1 July 2010 and 30 June 2011.
Site ID
SQ30162
SQ30166
SQ30193
SQ30175
SQ30369
SQ30426
SQ30400
SQ30332
SQ30245
SQ30249
SQ30253
SQ32750
SQ33426
HEATH04
WDC
CCC
Site ID
SQ33153
SQ32546
SQ32551
SQ32571
SQ32516
SQ32514
SQ32573
SQ34870
SQ32578
SQ35111
River Survey Site
Waipara River at Teviotdale Bridge
Kowai River at SH1
Saltwater Creek at SH1
Ashley River at SH1
Cam River at Bramleys Rd Bridge
Ohoka River at Island Road
Cust River at Skewbridge Road
Kaiapoi River at Island Road
Waimakariri River at Kairaki Yacht Club
Waimakariri River at Ferry Road
Waimakariri River at Stewarts Gully Yacht Club
Styx River at Teapes Road
Avon River at Gayhurst Road
Heathcote at Bowenvale Ave
Waimakariri District Council Outfall
Easting
2492020
2489416
2486153
2484738
2480578
2480220
2479939
2480317
2485901
2484371
2483406
2483978
2483514
2481183
2488000
Northing
5786592
5779565
5771249
5770021
5762608
5759083
5759498
5759031
5757524
5757548
5756278
5751260
5742835
5737387
5760200
Christchurch City Council Outfall
Coastal Survey Site
Amberley Beach Near Amberley Beach Road
Leithfield Beach at Leithfield Beach
Waikuku Beach at Surf Club
Woodend Beach at Surf Club
Pines Beach at Surf Club
Spencerville Beach at Surf Club
Waimari Beach at Surf Club
Brighton Beach Off end of New Brighton Pier
South Brighton Beach at Surf Club
Sumner Beach at Cave Rock
2492000
Easting
2492033
2490138
2487463
2486604
2486642
2486870
2487740
2488578
2488825
2490686
5742600
Northing
5781329
5777070
5768879
5763237
5758609
5752750
5746809
5744577
5742818
5737941
5
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
Figure 2: Water quality monitoring sites in Pegasus Bay, 1 July 2010 – 30 June 2011.
6
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
2.2 Additional datasets
Environment Canterbury undertakes a Regional Monitoring Programme from which data for the rivers
monitored in the 2010-2011 survey were also obtained. In most cases, datasets date back to at least 2000.
As part of their Regional Monitoring Programme, Environment Canterbury also undertakes quarterly
monitoring at ten coastal sites. Five of these sites are at the water’s edge, one is off the end of the New
Brighton pier and four sites are three kilometres from shore (Figure 2). There is also a site near the mouth
of the Ashley Estuary. Sampling of these sites began in September 2007, although some sites have data
dating back to 2005.
Table 2 provides a summary of the data used in this study.
7
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
Table 2: Summary of the water quality and flow data used in the 2010-2011 study on Pegasus Bay. Phys-Chem: Physico-chemical parameters (eg.
temperature, pH, conductivity and dissolved oxygen). Nutrients comprise nitrogens, phosphorus and dissolved reactive phosphorus (DRP).
Water quality data
2010-2011 Survey Monitoring site
Site ID
Overall Record Period
Phys-Chem
Flow data
Nutrients
Bact
Flow
Overall
Survey dates
Flow recorder
Flow recorder
Rivers

1999-2012



Waipara River at Teviotdale Bridge
SQ30162
Kowai River at SH1
SQ30166

Flow gauging
Saltwater Creek at SH1
SQ30193

Flow gauging
Ashley River at SH1
SQ30175
1999-2012




Cam River at Bramleys Rd Bridge
SQ30369
2001-2012




Flow gauging
Ohoka River at Island Road
SQ30426
2000-2012




Flow gauging
Cust River at Skewbridge Road
SQ30400
2000-2012




Flow gauging
Kaiapoi River at Island Road
SQ30332
2000-2012



Waimakariri River at Kairaki Yacht Club
SQ30245
2002-2012




Flow recorder
Flow recorder
Waimakariri River at Ferry Road
SQ30249
2002-2012




Flow recorder
Flow recorder
Waimakariri River at Stewarts Gully Yacht
Club
SQ30253
2002-2012




Flow recorder
Flow recorder
Styx River at Teapes Road
SQ32750
1991, 1992, 1999-2012




Flow recorder
Flow recorder
Avon River at Gayhurst Road
SQ33426
2000-2012



Flow recorder
Flow recorder
Heathcote at Bowenvale Ave
HEATH04
2000-2012



Flow recorder
Flow recorder
Waimakariri District Council Outfall
WDC
2006-2012



Flow meter
Christchurch City Council Outfall
CCC
2010-2012



Flow meter

8
Flow recorder
Flow gauging
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
2010-2011 Survey Monitoring site
Site ID
Water quality data
Flow data
Overall Record Period
Phys-Chem
Nutrients
Bact
Flow
2005-2012



Not applicable
Coastal Sites
Amberley Beach near Amberley Beach Rd.
SQ33153
Leithfield Beach at Leithfield Beach
SQ32546
Waikuku Beach at Surf Club
SQ32551
2005-2012



Not applicable
Woodend Beach at Surf Club
SQ32571
2005-2012



Not applicable
Pines Beach at Surf Club
SQ32516
Spencerville Beach at Surf Club
SQ32514
Waimari Beach at Surf Club
SQ32573
Brighton Beach Off end of New Brighton Pier
SQ34870
South Brighton Beach at Surf Club
SQ32578
Not applicable
Sumner Beach at Cave Rock
SQ35111
Not applicable
Scarborough Beach by the clock tower
SQ32596
Not applicable
Not applicable
2005-2012



Not applicable
Not applicable
2005-2012
2005-2012
9






Not applicable
Not applicable
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
2.3 Water quality data preparation
The dataset contained a small proportion of “less than detection limit” results. To conduct statistical
analysis, such censored data were replaced by numerical values. The “less than” values represented fewer
than 10% of the total dataset for each parameter and were replaced by half of the detection limit, which is
consistent with the recommendations of Scarsbrook and McBride (2007). Where values were greater than
the detection limit the actual value was used.
No monitoring data were available for February 2011 due to the occurrence of a magnitude 6.3
earthquake which struck the Canterbury region, and interrupted the normal monitoring through staff and
laboratory unavailability.
2.4 Waimakariri River Sites
Three sites on the Waimakariri River (at the Kairaki Yacht Club, at Ferry Road and at Stewarts Gully)
were monitored (Figure 3).
Figure 3: Map showing sites monitored monthly on the Waimakariri River from 1 July 2010 to 30 June 2011.
The site at the Kairaki Yacht Club appears to be within the tidal zone. Typical river contaminant load
calculations estimate the amount of contaminant carried by the river through one point, or more correctly
one transversal section of the river in a given length of time, and are thus not applicable to sites
influenced by tides without significant additional information and analysis.
10
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
The site at Ferry Road is located on the true left bank of the Waimakariri River, in close proximity to the
confluence with the Kaiapoi River. Full mixing of the waters from the Kaiapoi River and the Waimakariri
River is highly likely to be incomplete at the sampling point. Water quality data collected at the Ferry
Road site is considered unlikely to be representative of the fully mixed Waimakariri River water quality
in this river reach. Contaminant load calculation methods generally assume that the contaminant
concentration is homogenous across the section of river. Water quality data collected at the Ferry Road
site should therefore not be used to estimate contaminant load inputs from the Waimakariri River into
Pegasus Bay.
Consequently, the approach taken in this study was to use the data from the Waimakariri at Stewarts
Gully site in load calculations as this site was assumed to be upstream of any influence from inputs from
the Kaiapoi River. The inputs from the Kaiapoi River were estimated separately. It is important to note
however that the Stewarts Gully site is located downstream of the discharge of treated meatworks effluent
from the PPCS plant, which was still being discharged to the Waimakariri River during the period of
sampling. Consequently the nutrient load estimates presented in this report for the Waimakariri at the
Stewarts Gully site represent in fact the sum of the loads from the Waimakariri River catchment above
this point and the PPCS point-source discharge. It is our understanding that this discharge does no longer
occur to the Waimakariri River, and has since been diverted to the Christchurch City Council ocean
outfall. In other words the PPCS wastewater is still discharged to Pegasus Bay, but via the CCC outfall
instead of the Waimakariri River. There were insufficient data to confidently estimate, directly or by
difference, the nutrient loads from the PPCS discharge and/or the Waimakariri catchment above the
Stewart Gully site.
Significant differences were identified in key water quality indicators between the three lower
Waimakariri monitoring sites. Total nitrogen concentrations increase significantly between the most
upstream site at Stewarts Gully and the more coastal sites. Total phosphorus and ammonia concentrations
are three times higher at the Ferry Road site when compared with the Stewarts Gully and Kairaki Yacht
Club sites. These differences may require further investigation at a later date.
2.5 Ashley River
It should be noted that the Ashley River monitoring site (at SH1) is not located at the bottom of the
Ashley River catchment, and water (and contaminant) inputs to the Ashley River occur downstream of the
monitoring site via a number of tributaries. Consequently the nutrient load estimates based on data
collected at the SH1 site are likely to underestimate the actual loads from the Ashley River catchment into
Pegasus Bay.
2.6 Flow data
Flow data used in this report were provided by Environment Canterbury’s Hydrology team.
Continuous flow data are available at five sites: the Waipara River, the Waimakariri River, the Styx
River, the Avon River and the Heathcote River. Instantaneous flow data from direct flow gaugings were
available for the other water quality sites.
11
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
In some instances flow gaugings were not undertaken on the same day as water quality monitoring. In
each of these cases a decision was made whether to accept or reject the flow gauging data as an
acceptably likely representation of average daily river flow during closest day of water quality sampling.
The decisions were based on the number of days between gauging and water quality sampling dates and
the flow regimes within that time period at nearby flow recorders. Most, but not all, gauging flow data
were accepted using these criteria. Table 3 summarises the decisions made. Following this process, an
insufficient number of daily flow data were available for the Ashley River, and monthly average flows
were used in load calculations at that site. The Kowai River and Saltwater Creek were not able to be
included in load analysis due to insufficient flow data being available at these sites.
12
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
Table 3: Summary of the flow data accepted or rejected for use in the 2010-2011 study on Pegasus Bay.
Gauging Date
(where differs
from sampling
date)
WQ
Sampling
Date
No. of days
between
WQ
sampling &
Gauging
Accept /
Reject
Site ID
Site Name
SQ30162
Waipara River at Teviotdale Bridge
Accept
SQ30249
Waimakariri River at Ferry Road
Accept
SQ30245
Waimakariri River at Kairaki Yacht Club
Accept
SQ30253
Waimakariri River at Stewarts Gully Yacht Club
Accept
SQ32750
Styx River at Teapes Road
Accept
SQ33426
Avon River at Gayhurst Road
Accept
HEATH04
Heathcote at Bowenvale Ave
Accept
SQ30166
SQ30193
SQ30175
Kowai River at SH1
27-Jul-10
15-Jul-10
12
Reject
21-Sep-10
27-Sep-10
-6
Reject
26-Oct-10
21-Oct-10
5
Accept
23-Nov-10
18-Nov-10
5
Reject
23-Nov-10
4-Nov-10
19
Reject
18-Jan-11
11-Jan-11
7
Reject
Saltwater Creek at SH1
Ashley River at SH1
SQ30332
Kaiapoi River at Island Road
SQ30369
Cam River at Bramleys Rd Bridge
SQ30426
Ohoka Stream at Island Road
SQ30400
Cust River at Skewbridge Road
26-Oct-10
14-Oct-10
12
Accept
23-Nov-10
10-Nov-10
13
Reject
21-Dec-10
14-Dec-10
7
Reject
18-Jan-11
12-Jan-11
6
Reject
17-May-11
11-May-11
6
Reject
26-Aug-10
17-Aug-10
9
Reject
21-Dec-10
20-Dec-10
1
Accept
21-Dec-10
20-Dec-10
1
Accept
21-Sep-10
16-Sep-10
5
Accept
21-Dec-10
20-Dec-10
1
Accept
21-Dec-10
20-Dec-10
1
Accept
13
Comments
All water quality
sampling and gauging
dates correspond
Exclude from load
analysis as insufficient
flow records
Exclude from load
analysis as insufficient
flow records
Used monthly average
flows in load analysis
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
2.7 Data analysis
2.7.1
Descriptive and Exploratory Statistics
“Box and whiskers” plots were produced for each key water quality indicator to provide a summary of
water quality at each site in relation to national water quality guidelines. Appendix C provides
background information for the correct interpretation of box and whiskers plots.
More detailed descriptive statistics, such as mean, median, distribution percentiles, standard error and
confidence intervals, as well as the proportion of samples complying with the relevant guideline are
provided for both river and coastal survey sites in Appendices A and B. To provide more in-depth
analysis, Principal Components Analysis (PCA) was used to compare all variables between the main stem
rivers and coastal sites sampled. The PCA analysis was undertaken using PRIMER v6.1.13. Cluster
analysis was also performed in Primer using Euclidean distance and the group average clustering
algorithm. The SIMPROF procedure (P = 0.05, Permutations = 999) was also conducted to assess the
significance of groupings within the cluster analysis. A Spearman Rank correlation was used to compare
survey data with that collected from the Regional Monitoring Programme to determine if survey results
reflected a typical year. Spearman rank correlations were undertaken using Primer v6.1.13.
2.7.2
Annual Contaminant loads
Contaminant loads are the amount of contaminant carried by the river through one point, or more
correctly one transversal section of the river in a given length of time. Calculation methods generally
assume that the contaminant concentration is homogenous across the section of river.
When both continuous river flow and contaminant concentration data are available, instantaneous
contaminant flux can be calculated at any point in time, and an estimate of the contaminant load during a
given period of time can be calculated by simply summing up the instantaneous flux:
Load  yeari  
31 / 12 / yeari
 Pollut t   Flowt   dt
01 / 01 / yeari
When contaminant concentrations are known only at regular time intervals (e.g. monthly), the above
formula can be approximated using a number of approaches.
Annual loads were calculated for the survey sites for the year spanning 1 July 2010 -30 June 2011. Two
approximations methods were used in this report where data were sufficient.
2.7.2.1 Averaging approach
This method uses the monthly average river flow and the monthly average contaminant concentration to
estimate monthly loads. The annual load is then calculated by summing up the monthly loads. This
method is particularly applicable when the contaminant concentration and river flow are independent
variables (Richards, 1998).
14
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
Monthly load:
Load monthi   Pollut monthi  
31/ monthi
 Flowt   dt
01/ monthi
12
Load  yeari    Load monthi 
Annual load:
i 1
2.7.2.2
Ratio approach: The Beale ratio estimator
Ratio estimators use the year’s data to calculate a mean daily load, then use the mean flow from days
lacking concentration data to adjust the mean daily load. The annual load is obtained by multiplying the
mean daily load by 365 (Richards, 1998). Ratio estimators assume that there is a positive linear
relationship between river flow and contaminant load.
The basic assumption of a ratio estimator is that the ratio contaminant load/river flow for the entire year is
the same as on days the contaminant concentration was measured.
Average _ daily _ load year
Average _ daily _ flow year

Average _ daily _ load o
Average _ daily _ flowo
where the subscript “year” refers to an average for the year, and the subscript “o” refers to an average
over the days on which concentration was observed.
However, as daily load and daily flow are correlated variables, this ratio estimator is biased and a bias
correction factor must be used. The Beale Ratio estimator is one way to correct the bias:
Average _ daily _ load year  Average _ daily _ load o 
Average _ daily _ flow year
Average _ daily _ flowo
  1 1  slq
1    
  n N  l o qo
  1 1  s qq
 1   
  n N  qo 2






Where: Slq is the covariance between flow and pollutant flux, sqq is the variance of the flow based on the
days on which concentration was measured. N is the expected population size (365), and n is the number
of concentration measures (generally 12, as we have one measure for each month). lo and qo represent the
average daily flux and flow respectively on the days concentrations were measured.
The square root of the mean square error of the daily load (RMSE) provides an estimate of the standard
deviation, and is given by:
𝑅𝑀𝑆𝐸 =
2
2
𝑆𝑙𝑞
𝑆𝑙𝑞
𝑆𝑞𝑞
𝑆𝑞𝑞 𝑆𝑙𝑞
𝑆𝑞𝑞 𝑆𝑙𝑙
1 1 𝑆𝑞𝑞 𝑆𝑙𝑙
1 1 2
− )( 2 + 2 − 2
+
+ 2 2 )]
) + ( − ) (2 4 − 4 2
2
̅
̅
̅
𝑛 𝑁 𝑞̅𝑜
𝑛 𝑁
𝑞̅𝑜
𝑞̅𝑜 𝑙𝑜 ̅̅̅
𝑞̅𝑜 𝑙𝑜̅
𝑙𝑜
𝑙𝑜 ̅̅̅
𝑞𝑜
𝑞𝑜 (𝑙 ̅ ̅̅̅)
𝑞
√𝑙𝑜2 [(
𝑜
15
𝑜
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
This approach is consistent with that used by Ausseil (2011) and Kelly & Norton (2010) in work on the
Hurunui catchment and is considered standard practice by Environment Canterbury.
2.8 Water quality guidelines
Environmental guidelines are commonly used in describing the general state of a natural resource. This
report makes use of indicators based on the percentage of samples which comply with the guidelines used
in Environment Canterbury’s 2010 State of the Environment Report and/or the ANZECC 2000 guidelines
for river sites. There are no coastal guidelines for New Zealand waters (the ANZECC 2000 guidelines
state that values for the south eastern Australian coastal waters be used, however these are not suitable for
Canterbury coastal waters as the Australian coast is not impacted by riverine inputs to the same extent as
New Zealand). Reference values for the coastal sites have therefore been calculated by Environment
Canterbury as the 80th percentile values from local data.
Importantly, these guidelines are used in this report as reference points to describe the state of the
resource, and the comparisons to these guidelines made in this report should by no means be seen as a
compliance assessment.
Table 4: Summary of the reference guidelines used in assessing the state of rivers and coastal sites surveyed in
Pegasus Bay from 1 July 2010 – 30 June 2011.
River
Ammonia-Nitrogen (mg/L)
Total Nitrogen (mg/L)
Total phosphorus (mg/L)
Nitrate-Nitrite nitrogen (mg/L)
Dissolved Inorganic Nitrogen (mg/L)
Dissolved Reactive Phosphorus (mg/L )
Turbidity (NTU)
Ammonia-Nitrogen (mg/L)
Total Nitrogen (mg/L)
Total phosphorus (mg/L)
Nitrate-Nitrite nitrogen (mg/L)
Dissolved Inorganic Nitrogen (mg/L)
Dissolved Reactive Phosphorus (mg/L )
Turbidity (NTU)
0.9
0.614
0.033
1.7
<0.03
Unenriched
0.03-0.17 Low level enrichment
0.17-0.44 Moderately enriched
0.44-2.0 Enriched
>2.0
Excessive
<0.003
Unenriched
0.003-0.009 Moderately enriched
0.009-0.030 Enriched
>0.030
Excessive
<2
Clear
2-5.6
Opaque
>5.6
Turbid
Coastal
0.09
0.33
0.08
0.06
0.05
16
Source
Environment Canterbury (2010),
ANZECC (2000)
ANZECC (2000)
ANZECC (2000)
Environment Canterbury (2010)
Environment Canterbury (2010)
Environment Canterbury (2010)
Environment Canterbury (2010)
Source
Environment Canterbury (80th
percentile values calculated
from local data)
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
3 Water Quality State
3.1 Mean Annual Flows
Mean annual flows for the rivers included in the 2010-2011 survey are shown in Figure 4.
The Waimakariri River contributes 80% of the total annual flow from these sources. The remaining flow
is made up of 7% from the Ashley, 3% from the Waipara and 1.5% or less from each of the Cam, Ohoka,
Cust, Styx, Avon and Heathcote Rivers as well as the two outfalls. The CCC Outfall contributes 1.4% of
flow while the WDC outfall only contributes 0.9%. No flow data were available for the Kaiapoi River.
Mean Annual flow
1000000
Mean Flow (L/s)
100000
10000
1000
100
10
1
Site
Figure 4: Average Annual flow (log scale) for rivers surveyed from 1 July 2010 to 30 June 2011.
3.2 Nutrients
Different chemical forms of two key macronutrients, nitrogen and phosphorus, were monitored at all
sites. Dissolved forms of reactive phosphorus (mainly phosphates) and inorganic nitrogen (nitrate-,
nitrite- and ammonia- nitrogen) are directly available to plant growth. The sum of all forms of phosphorus
and nitrogen (termed total phosphorus and total nitrogen) provide an indication of the “pool” of nutrients
potentially available for immediate or future uptake (through cycling) by plants.
17
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
Information on these various water quality indicators at the sites is presented in the following sections,
with site-specific graphs provided in Appendix C. The boxplots represent median, 25th and 75th percentile
values. Whiskers indicate 5th and 95th percentile values. Reference guidelines represented by horizontal
dashed red lines in the box and whisker plots are as per Table 4.
3.2.1
Total Nitrogen
Total nitrogen concentrations vary for each of the rivers sampled in the 2010- 2011 survey (Figure 5).
While most rivers had median concentrations of 2mg/L or less, the Kaiapoi and its tributaries, the Cust
and Ohoka, had concentrations around 5 mg/L.
Only the Waipara, Ashley and Waimakariri Rivers had annual average and median total nitrogen
concentrations below reference guidelines (Table 4)
The WDC and CCC outfalls, although not presented in Figure 5, had median total nitrogen concentrations
of 19 and 28 mg/L, respectively.
Median total nitrogen concentrations for the coastal sites ranged from 0.21 mg/L to 0.29mg/L (Figure 6),
and all sites had concentrations below the recommended reference guideline for Canterbury coastal
waters (refer Table 4).
7
Total nitrogen (mg/L)
6
5
4
3
2
1
co
te
on
th
Av
ea
H
yx
St
iri
ar
W
ai
m
ak
ia
Ka
C
us
po
i
t
ka
am
ho
O
C
ey
hl
er
As
w
ai
Ko
ltw
at
Sa
W
ai
pa
ra
0
Site
Figure 5: Total nitrogen concentrations for the rivers sampled in Pegasus Bay, 1 July 2010 – 30 June 2011. The
dashed line represents the reference guideline value for total nitrogen concentrations (Table 4).
18
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
1.2
Total nitrogen (mg/L)
1.0
0.8
0.6
0.4
0.2
Am
be
rle
y
Le
Be
ith
ac
fie
h
ld
Be
W
ac
ai
h
ku
ku
Be
W
oo
ac
de
h
nd
Be
ac
Pi
h
ne
Sp
s
en
Be
ce
ac
rv
h
ille
Be
W
ac
ai
h
m
ar
N
iB
ew
ea
Br
ch
So
ig
ht
ut
on
h
Br
Pi
ig
er
ht
on
Be
Su
ac
m
h
ne
rB
ea
ch
0.0
Site
Figure 6: Total nitrogen concentrations for the coastal sites sampled in Pegasus Bay, 1 July 2010 – 30 June 2011.
The dashed line represents the recommended reference value for total nitrogen concentrations in Canterbury coastal
waters (Table 4).
3.2.2
Total Phosphorus
Median total phosphorus concentrations at river sites ranged from 0.01 to 0.08 mg/L (Figure 7). The
Heathcote River and Saltwater Creek had the highest median concentrations (0.07 and 0.08 mg/L
respectively). The Styx, Waimakariri and Avon rivers supported the next highest concentrations (0.040.06 mg/L), while concentrations in all other rivers were less than 0.04mg.L.
Half of the rivers surveyed (Saltwater Creek, the Waimakariri, Styx, Avon and Heathcote rivers) had
median and average concentrations of total phosphorus which exceeded the reference guideline (Refer
Table 4)
The CCC and WDC outfalls (again, not presented in Figure 7) had three to five times the total phosphorus
concentrations found in the rivers.
Coastal sites surveyed from 2010 to 2011 all had median total phosphorus concentrations below the
reference guideline for Canterbury coastal waters, ranging from 0.04 to 0.06 mg/L (Figure 8).
19
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
Total phosphorus (mg/L)
0.4
0.3
0.2
0.1
Av
on
ea
th
co
te
H
yx
St
iri
ar
ia
W
ai
m
ak
po
i
t
Ka
C
us
ka
ho
O
C
am
ey
hl
er
As
ltw
at
Ko
w
ai
Sa
W
ai
pa
ra
0.0
Site
Figure 7: Total phosphorus concentrations for the rivers sampled in Pegasus Bay, 1 July 2010 – 30 June 2011. The
dashed line represents the recommended reference guideline for total phosphorus (Table 4).
20
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
0.25
Total phosphorus (mg/L)
0.20
0.15
0.10
0.05
ch
rB
Be
Su
m
ne
ld
f ie
it h
ea
ac
h
ac
h
ille
Le
Sp
en
ce
ai
m
W
Be
ea
c
Pi
ar
iB
on
ht
ig
Br
ew
N
rv
er
h
ac
Be
ac
Pi
ne
s
Be
d
en
oo
d
W
ku
ai
W
h
h
Be
ac
on
ku
ht
Br
ig
h
ut
So
Am
be
rle
y
Be
ac
Be
h
0.00
Site
Figure 8: Total phosphorus concentrations for the coastal sites sampled in Pegasus Bay, 1 July 2010 – 30 June
2011. The dashed line represents the recommended reference value for total phosphorus concentrations (Table 4).
3.2.3
Total Ammonia-Nitrogen
Concentrations of total ammonia-nitrogen averaged less than 0.07 mg/L and were well below the
reference guidelines.
The highest median concentrations were found in the Avon (0.06 mg/L), Waimakariri (0.06 mg/L) and
Heathcote (0.05 mg/L) rivers (Figure 9). All other sites averaged less than 0.04 mg/L. The high
concentrations found in the Waimakariri River are most likely a result of discharges from Silver Fern
Farms freezing works (PPCS) entering the river during the survey period; such concentrations would
otherwise be unusual for an alpine river.
Concentrations of total ammonia-nitrogen at coastal sites appeared to increase towards the southern end
of the bay. Median concentrations ranged from 0.01mg/L to 0.03 mg/L (Figure 10).
21
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
1.0
Ammonia-nitrogen (mg/L)
0.8
0.3
0.2
0.1
W
ai
H
Av
on
ea
th
co
te
yx
St
iri
m
ak
ia
C
Ka
O
ar
us
po
i
t
ka
ho
C
am
ey
hl
er
Sa
As
ltw
at
w
ai
Ko
W
ai
pa
ra
0.0
Site
Figure 9: Total ammonia-nitrogen concentrations for the rivers sampled in Pegasus Bay, 1 July 2010 – 30 June
2011. The dashed line represents the reference guideline for ammonia-nitrogen concentrations (Table 4).
0.25
Ammonia-nitrogen (mg/L)
0.20
0.15
0.10
0.05
ch
h
rB
ea
ac
So
ut
h
Su
m
ne
on
ht
Br
ig
Br
ew
N
Be
Pi
ht
ig
ar
ai
W
on
ea
iB
Be
m
ille
rv
ce
en
Sp
er
ch
h
ac
ac
Be
s
ne
Pi
nd
de
oo
h
h
ac
h
Be
ac
Be
ku
ku
W
W
ai
fie
it h
Le
Am
be
rle
ld
y
Be
Be
ac
ac
h
h
0.00
Site
Figure 10: Total ammonia-nitrogen concentrations for the coastal sites sampled in Pegasus Bay, 1 July 2010 – 30
June 2011. The dashed line represents the recommended reference value for ammonia-nitrogen concentrations
(Table 4).
22
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
3.2.4
Dissolved Inorganic Nitrogen
The Kaiapoi, Ohoka and Cust Rivers all had high median concentrations of dissolved inorganic nitrogen
(DIN) (4.9, 4.3 and 4.3 mg/L respectively) (Figure 11). These exceed the reference guidelines and place
these sites in the excessively enriched category using ECan’s 2010 State of the environment report
classification (Table 4). Most other rivers averaged median DIN concentrations of less than 2 mg/L
indicating enriched to moderately enriched sites.
The Kaiapoi, Ohoka and Cust rivers are predominantly spring fed. Due to the large groundwater
catchment area and the intensification of land use in the area, the groundwater and hence the springs have
high DIN concentrations. The Avon and Heathcote rivers are also spring fed, however their groundwater
catchment area is not as large compared to the Kaiapoi, Ohoka and Cust, and fall partly within a
groundwater protection zone to the north west of Christchurch, which probably explains the relatively
lower DIN concentrations measured in these rivers.
Of the coastal sites, Pines Beach had the highest average and median concentrations (0.13 mg/L and 0.12
mg/L respectively), (Figure 12). Water quality at the Pines Beach site may be influenced by inputs from
the Waimakariri/Kaiapoi rivers and/or the Waimakariri wastewater ocean outfall, which flow into this
area. Waimari Beach and the Brighton sites presented the next highest DIN concentrations, around 0.07
mg/L.
23
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
6
5
DIN (mg/L)
4
3
2
1
co
te
on
ea
th
Av
yx
St
iri
ar
ak
W
H
ai
m
Ka
ia
C
us
po
i
t
ka
am
C
O
ho
ey
hl
er
As
w
ai
ltw
at
Sa
W
ai
Ko
pa
ra
0
Site
Figure 11: Dissolved inorganic nitrogen (DIN) concentrations for the rivers sampled in Pegasus Bay, 1 July 2010 –
30 June 2011. The dashed lines represent reference guidelines for un-enriched (red), low level of enrichment
(orange), moderately enriched (green) and enriched (blue) river systems (Table 4).
0.7
0.6
DIN (mg/L)
0.5
0.4
0.3
0.2
0.1
ch
h
m
ne
rB
ea
ac
Be
So
ut
h
Su
Pi
on
Br
ig
Br
ig
ht
iB
ar
ew
N
ht
on
ea
ac
Be
m
ai
W
en
Sp
er
ch
h
h
ille
ce
rv
ne
Pi
nd
de
oo
s
Be
Be
ac
ac
h
h
ac
Be
ku
W
W
ai
ku
fie
ith
Le
Am
be
rle
ld
y
Be
Be
ac
ac
h
h
0.0
Site
Figure 12: Dissolved inorganic nitrogen (DIN) concentrations for the coastal sites sampled in Pegasus Bay, 1 July
2010 – 30 June 2011.
24
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
3.2.5
Dissolved Reactive Phosphorus
The Heathcote River had the highest median concentration of dissolved reactive phosphorus (DRP) (0.04
mg/L) while the Ashley River had the lowest concentration (0.002 mg/L) (Figure 13). The Heathcote also
had the highest average DRP concentration (0.06 mg/L) while both the Ashley and Waipara Rivers had
the lowest average DRP concentrations (0.003 mg/L). Most other sites fell within the guidelines for
enriched to moderately enriched habitats.
Coastal sites all had very similar median DRP concentrations averaging around 0.01 mg/L (Figure 14),
well below the reference guideline of 0.05 (Table 4).
25
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
0.18
0.16
0.14
DRP (mg/L)
0.12
0.10
0.08
0.06
0.04
0.02
te
co
on
yx
ea
th
Av
iri
ar
ak
W
H
ai
m
Ka
St
i
po
ia
us
t
ka
C
ho
am
O
C
w
ai
ltw
at
er
As
hl
ey
Sa
W
ai
Ko
pa
ra
0.00
Site
Figure 13: Dissolved reactive phosphorus (DRP) concentrations for the rivers sampled in Pegasus Bay, 1 July 2010
– 30 June 2011. The dashed lines represent recommended guidelines (Table 4).
0.06
0.05
DRP (mg/L)
0.04
0.03
0.02
0.01
on
h
ut
So
N
ew
Br
Br
m
ai
W
ig
ar
ht
iB
Be
ille
ce
rv
Pi
ig
er
ht
on
Be
Su
ac
m
h
ne
rB
ea
ch
h
ac
ea
c
h
h
Be
s
ne
Pi
Sp
en
nd
de
oo
W
ac
h
h
Be
Be
ac
ac
h
ac
Be
ku
ku
ai
W
it h
Le
Am
be
rle
f ie
ld
y
Be
ac
h
0.00
Site
Figure 14: Dissolved reactive phosphorus (DRP) concentrations for coastal sites sampled in Pegasus Bay, 1 July
2010 – 30 June 2011. The dashed line represents the recommended reference guideline for DRP (Table 4).
26
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
3.2.6
Total Suspended Solids
Total suspended solids (TSS) were in highest median concentrations in the Waimakariri River (24 mg/L),
followed by Saltwater Creek (16 mg/ L), and then the Styx and Heathcote rivers (12 mg/L) (Figure 15).
The remaining sites averaged median concentrations of less than 6 mg/L over the months surveyed.
TSS concentrations at the two outfall sites were similar to those for the Waimakariri River for the WDC
outfall and to Saltwater Creek for the CCC outfall.
Of the coastal sites surveyed Amberley and Leithfield Beaches had the highest concentrations (Figure
16), with the amount of suspended solids declining the further south one moves along the bay. Water
samples at coastal sites are taken at the water’s edge (knee deep water), and TSS concentrations at times
reflect the re-suspension of seabed sediment stirred up by wav action, and do not typically represent
sediment carried to the sites by the rivers.. Waves are particularly frequent at Amberley and Leithfield
beaches, which probably explains the higher average TSS concentrations measured at these sites (Lesley
Bolton-Ritchie, pers. comm.).
27
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
400
200
TSS (mg/L)
100
80
60
40
20
ea
th
co
te
on
yx
Av
iri
St
ak
W
H
ai
m
Ka
ia
C
ar
us
po
i
t
ka
ho
O
As
C
hl
am
ey
er
w
ai
ltw
at
Sa
W
ai
Ko
pa
ra
0
Site
Figure 15: Total suspended solid concentrations for the rivers sampled in Pegasus Bay, 1 July 2010 – 30 June 2011.
14000
12000
TSS (mg/L)
10000
8000
6000
4000
2000
ea
ch
h
ne
rB
Be
ac
m
ht
ig
Br
So
ut
h
Su
ht
ew
N
on
on
Pi
er
ac
h
ig
Br
m
ar
i
Be
ac
Be
W
ai
rv
ille
s
en
ce
ne
Sp
Pi
h
h
ac
Be
ac
Be
en
d
oo
d
W
ku
h
h
ac
Be
ku
Be
ld
ai
W
ith
fie
Le
Am
be
rle
y
Be
ac
ac
h
h
0
Site
Figure 16: Total suspended solid concentrations for coastal sites sampled in Pegasus Bay, 1 July 2010 – 30 June
2011.
28
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
3.3 Comparison between Survey and Regional Programme data
Water quality in Pegasus Bay and its associated river systems is monitored by Environment Canterbury as
part of its Regional Monitoring programme. A statistical comparison of the data collected in the 20102011 survey and that collected during the regional programme (spanning the time period between 2000
and 2012) for both rivers and coastal sites was undertaken using Spearman Rank Correlation in Primer
v6.1.13. No significant differences were found, indicating that the results obtained during the survey
period reflect those that would be found in a typical year. This is also reflected in Figure 17 which shows
survey data (red line) following similar patterns to regional data (box plots) for a small selection of rivers.
Waimakariri River
Ashley River
1.0
1.2
1.0
Total nitrogen (mg/L)
0.6
0.4
0.2
0.8
0.6
0.4
0.2
ay
ril
ne
Ju
M
Ap
t
m
Se
pt
e
Au
Month
Month
Waimakariri River
Styx River
1.6
0.18
1.4
0.16
0.14
0.06
Ju
ly
Se
Au
Ju
ne
ay
M
Ap
Au
ril
0.00
Ju
ly
0.02
0.0
ay
0.04
0.2
M
0.4
0.08
Ju
ne
0.6
0.10
ril
0.8
0.12
Ap
1.0
gu
st
pt
em
be
r
O
ct
ob
er
N
ov
em
be
D
r
ec
em
be
r
Ja
nu
a
Fe ry
br
ua
ry
M
ar
ch
Total phosphorus (mg/L)
1.2
gu
Se
st
pt
em
be
r
O
ct
ob
e
N
r
ov
em
be
D
r
ec
em
be
r
Ja
nu
a
Fe ry
br
ua
ry
M
ar
ch
Total phosphorus (mg/L)
be
r
O
ct
ob
er
N
ov
em
be
D
r
ec
em
be
r
Ja
nu
a
Fe ry
br
ua
ry
M
ar
ch
ly
Ju
ne
Ju
ril
ay
M
Ap
t
m
Se
pt
e
Ju
gu
s
Au
be
r
O
ct
ob
e
N
r
ov
em
be
D
r
ec
em
be
r
Ja
nu
ar
y
Fe
br
ua
ry
M
ar
ch
0.0
ly
0.0
gu
s
Total nitrogen (mg/L)
0.8
Month
Month
Figure 17: Box plots of total nitrogen and total phosphorus data collected at a selection of rivers during
Environment Canterbury’s Regional Monitoring (2000-2012). The red line represents the monthly total nitrogen or
total phosphorus concentration based on data collected monthly from 1 July 2010 to 30 June 2011.
29
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
3.4 Comparison between River and Coastal sites - PCA Analysis
Principal Components Analysis (Primer v6.1.13) was used to compare variables (total nitrogen, ammonia
nitrogen, nitrate-nitrite-nitrogen, total phosphorus and dissolved reactive phosphorus) between the main
stem rivers and coastal sites sampled.
Coastal sites were similar to each other in their overall nutrient composition regardless of where they are
located in the Bay (Figure 18 and Figure 19).
With a few exceptions, most seasonal samples from each river site were also more similar to each other
and to the coastal sites in their nutrient concentrations, regardless of where they are located along the Bay.
The exceptions were the Ohoka, Cust and Kaiapoi Rivers (Figure 19), which appeared more similar to
each other (top right of figure).
The other exceptions were the Waimakariri and Heathcote Rivers (Figure 19, on the lower left) which
appear more similar to each other in nutrient composition.
The main drivers of the pattern can be seen in the vector plots (Figure 18) and appear to be total nitrogen
along axis 2 and total phosphorus along axis 1.
Figure 18: Plot of Axis 1 against Axis 2 from a Principal Components Analysis for all river and coastal sites
sampled along Pegasus Bay in 2010-2011.
30
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
Figure 19: Plot of Axis 1 against Axis 2 from a Principal Components Analysis for averages of all river and coastal
sites sampled along Pegasus Bay in 2010-2011
Cluster analysis identifies the above main groupings of sites further into:
-
the Kaiapoi River and its two tributaries;
the Avon River,
the Waipara and Ashley Rivers,
the Cam and Kowai Rivers,
the Styx River and Saltwater Creek,
the Waimakariri and Heathcote Rivers, and
the Coastal sites; (Figure 20).
The dark solid lines indicate significant groups while the lighter lines indicate no significance between
groups.
31
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
Figure 20: Cluster analysis for river and coastal sites sampled along Pegasus Bay in 2010-2011.
When only coastal sites are examined for differences in nutrients, the main drivers appear to be ammonia
nitrogen along axis 1 and total phosphorus along axis 2 (the vectors on Figure 21). Ammonia nitrogen
grades from higher concentrations at Waimari Beach to lower concentrations for the group of sites shown
at the right of axis 1 (Leithfield, Woodend, Amberley and Waikuku). Total phosphorus grades from low
concentrations at New Brighton and Waikuku to higher concentrations at Spencerville. Axis 1 accounts
for 75% of the variation while axis 2 accounts for 20%.
Cluster analysis shows no significant differences in nutrient composition between coastal sites (Figure
22).
32
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
Figure 21: Plot of axis 1 against axis 2 from a Principal Components Analysis for all coastal sites sampled along
Pegasus Bay in 2010-2011.
Figure 22: Cluster analysis for coastal sites sampled along Pegasus Bay in 2010-2011.
33
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
3.5 Annual Loads
The annual loads of nitrogen, phosphorus and suspended solids were calculated for all sites flowing into
Pegasus Bay for the 2010-2011 survey period, following the methodologies described in Section 2.7. The
results are presented in Appendix D and shown in the Figures below. Annual loads for each parameter
were also calculated as a percentage of the total from each source and are summarised in Appendix E.
The Kowai River and Saltwater Creek were excluded from analysis due to insufficient flow data.
3.5.1
Total Nitrogen
Total nitrogen loads average 1,970 T/year from the CCC outfall (46% of total nitrogen inputs from all
sources), 950 T/year in the Waimakariri River (22% of all inputs) and 600 T /year in the Cust (14% of all
inputs) (Figure 23, Appendix E). All other sites combined represented approximately 757 T/yr.
2000
1750
TN (T/Y)
1500
1250
1000
750
Annual
500
Summer
250
0
Site
Figure 23: Annual and Summer (November to April inclusive) loads (tonnes/year) of total nitrogen for rivers and
outfalls sampled throughout Pegasus Bay in 2010-2011.
34
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
3.5.2
Total Phosphorus
Total phosphorus loads followed similar patterns to those for nitrogen with the highest loads coming from
the CCC Outfall (1976 T/Yr) followed by the Waimakariri River (233T/Yr or 10% of all inputs) and the
WDC outfall (20 T/Yr or 1% of inputs) (Figure 24). All other sites averaged less than 12 T/year. The
CCC outfall alone represents 87% of the total inputs of total phosphorus to Pegasus Bay estimated in this
study.
2000
1750
TP (T/Y)
1500
1250
1000
750
Year- round
500
Summer
250
0
Site
Figure 24: Annual and Summer (November to April inclusive) loads (tonnes/year) of total phosphorus for
rivers and outfalls sampled throughout Pegasus Bay in 2010-2011.
35
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
3.5.3
Dissolved Reactive Phosphorus
The highest annual loads of Dissolved Reactive Phosphorus (DRP) come by far from the CCC outfall
(263 T/Yr or 84% of all inputs). The next highest from the Waimakariri River (23 T/Yr or 7% of all
inputs) and the WDC wastewater outfalls (15 T/Yr or 5% of all inputs), although these two sources
combined represent only 14% of the loads from the CCC (Figure 25). All other sites combined
represented approximately 9 T/yr.
300
250
DRP (T/Y)
200
150
Annual
100
Summer
50
0
Site
Figure 25: Annual and Summer (November to April inclusive) loads (tonnes/year) of dissolved reactive
phosphorus for rivers and outfalls sampled throughout Pegasus Bay in 2010-2011.
36
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
3.5.4
Dissolved Inorganic Nitrogen
Annual dissolved inorganic nitrogen (DIN) loads are highest from the CCC Outfall (1,887 tonnes/year or
50% of all inputs) followed by the Waimakariri River (863. tonnes/year, 23% of total inputs) and the Cust
Main Drain (544 tonnes/year, 14% of all inputs) (Figure 26).
2000
1750
DIN (T/Y)
1500
1250
1000
750
Annual
500
Summer
250
0
Site
Figure 26: Annual and Summer (November to April inclusive) loads (tonnes/year) of dissolved inorganic
nitrogen for rivers and outfalls sampled throughout Pegasus Bay in 2010-2011.
37
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
3.6
Daily Nutrient Loads
Inputs of total nitrogen, total phosphorus and total suspended solids from each of the rivers were
calculated as a daily load (kg/day) and as a percentage of the total from all rivers. Saltwater Creek and
Kowai River were excluded as there was insufficient flow data to calculate daily loads for these rivers.
3.6.1
Nitrogen
The Christchurch City Council Outfall contributed the highest nitrogen load over all months (47% per
month on average). The next largest contribution came from the Waimakariri River (on average 20% per
month) (Figure 27 and Figure 28). Further analysis, excluding the Waimakariri River and the two outfalls,
showed the Kaiapoi River and its tributary, the Cust River, to be the next main contributors (27% and
17% on average per month respectively). Most other rivers averaged monthly inputs of 2 to 10% (Figure
29 and
Figure 30).
The Waipara River did have higher loads in the first three months of the survey which is consistent with
increased flows over this period.
38
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
16000
Total nitrogen (kg/day)
14000
Waipara
12000
Ashley
WDC Outfall
10000
Cam
8000
Ohoka
6000
Cust
Kaiapoi
4000
Waimakariri
2000
Styx
Avon
0
Heathcote
CCC Outfall
Month
Figure 27: Total nitrogen inputs (kg/day) in rivers and outfalls sampled in Pegasus Bay, 1 July 2010 – 30 June 2011.
100%
90%
Waipara
Total nitrogen (%)
80%
Ashley
70%
WDC Outfall
60%
Cam
50%
Ohoka
40%
Cust
30%
Kaiapoi
20%
Waimakariri
10%
Styx
Avon
0%
Heathcote
CCC Outfall
Month
Figure 28: Total nitrogen inputs (as a percentage of the total) in rivers and outfalls sampled in Pegasus Bay, 1 July 2010
– 30 June 2011.
39
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
7000
Total nitrogen (kg/day)
6000
Waipara
5000
Ashley
4000
Cam
Ohoka
3000
Cust
2000
Kaiapoi
Styx
1000
Avon
0
Heathcote
Month
Figure 29: Total nitrogen inputs (kg/day) in rivers sampled in Pegasus Bay, 1 July 2010 – 30 June 2011 with the
Waimakariri River, Waimakariri District Council and Christchurch City Council outfalls excluded.
100%
90%
Total nitrogen (%)
80%
70%
Waipara
60%
Ashley
50%
Cam
Ohoka
40%
Cust
30%
Kaiapoi
20%
Styx
10%
Avon
0%
Heathcote
Month
Figure 30: Total nitrogen inputs (as a percentage of the total) in rivers sampled in Pegasus Bay, 1 July 2010 – 30
June 2011 with the Waimakariri River, Waimakariri District Council and Christchurch City Council outfalls
excluded.
40
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
3.6.2 Phosphorus
As with nitrogen, the Christchurch City Council Outfall and the Waimakariri River contributed the
highest loads for phosphorus in all months (61 and 25% on average per month respectively) (Figure 31
and Figure 32). All other rivers contributed less than 5%.
Excluding the Waimakariri River and two outfall sites from analysis resulted in 20% of the phosphorus
(on average per month) coming from the Heathcote River, 15% from the Avon, and 14% from each of the
Styx and Waipara Rivers. The remaining rivers contributed less than 10% each (Figure 33 and Figure 34).
The largest phosphorus loads over all months came from the Waipara River in July and September 2010
and from the Heathcote in August 2010.
41
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
4500
Total phosphorus (kg/day)
4000
Waipara
3500
Ashley
3000
WDC Outfall
2500
Cam
Ohoka
2000
Cust
1500
Kaiapoi
1000
Waimakariri
Styx
500
Avon
0
Heathcote
CCC Outfall
Month
Figure 31: Total phosphorus inputs (kg/day) in rivers and outfalls sampled in Pegasus Bay, 1 July 2010 – 30 June 2011.
100%
90%
Waipara
Total phosphorus (%)
80%
Ashley
70%
WDC Outfall
60%
Cam
50%
Ohoka
40%
Cust
30%
Kaiapoi
20%
Waimakariri
Styx
10%
Avon
0%
Heathcote
CCC Outfall
Month
Figure 32: Total phosphorus inputs (as a percentage of the total) in rivers and outfalls sampled in Pegasus
Bay, 1 July 2010 – 30 June 2011.
42
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
300
Total Phosphorus (kg/day)
250
Waipara
200
Ashley
Cam
150
Ohoka
Cust
100
Kaiapoi
50
Styx
Avon
0
Heathcote
Month
Figure 33: Total Phosphorus inputs (kg/day) in rivers sampled in Pegasus Bay, 1 July 2010 – 30 June 2011 with
the Waimakariri River, Waimakariri District Council and Christchurch City Council outfalls excluded.
100%
90%
Total Phosphorus (%)
80%
70%
Waipara
60%
Ashley
50%
Cam
Ohoka
40%
Cust
30%
Kaiapoi
20%
Styx
10%
Avon
0%
Heathcote
Month
Figure 34: Total phosphorus inputs (as a percentage of the total) in rivers sampled in Pegasus Bay, 1 July 2010 –
30 June 2011 with the Waimakariri River, Waimakariri District Council and Christchurch City Council outfalls.
43
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
3.6.3
Total Suspended Solids
On average 74% of inputs of total suspended solids per month come from the Waimakariri River (Figure
35 and Figure 36). All other rivers contributed less than 10% each on average per month.
Excluding the Waimakariri River and two outfalls shows most other rivers to be contributing 10-16%
each, per month, of the total suspended solids (Figure 37 and Figure 38).
Similar to loads for nitrogen and phosphorus, sediment loads were elevated in the Waipara and Heathcote
Rivers during winter in the first three months of the survey.
44
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
9000000
Total suspended solids (kg/day)
8000000
Waipara
7000000
Ashley
6000000
WDC Outfall
5000000
Cam
Ohoka
4000000
Cust
3000000
Kaiapoi
2000000
Waimakariri
1000000
Styx
Avon
0
Heathcote
CCC Outfall
Month
Figure 35: Total suspended solid inputs (kg/day) in rivers and outfalls sampled in Pegasus Bay, 1 July 2010 – 30 June 2011.
100%
Total suspended solids (kg/day)
90%
Waipara
80%
Ashley
70%
WDC Outfall
60%
Cam
50%
Ohoka
40%
Cust
30%
Kaiapoi
20%
Waimakariri
Styx
10%
Avon
0%
Heathcote
CCC Outfall
Month
Figure 36: Total suspended solid inputs (as a percentage of the total) in rivers and outfalls sampled in Pegasus Bay, 1 July
2010 – 30 June 2011.
45
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
Total suspended solids (kg/day)
140000
120000
Waipara
100000
Ashley
80000
Cam
Ohoka
60000
Cust
40000
Kaiapoi
Styx
20000
Avon
0
Heathcote
Month
Figure 37: Total suspended solids inputs (kg/day) in rivers sampled in Pegasus Bay, 1 July 2010 – 30 June 2011
with the Waimakariri River and the Waimakariri District Council and Christchurch City Council outfalls excluded.
100%
Total suspended solids (kg/day)
90%
80%
70%
Waipara
60%
Ashley
50%
Cam
Ohoka
40%
Cust
30%
Kaiapoi
20%
Styx
10%
Avon
0%
Heathcote
Month
Figure 38: Total suspended solid inputs (as a percentage of the total) in rivers sampled in Pegasus Bay, 1 July 2010
– 30 June 2011 with the Waimakariri River, the Waimakariri District Council and Christchurch City Council
outfalls excluded.
46
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
.
4 Conclusions















Three of the sites surveyed were on the Waimakariri River. The Waimakariri River at Kainga
Yacht Club was believed to be in the tidal zone, while the Waimakariri at Ferry Road was
downstream of the confluence with the Kaiapoi River and so influenced by inputs from there.
Consequently only data from the Waimakariri site at Stewarts Gully was used in analysis for this
report.
Analysis for the Ashley River is most likely underestimating nutrient loads as the sampling site
does not capture the whole catchment with tributaries draining into the Ashley River downstream
of the survey sampling point.
All rivers sites except the Waipara, Ashley and Waimakariri had total nitrogen concentrations
which were above reference guidelines (Table 4).
Half of the rivers surveyed had average concentrations of total phosphorus which exceeded the
reference guidelines (Table 4).
All rivers had ammonia-nitrogen concentrations that were within reference guidelines.
The Kaiapoi, Ohoka and Cust Rivers had DIN concentrations which were above reference values;
while the Heathcote River exceeded reference guidelines recommended for DRP concentrations.
All coastal sites were within the Canterbury coastal water reference values for total nitrogen and
total phosphorus.
The Waimakariri River contributed 80% of the flow from all the rivers surveyed between 2010
and 2011. The next highest flows came from the Ashley (7%) and the Waipara (3%) with the
remaining rivers and two outfalls contributing less than 1.5% each.
Principal Components Analysis (PCA) showed coastal sites were similar to each other in their
overall nutrient composition regardless of where they are located in the bay, and with a few
exceptions, most river sites were also more similar to each other and to the coastal sites in their
nutrient composition.
Cluster analysis identified four main groupings: the Kaiapoi and its tributaries, the Avon River,
the Waimakariri and Heathcote Rivers and the remaining river sites with all coastal sites.
The main drivers of the PCA patterns appear to be total nitrogen, total phosphorus and dissolved
reactive phosphorus for river sites while for coastal sites they were total phosphorus and ammonia
nitrogen.
The Christchurch City Council outfall contributes the highest annual loads of DRP, DIN, TN and
TP to Pegasus Bay.
Inputs of total nitrogen, total phosphorus and total suspended solids from each of the rivers were
calculated as a daily load (kg/day) and as a percentage of the total from all rivers.
The Christchurch City Council outfall contributed the highest daily total nitrogen (47%) and total
phosphorus (61%) loads followed by the Waimakariri River (20% and 25 % for TN and TP
respectively).
Excluding the Waimakariri River and WDC and CCC outfalls from analysis revealed the Kaiapoi
to contribute the next highest loads of total nitrogen (27%); the Heathcote and Avon Rivers,
47
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury


phosphorus (20% and 15% respectively) and most other rivers to be contributing similar daily
loads of suspended sediments.
The CCC and WDC outfalls combined contributed 49% of the daily total nitrogen and 66% of the
daily total phosphorus, compared with 51% of daily TN and 34% of daily TP from the rivers.
Physico-chemical parameters (eg. pH, dissolved oxygen and water temperature) although
measured, have not been included for assessment in this report due to their variable nature.
5 Recommendations
5.1 Site selection
The analysis presented in this report is primarily based on data collected by Environment Canterbury over
a relatively limited period of time. The survey period was also characterised by significant earthquakes
that hit the Christchurch area, and caused significant loss of life, damage to building and infrastructure,
and, of particular relevance to water quality, to sewage and stormwater collection and treatment
infrastructure. Also no monitoring was undertaken during one (February) of the 12 months in the period
covered by the survey. Further, extensive soil liquefaction is likely to have increased fine sediment
mobilisation and transport to streams and rivers.
The water quality results obtained during the survey period were checked against long-term data, and
were found to be not too dissimilar to long-term water quality at key monitoring sites, which provides a
degree of confidence that the results and the analysis based on these results are representative of the longterm situation. It is plausible however, that the earthquake damage and consequences might have had an
influence on water quality during the survey period. As a result, it may be advisable to repeat the survey
in the future, particularly if eutrophication issues are identified or suspected in Pegasus Bay.
If a similar survey was to be repeated, we make the following recommendations:
-
-
-
Site selection: Ideally, sites should be located at or near the bottom of the catchments in order to
estimate the load of contaminants being exported from the said catchment. Consideration should
for example be given to moving the Ashley River monitoring site closer to the bottom of that
catchment;
Timing of water quality and flow monitoring: Ideally, flow gauging’s and water quality sampling
should occur the same day. Some of the flow gauging data provided for this study could not be
used for the calculation of daily contaminant loads due to the flow gauging’s occurring several
days after the water quality sampling. Alternatively, robust flow correlations with existing flow
recorder sites could be established for some of the sites, in order to provide synthetic flow records
that could be used in contaminant load calculations;
Microbiological water quality could be included in the list of determinands monitored as part of
the survey
48
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
5.2 Eutrophication issues in Pegasus Bay
Nitrogen in the concentrations present at the coastal sites during the period of survey are not expected to
be toxic to aquatic life, and phosphorus forms are generally not toxic to aquatic life. The key potential
environmental issues associated with elevated nutrient concentrations in coastal waters relate to
eutrophication, i.e. the promotion of excessive benthic or planktonic algae growth. It is unclear at the
moment whether nutrient concentrations in Pegasus Bay are or are close to, causing excessive algal
growth issues. It is recommended that this should be the focus of targeted monitoring over the next few
years.
This report characterises the nutrient loads entering the Pegasus Bay nearshore area from a number of
non-point (rivers) and point- (wastewater outfalls) sources. It highlights in particular the significant
contribution of the Christchurch City Council ocean outfall to the total loads of both TN and TP entering
Pegasus Bay. Should significant actual or potential algal growth issues be identified in Pegasus Bay, the
findings presented in this report would assist in identifying key nutrient sources and prioritising their
management.
49
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
REFERENCES
1. ANZECC. (2000). Australia and New Zealand Guidelines for Fresh and Marine Water Quality.
Australian and New Zealand Environment and Conservation Council. Agriculture and Resource
Management Council of Australia and New Zealand. ISBN 09578245 0 5.
2. Bolton-Ritchie, L. 2007. The quality of coastal waters between Kaikoura and Pegasus Bay, July
1993 – June 2006. Environment Canterbury Report U07/16. 49pp.
3. Cox, D.R. and Hudson, R. M. 2003. Waimakariri outfall oceanographic data collection, 27 May
to 25 July 2003. WRL Technical Report 2003/24.
4. Fenwick, G. 1999. The benthos off South Brighton, Pegasus Bay: a preliminary assessment.
NIWA client report CHC99/53. Prepared for Christchurch City Council
5. Hadfield, M. and Zeldis, J. 2012. Freshwater dilution and transport in Canterbury Bight. NIWA
Client Report WLG2011-54 for Environment Canterbury. 39pp + animations.
6. Kelly, D., Norton, N. 2010. Current nutrient loads and options for nutrient load limits for a case
study catchment: Hurunui catchment. Environment Canterbury report R10/66. 50pp.
7. Miller, B.M., Glamore, W.C. and Hudson, R.M. 2004. Christchurch outfall: Twelve months
data collection and modelling. WRL Technical Report 2004/14.
8. Ngāi Tūāhuriri Rūnanga, Te Hapū o Ngāti Wheke (Rāpaki), Te Rūnanga o Koukourārata, Ōnuku
Rūnanga, Wairewa Rūnanga, Te Taumutu Rūnanga 2013. Mahaanui Iwi Management Plan.
392pp.
9. Reynolds-Fleming, J.V. and Fleming, J.G. 2005. Coastal circulation within the Banks
Peninsula region, New Zealand. New Zealand Journal of Marine and Freshwater Research.
39:217-225.
10. Richards R.P. (1998). Estimation of pollutant loads in rivers and streams: a guidance document
for NPS programs. Prepared for the U.S. Environmental Protection Agency Region VIII, under
Grant X998397-01-0.
11. Scarsbrook M. R. and McBride G. B. (2007). Best practice guidelines for the statistical analysis
of freshwater quality data. Prepared for the Ministry for the Environment by the National
Institute for Water and Atmospheric Research (NIWA). NIWA client report: HAM2007-088.
12. Stenton-Dozey, J. 2005. Supplementary evidence for resource consent hearing for Pegasus Bay
Marine Farm Joint Venture. 70pp.
13. Stevenson, M., Wilks, T. and Hayward, S. An overview of the state and trends in water quality
of Canterbury’s rivers and streams. Environment Canterbury Report R10-117. 80pp
50
Nearshore Coastal Water Quality,
Pegasus Bay, Canterbury
51
APPENDICES
52