water quality monitoring of Ō tū wharekai/ashburton lakes
TRANSCRIPT
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Water quality monitoring of Ō Tū Wharekai/Ashburton lakes and streamsSummary of findings
Tom Drinan & Hugh Robertson
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Arawai Kākāriki wetland restoration programme
Started in 2007 at three of New Zealand’s foremost wetland sites
Science to inform freshwater conservation
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Public conservation land within the basin
(showing Maori Lakes catchment boundary)
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Risks to the ecological health of the Ashburton Lakes
State and trend of water quality of the Ashburton Lakes
State and trend of water quality in streams of the Maori Lakes
catchment
Talk outline
What we’ll cover
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Trophic status (TLI)
Aquatic plants (LakeSPI)
Water quality (e.g. nutrients)
Hydrology
Models (e.g. nutrient load modelling)
Indicator species (e.g. freshwater mussels)
Cultural assessments
No one indicator, we use multiple methods to give the fullest picture
Lake health
How do we measure it?
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Eutrophication – high levels of nitrogen, phosphorus can lead to
increased risk of becoming algal-dominated. Loss of biodiversity
Water clarity – high levels of suspended sediment or algae
Hydrological change – flow reduction leads to less flushing
Pest fish – contribute to water quality issues. Displace native species
Risks to lake health
The key drivers of lake health and impacts on ecological values
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Freshwater Outcomes for Canterbury Lakes (CLWP)
Freshwater Outcomes
CLWP outcomes for Trophic status (TLI) and LakeSPI
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Lakes
Monitoring undertaken by Environment Canterbury
Samples collected from lakes Heron, Emma, Camp, Clearwater
(since 2004), Emily, Maori Lake East (front), Maori Lake West
(back) (since 2008), and Denny (since 2013)
Water sampling data used in the report where available up to
April 2018
Water quality monitoring – lakes and streams
Data availability
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Lake water quality monitoring sites
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Streams
Monitoring undertaken by DOC
Samples collected monthly from streams in the Māori Lakes
catchment since 2012
The outlet to Maori Lake East (front), was sampled along with its
inflowing tributaries of Jacobs Stream, Gentleman Smith Stream,
and Clent Hill Stream
Paddle Hill Creek serves as a low impact reference site
Water quality monitoring – lakes and streams
Data availability
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Stream water quality monitoring sites
(showing Maori Lakes catchment boundary)
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Summary of
results –
lakes
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Lake water quality
Total nitrogen – TN
Bands = A–D Attribute
States
(NOF, NPS-FM 2014)
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Lake water quality
Total phosphorus – TP
Bands = A–D Attribute
States
(NOF, NPS-FM 2014)
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Lake water quality
Chlorophyll a – Chl.a
(annual median)
Bands = A–D Attribute
States
(NOF, NPS-FM 2014)
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Lake water quality
Trophic level index –TLI3
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Lake water quality
Improving TP at Maori Lake East (front)
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Lake water quality
Degrading TN at Lake Camp
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Lake water quality
Degrading TN at Lake Heron
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Lake water quality
Degrading TN at Maori Lake East (front)
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Lake water quality
Degrading TLI3 at Lake Camp
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Lake water quality
Degrading turbidity at Lake Heron
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Lake water quality
Aggregated trends (quarterly)
Green = improving; red-orange = degrading
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Lake water quality
Aggregated trends (quarterly) with Attribute State (NOF)
Green = improving; red-orange = degrading
A C A
A
B
C
A
B
B
B
B
C
C
B
B
A
B
B
B
B
D
C
A
A
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Lakes are in a range of trophic states – degrading trends emerging
for some lakes
Many lakes have relatively high concentrations of N
Maori Lakes were mesotrophic; however, the trophic state of
Maori Lake East (front) is likely to be worse than indicated by TLI
score because it has extensive growth of benthic algae
TN has increased in lakes Heron, Camp, and Maori Lake East
(front)
Lake Camp has degrading trends for chlorophyll a, TLI, TN, and
turbidity
Turbidity is also degrading at Lake Heron
Lake water quality
Summary
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Summary of
results –
streams
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Stream water quality
Total oxidised nitrogen – TON
(Nitrate)
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Stream water quality
Total nitrogen – TN
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Stream water quality
Total phosphorus – TP
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Stream water quality
Total suspended solids – TSS
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Stream water quality
Improving TP at Gentleman Smith Stream
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Stream water quality
Improving TSS at Clent Hills Stream
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Stream water quality
Degrading TN at Gentleman Smith Stream
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Stream water quality
Degrading TN at Jacobs Stream
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Stream water quality
Degrading TN at Maori Lakes Outlet
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Stream water quality
Aggregated trends (quarterly)
Green = improving; red-orange = degrading
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TN has increased at Gentleman Smith Stream, Jacobs Stream, and
Maori Lakes Outlet
Nitrate (TON) has increased at Gentleman Smith Stream – more
recent results from this site are approaching/have shifted to
Attribute State B (from A) (NOF band)
TP highest at Clent Hills Stream
TP has decreased at Gentleman Smith Stream, TSS has decreased
at Clent Hills Stream, and TAN has decreased at Maori Lakes
Outlet
Stream water quality
Summary
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LakeSPI is a management tool that uses Submerged Plant
Indicators (SPI) for assessing the ecological condition of lakes
Other measures of lake health
LakeSPI assessment, NIWA 2017
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Majority of the OTW lakes have been stable over successive
LakeSPI surveys in 2007, 2012, and 2017 – exceptions have been a
deterioration detected for Lake Denny (and possibly for Maori
Lake West [back]) and an improvement for Maori Lake East (front)
Lake condition (based on LakeSPI indices)
Excellent: Donne
High (min. grade in CLWP): Camp, Spider
Moderate: Clearwater, Emily, Emma, Heron, Maori Lake
East (front), Maori Lake West (back), Roundabout
Poor: Denny
LakeSPI
OTW lake scores
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Freshwater Outcomes for Canterbury Lakes (CLWP)
Freshwater Outcomes
CLWP outcomes for Trophic status (TLI) and LakeSPI
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Conclusions
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Overall observations on lake health
The trends in lake and stream water quality are cause for concern
at a number of sites. Particularly in terms of nitrogen
Changes in water quality pose a significant risk of a state shift in
some lakes – i.e. a macrophyte collapse
Declining water quality (and associated habitat quality declines)
(e.g. sediment) poses major risks to biodiversity within the lakes
(and streams)
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Next steps – where to from here?
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Take actions to reduce the loss of N, P and sediment to streams
entering vulnerable lakes – especially the Maori Lakes, and lakes
Heron, Camp, and Clearwater
Focus management particularly on N – it has the greatest rate of
increase in streams and lakes
Ensure that lake and stream management to protect ecological
health is adequately addressed in Farm Environment Plans
Review the Trophic State (TLI) targets for the Ashburton Lakes
Prepare an ‘options analysis’ to safeguard the ecological health of
the Ashburton Lakes
Recommendations
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Thank you