Water quality monitoring of Ō Tū Wharekai/Ashburton lakes and streamsSummary of findings

Tom Drinan & Hugh Robertson

Arawai Kākāriki wetland restoration programme

Started in 2007 at three of New Zealand’s foremost wetland sites

Science to inform freshwater conservation

Public conservation land within the basin

(showing Maori Lakes catchment boundary)

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

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?

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

Freshwater Outcomes for Canterbury Lakes (CLWP)

Freshwater Outcomes

CLWP outcomes for Trophic status (TLI) and LakeSPI

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

Lake water quality monitoring sites

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

Stream water quality monitoring sites

(showing Maori Lakes catchment boundary)

Summary of

results –

lakes

Lake water quality

Total nitrogen – TN

Bands = A–D Attribute

States

(NOF, NPS-FM 2014)

Lake water quality

Total phosphorus – TP

Bands = A–D Attribute

States

(NOF, NPS-FM 2014)

Lake water quality

Chlorophyll a – Chl.a

(annual median)

Bands = A–D Attribute

States

(NOF, NPS-FM 2014)

Lake water quality

Trophic level index –TLI3

Lake water quality

Improving TP at Maori Lake East (front)

Lake water quality

Degrading TN at Lake Camp

Lake water quality

Degrading TN at Lake Heron

Lake water quality

Degrading TN at Maori Lake East (front)

Lake water quality

Degrading TLI3 at Lake Camp

Lake water quality

Degrading turbidity at Lake Heron

Lake water quality

Aggregated trends (quarterly)

Green = improving; red-orange = degrading

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

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

Summary of

results –

streams

Stream water quality

Total oxidised nitrogen – TON

(Nitrate)

Stream water quality

Total nitrogen – TN

Stream water quality

Total phosphorus – TP

Stream water quality

Total suspended solids – TSS

Stream water quality

Improving TP at Gentleman Smith Stream

Stream water quality

Improving TSS at Clent Hills Stream

Stream water quality

Degrading TN at Gentleman Smith Stream

Stream water quality

Degrading TN at Jacobs Stream

Stream water quality

Degrading TN at Maori Lakes Outlet

Stream water quality

Aggregated trends (quarterly)

Green = improving; red-orange = degrading

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

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

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

Freshwater Outcomes for Canterbury Lakes (CLWP)

Freshwater Outcomes

CLWP outcomes for Trophic status (TLI) and LakeSPI

Conclusions

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)

Next steps – where to from here?

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

Thank you