Ecologist sceptical about ECan’s Lake Benmore investigation

A leading freshwater ecologist has expressed concern there will be no action on the Ahuriri arm of Lake Benmore, despite it exceeding water quality limits.

Dr Mike Joy, of Victoria University, said he had no confidence in any solution being found to the news that the area had exceeded its Trophic Level Index (TLI) ‘‘as long as we continue to subsidise dairy farming’’.

The TLI – used across New Zealand as a measure of the nutrient status of a lake – has exceeded 2.75 in the Ahuriri arm catchment, meaning there is a risk of algal blooms and increased turbidity in the lake. Last year, the TLI was 2.3.

Joy is questioning what will happen following news that Environment Canterbury said the levels had triggered an investigation to be conducted by twoperson scientist panel.

‘‘ECan also found that dairy farming broke all the trigger levels for Te Waihora/Ellesmere and decided to do an economic study on how to reduce nitrate load or mitigate through wetland.

‘‘It turned out it would be $300 million loss for dairy farmers and/or $380m to build a wetland that might fix the problem so they decided it was too expensive so they will ignore it.’’

Joy said a proper investigation would ensure that farmers operated to their limits. We’re loading nitrogen at unacceptable levels into our important catchments.

‘‘We are paying farmers not to dairy farm in the Lake Taupo and Lake Rotorua catchments to protect those lakes.

‘‘If we applied the same process and logic and pricing to Canterbury it would be in the billions of dollars.’’

However, ECan chief scientist Dr Tim Davie said the study of Te Waihora/ Ellesmere was not instigated by a trigger level (unlike Lake Benmore) but was part of an analysis of long-term measures needed to improve Te Waihora water quality.

‘‘These are two very different situations,’’ Davie said.

‘‘Te Waihora is a shallow lowland lake/lagoon with a catchment much of which has been intensively farmed for over 100 years. The nutrients are slowly moving through groundwater in response to over 100 years of agriculture.

‘‘The situation is one where we are trying to claw back excessive nutrients, where they’re already there and farming systems have been in place for a very long time.

‘‘Lake Benmore is a deep, high country lake with a catchment that has only recently – in the last 20 years – seen intensification. Nutrients move reasonably quickly from land to the lake.

‘‘Nutrients from farms are being managed via farming consents.

‘‘The requirement for people to reduce nutrient discharges demonstrates a robust process to meet our community objectives for the lake.

‘‘Te Waihora is a much longer-term situation where we are managing longterm legacy issues of nutrients.’’