The Bay of Plenty Regional Council is on track with methods to improve the water quality of Lake Rotorua, according to a recent scientific review.
The review of water quality science for Plan Change 10 was completed by the Water Quality Technical Advisory Group (TAG) for the Rotorua Te Arawa Lakes Programme and showed that reducing land use losses of both nitrogen and phosphorus remains the right approach.
A summary report is available along with 12 science module reports investigating various aspects of the lake and catchment science that has led to RMA rules to regulate land use in the Lake Rotorua catchment.
Plan Change 10 has been implemented to improve water quality by introducing rules to limit the amount of nutrients from land use entering Lake Rotorua.
Current estimates show there are about 755 tonnes of nutrients entering Lake Rotorua every year. This needs to be reduced to about 435 tonnes to ensure the water quality target is met.
Excess nutrients are known to aid the growth of algae, pest weeds and cause the water quality to decline.
The key science conclusions from the review included:
• Dosing Lake Rotorua with alum has been the key action in improving water quality.
• The amount of nutrients entering Lake Rotorua was still in excess of the annual target of 435 tonne and significant reductions in both nitrogen and phosphorus were needed to achieve the water quality target for Lake Rotorua.
• The target of limiting 435 tonnes of nitrogen a year into Lake Rotorua is supported by the review.
• Climate change is predicted to make it more difficult to attain the water quality goals for the lake
• The focus of remediation in Lake Rotorua should still be on catchment control of nutrients, including new approaches that are being trialled by Rotorua farmers and showing promising results.
Bay of Plenty Regional Chairman Doug Leeder said the science review reinforced that Council was working in the right direction in improving Lake Rotorua’s water quality long term.
“We have to keep moving forward with the evidence we have. The current rules have been put together from almost 100 research and information reports from independent experts, community representatives and engagement groups.
"We need to be mindful that the rules are only one part of an integrated framework aimed at cleaning up Lake Rotorua. Other solutions include removing 50 tonnes through engineering initiatives and 100 tonnes through the $40 million Lake Rotorua Incentives Programme.”
The science review was peer-reviewed by Professor Warwick Vincent, of Laval University, Quebec, Canada in 2018 and was presented to the Bay of Plenty Regional Council Regional Direction and Delivery Committee this week.
Professor Warwick Vincent said Lake Rotorua was probably one of the most intensively researched lakes nationally, if not internationally.
Plan Change 10 requires the Regional Council to undertake a five-yearly science review of its work.