Good progress made on lake water quality
Thursday, 10 February 2011 12:00 a.m.
Bay of Plenty Regional Council has made good progress to improve water quality in Rotorua's lakes.
This week's Operations Monitoring and Regulation Committee heard that achievements included significantly improving Lake Rotoiti's water quality, completing all the actions in Lake Ōkaro's Action Plan, securing half the land use change required for the Lake Ōkāreka Catchment and commissioning the Puarenga Stream phosphorus-locking plant.
Project Manager Anna Grayling said that over the next six months key work areas would include developing policy to support nutrient reductions from land use in the Rotorua catchment and increasing efficiency of existing land use change projects.
"Operational works will continue to treat nutrient-rich inflows to the lakes, and nutrients within the lakes. Further research and development will assist with delivering the most cost effective tools to do this," she said.
Since signing the Strategy for the Lakes of the Rotorua district in 2000, the Regional Council, Rotorua District Council and Te Arawa Lakes Trust had embarked on an extensive work programme aimed at protecting and enhancing water quality in 12 of Rotorua Te Arawa Lakes.
The $200 million programme is in partnership with Te Arawa Lakes Trust and Rotorua District Council, with central government a major funding partner for work on four priority lakes - Rotorua, Rotoiti, Rotoehu and Ōkāreka.
Of the other eight lakes, four are in good condition (Ōkataina, Tikitapu, Tarawera and Rotomā), three are of concern but not a priority (Rerewhakaaitu, Rotokakahi and Rotomahana). The Regional Council was supporting a local landowner-led initiative on Lake Rerewhakaaitu, and is monitoring the others closely. Action will be taken if it is shown to be necessary, she said.
Lake Ōkaro remained Rotorua's most degraded lake, but this year had shown significant improvement in water quality.
"In conjunction with our partners we have made solid progress toward long-term restoration of the priority lakes.
A pilot de-nitrification plant has been constructed at Tikitere geothermal field, benchmarking nutrient outputs from properties is underway in the Rotorua Catchment, with nearly 70 properties now completed. An Action Plan has been completed for Lake Rotomā and a collaborative relationship established with Lake Rerewhakaaitu farmers.
"They are well on the way to having nutrient management plans in place on all large farms," she said.
A joint resource consent had been obtained with Te Arawa Lakes Trust to develop floating wetlands for 11 lakes, which will be built over time. A review of Navigational Safety and Bylaws had been completed and a tender awarded for intervention packages for Rotorua.
Trophic Level Indices (which indicate lake health) for Lake Rotorua had remained stable for the last six years, although algal blooms in the last two seasons had caused concerns, Ms Grayling said. Actions taken to prevent further decline and kerb the blooms included reducing phosphorous inputs with the new P-locking plant, and construction of the Tikitere de-nitrification plant which aimed to reduce nitrogen levels by up to 30 tonnes a year.
Gorse was identified as a major nitrogen contributor, with nearly 900 hectares in the Rotorua catchment leaching approximately 43 tonnes of nitrogen. Staff had actively engaged with land owners with significant gorse coverage, and three contracts had been signed to use Deed funding to subsidise converting gorse to pines.
At Lake Rotoehu aquatic weed harvesting last year removed between six and eight tonnes of nitrogen, and more than a tonne of phosphorus, exceeding nutrient removal targets.
"Although we are doing well to halt the decline in water quality in our most degraded lakes we must be vigilant in protecting our best as well. Some of our most pristine lakes are showing some signs of water quality decline. Most are still very clean with no algae blooms, but we want to make sure they stay this way.
"Lake Rotorua remains a challenge, and this year we will be focusing on developing policy to support land use change, in-lake and in-stream actions, and operational works for land use change."