The Waikato’s remaining peat lakes are under threat from changes in land use and farm development, this week’s Environment Waikato Environment Committee heard.
Freshwater ecologist Grant Barnes told the Committee than land management changes such as drainage, vegetation clearance and agricultural development had negatively affected the water quality and quantity, biodiversity and natural character of almost all peat lakes.
The Waikato’s wetland ecosystems were nationally important because they were the largest remaining collection of such habitats within one area in the country. They were valuable refuges for maintaining regional biodiversity, contained unique species of plants and animals adapted to live in acidic conditions and were important to local communities for recreation.
The Waipa peat lakes were particularly vulnerable to water level decline as much of the wetland area was drained for farmland, resulting in irreversible shrinkage and oxidation of the peat. Outlet drains have been deepened and widened over time, making the lakes much shallower and covering smaller areas. If drainage was not controlled, many Waipa peat lakes would disappear from the landscape.
Environment Waikato, Waipa District Council, DoC and the Fish and Game Council were working to develop a Waipa Lakes and Wetlands Accord to improve co-ordination of lake management. All agreed that lake level decline was the critical issue and were committed to protecting the lakes identified at greatest risk.
A considerable amount of work is being done at several of the most critical lakes, including Rotomanuka, Ngaroto, Cameron and Serpentine. Control structures are being designed on the outlets of lakes Rotomanuka and Serpentine to maintain a fixed minimum summer level while ensuring the efficient passage of winter flows and floods.
At Lake Mangakaware Waipa District Council has installed a lake level protection weir. Lake Care groups are also working to protect water levels and enhance the lakes.
Grant Barnes said Environment Waikato proposed setting formal lake water levels for peat lakes in its Regional Plan, but establishing a minimum level providing a suitable balance for the lakes’ ecological needs and appropriate moisture management on neighbouring farmland was complex.
Construction of water level control structures was programmed for in a number of peat lakes this summer, and the support of neighbouring landowners was critical to implementing minimum lake level controls.
Councillors supported the initiatives being taken by the various agencies and community groups to protect lake levels and praised the co-operative approach being taken.