Peat Lake Pre-Restoration

August 2013

The Department of Conservation works with farmers to restore a Waikato Peat Lake

While covenanting of areas of native bush on farms in partnership with organisations like the QE2 Trust has been going on for many years, increasing numbers of farmers are becoming involved in ecological restoration work of the waterways associated with their properties. A $20 million, 10-year partnership between Fonterra and Department of Conservation will focus on improving water quality in “five key waterways” around New Zealand including three Waikato peat lakes: Areare, Ruatuna and Rotomanuka. The DOC partnership is part of Fonterra’s Living Water programme.

Nearby to these lakes, one of more than 30 ecologically threatened lakes in Waikato is Tunawhakaheke (also known as Lake E) located in the Horsham Downs district. It is bounded by the large Henderson farm to the north and the Reese farm to the south. Restoration work is already underway with boundary fencing and riparian retirement, spraying of willow trees and native plantings along the lake edge. The lake is small (7ha in area) and shallow and has been heavily modified by drainage and land clearance.

The peat lakes in Waikato and Waipa regions are valuable conservation refuges for many unique plant and animal species, also for genetic diversity, cultural importance, scientific interest, recreactional opportunities and intrinsic values. Left alone within farming zones, the lakes silt up and water quality deteriorates because of nutrient loading. The banks of these lakes have in the past been planted with willows which contribute to the degradation. These have to be removed and the riparian zones planted with grasses and native trees and bushes. Peat lakes don’t normally have surface entry and exit waterways, but gather water filtered through the surrounding low-fertility peat soils. They are especially sensitive to nutrient run-off and tend to eutrophication.

When the lake ecosystems are functioning well, the damp soils and dense swards of native rushes and sedges are very effective in:

  • converting nitrogen from surface runoff and leaching and returning the resulting nitrate gas to the atmosphere (denitrification)
  • trapping sediments from overland flow, preventing the effects of infilling and smothering
  • filtering and trapping effluent particles and storing the resulting carbon
  • trapping harmful micro-organisms such as bacteria which are either retained by the soil, or killed by exposure to sunlight
  • retaining ground water tables and soil moisture levels
  • protecting down stream land from flood damage by absorbing and slowly releasing runoff

The Henderson family has been farming at Horsham Downs for over 90 years and Richard Henderson for the past 20 years. They have 810 cows on 310ha. They have two lakes, one completely enclosed within the property called Lake A or Whakatangi, and the other on their southern farm boundary called Lake E or Tunawhakapeka. It is a wildlife management reserve under DOC and partly owned by the two farms. It is over 7ha in area but only perhaps half a metre deep in spring. Restoration work has not begun on Lake A, which is 3ha, deep, ringed with willows and contains pest fish. After a Whole Farm Management Plan and Catchment Plan (done by John-Paul Praat of PA Handford and Associates three years ago), restoration began on Lake E with new boundary fencing in the middle of 2011. The work was done by a fencing contractor and the costs shared between land owners, Environment Waikato and DOC. It is a seven-wire high tensile and electric fence with close posts and no battens. There was some marginal loss of grazing land in three paddocks on the Henderson farm but the existing boundary fence did not reliably exclude cattle from the lake zone.

14 months ago the willows along the Henderson lake frontage were all sprayed from the air. Some regeneration has occurred. Spraying was an option because there were no native trees within the riparian zone. The willow trunks will be left to rot and fall and natives will be spot planted in the zone. The lake does not have a huge catchment area within the farm, perhaps 30ha. Silt traps and associated drainage will be installed in future.

Under the whole farm management plan, numbers of cows have been reduced by 100, the effluent irrigation area extended from 30ha to 100ha and different fertiliser applications have been used for different soil types. Richard is also moving towards liquid urea spreading with a Metalform Tow and Fert mixer and sprayer which cuts the urea down by half to 35kg/ha, dissolved and applied in 200litres/ha of water.

The second farm on lake edge belongs to the Reese family. Pat Kuriger, sharemilker for the Reese Trust, has been on the Horsham Downs farm for six seasons and is wintering 460 cows on 143ha effective, with a 40-a-side herringbone shed. Two years ago a new boundary fence was erected along the lake edge, enclosing a generous riparian zone. Where the zone is free of willows, Pat has mowed the grass prior to planting of native trees by Landcare Trust, conservation volunteers, local farmers, DOC and Fonterra. Some spot spraying has then been done to “release” those small trees from pasture regrowth. The eastern end of the lake zone contains three mai mais, which in May are well used for duck shooting.