Lake Ngaroto

General Information

Lake Ngaroto is not directly associated with the encroachment of peat bogs in the Waikato valley, but is instead affected by local wetland development around its margins (Selby & Lowe, 1992; Lowe & Green, 1987). Peat surrounding Lake Ngaroto extends to about 0.5 m deep at the lake margin and down to 2.5 m approximately 600 m from the lake edge. The peat associated with Lake Ngaroto tends to be lake peat, deposited when the lake area was much larger, and sedgy peat, which is comprised of marginal lake vegetation in a semi-decomposed state (Thompson, 1994).

Lake Ngaroto

Lake Ngaroto photo taken by Wendy Paul

Although the bottom sediments of Lake Ngaroto do not become anoxic in the summer, internal nutrient loading remains important. This occurs because in very productive lakes the sedimentation of organic material in summer is so high bacterial consumption of oxygen reduces the oxic layer of sediment to a few millimetres. Thus the capacity of the sediment to bind phosphorus is reduced and phosphorus is released from decomposed organic matter or deeper parts of the sediment (S√łndergaard et al., 2003).

Restoration Action

Lake Ngaroto is used extensively for recreation, although recreational activities often become impaired during the summer months when cyanobacteria reach toxic levels in the lake. Current restoration activities include; placing a weir on the main outflow to regulate water levels, building sediment traps on the main inflows, riparian planting, spraying pest willow species and establishing a fenced reserve margin.

Lake Ngaroto Statistics

Area 24.9 ha
Maximum depth 6.7 m
Trophic state Eutrophic
Recreation Power boating
Restoration progress Lake perimeter is fenced and riparian planting is underway
Peat influence High, Kainui peat bog
Reserve status Recreation, administered by the Waikato District Council
Submerged vegetation Submerged vegetation is not common, but marginal species that have been recorded are: Nitella hookeri/cristata, Potamogeton ochreatus and P. cheesemanii.
Harmful algae  
Invasive fish Catfish, rudd and gambusia

References

Boswell et al. (1985). Waikato small lakes: resource statement. Waikato Valley Authority.

Champion et al. (1993). The Vegetation of the Lower Waikato Lakes. Volume 2: Vegetation of thirty-eight lakes in the lower Waikato. NIWA Ecosystems Publication No.8 August 1993.

Faithfull et al. (2006). Waikato peat lakes sediment nutrient removal scoping exercise. Environment Waikato Technical Report TR06/15.

Thompson M. (1994). Substrate coring around the Waipa Peat Lakes to aid in the establishment of Esplanade Reserving. BSc (Technology) Industry Report. University of Waikato, Hamilton, New Zealand.

Selby M.J. & Lowe D.J. (1992). The middle Waikato basin and hills. In, J.M. Soons & M.J. Selby (Eds.). Landforms of New Zealand (2nd Ed.). Longman Paul: Auckland.