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Water quality trends in Lake Rotomanuka North: Implications for restoration and management

TR 2002/03
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Report: TR 2002-03

Author: Grant Barnes

Abstract

The Northern Waikato region has an abundance of freshwater ecosystems ranging from large peatbogs, minerotrophic wetlands, peat lakes associated with developed peatlands, and shallow riverine lakes. There are more than 40 lakes ranging in area from less than 0.01 km2 (Lake Posa, near Koromatua) to 34.4 km2 (Lake Waikare).

The peat lakes of the Waikato region are concentrated around the Waikato and Waipa districts, and Hamilton City where their association with peat formations has had a marked effect on their physical, chemical and biological nature. Dystrophic (peat) lakes are typically brownish in colour with high levels of dissolved organic substances associated with leaching from adjoining peat vegetation in the catchment. Generally mildly acidic (pH5.5 – 6.5), the bottom waters are often depleted in dissolved oxygen due to the decomposition of organic carbon. The Waikato peat lakes form the largest collection of peat lake habitat in New Zealand and are valuable conservation refuges for many unique plant and animal species. They also represent some of the few remaining areas of wetland in the formally extensive Komakorau, Rukuhia and Moanatuatua peat bogs, as well as being important recreational areas for hunting, boating and picnicking.

Lake water quality has been monitored continuously in Lake Rotomanuka North since October 1995. Earlier water quality monitoring was undertaken sporadically during the 1980’s in support of numerous research programmes underway at the time. There are generally two important aims of routine water quality monitoring programmes. To determine the productivity of the waterbody and to determine long-term changes, or “trends” in water quality conditions.

Water quality trends in Lake Rotomanuka North : implications for restoration and management [PDF, 277 KB]