A limnological survey of Lakes Rotokuru and Dry Lake, Rotokuru Ecological Reserve, Karioi State Forest

ll refs; 3 figs; 6 tables

A limnological survey of both lakes was made at the request of the Wildlife Service in order to provide information on their physical, chemical and biological status as a preliminary aid to decisions on the management of their rainbow trout fishery. Lake Rotokuru has a number of anomalous features which set it apart from most other lakes in the central North Island. Some of these are likely to adversely affect the suitability of this lake as a recreational fishery. Anoxia near the bottom in spring and summer clearly has an effect on the profundal benthic fauna. The benthic community of the littoral zone is sparse in both species and numbers. Habitats for trout food appear to be limited and there is no surface inflowing stream which might provide a further food source. The algal flora also demonstrates a number of unusual features. The inflows are as groundwater, and will be equal to or slightly exceed the 0.02 cubic metres per second outflow. Inorganic nitrogen levels are relatively high in Lake Rotokuru giving N/P ratios > 30:1. The zooplankton assemblage in Lake Rotokuru was typical of lakes of the Rotorua region in that there was only one calanoid copepod and this dominated the crustacean zooplankton. The dominance of <Chydorus sphaericus> in also displacing <C. dubia>, and the presence of <Daphnia carinata> probably indicates the pond-like nature of the lake. Dry Lake contrasts markedly with Lake Rotokuru in having a wide littoral zone of emergent macrophytes and relatively clear water such that submerged species cover over 70% of the bottom. This lake would be expected to support a reasonable trout fishery if water temperatures do not rise too high in summer. (auth/EIM)