Limnology of Lake Waikaremoana with special reference to littoral and pelagic primary producers

Lake Waikaremoana, the North Island's deepest lake (248 m), lies in a natural forested catchment, but the lake itself has been modified for hydro‐electric power generation and by the introduction of trout, smelt, and adventive aquatic plants. The lake is a warm monomictic water body of low conductivity (82 μS cm^‐1) and a high seasonal water column stability. The waters are oligotrophic, with epilimnetic dissolved reactive phosphorus concentrations typically < 1 mg m^‐3. The concentration of NO₃‐N is seasonally variable but generally high in winter and spring with maximum epilimnetic values approaching 70 mg m ³. This contrasts with other central North Island lakes. Horizontal variability in surface chlorophyll a is low as are the absolute values (< 1–2 mg m^‐3). A notable feature is the formation of a deep chlorophyll maximum within the metalim‐nion comprised largely of Sphaewcystis schweteri as opposed to diatoms and flagellates which normally dominate the epilimnion. Vascular macro‐phytes (maximum biomass 659 g m² dry weight) extended to 9 m and characeans (maximum biomass 447 g m²dry weight) to 16 m. Total phyto‐plankton primary production was calculated as 4524 tCy^‐1 and macrophyte production as 578 t C y^‐1. The proportion of macrophyte to phy‐toplankton production (0.14) is higher than in the other deep lakes of the central North Island.