Seasonal variation of heterotrophic potential in Lake Rotoroa

A 20‐fold seasonal variation in heterotrophic potential (V_max) for glucose uptake was observed in Lake Rotoroa during a 3‐year sampling programme. Peaks in activity coincided approximately with maximum surface water temperature, but the large variations suggest quantitative and/or qualitative changes in the heterotrophic microbial population. V_max, values in subsurface samples taken from within dense beds of Elodea canadensis were on average nine times greater than those in surface samples from above the beds. Values for V_max, ATP, and chlorophyll a (Chi a) decreased and nitrogen and phosphorus concentrations increased slightly after a drastic decline in the extent of Elodea beds occurred in 1974. The seasonal ranges of the above parameters were similar to published values for oligotrophic lakes: V_max, less than 0.001–0.02 μg.L^‐1 _.h^‐1; ATP, 0.01–0.09 μg.L^‐1; Chi a, 0.3–1.4 μg.L^‐1; total‐N, 0.03–0.22 mg.L^‐1; total‐P, 0.001–0.013 mg.L^‐1.

Keywords:

• Heterotrophic potentials
• Oligotrophic lakes
• Seasonal variation
• Elodea canadensis
• Nutrients
• Lake Rotoroa