Seasonal changes in respiratory enzyme activity and productivity in Lake Washington microplankton

Abstract

The seasonal cycle of respiratory electron transport system (ETS) activity, 14C uptake, chlorophyll, temperature, and nutrient concentration in the euphotic zone of Lake Washington during 1974 shows minimum ETS activity (4.2 mg Oeqm−2h−1), 14C uptake (84 mg C m−2d−1), and chlorophyll (10.1 mg m−2) occurred in the first few months of the year and coincided with minimum temperature (≃6.2°C) and maximum nutrient concentrations (PO43− = 250 mg m−2, NO3− = 3.5 g m−2). Maximum ETS activity (109.8 mg Oeqm−2h−1), 14C uptake (2,126 mg C m−2d−1) and chlorophyll (121.7 mg m−2) were observed during the spring bloom. Values were intermediate during the fall period of thermal stratification and nutrient depletion. Respiration rates were calculated from ETS activities and used to calculate production:respiration ratios (P:R). The P:R ratios were low in late summer and fall and high in winter. The percentage of primary production oxidized during a 12‐h dark period varied from >100% to 7%: high percentages in summer, low in late winter.