Variation in temporal [14C]plankton photosynthesis among warm monomictic lakes of coastal British Columbia

Seasonal patterns of [¹⁴C]phytoplankton photosynthesis (PP)were examined in six warm monomictic lakes of coastal BritishColumbia. Four of our study lakes followed typical lake patternswith maximum PP occurring in the spring and minimal rates occurringduring the winter. However, the spring maximum occurred severalweeks earlier than lakes in other climatic regions. In addition,maximum rates of daily photosynthesis were observed to occurduring the winter months in Maxwell Lake, rather than duringthe standard growing season. All study lakes except MaxwellLake had large Daphnia in the plankton community. Maxwell wasdominated by small crustacean zooplankton implying the importanceof trophic structure in mediating seasonal patterns of productivity.The four oligotrophic lakes in our study also exhibited P-deficiencyduring winter, as indicated by P-debt bioassays and rapid ³²PO₄^3–turnover rates. Our data suggest that these coastal oligotrophiclakes were co-limited by nutrients and light during winter.The importance of winter (November–March) photosyntheticproduction to the total annual carbon budget in the six lakesstudied here is greater than that typically reported for othertemperate zone lakes. If plankton community respiration decreasesmore than photosynthetic production with wintertime temperatures,then >50% of annual net pelagic carbon fixation could occurin winter in some coastal lakes.