Typhoon effects on phytoplankton responses in a semi-closed freshwater ecosystem

Abstract

Analyses of past typhoons have suggested that global climate change may result in increases in the intensity of these episodic events and that the effects of typhoons on the biogeochemistry of aquatic ecosystems will also be strengthened. We collected a 2-year time series of phytoplankton responses, including chlorophyll-a concentration, primary production and turnover rate in the Fei-Tsui Reservoir, Taiwan, on the basis of five typhoons in 2011 and eight in 2012 (21 weeks affected). We found approximately a two-fold increase in phytoplankton responses during the typhoon period compared with the non-typhoon period. However, there were no consistent correlations between phytoplankton responses and typhoon disturbance and length of typhoon stay. Vertical distributions of phytoplankton responses indicated that the peak values of these responses occurred both during the typhoon periods and during the non-typhoon periods occurring between two typhoons. Moreover, the strongest correlations were found between euphotic depth-averaged phosphate and primary production and turnover rate. Combined effects on phytoplankton responses could explain at least 70% of the variability. The regulation of phytoplankton responses by multiple processes and interactions among factors that operate during each typhoon event may add complexity to the challenge of detecting typhoon-driven mechanisms in such ecosystems.