Wind-driven physical processes and sediment characteristics affect the distribution and nutrient limitation of nearshore phytoplankton in a stratified low-productivity lake

Abstract

Wind-driven physical processes are expected to affect the distribution and composition of phytoplankton communities and to determine their access to nearshore nutrients. We examined the effect of wind-driven physical processes (surface waves, seiching activity) on the distribution of phytoplankton biomass, their growth rate, and nutrient limitation. We sampled nearshore and offshore phytoplankton on 11 days during the pre-, early-, mid-, and late-stratification periods. Phytoplankton biomass (measured as chlorophyll concentration) accumulated downwind, but growth rate was usually higher at upwind than at downwind sites. This suggests that the quantity and quality of algal food sources for higher trophic levels may vary in predictable but opposite ways. Wind-driven surface waves and upwelling activity were associated with changes in phytoplankton nutrient limitation in nearshore areas, but these differences were site specific. Our results suggest that wind-driven physical processes and sediment characteristics are both important in determining internal nutrient loading and phytoplankton nutrient limitation in nearshore areas. On windy days, nutrient limitation of offshore phytoplankton at the lake surface was always related to the conditions found upwind, suggesting rapid exchanges between nearshore and offshore areas. Wind-driven physical processes affect the distribution and nutrient limitation of phytoplankton in lakes, and are likely to influence the efficiency of trophic transfers in planktonic communities. These wind-driven processes should be included more specifically into food web models.