Distribution of biofilm exopolymeric substances in littoral sediments of Canadian Shield lakes: the effects of light and substrate

Benthic algal and microbial communities release organic compounds that perform many important functions in food webs and nutrient dynamics. In this study we compared the content and composition of extracellular substances from different types of sediments in the shallow littoral areas of clear and dark Canadian Shield lakes. We report high content of extracellular substances in these littoral sediments, in terms of both carbohydrates and proteins. Total carbohydrate contents increased with increasing sediment chlorophyll content in a relationship very similar to that reported for marine intertidal mudflats. Light availability and sediment type affected the content and composition of exopolymeric substances (EPS) in complex ways. More loosely bound (colloidal) EPS were measured in sandy sediments of dark lakes. Colloidal EPS content did not vary with changes in sediment particle size in clear lakes but may have been positively related to sediment particle size in dark lakes. Tightly bound (capsular) EPS increased with sediment water content with no effect of light availability. These relationships are consistent across the seven lakes. The role of these carbo hydrates and proteins in the productivity and nutrient dynamics of littoral areas in lakes remains to be tested.