Lake benthic algal extracellular material and the influence of the environment

Background/Question/Methods

            Much of the carbon fixed through photosynthesis is excreted as extracellular material by benthic algae. Several reasons for its excretion have been proposed, including attachment, movement, protection from desiccation, and photosynthetic overflow. Extracellular material can play a key role in benthic ecosystems, with effects ranging from stabilizing sediments, preventing nutrient and toxin resuspension, to providing a carbon source for bacteria and macroinvertebrates. The majority of the work on extracellular material comes from marine intertidal systems. However, there are important chemical and physical differences between marine intertidal systems and lakes that could affect the production of extracellular material. Using Lake Opeongo, a 5800 ha dystrophic lake in Ontario, Canada, we compared amounts of extracellular material found in the benthic zone in lakes to those found in marine intertidal zones. We also investigated how the amount of extracellular material changed with changing environmental and algal community factors. We used a permutation-based path analysis to test different models.

Results/Conclusions

The range in the amounts of extracellular material found in lakes was several orders of magnitude smaller than the range from the marine intertidal, but the two systems were centered on the same mode. The reduced range found in lakes may be due a lack of exposure of lake sediments. We found a negative effect of in situ primary production on loosely bound, colloidal extracellular material, indicating that extracellular material is released under stressful conditions which are not the conditions where high production occurs. There was also a significant effect of community composition. Total extracellular material was negatively affected by date, indicating that the tightly bound, capsular extracellular material is more refractory. We found no significant effects of the environmental factors (light, nutrients, or wind-driven disturbance). Although they could be acting indirectly through algal community composition and primary production, it is possible that these environmental factors have less influence on the production of extracellular material in lakes as they do in the marine intertidal.