Interactions Between Planktonic Community Structure and Nutrient Cycling Processes in Freshwater Ecosystems

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Major interactions between planktonic community structure and nutrient cycling in aquatic ecosystems will be researched; specifically the sites and rates of nutrient regeneration, including comparisons of nitrogen and phosphorus. Replicated pond experiments will be performed in a 2X2 matrix: fish added or not (to obtain different zooplankton assemblages), and ponds treated with fertilizer either with a high or low N:P ratio (to obtain different phytoplankton assemblages). Differences in the mechanisms of nutrient regeneration under these community structures will be examined. Four major hypotheses will be tested. (1) In plankton communities dominated by edible algae and cladoceran grazers, nutrient regeneration will occur principally in the water column. (2) In communities dominated by cyanobacteria, a significantly greater fraction of nutrient regeneration will occur in sediments (if dead cyanobacteria sink), or within the cyanobacterial mat (if dead cyanobacteria float). (3) In communities dominated by inedible eucaryotic algae, or in communities having a large calanoid copepod component, a significantly greater fraction of regeneration will occur in sediments. Finally, (4) the relative importance of the "microbial loop" to nutrient regenration will change as planktonic community structure changes. Results will not only test these ideas on how aquatic communities operate, but will provide valuable insight which may prove useful in lake management.