Three year study of plankton community response to changing water quality in a newly restored floodplain lake

Background/Question/Methods

This study examines the population dynamics of plankton communities in response to changing water quality, in a newly restored floodplain lake. Thompson Lake, located on the floodplain of the Illinois River, was historically connected to the river, but is now isolated since its restoration from row crop agriculture beginning in 2007. Water samples for nutrient analysis were collected weekly and plankton samples collected bi-weekly (n=3).

Results/Conclusions

Changes in DO, water temperature and depth, resulted in changes in nutrient levels, producing changes in plankton community number and species. Two critical points were observed during the study.  In July 2008, an increase in water temperature accompanied by a decrease in DO, (likely anoxic sediment) produced a phosphate release and a Cyanobacteria bloom, Aphanizomenon flos-aquae, mean biovolume 99.0%. A second critical point, July 2010, occurred during the pumping down of the lake after record high water levels. Increased total nitrogen and total phosphorus levels occurred, producing conditions for an algae composition shift from a predominantly Cyanobacteria community, mean biovolume 99% to a Chlorophyceae, mean biovolume 40%, and Bacillariophyceae, mean biovolume 42%, dominated community.

Zooplankton populations also showed increases at the two critical points with ciliate densities of 47,000 cells/L in July 2008 and 50,500 cells/L in July 2010. This data supports the concept of microbial population shifts in response to changes in water quality.