Effects of Zooplankton Density and Diversity on Water Clarity in Five Lakes within Itasca State Park, Minnesota

Abstract

The effects of zooplankton density and diversity on water clarity were studied on five different lakes within Itasca State Park (northwest Minnesota). Water turbidity is affected by suspended organic material and dissolved organic material, and zooplankton graze on this suspended organic material and thus clarity of the water increases. It has been shown that with increased density of zooplankton, especially herbivorous zooplankton, that there is a correlated increase in water clarity. In our study, zooplankton diversity also increased with greater zooplankton densities. It is not clear, however, that diversity has any effect on the clarity of the water itself since some zooplankton feed on other zooplankton and not phytoplankton. The lake with the lowest secchi reading showed the lowest diversity of zooplankton, although it did have the third highest density of zooplankton. The lake with the highest secchi reading, however, showed the highest density and highest diversity of zooplankton. All of the lakes tested followed a trend of increasing water clarity with increasing density and diversity of zooplankton, with the exception of Deming. Average absorbance of chlorophyll-a showed no statistical correlation between zooplankton density or zooplankton diversity. This suggests that there is a correlation between zooplankton density and diversity towards water clarity.