Effects of Zebra Mussel (Dreissena polymorpha) Populations on Dissolved Oxygen Levels in Eutrophic Lakes

Abstract

The threat of invasive species is rising as temperatures increase and the ability for international travel becomes more convenient. The effect of invasive species, such as zebra mussels (Dreissena polymorpha) on lake systems has been understudied as chemical and physical data has been gathered, but full-scale ecosystems effects has not been concluded from a comprehensive analysis. This study focuses on the effects of zebra mussel populations and their effect on dissolved oxygen levels in two eutrophic lakes in Wisconsin, USA. Lake Mendota (WBIC 805400) and Lake Monona (WBIC 804600) have been part of the North Temperate Lakes Long-Term Ecological Research since 1981 with additional data dating back to the 1800s, along with having zebra mussels known to exist since 2011 and 2016, respectively. Volumetric hypolimnetic oxygen depletion (VHOD) levels were calculated in both lakes from 2015-2019 to connect zebra mussel populations to decreased dissolved oxygen levels. Average chlorophyll-a concentrations, average Secchi disk depth, average hypolimnetic temperature, and precipitation levels from the Palmer Drought Severity Index (PDSI) were also considered as outside ecological driving factors. The results indicated zebra mussels were not the driving factor of decreased dissolved oxygen levels, suggesting a stronger connection to chlorophyll-a concentrations, Secchi disk depths, and precipitation levels for a given year. An increase in research regarding the effects of zebra mussels is recommended as it would allow for better management practices to be put in place from a better understanding the species has on lake systems.