ENVIRONMENTAL CONDITIONS FOR FISH SURVIVAL AT THE WATERSHED NATURE CENTER UPPER POND, EDWARDSVILLE, ILLINOIS

Relatively little is known about the hydrology and limnology of stormwater retention ponds (SWRPs). A study of Upper Pond at the Edwardsville Watershed Nature Center (WNC) was conducted to first, uncover why there have been fish kills at this small SWRP, and second, determine if bluegill, common carp, and largemouth bass can survive given the existing water parameters. With a better understanding of the water quality, resource managers can improve the pond’s fish stock and overall health of the aquatic ecosystem.

The pond is shallow and receives excess urban runoff supporting an abundance of aquatic plants. A set of electrofishing surveys conducted at the pond in 2013 and 2018 found that bluegill was the most prevalent species of fish, as their numbers were high in both years. European carp population increased as well, but largemouth bass notably decreased, possibly due to hypoxic conditions. To examine the reasons for changing fish populations, dissolved oxygen (DO) levels, an indicator of the health of a body of water, was assessed using a Milwaukee brand oxygen probe. Water temperature was also measured using HOBO sensors. These important data were collected from June to December 2019. Spatial analysis using geographic information systems (GIS) helped determine the classification of land cover types surrounding the watershed. The land cover information was used to explain the influence of surface runoff, a primary water input, and hence, present conditions of the pond.

Our findings revealed hypoxic conditions from August to mid-October at the pond, which can be explained by the high air temperatures during this period. Bluegill, which prefers warm waters, nevertheless would have struggled to survive in this low-oxygen environment. Largemouth bass would have found suitable waters only in the upper 30 cm. Even European carp, which needs relatively less oxygen, could only live in the upper few centimeters of the water. The expected result of these environmental conditions is periodic fish kills during late summer and early fall. Based on these results, we recommend designing a vegetative buffer strip at the points where water enters the pond as a control method to reduce eutrophication and fish kills.