Assessment of stormwater runoff and the health of their surrounding outfall ecosystems in Mackinaw City.

Abstract

During precipitation events, stormwater runoff flows over impermeable surfaces. This runoff picks up pollutants which flow into bodies of water and degrade ecosystems. We preformed this study to create a stormwater assessment of Mackinaw City that determines the concentrations of pollutants within stormwater runoff and the health of the surrounding ecosystems of its outfall. We wanted to know what best management practices and land uses were present within the city and to make suggestions to create healthier outfall ecosystems in the future. We created a map using ArcGIS to identify the outfall sites and discovered that the area we sampled in the city had approximately 45% cover of impermeable surfaces. We performed chemical analyses and tested the overall composition of the water at the outfalls. We found elevated levels of chloride, nitrate, total phosphorus, and sulfate at our sites. We found correlations between temperature and nitrate, longitude and nitrate, dissolved oxygen and nitrate, longitude and temperature, and HBI and macroinvertebrate species richness. We sampled macroinvertebrates and used the Hilsenhoff Biotic Index to assign a pollution tolerance level to each invertebrate family to under stand the level of pollution in an area. We found that most macro invertebrate species we sampled were highly tolerant to pollution. Overall, these results suggest that there is evidence for degraded ecosystems at each of our sample sites due to anthropogenic factors. Understanding the effects of pollution from stormwater is important to determine what may be the sources and what types of best management practices would help the health of the aquatic ecosystems for the future.