Graduate Program

Biological Sciences

Degree Name

Master of Science (MS)

Semester of Degree Completion

2012

Thesis Director

Charles Pederson

Thesis Committee Member

Scott Meiners

Thesis Committee Member

Richard Colombo

Abstract

Eutrophication of aquatic ecosystems may occur from several sources, primarily from anthropogenic inputs. Excess nutrient deposition can result in eutrophication and community compositional shifts in organisms located in impacted ecosystems. In the Sangamon River located outside Decatur, IL, discharge from the local reservoir, which receives inputs from both a city landscape and agricultural landscape and a wastewater treatment plant (WWTP). These may result in a large influx of nutrients into this system. Increased nutrient levels have the potential to shift benthic periphyton, and macroinvertebrate communities and cause extinction of low tolerance native species. To examine the impacts of inputs for the WWTP and reservoir, sampling was performed above the WWTP (upstream sites) which encompassed the sampling points from the discharge of the Decatur reservoir down to the WWTP discharge, and sampling was performed downstream of the WTTP (downstream sites). PCA analyses show a significant difference between upstream and downstream sites. During periods of high flow from the dam, a detectable increase in available total oxidized nitrogen was found in the water column. Additional water chemistry tests found significant differences between upstream and downstream sites when examining nutrient levels based on high periods of discharge, and seasonal variation. Our results show that there is a significant relationship between increased TON, and NH3 levels upstream of the sanitation district during periods of high flow (high reservoir discharge) and the downstream sites. This relationship shows that the reservoir is acting as a sink of nitrogen (as TON and NH3) from the surrounding watershed, and a source of eutrophication in upstream sites. Analyses also showed periods of no difference between upstream sites and downstream sites as reservoir discharge increased, and a negative correlation between water nutrient values of the downstream sites during periods of higher discharge. The lack of difference seen between the sites at high discharge may be a result of dilution of the WWTP discharge by reservoir water. Community structure metrics found significant differences in MIBI (p = .00039), and IBI (p = .000839) scores between the two reaches with the UPS site having lower scores compared to the DNS a finding that previous studies showed based on diatom assemblages.

Overall, we found that high periods of discharge appear to mediate the influence of the nutrient input from the WWTP, which in itself caused significant changes in the macroinvertebrate, fish and benthic algal communities.

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