IMPORTANCE OF TOTAL SUSPENDED SOLIDS IN EXPLAINING FISH COMMUNITY STRUCTURE IN AGRICULTURAL HEADWATER STREAMS
thesisposted on 16.10.2019 by Jennifer L Troy
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Agricultural headwater streams in the Midwestern United States are subject to contaminants from fields, increased sedimentation, and degradation of natural habitat. Previous research has shown that physical instream habitat degradation better explained variation in fish community structure than water chemistry. However, these studies did not include total suspended solids (TSS), which are considered a major freshwater contaminant. The objective of this study is to determine whether total suspended solids better explains fish community structure than other variables in agricultural headwater streams. Mixed linear effects modeling was used to determine the set of independent variables that best predicts each of the fish response variables of species richness, Shannon diversity index, fish density, and index of biotic integrity. Standardized coefficients were used to determine which independent variable in each of the models had the largest influence on fish response metrics. The set of independent variables that best explained species richness were mean total suspended solids, imidacloprid, discharge, and substrate richness. Shannon diversity index was explained best by the combination of maximum total suspended solids, mean total suspended solids, atrazine, total nitrogen, and discharge. Fish density was explained best by the percentage of silt and clay, dissolved oxygen, the percentage of canopy cover, cover type richness, and discharge. IBI was explained best by the combination of the percentage of silt and clay, total phosphorus, mean total suspended solids, and dissolved oxygen. Total suspended solids was the most influential independent variable for fish species richness and Shannon diversity, however the percentage of silt and clay in benthic sediments was the most influential independent variable for fish density and IBI. Results also indicate discharge and total phosphorus as being influential to fish community metrics. The results from this study suggest that models containing a combination of different types of independent variables best explain fish community structure. This study supports the use of conservation and restoration practices that reduce total suspended solids and the amount of silt and clay present in bed sediments to increase fish community integrity of agricultural headwater streams of the Midwestern United States.