The Impacts of Multiple Stressors on Aquatic Invertebrate Communities in the Umatilla River Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/vd66w295k

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  • Rivers impacted by human activities often have multiple stressors present. The effects of multiple stressors on biological communities can often be difficult to predict, due to the potential for complex interactions between stressors and communities. This thesis explores the impacts of two stressors often associated with agricultural land use, increased sediment and reduced discharge, on aquatic invertebrate communities and taxa behavior. The study design of these experiments allowed for the analysis of both independent and interactive effects of these two stressors on aquatic invertebrates. To test the impact of multiple stressors on aquatic invertebrate communities, in-stream techniques were used in the Umatilla River in the summer of 2014. The impacts of these stressors were analyzed by focusing on community metrics and total community structure. There was evidence for both independent and interactive effects of sediment and discharge on the aquatic invertebrate communities. Increased sediment and reduced discharge both had negative impacts on Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa, and both changed functional group proportions and taxa abundances in the communities. The presence of complex stressor interactions in this study highlighted the need to continue studying multiple stressors in rivers in order to better understand these complex relationships. To test the impact of multiple stressors on invertebrate behavior, laboratory techniques were used. Movement behavior (i.e. crawling and drift behavior) was assessed for stonefly nymphs (family: Perlodidae, genus Isoperla) to determine how increased sediment and reduced discharge impacted habitat selection. Perlodidae nymphs found in experimental channels in the Umatilla River were also assessed to test how these two stressors may impact their abundances in rivers faced with increased sediment and reduced discharge. There was evidence that increased sediment influenced Isoperla movement behavior, with more nymphs moving off of habitat subjected to added sediment compared to habitat without sediment. There was also evidence that increased sediment had a significant negative influence on Perlodidae absolute and percent abundance in the Umatilla River. Discharge was found to have a marginally negative influence on Perlodidae absolute abundance. Both of these studies show the important consequences of increased sediment and decreased discharge for individual taxa and functioning aquatic invertebrate communities. Continued study of multiple stressors in rivers will help us to better understand how to manage stressors to reduce the number of negative effects in river communities. In addition, continued use of laboratory studies may allow us to better understand the impacts on individual taxa within communities and may help us understand the mechanisms influencing taxa abundances found in nature.
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