Congratulations to Sara Nedrich who successfully defended her dissertation on July 12, 2017.

Advisor: G. Allen Burton

Abstract: Predicting the environmental fate and effects of metals is nuanced, due to the diverse interplay of biogeochemical and physicochemical variables, and is vital to protecting and preserving aquatic resources. Regulatory methods for toxicity testing and ecological risk assessment often lack sufficient data to address simple and critical changes in environmental conditions, such as hydrologic extremes (drought/flood), which are predicted to become more severe with climate change. This is a particular concern, as water quality criteria (e.g., regulatory standards for metal thresholds) are defined by laboratory toxicity test methods.

In this dissertation, the effects of altered hydrology on sediment metal biogeochemistry and associated effects to aquatic organisms are investigated. Water level fluctuation experiments are conducted on high carbonate sediments collected from coastal wetlands in the Great Lakes region, showing a significant release of porewater Zinc (Zn) due to altered geochemistry following drought conditions, with sublethal effects to benthic macroinvertebrates (Chapter 2-3). In a subsequent study (Chapter 4), Zn-release and effects to organism growth is again observed in more acidic reservoir sediments with different geochemical controls. Vanadium (V) redox biogeochemistry is also investigated and oxidation had relatively little effect on V speciation due to strong complexation with iron oxyhydroxide compounds. In the final chapter (Chapter 5), field validation of Zn-release is performed at the same wetland sites used for laboratory testing and demonstrated positive benthic community responses. The effects of elevated sediment Zn are confounded by a strong positive relationship between benthic community abundance, richness, and diversity with sediment pH. The pH shift was likely driven by periphyton photosynthesis, altering metal speciation and complexation and the periphyton served as a food source benefiting the benthic macroinvertebrate community.

General implications of this research are elucidated, including relevance to the management and restoration of aquatic systems, regulatory driven toxicology, and improving the extrapolation of laboratory to field studies. Finally, it appears that increases in hydrologic extremes, as predicted with climate change, will alter metal biogeochemistry in sediments, thereby resulting in wide-ranging effects on benthic macroinvertebrate communities.