State Water Resources Research Institute Program

Project ID: 2009MN250B
Title: Fate and bioavailability of litter mercury in Minnesota streams and rivers
Project Type: Research
Start Date: 3/01/2009
End Date: 2/28/2011
Congressional District: 4
Focus Categories: Toxic Substances, Water Quality, Ecology
Keywords: Mercury; Litter; Methylation; Water chemistry; Bioavailability
Principal Investigator: Finlay, Jacques C. (Univerity of Minnesota); Nater, Edward A (University of Minnesota)
Federal Funds: $ 30,446
Non-Federal Matching Funds: $ 57,824
Abstract: Mercury (Hg) contamination is widespread in many aquatic habitats over the world. The conversion of inorganic Hg to monomethylmercury (MeHg) represents the most important process in regulating the bioavailability of Hg and, ultimately the Hg concentrations in top predators in food webs such as fish. While the majority of previous research to understand environmental regulation of Hg bioavailability has focused on the methylation of Hg in the sedimentary phase, there is increasing evidence that non-sedimentary compartments, such as periphyton and leaf litter, can function as important sites for MeHg production in aquatic ecosystems. Leaf litter from riparian zones may play a particularly important role in stream Hg dynamics because leaf litter is a primary source of energy and nutrients to river food webs in the temperate region. However, litter is also an important source of Hg which is mainly derived from the atmosphere during the growing phase. Our recent work showed that stream water chemistry and litter species can influence Hg release and subsequent methylation of Hg in litters in laboratory incubation experiments. These results suggest that water quality variation as well as riparian tree species within and among streams and rivers may influence the cycling of litter Hg, especially during the autumn litterfall period. However, field evidence on Hg cycling via decomposing litter in streams and rivers is very limited. In this project, we propose to examine how watershed land cover effects on stream water chemistry and plant species composition influence litter decomposition and associated Hg release and methylation in streams and rivers. Specifically, to examine the environmental mediation of Hg uptake/release and methylation via litter decomposition, we will perform 10 week in-situ litter incubations in 12 streams and rivers across the three major ecoregions of Minnesota (i.e. agricultural, urban/mixed and forested). We will also examine differences among litter from different tree species (e.g. deciduous vs. coniferous) in a subset of these streams. We will monitor weekly water quality and hydrological conditions, and will measure litter Hg concentrations and speciation (i.e. total-Hg and MeHg) and decomposition (i.e. biomass, carbon and nitrogen contents) over the 10 week period. Overall, the research proposed here will increase our understanding of the environmental controls of transformation of litter Hg to highly toxic MeHg species in running waters. This research will provide information that can be used by environmental managers in predicting Hg input and fate in stream and river ecosystems and its subsequent potential for bioaccumulation, as well yielding new insight into the potential effects of watershed land use change on Hg methylation via litter inputs and decomposition. The work will fund a key piece of dissertation research for a graduate student, and will provide data for future experimental work on Hg transfer to the food webs in both laboratory and field settings.

Progress/Completion Report, 2009, PDF
Progress/Completion Report, 2010, PDF

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