Article

Mercury Bioaccumulation in a Stream Network

Graduate Program in Water Resources Science, Department of Ecology, Evolution and Behavior, University of Minnesota, St. Paul, Minnesota 55108, USA.
Environmental Science and Technology (Impact Factor: 5.33). 09/2009; 43(18):7016-22. DOI: 10.1021/es901525w
Source: PubMed

ABSTRACT

Mercury (Hg) contamination is common in stream and river ecosystems, but factors mediating Hg cycling in the flowing waters are much less understood than inthe lakes and wetlands. In this study, we examined the spatial patterns of methylmercury (MeHg) concentrations in the dominant groups of aquatic insect larvae across a network of streams (drainage area ranging from 0.5 to 150 km2) in northern California during summer baseflow conditions. We found that, with the exception of water striders, all invertebrate groups showed significant (p < 0.05) increases in MeHg concentrations with drainage area. The largest stream in our study watershed, the South Fork Eel River, had the highest aqueous MeHg concentration (unfiltered: 0.13-0.17 ng L(-1)) while most of the upstream tributaries had aqueous MeHg concentrations close to or below the established detection limits (0.02 ng L(-1)). A filamentous alga abundant in South Fork Eel River (Cladophora glomerata) had an exceptionally high fraction of total-Hg as MeHg (i.e., %MeHg from 50-100%). Since other potential hotspots of in-stream Hg methylation (e.g., surface sediment and deep pools) had %MeHg lower than or similar to surface water (approximately 14%), we hypothesize that Cladophora and possibly other autotrophs may serve as hotspots of in-stream MeHg production in this bedrock-dominated stream. Recent studies in other regions concluded that wetland abundance in the watershed is the predominant factor in governing Hg concentrations of stream biota. However, our results show that in the absence of wetlands, substantial spatial variation of Hg bioaccumulation can arise in stream networks due to the influence of in-stream processes.

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Available from: Martin Tsz Ki Tsui, Apr 07, 2015
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    • "This finding contrasts with other studies that have found a positive relationship between MeHg bioaccumulation and aqueous DOC for predatory macroinvertebrates from lakes (Rennie et al. 2005) and in macroinvertebrates from streams (shredders and predators, Riva-Murray et al. 2011; Diptera, Harding et al. 2006; filter feeders, Tsui and Finlay 2011). In another study, all FFGs had higher MeHg concentrations in streams with higher catchment areas, and DOC and nutrient concentrations also increased with catchment area (Tsui et al. 2009). In the current study, differences in OC quality and type among ecosystems may have masked effects, as this has been shown to affect the cycling of MeHg in other systems (Hall et al. 2008; Riscassi and Scanlon 2011). "
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