Fluxes of methylmercury to the water column of a drainage lake: The relative importance of internal and external sources

Abstract

We studied fluxes of methylmercury (MeHg) through a Precambrian Shield lake using a mass balance approach. The primary goal of the study was to determine the importance of various sources of MeHg to the water column of the lake. The relative importance of all sources was: in-lake production ϾϾϾ inflow from a brown-water lake with riparian wetlands ϾϾϾ wet deposition Ͼ inflow from an upstream oligotrophic lake Ͼ direct inflow from uplands surrounding the lake. MeHg accumulated in the hypolimnion of Lake 240 when oxygen was present. Watercolumn sinks for MeHg included photodegradation of MeHg, which was about 3.5 times greater than the loss of MeHg through outflow. At present, there are few studies available on mass balance fluxes of MeHg in lakes, and this is the first study that includes losses of MeHg by photodegradation. The inclusion of photodegradation in this study results in a clear demonstration that in-lake production of MeHg is very important. In drainage lakes, the relative importance of in-lake production versus inflow of MeHg from wetlands will vary according to the extent of wetlands in the drainage basin, as well as the volume of precipitation, which produces runoff and transports MeHg from wetlands to downstream lakes.

Distribution of particulate, colloidal, and dissolved mercury in San Francisco Bay estuary. 2. Monomethyl mercury

“…There could also be other sinks of MeHg within the estuary, such as photodegradation. In a recent study, Sellers et al (2001) showed that MeHg removal by photodegration in Canadian lakes is greater than the loss through outflow. However, it is unclear whether photodegration is an important loss mechanism of MeHg in an estuarine environment.…”

Methylmercury Photodegradation in Surface Water of the Florida Everglades: Importance of Dissolved Organic Matter-Methylmercury Complexation

“…12−14 It was reported that photodegradation could remove a large proportion of the MeHg loading into lake water. 15,16 Since its importance was demonstrated, 14 several researchers have attempted to mechanistically determine the MeHg photodegradation process in aquatic environments. 17−20 Although wavelength-specific photodegradation of MeHg has been observed in aquatic environments, 13,21 much remains unclear about the chemical processes governing MeHg photodegradation.…”

The Basis for Ecotoxicological Concern in Aquatic Ecosystems Contaminated by Historical Mercury Mining

“…Anaerobic zones in sediments, hypolimnia, and wetlands are the most important sites of microbial methylation, and a water body can receive MeHg from both internal and external sites (Watras et al 1994, Sellers et al 2001. Wetlands are important sites of MeHg production and export to adjacent or downstream waters (Hurley et al 1995, St. Louis et al 1996, Sellers et al 2001, Wiener et al 2006). Concentrations of MeHg in phytoplankton, zooplankton, and higher trophic levels can also be influenced by biodilution of MeHg at the base of the food web by algal blooms or high algal biomass (Pickhardt et al 2002.…”

“…Such processes include the production of MeHg via the microbial methylation of inorganic Hg II (Benoit et al 2003) and the destruction of MeHg by photodemethylation (Sellers et al 1996(Sellers et al , 2001) and microbial demethylation (Oremland et al 1991, Marvin-DiPasquale et al 2000. Anaerobic zones in sediments, hypolimnia, and wetlands are the most important sites of microbial methylation, and a water body can receive MeHg from both internal and external sites (Watras et al 1994, Sellers et al 2001. Wetlands are important sites of MeHg production and export to adjacent or downstream waters (Hurley et al 1995, St. Louis et al 1996, Sellers et al 2001, Wiener et al 2006).…”