Patterns of Mercury Release from Profundal Sediment of California Reservoirs

Oral Presentation

Prepared by B. Fuhrmann, M. Beutel
UC Merced, 1611 E Olive Ave, Merced, California, 95340, United States


Contact Information: bfuhrmann@ucmerced.edu; 714-329-6840


ABSTRACT

Inorganic Hg, predominantly from widespread atmospheric deposition, but also from point sources including mine and industrial sites, is transformed to methylmercury (MeHg) by anaerobic bacteria in oxygen-poor water and sediment. The profundal zone of productive lakes commonly exhibits summertime anoxia and associated accumulation of MeHg in bottom waters. MeHg in bottom water bioaccumulates in pelagic biota when it diffuses upwards across the thermocline or when MeHg-rich bottom water mixes into the upper water column [1]. With the shortcomings of conventional Hg control strategies, such as dredging, capping, watershed controls and source control, managers are increasingly interested in developing in situ strategies to repress Hg bioaccumulation in managed aquatic ecosystems. One potential strategy is to enhance the redox potential at the sediment-water interface to repress MeHg efflux to overlying water [2]. The impact of enhanced redox potential can then be correlated with changes in MeHg and inorganic Hg species, concentration, and distribution in the reservoir. This study utilizes a variety of analytical methodologies in order to determine theses changes in speciation, concentration, and distribution of MeHg/Hg. Afterwards, a conceptual model of MeHg cycling at the profundal sediment-water interface is presented and redox-mediated mechanisms that enhance MeHg efflux are summarized. Highlights of experimental sediment-water chamber incubations from a number of California reservoirs are also presented and summarized. With a more comprehensive understanding of MeHg cycling at the profundal sediment-water interface, managers will be better able to develop effective management strategies aimed at repressing MeHg bioaccumulations in lakes and reservoirs.

References:
[1] SM Ullrich, TW Tanton, & SA Abdrashitova, “Mercury in the Aquatic Environment: A Review of Factors Affecting Methylation”, Critical Reviews in Environmental Science and Technology, Vol. 31, June 2010, pp. 241-293.
[2] GN Bigham, KJ Murray, Y Masue-Slowey, & EA Henry, “Biogeochemical Controls on Methylmercury in Soils and Sediments: Implications for Site Management”, Integrated Environmental Assessment and Management, Vol. 9999, June 2016, pp. 1-14.