Biogeochemical Cycling of Methylmercury in Lakes and Tundra Watersheds of Arctic Alaska
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- 作者：Chad R. Hammerschmidt ; William F. Fitzgerald ; Carl H. Lamborg ; Prentiss H. Balcom ; and C.-Mao Tseng
- 刊名：Environmental Science & Technology
- 出版年：2006
- 出版时间：February 15, 2006
- 年：2006
- 卷：40
- 期：4
- 页码：1204 - 1211
- 全文大小：196K
- 年卷期：v.40,no.4(February 15, 2006)
- ISSN：1520-5851
文摘
The fate of atmospherically deposited and environmentallyactive Hg is uncertain in the Arctic, and of greatesttoxicological concern is the transformation to monomethylmercury (MMHg). Lake/watershed mass balanceswere developed to examine MMHg cycling in four northernAlaska lakes near the ecological research station atToolik Lake (68
38' N, 149 36' W). Primary features ofthe cycle are watershed runoff, sedimentary production andmobilization, burial, and photodecomposition in the watercolumn. The principal source of MMHg is in situ benthicproduction with 80-91% of total inputs provided bydiffusion from sediments. The production and contributionof MMHg from tundra watersheds is modest. Photodecomposition, though confined to a short ice-free season,provides the primary control for MMHg (66-88% of totalinputs) and greatly attenuates bioaccumulation. Solid-phase MMHg and gross potential rates of Hg methylation,assayed with an isotopic tracer, vary positively with thelevel of inorganic Hg in filtered pore water, indicating thatMMHg production is Hg-limited in these lakes. Moreover,sediment-water fluxes of MMHg (i.e., net production at steadystate) are related to sediment Hg loadings from theatmosphere. These results suggest that loadings of Hgderived from atmospheric deposition are a major factoraffecting MMHg cycling in arctic ecosystems. However,environmental changes associated with warming of the Arctic(e.g., increased weathering, temperature, productivity,and organic loadings) may enhance MMHg bioaccumulationby stimulating Hg methylation and inhibiting photodecomposition.
38' N, 149 36' W). Primary features ofthe cycle are watershed runoff, sedimentary production andmobilization, burial, and photodecomposition in the watercolumn. The principal source of MMHg is in situ benthicproduction with 80-91% of total inputs provided bydiffusion from sediments. The production and contributionof MMHg from tundra watersheds is modest. Photodecomposition, though confined to a short ice-free season,provides the primary control for MMHg (66-88% of totalinputs) and greatly attenuates bioaccumulation. Solid-phase MMHg and gross potential rates of Hg methylation,assayed with an isotopic tracer, vary positively with thelevel of inorganic Hg in filtered pore water, indicating thatMMHg production is Hg-limited in these lakes. Moreover,sediment-water fluxes of MMHg (i.e., net production at steadystate) are related to sediment Hg loadings from theatmosphere. These results suggest that loadings of Hgderived from atmospheric deposition are a major factoraffecting MMHg cycling in arctic ecosystems. However,environmental changes associated with warming of the Arctic(e.g., increased weathering, temperature, productivity,and organic loadings) may enhance MMHg bioaccumulationby stimulating Hg methylation and inhibiting photodecomposition.