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Stream Mercury Export in Response to Contemporary Timber Harvesting Methods

Timber harvest is a significant driver of mercury releases in some parts of the world. Yet, the impact of forest harvest on mercury mobilization has not been directly studied in the Pacific Northwest despite being an important timber producing region that also receives high atmospheric mercury deposition.

To address this, researchers measured stream discharge, and mercury and methylmercury concentrations monthly for 1.5 years following logging in a western Oregon forest. Mercury concentrations in water were 28 percent higher in harvested than unharvested catchments, and because of high stream discharge, harvested catchments had 80 percent higher mercury loads annually. However, there were no differences in particulate-bound mercury concentrations or loads in the harvested and unharvested catchments, likely because forestry practices minimized erosion. Despite these patterns, mercury concentrations were substantially lower than in other timber harvesting regions and methylmercury concentrations were low in both catchment types, possibly due to well-drained soils and steep slopes. Results have important implications for the role forestry operations have in affecting catchment retention and export of mercury.

Eckley, C.S., Eagles-Smith, C.A., Tate, M.T., Kowalski, B.M., Danehy, R., Johnson, S.L., Krabbenhoft, D.P., 2018, Stream mercury export in response to contemporary timber harvesting methods (Pacific Coastal Mountains, Oregon, USA): Environmental Science and Technology,

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