Timber Harvest Alters Mercury Bioaccumulation and Food Webs in Headwater Streams

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Land use change is an important driver of global mercury cycling. Timber harvest is a common land use that can alter associated aquatic ecosystems, yet little is known about how it affects mercury concentrations and associated food web changes. 

Researchers evaluated mercury bioaccumulation in ten paired catchments in the Coast Range, Oregon that were either entirely clear-cut, clear-cut with riparian buffer, or left unharvested. Mercury concentrations in stream insects and salamanders differed among all three catchment types, yet these concentrations were not related to the mercury in stream water. Instead, stream organisms in clear-cut catchments had the highest mercury concentrations because they relied more heavily on food from instream primary producers rather than terrestrial litter inputs, such as leaves. Streams in clear cuts had a less diverse food web base than unharvested streams or streams with riparian buffers. Mercury in songbirds was also elevated following timber harvest. Findings highlight the importance of understanding food web responses to landscape disturbances when assessing mercury bioaccumulation. 

Willacker Jr., J.J., Eagles-Smith, C.A., Kowalski, B.M., Danehy, R.J., Jackson, A.K., Adams, E.M., Evers, D.C., Eckley, C.S., Tate, M.T., Krabbenhoft, D.P., 2019, Timber harvest alters mercury bioaccumulation and food web structure in headwater streams: Environmental Pollution, https://doi.org/10.1016/j.envpol.2019.07.025

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