How does Mercury Methylation Respond to Intensive Forest Management and the Creation of Anoxia in Floodplain Soils?

Authors

James S. Coleman¹ (jscoleman@uncg.edu), Yener Ulus^1,2, Kristina Morales¹, Peyton Labonte^1,3, Martin Tsz-Ki Tsui^1,4, Alex T. Chow ⁵*, Carl C. Trettin⁶

Institutions

¹University of North Carolina–Greensboro, NC; ²Davidson College, Davidson, NC; ³Syngenta Corporation, Greensboro, NC; ⁴School of Life Sciences, Chinese University of Hong Kong, Hong Kong; ⁵Baruch Institute of Coastal Ecology and Forest Science, Clemson University, Georgetown, SC; ⁶Center for Watershed Research, U.S. Forest Service, Cordesville, SC

Abstract

It is well known that silvicultural practices such as clear-cutting and thinning would alter productivity and hydrology of forest watersheds, which may also mediate a mercury (Hg) cycling response involving methylmercury (MeHg) production. In this study, researchers conducted a field study with three transects covering the upland, midland riparian, and wetlands within thinned, clearcut and uncut control areas within a first-order watershed in the lower Atlantic coastal plain on the Santee Experimental Forest in SC, each transect is instrumented to monitor soil moisture, temperature, redox, water table depth, and insolation. Commencing July 2021, researchers collected monthly composite soil samples (0–10 cm) at each site. To date, researchers found that the soil organic matter content increased significantly from upland (7.46%) and midland (9.37%) to lowland (18.55%; p < 0.05). Due to the intimate association of Hg with soil organic matter, total Hg content has followed this trend, i.e., upland (35.00 ng/g) and midland (48.49 ng/g), to lowland (75.14 ng/g; p < 0.05). Researchers also observed a similar spatial trend of toxic MeHg, i.e., upland (0.34 ng/g) and midland (0.35 ng/g), to lowland (0.50 ng/g; p < 0.05). When researchers compared MeHg levels across treatments at the same spatial position of the transect, researchers found that soils had much significantly higher MeHg in both harvest (0.75–0.77 ng/g) and thinning (0.66–0.70 ng/g) treatments in both upland and midland than the control upland and midland (0.34–0.37 ng/g; p < 0.05), but researchers found the opposite results for the lowland wetland site (i.e., 1.59 ng/g for control, 0.79 ng/g for harvest, and 1.32 ng/g for thinning). Researchers completed mercury analyses in Spring 2023. This poster will present the near final analysis of the data.