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Abstract Title: Peatland Headwater Catchments as Sentinels of Decreasing Methylmercury with Climate Change and Cleaner Emissions
Presenter Name: Colin McCarter
Company/Institution: McMaster University
Session: Predicting the Impacts of Climate Change on Hg Cycling
Co-Authors: Colin McCarter,Stephen Sebestyen,Jeff Jeremiason,Randall Kolka,Edward Nater

Abstract Information :

Peatlands are sources of methylmercury (MeHg) in boreal and sub-boreal landscapes. The bioaccumulating neurotoxin, MeHg, is a contaminant of global concern that has been linked to adverse human health outcomes. However, the response in mercury (Hg) export from peatlands due to climate change and altered atmospheric Hg deposition since implementation of the Minamata Convention is uncertain. Here, we use an unprecedented hydroclimatic and streamwater chemistry dataset to investigate factors affecting MeHg and total mercury (THg) export from a headwater peatland catchment at the USDA Forest Service Marcell Experimental Forest in northcentral Minnesota. Hydroclimatic variables (air temperature, precipitation, potential evapotranspiration (PET), streamflow, and baseflow) were measured/calculated from 1962?2017 (daily), atmospheric Hg deposition from 1996?2017 (monthly), and streamwater chemistry from 2001?2017 (12-24 samples per year). Annual flow-weighted concentrations (FWC) and yields of THg and MeHg were compared to hydroclimatic and Hg deposition measures using linear regression, while the impact of climate change on hydroclimatic variables were assessed using a Mann Kendall Trend Test. Since 1962, annual average air temperature significantly increased by ~2? (ç=0.272, p=0.003), while baseflow significantly decreased (ç=-0.25, p=0.008). Total wet Hg deposition and concentration initially decreased through ~2005 then remained relatively constant. Methylmercury and THg FWC and yields declined until ~2007, then systematically varied through 2017. Methylmercury FWC was positively correlated with baseflow (R2=0.50, p=0.003), wet Hg deposition concentration (R2=0.61, p=0.0005), and summertime average temperature (R2=0.44, p=0.007), while negatively correlated with the 10-year moving average of PET minus Precipitation (PET-P, a measure of the cumulative water deficit) (R2=0.50, p=0.003). The correlation with 10-year average PET-P suggests that long-term variations in climate may partly control Hg export dynamics from headwater peatlands. Methylmercury concentrations and yields from headwater peatland catchments may continue to decrease over time if trends in baseflow and wet Hg deposition concentration declines persist.

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