文摘
This study characterized distribution patterns of monomethyl mercury (MeHg) and areal mass of total mercury (THg) and MeHg across U.S. upland forests. MeHg concentrations increased from surface litter (average: 0.14 渭g kg鈥?) to intermediate (0.47 渭g kg鈥?) and deeper, decomposed litter (1.43 渭g kg鈥?). MeHg concentrations were lower in soils (0.10 渭g kg鈥? at 0鈥?0 cm depth; 0.06 渭g kg鈥? at >20 cm depth). Ratios of MeHg to THg were higher in litter compared to soils. In soils, MeHg concentrations positively correlated with THg across all sites, and MeHg concentrations also increased with C content and latitude. THg areal mass ranged from 41.6 g ha鈥? to 268.8 g ha鈥?. Largest THg mass at all sites was sequestered in soils (average of 91%), followed by litter (8%) and aboveground biomass (<1%). MeHg mass (litter plus soils only) ranged from 75 to 443 mg ha鈥?, of which 88% was found in soils. Both THg and MeHg mass correlated with latitude, with average mass increases of 10.6 g ha鈥? (THg) and 20 渭g ha鈥? (MeHg) per degree latitude, indicating that highest THg and MeHg accumulation in upland forests are expected in northern sites.