Hydrological effects on the spatial and temporal variation of methylmercury in the temperate lakes and rivers in South Korea

Abstract

This research examines spatial and temporal variations of methylmercury (MeHg) and their influential factors in freshwater ecosystems like lakes and rivers. Extensive statistical analyses of environmental factors, including water quality, hydrology, and atmospheric parameters, were conducted to understand the dynamics of MeHg in these environments. A key discovery for lake study is the role of chlorophyll-a (Chl-a) and water residence time, in the spatial variations of Hg(II) methylation rate and sediment MeHg concentration, respectively. It is probably due to the fact that high Chl-a levels may reduce dissolved oxygen concentrations and block sunlight, fostering anaerobic conditions that promote the proliferation of sulfur-reducing bacteria and iron-reducing bacteria, subsequently leading to increased methylation rates. For the temporal variation of MeHg, physical factors such as the watershed area-to-lake area ratio and water residence time were critically important, as these parameters control the temporal variation of Chl-a and dissolved oxygen concentrations and thus MeHg concentrations. Moreover, our analysis of climate change effects on the MeHg levels in Yeongsan River indicates that currently there are significantly decreases in precipitation depths, which affects MeHg concentrations in surface river water. In the last chapter to develop a benthic flux chamber, the diffusive boundary layer thickness affected by the flow rate was found to significantly influence sediment diffusion rate of MeHg. In conclusion, spatiotemporal and temporal variations in hydrological factors, including residence time and wet precipitation depth, critically affect MeHg levels in freshwater ecosystems. This finding should be noted for the effective monitoring and management of MeHg in aquatic environments, particularly under ongoing climate change.