| 摘 要： |
Mining activities cause severe nitrogen pollution in watersheds, yet our understanding of the transport pathways, transformation processes, and control mechanisms of nitrate (NO3 -) in these areas is limited. Based on nearly 4-year observations of groundwater and river in China's largest ion-adsorption rare earth mining watershed, we revealed the dynamics of NO3 - and its drivers using stoichiometry-based load model, molecular biological, and multi-isotope approaches. Results indicated that the NO3 - dynamics were jointly controlled by sources (precipitation, terrestrial inputs, and sediment supply) and processes (hydrological and biological). The monthly NO3 - export load from the 444.4 km2 watershed was 3.72 x 105 kg. Groundwater (36 +/- 26%) and soil nitrogen (25 +/- 17%) were the primary exogenous sources of NO3 -. Baseflow was the main hydrological pathway for legacy nitrogen into the river, contributing 66.8% of the NO3 - load. Coupled nitrification-denitrification were key biological processes affecting the NO3 - transformation, with denitrification contributing 58%. Burkholderia were most associated with NO3 - transformation. Dissolved organic carbon and oxygen were major drivers affecting the NO3 - production and consumption. This study highlights effective control and management strategies for nitrogen pollution in mining-affected watersheds, considering not only reducing nitrogen inputs but also integrating hydrological pathways and nitrogen transformation mechanisms. |
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