School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ, UK.
Environ Sci Technol. 2011 May 1;45(9):3967-73. doi: 10.1021/es104322q. Epub 2011 Apr 11.
A dual-isotope and solute flux mass-balance was used to elucidate the processes that lead to attenuation of nitrogen contamination in an agriculturally impacted river. The River Wensum drains a lowland catchment with an area of 570 km² in East Anglia, eastern England. Analysis of nitrate concentration, δ¹⁵N(NO₃) and δ¹⁸O(NO₃) of samples from the River Wensum collected from upstream locations to the catchment outlet through all seasons and flow conditions showed a consistent pattern of increasing isotope values with decreasing nitrate concentrations downstream. δ¹⁵N(NO₃) and δ¹⁸O(NO₃) of catchment surface water and groundwater samples revealed a dominant influence from microbially cycled and nitrified source-nitrogen, which results in high nitrate concentrations in Chalk groundwater and upstream in the River Wensum. Denitrification of Chalk groundwater-baseflow in the hyporheic zone results in the downstream trend observed in the river. Hyporheic denitrification is estimated to remove 931 kg/day of nitrate-nitrogen by the catchment outlet, representing 31% of the potential riverine nitrate load. The use of dual-isotope and solute flux modeling at the catchment scale is a novel application to quantify denitrification within the river valley, demonstrating the importance of hyporheic zone processes in attenuating the impacts of anthropogenic contamination of hydrologic systems.
采用双同位素和溶质通量质量平衡法来阐明导致氮素污染在受农业影响的河流中衰减的过程。温瑟姆河（River Wensum）流经英格兰东部东安格利亚（East Anglia）低地流域，流域面积为 570 平方公里。对温瑟姆河（River Wensum）不同季节和流量条件下从上游位置到流域出口采集的硝酸盐浓度、δ¹⁵N(NO₃)和 δ¹⁸O(NO₃)进行分析，结果表明下游硝酸盐浓度降低时同位素值呈持续增加的趋势。流域地表水和地下水样品的 δ¹⁵N(NO₃)和 δ¹⁸O(NO₃)表明，微生物循环和硝化源氮的影响占主导地位，导致白垩含水层和温瑟姆河上游的硝酸盐浓度较高。地下潜流区白垩含水层基流的反硝化作用导致了河流下游的趋势。据估计，通过流域出口，地下潜流区反硝化作用每天去除硝酸盐氮 931 千克，占河流硝酸盐潜在负荷的 31%。在流域尺度上采用双同位素和溶质通量模型的应用是量化河谷内反硝化作用的一种新方法，证明了地下潜流区过程在减轻水文系统人为污染影响方面的重要性。
