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Riverine nitrogen export and its natural and anthropogenic determinants in a subtropical agricultural catchment
Agriculture, Ecosystems & Environment ( IF 6.0 ) Pub Date : 2020-10-01 , DOI: 10.1016/j.agee.2020.107021 Xinliang Liu , Yi Wang , Yong Li , Meihui Wang , Ji Liu , Liming Yin , Shuangmiao Zuo , Jinshui Wu
Agriculture, Ecosystems & Environment ( IF 6.0 ) Pub Date : 2020-10-01 , DOI: 10.1016/j.agee.2020.107021 Xinliang Liu , Yi Wang , Yong Li , Meihui Wang , Ji Liu , Liming Yin , Shuangmiao Zuo , Jinshui Wu
Abstract Protecting and restoring riverine environmental quality requires a quantitative understanding between riverine nitrogen (N) and various determinants, however, it is still challenging in highly naturally-and-anthropogenically differentiated agricultural catchments. The study observed riverine ammonium-N (NH4+−N), nitrate-N (NO3−−N), and total-N (TN) in the eleven Chinese subtropical agricultural catchments, to develop predicting functions for riverine N concentrations and loadings through integrating the multiple stepwise linear regression (MLR) and variation partitioning analysis (VPA). The results suggested severe riverine N pollution in the catchments, with the observed TN concentrations of 1.23–4.24 mg N L−1 and average annual TN loadings of 19.80 ± 24.72 kg N ha−1 yr−1. The mean annual flow-weighted N concentrations and loadings could be effectively predicted by the MLR (R2 = 0.49−0.87, relative error = 4.1%–153.1%), using the explanatory variables in the catchment hydrogeographic characteristics (catchment area and topographic wetness index (Twi)), land use compositions (forest and agriculture areal percentages), soil properties (bulk density (BD) and total soil N content (TSN)), and socioeconomic (livestock densities) categories. The land use compositions had the largest relative independent contributions to all the flow-weighted N concentrations (78.46%–86.11%), showing the importance of land use compositions on riverine N levels. The socioeconomic conditions had the largest relative independent contributions to the NH4+−N (47.92%) and TN (40.74) loadings, due to the discharge animal excretions of rich NH4+−N and TN into stream systems. The land use category independently contributed to 82.24% of the explainability of the NO3−−N loadings, probably explained to the unique characteristics of NO3−−N loss under different land uses. Therefore, the study provided useful ideas and tools to environment managers and agencies for controlling riverine N pollution in the subtropical China.
更新日期：2020-10-01
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