Modeling forest/agricultural and residential nitrogen budgets and riverine export dynamics in catchments with contrasting anthropogenic impacts in eastern China between 1980-2010

This study quantified the long-term response of riverine total nitrogen (TN) export to changes in net anthropogenic nitrogen inputs to forest/agricultural (NANI(FA)) and residential (NANI(R)) systems across three catchments affected by low (LD), medium (MD), and high (HD) human impacts in eastern China. Annual NANI(FA) increased by 63-87% in 1980-1999, followed by 0% (LD), -23% (MD) and -40% (HD) changes of NANI(FA) in 2000-2010, resulting in a net increase of 56-78% in NANI(FA) in 1980-2010. Annual NANI(R) increased by 101-152% in the three catchments in 1980-2010. Land-use showed a 58-65% increase in developed land area (D%) and a 96-108% increase in agricultural lands with improved drainage systems (AD%) over the study period. In response to changes in NANI(FA), NANI(R) and land-use, riverine TN flux continuously increased 3.0- to 6.1-fold in the three catchments over the past 31 years. For each catchment, an empirical model incorporating annual NANI(FA), NANI(R), water discharge, D%, and AD% was developed (R-2=0.93-0.97) for predicting and quantifying sources of annual riverine TN fluxes. The model estimated that NANI(FA), NANI(R) and other N sources (e.g., natural background, legacy, and industrial N sources) contributed 27-90%, 0-45%, and 10-28% of riverine TN fluxes, respectively. Model results were consistent with spatio-temporal changes of riverine chloride, ammonium, nitrate, dissolve oxygen and pH, as well as changes in available N levels in agricultural soils. In terms of N source management, reduction of NANI(FA) in catchment LD and NANI(R) in catchment HD would have the greatest impact on reducing riverine TN fluxes. Furthermore, changes in land use and climate as well as legacy N should be considered in developing N pollution control strategies. (C) 2016 Elsevier B.V. All rights reserved.