人类活动净氮输入时空变化特征及其影响因素——以香溪河流域为例

为了阐明人类活动对三峡库区第一大支流香溪河流域氮输入的影响程度，基于人类活动净氮输入（NANI）模型估算了2001~2015年间香溪河流域乡镇水平的人类活动净氮输入，分析了氮输入的主要来源及其动态变化.结果表明：时间尺度上，香溪河流域人类活动净氮输入（NANI）因氮素施用的变化而呈现先上升后下降最后上升的趋势，但2015年相对2001年的NANI下降了143kg N/（km²·a）；空间尺度上，香溪河流域NANI整体呈现北低南高的分布格局，其中NANI输入强度差异较大的区域主要有昭君镇、峡口镇和黄粮镇.从人类活动净氮输入的组成上来看，氮肥施用仍然是最主要的来源（40.06%），其次为大气氮沉降（29.98%）和食品/饲料净氮输入（27.75%），作物固氮仅占净氮输入总量的2.21%.香溪河流域的NANI与人口密度和耕地面积比例极显著相关（P<0.001）；而NANI与河流氮输出的相关性不显著，香溪河流域河流氮输出占NANI的比例仅为24.28%.因此，可以通过减少氮素施用降低流域尺度氮素净输入量，但该流域NANI与河流氮输出无直接的响应关系.

Spatio-temporal characteristics and influential factors of net anthropogenic nitrogen input: A case study of Xiangxi River Watershed

This study was conduct to better understand impacts of anthropogenic activities of mankind on nitrogen loads in the Xiangxi River Watershed (XRW), China, the largest tributary of the Three Gorges Reservoir Area. The net human activity on nitrogen input, its main sources and changes at the township level under XRW were investigated from 2001 to 2015 based on the Net Anthropogenic Nitrogen Input (NANI) model. The results showed that NANI in the study area was primarily affected by nitrogenous fertilizers from 2001 to 2015. It indicated an increasing trend in the beginning years (from 2002 to 2004). It was decreasing (from 2004 to 2006 and 2008 to 2009) and eventually increasing again (from 2013 to 2014). In general, the overall trend of NANI was descending. In case of spatial distribution, NANI of WRW was low at northern side and higher at the south. Areas with the higher NANI input intensity were Zhaojun Town, Xiakou Town, and Huangliang Town. Nitrogen from fertilizer application was the major cause of NANI (40.06%), followed by atmospheric deposition (29.98%), food/feed import (27.75%), and crop fixation (2.21%). NANI in XRW is significantly correlated with the population density andthe proportion of cultivated land (P<0.001). Nitrogen from runoff to the river was 24.28% of NANI and had no substantial relationships with NANI. Therefore, net nitrogen input at the basin level can be reduced by reducing nitrogen application, but the NANI in this basin is not the main cause of nitrogen output in rivers.