1980~2010年浙江某典型河流硝态氮通量对净人类活动氮输入的动态响应

以浙江某典型流域为研究对象,基于1980～2010年的水质水量和氮源数据及LOADEST模型,估算了逐年河流NO-3-N通量和净人类活动氮输入(NANI),分析了河流NO-3-N通量和NANI的年际演化特征及其动态响应关系,探讨了每年NANI、滞留氮库、自然背景源对河流NO-3-N通量的贡献.结果表明,1980～2010年,河流NO-3-N通量和NANI总体上都呈现出先增后减的抛物线型变化趋势,均在1998年左右分别达到峰值5.74 kg·(hm2·a)-1和77.5 kg·(hm2·a)-1;过去31 a,河流NO-3-N通量和NANI分别净增加了～42%和～77%.化肥氮和大气氮沉降是NANI的主要来源,分别占了NANI的～48%和～40%.河流NO-3-N通量的年际变化不仅与NAIN(R2=0.27**)和化肥氮输入量(R2=0.32**)显著相关,而且与河流年均流量(R2=0.79**)或降雨量(R2=0.63**)具有更强的相关性,意味着河流NO-3-N的来源除了当年的NAIN,还受滞留氮库的影响.所建立的以NANI和流量为自变量的回归模型能很好地模拟河流NO-3-N通量变化(R2=0.94**).该模型预测结果显示,在NANI和流量分别降低30%的情况下,河流年均NO-3-N通量将分别减少～21%和～30%;每年的NANI、滞留氮库、自然背景源对河流当年NO-3-N通量的贡献率分别为～53%、～24%、～23%.河流NO-3-N通量长期的年际变化是NANI和水文要素共同作用的结果;但是,由于滞留氮库的影响,与源控制方式相比,增加"汇"景观应该能更加快速地削减河流NO-3-N通量.

Dynamic Response of Riverine Nitrate Flux to Net Anthropogenic Nitrogen Inputs in A Typical River in Zhejiang Province over the 1980-2010 Period

Based on long-term records of river water quality and discharge and nitrogen sources as well as the LOADEST model, annual riverine NO₃^--N flux and net anthropogenic nitrogen input (NANI) were both estimated for a typical river catchment (2474 km²) in Zhejiang Province over the 1980-2010 period. Historical trends in both riverine NO₃^--N flux and NANI and their dynamic relationships were then fully addressed. Finally, the contributions of annual NANI, retained nitrogen pools, and natural background sources to riverine NO₃^--N flux were indentified. Results indicated that both riverine NO₃^--N flux and NANI showed parabolic changing trends with peak value of 5.74 kg·(hm²·a)^-1 for flux and 77.5 kg·(hm²·a)^-1 for NANI both occurring around 1998. In 1980-2010, net increase of riverine NO₃^--N flux and NANI was ~42% and ~77%, respectively. Chemical nitrogen fertilizer application and atmospheric nitrogen deposition, which accounted for ~48% and ~40% of NANI, respectively, were the major sources of NANI. Although interannual change of riverine NO₃^--N flux was significantly related to NANI (R²=0.27^**) as well as the chemical nitrogen fertilizer application amount (R²=0.32^** ), it showed higher dependence on the river water discharge (R²=0.79^**) or precipitation (R²=0.63^**), implying that annual riverine NO₃^--N was not only originated from current year's NANI, but also derived from retained N pools that were ultimately derived from NANI in previous years. A regression model developed by incorporating both NANI and water discharge could account for 94% of the variability of annual NO₃^--N flux. This model predicted that NO₃^--N flux could have been reduced by ~21% and ~30% if the annual NANI and water discharge had been cut by 30%, respectively. Annual NANI, retained nitrogen pools, and natural background sources contributed to~53%,~24%, and ~23% of the riverine NO₃^--N flux, respectively, suggesting that~77% of flux was derived from anthropogenic nitrogen sources. Although observed long-term interannual change of riverine NO₃^--N flux was dependent on the combined influences of NANI and hydroclimate, a more immediate reduction of riverine NO₃^--N flux may result from interception strategies than from cutting nitrogen source inputs due to the contribution of retained nitrogen pools.