基流对亚热带农业流域氮素输出的贡献研究

Contribution of Base Flow to Total Nitrogen Loading in Subtropical Agricultural Catchments

随着经济的迅猛发展和人民生活水平的逐步提高,亚热带农业小流域的面源污染日趋严峻,恶化的水体环境质量已经成为该区域可持续发展和生态文明建设的重要障碍.基流过程对流域生态水文过程有重要影响,因此本研究选取湖南省长沙县的脱甲和涧山两个农业小流域作为调查对象,通过流域观测和模型估算方法,对比分析2011年1月至2013年12月间流域基流过程对总氮(TN)输出的贡献.结果表明,在较高强度水稻种植的脱甲流域的月平均基流流量、平均基流TN流量加权浓度和平均基流对TN输出贡献[15.2 mm·month^(-1)、4.14 mg·L^(-1)和0.54 kg·(hm^2·month)^(-1)],均大于较低强度水稻种植的涧山流域[11.4 mm·month^(-1)、1.72 mg·L^(-1)和0.20 kg·(hm2·month)^(-1)].基流对TN输出贡献呈现明显的季节性变化,如在水稻生长季,脱甲和涧山流域基流对TN输出贡献分别为23.2%和18.6%,均低于休耕季的46.9%和40.0%,表明水稻种植会提高休耕季的流域基流过程对TN输出的贡献.因此,为缓解农业小流域水体面源污染,应当在农业小流域中实施合理的稻田管理措施来降低基流对TN输出的贡献.

With the fast development of economics and improvement of people＇s living standard,non-point source pollution of the agricultural catchments in subtropical China has become more and more severe,where water quality deterioration has become a main barrier for sustainable development and ecological restoration. The process of ecohydrology in catchment is greatly influenced by the process of base flow in channel. This study selected the Tuojia and Jianshan catchments located in Changsha County,Hunan Province,to quantify and compare the contribution of base flow to total nitrogen（ TN） loading from January 2011 to December 2013,through field observation and model estimation. The results suggested that the Tuojia catchment with higher intensity of rice agriculture had the greater volume of base flow,higher average flow-weighted TN concentration in base flow,and greater monthly TN loading via base flow[15. 2 mm·month^-1,4. 14 mg·L^-1and 0. 54 kg·（ hm^2·month）^-1,respectively] than those in the Jianshan catchment with lower intensity [11. 4 mm·month^-1,1. 72 mg·L^-1and 0. 20 kg·（ hm^2·month）^-1,respectively]. The base flow contribution to TN loading showed an apparently seasonal pattern. During rice-growing seasons,the contributions of base flow to TN loading were 23. 2% and18. 6% in the Tuojia and Jianshan catchments, respectively, lower than those in the fallow seasons（ 46. 9% and 40. 0%）correspondingly. These results suggested that rice agriculture increased the contribution of base flow in the fallow season to TN loading.Therefore,to alleviate the suffering of non-point source pollution in the rice agriculture catchments,reasonable management measure of rice fields should be implemented to decrease contribution of base flow to TN loading.