人类活动对长江河口硝酸盐输入通量的影响

利用长江口枯季潮区界大通站近 4 0年来的水文化学观测资料 ,求得长江径流来源的硝酸盐通量 ,并以此作为长江河口硝酸盐的输入通量。结合历年长江流域的社会经济统计资料和降水量资料等分析 ,发现长江河口硝酸盐的输入通量与流域的人口密度、农业氮肥施用量、灌溉面积以及降水量等显著正相关。随着人口的增长 ,流域内的人类活动不断加剧 ,直接或间接地对长江河口硝酸盐的输入通量产生影响。而降水及灌溉等活动促进了土壤中氮素向河流流失的过程 ,并经长江径流向河口、海洋输送。 90年代后期 ,由人类因素造成的硝酸盐通量的增加占长江河口硝酸盐输入通量的95 %以上。降水引起的水土流失和大气氮氧化物的沉降是硝酸盐通量增加的直接原因 ,而农业活动、燃料燃烧和污水排放等人类活动是该通量变化的主要控制因素

HUMAN IMPACT ON THE NITRATE FLUXTO THE CHANGJIANG ESTUARY

Nutrient input to the Changjiang (Yangtze) estuary via river, groundwater, wastewater and atmospheric deposition. In this paper, we paid attention to nitrate fluxes through the river runoff. Integrated with the social-economic data of the Yangtze watershed, the changes of nitrate fluxes at the tidal limit of the Yangtze estuary from 1963 to 2000 were analyzed. The fluxes of nitrate correlated with human population density (R+2=0.83, N=36), nitrogen fertilizer application (R+2=0.90, N=36), irrigation area and precipitation and so on. Both natural changes and anthropogenic factors influenced directly or indirectly the nitrate fluxes to the estuary.Our findings suggested that the fluxes of dissolved nitrate increased as anthropogenic inputs of N to the Yangtze watershed increased. Precipitation was only an incentive for the change of nitrate fluxes. Discharges of wastewater, agricultural activities and combustion activities in the watershed which were the major controlling factors of the changes of the nitrate fluxes to the Yangtze estuary, had direct or indirect influence on the fluvial nitrate fluxes. In 1990's, anthropogenic nitrate fluxes accounted for more than 95 percent of the nitrate fluxes to the Yangtze estuary due to the urbanization, industrialization and agricultural development.