中文摘要：

综合运用定位监测、野外试验、模型模拟与GIS技术等手段和方法，定量研究了南亚热带地区九龙江流域和五川小流域氮的大气沉降、河流输送（地表径流）、淋失、反硝化和氨挥发等输入输出（源汇）时空模式与机理．结果表明，九龙江流域氮“源”以化肥与饲料输入为主（占总输入125．6kg·hm^-2的86％），氮“汇”以氨挥发和河流输送为主（占总输出72．9kg·hm^-2的82％）．氮输入后50％以上进入大气和水环境，14．5％通过河流输送至河口与近海．大气氮沉降通量为14．9kg·hm^-2，其中干沉降占34％，湿沉降占66％，形成1：2的干湿沉降结构；源于化肥施用与畜禽养殖引起的强烈氨挥发，氮沉降集中在春夏两季（占全年80％），且以铵态氮为主（39％以上）．氮的径流输出及河流输送受人为氮输入与水文条件的双重控制，2004年九龙江向厦门海域输送无机氮11．5kg·hm^-2，其中90％发生在春夏秋季（同期流量占全年89％）；五川小流域总氮径流输出负荷为67．1kg·hm^-2，其中85％发生在施肥量大、降雨集中的春夏两季（作物生长期）；基流与降雨径流分别贡献25％和75％．总氮淋失负荷为27．5kg·hm^-2，占总输入的9％；pH〈5的酸性土壤带正电荷导致氮淋失以铵态氮为主（约占40％）．九龙江流域反硝化通量为7．7kg·hm^-2，而氨挥发高达42．1kg·hm^-2，氨挥发主要来自化肥施用与畜禽养殖（分别贡献50％和39％）．减少春夏时期肥料氮的输入（养分管理），有效截留雨季的降雨径流（水文控制）是该流域氮素管理的关键．

英文摘要：

Excessive reactive nitrogen （N） additions from human activities have resulted in serious and long-term environmental consequences for large regions of the Earth. An understanding of N sources and their export pattern is important for selecting the proper remedial strategies to control nutrient losses from the watershed. In this study, the N sources and exports were determined for the Jiulong River Watershed （JRW） , a coastal watershed with an area of 1.47× 10^4 km^2 in the southeast of China; and the Wuchuan subwatershed （ 1.88 km^2 ） , a small agricultural watershed in the up-stream Jiulong River. Water quality monitoring, field measurements, mechanism models and GIS techniques were linked to estimate the N flux of atmospheric deposition, streamflow discharge, leaching, denitrification, and ammonia volatilization. Two scale watershed N budgets based on 2004 data were used to identify N sources and the primary path of N losses. The N budget for JRW showed that fertilizer and animal feedstuffs contributed 86% of the total N input （ 125.6 kg·hm^-2 ） ; while streamflow discharge and ammonia volatilization contributed 82% of the total N output （72.9 kg·hm^-2 ）. More than half of the anthropogenic N input was lost to the air and water. About 14.5% of the N input was discharged to rivers and subsequently delivered to the estuary. The annual deposition flux of atmospheric N amounted to 14.9 kg·hm^-2, of which dry deposition and wet deposition accounted for 34% and 66% , respectively. About 80% of atmospheric deposition occurred in spring and summer, indicating that higher ammonia volatilization from fertilizer application in the growing season, and animal feeding together provided the largest N source. The Jiulong River provided dissolved inorganic N transport of 11.5 kg·hm^-2 to the estuary, of which more than 90% occurred from March through November （wet season） resulting from 89% of the total flow. Compared with the baseflow, stormflow contributed about 75% of the annual N export （67.1