中文摘要：

土壤养分累积引起的氮素（N）淋失是导致农区地下水污染的重要原因,也是农业面源污染的重要形式.本文以湖南省长沙县典型亚热带红壤丘陵流域为研究对象,通过连续定位观测,研究了林地、稻田、菜地和茶园4种代表性土地利用类型浅层（130~150 cm）地下水中N浓度的逐月动态变化特征.连续3年（2010—2013年）的观测结果表明：4种土地利用类型下浅层地下水总氮（TN）平均浓度差异显著（p〈0.05）,其中,林地最低（0.85 mg·L-1）,茶园最高（7.64 mg·L-1）;从N的形态构成来看,林地、菜地和茶园浅层地下水中N形态以硝态氮（NO-3-N）为主,分别占TN的46.7%、70.2%和72.8%,而稻田浅层地下水N形态则以铵态氮（NH＋4-N）为主,占TN 43.5%,表明土壤淹水条件是影响地下水N淋失形态的关键因子.地下水各形态N浓度的动态变化在不同土地利用下也迥然不同：林地地下水各形态N的含量低、变幅小,而稻田、菜地和茶园地下水N浓度变幅较大;采用单因子方法对不同土地利用下地下水的水质进行评价,结果表明：研究区浅层地下水中TN和NO-3-N无显著污染,NH＋4-N污染较为严重,而综合指数法（F值法）进一步表明研究区浅层地下水污染主要出现在稻田和茶园,因此,控制稻田和茶园N肥的施用量是预防亚热带红壤丘陵区地下水N污染的关键.

英文摘要：

Nitrogen （N） leaching, resulted from soil nutrient accumulation, is an important factor for groundwater pollution in rural area. A continuous in- situ observation of N concentrations in shallow groundwater （ 130~ 150 cm） under four representative land-use types was conducted in a typical hilly red soil watershed in Changsha County, China. The land use patterns included forest （F） , paddy field （PF） , vegetable land （V） and tea plantation （T）. Result of 3-year observation （2010--2013） showed that there were significant differences in monthly-mean total nitrogen （TN） concentrations in shallow groundwater under the four land-use types （p〈0.05） , with the lowest concentration value for F （0.85 mg·L-1 ） and the highest for T （7.64 mg· L-1 ）. With respect to the chemical composition of TN, the proportions of the nitrate （ NO3-N ） were 46.7%, 70.2% and 72.8% under F, V and T, respectively, and the proportion of ammonium nitrogen （NH4-N） reached 43.5% for PF. This result suggests that water logging condition plays a key role on the N chemical composition in the shallow groundwater. The concentration dynamics of different N forms under the four land-use types were significantly different. The N concentrations under F were relatively low and stable, while the changes in the N concentrations were more significant under PF, V and T. The assessment of water quality using single-factor method showed that shallow groundwater was slightly polluted by TN and NO3-N, while it was seriously polluted by NH4-N in the study area. Moreover, the result of water quality assessment using synthetic index method showed that the pollution under PF and T was more frequent than V and F. Therefore, to prevent N poUution in the shallow groundwater in the hilly red soil region in subtropics, controlling N fertilizer application rates in farmland, in particular in PF and T, should be of top priority.