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以位于北亚热带丘陵地区不同利用条件下的2个相邻小流域(F:森林、FA:森林/农田)为研究区域,2007年3月～2009年2月通过定期监测雨水和径流水以及对其NH 4+-N和NO 3--N的测定,分析了流域氮素的平衡与源汇特征.结果表明,雨水中无机氮的输入量为16.72 kg.(hm2.a)-1,NH 4+-N占56%;2个小流域(F、FA)径流水中无机氮的输出量分别为5.31kg.(hm2.a)-1和8.21 kg.(hm2.a)-1,NO 3--N占75%～82%,流域内农业活动加剧了径流水中氮素的输出.大气干湿沉降输入的无机氮总量为20.06～23.41 kg.(hm2.a)-1,约占当地氮肥施用量13%～15%.2个小流域(F、FA)由于氮沉降及其转化产生的H+量分别为355 mol.(hm2.a)-1和461 mol.(hm2.a)-1,流域内农业活动在一定程度上加速了土壤酸化进程.流域氮素收支平衡表明2个小流域(F、FA)氮素净滞留量分别为13.35～16.70 kg.(hm2.a)-1和17.89～23.38 kg.(hm2.a)-1,受到农业活动影响的流域(FA)氮素的净滞留率(33%～40%)远比森林流域(F)(65%～70%)低,表明我国亚热带地区以森林为主的流域目前仍具有氮汇作用,但流域内农业活动降低了生态系统的氮汇潜力.
Two adjacent small watersheds (F: forest and FA: forest / farmland) under different utilization conditions in the northern subtropical hilly region were selected as the study area. From March 2007 to February 2009, regular monitoring of rainwater and runoff water, The results showed that the input of inorganic nitrogen in rainwater was 16.72 kg (hm2.a) -1, and NH (superscript +) -N 4 + -N accounted for 56%; the output of inorganic nitrogen in runoff water of two small watersheds (F, FA) were 5.31kg. (Hm2.a) -1 and 8.21kg. (Hm2.a) --N accounted for 75% ~ 82%, and agricultural activities in the river basin exacerbated the output of nitrogen in runoff water. The total amount of inorganic nitrogen input by dry-wet deposition was 20.06 ~ 23.41 kg (hm2.a) -1, The amount of nitrogen fertilizer applied was 13% -15%. The amount of H + in the two small watersheds (F, FA) was 355 mol. (Hm2.a) -1 and 461 mol. (Hm2.a) - (1) The agricultural activities in the basin accelerated the process of soil acidification to a certain extent.Nutrient balance of nitrogen in the basin showed that the net nitrogen retention of the two small watersheds (F and FA) was 13.35-16.70 kg (hm2.a) - 1 and 17.89 ~ 23.38 kg. (Hm2.a) -1, net retention of nitrogen in the watershed (FA) affected by agricultural activities (33% ~ 40%) is far lower than that of forest watershed (F) (65% ~ 70%), suggesting that the forest-dominated watersheds in subtropical regions of our country still have the function of nitrogen sinks at present. However, Nitrogen potential.