长江三角洲地区雨水中NH4+-N/NO3--N和δ15NH4+值的变化

2003年6月至2005年7月，利用自行设计的雨水收集器对位于长江三角洲地区的常熟、南京和杭州3个观测点进行了全年性雨水观测，分析了雨水中NH₄⁺-N/NO₃^--N和铵态氮自然丰度(δ¹⁵NH₄⁺)值的变化.结果表明：研究区3个观测点雨水中NH₄⁺-N/NO₃^--N和δ¹⁵NH₄⁺值均呈相似的季节性变化规律，两者的规律性变化在以田间农事耕作为主的常熟观测点尤其明显，而位于市区的南京观测点和位于城乡结合部的杭州观测点的规律性次之；雨水中NH₄⁺-N/NO₃^--N的峰值出现在6月下旬到8月上旬，然后逐渐下降，冬季降到最低；雨水中δ¹⁵NH₄⁺值在6月下旬到8月中旬为负值，在8月下旬到11月中下旬为正值，12月至翌年3月又变为负值，5至6月中旬又转变为正值.雨水中NH₄⁺-N/NO₃^--N和δ¹⁵NH₄⁺值的季节变化与不同作物生育期间氮肥的施用、当地气候的季节性变化以及其他NH3释放源的NH3挥发有关（人和动物排泄物、氮污染水体及有机氮源中的氨挥发），其对大气湿沉降中NH₄⁺的来源、形态组成及陆地不同NH₃排放源的强度具有明显的指示意义.

Seasonal variation patterns of NH4+-N/NO3——N ratio and δ15NH4+ value in rainwater in Yangtze River Delta

By using a customized manual rainwater sampler made of polyvinyl chloride plastic, the molar ratio of NH₄⁺-N/NO₃^--N and the natural ¹⁵N abundance of NH₄⁺ (δ¹⁵NH₄⁺) in rainwater was monitored all year round from June 2003 to July 2005 at three observation sites (Changshu, Nanjing, and Hangzhou) in the Yangtze River Delta. The results indicated that at the three sites, the NH₄⁺-N/NO₃^--N ratio and the δ¹⁵NH₄⁺ value in rainwater had the similar seasonal variation trend, being more obvious in Changshu (rural monitoring type) site than in Nanjing (urban monitoring type) and Hangzhou (urban-rural monitoring type) sites. The NH₄⁺-N/NO₃^--N ratio peaked from early June to early August, declined gradually afterwards, and reached the bottom in winter; while the δ¹⁵NH₄⁺ value was negative from late June to mid August, turned positive from late August to mid or late November, became negative again when winter dominated from December to March, but turned positive again in next May and negative again in next July. These seasonal variation patterns of NH₄⁺-N/NO₃^--N ratio and δ¹⁵NH₄⁺ value were found in relation to the application of chemical nitrogen fertilizers during different crop growth periods, and also, the alternation of seasons and the NH₃ volatilization from other NH₃ emission sources (including excrements of human and animals, nitrogen-polluted water bodies, and organic nitrogen sources, etc.), which could be taken as an indicator of defining the sources and form composition of NH₄⁺ in atmospheric wet deposition and the intensity of various terrestrial NH₃ emission sources.