太湖地区稻作系统不同水体硝态氮同位素特征及污染源

为辨别稻作系统不同水体硝态氮来源,选择太湖地区典型稻作区域,应用硝态氮δ15N同位素技术,结合水化学方法(如NO3-, NH4+, TP, Cl-, SO42-),研究水稻施肥之前(4~5月),施肥期(6月),及施肥之后(7~8月)地表水和地下水硝态氮来源.结果表明,地表水和地下水硝态氮含量普遍较高.在施肥期,各水体硝态氮中δ15N均较低,表明该时期农业化肥是水体硝态氮的主要来源.在施氮前期,池塘水δ15N较低,其可能原因是受雨水的影响;而地下水δ15N较高,可能是水体发生了强烈的反硝化.在施肥后期,池塘水δ15N较高可能受养殖废水影响;地下水δ15N较低,可能受农田渗漏水的影响.河水和灌溉水硝态氮δ15N在各时期波动不大,其中河水硝态氮主要来源是生活污水和动物粪肥,但灌溉水硝态氮主要来源于雨水.本研究提出新的Cl-浓度和NO3-/Cl-物质的量比区间以辨别太湖地区水体硝态氮来源.

Nitrogen isotopic characteristics and source attribution of nitrate in different water bodies in the paddy rice system of the Taihu Lake region

To discriminate among NO3-–N sources in different water bodies in paddy rice system, δ15N-NO3- abundance and chemical compositions (e.g., NO3-, NH4+, TP, Cl-, SO42-) were measured in water samples from pond, irrigation ditch, river, and ground water in rice system of the Taihu Lake region at three periods. It was found that nitrate was the dominant nitrogen species in most water samples. During the fertilizing period (June), the δ15N-NO3- value of water samples were lower than those collected in other months, suggesting that the surface water and groundwater receive a significant contribution of NO3-–N from agricultural fertilizer at this period. In periods prior to fertilization (April to May), the low δ15N value in pond water was attributed to rainfall, and the high δ15N value in ground water resulted mainly from denitrification. In periods after the fertilization (July to August), the high δ15N value in pond water was caused by aquaculture wastewater, and the low δ15N value in ground water indicated main nitrate source of agricultural leaching. The δ15N values varied within a narrow range in river and irrigation water during all the three periods, but their nitrate source differed. Sewage and manure contributed nitrate to river water, while rainfall mainly control the nitrate of irrigation water. We put forward new intervals of Cl- and molar ratio of NO3-/Cl- to discriminate among NO3-–N sources in Taihu Lake region.