基于^(15)N同位素示踪技术的地下河硝态氮来源时空变化特征分析

Temporal and Spatial Variations of the Nitrate-nitrogen Sources in an Underground River Using ^(15)N Isotope Technique

根据2007年10月至2008年10月每月对青木关地下河水的监测,利用15N同位素示踪技术并结合水化学指标,分析地下河硝态氮来源的时空变化特征.结果表明,地下河出口S2硝态氮浓度(20.35 mg/L)比入口D1(3.20 mg/L)高6倍多.受农业生产施肥和降雨冲刷稀释效应的影响,地下河水硝态氮浓度2007年10月至2008年3月较低且比较稳定,2008年4月至7月较高但受降雨冲刷稀释影响变化较大,2008年8月至9月随降雨减少,土壤中残留的化肥造成地下河水硝态氮浓度偏高.根据NO3--δ15N值识别出了地下河硝态氮来源变化特征为:D1处2007年10月至2008年3月以及2008年7月至10月NO3--δ15N值为-0.857‰±2.01‰(n=9),其硝态氮来源为稻田中残留的化肥;2008年4月、6月中下旬NO3--δ15N值为2.50‰±0.29‰(n=3),其来源为稻田中施用的化肥与土壤有机氮的混合;2008年5月下旬至6月上旬NO3--δ15N值分别为-3.74‰和0.52‰,其来源为稻田中施用的化肥.S2处硝态氮不仅来自上游的化肥,更主要的是来自中下游的耕地、林地土壤渗透水或侧向裂隙水带来的土壤有机氮与化肥,其中2007年10月至2008年3月以及2008年7月至10月NO3--δ15N值为4.77‰±0.73‰(n=9),其硝态氮主要来自于土壤有机氮;2008年4~6月NO3--δ15N值为3.16‰±0.39‰(n=5),其硝态氮来自于土壤有机氮与化肥的混合.

Groundwater in Qingmuguan underground river was monitored using hydro-chemical and 15 N isotope techniques to investigate temporal and spatial variations of nitrate-nitrogen and its possible sources from October, 2007 to October, 2008. The results show that nitrate concentrations are 3.20 mg/L of the inlet （D1） and 20.35 mg/L of the outlet （S2） of the underground river. Affected by the fertilizers in agricultural field and the rainfall flush and dilution, nitrate concentrations of groundwater are higher but less stable from April to July, 2008 than that from October,2007 to March,2008. They are elevated during August and September, 2008 due to the residual fertilizers and decreased rainfall events. According to the NO3^--δ^15N values of - 0.857‰ ＋ 2.01‰ （ n = 9）, the sources of nitrate-nitrogen of D1 are dominated by residual fertilizers from the paddy fields from October, 2007 to March, 2008 and from July to October, 2008, while the NO3^--δ^15N values of 2.50‰ ＋ 0.29‰ （ n = 3） demonstrate that the mixture of soil organic nitrogen and fertilizers are the sources from April to middle and late June,2008. And the NO3^--δ^15N values of - 3.74‰ in late May and 0.52‰ in early June indicate that the nitrate-nitrogen comes from fertilizers applied in the paddy fields in 2008. The nitrate-nitrogen of S2 is partly from fertilizers in the upper basin, and also from fertilizers and soil organic nitrogen carried by lateral fissure and soil permeation water of forest and farm land in the middle and lower basin. The NO3^--δ^15N values of 4.77‰ ＋ 0.73‰ （n = 9） show nitrate-nitrogen of S2 mainly originates from fertilizers from October, 2007 to March, 2008 and from July to October, 2008 ,while NO3^--δ^15N values of 3.16‰ ±0.39‰ （n = 5） explain that the nitrate-nitrogen derives from the mixture of soil organic nitrogen and fertilizers from April to June, 2008.