黄河小浪底水库水沙调控与溶解性硝酸盐输出变化

Changes of dissolved nitrate output due to water-sediment regulation of Xiaolangdi Reservoir in the Yellow River

人为输入氮和磷通过河流体系输送到河流下游以及海洋,给河流以及滨海生态系统带来压力,但河流水沙调控过程带来的溶解性硝酸盐(NO_(3)^(-))输出变化尚不清楚。本研究借助黄河小浪底水库水沙调控过程,通过对比分析水库下游300 km范围河水在泄水阶段和泄泥沙阶段水NO_(3)^(-)含量以及硝酸盐氮和氧同位素(δ^(15)N_(NO3)和δ^(18)O_(NO3))组成,说明河水NO_(3)^(-)来源变化及其对水沙调控的响应。结果表明,2018年6月底泄清水阶段河水NO_(3)^(-)含量中间值为13.11 mg·L^(-1),均值为13.04±1.20 mg·L^(-1)(n=11),δ^(15)N_(NO3)和δ^(18)O_(NO3)中间值为1.8‰和8.8‰,均值分别为2.2‰±1.6‰(n=11)和9.2‰±2.1‰(n=11);2018年7月上旬泄泥沙阶段河水NO_(3)^(-)含量中间值为15.46 mg·L^(-1),均值为15.42±1.26 mg·L^(-1)(n=10),δ^(15)N_(NO3)和δ^(18)O_(NO3)中间值为1.3‰和9.4‰,均值分别为0.6‰±2.1‰(n=10)和8.9‰±1.7‰(n=9);单因素方差分析结果表明,泄水阶段和泄沙阶段NO_(3)^(-)含量以及δ^(15)N_(NO3)组成均存在显著差异(P<0.05),但δ^(18)O_(NO3)差异不明显(P>0.05);黄河干流河水NO_(3)^(-)主要来自于土壤NO_(3)^(-)和化肥NO_(3)^(-),泄水阶段贡献比例为15.1%±11.2%和63.7%±10.8%,泄沙阶段贡献比例为11.2%±10.6%和70.4%±11.6%。泄泥沙阶段化肥NO_(3)^(-)对河水NO_(3)^(-)贡献比例增大,与泄沙阶段河道内农田淹没导致化肥NO_(3)^(-)释放有关。研究结果初步探究了黄河小浪底水库水沙调控过程对河水NO_(3)^(-)行为的影响机制,在泄泥沙阶段,河水流量增加导致化学肥料NO_(3)^(-)输出量增加,对黄河下游水体生态系统存在潜在影响。

Anthropogenic nitrogen and phosphate inputs into river exert heavy pressure on the river and coastal ecosystems.The riverine nitrate flux impacted by water-sediment regulation scheme(WSRS)is unclear.Based on WSRS in the Xiaolangdi Reservoir in the Yellow River,we analyzed the nitrate(NO_(3)^(-))concentrations and dual nitrate isotope ratios(δ^(15)_(NO3) andδ^(18)_(NO3))of river water during water regulation and sediment regulation,respectively,to clarify nitrate sources and their responses to WSRS.The results showed that during water regulation in late June 2018,the median and mean value of NO_(3)^(-)concentrations were 13.11 mg·L^(-1) and 13.04±1.20 mg·L^(-1)(n=11),respectively,and the median and mean values were 1.8‰and 2.2‰±1.6‰(n=11)forδ^(15)_(NO3),and 8.8‰and 9.2‰±2.1‰(n=11)forδ^(18)_(NO3),respectively.During the sediment regulation in early July 2018,the median and mean values of NO_(3)^(-)concentrations were 15.46 mg·L^(-1) and 15.42±1.26 mg·L^(-1)(n=10),respectively.Theδ^(15)_(NO3) had the median and mean values of 1.3‰and 0.6‰±2.1‰(n=10),andδ^(18)_(NO3) had the median and mean values of 9.4‰and 8.9‰±1.7‰(n=9),respectively.The results of one-way ANOVA showed significant difference in NO_(3)^(-)andδ^(15)_(NO3) values(P<0.05)between the two phases,but not forδ^(18)_(NO3) values(P>0.05).The nitrate of main stream riverine was mainly derived from soil nitrate and chemical fertilizer nitrate.During water regulation,the fractions of soil nitrate and chemical fertilizer nitrate were 15.1%±11.2%and 63.7%±10.8%,respectively.During the sediment regulation,their contributions were 11.2%±10.6%and 70.4%±11.6%,respectively.The more contributions of chemical fertilizer to riverine nitrate during sediment regulation were probably resulted from chemical fertilizer nitrate in soil due to waterlogging.We discussed the factors affecting nitrate behaviors during WSRS in the Yellow River.The increases of nitrate fluxes in the sediment regulation were due to chemical fertilizer nitrate in the soil induced by the artificial flood,with potential impacts on the downstream aquatic ecosystem in the Yellow River.