University of California Davis, Davis, California 95616, United States.
Lawrence Livermore National Laboratory, Livermore, California 94550, United States.
Environ Sci Technol. 2021 Feb 16;55(4):2265-2275. doi: 10.1021/acs.est.0c03071. Epub 2021 Jan 28.
Nitrate is one of the most abundant contaminants in groundwater globally, in the United States, and in California (CA). We studied well construction information, water chemistry, stable isotopes, and noble gases to understand how groundwater travel time and recharge source and mechanism control nitrate concentrations in domestic wells in the San Joaquin Valley (SJV), CA, a large semiarid, irrigated agricultural region. Using nonparametric statistics, we find a decreasing trend in nitrates with groundwater travel time and well depth. Samples collected from wells that are closer to rivers and that show indications of river water recharge, either low recharge temperature or low δO signature, have lower concentrations of nitrates than samples with isotopic signatures indicating mixed source or local precipitation recharge. The curbing effect of river water recharge on nitrate concentrations in domestic wells is similar for direct river recharge and water applied as irrigation. This suggests that irrigation with river water also has a diluting effect that reduces the concentration of nitrate found in groundwater. This conclusion supports the idea that flood-managed aquifer recharge may be considered for remediation of groundwater nitrate when designing replenishment of aquifers.
硝酸盐是全球、美国和加利福尼亚州（CA）地下水中最丰富的污染物之一。我们研究了水井建设信息、水化学、稳定同位素和稀有气体，以了解地下水流动时间以及补给源和补给机制如何控制加利福尼亚州圣华金河谷（SJV）地区的家庭水井中硝酸盐的浓度，该地区是一个大型半干旱、灌溉农业区。我们使用非参数统计发现，硝酸盐浓度随地下水流动时间和井深的增加而降低。与具有混合来源或当地降水补给的同位素特征的样本相比，从靠近河流且表明有河水补给的水井（补给温度低或 δO 特征低）中采集的样本硝酸盐浓度较低。河水补给对家庭水井中硝酸盐浓度的遏制作用对于直接河水补给和灌溉用水补给是相似的。这表明，用河水灌溉也具有稀释作用，降低了地下水中发现的硝酸盐浓度。这个结论支持了这样一种观点，即当设计含水层补给时，洪水管理含水层补给可能被认为是地下水硝酸盐修复的一种方法。
