Effect of Groundwater Age and Recharge Source on Nitrate Concentrations in Domestic Wells in the San Joaquin Valley

Abstract

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 δ 18 O 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.

Strong Precipitation and Human Activity Spur Rapid Nitrate Deposition in Estuarine Delta: Multi-Isotope and Auxiliary Data Evidence

“…Then the proportion of precipitation sources in the Guangli and Yihong Rivers increased from 0.5% to 27.0% and then to 24.0%. This was similar to what was observed for precipitation recharge to surface water by Castaldo et al [50] and Zhang et al [47]. Before the rains, the contribution rate of nitrate from surface water of the Xiaodao and Zhangzhen Rivers from chemical fertilizers, soil organic nitrogen, and human/animal manure decreased in trend.…”

Characterizing Groundwater Chemistry and Recharge in the Critical Zone of an Agricultural Claypan Watershed

“…Deep groundwater sources can be a significant source of $${\mathrm{N}\mathrm{O}}_{3}^{-}$$ to streams in GCEW, accounting for nearly 100% of transport, especially during low stream flow periods (Liu et al., 2020). While the shallow interflow and near surface runoff above the claypan horizon are dominant pathways for the transport of sediment, pesticides, and nutrients to surface waters in this agricultural watershed, deep groundwater plays an important role as a relatively constant source of legacy N in this region, as has been observed in other agricultural regions across the U.S. (Castaldo et al., 2021; Johnson & Stets, 2020; Lerch, Kitchen, et al., 2015; Stackpoole et al., 2021; Van Meter et al., 2017; Zhi & Li, 2020). Spatial variability of $${\mathrm{N}\mathrm{O}}_{3}^{-}$$ sources as well as temporal variability in the connections between these sources, deeper groundwater, and the stream can result in variation in how and when these legacy $${\mathrm{N}\mathrm{O}}_{3}^{-}$$ stores are mobilized (Shishaye et al., 2021; Van Meter et al., 2016).…”

Vulnerability Assessment of Farmland Groundwater Pollution around Traditional Industrial Parks Based on the Improved DRASTIC Model—A Case Study in Shifang City, Sichuan Province, China

“…Recharge water is the main carrier of leaching and transmitting pollutants; the more water that seeps in, the more pollutants that are brought to the submersible aquifer from recharge water, and the worse the vulnerability of groundwater is. At the same time, when the recharge is large enough to dilute the pollutants, the likelihood of pollution decreases, and the vulnerability of groundwater improves [35,40]. The source of supply in the study area includes rainfall infiltration resupply and surface water infiltration resupply.…”