US Geological Survey, 6000 J St Placer Hall, Sacramento, CA, 95819, USA.
Environ Monit Assess. 2020 Mar 25;192(4):250. doi: 10.1007/s10661-020-8180-y.
Areas of improving and degrading groundwater-quality conditions in the State of California were assessed using spatial weighting of a new metric for scoring wells based on constituent concentrations and the direction and magnitude of a trend slope (Sen). Individual well scores were aggregated across 2135 equal-area grid cells covering the entire groundwater resource used for public supply in the state. Spatial weighting allows results to be aggregated locally (well or grid cell), regionally (groundwater basin), provincially, or statewide. Results differentiate degrading (increasing concentration trends) areas with low to moderate concentrations (unimpaired) from degrading areas with moderate to high concentrations (impaired). Results also differentiate improving areas (decreasing concentration trends) in the same manner. Multi-year to decadal groundwater-quality trends were computed from periodic, inorganic water-quality data for 38 constituents collected between 1974 and 2014 for compliance monitoring of nearly 13,000 public-supply wells (PSWs) in the State of California. Mann-Kendall (MK) rank correlations and Sen's slope estimator were used to detect statistically significant trends for the entire period of recorded data (long-term trend), for the period since 2000 (recent trend), for different pumping seasons (seasonal trend), and for reversals of trends. Statewide, the most frequently detected trends since 2000 were for nitrate (36%), gross alpha/uranium (10%), arsenic (14%), total dissolved solids (TDS) (23%), and the major ions that contribute to TDS (19-28%). The Transverse and Selected Peninsular Ranges (TSPR) and the San Joaquin Valley (SJV) hydrogeologic provinces had the largest percentage of areas with moderate to high nitrate concentrations and groundwater quality trends. Improving nitrate concentrations in parts of the TSPR is associated with long-term managed aquifer recharge that has replaced historical, agriculturally affected groundwater with low-nitrate recharge in parts of the TSPR. This example suggests that application of dilute, excess surface water to agricultural fields during the winter could improve groundwater-quality in the SJV over the long term.
加利福尼亚州地下水质量状况改善和恶化的区域采用基于组分浓度和趋势斜率（Sen）方向和幅度的新指标对井进行空间加权评估。将个体井的分数汇总到覆盖全州公共供水地下水资源的 2135 个等面积网格单元中。空间加权允许结果在局部（井或网格单元）、区域（地下水盆地）、省或全州范围内进行聚合。结果将低到中等浓度（未受影响）的恶化（浓度增加趋势）区域与中等到高浓度（受损）的恶化区域区分开来。结果还以同样的方式区分改善区域（浓度下降趋势）。从 1974 年至 2014 年收集的 38 种成分的定期无机水质数据中计算了多年到十年的地下水水质趋势，这些数据是为了监测加利福尼亚州近 13000 口公共供水井（PSW）的合规性。Mann-Kendall（MK）秩相关和 Sen 的斜率估计用于检测整个记录数据期间（长期趋势）、自 2000 年以来（近期趋势）、不同抽水季节（季节性趋势）和趋势反转的统计上显著的趋势。自 2000 年以来，全州范围内最常检测到的趋势是硝酸盐（36%）、总α/铀（10%）、砷（14%）、总溶解固体（TDS）（23%）和导致 TDS 的主要离子（19-28%）。横断层和半岛山脉（TSPR）和圣华金河谷（SJV）水文地质省的硝酸盐浓度中等到高的区域百分比最大，地下水质量趋势也是如此。TSPR 部分地区硝酸盐浓度的改善与长期管理的含水层补给有关，该补给用 TSPR 部分地区的低硝酸盐补给替代了历史上受农业影响的地下水。这一例子表明，在冬季将稀释的地表水应用于农业领域可能会长期改善 SJV 的地下水质量。
