Phosphorus is a necessary nutrient for all organisms. However excessive phosphorus can cause eutrophication in surface water. Groundwater can be an important nonpoint contributor of phosphorus to surface water bodies. Most groundwater phosphorus is in the form of orthophosphate and orthophosphate concentrations in California groundwater vary temporally and geographically. This study quantifies orthophosphate concentrations in water samples from public supply wells in California, evaluates temporal trends (both step and monotonic trends) in orthophosphate concentration for different areas of the state, and explores potential explanatory factors for the trends observed. Orthophosphate concentrations are low in 42 percent of the groundwater used for public supply in California, moderate in 43 percent, and high in 15 percent of this groundwater relative to reference conditions and a goal expressed by the USEPA for streams overlying the aquifers. The findings also suggest that orthophosphate concentrations increased in approximately one-third of this groundwater during the study period (2000 to 2018). The timing of orthophosphate increases observed in time-series evaluations coincided approximately with the timing of increases observed in step-trend evaluations, with both suggesting that the increasing trend occurred mostly before 2011. Principal component analysis (PCA) of the statewide dataset indicates that orthophosphate concentrations are antithetically related to dissolved oxygen (DO), and weakly associated with boron, arsenic, and fluoride. Step trend and time-series trend analyses using PCA were inconclusive.

中文翻译：

---

加利福尼亚州用于公共供水的地下水中正磷酸盐浓度的现状和趋势。

磷是所有生物的必需营养素。但是，过量的磷会导致地表水富营养化。地下水可能是磷对地表水体的重要的非点源贡献者。大多数地下水磷的形式为正磷酸盐，加利福尼亚地下水中的正磷酸盐浓度随时间和地理位置而变化。这项研究量化了加利福尼亚州公共供水井中水样中的正磷酸盐浓度，评估了该州不同地区的正磷酸盐浓度的时间趋势（阶跃和单调趋势），并探讨了观察到的趋势的潜在解释性因素。在加利福尼亚州，用于公共供水的地下水中正磷酸盐浓度较低，为42％，中等水平为43％，相对于参考条件而言，该地下水的含量要高出15％，这是美国环境保护局（USEPA）表示的对覆盖含水层的水流的目标。研究结果还表明，在研究期间（2000年至2018年），正磷酸盐的浓度大约增加了三分之一。时间序列评估中观察到的正磷酸盐增加的时间与阶跃趋势评估中观察到的增加的时间大致重合，都表明增加趋势主要发生在2011年之前。全州数据集的主成分分析（PCA）表明正磷酸盐从理论上讲，其浓度与溶解氧（DO）相关，而与硼，砷和氟化物的相关性较弱。使用PCA进行的步态趋势和时间序列趋势分析尚无定论。