Spatial distribution and sources of groundwater phosphorus in Dezhou Region

Groundwater quality has been related to drinking water safety and human health, and groundwater pollution directly affecting hydro-ecological environment. High phosphorus in the drinking water has been noted to reduce calcium and vitamin D absorption in humans, which has the potential negative effects on the health of the elderly. In this study, 27 water samples were collected from the groundwater system in the Dezhou Region located in the lower reaches of the Yellow River where many residents use groundwater for drinking. Site electrical conductivity (EC) and pH were determined in situ. The samples were analyzed for concentrations of total phosphorus (TP), orthophosphate (P-ortho), dissolved total phosphorus (TDP) and dissolved orthophosphate (P-D-ortho) in groundwater using UV spectrophotometer as described in the methods for Water and Wastewater Monitoring and Analysis of China and Environmental Protection Agency (EPA) of the United States. The sources and spatial distribution of phosphorus were interpreted using the spatial statistical analysis method. Results showed that the concentration ranges of TP, P-ortho, TDP and P-D-ortho were 0~1.49 mg·L^-1, 0~0.11 mg·L^-1, 0.04~0.69 mg·L^-1 and 0~0.06 mg·L^-1, respectively. EC and the concentrations of TP, P-ortho, TDP and P-D-ortho showed large spatial variations. There was high groundwater EC (770~ 5 530 μS·cm^-1) in the study area, which obviously increased from the upstream to the downstream of the river. The spatial distributions of TP and TDP gradually decreased from upstream to downstream. Although high-value areas of P-ortho were noted, P-D-ortho distribution did not significantly change. Dominant factors that influenced phosphorus concentrations in groundwater included phosphorus infiltration in surface water and human activity. Groundwater samples in the study area were collected at a depth of less than 50 m. The shallow aquifer was the Yellow River alluvial sands which mainly comprised of silt, fine sand and medium sand of 10~25 m thickness. The river was the main source of recharge to the groundwater system. Hence surface water phosphorus easily leaked into the underlying groundwater in the geological formations. This was especially the case for groundwater systems in the vicinity of the river. Human activity included point source pollution (from improperly handled industrial wastes, domestic sewages) and non-point source pollution (from pesticides and agricultural fertilization). The maximum concentration of TDP in Dezhou Region was 0.69 mg·L^-1 with an average of 0.20 mg·L^-1. The overproof rates of TDP were respectively 7.41%, 62.96% and 40.74% based on the drinking water standards of the European Community (0.5 mg·L^-1) and Class II (0.02 mg·L 1-1) and Class III (0.1 mg·L^-1-1) of the Surface Water Environment Quality Standard of China (GB 3838-2002). This study provided the needed scientific basis for evaluating the impact of groundwater phosphorus pollution on human health and hydro-ecological environment.