摘要：Factors controlling the spatial distribution and temporal trend of groundwater quality at a national scale are important to investigate for sustaining livelihood and ecological balance. This study evaluated groundwater quality data for 12 parameters (n = 6405 for each parameter), collected from 97 groundwater monitoring stations (=289 monitoring wells) for ten years. Spatial distribution of groundwater quality parameters varied through the regional scale. Six parameters: T, EC, Casup2+/sup, Mgsup2+/sup, HCOsub3/subsup−/sup, and Clsup− /supwere having dominant increasing trend, remaining pH, Eh, Nasup+/sup, Ksup+/sup, SOsub4/subsup2−/sup, and NOsub3/subsup−/sup showed a dominant decreasing trend over time. Among land use types, the upland fields had the highest mean of groundwater NOsub3/subsup−/sup (22.2 mg/L), confirming plenty of application of fertilizers (5–10 kg/ia/i more than standard) to upland fields. Means of groundwater Clsup−/sup and Nasup+/sup (705.3 and 298.4 mg/L, respectively) in the residential areas are greater than those in other land use types by 408–685.9, 154.3–274.2 mg/L, respectively. Agricultural activities were the main controlling factor of groundwater NOsub3/subsup−/sup contamination in rural areas, domestic activities were responsible for groundwater Clsup−/sup and Nasup+/sup in urban areas, and seawater intrusion was controlling groundwater Clsup−/sup in coastal areas (within 10 km from sea). Groundwater hydrochemistry was controlled by the mechanism of geogenic rock and evaporation dominance. The rock dominance mechanism indicated that groundwater was interacting with rocks and resulted in groundwater chemistry. The findings of this study showed that groundwater was mainly contaminated by anthropogenic factors in some rural and residential areas. Effective measures by government authorities are needed to improve the groundwater quality.
