Study On Spatial And Temporal Variation Characteristics Of Groundwater Dynamics Of Dongshan County In Fujian Province

Dongshan County is an island in southeastern of Fujian Province, its production and living water is mainly rely on groundwater resources. The groundwater in this area is shallow groundwater, which is characterized with relatively small buried depth, fast renovation and vulnerability to pollution. In recent years, with the rapid development of the economic society and the increasing of urban and rural population, the increasing demand for groundwater has caused the groundwater depth changed and the pollution of water body. Therefore, it is urgent to study spatial and temporal variations of groundwater depth and water chemistry characteristics of Dongshan County in order to provide scientific and reliable basis for the sustainable utilization of groundwater.Based on the natural geography, geology and hydrogeological conditions of Dongshan County, groundwater dynamic data（buried depth and water quality） monitored during 2000-2011 were selected for making spatial and temporal analysis. Firstly, using the ArcGis software as a platform and drawing the diagrams of the groundwater depth changes in the area in 2003, 2007 and 2011, respectively, and analyzing the spatial changes of the groundwater depth; then the correlation between the groundwater depth and precipitation & evaporation in this area was performed by correlation analysis method in order to analyze the temporal variation tendency of the groundwater depth; then the correlation between the groundwater depth and precipitation & evaporation in this area was performed by correlation analysis method in order to analyze the temporal variation tendency of the groundwater depth. After that, using the Shorclife classification and piper trilinear graph to classify the water chemistry characteristics of the study area; and using factor analysis method to analyze the chemical composition of groundwater and to determine the main water quality indexes which influence the groundwater quality in the study area. Finally, the single factor analysis and comprehensive evaluation method are applied to evaluate groundwater quality in the study area, and the results are visualized by ArcGis software. The following conclusions are obtained:（1）The variation of groundwater depth in the study area is affected by the change of precipitation, and the effect of evaporation is very small; The groundwater depth in the study area has a slightly decreasing tendency, which indicates that the groundwater level in the area is rising.（2）The main chemical types of groundwater in the dry season is Cl-Ca?Na?Mg and Cl-Na?Ca?Mg, the major ions are Na+、Ca2+、Mg2+ and Cl-, while the main chemical types of groundwater in the wet season is Cl-Na and Cl-Ca?Na, the major ions are Na+、Ca2+ and Cl-.（3）Factor analysis method indicated that the first main factor of groundwater quality in the study area is TDS、Cl-、Na+、TH、Mg2+、K+、SO42- and Ca2+, it indicates that the leaching effect and brackish water mixing plays a major role for the composition of groundwater.（4）（4）TDS、Cl-、NO₃^-、NO_<sup>2-、NH₄⁺、Fe³⁺、COD and Mn²⁺ are the main impact indicators of the groundwater quality in the study area during the dry season, TH、TDS、Cl-、NO3-、NO2-、NH4+、Fe3+、COD、Cu2+ and Mn+ are the main influence targets of the groundwater quality in the study area during the wet season. The results of the single factor of groundwater quality assessment showed that the majority of groundwater is within Class Ⅳ and Ⅴ, among them, Cl- and NO3- evaluation indexes reaching Class V of groundwater quality standard accounts for maximum number of total groundwater samples, indicating the domestic pollutants and human and animal wastes in this area. While the SPA evaluation of groundwater quality results showed that groundwater quality is better. But from the perspective of the safety of drinking water, the results of the single factor evaluation method is more reliable.