| Groundwater is an important resource in coastal areas mainly for irrigation and drinking, which is directly related to human health. And groundwater in coastal areas is easily affected by land-based activities or sources and seawater intrusion. Seawater intrusion caused changes of chemical composition in groundwater and salinization of groundwater. Besides, salty irrigation water could easily cause soil salinization and damage to crops growth. Land-sourced pollution brought heavy metals and other harmful substances to groundwater, thus resulting in metal accumulation in soil and plant as well as health hazards to human through the food chain.High dependence on groundwater existed in Leizhou peninsula and Hainan Island. Groundwater consumption was 646 million m3 in Leizhou peninsula, accounting for 24% of total water consumption; groundwater water supply capacity is 302 million m3 in Hainan Island, accounting for 6.7% of total water flow. But so far, there is no systematic evaluation and analysis on chemical characteristics of groundwater and heavy metal pollution in the area. Groundwater in Leizhou peninsula and Hainan Island was selected in this study and analysis on applicability of long-term use of groundwater was carried out. In this study, 40 meters deep well were selected to analyze formation conditions; water chemical data were analyzed, long-term effects of groundwater irrigation were investigated; heavy metal contents were tested and analyzed; potential of health risk was studied; technological and management methods were proposed to control risk.In this paper, the main results are as follows(1) Concentrations of all ions except HCO3- exceeded the acceptable limits of drinking water standard; the most dominant ions are Cl- and Na+ in groundwater, followed by SO42- and Mg2+. The four ions increased with TDS; tide period had little impact on content of chemical compositions of groundwater; hourly variation pattern of main chemical parameters was influenced by stratums, which belong to the weak variation and moderate variation.(2) Nemerow index method for evaluating groundwater was applied to obtain results that groundwater was V class, differences of irrigation water of cannot be distinguished. So Shoka Lev classification method, Sulin classification and Piper method were used to classify groundwater chemical type. Groundwater is mainly Cl–Na type. Based on the rate of hydrogeochemical factors, Gibbs diagram and the formation geological background, the formative mechanism was investigated, and results showed that groundwater formed relatively stable component features based on seawater intrusion, evaporation and evaporation sourced pollution..crystallisation, and cation exchange process(3) Groundwater has posed a threat because of heavy metals pollution. Cd, As and Al content of all water samples were exceeded the permissible limits of drinking water standard and exceeded rate were 100%. The concentrations of Pb, Ni, Fe and Mn in some samples were higher than the drinking water standards and exceeded rate respectively were 66.7%, 16.7%, 16.7%, and 16.7%. Accounting for 66.7% of total samples, were having Cd concentration higher than the irrigation water standard. Groundwater heavy metal exceeded mainly because of effect of rapid development of industry, agriculture and aquaculture.(4) Set pair analysis evaluation was carried out based on rough set theory model and comprehensive evaluation of groundwater to irrigation suitability was conducted. Results showed that 83.3% of groundwater in the study area was not suitable for irrigation. Effect to the quality of irrigation water is mainly caused by high degree of mineralization and salinization, which is not conducive to plant growth, and cause soil salinization. Besides, the second reason is that heavy metals exceeded seriously and do harm to human health by accumulative toxicity.(5) Preparing water hyacinth into biological carbon could remove most harmful heavy metals Cd in the groundwater. Experimental results showed that removal rate exceeded 80% with perfect effect of removal. This study provided a new way to control groundwater pollution and improve local groundwater availability.(6) High salinity groundwater not suitable for irrigation directly can be mixed with fresh water to meet irrigation requirements. Meanwhile, environment management should be strengthened to reduce the impacts of land-All in all, Groundwater is threatened by sea water intrusion and land-source pollutions. There is a risk in terms of availability. In order to achieve sustainable development, measures should be made to reduce risk and improve the availability of groundwater. |
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