Research On Variational Characteristics And Sources Of Hydrochemical Components In Huaibei Plain, Anhui Province

Huaibei Plain, which lies in the north of the Anhui Province and the south of the Huanghuaihai Plain, is the important foundation of food and agricultural bypriducts commodity of our country. Because of the temporal and spatial maldistrubution of precipitation and evaporation, and the serious contamination of the runoffs in this plain, groundwater has become an important source for local residents, and it's necessary to study the condition of the groundwater. Based on the investigation of the groundwater geochemical data from the available 44 national or provincial surveillance sites, the characteristics of the shallow groundwater in Huaibei Plain was analyzesed systematically, the variation characteristics of the hydrochemical components with the depth, time and rainfall was clarified; the main pollutants were identified, then the correlation between the main pollutants and their correlative ions were studied, and the main source and influent factors of the contamination in the shallow groundwater of the study area were revealed. The main conclusions were as follows:1) the concentrations of alkaline earth metals were higher than that of alkaline metals in shallow groundwater, but situations in medium-deep and deep groundwater were opposite. The water type changed from HCO₃ to HCO₃-Cl as the depths increased. Na⁺, Cl^-, HCO₃- and SO₄^2- concentrations showed the increasing trend as the depths increased, Ca²⁺ concentration was higher in shallow water, and Mg²⁺ distributed well. The pH values were more close to neutrality during the rainy season than those during dry season, the conventional ions contents were higher during the rainy seasons than those during the dry seasons.2) Fluoride, nitrate nitrogen, iron, manganese were found to the main pollutants of the study area, through the analysis on the detected ions. The concentrations of all the main pollutants except Fe, were higher in the north of the study area than those in the south,especially those in the northeast, which were usually several or even multiple times as the concentrations in other districts. Of all the towns in the study area, Louzhuang Town in Lingbi County is the most seriously polluted town. Moreover, the F^- and Fe contents in groundwater increased as the depth increasing, while the NO₃—N content decreased as the depth increasing. The concentrations of Mn in half of the groundwater samples increased as the depth, but showed the opposite trend in the other half of the samples. Most of the study ions showed the increasing trend with the time. The highest concentrations of all the study ions except Mn, were found in 2008. According to the comparison of the main pollutants contents during the dry seasons and rainy seasons, the higher contents were found during the rainy season.3) Through the analysis on the correlations between F^- and Cl^-, Ca²⁺,( K⁺+Na⁺)/Ca²⁺ ratio and pH value, the fluoride was found to derived from the solution of fluorine minerals, which is probably fluorite (CaF2), and the alkaline environment provided advantage to the release of fluoride. High fluoride groundwater is probably exist, when the (K⁺+Na⁺)/Ca²⁺ ratio reaches 2.2137. NO₃—N was believed mainly derived from nitrogenous fertilizer and animal excrement rather than from human living filth, and there were not many wells that effected by the living filth and animal excrement directly, based on the some synchronized growth of NO₃—N and Cl^-, and the high concentrations of PO₄^3- and NH₄⁺ in some wells. So the domestic sewage may penetrate into the stratum from drainpipes such as cloaceas.4) According to the results of the factor analysis, the pollutants in the groundwater of the study area were affected by water-rock interaction, groundwater mixture process and anthropologic activities, the contribution ratio of which were 33%, 32% and 25%, respectively, and anthropologic activities also influenced the release of the ions in nature process.