Comparative Characteristics Of The Water Quality In Subterranean Streams For Karst Area

In Southwest China, karst is common geographic feature. Groundwater is a major form of water resource, and the surface-subsurface double layer structure is controlled by specific natural conditions in karst region. It plays an important role in improving people’s living standard and in agricultural production. There are two north-south subterranean streams flowing through a typical developed karst valley at the junction of Shapingba, Beibei and Bishan in Chongqing. Samples were taken from the two subterranean stream systems to study chemical characteristics of the water, to evaluate its water quality, to analysis major pollutants (nitrates and DIC) sources, ultimately to combine the land use types, soil properties and human activities so as to identify the reason and the impactions for deteriorations of water quality. It helps to understand water quality characteristics and the trends of two subterranean streams north and south in QingMuguan., so as to provide complementary recommendations for the protection of water quality trough the subterranean stream in the karst region of Southwest China.In the research process, water samples were collected in the field and the experimental work was performed in the lab from November in2012to November in2013. Combining with existed research data in2007and2010, water quality of the two subterranean stream was studied comprehensively. Preliminary conclusions are as follows: (1)The hydrogeochemical type of the two subterranean streams is HCO3-Ca. Concentration ratio of Na+is higher than K+in subterranean stream of both north and south sections, and it results from huge amount of plan absorption of K+. The concentration of ions which are related to dissolved of the limestone is higher in downstream than in upstream. The main reason is the migration process continues to dissolve the rock around in media channels of subterranean stream in karst areas. Values of SO42-of subterranean stream is relatively high in both northern and southern subterranean streams, mainly due to the abandoned coal hole in Qingmuguan, where the main component of the coal cave is pyrite. The mean ranges of pH and EC of subterranean stream in southern section is higher than the subterranean streams in northern section, this means that water quality of the subterranean stream in southern valley of Qingmuguan is worse than in northern valley, and it is more affected by human activities.In the subterranean stream of northern valley, there are many residual fertilizers and poultry metabolites flow from upstream to downstream in forms of surface runoff and subsurface run off. Values of NO3-and Cl-are higher than the subterranean stream in the southern valley, and it is more affected by the pollution of fertilizer, which contains N and Cl. Values of Cl-and SO42-are higher at the exit of subterranean stream in the southern valley because it is affected by human activities.(2) The water quality of two subterranean stream were evaluated by statistical methods, which shows that the mean score principal component analysis’s complex is-0.95of the subterranean stream in northern valley; the water quality is affected by residual fertilizers,poultry metabolites while in the abandoned coal hole. The mean score principal component analysis’s complex is0.15of the subterranean stream in southern valley.The result is matching the result which measured by the national groundwater quality standard.which proves water quality of the subterranean stream in southern valley is polluted by some extent, it is bad than the water quality in north.(3) The evaluation of δ15N in the subterranean stream in Qingmuguan shows that:The value in northern valley’s subterranean stream is lower than the south, with even less than10‰. Amount of Nitrate depends on fertilizer and the mineralization of soil organic nitrogen. In southern valley’s subterranean stream, sources of Nitrate from Tianchi to Gantianchi are fertilizer and the mineralization of soil organic nitrogen. Values about815N of Laijiacao and Dingjia Cave is higher and changes significantly, and sources of Nitrate may be manure and sewage.The subterranean streams of both northern and southern valleys, Carbonic acid, Sulfuric acid and Nitrate’s dissolution of carbonate rocks, constitute the main source of DIC. With the influence of acid rain and agricultural activities, the degree of corrosion to carbonate rocks in the subterranean stream by sulfuric acid and nitric acid increased, the values of SO42-and NO3-also increased. The value of δ13CDIC can be used to trace part of the source of pollutants in subterranean streams. (4) We should pay attention to the impact of land use on water quality in subterranean stream basin of northern valley. There are more paddy fields in the northern valley, and the demand for agricultural fertilizer is large, which contributes to more NO3-Vand Cl-than the southern valley. Therefore, Organic matter of the soil must be combined to adjust the land use, and the fertilizer’s application should be limited to reduce pollution caused by residual fertilizers on downstream water quality. The water quality of subterranean stream in southern section is influenced by anthropogenic more seriously. The reduction water flow in the large karst depressions is mainly caused by anthropogenic drainage, poultry breeding and the aquaculture, which caused deterioration of water quality.Hard work to protect water sources and a reasonable standard of rural aquaculture are needed.