[Investigation of nitrogen, phosphorus and microbial contamination in Laolongdong underground river system of Chongqing].

With urbanization, groundwater in China has been widely polluted. Karst groundwater is important in southwest China, and would be difficult to recover once contaminated. NO3(-), PO4(3), NH4(+), total coliform, total E. coli and fecal coliform were chosen as indexes in the study of groundwater of Laolongdong Underground River System in Nanshan Mountain, Chongqing. After a few years of survey, the results showed that NO3(-), NH4(+) and PO4(3-) concentrations in the water were all above the nature value, especially NH4(+) and PO4(3-). The NO3(-) concentration of Guihuawan spring ranged from 19.78-68.55 mg x L(-1), in some months, above the recommended water quality guideline (50 mg x L(-1)) according to Standards for Drinking Water Quality set by World Health Organization. NH4(+) and PO4(3-) concentrations in Laolongdong underground river varied from 2.71-12.92 mg x L(-1) and 0.16-11.22 mg x L(-1). The NO3(-) concentration in Laolongdong underground river was lower than in karst spring; however, the concentrations of NH4(+) and PO4(3-) were higher than in the spring. It seemed that the NO3(-) concentration tended to decrease from 2008 to 2013 in the underground river caused by urbanization, reduction of farmland and reducing environment. However, waste water with a high PO4(3-) concentration led to an increasing trend in the PO4(3-) concentration in underground river. Microbial contamination was extremely serious, and even far exceeded class V of water quality standards of China. For example, the concentration of fecal coliform in the groundwater ranged from 3.4 x 10(4)-3.68 x 10(4) CFU x mL(-1). Because of the special hydrogeological structure, karst depressions, skylights and sinkholes can lead pollutants easily to the underground water. Agriculture activity, sewage from towns, enterprises and residential areas were the major sources of nitrogen, phosphorus and microbial contamination.