Hydrochemical Response of Epikarst Spring to Rainfall: Implications of Nutrition Element Loss and Groundwater Pollution
Qiang Li, Hailong Sun, Jinliang Wang
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Institute of Karst Geology, CAGS, Karst Dynamics Laboratory, MLR, Guilin 541004, China
Pol. J. Environ. Stud. 2010;19(2):441–448
High-resolution measurements of rainfall, water level, pH, conductivity, temperature, [K+], [NO3¯] and [Ca2+] of the Landiantang epikarst spring at Nongla, Mashan County in Guangxi Province, China were recorded by using data loggers with a time interval of fifteen minutes. The results showed that the pH of the Landiantang Spring dropped and the conductivity fell as well. As Ca2+, Mg2+ and HCO3¯ were the dominant ions, the linear relationships between conductivity and those ions were developed to calculate variations in SIC, SID and LogPCO2 of the spring during rainfalls. The LogPCO2 of Landiantang Spring during rainfalls was lower than that at lower flows, and its SIC and SID also were lower. It can be figured out that the dilution of precipitation controls the hydrochemical variations of Landiantang Spring during rainfall, and the water-rock-gas interactions control the hydrochemical variations of the spring at the usual time. The process of water-rockgas is universal to Landiantang Spring because after rainfall, gas with high CO2 concentration dissolves in water flowing as spring, which in turn becomes more highly undersaturated, dissolves more dolomite to make up for the effect of precipitation dilution, and the conductivity renews slowly after rainfall. However, to explain the hydrological and chemical changes, the dilution of precipitation may be more important during rainfall, because it is the key process to controlling the chemical evolutions of the spring. The [K+] and [NO3¯] rise rapidly as the [Ca2+] falls during rainfall. Therefore, an important conclusion is hypothesized that the restricted growth of plants in karst regions is possibly caused not only by the low labile trace elements in soil, but also by the loss of these nutritional elements in the ecosystem. Moreover, fertilizers, for example, can also be brought away through the epikarst zone by flowing water due to high fissure and permeability of the epikarst zone, which will contaminate epikarst spring and groundwater, and may produce serious environmental problems. Thus, how to develop effective solutions to karst water-related environmental challenges will become the primary study of karst aquifers and water resources in the future.