Water geochemical characteristic variations in and around a karst-dominated natural reserve area, southwestern China

This paper reports original data on the physical and chemical parameters of precipitation, river water and groundwater in and around the Longhushan Nature Reserve Area, located in southwestern China karst region, and provides a preliminary characterization of the hydrogeochemical process governing the natural water evolution in this area. The rainfall and river water mainly pertain to the HCO₃ ⁻–Ca²⁺ type and groundwater mainly pertain to the HCO₃ ⁻–Ca²⁺ + Mg²⁺ type. The HCO₃ ⁻ was the predominant anion and Ca²⁺ was the predominant cation in all waters, respectively. The Gibbs Boomerang Envelop model, the 1:1 relationship of Na⁺ plus K⁺ versus Cl⁻ as well as the 1:1 relationship of Ca²⁺ plus Mg²⁺ versus HCO₃ ⁻ all suggested geochemical weathering is the main controlling factor for the geochemical compositions of this natural water. In surface water, the Mg²⁺/Ca²⁺ ratios ranged from 0.32 to 0.42 and the Na⁺/Ca²⁺ varied between 0.04 and 0.05. In the groundwater, the Mg²⁺/Ca²⁺ ratios varied from 0.37 to 0.62 and were below the ideal ratio of 0.8. These ratios showed the presence of a dolomite source. Analysis of trace elements showed that As, B, Pb, Se, Sr, V and Zn elements were abundant in the natural water during summer in this region.