Hydrochemical Characteristics and Controlling Factors of Typical Dolomite Karst Basin in Humid Subtropical Zone

Abstract

The hydrochemical characteristics and variation rules of water in karst areas are important for the basic research of karst field. Because only a few researches focused on the hydrochemical characteristics of humid subtropical dolomite karst basins in the past, the Shanmuhe Basin and its subbasin Huangzhouhe Basin in Shibing Dolomite Karst World Natural Heritage Site in China were selected as the study area. A total of 215 water samples were collected and analyzed. It was found that the hydrochemical type of subtropical dolomite karst basin is HCO3-Ca·Mg type, which is different from that in limestone areas and shale districts, which is HCO3-Ca type for both; EC, Ca2+, Mg2+, HCO3-, Mg2+/Ca2+, and Mg2+/HCO3- have similar spatial variations, which are lower in allogenic water in the upstream in the northwest of the basin and become higher when the water enters the dolomite karst area in the mid and downstream of the basin, and SIC and SID of the allogenic water in the upstream are below zero, while those become saturated after entering the dolomite area in the mid and downstream; the monthly variation of hydrochemistry shows that the seasonal variation of ion concentration is not obvious, and there is a dilution effect in rainy seasons, but the variation of ion concentration is small and relatively stable; higher HCO3- concentration and Mg2+/Ca2+ in the pure dolomite basin are higher than those in the impure dolomite basin; the main influencing factors of the hydrochemical features are geological background especially the lithology, and the water chemistry is mainly controlled by rock weathering and water-rock interaction; rainfall import is low and the low concentrations of K+, Na+, NO3-, Cl-, and SO42- in water indicate that human activities have little effect on the hydrochemistry in the study area.

Study on the Equivalent Permeability Coefficient of Karst Conduit with Single Conduit and Multigroup Fissures

“…e indoor test model can be divided into four parts: water supply system, in which water from nearby lakes is pumped by submersible pumps and enters the water supply tank; monitoring system, which is a row of observation hole preset above the conduit, and the observation hole is connected with the conduit and the fissures nearby, and the water level of the conduit in the flow field can be directly measured by a steel tape; water storage system, in which the water discharged through the conduit enters the overflow tank and then flows into the water tank, and the water discharge will be recorded by reading the water level and bottom area of the water tank; rock mass model, including rock block, karst conduit and two groups of fissures which are perpendicular to each other, simulates rock block by the module bonded with acrylic board (i.e., without considering seepage inside rock block), simulates karst fissure by space between modules (two surfaces of crack are parallel to each other and the distance remains constant), and simulates karst conduit by presetting round pipes in the module (the pipe is straight and its diameter remains unchanged) [12][13][14][15]. e pipe is separated by vertical fissures, and water in the fissure and water in the pipe can be exchanged with each other in the process of groundwater flowing [16].…”

Experimental Investigation on Influence of Acidic Dry-Wet Cycles on Karst Limestone Deterioration and Damage

“…Karst landscapes are gradually suffering from human activity and climate change, and the acceleration of karst landscape degradation in Guilin caused by acid rain is noticeable [1,2]. Owing to the adverse effect of acid rain, some active minerals in rocks will be dissolved, and mineral dissolution often produces microstructural variations that change the macroscale properties, such as permeability, porosity, pore size distribution, strength, hardness, fracture characteristics, and creep [3][4][5][6][7][8][9][10]. In addition, more than 70% of the rainfall occurred from April to August according to the recorded data from 1951 to 2019 in Guilin [1].…”