Chemical weathering and CO2 consumption rates of rocks in the Bishuiyan subterranean basin of Guangxi, China.

To investigate the influence of chemical weathering on CO2 consumption, an analysis was performed of water chemistry by applying water chemistry equilibria methods in the Bishuiyan subterranean basin, SW China. The average value of total ion concentrations (TZ+) was 1,854.97 µEq/L, which was significantly higher than the global average value (TZ+ = 1,250 µEq/L). Ca2+ and HCO3- were the main ionic constituents in the waters. SO42- and NO3- concentrations were relatively higher than other anion concentrations, and Cl- concentrations were consistently the lowest. Dissolved load balance models result showed that carbonate weathering, silicate weathering, and atmospheric input were the primary ionic contributors, wherein the effects of carbonate weathering > silicate weathering > atmospheric input for the whole catchment, with the exception of Taiping, where silicate weathering was prominent over carbonate weathering. In addition, these analyses indicated that the erosion via rock weathering was also affected by atmospherically derived CO2 and allogenic acids. The estimated yield by quantitative calculation for the carbonate weathering rate was 59.7 t/(km2 year), which was 4.40 times higher than that of silicate weathering rate. Further, the carbonate and silicate weathering components of the carbon sink accounted for 71.2% and 28.8%, respectively, of the total basin rock weathering carbon sink.

[Response Mechanism of Trace Metals in the Bishuiyan Subterranean River to the Rainfall and Their Source Analysis].

High-frequency sampling was conducted at the outlet of Guangxi Bishuiyan karst subterranean river using an automatic sampler during the rainfall events. The hydrochemical drymanic variation characteristics of trace metals (Cu, Pb, Zn, Cd) at the outlet of Guangxi Bishuiyan karst subterranean river were analyzed, and the sources of the trace metals in the subterranean river as well as their response to rainfall were explored. The results showed that the rainfall provoked a sharp decrease in the major elements (Ca²âº, Mg²âº, HCO3⁻, etc.) due to dilution and precipitation, while it also caused an increase in the concentrations of dissolved metals including Al, Mn, Cu, Zn and Cd, due to water-rock reaction, sediment remobilization, and soil erosion. The water-rock reaction was more sensitive to rainfall than the others, while the sediment remobilization and soil erosion took the main responsibility for the chemical change of the heavy metals. The curves of the heavy metal concentrations presented multiple peaks, of which the maximum was reached at 9 hours later after the largest precipitation. Different metal sources and the double-inlet structure of the subterranean river were supposed to be the reasons for the formation of multiple peaks. During the monitoring period, the average speed of the solute in the river reached about 0.47 km · h⁻¹, indicating fast migration of the pollutants. Therefore, monitoring the chemical dynamics of the karst subterranean river, mastering the sources and migration characteristics of trace metal components have great significance for the subterranean river environment pollution treatment.