[Analysis of Temporal and Spatial Variations in Trace Element Migration in Karst Critical Zone:An Example of Jiguan...

To explore the temporal and spatial variations and the process of trace element migration in the karst critical zone, continuous fixed-point monitoring and sampling analysis was applied to measure each cave system component, which includes rainfall, soils, bedrock, drip waters, and their aerial sediment. Approximately 650 experimental data were obtained from October 2009 to May 2015 in a typical karst critical zone in north China-an interactive zone of the Jiguan Cave in the west Henan Province. The variations in and the migration rules of Ca, Mg, Ba, Sr, and δ¹³C as well as their ratios to different components were studied. The results show that:① Soil and bedrock are the main sources of drip water. The values of Mg, Ba, and Sr are consistent with the "soil-bedrock" two end-members model and their respective proportions are 43.6:56.4, 1.01:98.09, and 47.2:52.8. ② From the spatial perspective, element migration of each component in the cave system interactive zone is interrelated. Drip water inherits the signals of the soil and bedrock and the modern sediment can continue the element information of the drip water. Elements in the soil profile cause the leaching and deposition effect and the subsoil better inherits the information of trace elements in the bedrock. ③ From the temporal perspective, the migration of elements in the cave system interactive zone is complex. Because of the leaching effect, soil and drip water show obvious seasonal discrepancies. However, under the influence of karst water migration path, the prior calcite precipitation (PCP), and extreme arid and annual precipitation type, the seasonal discrepancy in the element concentrations in drip water is smaller than in soil. The PCP effect, selective leaching, and other factors change the continuity of elements released from sediment to drip water. ④ In order to systematically and comprehensively ascertain the trace element migration in the karst critical zone and energy transformation rules, the study of cave system should be based on the research of the cave's critical zone and should consider comprehensive information ranging from the atmospheric origins to secondary sediments.