As global warming becomes more and more serious due to the increase of greenhouse gases, especially CO2, the global carbon cycle research has attracted increasing attention. Karst processes-related carbon cycle, as a key part of the global carbon cycle and a result of the water-carbonate rock-CO2 gas-aquatic organism interaction, significantly affects the global carbon budget. Analyzing the relevant karst hydrochemical changes could not only enhance the understanding of the karst processes but also reveal the driving forces and intensity of the karst processes-related carbon cycle.
Prof. LIU Zaihua’s group from the State Key Laboratory of Environmental Geochemistry (SKLEG) at the Institute of Geochemistry, Chinese Academy of Sciences (IGCAS) collected monthly hydrochemical data and stable carbon isotope composition (δ13C) of dissolved inorganic carbon (DIC) in karst water samples from September 2007 to October 2012 to study the controlling mechanisms on DIC geochemistry and δ13CDIC under different conditions of climate and land cover in three karst catchments: Banzhai, Dengzhanhe and Chenqi, in Guizhou Province, SW China.
The research finds that the root respiration and organic carbon decomposition with weak carbonate bedrock dissolution result in the lowest δ13CDIC, low pCO2 and EC, low cation and anion concentrations at Banzhai where there is dense vegetation coverage but thin soil layer with less land use activity. Chenqi has large soil CO2 input due to a thick soil layer and strong farming activity, and very weak carbonate bedrock dissolution because of a short groundwater flow path and steep surface slope; consequently, the karst water has low pH and δ13CDIC, high pCO2 and low SIc. At Dengzhanhe, strong carbonate and gypsum bedrock dissolution and lesser soil CO2 input due to more karst rocky desertification contribute to heavier δ13CDIC, high EC and high cation and anion concentrations.
In addition, there are clear seasonal cycles observed in hydrochemical parameters and δ13CDIC in the karst waters of the study areas, with high pCO2 and low pH, EC, SIc and δ13CDIC in the warm and rainy seasons, and vice versa during the cold and dry seasons.
Furthermore, a strongly positive shift (>3‰) in δ13CDIC occurred in the drought year, 2011, indicating that δ13CDIC in groundwater systems can be an effective indicator of environmental and/or climate changes. The δ13C records of travertine deposited from these karst waters may permit the reconstruction of high-resolution records of paleoclimate change and extreme events.
The study results have been published in Geochimica et Cosmochimica Acta.
1. M. Zhao, C. Zeng, Z. Liu, S. Wang, Effect of different land use/land cover on karst hydrogeochemistry: a paired catchment study of Chenqi and Dengzhanhe, Puding, Guizhou, SW China, J. Hydrol., 388 (2010), pp. 121–130.
2. Min Zhao, Zaihua Liu*, Hong-Chun Li*, Cheng Zeng, Rui Yang, Bo Chen, Hao Yan (2015), Response of dissolved inorganic carbon (DIC) and ?13CDIC to changes in climate and land cover in SW China karst catchments, Geochimica et Cosmochimica Acta. doi:10.1016/j.gca.2015.05.041.
State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, CAS
Department of Geosciences, National Taiwan University
(By LIU Zaihua Group)