Impact of global change on karst groundwater mineralization in the Jura Mountains

Chemistry of karst groundwater is related to conditions prevailing within the karst underground as well as at the land-surface within the recharge area. It is dominated by the dissolution of calcite and/or dolomite, which is strongly triggered by the presence of high pCO2 in soils at the top of the bedrock. Dissolution (water mineralization) is clearly influenced by soil pCO2, i.e. by global changes such as land-use, agriculture practices and climate change. However, the dissolution of carbonates is considered as a quite significant carbon sink for the Earth Atmosphere. Assessing the evolution of carbonate water mineralization can thus help characterizing the evolution of the carbon sink related to carbonate dissolution. The main goal of the study is to check the presence of trends with a high statistical relevance in groundwater quality data along the past 20 years. Causes potentially explaining the observed trends, such as land-use, agriculture practices and global warming are analyzed and discussed. The long term evolution of parameters related to carbonate dissolution are discussed and extrapolated as they may have consequences for the Global Carbon Cycle. The analysis is based on three independent data-sets stretching over more than 20 years each, coming from more than 40 sources. Statistical tests (Mann-Kendall trend test) indicate clear trends for compounds related to groundwater mineralization: increase in temperature (by about 0.5 °C/25 years), decrease in pH, increase in bicarbonate (by about 5%), and positive or negative trends for major ions directly related to human practices. Data and analysis suggest that carbonate dissolution is quickly increasing as a consequence of climate warming. Considering the largely accepted fact that carbonate dissolution acts as carbon sink for the atmosphere, it can be postulated that the observed increase could act as a negative feedback mechanism, tending to slow down the atmospheric increase in CO2.