Assessment of land subsidence mechanisms triggered by dolomitic marble dissolution from hydrogeochemistry and stable isotopes of spring waters

Johannes Barth1, Rohana Chandrajith2, H.A.H. Jayasena2, Robert van Geldern1
1 Lehrstuhl für Angewandte Geologie / GeoZentrum Nordbayern, Friedrich-Alexander-Universität Erlangen-Nürnberg
2 University of Peradeniya, Department of Geology, Peradeniya, Sri Lanka

P 2.10 in Aquifer systems in Europe and beyond

Springs draining a small humid tropical watershed composed of geologically dolomitic marbles in Central Sri Lanka were investigated for their major ion chemistry, water stable isotope composition (δ18O and δ2H) and the carbon isotope composition of dissolved inorganic carbon (δ13CDIC). Dissolved Ca2+ and Mg2+ were the dominant cations and were balanced largely by bicarbonate. All collected spring water samples scattered around the local meteoric water line with values from -31.9 ‰ to -46.8 ‰ for δ2H and from -5.5‰ to -7.4‰ ford δ18O against VSMOW. This indicates local groundwater recharge pathways by regional precipitation rather than water from deeper aquifer systems. Concentrations of dissolved inorganic carbon (DIC) ranged from 0.91 to 9.38 mM/L and δ13CDIC ranged from -22 ‰ to -14 ‰ against the international Vienna Pee Dee Belemnite Standard (VPDB) with an average of -16 ‰. Our interpretation is that spring waters from carbonate rocks had increased DIC and δ13CDIC along with elevated pH values. Combined δ13CDIC and Ca2+ and Mg2+ contents suggest that groundwater evolution was dominated by dissolution of usually difficult to weather dolomitic marble. This unexpected weathering process was favoured by intense rain and high ambient temperatures contributed to excessive CO2 production in tropical soils. This weathering resulted in karst structures with high hydraulic conductivities that rendered the terrain tectonically less stable.

 



Chandrajith, R., Jayasena, H.A.H., van Geldern, R. and Barth, J.A.C. (2015) Assessment of land subsidence mechanisms triggered by dolomitic marble dissolution from hydrogeochemistry and stable isotopes of spring waters. Applied Geochemistry, 97-105. doi: 10.1016/j.apgeochem.2015.03.020