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

作者：Chandrajith Rohana^*; Jayasena H A H; van Geldern Robert; Barth Johannes A C

来源：Applied Geochemistry, 2015, 58: 97-105.

DOI：10.1016/j.apgeochem.2015.03.020

This study presents geochemical results of springs draining a small humid tropical watershed composed of geologically dolomitic marbles in Central Sri Lanka. Water samples were investigated for their major ion chemistry, water stable isotope composition (delta H-2(H2O) and delta O-18(H2O)) and isotope composition of dissolved inorganic carbon (delta C-13(DIC)). From major ion chemistry Ca2+ and Mg2+ were the dominant cations and were balanced mostly by HCO3-. All collected spring water samples scattered around the local meteoric water line with values from -31.9% to -46.8% for delta H-2(H2O) and from -5.5% to -7.4% for delta O-18(H2O) 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-1 and delta C-13(DIC) ranged from -22% to -14% against VPDB with an average of -16%. Samples of spring water from carbonate rocks had increased DIC and delta C-13(DIC) together with elevated pH values. Combined delta C-13(DIC) and Ca2+ and Mg2+ contents suggest that groundwater evolution was dominated by dissolution of dolomitic marble. This unexpected weathering process was favored by intense rain and high ambient temperatures and excessive CO2 production in tropical soils. The intense weathering resulted in karst structures with high hydraulic conductivities that rendered the terrain tectonically less stable.

• 出版日期2015-7