Isotopic and geochemical evolution of ground and river waters in a karst dominated geological setting: A case study from Lijiang basin, South-Asia monsoon region

Abstract

Analysis of O isotopes and major ions in river and spring waters in Lijiang basin–Yulong Mountain region, SW China was carried out to identify the geochemical evolution affecting water quality and recharge sources of ground water. Both the river and ground water in the area were of the Ca2+–Mg2+–HCO3- type with similar ion compositions and showed small seasonal variations, normally high in the dry season and low in the wet season. From the upper basin downward there was a general increasing trend for the total ion concentrations in the river and ground water. Water–Rock interaction is the significant contributor to water geochemistry while there is little anthropogenic influence as a whole in the region. The co-relationship of Mg2+/Ca2+ versus Na+/Ca2+ indicated that limestone and dolomite were the main end-members controlling the variations in chemical composition of river and spring waters. The groundwater showed relatively depleted stable isotopic composition compared to modern rainfall, meltwater and river water. The similarity of δ18O for both surface and groundwater samples was due to their frequent transformation in karst regions and suggested rapid recharge of the groundwater aquifers by surface water coming from precipitation and ice–snow melt water from Yulong Mountain. The predominant recharge area of the Lijiang water resource is located at the high elevation with groundwater discharge southwards to the lowlands of the basin, providing water for Lijiang city.