干旱区生态环境知识资源中心

Geochemical analysis of groundwater samples and brines from the Sambhar Salt lake shows a predominance of NaCl with respect to total salt content (TDS), which varies from 0.5 to similar to 400 g/L. All brine (lake + shallow subsurface) samples indicate a Na-Cl type alkaline, solutions with pH varying from 8.5 to 10. All this suggests a general provenance for halite or dissolution of desiccated salt minerals in the catchment and drainage areas of the lake. Adjacent groundwaters are mostly neutral Na-Cl type with TDS ranging from 0.5 to 13 g/L. In contrast to groundwaters, the river waters from Roopangarh and Mendha reflect that out of the TDS, the major ions constitute Na, Alk and Cl with an average equivalent Na/Cl ratio of 2.7, indicating dissolution of Na from silicate weathering of rocks. However, the lake water composition overwhelms the river water upon mixing during the recharge. period. A complete annual wetting and drying cycles of evolution of lake brine shows generation of Na-Cl type of brine with steady increase in major ions except Ca and Mg ions which decrease in successive stages of evaporation. Relative change in Na and Cl ions is also observed during the late stage of evaporation at or beyond halite saturation stage. Observation of such chemical change in brine composition is in line with the identification of salt minerals in lake sediments and salt encrustation by XRD technique.

In present-day hydrologic set-up, the estimated salt inventory in lake is similar to 10(6) tons as compared to riverine input of 6 x 10(4) tons and an upper limit of aeolian input of about 5 x 10(4) tons. Such an estimate indicates that majority of salt is derived from the recycling and re-solution of salt encrustation from the lake bed during recharge period.