Hydrogeochemistry and brine evolution of Maharlou Saline Lake, southwest of Iran

Maharlou Lake, located in southwest Iran, is an intra-continental sedimentary basin. Its area is about 280 km(2)- with an average water depth of 1.5m during wet seasons. The water level in the lake is controlled by several factors, including runoff from Maharlou catchments, groundwater seepage, and direct rainfall over the lake and the evaporation rate. Hydrochemistry of the catchments water resources showed mainly chloride and sulfate waters due to the geology of the surrounding areas and its variable lithology. Hydrochemical investigations were carried out over a time period from 1975 to 2002 using previously published analysis, together with newly collected water samples. Two hundred thirty samples were collected during summer 2002 and spring 2005. Results showed distinct changes in the brine type over time; from Mg-SO4-Cl type reported in 1970 to a recent Na-Mg-Cl -(SO4) type, which is comparable with Great Salt Lake in the USA. A Change in diluted water composition going from HCO3 <= Ca + Mg to HCO3 Ca + Mg has taken place. That is, the path of brine composition on the Eugster and Hardie flow diagram has changed from row III2b to the path II, and may finally result in a Ca-Na-Cl or Na-SO4 Cl brine type in the future. In this study, two mixed zones of fresh and saline waters were recognized in the northwest and center of the lake, with the lowest ionic concentrations, located where there is significant river and ground water supply.