Hydrogeochemical assessment of Cheshmeh Kileh catchment (Mazandaran Province) by ArcGIS and AqQA software, case comparison of Dohezar and Sehezar sub-basins

Rivers are crucial for the society because they provide fresh water for agriculture, human needs, industry and transportation. Therefore, water quality assessment has been considered as an important issue by many researchers in the field of hydrology and hydrogeology. Water quality is influenced by natural and anthropogenic effects including local climate, geology, irrigation practices and the use of water resources.

Cheshmeh Kileh catchment is one of the most important basins in the west of Mazandaran province and has two main tributaries, Dohezar and Sehezar, which, after surveying mountainous areas, join in a plain area and form the Cheshmeh Kileh river. This catchment originates from Nosha Heights, northern heights of Alamut and Alam Kooh Glacier. According to the Meteorological Organization report, it has a humid climate with hot summers and slightly cold winters. . The center of gravity and grading of the canals were determined using a Digital Elevation Model (DEM). Sampling points were determined based on the degree of waterway and possible terrestrial and anthropogenic pollutants. After sampling, the samples were sent to the laboratory to determine the concentration of the main anions and cations, Acidity, TDS, Conductivity and Alkalinity. To study the hydrogeochemical changes in the catchment area, Piper, Durov, Stiff, Schoeller and radial Plot diagrams were drawn in AqQA software and Gibbs diagram and role index diagram were drawn in Excel. Then the process of hydrochemical evolution, type and hydrochemical facies of water were determined and the hydrogeochemical control mechanism was investigated.

The two sub-basins of rivers Dohezar and Sehezar have different chemical compositions of water at the source, which are influenced by the lithology of the region in their path, and finally, by joining together, the water type has evolved as bicarbonate-calcium. In the meantime, the sample that originates from the landfill effluent (CH16) also flows into this river, but due to the high volume of water flowing in the river, it does not have a significant effect on the overall water quality downstream. According to the Gibbs diagram, the main factor controlling water chemistry in the Cheshmeh Kileh catchment is the chemical weathering of the minerals that make up the rocks, and only in the CH16 sample (landfill) was the anthropogenic factor effective. Also, with the help of the roll index, it was found that saline seawater or trapped fossil saline water did not affect the composition of ions in the surface water of this catchment. With the help of the models provided for the Stiff diagram by Hounslow, the origin of water in CH1 sample was determined from gypsum lithology and other samples were mostly from limestone lithology. The presence of gypsum interlayers in the structure of Karaj Formation upstream of CH1 station in Maran village can be a proof of this analysis. Based on the relationship between origin and water composition, the origin of some stations was identified from the dissolution of evaporative rocks and others due to dewatering of silicates.

In general, it can be concluded that the chemical composition of water in Cheshmeh Kileh catchment has been affected by dissolution and oxidation of calcites and sulfides, as well as oxidation and weathering of silicates and sulfides.