Effects of Land Use Change on Groundwater Quality (Case Study: Damghan Watershed)

Most of the water needs in arid and semi-arid regions is supplied through groundwater, so it is important to study the quantitative and qualitative changes of these waters and the factors affecting them. Land use changes can cause changes in groundwater quality. Here, land use changes in the period 2003 to 2020 in Damghan watershed were studied using Landsat 8, 7 and 5 satellite images, eCognition software and GIS. 1760 wells data in Semnan province were used for intermediation and accurate preparation of groundwater quality maps and extraction of geostatistical maps. Also, the information of 58 deep wells inside the watershed was used to analyze and study the groundwater quality changes. The results showed that the area of rangelands, forests and agricultural lands decreased and the area of gardens, urban areas, barren lands and surface water resources (due to the construction of the dam) increased. During this period, groundwater quality changes included Cl increased by 1.01 mEq, SO₄-2, decreased by 0.34 mEq, HCO3- increased by 0.46 mEq, Mg increased by 0.32 mEq, Ca decreased by 2.25 mEq, Na increased 3.58 mEq, electrical conductivity increased  by 44.81 μmohs / cm, Total dissolved solids increased by103.88 mg / l and pH increased by 0.09. These changes were evaluated with R software and the results showed that changes in groundwater quality are related to land use changes.