effects of land use change and erosion on physical and chemical properties of water(karkhe watershed)

karkhe watershed (kw) with more than 5 million hectares recently encountered many problems in the natural, social and man-made habitats. unsuitable use of land, soil erosion and lack of rainfall are the most destructive factors in this watershed affecting the whole region fundamentally. as expected, these problems have caused a considerable fall in biodiversity in fauna and flora, a decrease in volume and quality of water resources in watershed and a rise in probability of destructive floods. in this study the changes in land use levels and erosion were assessed in 5 sub-regions of karkhe watershed in two periods of time ’1988 and 2002’ using images of landsat. in addition, the effects of these manipulations on the physico-chemical qualities of water such as, cation and anion concentration, acidity and salinity were quantified. the results show that erosion changes in karkhe watershed are inconsiderable from 1988 to 2002. the extent of urban area and irrigated agricultural lands in karkhe sub-regions (gamasiab, gharresu kashkan ) are around 1000 and 2000 km2 respectively , the decrease in river discharge around 121.6 m3/s , is the most effective factors for the reduction in acidity(from 7.9 in 1988 to 8.1 in 2002), an increment in salinity ( from 1.6 mg/l in 1988 to 3.6 mg/l in 2002 as average amount of sar in all sub-regions of watershed) and the high density of the anions (from 8.1 mg/lin 1988 to 16.4 mg/l in 2002) and cations (from 8.8 mg/l to 16.5 mg/l) in karkhe river.