Water yield and quality research of two watersheds that have different land use intensity

The Big Melen River that supplies İstanbul's water is affected by nonpoint source pollution due to fertilizer use in agricultural activities. Hazelnut production is the largest among the agricultural activities. This study investigated the effects of land use on water quality and yield at the subwatershed level. For this purpose, precipitation, discharge and water quality parameters were measured for two years in two adjacent subwatersheds that have different forest and agricultural (hazelnut) land uses areas. To investigate the effects of settlements on water quality the parameters were measured at two different locations of subwatersheds: one on upper watershed before settlements and the other on the lower watershed after settlements. Subwatersheds and measurement locations were compared in terms of water quality. The two-year total water yield of the forested and agricultural watershed was found to be 867,5 and 654,9 mm. During the study period, the average electrical conductivity (EC), turbidity, total suspended solids (TSS), total nitrogen (TN), chlorine, nitrate, sulphate, magnesium and calcium values were found to be significantly higher in the agricultural subwatershed while average dissolved oxygen (DO) value was found to be lower in comparison to the forested subwatershed. No significant differences were found for pH, total organic carbon (TOC), fluorine, bromine, nitrite, phosphate, ammonium, sodium, potassium values between the subwatersheds. Average EC, chlorine, phosphate, sodium, potassium, calcium values measured after the settlements location of both subwatersheds were found to be significantly higher than those values measured before the settlements location. For the forested subwatershed average pH and DO values measured before the settlements location and average TSS, sulphate, magnesium values measured after the settlements location were found to be significantly higher and no significant differences were found for turbidity, TOC, TN, fluorine, nitrite, bromine, nitrate, ammonium between two locations. For the agricultural subwatershed average DO and TSS values measured before the settlements location and average TN, nitrite and ammonium values were found to be higher at after the settlements location and no significant differences were found for pH, turbidity, TOC, fluorine, bromine,nitrate, sulphate and magnesium between two locations.