Determination of water quality characteristics of Shahid Rajaei reservoir (Sari) based on physic-chemical parameters

The water quality provides the valuable information about the available resources for human usage. The reservoirs are the important resources of surface water which could be considered as an appropriate water resource for irrigation, drinking water and also fish culturing. The Shahid Rajaei Reservoir- Sari is an important reservoir in Iran, which conducted to study on its water quality in this survey. In this study, some of the physicochemical parameters and Chlorophyl- a of Shahid Rajaei reservoir were measured at 4 stations (Shirin Roud branch, Sefid Roud branch, the crossing point of branches, near the tower) during six sampling months (June, July, August, September, November and February) in 2012-2013. The water quality and trophic status of reservoir calculated based on some reference values and the modified Carlson formula. The results showed that the mean (±Standard Error) of temperature, dissolved oxygen, pH, phosohate, amonium and nitrate concentrations and Chlorophyl a were 21.35 (±1.30) ºC, 10.48 (±0.37), 8.54 (±0.04), 0.050 (±0.004), 0.036 (±0.004), 0.75 (±0.03) mg/l and 18.00 (±7.23) mg/m^3 , respectively. In the present study, temperature between surface and deep layer was stratified in June and July, which the stratification was registerd 0.47 and 0.69 °C decreases with increasing of each meter depth in 15 to 30 meter culumn. But, these changes for each increasing meter of water depth were 0.2 to 0.26 °C in August and September, respectively, and finally was close to zero in November. In the warm months (July, August and September) with the formation of thermal stratification in the reservoir was formed oxygen stratification, but in the cold season (November and February), with vertical mixing of water oxygen and percent saturation of the reservoir was nearly homogeneous. The results showed that the European authorities (OECD) trophic status varied between mezotrophic to hypertrophic during the sampling period at all stations. The comparison with the values listed in the references of Iranian dams based on transparency and chlorophyll variables showed similar results. However, phosphorus variable (due to limited for phytoplankton) was not showing the true conditions of trophic status. As a conlusion, trophic status of Shahid Rajaei dam based on Carlson trophic index (TSI) was obtained oligotrophic (May and October), mezotrophic (February) and eutrophic (August and September) condintion during diferent months. Therefore, water management of the reservoir was more attention during warm months.