Evaluation of nutrients and algal growth in Sahand reservoir

Abstract

Abstract Today, most water reservoirs (dams) are faced with environmental problems such as water quality deterioration due to chemical and microbial contamination and also eutrophication. Monitoring water resource quality is a required step to determine water characteristics, considering human health, ecological conditions, and other intended consumptions. The present study was conducted in the Northwest Iran on Sahand Reservoir, an important dam in East Azerbaijan Province with a maximum storage capacity of 135×106 m3 which supplies potable, agricultural, and industrial water to the city of Hashtrood. During the study, physico-chemical analysis of water and qualitative and quantitative analyses of phytoplankton and trophic state were conducted. Eutrophication index was calculated for each indicator of eutrophication on a scale of 0-100 by measuring Secchi disk depth (SDD), chlorophyll a (Chl a), total phosphorus (TP), total nitrogen (TN), total suspended solids (TSS), and the P / N ratio. Moreover, using the overlapping method, the reservoir was mapped based on the gathered qualitative data. According to the results of laboratory assay values are in the range of 75- 180 cm for SD, chlorophyll-a was in the range of 204.6- 5360 µg/ l, TP between 0.04- 0.24 mg/l, TN between 0.5- 3 mg/l and TSS between 2- 38.4mg/l. Based on Trophic State Index, the whole area of the lake (~10 km2) was found to be in almost moderately upper-mesotrophic condition and in some target stations, was very close to eutrophic condition. According to the results, 5 phytoplankton taxonomic groups with 20 genera were established for the reservoir. The groups with highest frequency and greatest number of genera were first established within Chlorophyta Division and then within Diatoma. PredominantII algae included Cyclotella and Scenedesmus. The results indicated necessity of having a suitable basin management to protect water quality.