Water quality based on the species composition and abundance of phytoplankton in Shahid Rajaei Dam- MazandaranProvince (Sari)

Shahid Rajaee Dam was constructed on Tajan River (basin of the Caspian Sea) and it is two arch typed. The major objectives of dam instruction are flood control, irrigation purposes, and electricity power. However the dam is going to supply drinking water for the people. In order to prevent threats of unsuitable water to human health risks and economic losses, it is necessary to monitor the water quality before offering it to people. Many of algal blooms happening in Dams indicate that microbial evaluation is necessary but it is not sufficient.in water quality assessmens. Therefore in order for comprehensive evaluation of water quality, phytoplankton structure and population studied in the reservoir, then some water quality indices calculated based on the obtained information. Seasonal sampling was carried out in the year of 2012. However in summer monthly sampling was performed due to the increasing of algal blooms probability. Water samples were collected in 4 stations which were located entrances of Shirin Rood and Sefid Rood to the lake of dam, Cross of the two entrances and near the crest respectively. Based on the results, 107 phytoplankton species were identified during the period of study. The species were classified in 8 divisions namely Bacillariophyta, Pyrrophyta, Cyanophyta, Chlorophyta, Euglenophyta, Chrysophyta, Xantophyta and Cryptophyta. The numbers of species were 27, 22, 17, 26, 10, 3, 1 and 1 respectively in each phylum. Maximum and minimum values of mean (SE) abundance observed in July and January, 661 (±286) and 10 (±2) million cells/m^3 respectively at the surface layer. The values for biomass were 9264(±3242) and 103(±15) mg/m^3 which were recorded at the same months. The One way analysis of abundance and biomass data showed temporal significant variances (P< 0/05), however the spatial variances of data were not significant (P> 0/05). Bacillariophyta and Pyrrophyta formed more than 95% of phytoplankton abundance and biomass. Abundance percentage of Bacillariophyta was slightly higher than Pyrrophyta While biomass percentage of Pyrrophyta was about 3 fold of the Bacillariophyta. 3 dominant species namely, Cyclotella meneghiniana, Goniaulax polyedra and Ceratium hirundinella formed about 70% of phytoplankton aboundance. Comparison of diversity indices (Shannon and Evenness) showed higher values in May and January; however the indices reached its lowest level (0.58 and 0.16) in August. Water quality assessment using Shannon index showed the lowest quality of water (moderately to high polluted) in July and August. This index demonstrated the highest water quality (slightly polluted) at station 1 and 4 respectively. The results of the water quality assessment using Saproby index (based on the resistant phytoplankton species to organic pollution) also indicated to organic pollution of water in the months of summer. The saproby assessment in stations categorized most of the stations in “moderately polluted” class of organic pollution except at station 4 which was in "slightly polluted" class. In conclusion, the removal (transfer) place and time of water to the water treatment plants.are impratnt because of temporal and spatial variation of water quality due to changes of phytoplankton structure in Shahid Rajaee Reservoir.