Effects of drought on ecological properties and water quality of Dorudzan reservoir

Dorudzan reservoir is the main provider of drinking water for the capital Shiraz, as well as the most significant storage of water in the Kor river course. In addition of eroded material, a load of agricultural outputs from upstream are moved to the lake every year. Main physiographic, physical and chemical, and biological components of the lake were monthly sampled and analysed from Novembr 2010 to October 2011. Mean annual measures were water temperature 16.7˚C (SD=5.8), pH 8.2 (SD=0.3), dissolved oxygen 7.6 mg/l (SD=1.7), ammonium 0.05 mg/l (SD=0.08), nitrite 0.004 mg/l (SD=0.003), nitrate 0.44 mg/l (SD=0.44), phosphate 0.20 mg/l (SD=0.23), silicate 7.00 mg/l (SD=2.49), BOD 2.29 mg/l (SD=1.00), COD 24.49 mg/l (SD=15.47), electrical conductivity 720 µs/cm (SD=219), total dissolved solids 457.67 mg/l (SD=138.72), calcium hardness 61.30 mg/l (SD=13.45), and magnesium hardness 20.23 mg/l (SD=9.18). Living parts of the ecosystem including species of fish, orders and families of benthic invertebrates, zooplanktons, and phytoplanktons were investigated. Benthic macroinvertebrates included various nematodes, oligochates, gastropods, bivalves, and insect larvae (dipteral and coleptera), most abundant of which were dipteran larvae, mollusks, and nematodes. Dominant zooplankton was Bosmina, with Daphnia and Cyclops in next ranks. Among rotifer, Trichocera was more abundant than Lecanae. Bosmina showed the most abundance in summer and Daphnia in spring. Trichocera had its most abundance in summer as well, while Lecanae was more abundant in Automn and winter. A total of 41 algal genera from 8 divisions were found. Dominant phytoplankton division was Chlorophyta, with genus Pediastrum. Dominant microalga was Dynobrion (Chrysophyta) in Spring, Cylindrospermum and (both Cyanophyta) in Summer, Microsystis in Automn, and Ceratium (Dynophyta) in Winter. Ceratium were found in all seasons in most of the sampling sites, and showed highest abundance compared to other genera of its division. Dominant genus of diatoms was Fragilaria. Fish populations include Alburnus mossulensis, Capoeta aculeate, Capoeta damascina, Carasobarbus luteus, Carassius gibelio, Cyprinus carpio, and Hypophthalmichthys molitrix. Main different parts of the lake showed quite different composition of fish species. An epidemic occurance of the crustacean ectoparasite Lernea cyprinacea among most fishes was another important finding. These findings will serve as a base for future studies as a set point of drought situations