Limnological study and fisheries potential in Karkheh reservoir

Abstract

This study was carried out in Karkheh reservoir in North of Khuzestan Province from January to December 2003.Monthly sampling was done from 3 stations in lake with different depth and also 2 stations in input and out put points of reservoir in Karkheh river. Average volume and surface of reservoir were 2870 milioncubic and 10427 hectares respectively. Mean depth in stations 2, 3 and 4 were 36.07, 53.42 and 31.71 meter respectively. The DO content was recorded as optimum level, the highest Nitrite, TDS and TSS were observed in 20 meter depth layer. The ranges of nutrients were: Nitrate (1.2-31.8), Phosphate (0.01-2.11), and Silicate (2.1-18.7) mg/liter.EC and pH range were 599- 1629µs/cm and 7.42-8.78 respectively. The amount of ammonia and co2 were very little during the year.BOD5 was below 5 mg/liter, that is indicator of clear waters. Dam water was classified in hard to very hard water group. Other factors of water were in acceptable range. The most frequent occurrence of phytoplankton classes were: cyanophyceae (72.04%), Bacillariophyceae (12.39%), Dinophyceae (10.46%), Chlorophyceae (4.88%) and Chrysophyceae (0.22%).The most frequent genuses of each group phytoplankton was chroococcus, cyclotella, Melosira XPeridinium XScenedesmus X Gelocapsa. Cyanophyceae was in surface and 20meter depth and other classes only in 20 meter depth observed. The most abundant of zooplankton group were Copepoda (44.8%), Protozoa (27.32%), Rotifera (22.45%) and Cladocera (5.43%) and genuses including are Cyclops, Tintinopsis, Keratella, Brachionus and Daphnia were abundant. Protozoa in 20, Cladocera in 20 and 40 and Copepoda in 60 meter depth were more abundant. The chlorophyll a in stations 3, 4 was higher than stations 2. The mean and total primary production were 0.33, 93.44 gc/m2/day respectively. The highest abundant benthic group were: Oligocheta (74%), Ephemeroptera (13%) ( Chironomidae (5%) and others (8%).The most and the lowest abundant macro benthic were observed in February and October. The Lowest density of benthic fauna was found in the deepest stations 3. station 4 was showed the lowest amount of silty-clay ,but the most organic matter was found in station 3.Identified nektons were include: 18 species from 6 families: cyprinidae (13 sp.), mugilidae (1 sp.), mastacembelidae (1 sp.), Sisoridae (1 sp.), Graspidae (1 sp.), bagridae (1 sp.).The most abundant fishes were: Capota trutta (25.4%), Cyprinion macrostmum (18.3%), Barbus esocinus (15.4%) and others species (40.9%). Potential of Fish production based on primary production was measured about 102.7 kg/Hectares in year. Trophic State Index (TSI) was 16.06, that indicator of oligothrophic waters.