Valasht Lake Investigation of Copepoda density changes

In this research the structure of zooplankton populations as well as physicochemical properties of water including water temperature, total suspended solids (TSS), water clarity depth, total phosphorus (TP), dissolved phosphate (PO4-3) were studied in three sampling points during April 2009 to April 2010 (13months period). Nutrients and total suspended solids of samples were determined by spectrometry and colorimetric methods respectively. Depth of water clarity was determined using Seccchi with 30 cm diameter which was read at sunlight and half-standing position. Zooplankton samples were collected using column stretching conical plankton net with 45 microns mesh size from the one meter above water bed to water surface level. In this study, about 9 genera of Copepoda were identified and the most and least densities were related to Cyclops genus with average of 149 individuals per m3 of water and Diaptomus genus with average of 0.1 individual per m3 of water respectively. Total mean density of Copepoda in Valasht lake estimated to be 249 individuals per m3. Maximum and minimum density of Copepod observed in May with average of 638 individuals per m3 and in January with average of 8 individuals per m3. A strong positive correlation was observed between the density of Copepoda and dissolved phosphate (PO4-3) and total phosphorus (TP) concentrations.