Abstract:
This research was carried out in the Bang Pakong estuary, Bang Pakong district, Chacheongsao province. The objective of the study was to compare the effect of monthly change of water quality on zooplankton abundance. Eight experimental stations, along the Bang Pakong river about 17 km. from the mouth of the river, were selected. Samples were taken monthly, during lowest tide, from February 1984 to January 1985. The results were as follows: The water salinity ranged from 0.00-31.60 ppt and could be divided into two categories, the upper range of 23.60-29.50 ppt was found in December-May and the lower range of 0.00-3.60 ppt was found in June-November. Interaction of salinity and zooplankton density showed positive correlation. For example, the density as high as 194.03 x 10³ per cubic meter was taken from the high salinity plot whereas only 36.31 x 10³ per cubic meter from the low salinity plot. Thirty seven species of 11 phyla of zooplankton were reported but only those in the order Copepoda (class Crustacea, phylum Arthropoda) always had the highest number of about 70-90%. The water turbidity at the high level of 213.40 NTU. And 205.40 NTU. Were found in June and July, respectively. For the rest of the year, the low range of water turbidity, 12.90-135.80 NTU, was shown. There was a tendency of negative correlation between turbidity and zooplankton density. The water pH ranged from 6.30 to 7.50 showed positive correlation to salinity and zooplankton density. Statistical analysis showed monthly significant differences of salinity, turbidity, pH, temperature and zooplankton density, but no differences among stations during the same month.