Studies on the physico-chemical characteristics and productivity of a concrete reservoir

Abstract

Studies on the physico-chemical characteristics and biological production in a new concrete reservoir in Umudike were carried out from February 1998 to February, 1999. The temperature of the water ranged from 25oC to 29oC with a mean of 26, 75oC 1.17. The water had high levels of nutrients, nitrates (NO3) ranged from 0.5 to 1.0mg/1, while phosphates ranged from 2 to 16 mg/1. the PH with slight fluctuations to alkaline and acidic conditions obtained in this study was adequate for fish production. Dissolved oxygen was also high, with values ranging from 5.8 to 7.6 mg/1. Dissolved organic matter was high during the rainy months. Values ranged from 6.4 to 7.4 mg/1. Highest transparency was obtained in March and lowest in August during the rains with values ranging from 25 to 50cm. Estimates of plankton cells/ml. showed increase in the number of cells from June to September, during the rainy months with values ranging from 34 to 149 cells/ml. The standing crop estimate of net phytoplankton and zooplankton showed a unimodal curve with highest densities in June. This trend seems to be correlated with the start of the rains and also improved nutrition of the plankton with the application of organic manure and uneaten feed. A high concentration of organic matter of 20 to 95.42 mg/l and phosphate phosphorus of 2 to 10mg/l accounted for the nutrient enrichment of the reservoir water. A strong correlation occurred between dissolved organic matter and phytoplankton, both greens and blue-greens and the flagellates. Correlation values ranged from r = 0.794 for Coelastrum, 0.812 for Chlorella, 0.964 for Staurastrum for the greens; r = 0.868 for Microcystis, 0.957 for Gleocapsa for the blue-greens; to r= 0.920 for Euglena, 0.939 for Phacus and0.874 for Trachelomonas for the flagellates. Also, the water level had a strong correlation with the preponderance of plankton. High water level correlated strongly with the green algae and rotifers, r= 0.775 for the green plankton and r = 0.732 for the rotifer Asplanchna. Low water level correlated with the blue-greens and correlated strongly with nematodes (r = 0.853 for nematodes worms). Thus high nutrient level favours high plankton production.
A general positive correlation between the concentrations of the principal nutrients and primary production is apparent from the results observed. The other interactions between the concentrations of nutrients and other factors influencing production especially transparency or turbidity, and water level are also pertinent.
Keywords: Concrete, Reservior, Physico-Chemical Characteristics, Plankton, Production, Umudike.