Water quality of collapsible, concrete, earthen and natural ponds under different culture systems were assessed using of Photometer and tester. Temporal and spatial replications of samples were done in triplicates. Dissolved oxygen ranged between 4.6 to 6.8 mg/l, carbon dioxide 1.4 - 3.0 mg/l, nitrate 1.6 - 3.2 mg/l, phosphate 0.8 - 2.3 mg/l, calcium hardness 65- 100 mg/l, magnesium hardness 30 - 50 mg/l and total hardness 80 and 165 mg/l. Conductivity ranged between 346 - 472 μS/cm, total dissolved solids 232 - 316 mg/l, transparency 36 - 82 cm, alkalinity 105 - 245 mg/l, pH 6.35 - 8.03 and temperature 29.1 to 35.9 °C. Significant difference (P<0.05) was obtained among the parameters in the ponds showing the effects of the different culture systems on the water quality. Variations in the water quality was due to the presence of plankton and macrophytes found in earthen and natural ponds where semi-intensive and extensive culture were practiced, use of artificial feed in collapsible and concrete ponds where intensive culture was done, effects of respiration, photosynthesis and decomposition, source of water and materials used for the construction of the ponds. Water quality in the ponds under the different culture systems was good.
Heavy metals are present in low concentrations in reservoirs, but seasonal anthropogenic activities usually elevate the concentrations to a level that could become a health hazard. The dry season concentrations of cadmium, copper, iron, lead, mercury, nickel and zinc were assessed from three sites for 12 weeks in Oyun reservoir, Offa, Nigeria. Triplicate surface water samples were collected and analysed using atomic absorption spectrophotometry. The trend in the level of concentrations in the three sites is site C > B > A, while the trend in the levels of the concentrations in the reservoir is Ni > Fe > Zn > Pb > Cd > Cu > Hg. Ni, Cd, Pb and Hg were found to be higher than the WHO guidelines for the metals in drinking water. The high concentration of these metals was from anthropogenic watershed run-off of industrial effluents, domestic sewages and agricultural materials into the reservoir coming from several human activities such as washing, bathing, fish smoking, especially in site C. The health effects of high concentration of these metals in the reservoir were highlighted. Methods for the treatment and removal of the heavy metals from the reservoir during water purification such as active carbon adsorption, coagulation-flocculation, oxidation-filtration, softening treatment and reverse osmosis process were highlighted. Other methods that could be used include phytoremediation, rhizofiltration, bisorption and bioremediation. Watershed best management practices (BMP) remains the best solution to reduce the intrusion of the heavy metals from the watershed into the reservoir.