EFFECTS OF TURBIDITY AND MECHANICAL AERATION ON WATER TEMPERATURE AND POND EVAPORATION

This study was conducted to determine the influence of mechanical aeration, clay and phytoplankton turbidity on evaporation rate and water temperature. The experiment was conducted in 0.04-ha research ponds located in the Auburn University E. W. Shell Fisheries Center on two phases. The first phase was carried out in six research ponds. One pond had no aeration and served as the control, while the other five ponds were treated with nitrogen and phosphorus fertilizer twice per month to promote phytoplankton blooms. Aeration was not applied to one nutrient-enriched pond to provide a nutrient-enriched control, and either one, two, three or four 0.37-kW Air-O-Lator aerators were installed in each of the other ponds. The second phase was carried out in nine research ponds. Three ponds had clear water, three ponds were treated with nitrogen and phosphorus fertilizer twice per month, to maintain phytoplankton turbidity. Kaolin clays were added to three ponds to develop clay turbidity.

Water exchange was not used and overflow did not occur in ponds. Surface water temperature, water temperature at 70-cm depth in each pond and air temperature were monitored at 1-h intervals with HOBO data loggers. Water level was measured by hook gauge, and water turbidity was measured in each pond. A rain gauge was used to measure rainfall and a Class-A evaporation pan was used to measure pan evaporation. Water budget was calculated for each pond.

The greater the aeration rate, the cooler was water, both at the surface and at 70 cm. Evaporation rates were found to increase with greater aeration rate. Water loss increased by 32%-92% over 24-hr periods in ponds with one to four 0.37-kW Air-O-Lator aerators, respectively. Increased water turbidity increases the evaporation rate, which in turn, lowers water temperature. Clay turbidity has more effect on decreasing water temperature and increasing evaporation than phytoplankton turbidity.