Gas supersaturation in surface waters of aquaculture ponds

Abstract

During the 1988 and 1989 growing seasons, dissolved gas pressures were measured in 0·04 ha to 0·06 ha earthen ponds (n = 17) used to produce channel catfish or bluegill sunfish, both with and without supplemental aeration. Surface waters in early morning hours (0630 to 0830 h) were typically saturated with nitrogen (N2) and argon (Ar), undersaturated with dissolved oxygen (DO), and supersaturated with carbon dioxide. Total gas pressures (ΔP) were low, averaging -40 mmHg (range -127 to 62 mmHg). During afternoon hours (1300 to 1500 h) ΔP increased to a mean of 111 mmHg (range -46 to 334 mmHg); 34% of afternoon ΔP values were above that known to cause mortality in channel catfish during continuous exposure bioassays (115 mmHg), yet no excessive mortality was observed. High afternoon ΔP values resulted from DO supersaturation caused by phytoplankton photosynthesis and, to a lesser extent, N2 and Ar supersaturation. The N2 and Ar supersaturation apparently resulted from cooling and saturation of surface waters with air during evening hours, and the subsequent increase in water temperature during daylight hours (daily increase X = 3·4°C; range 1·1 to 7·9°C) without sufficient gas release. © 1994.