Quality of Potential Effluents from the Hypolimnia of Watershed Ponds Used in Aquaculture

Watershed ponds that have maximum depths of 3–5 m and that thermally stratify during warm months are sometimes used for commercial aquaculture. Hypolimnetic waters in six watershed ponds used for aquaculture in Alabama were depleted of dissolved oxygen and had per-liter concentrations of 2.4–43.2 mg of ferrous iron, 0.01–0.25 mg total manganese, 0.24–3.59 mg total ammonia nitrogen, and 0.07–1.29 mg total sulfide. Concentrations of nitrite-nitrogen and 5-d biochemical oxygen demand were no higher in hypolimnetic water than in normal surface water of aquaculture ponds. Volumes of oxygen-depleted water averaged 3.2 to 20% of total pond volumes, but much greater volumes of pond water contained dissolved oxygen concentrations less than 3 or 5 mg!L. Discharge of hypolimnetic water from aquaculture ponds into natural waterways could have negative impacts on water quality.