QUALITY OF POTENTIAL EFFLUENTS FROM THE HYPOLIMNIA OF WATERSHED PONDSUSED IN AQUACULTURE

Watershed ponds that have maximum depths of 3-5 m and that thermally s tratify during warm months are sometimes used for commercial aquacultu re. Hypolimnetic waters in six watershed ponds used for aquaculture in Alabama were depleted of dissolved oxygen and had per-liter concentra tions 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. Con centrations of nitrite-nitrogen and 5-d biochemical oxygen demand were no higher in hypolimnetic water than in normal surface water of aquac ulture ponds. Volumes of oxygen-depleted water averaged 3.2 to 20% of total pond volumes, but much greater volumes of pond water contained d issolved oxygen concentrations less than 3 or 5 mg/L. Discharge of hyp olimnetic water from aquaculture ponds into natural waterways could ha ve negative impacts on water quality.