On the use of micro-electrodes in fish pond sediments

The surface layer of fish pond sediments is characterized by very high micr obial activity. Oxygen uptake by the microbes at the sediment surface leave s little oxygen to penetrate the sediment. In marine and freshwater lake se diments, oxygen only penetrated a few millimeters. In this study, oxygen pe netration into the sediment layer in fish ponds and simulated fish ponds wa s measured with an oxygen micro-electrode. Oxygen profiles determined with micro-electrodes showed that oxygen does not penetrate deeper than 1 mm und er quiescent conditions in intensive and semi-intensive fish pond sediments . Sediment oxygen consumption (SOD) at approximately 25 degrees C, calculat ed from measured oxygen profiles, ranged from 45 to 50 mg O-2/m(2) per h. C hange in water temperature and the addition of formaldehyde showed that mos t of the oxygen consumption in the sediment surface layer is related to bio logical activity. Redox potential profiles of fish pond sediments measured with a micro-platinum electrode, showed reducing conditions conducive to su lfide formation at 2-4 mm below the sediment surface. Nitrate addition to t he overlying water poised redox potential above 300 mV to a sediment depth of about 15 mm. Nitrate thus buffered the sediment-water interface against reducing conditions in the sediment and the possible diffusion of toxic red uced end products to the water. (C) 1999 Elsevier Science B.V. All rights r eserved.