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The Oxygen Status of Lake Sediments¹

ABSTRACT

The presence of oxygen in the surface layer of sediments greatly affects the abundance and availability of Fe, Mn, nitrates, phosphates, and sulfates. The concentration of O₂ in the oxidized layer depends on the balance between the rate of O₂ diffusion into the sediment and the rate of consumption by the sediment. Several mathematical diffusion models were developed to describe this relationship between diffusion and consumption. With these models the flux of O₂ across the water-mud interface and the thickness of the oxidized zone can be calculated. Experimental testing of the models showed that the steady state O₂ consumption rates were proportional to the square root of the O₂ concentration at the mud surface. The relative contribution of biological and chemical O₂ consumption depended mainly on the organic matter content of the sediment, the biological consumption being highest in high-organic matter soils. Determination of the Fe distribution near the sediment surface showed that Fe diffused upward from the reduced soil and accumulated in the oxidized zone. This freshly precipitated Fe could function as a phosphate sink, absorbing phosphates from the water and storing it in the sediment.

Key Words: lake nutrients • microbial respiration • reductant oxidation • iron diffusion

¹ Contribution from the Agronomy Dep., Cornell Univ., Ithaca, New York. Dep. of Agronomy Pap. No. 906. Paper presented Aug. 18, 1971, in New York City at the annual meeting of ASA and SSSA as part of the Division S-2 symposium "Sediments and Water Quality."

² Graduate Assistant, Cornell Univ. Presently Assistant Soil Scientist, CIAT, Apartado Aereo No. 67-13, Call, Colombia.

Received for publication September 2, 1971.