Previous studies utilizing oxygen-sensitive microelectrodes have demonstrated that as a result of epipelic algal photosynthesis and microbial metabolism, and regardless of the oxygen concentration of the overlying water, sediments within the euphotic zone of lakes undergo marked diel fluctuations in the extent of oxygen penetration. This investigation utilized oxygen-sensitive microelcctrodes, 32P0,3-radiotracer, and a novel flow-through system to examine the effect of epipelic algal photosynthesis on sediment oxygen dynamics and the concomitant pattern of phosphorus release from lake sediments. Epipelic algae mediated release of phosphorus from sediments to overlying water via daily formation and breakdown ofthe oxidized microzone. During illumination, surficial sediments rapidly became oxygenated, and release of phosphorus diffusing from deeper sediment layers was inhibited. During darkness the microzone became anoxic, and phosphorus was released to overlying water at an accelerated rate, producing marked diel fluctuation in efflux rate. Observed patterns of release are consistent with recent evidence for a mechanism consisting of rapid uptake or rclcase of dissolved phosphate by sediment microorganisms in response to respective oxic or anoxic conditions. Microbial metabolism in aquatic sediments regenerates inorganic phosphate that accumulates in interstitial water and forms concentration gradients. Subsequent diffusive transport to overlying water can be retarded by a number of processes that either temporarily or permanently immobilize phosphate. Mortimer (1941Mortimer ( , 1942 demonstrated that the presence of an oxidized microzone at the sediment surface inhibited phosphorus release but that a decrease in redox potential of the microzone following the onset of anoxic conditions in the overlying water stimulated the reduction of Fe(III), thus releasing phosphate bound in hydrous oxides and gels at the sediment surface. This key role of oxygen has been substantiated in numerous studies in various lake and sediment types @Lamp-Nielsen 1974;Patrick and Khalid 1974;Frevert 1980). Also identified as factors affecting the rate of P flux from sediments are pH, tem-
Black band disease is caused by a horizontally migrating microbial consortium which overgrows and kills reef‐building corals in many areas of the world. The cyanobacterium Phormidium corallyticum, the sulfide‐oxidizing bacterium Beggiatoa sp., fungi, and sulfate‐reducing bacteria dominate the consortium, which is generally several mm to 1 cm in width and ca. 1 mm in thickness. Microelectrode measurements revealed photosynthetically produced O2‐supersaturation in upper layers during day, although conditions at the band‐coral interface were consistently anoxic and, at night, sulfide‐rich. Diel distributions of oxygen and sulfide resembled those from cyanobacterial mats in sulfur springs, intertidal mats and hypersaline lagoons.
Black band disease is caused by a horizontally migrating microbial consortium which overgrows and kills reef‐building corals in many areas of the world. The cyanobacterium Phormidium corallyticum, the sulfide‐oxidizing bacterium Beggiatoa sp., fungi, and sulfate‐reducing bacteria dominate the consortium, which is generally several mm to 1 cm in width and ca. 1 mm in thickness. Microelectrode measurements revealed photosynthetically produced O2‐supersaturation in upper layers during day, although conditions at the band‐coral interface were consistently anoxic and, at night, sulfide‐rich. Diel distributions of oxygen and sulfide resembled those from cyanobacterial mats in sulfur springs, intertidal mats and hypersaline lagoons.
Direct measurements with oxygen microelectrodes demonstrated that the distribution of dissolved oxygen in periphyton communities varied on a diurnal basis and was markedly different among periphyton types. During illumination, photosynthesis in periphyton resulted in oxygen supersaturation in microzones that were subsaturated or anoxic during darkness. The fate of oxygen produced within periphyton depended on the relative rates of production and consumption, the diffusion characteristics of the periphyton, physical and chemical interactions with the substratum, and the transport rate across the boundary layer, which was affected significantly by water currents. During constant environmental conditions, steady-state oxygen distributions occurred within periphyton, but equilibrium with the surrounding water was rare.
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