Phosphorus flux from lake sediments: Effect of epipelic algal oxygen production

Abstract

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-

Significance of euphotic sediments to oxygen and nutrient cycling in a temperate estuary

“…However, freshwater ecosystems, particularly lakes, often have phosphorus-lirmted primary production (Schindler 1977). In freshwater systems benthlc microalgae typically reduce phosphorus releases (Carlton & Wetzel 1988, Kelderman et al 1988, Forsberg 1989, Hansson 1989) in a manner similar to our results for NH4 fluxes. Several estuarine and coastal researchers also report benthic microalgal effects on phosphorus fluxes (Sundback & Graneli 1988, Nilsson et al 1991 although Rizzo (1990) found no impacts of lightincubation for the York River sand shoal.…”

Microphytobenthos in Shallow Arctic Lakes: Fine-Scale Depth Distribution of Chlorophylla, Radiocarbon Assimilation, Irradiance, and Dissolved O2

“…Determinations of O 2 penetration depths in lakes are few, with the reported values of 0.4-14 mm spanning a factor of 35 for lakes of small to moderate size (Sweerts et al, 1986(Sweerts et al, , 1991Carlton and Wetzel, 1988;Frenzel et al, 1990;Sass et al, 1997;Gerhardt et al, 2005). Our values of 1.5 mm (Island Lake) and about 5 mm (S-3 and E-4) fall midway among those in previous reports.…”

Modeling vertical excursions of the redox boundary in sediments: Application to deep basins of the Arctic Ocean

“…The most common causes are variations in temperature, bottom-water oxygen concentration, and the flux of degradable organic matter to the sediment surface. Epipelic photosynthesis (Carlton and Wetzel 1988), turbidite or sapropel burn-down (Gehlen et al 1997;Jung et al 1997), or leaking of oxygen from aquatic plant roots (Mendelssohn et al 1995;Sundby et al 2003) may also be involved.…”