OXYGEN-CONSUMPTION AND PRODUCTION-RATES AND ASSOCIATED FLUXES IN SEDIMENT-WATER SYSTEMS - A COMBINATION OF MICROELECTRODE, INCUBATION AND MODELING TECHNIQUES

Intertidal sediment-water systems of the Elbe estuary were studied wit h regard to oxygen dynamics. This was in order to determine the consum ption rates of oxygen in sediments and the relative importance of oxyg en production by benthic microalgae in such systems. A combination of microelectrode and incubation techniques with dark/light illumination phases was used to calculate the effective diffusion coefficient. Prod uction fluxes of oxygen of between -30 and -170 mmol . m(-2). d(-1) we re measured in the light phases of the incubations during which algal production occurred; in the dark phases the fluxes amounted to between +10 and +30 mmol . m(-2). d(-1). The measured oxygen penetration dept hs were between 0 and 0.1 cm during periods without oxygen production, and 0.16 and 0.4 cm during periods of photosynthesis. The measured fl uxes and the microelectrode profiles were used in a diagenetic two-lay er steady-state model, resulting in calculated production and consumpt ion rates and effective diffusion coefficients. The corresponding prod uction rates were 1 to 4 . 10(-6) mmol . cm(-3). s(-1) and the consump tion rates 1 . 10(-7) to 6 . 10(-6) mmol . cm(-3). s(-1). The effectiv e diffusion coefficients ranged from 1.2 to 2.8 . 10(-5) cm(2) . s(-1) . Evidence of a change of consumption kinetics from zero order to firs t order at oxygen concentrations below 0.02 mg . l(-1) was found.