Primary production of microalgae in sediments measured by oxygen microprofile, H₁₄CO₃ ‐ fixation, and oxygen exchange methods1

Abstract

A platinum microelectrode was used to measure changes in dissolved oxygen profiles in surface sediment exposed to light and darkness.

Microphytobenthic primary production in the Bodden estuaries, southern Baltic Sea, at two study sites differing in trophic status

“…For sediment samples, microelectrodes gave much more reliable results on benthic primary production than more integrative methods such as oxygen exchange measurements. Microelectrodes measure photosynthetic activity directly at the production spot within the sediment, and both upward and downward oxygen fluxes are included (Revsbech et al 1981). Hence, gross benthic primary production rates calculated on a monthly basis in the present paper (KB: 2 to 17 g C m -2 mo -1 ; RS: 0.2 to 7 g C m -2 mo -1 ) were on average 2 times higher than those reported by , who used the oxygen exchange method.…”

“…The resulting oxygen fluxes (upwards out of the sediment into the water column and downwards into deeper sediment horizons) have been used to calculate oxygen consumption/production (Revsbech et al 1981, Sommer 1994. For these calculations, the diffusion coefficient of oxygen in the water and sediments as well as the porosity of the sediment must be taken into account (Li & Gregory 1974, Ullmann & Aller 1982, Revsbech & Jørgensen 1986, Rasmussen & Jørgensen 1992.…”

“…For these calculations, the diffusion coefficient of oxygen in the water and sediments as well as the porosity of the sediment must be taken into account (Li & Gregory 1974, Ullmann & Aller 1982, Revsbech & Jørgensen 1986, Rasmussen & Jørgensen 1992. Oxygen microelectrodes can also be used to directly determine gross photosynthesis by the light/ dark shift method (Revsbech et al 1981, 1986. Thereby a steady state of oxygen distribution will be achieved under constant conditions and the initial decrease in oxygen within 1 s after darkening the sediment reflects gross photosynthesis , Karsten & Kühl 1996.…”

“…Pelagic gross photosynthesis was calculated as the sum of respiration and net photosynthesis. Microphytobenthic photosynthetic activity was determined similarly, but also directly by the light/dark shift method, whereby the gross photosynthesis rates for the different sediment layers were related to volume and multiplied by the vertical expansion (z phot ) of the measured profile of photosynthetic activity (Revsbech et al 1981, 1986 Gross primary production rates were expressed as C-equivalents using the conversion factor 1.2 (Mills & Wilkinson 1986) and taking main substrates and products of dioxide fixation into account (Burris 1981, Raine 1983, Sakshaug et al 1997. Gross primary production rates of pelagic and microphytobenthic area were normalised to chlorophyll a concentrations in the water samples and in the flocculent sediment surface layer, respectively, to correct for algal biomass.…”

“…Moreover, interpolation of the data for the time intervals between measurements was done using the Walsby (1997) model. Especially in the low light range, microelectrode measurements are far more sensitive than other integrative methods, and allow the direct determination of gross photosynthesis rates within the sediment (Revsbech et al 1981, Sommer 1994, Karsten & Kühl 1996, Gerbersdorf 2000. Thus, the measurements of benthic production rates are more reliable, and hence calculations on the sediment oxygen budget and carbon supply to the benthic habitat as well as to the pelagic habitat after resuspension are more precise.…”