Notes: Summary A mathematical simulation model was used to ascertain the relation between the diffusion of oxygen and inorganic carbon into layers of marine microphytes and the carbon metabolism of these microphytes. The simulation model included physiological and physico-chemical parameters and was validated using the few data available from the literature on production determinations, on oxygen and pH values, and on growth dynamics of natural populations. The model was tested with various modifications to mimic experiments with suspended algae and algal films on inert substrates, and also to simulate microphytobenthos in sediment cores with or without grazing. The simulated variations in oxygen concentrations and pH values over time scales of min and days were consistent with field and experimental observations. The model predicted upper limits of primary production and biomass observed in well developed natural populations; these limits are caused by a combination of oxygen accumulation and depletion of inorganic carbon resulting from diffusion limitations and the recirculation of organic carbon in photosynthetic, respiratory and excretory processes. The model calculations were used to check on the adequacy of the various methods used to determine the primary production of benthic microphytes.

Notes: Summary Primary production measurements of benthic micro-algal vegetations were carried out with samples from six permanent plots. These permanent plots were assumed to cover the range of salinities and sediments in the estuary. A modification of the standard14C-procedure (COLIJN and VAN BUURT, 1975) was used throught this study. The sensitivity and reliability of the modified method, based on combustion of the filtered sediments and subsequent scintillation counting, is discussed. The method proves to be a fast one, and reliable with recoveries over 95%. Moreover, counting efficiences can be based on one quench curve only for all sediment samples. The method is also applicable for planktic primary production. To make a direct comparison of the six permanent plot possible, the potential primary production was measured under saturating light intensities. The incubation temperature corresponded with the temperature during sampling. The results show a spring peak in both production and chlorophyll-a values on all permanent plots. Daily fixation rates were calculated, using daylength and tidal emersion data. No corrections for respiration during the dark period have been made. Production over 1975 was calculated, using 7 to 12 measurements per permanent plot. The results are given in Table I, which also shows the relative sediment composition and exposure time for the six permanent plots. The sediment composition is given as the mean extinction at 430 nm of a partly settled sediment suspension (SCHRÖDER, 1976). Partial correlation coefficients of primary production with five variables (station, level, chlorophyll-a, salinity and temperature) were computed. Only chlorophyll-a showed a positive significant correlation coefficient (r=0.683; n=53). In contrast to the results of CADÉE and HEGEMAN (1974) in the western Wadden Sea no correlation could be found between primary production and temperature. The absence of a spring peak in the western part of the Wadden Sea is another striking difference with our results, for which no explanation can be given. More measurements are needed over a longer period to model the benthic production of micro-algal vegetations. Such a model is needed to predict the primary production under changing environmental conditions.