Planktonic primary production in the western Dutch Wadden Sea

Abstract

Pelagic primary production measurements provide fundamental information about the trophic status of a marine ecosystem. Measured carbon fixation rates generally have a limited temporal and spatial resolution, but can be combined with Earth Observation data to extrapolate the measurements. Here,P-Ecurves were fitted for 3 yr of14C incubation data from the western Wadden Sea, using 4 different models; 2 with and 2 without photo-inhibition. The curve-fit model by Jassby & Platt (1976) best fit the data. Applying this model showed that the photosynthetic parameters, normalised for chlorophyllaconcentration, of maximum production (PBmax) and initial slope of theP-Ecurve (αB) were correlated. Seasonality in photosynthetic parameters of this model and the relationship with environmental variables were explored, with a focus on variables that can be inferred from satellite algorithms. There were no significant correlations between αBand any of the environmental variables measured. WhilePBmaxcorrelated with sea surface temperature (SST), the vertical light attenuation coefficient, silicate and nitrate + nitrite concentration, the multivariate model that best explained the variation in estimates ofPBmaxwas a model that included SST and year. In the period from 2012-2014, daily and annual production ranged between 3.4 and 3800 mg C d-1and between 131 and 239 g C m-2yr-1, respectively. Comparison of these results with historical data (1990-2003) indicates that the decline in planktonic primary production that has been happening since the 1990s has halted. Although not tested, we believe that our approach is generally applicable to coastal waters.