The assessment of benthic phosphorus regeneration in an estuarine ecosystem model
Van Raaphorst, W.; Ruardij, P.; Brinkman, A.G. (1988). The assessment of benthic phosphorus regeneration in an estuarine ecosystem model. Neth. J. Sea Res. 22(1): 23-36
In: Netherlands Journal of Sea Research. Netherlands Institute for Sea Research (NIOZ): Groningen; Den Burg. ISSN 0077-7579; e-ISSN 1873-1406, meer
Benthic phosphorus regeneration is an important factor in eutrophication processes of shallow water systems. In any ecological modelling approach of such systems an adequate description of the sediment-water interactions is necessary. With this aim a fairly simple concept with a low number of variables and parameters has been formulated and analysed. The most important parameter regulating the benthic phosphorus fluxes is the Damköhler number (Da), which represents the combined effect of the aerobic first order adsorption/desorption rate K [T -1], the oxygen penetration depth H [L] and the apparent diffusion coefficient D [L2·T-1]: Da = K·H²·D-1. For Da < 0.3 anaerobic processes dominate P-fluxes across the sediment-water interface, for Da >12 chemical transformations in the aerobic layer are the most important. The concept is applied to EMOWAD, an ecological model of the western part of the Dutch Wadden Sea. In the subtidal sediments of this estuary, Da is estimated at 0.4 in summer and 5.8 in winter. For the intertidal areas these numbers are 3.9 and 23, respectively. According to the model, benthic phosphorus fluxes are almost absent in winter and reach values of up to 1.75 mmol·m-2·d-1 in summer. Approximately 70% of the organic phosporus compounds reaching the sediments is regenerated within the same year. The model results suggest that organic phosphorus accumulated in the sediments during the winter and spring is released to the water column during the summer. Part of the phosphates produced by mineralization is retained temporarily in the sediment due to adsorption to the sediment particles.
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