Drivers of the spatial phytoplankton gradient in estuarine-coastal systems: generic implications of a case study in a Dutch tidal bay [post]

Long Jiang, Theo Gerkema, Jacco C. Kromkamp, Daphne van der Wal, Pedro Manuel Carrasco De La Cruz, Karline Soetaert
2020 unpublished
<p><strong>Abstract.</strong> As the primary energy and carbon source in aquatic food webs, phytoplankton generally display spatial heterogeneity due to the complicated biotic and abiotic controls, but our understanding of its causes is challenging as it involves multiple regulatory mechanisms. We applied a combination of field observation, numerical modeling, and remote sensing to display and interpret the spatial gradient of phytoplankton biomass in a Dutch tidal bay (the
more » ... h tidal bay (the Oosterschelde) on the east coast of the North Sea. The 19-year (1995–2013) monitoring data reveal a seaward increasing trend in chlorophyll a concentrations during the spring bloom. Using a calibrated and validated three-dimensional hydrodynamic-biogeochemical model, two idealized model scenarios were run, switching off the suspension feeders and halving the open-boundary nutrient and phytoplankton loading. Results indicate that bivalve grazing exerts a dominant control on phytoplankton in the bay and that the tidal import mainly influences algal biomass near the mouth. Satellite data substantiate the roles of benthic grazing and tidal import. Based on a literature review, the spatial phytoplankton gradients in global estuarine-coastal ecosystems are classified into five types: seawards increasing, seawards decreasing, concave with a chlorophyll maximum, weak spatial gradients, and irregular patterns. We highlight the temporal variability of these spatial patterns and the importance of anthropogenic and climatic perturbations.</p>
doi:10.5194/bg-2020-40 fatcat:4afa3q2zfbenplpf4zrxfsrvlq