Modelling phytoplankton successions and nutrient transfers along the Scheldt estuary (Belgium, The Netherlands)

The freshwater (RIVE) and the marine (MIRO) biogeochemical models were coupled to a 1D hydro-sedimentary model to describe contemporary phytoplankton successions and nutrient transfers in the macrotidal Scheldt estuary (BE/NL) affected by anthropogenic nutrient loads. The 1D-RIVE-MIRO model simulations are performed between Ghent and Vlissingen and the longitudinal estuarine profiles are validated with physico-chemical and phytoplankton observations available for the year 2006. Results show the occurrence of two distinct phytoplankton blooms in the upper and lower estuary, suggesting that neither the freshwater nor the marine phytoplankton is crossing the maximum turbidity zone (MTZ) at the saline transition. Sensitivity tests performed to understand how changing conditions (salinity, turbidity and nutrients) along the estuary are controlling this bimodal spatial phytoplankton distribution point salinity and light availability as key drivers while the grazing pressure and nutrient limitations are negligible. In the absence of species-specific salinity control or in low light limitation, freshwater phytoplankton is able to cross the MTZ and grow in the lower estuary where they compete with marine phytoplankton for nutrients. Additional tests with varying salinity-resistant (euryhaline) species in the freshwater assemblage conclude that the presence (or absence) of euryhalines determines the magnitude and the extension of freshwater and marine phytoplankton blooms in the estuary. Annual nutrient budgets estimated from 1D-RIVE-MIRO simulations show that biological activities have a negligible impact on nutrient export but modify the speciation of nutrients exported to the coastal zone towards inorganic forms

The dimethylsulphide propionate (DMSP) content in microalgae and its influence on DMS emission: Experimental and modelling study in the Southern North Sea

info:eu-repo/semantics/nonPublishe

Trait-based representation of diatom functional diversity in a plankton functional type model of the eutrophied southern North Sea

We introduce a trait-based description of diatom functional diversity to an existing plankton functional type (PFT) model, implemented for the eutrophied coastal ecosystem in the Southern Bight of the North Sea. The trait-based description represents a continuum of diatom species, each characterized by a distinct cell volume, and includes size dependence of four diatom traits: the maximum growth rate, the half-saturation constants for nutrient uptake, the photosynthetic efficiency, and the relative affinity of copepods for diatoms. Through competition under seasonally varying forcing, the fitness of each diatom varies throughout time, and the outcome of competition results in a changing community structure. The predicted seasonal change in mean cell volume of the community is supported by field observations: smaller diatoms, which are more competitive in terms of resource acquisition, prevail during the first spring bloom, whereas the summer bloom is dominated by larger species which better resist grazing. The size-based model is used to determine the ecological niche of diatoms in the area and identifies a range of viable sizes that matches observations. The general trade-off between small, competitive diatoms and large, grazing-resistant species is a convenient framework to study patterns in diatom functional diversity. PFT models and trait-based approaches constitute promising complementary tools to study community structure in marine ecosystems

A model study of the evolution over the past 50 years of air-sea CO2 fluxes in the Belgian coastal zone (Southern Bight of the North Sea)

The coupled river-coastal sea model RIVERSTRAHLER-MIRO-CO2 (R-MIROCO2) is used to appraise how nutrient loads and increased atmospheric CO2 are affecting contemporary air-sea CO2 exchanges in the Belgian coastal zone (BCZ) (Southern Bight of the North Sea). R-MIRO-CO2 results of the offline coupling between RIVERSTRAHLER C, N, P and Si river loads to the coastal zone constrained by meteorological conditions and human activity on the watershed and the MIRO-CO2 model of C, N, P, Si cycles in the coastal sea. For this application, the marine MIROCO2 model is implemented in a 0D multi-box frame covering the eutrophied Eastern English Channel and Southern North Sea and receiving loads by the river Seine and Scheldt. Model simulations are performed for the period between 1951 and 1998 using real forcing fields for sea surface temperature, wind speed and atmospheric CO2 and RIVERSTRAHLER simulations for river C and nutrient loads. Model simulations suggest that the BCZ shifted from a source of CO2 before 1970 (low eutrophication) towards a sink during the 1970-1990 period when anthropogenic N and P loads increased. The period after 1990 is characterized by a progressive decrease of P loads concomitant with a decrease of the CO2 sink. At the end of the simulation period, the area acts again as a source for atmospheric CO2. Additional simulations investigating the relative impact of temperature, wind speed, atmospheric CO2 and river loads variability (compared to 1951) on the simulated air-sea CO2 fluxes point these latter as drivers of the magnitude and the direction of the air-sea CO2 fluxes in the BCZ