A new trend in the development of the phytoplankton in the Oosterschelde (SW Netherlands) during and after the construction of a storm-surge barrier

Abstract

During the pre-barrier period , the Oosterschelde phytoplankton were a diatom-dominated community, comprising a species-rich assemblage throughout the year . Assemblages of spring, early summer and summer, developed in response to a gradually evolving turbidity-light gradient during the course of the year.During the barrier-construction period , characterized by decreasing current velocities, increasing sedimentation of suspended matter, increasing water transparencies and unchanged nutrient conditions, the growth season for the phytoplankton started earlier and lasted longer . Some flagellate species responded by much higher biomass than before . The impact of short-term climatic factors during this period, notably severe winters, could be illustrated with examples of clear responses of some species (e .g . Biddulphia aurita) .In the post-barrier years (1987-90) a changed light-nutrient-salinity regime (i.e . much light, limitation of nitrate, high salinity) was demonstrated and an extended summerseason developed, without the original gradual transitions . This was reflected in an a-seasonal trend of the phytoplankton assemblage, where summer species were already observed in spring and spring species decreased in abundance . In summer small flagellates increased and some weakly silicified diatom species made their appearance . In the eastern compartment no colony formation of Phaeocystis occurred in summer and this was thought to be due to nitrate limitation . Changes in abundance of some species (Phaeocystis, Ditylum brightwellii, Skeletonema costatum), occurring during the entire period of investigation , could be explained using field observations compared with experimental evidence from the literature .The relationship between species composition and biomass on the one hand and environmental variables on the other hand, was analysed in a Canonical Correspondence Analysis, for both compartments separately .

Long-term changes (1979–89) in the intertidal macrozoobenthos of the Oosterschelde estuary: are patterns in total density, biomass and diversity induced by the construction of the storm-surge barrier?

“…Only when the system is affected abruptly and severely (heavy pollution : Dauvin & Ibanez, 1986 ;Pearson et al, 1986 ; complete closure of an estuary : Lambeck, 1981 ;dredging activities : Lopez-Jamar et al, 1986), general parameters of the macrozoobenthic community react clearly upon these changes . Neither the changes in the sediments of the Oosterschelde nor the change in primary production were so drastic (Wetsteyn & Kromkamp, 1994) although the plankton communities did change (Bakker et al, 1994). However, this input was on average 4-14 times larger than the natural carbon input from planktonic sources.…”

Drivers of the spatial phytoplankton gradient in estuarine–coastal systems: generic implications of a case study in a Dutch tidal bay

“…Worldwide, shellfish culture can be an important source of benthic grazing. Examples include the farmed oyster in Willapa Bay (Banas et al, 2007) and cultivated mussels in the Baie des Veys Estuary (Grangeré et al, 2010). Invasive shellfish species can also exert significant grazing pressure.…”

“…In situ observation, remote sensing, and numerical modeling are common techniques to reveal spatial patterns and detect their biophysical controls (Banas et al, 2007;Grangeré et al, 2010;Srichandan et al, 2015). Shipboard measurements of chlorophyll a (chl a) provide a precise and dynamic assessment of the phytoplankton variability; however, the temporal (usually monthly) and spatial (usually tens of kilometers) resolutions are limited compared with satellite images and numerical models (Soetaert et al, 2006;Valdes-Weaver et al, 2006;van der Molen and Perissinotto, 2011;Cloern and Jassby, 2012;Kaufman et al, 2018).…”

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

“…The phytoplankton composition in the Oosterschelde has also changed since the Delta Works: the previously dominating diatoms have decreased, while the small flagellates and weakly silicified diatoms became more abundant, especially in summer (Bakker et al, 1994). The annual cycle of phytoplankton biomass is characterized by a spring bloom and a much weaker late summer peak (Wetsteyn and Kromkamp, 1994).…”