Structural characteristics of phytoplankton assemblages in tidal and non‐tidal freshwater systems: a case study from the Schelde basin, Belgium

Abstract

1. The Schelde estuary, its side basins and their tributaries were sampled in August 1995 and April 1996 for phytoplankton abundance, biomass, diversity and species composition. In order to clarify the underlying causes of differences in phytoplankton communities, the results were related to some important abiotic variables. 2. Although species richness and diversity did not differ significantly between the riverine and the freshwater tidal stations, multivariate ordination techniques based on species abundances differentiate between these two ecosystems. While in the rivers phytoplankton standing stocks were as high in summer as in spring, standing stocks in the freshwater tidal estuary were significantly higher in the August samples. 3. It is postulated that due to the resuspension of suspended solids by estuarine currents, light is limiting phytoplankton development in the freshwater tidal reaches in spring. At that stage, phytoplankton populations have already developed in the rivers. In summer, zooplankton prevent any further increase of riverine phytoplankton populations. In the freshwater tidal estuary, however, increased light levels, a higher residence time compared to rivers and the absence of zooplankton due to low oxygen concentrations permit phytoplankton populations to bloom.

Photosynthetic characteristics of the phytoplankton in the Scheldt estuary: community and single-cell fluorescence measurements

“…In the Scheldt estuary, a dependence of F v /F m on salinity was found for only a few species and most cells in the community were in good health. This seems to be in contrast with massive algal mortality taking place along the salinity gradient, as is implied by the large decline in biomass and complete change in species composition from freshwater to seawater (present manuscript; Muylaert et al, 1997Muylaert et al, , 2000Koeman et al, 2004;Lionard et al, 2005a). Obviously, unhealthy cells are removed rapidly from the phytoplankton community, leading to the low abundance of moribund cells in the estuary.…”

“…The gradient in salinity is probably the most obvious factor, causing changes in the composition and abundance of phytoplankton (Muylaert et al, 1997(Muylaert et al, , 2000Koeman et al, 2004). Depending on the flushing rate and estuarine morphology, some true estuarine species may develop at intermediate salinity (Ferreira et al, 2005).…”

“…A maximum in green algal abundance is often observed in the zone with highest turbidity, and a bloom of the haptophyte Phaeocystis sp. may occur in spring in the mouth of the estuary (Muylaert et al, 1997;Lemaire et al, 2002;Lionard et al, 2005a;Dijkman & Kromkamp, 2006). Along the salinity gradient, freshwater species are replaced by marine species (Lionard et al, 2005a).…”

Dynamics of dissolved and biogenic silica in the freshwater reaches of a macrotidal estuary (The Scheldt, Belgium)

“…A local maximum in diatom production in the lower part of the Nete was indeed predicted by the model simulation of ) during summer 2003. In August 1995, when discharge in the Scheldt tidal river was similar to that in 2003, the diatom biomass in the Nete was also among the highest of the tidal river (Muylaert et al 1997).…”

Études préliminaires de la distribution spatio-temporelle du phytoplancton dans un système fluvio-lacustre africain (Bassin Bia ; Côte d'lvoire)

“…Quatre stations ont été retenues et prospectées mensuellement de novembre 1996 à octobre 1997 sur le système iiuvio-lacustre de la Bia (Muylaert et al, 1997 ;Van Tongeren et al, 1992), a été appliquée. C'est une méthode qui permet une interprétation aisée des ordinations par une analyse simultanée des variables abiotiques et bio-tiques.…”