Buyze, E.

Maris, T.

Meire, P.

Sabbe, K.

Van Burm, E.

Van Wichelen, J.

Vanormelingen, P.

Vyverman, W.

Open Marine Archive

 - 22 -  
Compositional changes in the microalgae communities of the Scheldt 
Estuary: a result of improving water quality? 
Buyze Evelyn
1
, Jeroen Van Wichelen
1
, Els van Burm
2
, Pieter Vanormelingen
1
, Tom Maris
3
, 
Patrick Meire
3
, Koen Sabbe
1
 and Wim Vyverman
1
 
1
 Protistology and Aquatic Ecology, Biology Department, Ghent University, Belgium 
E-mail: Evelyn.buyze@Ugent.be 
 
2
 Quantitative and Applied Ecology, School of Botany, University of Melbourne, Australia 
 
3
 Ecosystem Management Research Group, Biology Department, University of Antwerp, Belgium 
 
The river Scheldt has an estuarine zone that extends 160km inland. Due to high anthropogenic 
pressures and pollution during the second half of the twentieth century, water quality in the 
freshwater tidal reach was very poor, characterized by severe hypoxia and high ammonium 
conditions. Wastewater treatment since the 1990’s has led to an improved water quality and caused 
a shift from a heterotrophic to an autotrophic system (Cox et al., 2009). 
 
Since 1996, the microalgae communities of the Scheldt freshwater estuary have been monitored as 
part of the OMES project. Here we describe the spatial-temporal changes in phytoplankton biomass 
and composition and link these with bottom-up (hydrology and abiotic parameters) and top-down 
(zooplankton) control mechanisms. 
 
From 2003 onwards, the gradual increase in oxygen and decrease in ammonium concentration were 
associated with the formation of intense summer diatom blooms. Moreover this biomass increase 
was characterized by a shift from small centric diatoms, including Cyclotella scaldensis, to the 
larger Actinocyclus normanni. Laboratory experiments suggest that ammonium concentrations may 
have been an important driver for this shift, as Actinocyclus normanni showed very low tolerance 
for ammonium. However, other factors, appear to determine the relative success of small versus 
large centric diatoms as since 2011 Cyclotella scaldensis became again the dominant diatom 
species while ammonium concentrations remain low. Another remarkable change involved the 
development of a Thalassiosira nodulineata bloom in the brackish part of the estuary since 2008.  
The general increase in diatom biomass in the brackish and freshwater reaches of the Scheldt 
Estuary is considered as an indicator for an improving water quality and is in line with an increase in 
zooplankton abundance (Tackx et al., 2005), suggesting a more direct energy flow to higher trophic 
levels.  
 
References
Cox T., T. Maris, K. Soetaert, D. J. Conley, S. Van Damme, P. Meire, J. J. Middelburg, M. Vos and 
E. Struyf. 2009. A macro-tidal freshwater ecosystem recovering from hypereutrophication: the 
Schelde case study. Biogeosciences 6:2935-2948. 
Tackx M., F. Azemar, S. Bouletreau, N. De Pauw, K. Bakker, B. Sautour, S. Gasparini, K. Soetaert, 
S. Van Damme and P. Meire. 2005. Zooplankton in the Schelde estuary, Belgium and the 
Netherlands: long-term trends in spring populations. Hydrobiologia 540:275-278. 
 
 
 


Compositional changes in the microalgae communities of the Scheldt Estuary: a result of improving water quality?

Compositional changes in the microalgae communities of the Scheldt Estuary: a result of improving water quality?

Abstract

Similar works

Full text

Available Versions

Open Marine Archive