Etienne Everbecq

The phytoplankton community of the River Meuse, Belgium: seasonal dynamics (year 1992) and the possible incidence of zooplankton grazing

Qualitative and quantitative aspects of the phytoplankton of the River Meuse were studied during 1992, at a point 537 km from the source. The phytoplankton was dominated by diatoms and green algae. The Stephanodiscus hantzschii-group was especially prominent. Other important taxa were Cyclotella meneghiniana, small Cyclotella and Thalassiosira, Aulacoseira ambigua and Nitzschia acicularis. Cell abundances varied from less than 1000 units ml−1 to about 25 000 – 30 000 units ml−1 during the blooms. The Stephanodiscus hantzchii-group constituted almost entirely the first spring bloom. During the summer period, small Thalassiosiraceae developed markedly and large Thalassiosira weissflogii appeared. During this period, green algae dominated diatoms as expressed in cell abundances. The main Chlorococcales were Scenedesmus quadricauda, Scenedesmus div. sp., Dictyosphaerium ehrenbergianum and Pediastrum duplex. Dinophyceae contributed a significant biomass during the summer period. Total biomass varied between 100 and 3 650 µg Cl−1. As previously observed (Descy, 1987), the factors regulating the phytoplankton growth were clearly physical variables: discharge, temperature and irradiance. However, in the summer period, low abundances might indicate a regulation by biotic factors. The impact of grazing by zooplankton is discussed, on the basis of observations of zooplankton development in the River Meuse and on the basis of simulation by a mathematical model. A comparison is carried out with recent data of phytoplankton in large European rivers.

Phytoplankton biomass and production in the River Meuse (Belgium)

Abstract The biomass and production of the phytoplankton in a relatively unpolluted reach of the River Meuse (Belgium) were followed through two years (1983 and 1984). Chlorophyll a varied from 0.2 to about 120 mg m −3 , and production ranged between 0.05 and 5.78 gC m −2 d −1 . The mean photosynthetic quotient (PQ) was 1.25. The parameters of the light-photosynthesis relationship ( P opt and l k ) were calculated and related to the variations of temperature and light in the water column. A simple model allowed calculations of the annual production, which was estimated to be 494 gC m −2 yr −1 in 1983 and 547 gC m −2 yr −1 in 1984. Finally, a simple model is developed, which explains the relationship between phytoplankton development and discharge; this model shows how the effect of discharge can be described by a “dilution rate” of the plankton growing in the river water.

PEGASE, an integrated river/basin model dedicated to surface water quality assessment: application to cocaine

Abstract The scientists of the Aquapôle of the University of Liège have been involved in environmental modeling for more than 20 years. Among other, its current R&D unit focuses on the compartment of surface water, and – for modeling processes – is specialized on the water quality. One of its environmental models, called PEGASE (Planification Et Gestion de l’ASsainissement des Eaux), French acronym for “Planning and management of water purification” is devoted to the modeling of the environmental state of surface water, at different scales from small watersheds (10 km2) and basins up to entire transnational Districts (more than 100.000 km2). The software is used operationally by several administrations (Agencies and Ministries) mainly through Europe (France and Benelux, Germany …), and several calculations have also been performed at international District levels for international commissions (Scheldt, Meuse, Moselle …). Recently, the PEGASE model has been adapted to describe the cocaine’s behavior (using a stable metabolite of the cocaine in the environment: the benzoylecgonine) in waste water, waste water treatment plants (WWTP) and surface water. The cocaine is newly described in the model as an additional micropollutant (Pegase already treats numerous heavy metals), thanks to the implementation of new state variable equations and their specific parameterizations. At a first stage, only the urban sources (releases associated to the consumption by inhabitants) were considered as the industrial releases and the soil loads are assumed to be negligible. Simulations of benzoylecgonine have been done in the Walloon and Flemish regions, where many measurements from the COWAT project were available. These first results are showing a good agreement between calculated and measured values. This ability of the model to simulate the fate of the cocaine derivatives in surface waters should be continued and extended to other metabolites.

Modelling Catchment Scale Agricultural Pollution in North Tunisia Using the PEGASE Model

Diffuse pollution in agricultural watershed may contribute to unsustainable use of water resources and implies new challenges in water management.

Lessons Learned from a Partnership Between the University of Liège and Water Agencies for the Management of Surface Water Quality

An innovative partnership has been established between a university team (R&D unit of Aquapole, University of Liege) and public stakeholders managing surface water quality (Water Agencies and Administrations) in order to develop a mathematical model included in a software suite that meets the expectations of operators. This development strategy based on the needs of partners is a guarantee of success, directly benefiting from the quality improvement of aquatic environments. The partners have complementary missions consisting in the monitoring of aquatic environment and in scientific research. The research was carried out in the European context where public water policy has to be supported by robust knowledge to establish the relationships between the state of environment and the associated pressures. In this context, the PegOpera software suite is a tool supporting the management of surface water quality, from local scale to transnational level, up to the River Basin District scale. The main purpose of this operational tool is its ability to explicitly describe the pressure/impact relationships and to help Administrations in their planning missions through prospective simulation of measures (River Basin Management Plans in the scope of the Water Framework Directive 2000/60/EC).