The cluster Aquatic Ecology studies the functioning of aquatic ecosystems. It focuses on the role that macro-invertebrates, macrophytes and fish play within the cycles of nutrients and sediments and vice versa. Furthermore the impact of different types of stress such as eutrophication, habitat detoriation and pollution on the ecosystem functioning is analysed by a combination of fieldwork, laboratory experiments and modelling. The main themes that are addressed are:
- Modelling stream and river ecosystems with special emphasis on the role of macrophytes and sediments.
Mathematical modeling is used as a multifunctional tool in our aquatic research. It may serve as a tool for data-analysis, study on complex process interactions and for simulation purposes. Therefore, the STRIVE-package (STReam RIVer Ecosystem) was developed*, designed to build aquatic ecosystems from basic components (hydraulic module, plant growth and decay, nutrient turnover in sediments, etc…), tailoring the model to the specific questions of interest. The modeling activities started from the general question on retention of matter in river basins, focusing on the role of process interaction and lateral exchanges of the stream or river with its bordering systems, i.e. the riparian margin, floodplains and the hyporheic zone.
The presence of macrophytes leads to in-stream heterogeneity (patch formation and related characteristics). Recently, we started on 2D-modelling of rivers to capture the effect of this heterogeneity on ecosystem functioning. Modeling at the scale of ecosystems requires formulation of its components. So, ‘plot’-scale models of plant growth and decay, and biogeochemistry in water bottoms are developed, first as an analysis tool in experiments, thereafter as functional parts of the ecosystem model. At present the coupling of spatial data, obtained with optical imaging techniques, to 2D-river ecosystem models is topic of interest. Also further development of the STRIVE-package continues as part of different projects.
* The STRIVE-package is developed together with the Laboratory of Hydraulics (University of Ghent) and the department of Hydrology and Hydraulic Engineering (Free University of Brussels), with support of the Centre for Estuarine and Marine Ecology (NIOO).
- The interaction between macrophytes and nutrient and metal dynamics.
Macrophytes play an important role in physico-chemical processes in aquatic ecosystems especially for oxygen production, nutrient cycling, controlling water quality, sediment stabilization and providing habitat and shelter for aquatic life. Macrophytes actively take up nutrients and metals from the water and the sediment. During senescence the nutrients and metals will be translocated to the roots or released to the water phase. The quantification of these processes and their relative importance for nutrient and metal dynamics in aquatic ecosystems is addressed.
- Impact of macrophytes on water discharge and sediment dynamics
Macrophytes, as ecosystem engineers, form discrete patches that have a clear impact on stream velocity profiles and consequently on sediment dynamics. The reduction of flow velocity increases sedimentation and decreases the potential for re-suspension. Nevertheless sudden increases in discharge, mowing or senescence of macrophytes, will lead to re-suspension and entrainment of fine particles and organic matter.
- Ecological and ecotoxicological assessment of water and sediments.
Water and sediment quality have an impact on the biodiversity and the ecological status. Biotic indices, especially based on the macro-invertebrate community, have been used already for more than a century to assess the trophic status. However last decades there are several other (risk) assessment tools developed which specifically aim to identify a certain type of stress caused by either the sediment or the water phase.
- The role of sediments in the aquatic system
Reaching a good ecological status in water bodies is hampered by the presence of huge amounts of contaminated sediments. Ecosystem functioning is also affected by high sediment loads. However sediments are also essential to maintain a lot of the ecosystem functions and the development of coastal zones depends also strongly on the sediment transport out of river catchments. Therefore changes in sediment characteristics and sediment dynamics due to physical processes, namely transport, sedimentation and erosion, and to biological activity is addressed as well as the risk of contaminated sediments on the ecosystem functioning.
- Impact of pollution on the ecological status with special emphasis on macro-invertebrates, macrophytes and fish
One of the major stressors in river basins is the presence of contaminants both in the sediment and the water. The impact depends on the bioavailability, the exposure route and the mood of action of the contaminants present. Thereby synergistic and antagonistic effects of the contaminants and the presence of other stressos make it even more complex to estimate the impact on the ecological status. Within this them we try to bridge the gap between ecotoxicological impact and the impact of contaminants on macro-invertebrates, macrophytes and fish in the field.
- Habitat quality evaluation and restoration
n aquatic systems the state of the habitat is essential for an optimal ecological development. Therefore it is important to work out methods to evaluate different types of systems (small streams, lakes, canals, …) to check out the constraints and also to evaluate restoration works.
- Aquatic ecosystems and the occurrence of fish
Fish populations are an important indicator for the state of an aquatic ecosystem and are therefore often used in assessment methods. It is essential to get a good analysis of the habitat. Therefore we not only perform fish monitoring campaigns, but combine them with habitat analysis as to get a global view on the problems: migration issues, water quality, deficient habitats, …
- Water quality monitoring and ecological inventories
The European Water Framework Directive stresses the importance of monitoring to protect and improve the ecological and chemical status of water bodies. Our lab has already a long history of water quality monitoring and based on these experiences new insights and suggestions are worked out to try to improve monitoring programs.