The most important natural functions of wetlands (biological and mechanical filters, habitats with high biodiversity) were in the past confronted with their values as converted productive grasslands for dairy farming. Recently the remaining areas have the status of nature reserves.
Wetlands research group contributes to knowledge on protection and restoration of wetlands where most important factors regulating the sites conditions are studied:
Water levels and quality
Soil structure and quality
Nutrient availability and vegetation types
In this context, particular attention is paid to the effects of desiccation and eutrophication on plant nutrient availability, productivity and biodiversity. We use specially the N/P ratio as indicator of nutrient limitation in wetlands vegetation and try to found wish factors (biotic and abiotic) best describes the nutrient pools in soil, groundwater and plant.
To obtain a better understanding of the function of wetlands in agricultural landscapes, it is necessary to investigate key nutrient cycling processes in these wetlands and to evaluate their response to different management practices. The function of the wetlands vegetations in the flux of the nutrients are determined too.
We aim to determine the contribution of each process ( nutrients uptake, immobilisation, nutrient turnover, decomposition and mineralisation) in determining the nutrient pools for the vegetation.
Project & study areas:
Important research areas are the various brooks in the Nete basin, Mechelsbroek floodplain, the Abeek, the Zeeschelde ( Belgium) and the Biebrza basin (Poland).
1. Mechels Broek
During the last decades hydrology is of major concern in the Flanders and the Netherlands. By the implementation of drainage for agriculture, by the deepening, the straightening and the embankment of rivers, the water retention capacity of valley systems is often decreased and the run off accelerated. This caused at one hand a decrease of wet, and often valuable, ecosystems by eco-hydrological processes like acidification and desiccation, at the other hand during wet periods more extreme run off and flooding do occur. It is expected that during the next decades climatic change will cause more wet winters, drier summers and an elevation of the sea level. It is thus expected that more extremes in water input will occur in the future. To minimize effects of excess water the Commission for Water Management 21° Century advises a three step strategy for the implementation of water systems: water retention as a first objective, then the containment of water and if necessary the control of the run off water. In practice this means that bigger areas for the implementation of water reservoirs is needed, but since space is scarce in Flanders and the Netherlands, the water containment has to be stimulated in areas with other land use practices. Hereby especially the potentials for water retention and run off buffering can be coupled with agricultural land use and nature.
The possibility to combine water retention strategies with venerable nature is subject to many questions. The quality of surface water has decreased as a consequence of intensive use of fertilisers and the hydrological characteristics of typical flood zones have altered fundamentally. As a consequence flooding can induce changes in nutrient availability, first by direct input (dissolved or absorbed to sediment particles) and secondly by inducing changes of internal biogeochemical processes (soil humidity, redox potential, oxygen availability,...) by which nutrients can be released. One of the main questions of the effects of water containment for the vegetation is the influence of flooding on the productivity and the nature value of semi-natural terrestrial vegetations. Unknown are the quantities of nutrients which remain after flooding and which are available for plant uptake and unknown is how much of the nutrients from the floodwater are plant available in relation to the availability of nutrients by internal processes and other sources. Further it is not clear if summer or winter flooding do have a similar impact on the nutrient cycling processes. The main objective is to study the effects of restoration of water retention on the vegetation in an historical flooded area. In a first step this study focuses on the relative importance of the different processes which determine the availability of nitrogen, potassium and phosphorus, i.e. input of dissolved nutrients, by organic material and sediment, en de mobilization of nutrients in the soil. Testing the hypothesis that during winter flooding the relative importance of the input of nutrients and the internal release of nutrients is smaller than during a summer flooding. The methodology is twofold, an in situ mesocosm installation in the Mechels Broek and a microcosm installation at the UIA will be used. In the mesocosm installation winter- and summer flooding will be simulated in 5 plots of 2X2m for each treatment, whereby water of the nearby Dijle will be used. During flooding nutrient availability will be monitored by measurements of input water and soil nutrients. In each season above- and belowground biomass compartments will be sampled to evaluate the effects of flooding on nutrient uptake, productivity and litter production. The effects of re-flooding on decomposition and mineralisation will be studied by standard techniques. The inlet of flooding water will be enriched with a 15N tracer, which after determination in different compartments will allow a better description of N cycling in the ecosystem. In the microcosm experiment 20 soil cores will be sampled from the study site where the ground water table dynamics will be simulated at the UIA. After an acclimatisation period of 4 weeks following treatments per 5 cores will be performed: no flooding, flooding with a basic medium, flooding with basic medium + extra sulphate and flooding with basic medium + sulphate + N + P. Nutrient availability will be monitored on different depths in the cores during the experiment, in order to determine the relative importance of external input of nutrients in comparison with internal mobilisation of nutrients during flooding. The 15N isotope will be used to allow a better description of N cycling between soil and vegetation compartments.
2. The Mass river.
In this project the relationship between the quantity/quality of groundwater and vegetation will be investigated in two study areas along the river 'Maas' in the eastern part of Belgium.
'Vijverbroek' is a nature reserve that is located outside the winter bed of the river 'Maas'. It mainly consists of wet Alder forest with Alnus glutinosa, Carex elongata and other typical species for this type of vegetation. This part used to be an arm of the river 'Maas', which has been cut off from the river. Groundwater enters the area coming from the 'Campine Plateau' and runs off to the river 'Maas'. Because of exploitation of gravel along the 'Maas', the bed of the river has become deeper and many pools are created. As a result, the runoff of groundwater to the 'Maas' has increased. This has an effect on groundwater level in 'vijverbroek', as well as on the distribution of groundwater dependent plant species: Some specific species such as Ranunculus lingua and Menyanthes trifoliata have decreased or even disappeared. On the other hand, other species that indicate disturbance (desiccation, eutrophication), such as Glyceria maxima and Urtica dioica, have increased.
As the exploitation of gravel has stopped now, the pools are refilled with loam from the original top layers that were above the gravel before the exploitation. This research will investigate the effect of the refilling of the pools on the groundwater level in 'vijverbroek', as well as on the vegetation, especially on the distribution of groundwater dependent species. A groundwater model will be made at VUB. This will be used to predict the effect on groundwater level. Effects on vegetation will be investigated at UIA.
The second study area is 'Maaswinkel'. It consists of a varied landscape with 8 small pools in which the water level is strongly dependent of the water level in the river 'Maas'. On the border of these pools, groundwater dependent plant species are found.
Near 'Maaswinkel', an old arm of the river 'Maas' will probably be recovered. This research will investigate the effects of the recovering of the arm on the water level in the pools and the groundwater dependent vegetation on the borders.
The aim of this project is to examine the potential for nature restoration and conservation in the ecosystem valley of 'Abeek'. It's one of the several projects outgoing of the environmental policy of Flanders to halt the loss of biodiversity. In this project the potentials for the Abeek were evaluated. De stream is located in the North-eastern part of Flanders near the border with the Netherlands. Recent research has proved the underestimated biodiversity in the valley.
During the year of 2001 the vegetation in the valley is been mapped to examine the different vegetation types. These results will show us the influence of different types of conservation management on the development of the vegetation types. Five types of vegetation succession were distinguished, meanly differing in groundwater level during spring and summer and the type of soil. Furthermore, the valley ecosystem will be investigated in accordance with policy, administrative and the most important a biotic factors which limit the possible development of typical valley ecosystems in the future.
All this information will be used to develop at least two different scenarios. The first one is based on a situation of unchanged abiotic parameters, thus still desiccation and eutrofication in the valley. In the second scenario the natural processes will be restored. This implies a raise of groundwater level and removes the dykes of the Abeek in de downstream area. These intervening will hopefully restore the natural habitats like Parvocaricetea and Magnocaricion, which are internationally protected
4. The Grote nete and The Visbeek.
Belgium has a large area of riverine valleys. These valleys used to have a distinguished pattern with regard to the distribution of vegetation types and plant species. The distribution of the vegetation types is a result of hydrology and nutrient availability. However, as mentioned before, the hydrology has changed dramatically in large areas of these valleys. Consequently, the nutrient availability have changed too. Areas, which were characterized by a poor nutrient availability, have become euthropicated.
Therefore, a large number of plant species from a poor environment have become very rare. To preserve these species, protective measures have become necessary. For an effective protection, and a possible restoration in the future, it is important to know:
Which is the limiting nutrient for these vegetation types?
Which is the role of hydrology on the nutrient availability?
A number of vegetation types and key species from nutrient poor areas have been selected. Abiotic conditions will be determined. The availability of important limiting nutrients, (Nitrogen; Phosphate, Potassium) will be researched and linked to hydrology.
When the relation is clear, different scenario's, with groundwater level as a variable, will be calculated. This will result in map's with the distribution of the vegetation types.
5. Bierbza Valley (Poland).
The Biebrza valley are sparsely populated and agriculture is extensive and groundwater surface water pollution is still insignificant. The presence of intact peat land area, an undisturbed groundwater flow systems and presence of large herbivores make the Bierbrza valley an exceptional reference for wetlands systems in Belgium.
First, nutrient dynamics will be studied over a period of 3 years in wetlands in Poland. Decomposition, mineralization, the availability of nutrients, and vegetation characteristics like productivity and species richness will be measured. The nutrient limitation will be studied on the levels of vegetation and species. Factors (biotic/abiotic) like groundwater level, pH and conductivity, which can influence the nutrient dynamics are also collected.
Second, in a microcosmos experiment, external eutrofication will be simulated by changing the composition of the groundwater. This in combination with fluctuations in groundwater levels causing internal eutrofication, allows us to study the influence of eutrofication on the nutrient dynamics. The soil cores used in the experiment will be collected on the field. After a perturbation period, changes in decomposition rate and nutrient availability will be measured.
The integration of these field and experimental results will allow us to make predictions on the possible impact of changes in the environment of the wetlands in Poland and other European countries.