The Purifying Function of the Dutch Delta

Researcher: Michel Vorenhout

Email the Author

Project runs from 01 December 1998 to 01 March 2004

Added on February 19, 2003

Introduction:

In the coastal zones all over the world, many wetlands are under stress. Besides the loss of area, the input of pollutants has been -and sometimes still is- considerable. In the plans of many conservational organisations, both the enlargement of natural area in the deltas and the restoration of natural processes are important. The objectives of the plans are simple: more area, more species, and more nature. Most of the times 'nature' is described by the presence of certain species. The way to get to more nature is a difficult one however, due to the unpredictability of the development, the presence of only few species in the initial phase, the slow migration of new species and the possible negative effects of pollutants. The bioaccumulation of pollutants is studied thoroughly, but still only predictions of two species accumulation can be made; extrapolation to natural areas is very difficult as labconditions are far more regulated than the processes in the field. In some cases it is posed that the ecosystem can sustain itself by allowing a low flow of pollutants through the system. As long as the flows are not exceeding the natural cleaning capacity of the system, no harm is found. The effects of the present and incoming pollutants on newly developed nature are mostly unknown. For instance, eutrophication, due to high inputs of both phosphate and nitrogen, is well described, but the interaction of eutrophication with other pollutants is less described.
It is reckognised that more studies should focus on the real processes appearing in the field. As the measures taken to obtain more nature most always include changes in the physical appearance of the areas, it is important to know to what extend these changes influence processes in the areas. One of the known factors that can change considerably is the redox potential, because it is strongly related to the water levels in the area. At present, reseach on this matter is performed on freshwater systems (by the WAU, and UU), but no projects on the saline areas are known.

Many studies in the world have focused on the use of wetlands as 'purifying objects'. The most studied group of pollutants in this respect are nutrients. Capacities for nutrient retention can be enormous in both natural and artificial systems. In the artificial areas the influence of oxygen transporting helophytes is thought of to be important in the removal processes in the wetland's soil. These rooting plants can provide alternating aerobic and anaeurobic sites in the soil. In this way the necessary transport from and to sites in the soil with different redox conditions is facilitated by lowering the distance that substances need to travel (diffuse). Retention of sediment-bound contaminants in flat wetlands with a low flow is known to be significant due too high sedimentation-rates and it can be enlarged by vegetation. However, these described purifying functions have hardly been studied in saline areas. Estuaries are sometimes looked at in this cleaning respect, but not to an extend as in freshwater areas. Questions about the interaction between biodiversity and nutrient-retention and loading of pollutants are important for nature development, but still are un-answered.

Aim:

In short, the main issue that will be dealt with in this project, is the interaction between the different physico-chemical parameters in the field and the availability in and subsequent potential flows of several pollutants through wet, saline systems. This research will focus on the expected problems and cleaning possibilities in areas that are included in nature development plans in the Dutch Delta zone. Also, only areas with at least saline influence will be included, as these areas are not under investigation yet in the Netherlands.

Research:

Web page

http://www.bio.vu.nl/do/

External funding

Yes

External Funding Sponsors

WWF-Netherlands

Research Group

VU - Animal Ecology

FTE

0.80