The role of bioturbators in the purifying capacity of floodplains (NWO-SSEO-project)

The role of bioturbators in the purifying capacity of floodplains:

Small mammals in cadmium and zinc contaminated environments.

A 4-year PhD-project (2000-2004) within the NWO-SSEO program.

MSc S. Wijnhoven

Section Nature Conservation of Stream Corridors

Problem definition

The floodplains of the River Rhine tributaries and the River Meuse offer many perspectives for the restoration of riverine nature. Unfortunately, large parts of these floodplains are contaminated due to unbridled emissions in the past. Both the concentration and composition of the contamination varies per river and its section. Much effort has been made to gain insight in the effects of this contamination on the riverine biota. This has partly resulted in the standardisation of handling and managing activities concerning contaminated floodplain sediments. Due to the high costs arising from these standards, a large number of planned nature restoration projects is no longer feasible (e.g. Maaswerken).

Partly due to the necessity to enlarge the water discharge capacity of the River Rhine tributaries and the Meuse River, the policy dealing with handling diffuse contaminated floodplain sediments, is once more under discussion. Knowledge concerning the ecotoxicological effects and mid- and long-term processes in contaminated floodplains is of vital importance for the environmental policy. Within this context, a better understanding of the purifying capacity of floodplains can induce completely new views regarding floodplain management. There are strong indications that bioturbators play an important role in the purifying capacity of floodplains. Until now, this issue has been neglected in ecotoxicological studies. 

Afferdensche en Deestsche Waarden floodplains; fall 2000.

Scientific objectives

The goal of this research is to test the hypothesis that bioturbators provide a major contribution to the purifying capacity of floodplains and as well, play an important role in the succession processes during nature restoration (‘dominoes-effect’).

Bioturbators particularly earthworms and voles, have a significant effect on the redistribution of contaminants in the upper soil section. On one hand, this can result in an enhanced exposition of contaminants to the bioturbators and their predators (food chain transfer). On the other hand, bioturbation can cause a change in the geo-physical conditions (aeration of the soil) and a subsequent increased mobilisation of contaminants. Eventually, this can promote biodegradation of organic contaminations and/or leaching of heavy metals by rain and floods.

To assess the over-all effect of bioturbators to the distribution and destiny of contaminants and its effect on food chain transfer, it is important to examine the floodplain characteristics which determine the population density and activity of bioturbators. In the floodplains, three major factors can be distinguished that shall have a substantial impact on the life cycle of biota in general:

1) the effect of the present diffuse contaminants in the floodplain sediments;

2) management of the floodplain (agricultural or nature management);

3) the impact of flooding.

A well-selected number of mesocosm experiments, laboratory studies and field studies shall test the above-mentioned hypothesis, focussing on turbating small mammals (especially voles). The research programme shall focus on cadmium and zinc, as a large part of the diffuse contamination of floodplains is caused by these metals. Moreover, as opposed to cadmium, zinc is a physiological important metal. The mobility of both metals is largely determined by the aeration of the soil section (relation redox potential and pH), which is greatly influenced by bioturbation.

This research project should generate important data sets that shall be used to validate and compare theoretic food chain transfer models (CATS and OMEGA).

Specified research objectives

1) What is the impact of turbation activity of small mammals on the present cadmium and zinc concentrations in the soil, and how are these concentrations influenced?

2) What does the small mammal composition of the diffuse contaminated floodplains look like, and are there spatial and temporal variations in these populations?

3) Are the present heavy metal concentrations of the floodplains in potential a thread towards biota, and to what extent do cadmium and zinc (through presence in the food chain) influence nature development planned?

The research will be executed during the period August 2000 – August 2004, containing fieldwork and experiments in the Afferdensche en Deestsche Waarden, a floodplain near the river Maas and microcosm and laboratory experiments at the University of Nijmegen. The project is part of the NWO-SSEO (Stimulation Program System-Oriented Ecotoxicological Research) programme

Microtus oeconomus (the root vole); an endangered small mammal of the Dutch floodplains (foto by R. Krekels).


The following researchers are involved:

Sander Wijnhoven (MSc),  full time PhD-student (Section Nature Conservation of Stream Corridors)

Prof. dr. A.J.M. Smits,  promoter (Section Nature Conservation of Stream Corridors)

Prof. dr. G van der Velde, co-promotor ( Laboratory of Animal Ecology)

Dr. R.S.E.W. Leuven, co-promotor ( Department of Environmental Studies)

A. Corporaal, attendant/technical assistance (Section Nature Conservation of Stream Corridors)

The research project will be executed in close co-operation with MSc M.I. Zorn (PhD-student), Prof. dr. H.J.P. Eijsackers and dr. Ir. C.A.M. van Gestel (VU Amsterdam), working within the same project but focussing on earthworms as bioturbators. 

Monitoring small mammal populations with lifetraps in the Afferdensche en Deestsche Waarden floodplains.

Student research objectives

Along the period 2000 to 2004, there are several opportunities for students to execute trainee posts or scientific research topics within this project. Topics are available for students Biology, Environmental Sciences, Biomedical Sciences, ed., interested in one of the disciplines; Ecology, Chemistry, Toxicology or Pathology or a combination. Main topics contain:

  • Monitoring small mammal populations in the field using lifetraps and observations on burrying activities.
  • Heavy metal mobility studies in experimental settings (turbation simulation in microcosms).
  • Heavy metal accumulation studies by analyses of cadmium and zinc contents within different compartments of floodplain foodwebs (in the field and in experimental settings).
  • Morphology studies of small mammal organs and tissues, using light microscopy and/or transmission electron microscopy.

Contact me for up to date trainee objectives! (I will also welcome new ideas within the scope of this project). 


Collection of soil samples in the Afferdensche en Deestsche Waarden floodplains. 

More information

Information on the project can be obtained from, and reactions on the project can be submitted to:

Sander Wijnhoven (MSc)

Section Nature Conservation of Stream Corridors

Department of Environmental Studies

University of Nijmegen

P.O. Box 9010

6500 GL Nijmegen

The Netherlands

Tel:  + 31 24 365 29 23

Fax: + 31 24 355 34 50