Drs. D. (Daniel) Bontje

Room: T527
Phone: +31-(0)20-5987133
Email: daniel.bontje@falw.vu.nl
Curriculum vitae: 1978/09/08: born, Zoetermeer
2003/08/29: Master's biology, Utrecht
Specialization: Cellular and molecular biology
Project: Toxic effects on canonical communities
DEB tele course

Predicting Unexpected Effects of Chemicals on Ecosystems


Standard bioassays on the potential of chemicals for biological effects focus on acute or chronic survival, growth and reproduction of single species under constant optimal physiological laboratory conditions. The effects of a chemical depend on its concentration, its mode of action, the choice of test species and the exposure time. Due to absence of interactions among organisms (food competition, predation, crowding) and (nutrient) recycling, it is difficult to translate these single-species effects to a community. The variability of field conditions, which affect a.o. the bio-aviability, further contribute to the problem of translating effects from single-species bioassays to effects on communities in the field. Interactions among biota and feedback loops via nutrient availability make that it might be difficult even to recognize a deviating behaviour of a community as an effect of a toxic substance.


The first aim of this project is to understand the effect on a community, given observed effects on the species that occur in this community for low concentrations of a number of key chemicals (i.e. industrial chemicals that are frequently released in the environment, and have different modes of action). To this end we use a simple microcosm consisting of a decomposer, a producer, a consumer and a predator (which eats both producer and consumer). The role of the producers is to fix energy (light) and inorganic carbon for metabolic work, of the decomposers to unlock nutrients that are locked in organic compounds and of the consumers and the predators to speed up the recycling of nutrients.

Canonical community

We choose the single species for each category of organism and call this simple system a canonical community as within this community all basic activities are found that are present in a larger ecosystem. For the role of producer we choose the mixotrophic cryptophyte Cryptomonas spec.; it has proven to be an excellent food source for several species of ciliates and can easily remain in suspension with help of its flagella. The consumer will be the planktonic ciliate Urotricha furcata, which is abundant in many stratifying temperate lakes. It feeds on both bacteria and cryptophytes, with a preference for the latter. The predator will be the rotifer Brachionus calyciflorus, which is also unbundant in many freshwater systems. It has a relatively short generation cycle and was used in many studies on feeding behavior and predator/prey relationships. It is able to consume cryptophytes, ciliates and even bacteria. The decomposers will be bacteria that originate from non-axenic ciliate stocks cultures; their species composition will not be determined.

We try to simplify further and select nutrient regimes where only nitrogen is limiting. Thus we give our test-organisms in the microcosm a constant amount of light and temperature and a surplus of all other resources.


As a second choice for a simplified community, we will study biofilms in this project, in close collaboration with ms. dr. Mechthild Schmitt-Jansen (UFZ) and ms. Christina Klünder (UFZ) on Modelkey SITE 3. The system has many aspects in common with the canonical community in terms of the biota and their interactions, but differs in having more species, a spatial structure and an open (nutrient) exchange with their surroundings. Moreover it has the possibility to expose biofilms under field conditions.

Determination of the normal behavior

All organisms need at least carbon, oxygen, nitrogen and phosphorous molecules and energy to build new biomass and to maintain and repair themselves. Homeostasis (i.e. the ability to have a relatively constant body composition) comes with stoichiometric constraints on community dynamics. Chemicals can influence the uptake rates, and all other metabolic rates and efficiencies. To be able to determine the effects of the chemicals on the canonical community we first need to know the normal behavior of this community, and understand this behaviour in terms of eco-physiological properties of species. E.g.: what is the growth rate of Cryptomonas given a certain nutrient level. How many Cryptomonas can maximal be eaten per Urotricha per day? How many Cryptomonas are there needed to make one new Urotricha? Given an initial nutrient level how much of each organism will there be after a few weeks? Does cyclic behavior occur? (Models frequently predict cyclic behaviour at high nutrient levels, a phenomenon known as the paradox of enrichment.)

Modeling approach

We use the Dynamic Energy Budget theory to quantify the eco-physiological behaviour of the species and to predict the behaviour of the canonical community, given parameter estimates that are derived from single-species experiments.

The toxicity module of this theory captures effects of chemical compounds as changes of parameter values as functions of the internal concentration of compounds. The modes of action of the compound determines which parameters are effected; this can be species-specific and can depend on the concentration. The compound can e.g. increase the maintenance requirement or the costs of growth, or decrease the (maximum) nutrient/food uptake rate.

By comparing the deviating behavior with the expected normal behavior we will be able to say which variables (amounts of nutrients and of the various biota, turnover rates) have changed in the exposed canonical community or biofilm. To this end, the parameter values needed to feed the model will be estimated on the basis of single-species experiments and the literature.

Search Image for effects in more complex systems

The second aim of this project is to develop a search image for mild forms of toxic stress in communities, and use this to recognize effects of toxicants under field considitions. Functional aspects (i.e. nutrient recycling) depend on structural aspects (biomass amounts in the various trophic levels), but how mild toxic effects will show up in both aspects is presently not known. Complex feedback mechanisms in these integrated systems make application of a modeling framework essential. We also want to determine the most relevant single-species effects, to supplement and interpret measurements in the field.

Food chains

The third aim of this project is to extend the search image for effects on communities by accumulation of toxicants in food chains, coupled to effects, and to apply our search image for effects in communities to recognize effects of toxicants in field data. The species here involve fish and bentic fauna. Most parameters will be obtained from the literatire, but we will set up a limited experimental program to estimate key parameters from single-species toxicity tests. This effort will be started in 2006.

2010/06/29/11:45 Daniel Bontje: defense thesis in the Aula

11:45 welcome by Prof. Dr. Nico van Straalen
(Rector Magnificus)
promotor Prof. Dr. Bas Kooijman;
copromotor Dr. Bob Kooi
11:45 Introduction by Daniel
11:55 Dr. Markus Liebig ECT Oekotoxikologie, Flörsheim Main, Germany
12:05 Dr. Bert van Hattum Instituut voor Milieuvraagstukken, FALW, VU
12:15 Dr. Dick de Zwart RIVM, Bilthoven
12:25 Dr. Kees van Gestel Instituut voor Ecologische Wetenschappen, FALW, VU
12:35 Dr. Tjalling Jager Sectie Theoretische Biologie, FALW, VU
12:45 end of defence; start of closed meeting
13:10 ceremony
13:20 end of ceremony; lunch in the Basket

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