Interactions between nutrients and toxicants in shallow freshwater model ecosystems Promotor: Prof. Dr. A. A. Koelmans Persoonlijk hoogleraar bij de leerstoelgroep Aquatische Ecologie en Waterkwaliteitsbeheer, Wageningen Universiteit Co-promotor: Dr. T. C. M. Brock Senior wetenschappelijk onderzoeker Alterra, Wageningen Universiteit en Research centrum Samenstelling promotiecommissie: Prof. Dr. W.P. Cofino Wageningen Universiteit Prof. Dr. A.J. Murk Wageningen Universiteit Prof. Dr. W. Admiraal Universiteit van Amsterdam Prof. Dr.ir. A.J. Hendriks Radboud Universiteit Nijmegen Dit onderzoek is uitgevoerd binnen de onderzoeksschool SENSE (Socio- Economic and Natural Sciences of the Environment). Interactions between nutrients and toxicants in shallow freshwater ecosystems Ivo Roessink Proefschrift Ter verkrijging van de graad van doctor op gezag van de rector magnificus van Wageningen Universiteit, Prof. Dr. M. J. Kropff, in het openbaar te verdedigen op woensdag 27 februari 2008 des namiddags om half twee in de Aula CIP-data Koninklijke Bibliotheek, Den Haag Interactions between nutrients and toxicants in shallow freshwater ecosystems / Roessink, I. PhD-thesis Wageningen University, Wageningen, The Netherlands – with references – with summary in English and Dutch ISBN: 978-90-8504-875-6 “Not everything that counts can be counted, and not everything that can be counted counts.” Albert Einstein Voor mijn schatjes Ivo Summary Summary The structure of a freshwater community is influenced by several factors, including the trophic ( i.e ., nutrient) status of the specific system and the background concentrations of persistent pollutants in the sediment. Since these factors are subject to spatio-temporal variation, it is likely that the response of an aquatic community to an additional stressor also varies in space and time. Additional stressors may comprise toxicants that enter the aquatic environment through agricultural or industrial use. This thesis investigates the influence of the trophic status of a shallow freshwater system and/or the presence of persistent pollutants in the sediment on the fate and ecological effects of an insecticide and a fungicide/biocide. Additionally, this thesis aims to shed light on the influence of macrophytes and fish on the partitioning and redistribution of sediment-bound polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). PAHs and PCBs are predominantly ‘historical’ pollutants that accumulate in sediments and are rather persistent. What is the effect of an insecticide on the aquatic community of a eutrophic phytoplankton-dominated or a mesotrophic macrophyte- dominated shallow freshwater ecosystem? To answer this question, 12 cylinders were inserted in both a eutrophic phytoplankton-dominated and a mesotrophic macrophyte- dominated freshwater ecosystem. Both types of freshwater ecosystem were treated with the insecticide lambda-cyhalothrin 3 times, at weekly intervals, at concentrations of 0, 10, 25, 50, 100 and 250 ng/L ( n= 2). The dissipation rate of the insecticide from the water phase proved similar between the two types of test system. After 1 day, only 30% of the amount of lambda-cyhalothrin applied was still present. Direct toxic effects were predominantly observed on insects and crustaceans. These effects on sensitive taxa matched the results of short-term laboratory experiments. A remarkable result is that of the small differences in ecological threshold values of direct toxic effects between the phytoplankton-dominated and macrophyte-dominated systems. The ecological threshold value is the concentration at which few or no effects of the test compound are observed. Larger differences in the response of the two systems comprised the rate of recovery and indirect effects on less sensitive organisms ( e.g. , through shifts in predation and competition) at concentrations higher than the threshold level. Effects were more pronounced in the plankton-dominated system, and the rate of recovery was faster there as well. This phenomenon can be explained by the presence in the plankton-dominated systems of generally smaller 7 Summary organisms, which have a shorter life-cycle than those in the macrophyte- dominated systems. The results of this experiment are presented in detail in chapter 2. What is the influence of historical pollution in the sediment on the response of the aquatic community to fungicide/biocide exposure? To answer this question, 10 model ecosystems with polluted sediment and 10 model ecosystems with clean sediment were constructed. The sediments originated from floodplain lakes along the river Waal in the Netherlands. The quality of the sediment determined the type of aquatic community that developed in the two types of system. From the start, the macrophyte vegetation developed better on the polluted sediment, which contained not only more toxicants but also more nutrients. The fungicide/biocide triphenyltin acetate (TPT) was applied once, at concentrations of 0, 1, 3, 10, 30 and 100 µg/L ( n= 2 per sediment type). Dynamics of the TPT concentration in the water phase were similar between the two system types. Nevertheless, higher concentrations of TPT were observed in the clean sediment systems, where fewer macrophytes were present. In both system types, representatives of several taxonomic groups (snails, worms, crustaceans and insects) showed a clear response to the TPT treatment. Despite the fact that TPT was very persistent in the sediment, no treatment-related effect on sediment-dwelling nematodes was observed. Although some differences in intensity and duration of effects were observed between the two system types, the presence of historical pollutants in the sediment hardly influenced the overall sensitivity of the aquatic community. The results of this experiment are presented in detail in chapter 3. Can TPT-related effects observed in model ecosystems be predicted by short-term toxicity experiments in the laboratory? To answer this question, representatives of taxonomic groups sensitive to TPT in the microcosms were also tested in the laboratory by means of so-called ‘single species tests’ (SST; duration 96h). In total, 32 different aquatic taxa were studied. When possible, the responses of these taxa were used to calculate the concentration at which 50% of the test organisms showed a treatment-related effect to TPT application (EC 50 ). Additionally, EC 50 values were calculated for populations of taxa that showed a treatment-related response to TPT application in the two types of model ecosystem. These microcosm EC 50 values were calculated 2, 4 and 8 weeks post TPT application, since this was the period in which the largest effects were observed. The EC 50 values calculated for different taxa were used to obtain a so-called species sensitivity distribution curve 8 Summary (SSD), from which a value can be derived at which 95% of the species tested are protected. This value is called the hazardous concentration to 5% of the species tested (HC 5). The calculated HC 5 value, based on 96-h SST, was 1.3 µg/L. The calculated HC 5 values for microcosms (2–8 weeks after application) varied between 0.2 and 0.6 µg/L (based on peak concentrations of TPT in the water phase of the test systems). The taxa that were sensitive in the microcosm also showed a sensitive response in the laboratory SST, with the exception of insects, which sometimes showed a pronounced treatment-related response in the microcosms but were rather insensitive in the laboratory. In general, the taxa tested responded less sensitively in the laboratory SST than in the microcosm experiments. Possible explanations for this phenomenon include the potentially long time needed (>96h) to express effects, and additional chronic exposure via the food chain in the model ecosystems. A remarkable finding is that the HC 5 values hardly differed between the microcosms with clean and polluted sediment. This implies that ecological threshold levels for toxic effects of TPT are apparently not influenced by background pollutants present in the sediment. The results of this experiment are presented in detail in chapter 4. Can the presence of background pollutants and recently added TPT in sediments be measured with standardized bio-assays? The observations described above concern taxa that occur more or less ‘naturally’ in the model ecosystems. Another technique to assess the impact of toxicants under field conditions is that of using standardized bio-assays. Two aquatic species that are frequently used to test sediment quality are the midge Chironomus riparius and the mayfly Ephoron virgo , however these species were not observed in the model ecosystems. Sediment from our TPT model ecosystem experiment was used to assess the response of both species to pollutants in the sediment. Fifteen weeks after the TPT application, sediment samples were taken from each individual test system, with the exception of the 3 µg/L level in both types of test system, and transferred to the laboratory for use in the bioassays. A previous study had already determined the contaminants in the sediment (PAHs, PCBs and metals), and TPT concentrations were measured in the control and the 30 µg/L test immediately after sampling. Linear regression was used to determine the TPT concentrations in the other sediments. For each of the test systems, 25 mL mixed sediment was put in a glass jar, and 20 larvae of E. virgo or 5 larvae of C. riparius were added. After 10 days, the growth and survival of the organisms was assessed.