H.G. van der Geest

Influence of phosphorus on copper sensitivity of fluvial periphyton: the role of chemical, physiological and community-related factors.

The influence of eutrophication of fluvial ecosystems (caused by increased phosphorus concentrations) on periphyton Cu sensitivity is explored from a multi-scale perspective, going from the field to the laboratory. The study design included three tiers: a field study including the characterization of land use and the ecological state of the corresponding river sections in the Fluvià River watershed, an experimental investigation performed with natural periphyton from the previously studied stream sites in indoor channels, and finally a culture study in the laboratory. Results showed that differences in copper sensitivity of natural periphyton communities followed the gradient of nutrient concentration found in the field. Results from the culture experiments demonstrated that both, P-conditions during growth and P-content in the media are important factors modulating the toxicological response of algae to Cu. The observations from this study indicate that the ecological effects of metal pollution in rivers might be obscured by eutrophication.

Dynamics of metal availability and toxicity in historically polluted floodplain sediments.

Many floodplains contain high concentrations of sediment associated contaminants that might be subjected to large changes in terms of mobility, transformation and bioavailability. Therefore, this study describes 1) changes in the redox conditions and the mobility of metals in artificially uncovered polluted floodplain sediments, 2) metal uptake by organisms and 3) colonization, succession and functioning of benthic algae on these sediments. Flooding caused long term changes in redox potential (Eh) profiles. In top layers strong gradients in redox potential established quickly, while in deeper layers changes occurred more gradually. The availability of copper as measured by Diffusive Gradients in Thinfilms (DGT) showed a consistent relationship with fluctuations in Eh. However, this relationship was restricted to deeper layers in the sediment. Within 1 week high amounts of total copper were immobilized. Differences in total copper concentrations between polluted and clean sediments became only partially apparent when comparing the available copper fraction (DGT-Cu). Introduced Tubifex shows only marginal differences in levels of accumulated Cu. Colonization, growth and succession of algal communities on polluted sediments was not impaired, most likely due to low bioavailability. It is concluded that changing environmental conditions, such as flooding, can result in stable chemical conditions with low a availability of metals and hence in a diminution of actual ecological risks.

Linking ecological and ecotoxicological techniques to support river rehabilitation.

Human activities in river catchments interfere with natural fluxes of water and materials. Diffuse inputs and point-sources of toxicants have modified the ecological state of riverine communities considerably, and sanitation schemes are now under development for various rivers. To improve analysis, monitoring and prospecting the role of toxicants in river ecosystems a review of the available methods is undertaken. Ecotoxicological techniques are discussed in relation to basic ecological principles that are thought to regulate the functioning of communities. The response to toxicants among species is highly diverse and therefore the choice of test species (e.g. of typical riverine insects as caddisflies or mayflies) is critical, as it is the use of test-batteries. Long-term exposure may lead to developmental disturbances that may be assessed through morphometric techniques like analysis of asymmetry. Multi-generation exposure, although rarely studied, provides a useful insight into the genetic consequences of pollution. Selection for tolerant species or varieties has been experimentally assessed for smaller organisms such as insects, micro-algae, and bacteria. There is also perspective for multivariate analysis of species distribution in relation to pollutant exposure. Furthermore, a system approach to benthic ecology and sediment testing is needed. Such an approach reflects the strong linkage of ecological and ecotoxicological processes. Toxicants are transformed by biological activity; in some cases this alleviates toxicant stress, but in other cases degradation products are toxic as well. The risk of transformation to mutagenic products in the environment is indicated. The re-assessment of some of the classical ecotoxicological techniques is needed to adequately fulfil the needs of ecological recovery programs. To this purpose integration of ecotoxicological and ecological tools is needed.

Hazard and risk of herbicides for marine microalgae

Due to their specific effect on photosynthesis, herbicides pose a potential threat to coastal and estuarine microalgae. However, comprehensive understanding of the hazard and risk of these contaminants is currently lacking. Therefore the aim of the present study was to investigate the toxic effects of four ubiquitous herbicides (atrazine, diuron, Irgarol(®)1051 and isoproturon) and herbicide mixtures on marine microalgae. Using a Pulse Amplitude Modulation (PAM) fluorometry based bioassay we demonstrated a clear species and herbicide specific toxicity and showed that the current environmental legislation does not protect algae sufficiently against diuron and isoproturon. Although a low actual risk of herbicides in the field was demonstrated, monitoring data revealed that concentrations occasionally reach potential effect levels. Hence it cannot be excluded that herbicides contribute to observed changes in phytoplankton species composition in coastal waters, but this is likely to occur only occasionally.

An improved datalogger and novel probes for continuous redox measurements in wetlands.

In soils and sediments, the redox potential (Eh) is an important parameter controlling the persistence of many organic and inorganic compounds. Especially in wetlands, fluctuations in redox potential values can be very large and depth dependent. For this reason, field deployable logging systems have previously been developed, yet these systems were limited in several aspects. Here we report the development of an improved multichannel datalogger (HYPNOS) and two novel probes for continuous monitoring of Eh profiles, and briefly illustrate the potential applications. The combination of a multichannel logger with different types of probes allows characterisation of spatial and temporal variability of redox potential in relation to environmental and ecological parameters, and we expect this will greatly enhance our knowledge of the functioning of wetlands.

Sensitivity of characteristic riverine insects, the caddisfly Cyrnus trimaculatus and the mayfly Ephoron virgo, to copper and diazinon.

This study reports the effects of two model toxicants, copper and diazinon, on two characteristic riverine insect species, the caddisfly Cyrnus trimaculatus and the mayfly Ephoron virgo. It was demonstrated that these species are very sensitive to both compounds in comparison with aquatic insects traditionally used in ecotoxicity tests. For diazinon, the 96-h LC(50) value of Cyrnus trimaculatus (1.1 microg/l) is lower than for any other insect species known from the literature and for copper it was demonstrated that Ephoron virgo is among the most sensitive aquatic insect species. The observed low LC(50) values stress the importance of using these indigenous species in assessing the risk of environmental contaminants in large European rivers and in defining conditions for ecological recovery.

Predictability of bacterial activity and denitrification in aquatic sediments with continuous measurements of redox potential.

Redox potential has been adopted as a qualitative parameter for interpreting solubility changes of nutrients and contaminants and the biological activity within wetland systems for several decades. The majority of studies considering the redox geochemistry in sediments used measurements of bulked material and single point measurement of biogeochemical parameters for interpretation, yet it remains questionable whether this information is reliable for environments that are very dynamic, such as wetlands. In this study it is evaluated whether variations in redox potential reflect dynamics of denitrification and overall bacterial respiration using continuous measurements of redox potential in time-series experiments in laboratory microcosms, in which the biogeochemical variation was enhanced by bioturbation. The results presented here suggest that measurements of redox potential have predictive potential in approximating rates of denitrification and overall bacterial respiration in aquatic sediments. The data clearly suggest that, while sediment bulk measurements and measurements of single profiles of redox potential, denitrification and bacterial activity often fail to provide ecological relevant information in dynamic systems, measurements of spatial and temporal redox potential profiles provide a useful parameter that reflects biogeochemical processes and functioning of sediments.

Impact of a diazinon calamity in 1996 on the aquatic macroinvertebrates in the river Meuse, The Netherlands.

A more or less continuous load of pesticides has been noted in the River Meuse in recent years. In April 1996, when high concentrations (up toca. 1 μg 1−1) of the insecticide diazinon were measured in the River Meuse at the Belgian-Dutch border, the maximum concentration for drinking water production was exceeded. This was alerted after activity changes of fish and daphnids in the biological monitoring systems (RIZA). These observations were compared with literature toxicity data of diazinon, in order to determine the ecological impact of this diazinon discharge on the aquatic macroinvertebrates. LC50 values of several aquatic macroinvertebrate species were exceeded. In addition, a high mortality was observed in bioassays with the midgeChironomus riparius and the caddisflyHydropsyche angustipennis. It is inferred that the species composition of the macrofauna community in the River Meuse is likely to be reduced by such an accident. Recolonization of the River Meuse by sensitive macrofauna species may therefore be prevented by incidental pesticide discharges.

Sediment composition mediated land use effects on lowland streams ecosystems

Despite the widely acknowledged connection between terrestrial and aquatic ecosystems, the contribution of runoff to the sediment composition in lowland stream deposition zones and the subsequent effects on benthic invertebrates remain poorly understood. The aim of this study was therefore to investigate the mechanisms by which runoff affects sediment composition and macroinvertebrates in deposition zones of lowland stream ecosystems. To this end, sediment from runoff and adjacent instream deposition zones from streams with different land use was chemically characterized and the biological effects were assessed at the species, community and ecosystem level. Runoff and deposition zone sediment composition as well as biological responses differed clearly between forest and agricultural streams. The stream deposition zone sediment C/N ratio reflected the respective runoff sediment composition. Deposition zones in the forest stream had a higher C/N ratio in comparison to the agricultural streams. Growth of Hyalella azteca and reproduction of Asellus aquaticus were higher on forest stream sediment, whereas chironomids and worms suffered less mortality on the agricultural sediments containing only natural food. The forest stream deposition zones showed higher values for indices indicative of biological integrity and had a lower sediment oxygen demand. We concluded that agricultural land use affects lowland stream ecosystem deposition zones at the species, community and ecosystem level via altered food quality (C/N ratio) and higher oxygen demand of the sediment.