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 revi ew of the available methods is undertaken. Ecotoxicological techniques are discussed in relation to basic ecological principles that are thought to re gulate the functioning of communities. The response to toxicants among spec ies is highly diverse and therefore the choice of test species (e.g. of typ ical riverine insects as caddisflies or mayflies) is critical, as it is the use of test-batteries. Long-term exposure may lead to developmental distur bances that may be assessed through morphometric techniques like analysis o f asymmetry. Multi-generation exposure, although rarely studied, provides a useful insight into the genetic consequences of pollution. Selection for t olerant species or varieties has been experimentally assessed for smaller o rganisms such as insects, micro-algae, and bacteria. There is also perspect ive for multivariate analysis of species distribution in relation to pollut ant exposure. Furthermore, a system approach to benthic ecology and sedimen t testing is needed. Such an approach reflects the strong linkage of ecolog ical and ecotoxicological processes. Toxicants are transformed by biologica l activity; in some cases this alleviates toxicant stress, but in other cas es degradation products are toxic as well. The risk of transformation to mu tagenic products in the environment is indicated. The re-assessment of some of the classical ecotoxicological techniques is needed to adequately fulfi l the needs of ecological recovery programs. To this purpose integration of ecotoxicological and ecological tools is needed. (C) 2000 Elsevier Science Ltd. All rights reserved.