Diagnostic capacity of laboratory mesocosms, response of macroinvertebrate communities to sediment contamination

There is now widespread recognition that chemical monitoring of the environment is not suficient given that pollution is essentially a biological phenornenon because of its impact on living organisms. Careful interpretation of the biota, in light of the known ecology of the species involved, is needed to ascertain whether there is impact, and may even indicate the nature of the cause. An approach developed in Great Britain (RIVPACS) provides a method for biological surveillance, conservation, and environmental impact assessment in rivers. It predicts the macroinvertebrate fauna to be expected at a given site based on a small number of environmental features. Using the mode! , it is possible to predict the benthic community that should occur at a site. A modified approach to that described in the British Riven study has been used in the assessment of the Great Lakes. A goal of that study was to predict what the benthic community should look like at a site if it were undisturbed. The approach also provides an appropriate reference for determining the degradation at a site due to anthropogenic contamination. However, when there is divergence fiom an expected state, as yet it is not possible to define what ishre the causative agent@). In a site exposed to multiple stresson, no clear statement can be made as to which potential sources should be controlled, other than by inference fiom chemicai anaiysis. As divergence fiom an expected state is due to changes in abundance of species corn those predicted, it is reasonable to assume that communities of organisms will have characteristic responses to certain stresson. Therefore, the way in which a site diverges fkom its expected state rnay provide useN diagnostic information as to the nature of a stress. This study was intended to complement the predictive mode1 designed for the Great Lakes. The invertebrate communities contained within the sediment of intact box cores, coiiected from the field and manipulated under laboratory conditions, were used to investigate the directional changes in cornmunity composition as a result of contamination. This study showed that the intact box cores could be maintained in the laboratory with little change in the resident fauna. Despite reductions in the overall abundance of species, which was evident in the separation of the field and control boxes in ordination space, univariate analysis of the most abundant taxa and a number of diversity and richness measures showed that there was little significant change between the field and laboratory boxes on collection, or over time. It was also established that the addition of low levels of nutrients had little effect on the communities. Clean sieved sediment spiked with cadmium, atrazine or nutrient enriched was added to intact box cores. Upon sarnpling the boxes, the benthic macroinvertebrate community composition was analysed using the ordination technique Multi-Dimensional Scaling. The consistency and pattern of change in the community composition as a result of the contaminants was identified with respect to the direction in which each treatment moved the community in ordination space. Not al1 of the contaminants were identified as having an impact when compared to the field data. However, this study did establish that different contaminants did have distinct impacts on community composition. Intact cores of naturally CO-adapted species show potential as a diagnostic tool and are a usefid technique for the analysis and identification of sediment contamination. They combine the reaiism of naiural communities fiom the environment uith the power of controlled laboratory experiments. Their use may avoid some of the problems encountered when extrapolating data obtained from in vitro studies to natural communities.