Enhancing the ecological significance of sediment contamination guidelines through integration with community analysis.

The underlying basis of sediment quality guidelines needs to be accepted both by the international scientific community and socially before they can be of use. Increasingly, this means that just saying that a certain number of species will be affected is not sufficient. Instead guidelines need to be related to changes in community composition and predicted changes in biodiversity and ecosystem function. This study derived guidelines for copper, zinc, and lead, from field-based SSDs, that predicted a 50% decrease in abundance of 5% of the taxa, well below present management guidelines. However, a multivariate model of effect demonstrated considerable changes in community composition occur at levels below these derived guidelines. Changes in the degree of rarity also occurred signaling potential changes to meta-community structure and resilience of the region. Furthermore, the most sensitive taxa indicated by the multivariate analysis were frequently of large size and those likely to affect oxygen, carbon, and nutrient exchanges between the water column and the seafloor, leading to ecological effects beyond the obvious change in composition. We suggest that guidelines should preferentially be field derived, backed where possible by experimental work. Community and functional responses should be calculated, from the same field studies, and explicitly mentioned whenever the guidelines are used to allow environmental costs to be more realistically determined.