Development of ecologically relevant quality indicators for sediment microbial communities

Abstract

With the implementation of European Water Framework Directive, good chemical status for all water bodies and good ecological status for all natural waters are to be reached by 2015. Considering sediments as an inseparable part of river basins, current sediment quality guidelines derived only from chemical concentrations can not guarantee the ecological services of sediments in supporting aquatic ecosystems. There is therefore a need to develop an integrated quality indicator (IQI) addressing the ecological relevance to assist the chemically dominant sediment assessment for a better river basin management. A weight of evidence approach integrating sediment ecotoxicities and functional diversity of sediment microbial community in nutrient cycling was employed. The sediment ecotoxicity describes the potential risk of contaminants on biota through bioassays, which integrate effects of pollutants and environmental conditions. Two standardised bioassays, algal growth inhibition test and bacterial contact assay, were applied for different exposure routes. The functional diversity of microbial community in nutrient cycling provides the supporting service in aquatic ecosystem, which is necessary for the production of other organisms and maintain the conservation of nature. The diversity in nutrient cycling was addressed by the heterotrophic carbon substrates utilisation patterns and autotrophic nitrification was tested as the key ecological function. In addition, substrates induced DMSO reduction method was proposed to characterise the microbial functional diversity including both heterotrophic and autotrophic activities. A temporal investigation of sediment quality using these lines of evidence was carried out in the river Elbe to define a possible response range. The results were further integrated using a fuzzy rule based model taking biological uncertainties into account to develop quality classes and indices characterising sediment quality in ecotoxicities, functional stability (heterotrophic), and nitrification (autotrophic). All three quality classes and indices were combined and presented using quantitative triangles and linguistic tables as the final IQI. The effect of aging and resuspension on sediment quality was evaluated with the developed IQI as an example to illustrate its unexpected impact on nutrient cycling despite the reduced risk from contaminants on biota. The IQI provides a transparent measure communicating the complex ecological relevant sediment quality with simplicity, which offers a clear overview coupling causes as well as actions for decision makers and can be explained to and understood by non scientists.