An evaluation of weight of evidence approach to assess sediment quality in the Mvoti Estuary, KwaZulu-Natal, South Africa

Abstract

A weight of evidence approach was evaluated in the Mvoti Estuary, which is affected by point and non-point sources of contaminants. Four sites were sampled in 2005 and assessed along the standard sediment quality triad lines of evidence: sediment chemistry, benthic diversity and sediment toxicity, as well as for bioaccumulation, in order to determine if this approach can be used to assess sediment quality in an estuarine environment. Benthic species composition showed a strong relationship with salinity gradient. Toxicity did not exhibit acute effects (>50% mortality) and total metal concentrations in the sediment were below available probable effects levels. Changes in the benthic community could not be directly correlated with contaminant levels due to the naturally stressed benthic environment which exists in estuaries. The study showed that, when applying the weight of evidence approach in an estuary, it is necessary to include bioaccumulation data with benthic community structure results. Without this integration, there is increased uncertainty when determining the potential for effects using the metal concentrations. The inclusion of the bioaccumulation data ensures that the information gathered during sediment quality assessments is interpreted correctly, by taking potential and current ecological effects into account.

Keywords: benthos, bioaccumulation, invertebrates, sediment quality triad, sediment toxicity