Weight of evidence (WOE) describes the process to collect, analyse and evaluate a combination of different qualitative, semi-quantitative or quantitative lines of evidence to make an overall assessment of water/sediment quality and its associated management. The water/sediment quality guidelines recommend measuring indicators from multiple lines of evidence across the pressure–stressor–ecosystem receptor (PSER) causal pathway. This gives greater weight to assessment conclusions and subsequent management decisions to meet the water/sediment quality objective than basing evaluation on a single line of evidence.
Mining operations develop and implement Receiving Environment Monitoring Plans (REMP) to monitor and record the potential impacts of the release of contaminants on the receiving environment periodically and whilst contaminants are being discharged from the site, with the aims of identifying and describing the extent of any adverse impacts to local environmental values and monitoring any changes in the receiving waters in accordance with conditions in their Environmental Authority (EA). Environmental Authorities also impose compliance with a REMP, which include routine monitoring of total and dissolved metals. If a concentration in dissolved metals exceeds the trigger level listed in the EA, an investigation must be undertaken.
A weight of evidence model was used to assess the pressures and stressors of water/sediments in a specific receiving environment with temporary waters and water/sediment chemistry, bioavailability, and bioassay were used as the multiple line of evidence. Determining the bioavailable fractions of metals in water/sediment is a necessary step for assessing their effect on biota and for assessment of water/sediment quality. Bioavailability of trace metals associated to sediments was evaluated using pore water analysis and DGT application. The evaluation of sediment toxicity through laboratory or field bioassays is also an important additional line of evidence for assessments of sediment quality. Recent results in more detail will be presented.