Page 240 - Freshwater-Biology-and-Ecology-Handbook

CHAPTER 5 3.1.17 3.1.17 MetTol (Metal Tolerance) index

The Metal Tolerance (MetTol) index is used to evaluate ecological damage caused by metal
contamination. At ecologically degraded sites, it can be used to assess the degree to which
metal contamination is a contributory cause.

MetTol – Metal Tolerance index

The Metal Tolerance index is for evaluating ecological damage caused by metal
contamination.

MetTol uses species-level data and is expressed as an ASPT. It was designed to be
compatible with current monitoring methods and for use with RIVPACS as an EQR
(Environmental Quality Ratio).

MetTol = sum of MetTol value for each
taxon / number of MetTol-scoring taxa

MetTol was derived from a survey of sites in 20 spatially independent river catchments in
areas affected by metal mine facilities. (108) Ordination techniques were used to determine
the influence of the metal stress gradient on macroinvertebrate community composition,
whilst accounting for natural background variation among stream types. Using this
approach, the relative sensitivity of a range of macroinvertebrates to metals stress was
quantified and used as the empirical basis of MetTol.
Tests confirmed that the MetTol index is sensitive to bioavailable metal contamination,
whether it is determined from analysis of tissue concentrations in selected biomonitoring
taxa, predicted from stream water chemistry, or inferred from metal concentrations in the
bed sediment.

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