TEST METHOD: GENERIC DIATOM INDICES

Revised: 30 May 2007 (first issue)

RISK ASSESSMENT

Assess the Quality, Safety and Environmental risks of each step.

OVERVIEW

Diatom assemblage data from waterbodies such as rivers, streams, wetlands, estuaries and salinas may be used to assess water quality. Assemblages of pollution/salinity/dessication tolerant diatoms may be used as an early indicator of a deterioration in water quality or quantity. The following indices are based on identification to genus. Raw data at species level may be amalgamated for use with the indices.

While using indices based on generic level taxonomy reduces the time and taxonomic expertise levels required, identification should ideally be carried out to the lowest level possible. Ecological preference data exists for a sizeable percentage of species and this information may provide further insights into the habitat.

TASK SAFETY REQUIREMENTS

Delta dress code applies

PRINCIPLE OF METHOD

Data collected using the diatom sampling and identification method may be assessed with these indices. The data is collated and input as "% relative abundance" of different genera. Not all genera will be used in the indices, as many genera are indifferent to pollution, or have mixed responses from member species. Genera that contain a small number of species are also excluded. Those genera assessed by Van Dam (1994) as either specifically tolerant or sensitive are used.

Indices have been developed for various impacts; salinity, pH, oxygen requirement, N metabolism, trophic state (inorganic N & P concentrations), saprobity (organic enrichment with biological oxygen demand) and dessication. The most useful index will vary, depending on what impact you are assessing. Refer to Van Dam, Mertens and Sinkeldam (1994), "A coded checklist and ecological indicator values of freshwater diatoms from The Netherlands" for an explanation of the derivation of the impact indices.

INDICATOR GENERA

CALCULATION

For each sample, record the % relative abundance of genera used in the selected Index.

Sum the % relative abundances of the sensitive genera. Sum the % relative abundances of the tolerant genera.

Plot the resulting indices for sample sites and reference sites, against themselves, on an XYplot to see any clustering.

WORKED EXAMPLE

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