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Lakes and Watercourses

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APPENDIX 2<br />

Calculation of index <strong>and</strong> other<br />

parameters for assessing<br />

benthic fauna<br />

(1) Shannon-Wiener’s diversity index (Shannon, 1948) is calculated as:<br />

s<br />

n i<br />

n i<br />

H’= – Σ — log 2 —<br />

i=1 N N<br />

where N = the total number of individuals, <strong>and</strong> n i = the number of<br />

individuals of the ”i”th species.<br />

(2) The ASPT index (average score per taxon) (Armitage et al., 1983) is<br />

calculated by identifying organisms found in the sample at family (taxon)<br />

level (class for Oligochaeta). Each family is given a point score representing<br />

its tolerance to pollution (see below). The scores are added up <strong>and</strong><br />

the total divided by the total number of families recorded<br />

The following families score 10:<br />

Siphlonuridae, Heptageniidae, Leptophlebiidae, Ephemerellidae,<br />

Potamanthidae, Ephemeridae,Taeniopterygidae, Leuctridae, Capniidae,<br />

Perlodidae, Perlidae, Chloroperlidae, Aphelocheiridae, Phyrganeidae,<br />

Molannidae, Beraeidae, Odontoceridae, Leptoceridae, Goeridae,<br />

Lepidostomatidae, Brachycentridae, Sericostomatidae.<br />

The following families score 8:<br />

Astacidae, Lestidae, Agriidae, Gomphidae, Cordulegasteridae, Aeshnidae,<br />

Corduliidae, Libellulidae, Psychomyiidae, Philopotamidae.<br />

The following families score 7:<br />

Caenidae, Nemouridae, Rhyacophilidae, Polycentropodidae,<br />

Limnephilidae.<br />

The following families score 6:<br />

Neritidae, Viviparidae, Ancylidae, Hydroptilidae, Unionidae, Corophiiidae,<br />

Gammaridae, Platycnemididae, Coenagriidae.<br />

The following families score 5:<br />

Mesoveliidae, Hydrometridae, Gerridae, Nepidae, Naucoridae,<br />

87

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