M ultim etric A nalysis
M ultim etric A nalysis
T his approach is the sam e as that used for L evel 2, except m ore m etrics are incorporated into the analysis. T he m etrics and associated scoring criteria for L evel 3 m etric assessm ents are listed below .
T axa R ichness T his is the total num ber of invertebrate taxa identified from the sam ple.
M ayfly R ichness T his is the total num ber of m ayfly taxa identified from the sam ple.
Stonefly R ichness T his is the total num ber of stonefly taxa identified from the sam ple.
C addisfly R ichness T his is the total num ber of caddisfly taxa identified from the sam ple. Sensitive T axa T his is the num ber of taxa identified that are know n to be very sensitive to stream disturbance. T he list of taxa that qualify as “ sensitive” are listed in
A ppendix F.
Sedim ent Sensitive T axa Som e taxa are know n to be very sensitive to inputs of fine sedim ent. T he presence of one or m ore of these taxa indicate that fine sedim ents are probably not a m ajor concern.
M odified H B I “ H B I” stands for H ilsenhof B iotic Index. T his is an index of a taxa’s sensitivity to organic enrichm ent that typically occurs as a result of excessive nutrient inputs. Index values for individual taxa range from 1 to 10. L ow scores indicate high sensitivity (found only in w aters w ith low organic enrichm ent). H igh scores indicate low sensitivity (tolerant of w aters w ith high organic enrichm ent). H B I index values for each taxa are listed in the taxa list for O regon stream s in
A ppendix F. % T olerant T axa
T his is the percent of the invertebrate com m unity m ade up of taxa tolerant to disturbance. T axa counted as “ tolerant” taxa are listed in A ppendix F.
D ivide the abundance of tolerant taxa by the total num ber of organism s sorted from the sam ple, and m ultiply by 100.
% Sedim ent T olerant T axa T his is the percent of the invertebrate com m unity m ade up of taxa tolerant to fine sedim ents (see
A ppendix F). D ivide the abundance of sedim ent tolerant taxa by the total num ber of organism s sorted from the sam ple, and m ultiply by 100. % D om inant (single taxa) T his is the total abundance of the single m ost abundant taxon in the sam ple divided by the total num ber of organism s sorted from the sam ple, m ultiplied by 100. A high percent of a single taxon indicates som e disturbance has likely occurred to the invertebrate com m unity.
A fter calculating each individual m etric score add them together for the total score or biotic index. Stream condition levels are based on the ranges of total scores listed below .
T ab le 12-5. G en u s/sp ecies level metrics an d scorin g criteria.
Scorin g C riteria
Score M etric
R aw
V alu e
5 3 1 (C ircle)
M ayfly R ich n ess
Ston efly R ich n ess
3 -5
C addisfly R ich n ess
5 3 1 Sedim en t sen s. T axa
Sen sitive T axa
M odified H B I
% T oleran t T axa
(sin gle taxa)
Score R an ge
Stream C on dition
>39 N o Im p airm en t: p asses level 3 assessm en t. In dicates good diversity of in verteb rates an d stream con dition s w ith little or n o distu rb an ce.
3 0 -3 9
Sligh t Im p airm en t: eviden ce of som e im p airm en t exists.
2 0 -2 9
M oderate Im p airm en t. clear eviden ce of distu rb an ce exists.
<20 Severe Im p airm en t. con dition s in dicate a h igh level of distu rb an ce.
M ultivariate A nalysis