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