Appendix 2:


Environment Agency Biological Indices



This is based on groups of macro-invertebrates (small animals including mayfly nymphs, snails, shrimps and true worms) that are found on the riverbed.

Macro-invertebrates are used because they:



Samples are collected using a standard method of 3 minutes active sampling with a pond net, plus a 1 minute visual search for animals living on the water surface, or attached to rocks, logs or vegetation. Other features of the sampling area are recorded (substrate type, sampling depth, watercourse width, channel depth, aquatic vegetation, fish, land use, shade, evidence of weed management, pollution, turbidity, etc). In the laboratory, the macro-invertebrates are identified to family level, as a minimum requirement, and to species level (where possible) and their relative abundances estimated, according to the following scheme:


Abundance category

Interpretation

A

1 to 9 specimens in sample

B

10 to 99 specimens in sample

C

100 to 999 specimens in sample

D

1000 to 9999 specimens in sample

E

>10, 000 specimens in sample



Terms used in routine reporting of biology data.


BMWP Biological Monitoring Working Party Score

Scores are assigned to invertebrate families depending on their tolerance of organic pollution.  The individual family scores are added together to give a sample BMWP score, higher scores indicate cleaner conditions.  BMWP scores can vary from 0 (grossly polluted) to 150+ (excellent quality).  


TAXA

This is the number of BMWP scoring families found in the sample.  There may be additional non-scoring taxa in the sample which are not recorded here.


ASPT Average Score Per Taxon

This is the total BMWP score divided by the number of BMWP scoring taxa and is therefore independent of sample size.  ASPT can vary from 0.00 (grossly polluted) to 6.00+ (excellent quality).


LIFE (Family)/ LIFE (Species) Lotic-invertebrate Index for Flow Evaluation

A flow score is derived for each species/family using the species/family abundance and ecological association with different flows (see conversion table below). An overall LIFE score is calculated for the sample from the sum of the individual species/family flow scores divided by the number of scoring species/families. LIFE scores less than 6.00 generally indicate sluggish or still water conditions.  As current velocity increases, so do LIFE scores.  LIFE values greater than 7.5 indicate very fast flows.



Abundance categories

Flow group

A (1-9)

B (10-99)

C (100-999)

D/E (1000+)

I Rapid

9

10

11

12

II Moderate/fast

8

9

10

11

III Slow/sluggish

7

7

7

7

IV Flowing/standing

6

5

4

3

V Standing

5

4

3

2

VI Drought resistant

4

3

2

1



Reference


Extence C., Balbi DM. and Chadd RP. 1999. River flow indexing using British benthic macro-invertebrates: a framework for setting hydro-ecological objectives. Regulated Rivers Research and Management 15: 543-574.


For more information on these indices contact the Biology team at the Environment Agency, Spalding.