Mtr Data Analysis; Calculating Mean Trophic Ranks - Planet WGSW-24010 User Manual

5

MTR DATA ANALYSIS

This Chapter describes how to use the macrophyte data collected to calculate a Mean Trophic
Rank score for the survey and how to express the confidence in that score. It also provides
guidance on data storage.
5.1 Calculating Mean Tr ophic Ranks
Selected, usually common, aquatic macrophytes have been assigned a number from 1 to 10
according to their tolerance/preference for enriched or un-enriched waters; this is the Species
Trophic Rank (STR). The STR for each selected species can be found on the standard record
sheet and the species checklist in Appendix 5.
Mean Trophic Ranks (MTR) are to be calculated for 100m survey lengths only. All scoring
species should be included in the calculation of the MTR, but non-scor ing species should be
excluded. MTR scores are calculated as follows:
1. For all scoring species recorded, multiply the Species Trophic Rank (STR) by the Species
Cover Value (SCV) to give a Cover Value Score (CVS) for each scoring species.
Example: Scoring species
Enteromorpha sp(p)
Cladophora agg.
Nuphar lutea
Lemna minor
Potamogeton pectinatus
Mentha aquatica
Zannichellia palustris
Amblystegium riparium
Ranunculus fluitans
TOTAL
2. Add up all the numbers in the CVS column.
3. Add up the numbers in the SCV column associated with scoring species only. Do not
include non-scoring species in this calculation.
4. Divide the total score for the CVS by the total for the SCV and multiply by 10 to give the
Mean Trophic Rank (MTR):
In the above example:
5. Present MTR to ONE decimal place only.
R&D Technical Report E38
STR SCV
´
1 1
´
1 1
´
3 1
´
4 7
´
1 1
´
- (2)
´
2 1
´
1 1
´
7 7
20
MTR = (sum of CVS ¸ sum of SCV) ´ 10
MTR = (86 ¸ 20) ´ 10 = 43.0
64
CVS
= 1
= 1
= 3
= 28
= 1
= -
= 2
= 1
= 49
86