Planet WGSW-24010 User Manual page 86

Table 1 MTR scor es summar ised accor ding to r iver community types
R
IVER
C
OMMUNITY
1.
T
YPE
I Lowland rivers with minimal gradients. Predominantly in south and east England, but may occur
wherever substrates are soft and chemistry enriched
II Rivers flowing in catchments dominated by clay
III Rivers flowing in catchments dominated by soft limestone such as Chalk and Oolite
IV Rivers with impoverished floras, confined to lowlands or eutrophic systems
V Rivers of sandstone, mudstone and hard limestone catchments in England and Wales, with similar features
to those of Type VI
VI Rivers predominantly in Scotland and northern England in catchments dominated by sandstone, mudstone
and hard limestone; substrates usually mixed coarse gravels, sands and silts mixed with cobbles and
boulders
VII Mesotrophic rivers where fine sediments occur with boulders and cobbles, so a mix of bryophytes and
higher plants is typical; often downstream from Type VIII communities
VIII Oligo-mesotrophic, fast-flowing, rivers, where boulders are common and bryophytes typify the plant
assemblages; intermediate, and often between, Types IX and VII
IX Oligotrophic rivers of mountains and moorlands where nutrient and base levels low; bedrock, boulders and
coarse substrates dominate
X Ultra-oligotrophic rivers in mountains, or streams flowing off acid sands; substrates similar to Type IX but
often more bedrock
1. Revised classification of Holmes et al (1998) from the version previously published in the SSSI selection guidelines (Nature Conservancy Council, 1989).
R&D Technical Report E38 72
(DO NOT USE THIS TABLE TO PREDICT MTRs)
1.
G
ENERAL DESCRIPTION
Mean Mean No. of
2. 2.
MTR of top samples
10%
34.0 40.8 49
32.9 42.9 429
40.2 47.3 136
39.5 58.2 361
47.6 65.3 559
46.2 59.6 258
52.9 75.0 97
68.1 82.0 537
68.8 86.2 70
83.0 95.5 327