Trust 100 Anglicans to conserve river garden (8)
I believe the answer is:
credence
'trust' is the definition.
(thesaurus)
'100 anglicans to conserve river garden' is the wordplay.
'e00' becomes 'c' ('C' can be a synonym of 'e00').
'anglicans' becomes 'ce' (Church of England).
'to conserve' is an insertion indicator.
'river' becomes 'r'.
'garden' becomes 'eden' (I've seen this before**).
'c'+'ce'='cce'
'r'+'eden'='reden'
'cce' going around 'reden' is 'CREDENCE'.
(Other definitions for credence that I've seen before include "Acceptance" , "Sort of table" , "Belief in something as true" , "Faith or belief placed in something" , "that creates confidence" .)