He planned reconstruction entirely on wetlands (8)
I believe the answer is:
marshall
'he planned reconstruction' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'entirely on wetlands' is the wordplay.
'entirely' becomes 'all' (all can mean entirely or completely).
'on' is a charade indicator (letters next to each other).
'wetlands' becomes 'marsh' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'all' put after 'marsh' is 'MARSHALL'.
Can you help me to learn more?
(Other definitions for marshall that I've seen before include "Law officer in the old West" , "Scottish sculptor" , "Author of European post-war recovery plan" , "- - plan (post WW2)" .)