Michael:

This link would provide you with interesting insights:

http://sfrc.ufl.edu/facultysites/ewel/pubs/Mangrove/Gleason%20et%20al%202003.pdf

Best

Syed

I think you need to measure redox potential of the sediment, and suggest you read the book as below

Douglas, D., & McConchie, D. (1994). Analytical sedimentology. London, UK: Chapman and Hall.

Michael,

These papers may be of help. There are many meters and electrodes available on the market that measure Redox potential.

Tom

Some time study of marshy benthic foraminifera can also very helpful....