Why does the flux of methane to the atmosphere from coastal marshes drop (relative to freshwater)to near zero?

Question

Quizplus · Accepted Answer

A) The increase in salinity and sulfate concentrations in coastal marshes can inhibit methane formation by discouraging the growth of methanogenic communities. Sulfate is a preferred electron acceptor for some bacterial communities, which ultimately leads to the reduction of sulfate with methane production inhibited. 
D) Sulfate reduction is a dominant microbial process in coastal marshes due to the abundance of sulfate in the water. This process competes with methanogenesis for organic substrates resulting in less methane being produced and released into the atmosphere.

Why Does the Flux of Methane to the Atmosphere from Coastal