I'm speaking more to Wildlife Management Areas rather than Waterfowl Management Areas. But it applies to both.
"Each WMA operates according to its own habitat management plan. Some WMAs and portions of WMAs are closed to the public, while others have limited access during certain times of the year. Unlike other public or state-owned lands, WMAs are not multi-use lands, and the types of recreation allowed are limited."
It seems there was quite a discussion during one of the WB meetings concerning bikes and motorized vehicles and I thought they said it was pretty simple. Post a sign with any restrictions. I might be completely off but that was my recollection. They certainly have had no problem closing them to overnite camping when they are having problems.