I don't know if I've got the same variety of Lemna, but by this time of year, most of mine has sunk down below the water. In the spring, it comes back up. If it keeps blowing out, you could try putting it in something mesh-like that you can weight down at the bottom for the winter?
My ponds are both far more sheltered from the sound of things, but we get some impressive winds (but ours speak metric, so you'd have to translate 60 km/hour with gusts up to 90 km/hr.) Our chickens have never shown much interest, but our ducks go crazy over it. I wasn't all that impressed with it as a
mulch either - I'm thinking that the micro-bugs that digest it are more prevalent in the water than on
land. Now that we've got ducks it's a non-issue - the ducks turn it into shit which my growies like just fine! That said, my particular desire in my ponds is to support the
local tree frogs. The lemna seems to support the tadpoles, so I don't harvest more for than I think the system can tolerate.