The well at the pond (simple on-off switch) has a valve stem on it, but I'm guessing that's to blow out the lines to winterize? But that is purely a WAG!
That's what it's for, so good guess!
Usually on stuff up here that is seasonal and can freeze, like outdoor hydrants and such. Just pump some compresses air in them to blow water out of the lines. Saves having to replace piping and such that can't expand when water freezes.
