The family cabin is in northern Minnesota - Aitken County. Lots of time spent hunting the flat marshes hopping between islands of trees (rabbit, grouse, and sometimes a woodcock. Never saw a pheasant that far north.) Even with the ditches I think the only thing the few farms there grew were potatoes.
So with the existing berm - I’m guessing that it isn’t planted or anything - it just has the normal brush and weeds and such that will grow there? Although I’m guessing that this new “buffer” extends far beyond the berm into your existing fields. Do you know why the increase of phosphates in the water due to the buffers? I suppose to fertilize the new “wild” growth that has been planted so close to the ditch?
Years ago I was at a relative’s ranch in Oregon. The government was re-doing a creek, adding in bends and stumps and large rocks for increased trout habitat. The relative explained that years ago that was how the creek used to be. But, the government determined that the trout needed to get to their habitat without all of those obstructions, so cleared the creek of boulders and stumps and straightened it out. And they also required the ranchers to fence off the creek where they had cattle so they wouldn’t get into the creek. (BLM land).
Turns out that the cattle also did their part in managing the creek habitat - tromping around in it caused muddy spots in some areas, but in general released the silt from the gravel beds, making the gravel beds better spawning areas for the trout!
Years ago I thought that the government provided incentives to the farmers to leave buffers and/or leave the edges of their crops unharvested as food and shelter for the various animals. I guess they figure if they can make a law forcing one to do that, that is easier. And of course it is favored by the majority of voters in Minnesota (city dwellers).
Decaying vegetation creates phosphates which are dissolved and carried into surface water during snow melt. Buffers are supposed to trap particulate phosphate (fertilizer, which is attached to soil) during rainfall. The phosphate loading in the river systems are dissolved phosphates, created by decaying vegetation. Buffer strips will create more decaying vegetation unless they are hayed.