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Needed: watershed maps

The first extension meeting I remember was for a Watershed Co-op south of Birch Hills, Sask. The Watershed Co-ops were formed so farmers could work together to reduce runoff and the erosion that went with it. It is great to see work once again being organized on a watershed basis. This time around, the focus is on farm management practices to minimize what we spill into surface water bodies. But, step one ought to be the preparation of a watershed map so efforts can be focused.

The Lake Winnipeg watershed

Lake Winnipeg is much in the news these days. Extra nutrients, particularly phosphorus, lead to algae blooms and agriculture gets too much of the blame. For sure, agriculture does contribute and we need to do our part to minimize our nutrient loss and its unwelcome appearance in water bodies.

The same map is usually used to show the Lake Winnipeg watershed.

That map gives the impression that every acre of farmland in most of the Canadian Prairies can contribute phosphorus to Lake Winnipeg. Not so!

In many parts of the world with geologically old landscapes, there are well developed drainage channels that all hook up to deliver water to the ocean. In much of Western Canada we have very young landscapes, left behind by a series of glaciations that left myriad potholes — we call them sloughs. In such landscapes the watershed is all the way from the hilltop to the slough. And there it ends.

A very different map has been prepared by the Prairie Farm Rehabilitation Administration (PFRA), now the part of the Agri-Environment Services Branch of Agriculture and Agri-Food Canada (AAFC). The red areas show the non-contributing areas, which is most of Saskatchewan. In this map the red areas are essentially the pothole country where drainage is all the way to the nearest slough.

Now, this is a bit of an oversimplification. Real wet years like we’ve experienced recently can overspill some sloughs that find a way to a major river or lake. But in much of pothole country, our land must absorb whatever rainfall or snow melt comes along.

The South Saskatchewan River system is about to undergo scrutiny with the new Global Institute for Water Security that has been formed at the University of Sask-atchewan. I look forward to helping with that work. The first thing I will be pushing for is the preparation of a true watershed map, so we know where to focus the work.

Runnoff and phosphorus

On my Dundurn farm, little water leaves any of the quarters. Most of it ends up in sloughs I have to go around when seeding ­­— or pump up to the hilltops in spring. And, of the water that does leave, some could end up in Blackstrap Lake — a man-made lake which receives water from Diefenbaker Lake via the Saskatoon South East Water Supply (SSEWS) canal. But, for any water from my quarters to get to the Saskatchewan River and hence Lake Winnipeg, we would have to put it in a truck and haul it there.

Our situation in Western Canada is much different than warmer areas of the U.S. where most press comes from. Down there, summer rains carry soil and the attached phosphorus with it. But here, it is the dissolved phosphorus that flows along with the spring snow melt that makes the biggest contribution.

In both Alberta and Manitoba it has been shown that phosphorus levels in spring runoff are highly correlated with soil test phosphorus. In my experience most very high soil test phosphorus fields are ones that have received lots of manure over the years. And, high soil test phosphorus values can have residual effects for many years. But that is a story for another day. Stay tuned. †

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