Thanks for reaching out and sharing these questions with us. As Jeff mentioned it was too bad that Alice was unable to present but you may want to direct this person to Alice's recorded presentation (see button at bottom). https://youtu.be/LIbSVaJoh-M
Alice went into greater detail in a earlier presentation she gave last winter: https://youtu.be/hHrMIlSqCio In both webinars she highlights the findings of a 3 year water quality testing study they undertook before Regina upgraded it’s water treatment plant. Even then waste water was not the greatest source of nutrients. With the new treatment plant now in place waste water would be even less of a source but its still a source and we all need to minimize sources as best as possible.
In terms of run off, as Jeff pointed out there’s more run off than what would be considered natural these days and that amount is always increasing as farmers and cities drain more wetlands and create new pathways for water to flow that it never did before.
Despite all the advances in continuous cropping most of our run off in Saskatchewan occurs in the spring when the snow melts and the ground is frozen and no crop is growing. That water runs off the land and carries with it nutrients and if there’s no place to hold that nutrient rich water (like a wetland) then it flows into a river and our lakes.
It should also be noted that for over a decade zero till has been recognized as increasing nutrient runoff as Jeff pointed out.
Scientific studies all over Canada are showing the impacts of nutrients from agriculture. Even agriculture realizes this and promotes the wise use of fertilizers. Dr. Leavitt has also pointed out fertilizers are a concern.
While every watershed is as unique as its sources, we all have a part to play including agriculture.