Frozen soils increase nutrient leakage by keeping water from soaking into the ground. When the soil itself is hard and sealed by ice, rain or melting snow stays on the surface and moves downslope rather than filtering through the soil. As this water travels, it picks up nitrogen and phosphorus that would normally be held in place by unfrozen soil.
Freeze–thaw cycles can also loosen surface material, making it easier for nutrient-laden soil particles to be carried away. This means that even small amounts of runoff can transport a noticeable load into nearby waterways.
