Nutrient pollution tends to increase in winter because the soil can't absorb water once it freezes. Instead of soaking into the ground, any rain, melting snow, or mid-season thaws tend to flow across the surface, carrying nitrogen and phosphorus with it. At the same time, vegetation is dormant, so plants aren’t taking up nutrients the way they do in warmer months.
Manure piles and exposed soils are more vulnerable during the cold season since freeze–thaw cycles can create small channels that let runoff escape. Even well-managed fields can experience nutrient loss when a warm spell follows a storm, creating a sudden surge of water moving across frozen or saturated ground. Because much of this happens beneath snow cover, it’s easy for runoff to go unnoticed until it reaches nearby ditches or waterways.
