Red circles show the location and size of many dead zones.
Phosphorus and nitrogen fertilizers can affect soil, surface water, and groundwater due to the dispersion of minerals into waterways due to high rainfall, snowmelt and can leaching into groundwater over time. Agricultural run-off is a major contributor to the eutrophication of freshwater bodies. For example, in the US, about half of all the lakes are eutrophic. The main contributor to eutrophication is phosphate, which is normally a limiting nutrient; high concentrations promote the growth of cyanobacteria and algae, the demise of which consumes oxygen. Cyanobacteria blooms ('algal blooms') can also produce harmful toxins that can accumulate in the food chain, and can be harmful to humans. Fertilizer run-off can be reduced by using weather-optimized fertilization strategies.
