The report by USGS scientists Richard Alexander, Richard Smith and Gregory Schwarz was published in the Feb. 17 issue of Nature. Large amounts of nitrogen are found naturally in the air and soil, and in living organisms. Nitrogen is also plentiful in animal waste and fertilizer. All of these sources contribute to the nitrogen that finds its way down the Mississippi River to the Gulf. One of the most important ways that nitrogen is removed from water in the bottom sediments of streams is through a natural process called denitrification, where nitrogen is converted by bacteria to harmless nitrogen gas and vented to the atmosphere.
Animal waste is a major non-point source of nitrogren pollution in waterways.
Non-point nitrogen sources such as fertilizer, animal waste, runoff from developed land, deposits from the atmosphere and soil erosion account for 90 percent of the nitrogen pollution in waterways. Point sources such as sewage and industrial discharge contributes 10 percent. The amount of nitrogen removed from water depends on the amount of water in contact with sediment. Because water in streams has more contact with sediment than water in rivers, more nitrogen is removed from the streams. Then, the decay of the algae depletes the oxygen in the water, causing bottom-dwelling organisms to die and stressing the fishing resources in the Gulf.