As spring comes and the heavy flow of the Mississippi brings a lot of nutrients, oxygen is used up and doesn't get replaced. By the middle of July, we have a very large area that has no oxygen in it called the dead zone. Many organisms that are important for fisheries live on the bottom or have to migrate through the bottom. There are many reasons to think hypoxia affects the fishing industry, according to Dr. Dortch. Because of a variety of factors, including stagnant prices for shrimp and other fish, it is very difficult to arrive at hypoxia's exact contribution to the sharply declining fishing industry in the Gulf.
Estimates vary, but it is clear Iowa's contribution of nutrients is very significant.
Farmers need to test the soil and apply only the nitrogen and phosphorus fertilizer that is needed, according to Dan Specht. Buffers and grass waterways are important. Also, fertilizers put on lawns and golf courses must be reduced. Farmers should be supported with educational and technical assistance and cost-share programs so that conservation plans, including a manure management component, are used on all farms, says Specht.