What is hypoxia and what causes it?
Hypoxia means low oxygen and is primarily a problem for estuaries and coastal waters. Hypoxic waters have dissolved oxygen concentrations of less than 2-3 ppm. Hypoxia can be caused by a variety of factors, including excess nutrients, primarily nitrogen and phosphorus, and waterbody stratification due to saline or temperature gradients. These excess nutrients, eutrophication, promote algal growth. As dead algae decompose, oxygen is consumed in the process, resulting in low levels of oxygen in the water. Nutrients can come from many sources, including any of the following: • Fertilizers from agriculture, golf courses, and suburban lawns • Erosion of soil full of nutrients • Discharges from sewage treatment plants • Deposition of atmospheric nitrogen The hypoxic zone in the Gulf of Mexico forms every summer and is a result of excess nutrients from the Mississippi River and seasonal stratification (layering) of waters in the Gulf. Nutrient-laden freshwater from the Mississippi River flows
