HYPOXIA AND NUTRIENT POLLUTION

WHY IS THIS ISSUE IMPORTANT?

Hypoxia is a major concern for many of our nation's waterways. Hypoxia occurs when the amount of dissolved oxygen in water becomes too low to support most aquatic life (typically below 2 mg/l). Most organisms avoid waters that are hypoxic because it can cause physiological stress and impact their growth, reproduction, and survival. If organisms cannot escape, hypoxia can be fatal, reducing overall populations and, in some cases, negatively affecting commercial and recreational harvests of fish and shellfish. While hypoxia can occur naturally, the frequency and intensity of occurrence in coastal areas is increasing, largely due nutrient pollution (such as nitrogen and phosphorus) from human activities. Over half of the U.S. estuaries now experience natural or human-induced hypoxic conditions at some time each year and evidence suggests that the frequency and duration of hypoxic events have increased over the last few decades. The importance and national scale of hypoxia in U.S. waters is evidenced by the recently documented exponential increase in number of coastal systems experiencing hypoxia worldwide and in the US (Diaz & Rosenberg 2008, Science).