When the algae die, their remains sink to the bottom of the bay, where they are consumed by bacteria. As they dine on algae, the bacteria utilize dissolved oxygen in the water. This leads to a condition called hypoxia, or depletion of oxygen. As this process continues through the spring and summer, the lack of oxygen turns vast stretches of the Chesapeake into dead zones. Hypoxia sometimes results in fish kills.
To find out whether these dead zones are expanding or diminishing, the Johns Hopkins and Maryland researchers retrieved and analyzed bay water quality records from the past 60 years. They determined that the size of the dead zone in mid-to-late summer has decreased steadily since the late 1980s and that the duration -- how long the dead zone persists each summer -- is closely linked each year to the amount of nutrients entering the bay.
That timeline coincides with the launch of state and federal efforts to reduce the flow of algae-feeding pollutants into the bay. For example, farmers were encouraged to plant natural barriers and take other steps to keep fertilizer out of waterways that feed the Chesapeake. Also, water treatment plants began to pull more pollutants from their discharge, and air pollution control measures curbed the movement of nitrogen from the atmosphere into the bay.
"By looking at existing data, we have been able to link decreasing hypoxia to a reduction in the nutrient load in the bay," said study co-author Michael Kemp, an ec
|Contact: Phil Sneiderman|
Johns Hopkins University