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Mon January 16, 2012
Rebecca Murphy, Johns Hopkins University - Chesapeake Dead Zone
Albany, NY – In today's Academic Minute, Rebecca Murphy of Johns Hopkins University reveals how decades of pollution control efforts are paying off for the Chesapeake Bay.
Rebecca Murphy is a Ph.D. candidate in the Department of Geography and Environmental Engineering at Johns Hopkins University where her research focuses on developing and applying methods that integrate statistical and dynamic models to evaluate water quality data in the Chesapeake Bay. She also serves as Project Manager for the Chesapeake Bay Environmental Observatory, a multi-institutional effort to develop a prototype system for integrated use of data, models, and analysis tools for research and management. She holds a MEng in Biological and Environmental Engineering from Cornell University.
Rebecca Murphy - Chesapeake Dead Zone
Our research is focused on understanding one of the major water quality concerns in the Chesapeake Bay - the depletion of oxygen from the deep waters. This depletion of oxygen, called the dead zone, is a problem every summer for fish and other animals that require oxygen to live. There are two major factors that are at play in the creation and persistence of the dead zone. The first is nutrient pollution that causes excessive algae blooms to grow in the spring. When the algae die, their decomposition uses up oxygen. The other major factor is the natural stratification of the Chesapeake Bay, which forms when fresh water from the tributaries stays on top of the salt water that comes in from the Atlantic Ocean and restricts the vertical mixing of oxygen.
We computed and analyzed a 60-year record of the dead zone size, nutrient loads, and stratification in order to learn how the Bay has responded to a decrease in nutrient loads over the last half of that period. We found some good news -- that in the mid- to late-summer there has been a slight, but significant long-term decrease in the dead zone volume that is related to the long-term decrease in nutrient loads. In addition, we found that the number of days that low oxygen conditions persist in the deep waters is directly correlated to nutrient loads.
We also investigated a troubling finding that the early summer dead zone volume is actually increasing. We discovered that the cause of this increase is an increase in the Bay's stratification due to changing climatic forces. Despite this finding, we can confidently say that without efforts to reduce nutrient pollution in the Bay watershed, conditions during the entire summer - both early and late - would be worse than they currently are. Also, with further nutrient reductions we will see even better water quality in the Chesapeake Bay.