The duration of the Chesapeake Bay’s annual “dead zone” has declined over time, according to research published last month in the scientific journal “Limnology and Oceanography.”
First reported in the 1930s, the Bay’s dead zone, or conditions of low dissolved oxygen also known as hypoxia, results from excess nutrients, which fuel the growth of algae blooms. As these blooms die, bacteria decompose the dead algae. This decomposition process removes oxygen from the surrounding waters faster than it can be replenished, suffocating marine life. While intensified agriculture and development continue to push nutrients into rivers and streams, research by Yuntao Zhou and others shows the duration of the Bay’s dead zone decreased from five months to four months between 1985 and 2010, and the end of the hypoxic season moved up from October to September. This could suggest that efforts to manage nutrient loads—through upgrades to wastewater treatment plants, cuts to vehicle and power plant emissions and reductions to runoff from farmland—are working.
This same research showed no change in the average onset of the Bay’s dead zone or for its average volume, whose peak has moved from late to early July. In other words, while the duration of the Bay’s dead zone has declined, its size and severity have not.
While Zhou points out that nutrient pollution is the foremost factor that fuels the development of our dead zone, his research also shows that weather patterns can act as an additional driver. Northeasterly winds, for instance, can create conditions that reinforce the separation between the Bay’s fresh and saltwater, leading to larger hypoxic volumes.