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Below-Average ‘Dead Zone’ Predicted For 2015
August 3, 2015

Recently released by the National Oceanic and Atmospheric Administration (NOAA) which sponsors the work, the 2015 Chesapeake Bay forecast calls for an oxygen-depleted, or hypoxic, region of 1.37 cubic miles, about 10 percent below the long-term average.

Farmland runoff containing fertilizers and livestock waste is the main source of the nitrogen and phosphorus nutrients that cause the annual Chesapeake Bay hypoxic region, which is also known as a dead zone.

Fish and shellfish either leave the oxygen-depleted waters or die, threatening the bay’s production of crabs, oysters and other important fisheries.

The hypoxia forecast is based on models developed by NOAA-sponsored researchers at the University of Michigan and the University of Maryland’s Center for Environmental Science. The models use nutrient-level estimates and stream-flow data provided by the U.S. Geological Survey (USGS) that estimates 58 million pounds of nitrogen were transported to the Chesapeake Bay, the nation’s largest estuary, from January to May 2015, an amount that is 29 percent below average conditions.

Low river flow and below-normal nutrient loading from the Susquehanna River this spring account for the smaller predicted size of the dead zone.

Nutrient-rich waters flowing into the bay trigger explosive and extensive algae growth. When the algae die and sink, bottom-dwelling bacteria decompose the organic matter, consuming oxygen in the process and forming the dead zone.

Weather variables—including wind speed and direction, precipitation amounts and temperature—also affect the size of dead zones.

In addition to forecasting the size of the mid-summer low-oxygen zone, the computer models assess the portion that is entirely oxygen-free — the so-called anoxic zones that form in early and late summer. The anoxic portion of the Chesapeake Bay dead zone is expected to be 0.27 cubic miles during the early summer, growing to 0.28 cubic miles in the late summer.

Later this year, oxygen levels will be measured by the Chesapeake Bay Program’s partners at the Maryland Department of Natural Resources and the Virginia Department of Environmental Quality. The program coordinates a multi-year effort to restore the bay’s water quality and habitat quality and to increase its productivity.

The Chesapeake data are collected and analyzed through a cooperative agreement between USGS and the Maryland Department of Natural Resources. USGS operates more than 400 real-time stream gages and collects water-quality data at numerous long-term stations throughout the Chesapeake Bay basin to track how nutrient loads are changing over time.

This article reprinted from materials provided by the University of Michigan.

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