Scientists Forecast Smaller Low-Oxygen Zone in Chesapeake Bay This Summer

June 2009 -- Scientists with the University of Michigan are predicting that the Chesapeake Bay’s low-oxygen “dead zone” will be the smallest in eight years due to dry weather this winter and early spring.

The Bay’s low-oxygen zone is expected to shrink to between 0.7 and 1.8 cubic miles, most likely measuring 1.2 cubic miles, according to University of Michigan aquatic ecologist Donald Scavia. This would be the lowest level since 2001 and the third-lowest on record.

The decrease is largely due to a dry spell that lasted from January through April, according to Scavia. However, wet weather in May and June may cause the size of the low-oxygen zone to be near the high end of the forecast range.

“While it's encouraging to see that this year's Chesapeake Bay forecast calls for a significant drop in the extent of the dead zone, we must keep in mind that the anticipated reduction is due mainly to decreased precipitation and water runoff into the Bay," Scavia said. "The predicted 2009 dead-zone decline does not result from cutbacks in the use of nitrogen, which remains one of the key drivers of hypoxia in the Bay.”

Low-oxygen zones form in the Bay each summer due to a combination of high temperatures and polluted runoff from the land. Excess nutrients in the Bay fuel the growth of algae blooms that rob the Bay of oxygen, which all underwater life needs to survive. Algae blooms also block sunlight from reaching bay grasses growing at the bottom of the Bay’s shallows.

Years with more rainfall cause more nutrient pollution to run off the land into the streams, creeks and rivers that flow to the Bay, increasing the amount of pollution in the water. In drier years, less pollution enters local waterways, which often results in smaller low-oxygen zones.

Annual forecasts of Bay conditions help Bay managers, policy makers and the public better understand the factors that cause dead zones.

The low-oxygen forecast is based on spring river flow data from the U.S. Geological Survey.

What You Can Do: Reduce Nutrient Pollution to the Bay and its Local Waterways

• Don't fertilize your lawn this summer. Chemical lawn fertilizer is a major source of nitrogen pollution to the Bay. Instead of fertilizing, leave your leftover grass clippings on your lawn as a natural fertilizer.
• Drive your car less. Emissions from vehicles and other sources is one of the top sources of nitrogen pollution in the Bay. Combine trips, carpool or take public transportation and you'll reduce pollution while saving money.
• Plant trees near the edge of your property to absorb and reduce excess polluted runoff, especially if you live by a stream, creek, river or the Bay itself.