The dead zone bedeviling the upper Chesapeake Bay still hasn't shrunk in overall size and now is considered the fifth-largest in 30 years of record-keeping, experts say.
New data just released by the Maryland Department of Natural Resources shows that the oxygen-starved portion of the bay was still 1.32 cubic miles in late August, although the portion that extends into Virginia's lower bay had shrunk a bit since early-August testing.
The findings come from water samples taken every two weeks throughout the summer during science cruises along the bay's main stem. The effort is funded by Virginia and Maryland in partnership with the Chesapeake Bay Program under the U.S. Environmental Protection Agency.
Local researchers say they're not surprised by the data, but caution against drawing broad conclusions before the summer is over.
"Given that the wet spring brought in above-normal nutrient loads, and the weather was less windy in August than in July, it makes sense that the larger-than-average dead zone that appeared in early August persisted throughout the month," said Marjy Friedrichs, a biologist at the Virginia Institute of Marine Science (VIMS) in Gloucester Point. Friedrichs studies dead zone phenomena.
Measurements of the dead zone in early August constituted the eighth-largest on record for that time period. But because Virginia's portion of the dead zone has receded a bit since then, she said she wouldn't describe this summer as a "record year" overall for bay dead zones.
Dead zones are caused when massive amounts of algae bloom and then decay, sucking up dissolved oxygen in a water column and suffocating marine life.
Algae blooms are fueled by nitrogen and phosphorus dumped into the estuary by stormwater runoff from fertilized cropland, suburban lawns and sewage overflows.
Forecasters funded by the National Oceanic and Atmospheric Administration (NOAA) had predicted bigger dead zones this summer after rains earlier in the year dumped about 20 percent more nitrogen into the bay, mostly from the Susquehanna and Potomac rivers.
But weather also plays a role in dead zones, and can quickly alter their formation and size. In July, for instance, researchers recorded the smallest dead zone in 30 years of sampling, mostly because Hurricane Arthur passing along the coast had churned up and oxygenated the water.
"The rapid changes in the size of the dead zone between monitoring cruises this summer highlight two properties of the dead zone we've been studying at VIMS," said Carl Friedrichs, chairman of the physical sciences department at VIMS. He is married to Marjy Friedrichs.
"First, weather patterns can cause very large changes in the size of the dead zone in both space and time. And second, the boat-based measurements performed once every two weeks lead to uncertainties in the estimated size of the dead zone.
"It may not make sense to focus too much on the results of a single cruise in a single state," he added. "It might make more sense to sum up the size of the dead zone over the entire bay and over the entire summer before concluding that it is larger or smaller than in past years."
Reposted from: http://articles.dailypress.com/2014-09-07/news/dp-nws-dead-zone-update-20140907_1_dead-zone-marine-science-chesapeake-bay-program
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