Bay 'dead zone' sets new record in fall
The Chesapeake Bay's 'dead zone' has set another record - reappearing this fall after Tropical Storm Lee washed millions of tons of nutrients and sediment into the estuary.
State officials and scientists with the University of Maryland say the expanse of oxygen-starved water in the bay, which had virtually disappeared by the end of August, re-formed in September and was still growing in late October.
"It's surprising we're seeing it this late," said Tom Parham, director of tidewater ecosystem assessment for the state Department of Natural Resources.
The dead zone reached record size earlier in the summer, spreading to cover 40 percent of the bay from the mouth of the Patapsco River practically to the Virginia line. At the time, scientists blamed that on an unprecedented influx of fresh-water into the bay in spring. With it came an extra-heavy load of fertlizer, sewage and other pollutants, which feed massive algae blooms and ultimately consume the oxygen in the water that fish need to breathe.
The winds of Hurricane Irene in late August stirred up the bay, breaking up the dead zone by reintroducing dissolved oxygen into deeper waters. Scientists and others breathed a sigh of rellief after the rough summer.
But the torrential rains of Tropical Storm Lee in early September flooded the bay with more water-fouling nutrients, in addition to millions of tons of sediment that turned the water brown. Scientists predicted the influx could revive the dead zone, and by the end of September, water monitors were detecting its reformation.
When scientists went out again to check in late October, oxygen-starved water covered the bottom in the deep waters down the middle of the bay. The 'dead zone' stretched from the Bay Bridge south to the mouth of the Patuxent River, according to marine ecologist Diane Stoecker of the University of Maryland Center for Environmental Science. About 10 percent of the bay was plagued with extremely low oxygen levels, DNR's Parham estimates, when by this time of year the zone normally covers no more than 2 percent.
"It's probably the worst we've seen in October," said Bruce D. Michael, DNR's director of resource assessment. To see the October extent of the 'dead zone,' go here.
Another odd thing about this dead zone - it didn't appear to form the typical way, after massive algae blooms spread across the bay. Scientists say they didn't detect any spikes in chlorophyll in the water indicative of algae's presence. The murkiness of the water - from all the sediment washed into the bay - may well have prevented sunlight from penetrating the water to stimulate algae growth, they say. Instead, they think oxygen in the water may have been consumed by the breakdown of all the organic matter washed into the bay by the storm.
"It's just another indication of how much impact storms, and particularly tropical storms, have," says Parham.
It's also a reminder of how nature can play havoc with efforts to restore the bay. A recent study by Johns Hopkins and UM scientists found that despite natural variations, the dead zone has gradually shrunk in size and duration since the late 1980s - evidence, they said, that efforts to reduce the flow of nutrients into the bay was beginning to work.
But the analysis only covered conditions through 2008. Scientists say they think the record fresh-water flows this year and the accompanying pollution have set the bay back, but they don't know yet how much.
DNR this week confirmed watermen's reports of a die-off of most of the oysters in the upper bay, apparently from heavy spring flows of fresh water that the bivalves could not survive. Bay grass beds in the Susquehanna Flats also were ripped out by the late-summer storm flooding, but researchers say it won't be clear until next spring the extent of impacts on all the bay's underwater grasses, which serve as nursery, food source and shelter for crabs, fish and other wildlife.
Parham says he expects the dead zone has dissiipated by now or at least started to shrink, as falling temperatures tend to mix the water and restore oxygen levels. DNR will be doing water sampling next week to check.
But he and others are wondering whether the nutrients washed into the bay in late summer will get flushed out over the winter - or hang around to feed massive algae blooms and another severe dead zone next year.
"That's kind of the million-dollar question - what are we going to see next spring?" Parham said.
To keep tabs on water quality in the Chesapeake, check out DNR's "Eyes on the Bay."
(Debris and sediment in the Chesapeake Bay the week after Tropical Storm Lee; DNR biologists Zofia Noe and Jamie Strong sample water conditions in wake of storm, September 2011. Baltimore Sun photos by Kim Hairston)
