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June 27, 2011

Near-record runoff washes salt from Upper Chesapeake

Like a gigantic spigot, the Conowingo Dam unleashed a three-month gusher of fresh water last spring that flushed the salt from the Chesapeake Bay and its tributaries above the Bay Bridge.

From March through May, the dam released 5 trillion gallons of water, enough to replace the entire volume of the upper bay every 30 days. This year's spring total is surpassed only by 1993, when 5.5 trillion gallons gushed from the river's mouth.

As a result, salinity levels from Turkey Point to the Bay Bridge are at their lowest point since 1985, when monitoring stations were established. Even Eastern Bay and points as far south as Cove Point in Calvert County are seeing record-low marks.

What does it all mean?

"This is going to be an unusual year," said Lynn Fegley, assistant fisheries director for the Department of Natural Resources.    

Biologists expect there will be guest appearances by creatures confused by the change. But more worrisome is the thought that some invasive species, such as northern snakehead and blue catfish, that have been bottled up in freshwater tributaries will escape to other rivers and streams now that the saltwater barrier is down.

"They sense it's still fresh and they just keep going," Fegley said.

Strong spring flows often push more sediment and nitrogen into fragile areas, fueling massive algae blooms and large dead zones, as happened in 1994. But sometimes -- as in 1993 -- it does not, for reasons not quite understood.

Low salinity is the kiss of death for oysters. In 1993, watermen in certain areas reported losing half of their oysters. The following year, when the flow wasn't as strong but lasted longer, beds in the Choptank and Chester rivers and in the upper bay near Rock Hall were hard hit.

With salinity levels below 6 parts per thousand threshold, the Oyster Recovery Partnership has had to give up on plans to plant spat north of the Choptank River, executive director Stephan Abel said.

"We can't put seed out knowing it's going to die," he said. "We're not going to take any chances so we're sending divers out to ground-truth the bottom before we plant."

Instead of trying to plant oysters in Harris Creek and in the Severn River, ORP has switched to the Honga River and Point Lookout.

"It's awful, but you adapt," Abel said of the low salinity. "We've got plenty of bottom in the south, just not where we planned."

Fegley said Chesapeake species most likely will ride out the unusual conditions.

"It's not estuary Armageddon," she said. "Part of the deal, if you're a critter living in the Chesapeake Bay, is being asked to put up with an incredibly wide range of conditions, including great swings in salinity."

And low spring salinity levels, she noted, may help juvenile fish, especially striped bass -- a good sign in Maryland, where the Young of the Year survey recently has recorded several subpar years.

DNR statistics show 1993 was second only to 1996 for number of baby stripers. The late winter and early spring flow in 1996 also was extremely strong. Spawning spot, yellow perch and white perch also benefited by conditions in 1993.

Recent dry conditions have allowed salinity to begin their creep toward normal levels, and unless there's a deluge from a tropical storm to top off the Chesapeake's freshwater supply, the upper bay may return to more normal levels.

Until then, the good news for waders, swimmers and watercraft riders: Low salinity will slow the summer invasion of jellyfish.

Posted by Candus Thomson at 5:04 PM | | Comments (1)


Visit Maryland DNR's Eyes on the Bay website to see Chesapeake Bay water quality conditions, including salinity.

Eyes on the Bay

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About Candus Thomson
In a world of paper vs. plastic and candy mint vs. breath mint, my early memories involved a debate about the merits of freshwater vs. saltwater.

On the one hand, a great uncle’s fishing cabin on the Susquehanna River beckoned, but so did family gatherings on the Jersey Shore.

The correct answer, thankfully, was, “both.”

As The Sun’s outdoors writer for more than a decade, I’ve fished across Maryland in one day, hiked the width of the state in one hour, camped overnight in the median of I-95 to experience the wildlife between the fast lanes and chased mountain bikers in a 24-hour marathon race.

Those are some of the highlights. I’ve also fallen in a raging Gunpowder River during a trout survey (photo available upon request), had a shark spill its guts on my clothes and been stuck in a sub-freezing Vermont wilderness with men armed with flintlocks and hatchets, shuffling along on ancient wooden snowshoes.

And, in my travels I’ve met lots of you, who share a love of the outdoors and the good times and mishaps that go along with it.

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