Thursday, June 23, 2011

Scientists Predict Big "Dead Zones" for Chesapeake Summer

Scientists Predict Moderate to Poor Oxygen Levels in Chesapeake Bay for Early Summer
The Chesapeake Bay is expected to have moderate to poor dissolved oxygen conditions during the early part of the summer, according to a team of scientists with Chesapeake Eco-Check.

The early summer dissolved oxygen forecast (called an “anoxia forecast”) is based on nitrogen loads to the Bay during winter and spring, as well as high river flow in May due to heavy rainfall. According to scientists, the Bay’s 2011 low-oxygen area – commonly called the “dead zone” – could be the fourth-largest since 1985.

The annual summer ecological forecast uses data such as nitrogen loads, wind direction and sea level to predict dissolved oxygen levels in the Bay’s mainstem. The forecast is split into early summer (June to mid-July) and late summer (mid-July to September) because scientists have observed a significant change in oxygen levels following early summer wind events.

The forecast is supported through research at the Chesapeake Bay Program, Johns Hopkins University, Old Dominion University, and the University of Maryland Center for Environmental Science Horn Point Lab.
We've had a lot of rain in the watershed this spring, and that traditionally means a bad summer for anoxia for a couple reasons.  First, the additional freshwater brings in lots of excess nutrients which fuel algae blooms, which die, sink to the bottom, and feed bacteria which use the oxygen in the bottom water.  Second, lots of freshwater sits on top of saltier seawater, and prevents the wind from mixing the bottom water to the surface (and vice versa) and traps the bottom water in the dead zone.  You can actually see the pycnocline (the area where the water becomes saltier as you go down, and where oxygen usually stops) on a good depth finder.  You won't find fish below that line.

The area we live in is one of the "hot spots" for the anoxic water.  It usually builds up until it reaches about 30 ft, or even less, from the surface, and kills all the non-mobile animals on the bottom to that depth.  The wrong wind (a good steady southwest wind, for a couple of days or more) will bring that dead water to the shore at our beach.  Often it pushes fish and crabs in front of it, and they pile up in the shallow waters near the beach.  People come to catch the crabs, and some of the fish.  Old timers call it a "crab jubilee", and people often call it a red tide, which it is not.  We may also have red tides about the same time though, so the confusion is understandable.  In a really extreme event, the dead water it brings up is often very clear and blue, as anything living in it has died and rotted.  It also stinks of hydrogen sulfide.

I'll likely post about one on the beach before the summer is through, although I'd prefer not to.

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