Chesapeake Bay - Less Dead in 2013

Forecast: Smaller Bay dead zone this summer

Scientists expect a smaller than average hypoxic level in the Chesapeake Bay this year, according to a forecast from researchers at the University of Maryland Center for Environmental Science.

The forecast calls for a mid-summer hypoxic, or low oxygen, zone of 1.46 cubic miles, a mid-summer anoxic, or oxygen-free, zone of 0.26 to 0.38 cubic miles, and a summer average hypoxia of 1.108 cubic miles, which are all at the low end of previously recorded zones. Last year, the final mid-summer hypoxic zone was 1.45 cubic miles...

That's a 27% improvement!  Four years of that, and the bay will be all clean again, right? 

But wait, there's more...

Kelsey said the estimates are based off the amount of nutrients that are entering the Bay, and what people do in the watershed to reduce nutrient concentration will hopefully have an effect on the amount of nutrients and low-oxygen waters that reach the Bay.

But, he said people taking care of their local watersheds and the surrounding land only helps hypoxia levels so much, as weather is still a large cause of hypoxia zone variability.

If there's more river flow from the Susquehanna and Potomac rivers due to higher rainfall, there are generally higher nutrient loads coming from point-sources of pollution, like sewage treatment plants, which is what the hypoxic and anoxic levels are responding to, he said...

So, what's being said here, albeit in an understated manner, is that the interannual variability of the size of the dead zone is largely caused by weather, and that any improvement in the yearly "dead zone" problem from pollution control is a small incremental effect imposed on a wildly swinging signal.

He said hypoxia zone awareness is important during hot summers, because the fish won't want to be near the top of the water because it's too hot and won't want to be in the hypoxia zone because they can't breath, so it limits the area they will swim in.

When that happens, he said it also limits the area the fish can hunt for prey.

As for how large 1.108 cubic miles is, Kelsey said, "If you can image a mile ... in one direction and make a right angle so that makes a square and go up into the atmosphere one mile, that's a big cube. That's a big volume, and that's what we're talking about."

It's interesting that every news report I could find on this gave the size of the "dead zone" in units of cubic miles.  Now, a cubic mile is a lot of water, but it's not a unit that most people are familiar with.  I would think the number would have more scare value expressed in trillions of gallons of water, or something else with tons of trailing zeros  (the entire volume of the bay is approximately 18,000,000,000,000 gallons).  Why not teaspoons or milliliters?  I guess maybe the image of the mountainous cube of water was irresistible  

Just to put this in scale, taking the surface area of the bay 4,480 square miles, and it's average depth of 46 ft , we can calculate the approximate volume of the bay, which turns out to be about 39 cubic miles.  So the size of the "dead zone" is about 2.8% of the volume of the Bay this year.  That is certainly a perspective you'll never see publicized, because it make is look small in comparison, and that is not the desired message.

That's not to say it is not important.  Bottom area is important as well because that's where much of the biota live.  But again, the anoxia only covers about 5% of the bottom area of the bay, only the deep channels.