Both nature and humanity affect bay's oxygen levels

ON THE BAY

November 07, 1992|By TOM HORTON

It is probably no coincidence that the summer of 1992 was an excellent one for fishing and also the healthiest in at least eight years for oxygen levels throughout the bay.

You can't prove that link conclusively. It's not what a scientist would call hard evidence; but baked, fried or poached, it tasted good just the same; and it gave us a little taste of why we're spending so much time and money restoring the bay.

Although the bay is far from dead, it's been down so long that fewer each year can recall how good it really could be. "I worry more and more about leaving a generation that has no idea of what this river was like," Bernie Fowler, a state senator from southern Maryland, told me at an environmental rally this summer on his native Patuxent.

"If we can't make some headway soon, these children will never, never have the hope and the dream of bringing the water back, because they just won't have any idea how enriching it used to be," Bernie said.

So it is that we look anxiously for signs that pollution controls are finally paying off; and strive to identify "indicators" -- key species of fish or plants, or chemical and biological standards -- that tell us whether we are making progress.

One of the most compelling indicators we have for the bay as a whole is the amount of oxygen in its waters. It is just as essential to life in the water as it is in the air for land dwellers.

To understand what has been happening in the bay during some recent summers, the time of year when oxygen levels are worst, imagine Maryland were sealed off with a dome, and across more than a third of the state, some of the air was pumped out -- not enough to kill anyone, just enough to make us sluggish, lethargic and uncomfortable.

But in half this area, we would pump more air out, to the point where breathing was a struggle, and many people would have to flee or die; and in substantial portions of this highly stressed zone it would get even worse; no oxygen at all -- instant death.

That's the way it is many summer days on the bottom of the bay, and why we are trying to clean things up. When we began a decade ago the problem, and the solution, seemed straightforward.

A compelling image

Joseph Mihursky, a longtime bay scientist and director of the Chesapeake Research Consortium, maintains that a single article and graphic on bay oxygen, published a decade ago by The Evening Sun, did more to galvanize public attention to the need for action than any other single piece of information.

It showed the bay -- during a summer in the 1950s, with a small black spot in the center depicting the volume of water with depleted oxygen that summer -- and in a 1980s summer, covered by a giant black blob grown 15 times as large.

It explained that too much fertilizer in the form of nitrogen and phosphorus was getting into the estuary from sewage and farms and suburban lawns, and (as we have learned since then) even via airborne fallout from the discharges of cars and power plants.

The overfertilization produced masses of floating algae which used up vital oxygen when they died and decomposed. Accordingly, a primary goal of the bay restoration effort has been to reduce nitrogen and phosphorus enough to allow healthy levels of oxygen.

It remains a worthy goal, but the concept of oxygen as an indicator of bay cleanup has gotten messier. The compelling simplicity of good times in the '50s and bad times in the '80s has gotten complicated.

This year, for example, oxygen improved dramatically; yet we are less than halfway to our cleanup goals in reducing phosphorus bay-wide, and levels of nitrogen, probably even more critical to improving oxygen, are still going up.

We now know the impacts of natural events can simply overwhelm human factors in a given year. Low river flow last spring prevented the bay from becoming "stratified" -- strongly defined layers of fresh water from its rivers flowing atop heavier salt water pushing up from the ocean. The weak flows helped produce oxygen levels as good as any in modern history.

Conversely, in years when the layering of sweet water and salt is strong it forms a barrier so new oxygen from the surface can't replenish what algae consume from the bottom. A zone of water hostile to life results, stretching from the bay bridge well into Virginia, lasting until cooler weather.

This penchant for huge, natural variability is a striking feature of the Chesapeake, where the ocean struggles constantly for dominance with the flows from nearly 50 rivers; and it affects much more than oxygen levels.

In a year when the bay collects heavy rains from across its six-state drainage basin, pollutants washing from fields and pavements can soar by tens of millions of pounds, and huge portions of the estuary turn from salty to fresh. In a dry year it is all reversed. Such environmental swings reverberate in the ups and downs of a range of bay species.

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