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Both nature and humanity affect bay's oxygen levels

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.

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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.

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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.

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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.

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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.

With oxygen, a closer look at decades-old data indicates there was no neat trend from good to bad. You could indeed show a 15-fold increase in oxygen-poor water, but only if you selected the right two years to compare. You can also find years like 1958, when oxygen may have been worse than in, say, 1985.

And from ancient sediments cored from the bay bottom have come recent evidence that even under pristine conditions before European settlement, the estuary's depths were prone to unhealthy oxygen levels in some years.

The human factor

So what does it all mean for the complex and expensive programs now implemented to reduce fertilizers and boost oxygen levels? How will we even know, amid all the natural variability, if they are working? Is the human part of the equation even significant?

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Here are some answers, based on a recently-concluded six-year study, "Oxygen Dynamics in the Chesapeake Bay," available from the University of Maryland's Sea Grant College.

* Yes, we have worsened the oxygen situation with human inputs of fertilizers, especially in the last 40 years. There is evidence that the extent and duration of low oxygen conditions has gotten worse in the last decade or two.

There were always were peaks and valleys caused by nature; but we are making the peaks of health lower and the valleys of death deeper.

* We are quite likely saturating the bay now with so much fertilizer that we may not see any positive response (outside of natural variations) until we reduce our impacts to some lower level -- we don't know yet where that break-point will be.

Think of it like a glass of water which you have saturated with so much salt that the water can't hold anymore, and salt lies an inch thick at the bottom. You begin removing salt, bit by bit. You are going in the right direction, but for a while you won't see the water get fresher.

* The best we can hope for, if we meet our ambitious goals of reducing nitrogen and phosphorus going in the bay by 40 percent, is a very modest increase in oxygen -- from zero to perhaps 1 or 2 parts oxygen per million parts of water. Five parts is considered healthy.

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But many bottom dwelling creatures -- food for larger creatures -- can manage at those levels, so even a modest increase in oxygen could translate into a huge increase in bay life.

In addition, it looks like meeting the 40 percent goals might set off a sort of vicious cycle in reverse -- a minor improvement in oxygen triggers a change in the chemistry of the bottom sediments, and that in turn sets off a cascading chain of events that causes major improvements.

The goal is worth the effort; but for awhile, teasing out our impacts on the bay's oxygen versus nature's will be like hunting for a faint radio signal in heavy static.


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