Tipping Points For The Bay

By Tom Horton

06/02/2009

In the upper Chesapeake Bay, cutting pollution has lagged well behind goals scientists say are needed to restore the estuary.

Yet across thousands of acres there, all-important underwater grass habitats have exploded in recent years to levels not seen in half a century.

Downstream, throughout much of the bay's mainstem, excessive pollution levels have held fairly steady during recent decades.

Yet deepwater "deadzones," massive volumes of water with too little oxygen for aquatic life, have steadily worsened and expanded there.

And another wrinkle. Just in the last couple years there are tantalizing hints the bay mainstem might be getting better--again with scant change in pollution levels.

Upstream and down are examples of "thresholds", or tipping points that perplex and intrigue scientists, who say there's still a lot we don't understand about managing big, complex natural systems back to health.

It's critical to know why we're doing better than expected some places, and worse in others, says Michael Kemp, a University of Maryland researcher who recently co-edited "Thresholds in the Recovery of Eutrophic (polluted) Coastal Ecosystems."

Kemp says such knowledge can help us target limited cleanup resources, and also help maintain support for extended and costly restoration efforts that often won't follow a neat script of pollution-down, water quality-up.

Indeed, last month Maryland Gov. Martin O'Malley, media aboard, was out on a section of the upper bay that scored an all-too-rare grade of B-minus in an annual survey of Chesapeake water quality (the bay overall got a C-minus, with some tributaries getting D's and F's).

O'Malley's point: "We're quick to say humans are the cause where there's degradation. . . but there are places where we're winning, so we're doing some things right too."

But what things? That may be the real point. Some are known: in the upper bay a big pollution cut from Harford county's Sod Run sewage treatment plant, many intact buffers of wetlands and forests that filter polluted runoff, and a lack of deep channels where dead zones occur helped the water quality grade.

Kemp noted in his report that for many reasons both chemical and biological, it's usually in the freshwater, shallow parts of systems like the Chesapeake where comebacks first happen.

"But even after we list all the factors we know, we still don't understand why we achieved a B-minus," said Bill Dennison, the University of Maryland scientist who oversees the baywide water quality survey.

Downstream, something flipped a switch the other way between 1980 and 1985, Kemp says. At that point, even though pollution loads hadn't increased, for every pound of pollution coming in, the bay began losing twice as much oxygen as before.

This "regime change" as Kemps puts it was not well understood until Environmental Protection Agency scientist Jim Hagy pulled together all the evidence in a 2004 report. The implications were sobering: "you almost couldn't get back (to healthy water quality)," Kemp says.

Now, based on some "very preliminary monitoring," there's reason to suspect the bay's mainstem may have crossed a threshold where each pound of pollution is causing substantially less dead zone impact, Kemp says.

Just as with the upper bay rebound, we need to know what is triggering these thresholds downstream, he says.

For example, if the bay's entering a state now where it is dealing better with pollution, it would be time to redouble efforts to cut the incoming nitrogen and phosphorus that causes dead zones and the loss of submerged grasses..

As in the upper bay comeback, there are some likely contributors to the downstream's deterioration: continued loss of oysters that filtered pollution; losses of worms that burrow in the bay's bottom, oxygenating it; additional chemical releases of pollution lodged in bottom sediments, triggered by lower oxygen in the deeps.

But again, what's known still doesn't add up to an answer.

Kemp says he's got "a gut feeling" there might be something not on the list of usual suspects that caused the bay's mainstem to reach a tipping point back in the 80's, and to perhaps be tipping back now to a better state.

He's considering influences outside the bay, such as oscillations in North Atlantic Ocean currents. These could influence how water circulates within the Chesapeake, which can affect the bay's ability to deal with pollution. He says it's still speculation at this point.

The bottom line, bay scientists say, remains that only large scale reductions of both nitrogen and phosphorus will restore the Chesapeake.

But the path there will almost certainly not follow a smooth or predictable slope--rather more like bounding up a staircase, or slipping off a ledge, or some of both.

Ironically, just as scientists are calling for additional monitoring of bay processes to try and understand these tipping points, the EPA Chesapeake Bay Program is considering significant cuts in those monitoring programs.