Bottom seems healthier, but plants lack diversity

ON THE BAY

March 26, 1994|By TOM HORTON

It would be foolish to evaluate a lawn solely on the basis of square footage, unheeding of whether it more resembled crab ** grass or a putting green.

Neither, would anyone price farmland without knowing its soils and crop yields, or judge a forest's worth without regard to whether it was seedling scrub pine or old-growth hardwoods.

Yet we are nearly that simplistic in the way we perceive one of Chesapeake Bay's most important habitats -- one whose recovery will be used as a major indicator of success in restoring the estuary to health.

I'm talking about the dozen or so varieties of rooted, underwater plants that usually get lumped into the catch-all category of SAV, or submerged aquatic vegetation.

They have been a glorious fixture of the bay bottom since the glaciers melted, and rising seas glutted the gorge of the Susquehanna, forming a broad, shallow embayment some 6,000 years ago.

Wherever enough sunlight could penetrate, they flourished, food and refuge for a host of fish and fowl, lushly carpeting a fifth or more of the 2.8 million acres making up the bay and its tidal rivers.

Thus, it remained from about 4,000 B.C., when Sumerians in Asia were inventing writing, until about A.D. 1972. Then, sewage, and runoff from farms and development clouded the water, dimmed the light; cut the subaqueous jungle from hundreds of thousands of acres to just 38,000 in 1978, the first comprehensive survey undertaken. Research between 1978 and 1983 would make it clear that the submerged aquatics made a prime indicator of our success or failure in saving the bay.

They respond quickly to worsening or improving water quality, and their presence or absence can be seen by scientists and public alike. They don't move around like fish, so they are indicative of conditions year-round in specific locations.

And they are affected by virtually everything -- sewage, agriculture, construction, air quality, deforestation and loss of wetlands -- that needs to be better managed to restore the estuary.

So it would seem to be unadulterated good news that the acreage of SAV, according to the federal-state Chesapeake Bay Program, has edged steadily upward since 1978 to more than 70,000 acres.

It is nothing near the 400,000-600,000 acres thought to be normal in a healthy bay; but it is a near-doubling from 1978, enough of a trend to convince scientists that cleanup efforts are slowly bearing fruit. More acres of SAV are virtually always better than less, but the kinds of plants in those acres can tell us a lot, too. And the kinds of vegetation out there seem to be telling us that we should temper our enthusiasm about the recovery.

Think of what is happening in terms of what ecologists call "r" and "k" species. The former are the plant kingdom's colonizers, the supreme opportunists, able to take early and quick advantage of even marginal resources to get a head start and outgrow the competition.

The latter tend to start more slowly, but put a lot of energy into establishing good root systems. Once established, they have staying power.

An "r" species familiar to Baltimoreans is the shrubby, short-lived, weak-wooded ailanthus trees, of little value to wildlife, that spring up in inner city backyards and along railroad tracks.

At the other extreme would be a classic "k" system, a forest of oaks and other hardwoods that might persist for thousands of years, feeding and sheltering a huge diversity of lesser plants and animals.

And if some government agency were to claim a near-doubling of forest in Maryland, it would certainly behoove us to know whether it more nearly resembled ailanthus or oak.

The same goes for the bay's SAV. Unfortunately, the annual aerial surveys used to monitor their comeback cannot differentiate among species. And a state survey that could, a 20-year monitoring effort carried out cheaply (about $15,000 a year) using summer students and boats, was discontinued a few years ago.

Still, from a variety of sources, we can put together a rough picture of what species are responsible for the bulk of the 32,000 acre SAV comeback. And it looks as if the "r's" are outdoing the "k's."

By far the two dominant species involved are hydrilla, which has colonized more than 5,000 acres of once-barren bottom in the tidal Potomac below Washington; and widgeon grass, which has colonized even larger portions of the main bay and its river mouths from Smith Island, north. "Our concern is that these colonizers have shallow roots, and are very susceptible to catastrophic disappearances as well as rapid appearances," says Robert Orth, a scientist at the Virginia Institute of Marine Sciences, and an internationally recognized expert on SAV.

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