By Tom Horton, Bay Journal News Service

Notes to myself on preparing to teach my Chesapeake Bay course at Salisbury University for the 10th year:

Teach oysters? Always, but this time I’m also going bigger, with beavers. Both are “keystone” species, and Castor canadensis, aka the North American beaver, is potentially the more important, even if restoring bivalves gets more press…. Sewage treatment? Can’t ever ignore 17 million toilet flushers, but as with beavers over oysters, I’m moving inland, traveling upslope, emphasizing the lands of the Bay’s watershed vs. the Bay itself.

And that word, “watershed,” let’s reimagine it — it only entered the language around 1800, by which time we’d already eliminated most beavers and their dams and ponds throughout the Chesapeake region. And, that fundamentally altered and accelerated the way water moved off the landscape…. So what’s a better word? Waterkeep? Waterseep? Waterooze? Waterhold?… Something to get us back conceptually to the way it was when the Bay was healthy, its lands more fiercely retentive of life (water equals life).

You want to tell students everything you know. But when you have just 16 three-hour classes a semester, and you’re trying to spend four or five of those sessions outside with watermen and farmers and scientists, or paddling through climate-changed landscapes, you have to choose.

Recently, my choices have moved upslope, come ashore, for a couple of reasons.

Land use is most of the ballgame in our estuary, more so than almost any other on Earth. The watershed/waterkeep is about 16 times the area of the tidal waters into which it drains. And the Bay is so shallow that there’s astoundingly little volume of water, given its long, broad surface. Clearly too little to dilute the runoff from 48 million acres.

The other reason is that the advanced sewage treatment and air pollution control technologies that have carried the Bay restoration to its current, modest success don’t have enough juice left to get us to our 2025 cleanup goals.

This is especially so in light of a growing population — and in light of no population-control policies at any level of government, or even among most environmental groups.

Success by 2025 is going to depend more and more on how well we can halt pollution running from the land — specifically the land that our population radically alters wherever it goes.

Stormwater controls from developed landscapes are better designed than ever, but expensive. It’s uncertain they will be deployed, maintained, inspected and enforced anywhere near 100 percent. Sediment control, for example, decades after it became law in places like Maryland, remains inadequate.

Agriculture, a far larger pollution source, is moving in some good directions with a new phosphorus-based manure control mandate in Maryland and the increasing use of winter cover crops that suck up fertilizers from groundwater before it carries them to the Bay.

But this is not happening everywhere, particularly not in Pennsylvania; and even where it is happening, we still don’t have convincing evidence that we’ll get big enough pollution reductions from the intensive row cropping and concentrations of animals that typify modern farming.

Add to this the real possibility that national policy may soon call for greater use of corn-based ethanol in gasoline. It saves little or no energy and would likely result in clearing more acres around the Bay for more corn.

There are promising programs to counteract polluted runoff, such as planting thousands of miles of vegetated buffers along rivers and streams. But those efforts are far behind schedule, and they don’t specifically call for the vegetation to be forest, the best buffer.

And while such greening of the Bay’s lands is good, we know that far better would be green and wet; and that’s where we need to reconsider and actively restore the beaver.

No creature on Earth, save for modern humans, has more capacity to transform a landscape than the beaver; and in designing a landscape that produces excellent water quality, the animal has no equal.

Beavers ruled the hydrology of North America for a million years or more, until just the last few centuries, when fur trapping reduced populations from an estimated 100 million or more to less than half a million. In the Chesapeake, from millions to thousands is a fair estimate.

Through damming and ponding, beavers stanched the shedding of water from the watershed, cleansed it, filtered it, held back floods, let rain soak in to keep water tables high and streams running even in drought. They created luxurious habitats for a stunning variety of amphibians, fish, waterfowl and mammals.

In recent decades, beavers have come back to the point where a solid body of science in Canada and the United States confirms they were this continent’s most important keystone species — a species whose functioning underpins a whole ecosystem.

My class this year listened to a young man in the stream-restoration business say that in many cases, the work that his company does might be done as well or better by just releasing beavers.

But it is illegal to do that, he said.

That’s a mindset that needs to change. It will take education to overcome prevailing views of beavers as tree-chewing, property-flooding nuisances. They can be just that, but there are technologies to help us coexist — piping, for instance, that keeps beaver ponds deep enough for the animals without also causing flooding.

You will hear more about beavers in the news, I hope. A good place to start: Should the Chesapeake restoration effort include a beaver goal?

In the meantime, we must emulate the animal any way we can, creating wetlands throughout the landscape wherever there is opportunity, moving rapidly toward a “slower” watershed, one that sheds water only grudgingly.

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Tom Horton has written about Chesapeake Bay for more than 40 years. He lives in Salisbury, where he is also a professor of Environmental Studies at Salisbury University.