Posted by Walter Boynton
This part of the story (see part one) starts with work done by Dr. Grace Brush, a long-term faculty member at Johns Hopkins University. Grace and her students use a variety of techniques to “look back in time” to reconstruct what the Chesapeake Bay and watershed looked like in the past, even as far back as 14,000 years ago.
What they found was interesting and useful for all people living in this basin. For example, Grace found when John Smith starting exploring the Chesapeake the basin was “almost entirely covered with a diversity of forests on a wide variety of soils, drained by an intricate and dense system of over 100,000 streams and 150 major rivers surrounded by large marshes.” In addition, “beavers were abundant…building local dams and impoundments on ..virtually all… streams…the environment was wet and marshy throughout.”
I took some of Grace’s data and estimated that at the time of European settlement there were about 3 million beavers at work in the basin…by the early 1700s there were no beavers left and by the mid-1930s the Chesapeake human population reached the same level as the beavers in1600. Lots of change, again!
What’s the message here? The message is that we need to think differently about the land we all live on, especially because there are so many of us. It is clear that wetlands of all sorts, including those engineered by beavers in the 1600s, were more common in the past than they are now.
These systems RETAIN and CLEAN water as it moves (slowly) from the land to waterways. Sediment, nitrogen and phosphorus are all removed, some of it permanently. We need to engineer wetlands back into the landscape just as we are now trying harder than ever to engineer oysters back onto the waters of the Chesapeake…in part because they also do a heck of a job in keeping water quality (and habitat) in good shape.
Some may think this just pie-in-the-sky nonsense, but there is good evidence that making parts of the landscape “wetter” will make a large difference in water quality. A few years ago I was involved in putting together a nitrogen budget for the whole Patuxent River and watershed. Many people know the general story of the Patuxent where an over-supply of nitrogen and phosphorus have led to turbid water, loss of seagrasses, algael blooms and dead zones where there is little or no oxygen in the water. What we wanted to know was where nitrogen came from and where it went.
While the science folks can make a budget sound awfully complicated, it comes down to the same sort of budget my wife insists on keeping…where does the money come from and where does it go…and no, there can be no red ink and no, we do not get to print some more if we happen to run low. That’s what we did in the Patuxent but with nitrogen rather than cash.
What we found was astonishing. In a nutshell, half of all the nitrogen that comes from the drainage basin into the Patuxent is removed in the tidal wetlands of the Patuxent. These wetlands make up just less than 2 percent of the full basin…a tiny bit of land yet they exert a powerful effect…for free, I might add…on cleaning up the water.
I’ve started thinking of them as a natural kidney placed between the land and water, doing a job akin to the kidneys in our bodies. Similar results have been seen in the Choptank and Corsica Rivers, both of which have wetlands at the head of tide; this effect is missing in the Potomac where the wetlands at the head of the estuary have long-since been paved into a city.
So, this wetland kidney effect does not seem to be just a fluke of the Patuxent but a more general feature of the land-sea interface. Unfortunately, even these wetlands are not enough to adequately clean up the water and serious water quality problems persist in all these estuaries. More needs to be done.
The point here is that we need to take Grace Brush’s ideas to heart and add wetness to the landscape. Evidence to date suggests it can have important water quality benefits and this seems especially important given that more of us want to live in Bay Country. I’m not recommending we build beaver hatcheries akin to oyster hatcheries but we can build wetlands without the help of these native rodents.
Some outfits like the University of New Hampshire have been building experimental wetlands and testing them under real-world conditions. Results have been heartening and that’s the good news I referred to at the beginning of this piece. We need to get busy and start some serious beaver-like behavior.