It’s a jungle down there! Visiting Susquehanna Flats’ underwater meadow
Surveyors mapped the Susquehanna Flats accurately before the end of the 18th century, but their charts and the historical record leave considerable uncertainty about the status of submerged aquatic vegetation beds during the early years of the United States. The record is clear, though, that by the mid to late 19th century, vast grass beds covered these well-lit shoals and provided abundant resources for wintering and migrating waterfowl.
In the 20th century, the beds began to disappear. Their loss and a concurrent decline in waterfowl populations paralleled growth, development and pollution across the Chesapeake watershed. In 1972, massive floods accompanying Tropical Storm Agnes appeared to deliver an insurmountable blow to the Bay's ecosystem.
But in the late 20th century, a resurgence of the once-extensive underwater grass beds slowly spread across the Susquehanna Flats. First, some nonnative and opportunistic species like Eurasian milfoil (Myriophyllum spicatum) took advantage of the abundant nutrients flowing from the Susquehanna and colonized areas once swept bare. Slowly over the last two decades, once-strong native species, like wild celery (Vallisneria americana) and water star grass (Heteranthera dubia) have joined to build immense and expanding populations. It's uncertain if natural forces dominated, or if programs put in place to restore the Chesapeake Bay played a role in the change.
In the summer of 2005, while sailing through the C & D Canal en route home from New England, I shifted my yawl Nimble's course westward from Turkey Point and headed toward the mouth of the Susquehanna River, seen dimly through the Chesapeake's humid haze. This direction took me out across the vast flats, or shoals, carefully mapped by Hardecouer in the 18th century, and now expanded even farther. Nimble's draft is a modest 39 inches and I figured to work my way far out onto the flats and find these reviving grass beds. All along this route I was surrounded by the floating, detached blades of wild celery, evidence that the plants could not be far away. There were also clumps of what appeared to be parts of a bottom-coating cyanobacteria mat.
My logbook recorded two areas on the flats, one about a meter across, where decomposition gasses were "dramatically effervescing thousands of 1 centimeter bubbles per minute. Many liters of gas were emerging, which I assumed to be methane. I should have thought to test-light it with a torch on the end of my boathook."
I saw, however, none of the dense rooted patches of SAV that Mike Naylor of the Maryland Department of Natural Resources had assured me were growing there. Eventually, my keel struck hard on what must have been a large, waterlogged tree trunk. I thought better of continuing so far away from boat traffic in a place where I could be embarrassingly stranded!
Backtracking, Nimble scuttled southeastward and into the C & D Canal approach channels again.
I had thought that experiencing the Susquehanna Flats regrowth firsthand had eluded me until one day this summer when I spoke to Lee Karrh, a field biologist with Maryland's Department of Natural Resources.
"Kent, you have to see this!" he said. "Remember years ago I took you out to Dundee Creek to see the Vallisneria beds there? This will still knock your socks off!"
So, at the cusp between August and September last summer, I and other scientists stayed at the Vandiver Inn, a bed & breakfast in Havre de Grace, MD, at the head of Chesapeake Bay. The inn was once a posh Victorian mansion built in 1885 by Havre de Grace businessman Murray Vandiver. It was not the kind of place to which poor field biologists are accustomed. Breakfast was served outside on the front patio that steamy August morning, which promised to culminate in a broiling hot day.
Vandiver owned and farmed nearby Spesutie Island. Among his crops were Maryland peaches, a delicacy then as now, but very challenging to ship and still have them arrive in urban markets to the north and south unblemishedâ€”or at least suitable for pies and jams.
Vandiver owned a schooner and a yacht, and had financial interests in the railroad. In later years, he transformed himself from entrepreneur to Maryland politician. The old home was redolent with Chesapeake history and a sitting room cabinet was stuffed with artifacts from his life and times.
I wondered what Vandiver had thought of the vast grass beds hardly a half mile from his door. I'll wager not much, and if at all I suspect he mused on the income from railroad shipments of the barreled duck carcasses shot by market gunners on the flats, or the speed with which his peaches could reach customers hundreds of miles away. I suspect he gave the vast Chesapeake ecosystem no further thought.
After breakfast, I joined a group consisting mostly of biologists, including many the Chesapeake's most eminent submerged aquatic vegetation experts, aboard four small boats heading down-channel toward Vandiver's Spesutie Island. There, we turned east around the lower edge of the immense flats.
On this shallow plateau, occupying the whole central part of the Bay at this latitude, hunters stood among their decoys a mile from shore, participants in the long, early season directed at reducing non-migratory populations of Canada geese. Non-migratory birds like these geese and farm-and-release mallards can seriously deplete SAV resources.
Elsewhere in the Chesapeake, non-migratory waterfowl like the mute swan have severely damaged SAV beds by grazing them in summer, their period of maximum growth and reproduction, and leaving fewer food resources for tired and hungry waterfowl that arrive from their Canadian breeding grounds to these wintering areas.
We saw ahead of us, all to the north, northeast and northwest, areas of mirror calm water into which our boats edged. We checked for signs of grasses, which almost immediately appeared. Bob Orth, of the Virginia Institute of Marine Science, dove overboard to check and we moved up what geologist Peter Vogt described as a "prograding slope," then onto the shallower flats themselves.
As the water shoaled even more, SAV plants broke the surface, forming a dense forest of fronds reaching up to sunlight at the surface. The bottom was entirely covered-actually thick-with SAV, like nothing I had ever seen.
We were all in the water within a few minutes and with snorkels and masks we glided through the half light of this incredible underwater jungle. The original invasive water milfoil was still dominant, but it provided a matrix for burgeoning native species, the plants that had occupied these habitats for centuries. I rose from my view of this alien world with my head and mask literally hung with long strands of the plants.
Ecologist Mike Kemp, from the University of Maryland at Horn Point, had discussed this with us the day before. He said that during a recent trip out on the flats, he had climbed atop the boat's cabin, and standing there, elevated a few yards above the water's surface, had found himself surrounded by grass beds as far as the most distant shore miles away. Twelve square miles of grass beds, he figured, which was quite remarkable. We each had the same experience this unusual day.
We worked on through these beds. The milfoil was in reproductive mode and the tips of the plants rose above the water's surface, stippling the view as far as the eye could see. The water's surface was streaked with the white dust of their aerially spread pollen.
Diving in, one quickly lost light the deeper one went. On the bottom was the finest possible silt, spared from suspension only by the stilling effect of the grasses themselves, stilled even from winds sweeping over the surface. This was how the flats grew, but likely when the plants died each winter, wave action was able to reach down to this level and distribute the sediments via currents, allowing deposition again at the margins of the flats, which seem to have slowly expanded over the last two or more centuries.
Also on the bottom were the cohesive cyanobacteria (blue-green algae) mats that I'd seen five years before. Orth brought up several samples, and I took a bit home. Examining it later, under a microscope in my library, confirmed the filamentous blue green algal matrix, indurated with that fine silt.
None of us emerged from the water without being festooned with yards and yards of dense plant materials. Orth, reveling in the stuff, gleefully stretched 2-meter lengths of it to his spread arms extent. I've known Orth since the late 1960s when, as a student at Rutgers University, he showed the same enthusiasm for beds of eelgrass (Zostera marina) in New Jersey's coastal Barnegat Bay. I thought at the time that this was just youthful exuberance, but he has sustained his love and stewardship for these natural resources all these 40-odd years. I, personally, came up several times, my vision entirely blocked by masses of plant wrapped around my snorkel and covering my whole face mask! Each of us on all the boats were similarly fascinated and enthralled by the unique experience.
What struck me, as I reflected upon the history I'd researched and the many sharp minds who had traversed these flats in centuries past, was that no one, from Capt. John Smith to businessman Murray Vandiver, had seen fit to mention this remarkable biological wonderland, questioned its role in the Bay's life, nor even complained about the challenges of getting a boat through the grasses, a challenge even we faced with our well-powered modern boats.
That day we travelled from site to site across the flats and around their perimeter, as far north as Furnace Bay-named after the Revolutionary War period Principio Iron Works-appreciating the variation and the homogeneity of this remarkable place. We saw wide areas with just one species; in other areas we found a matrix of two or more species.
Karrh had promised that this experience would "knock my socks off" and I was indeed, most of the day, without my socks!
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