After the 1907–08 survey of the lower Patuxent concluded in cold December weather, (See "Past is Prologue," November 2012) the mapping of St. Leonard Creek and Osborn Cove went to sleep again, while technology advanced another couple of decades.

By 1920, the U.S. government was surveying and photographing coast shoreline from airplanes — only 16 years after Wilbur and Orville Wright's first flight in December 1903.

By the 1930s, better aircraft with high-resolution cameras were flying for the U.S. Department of Agriculture, collecting information that reflected broader concerns about the nation's agricultural land amid the Great Depression and the Midwest "Dust Bowl" droughts.

In Southern Maryland's Calvert County, the USDA Soil Conservation Service annotated copies of the photography with ground truth about what crops had been planted on each of the fields. I've always thought these photos were an untapped resource for understanding agricultural practices. It was clear that some riverfront farms had serious erosion problems with outflow deltas of sediment spilling from their embedded streams. In those days, everyone plowed their planted fields every year.

These black and white photographs, of wonderful quality, had a life of their own and in the 1990s, Mike Naylor of Maryland's Department of Natural Resources started a census of these images for the entire Chesapeake. His product is an extraordinary, comprehensive map of the Chesapeake's submerged aquatic vegetation, the earliest historical baseline we have for the once-guessed-at historical abundance of this Bay milestone resource.

A single one of this multitude of images, taken in late April 1938, captured most of St. Leonard Creek in extraordinary detail. At the mouth, where it joined the Patuxent, even at the very start of the plant growing season, large beds of submerged aquatic vegetation stretched up to 1,000 feet offshore. Fields prepared for various crops crisscross the back acreage. A boat caught in mid journey, has the vee of its wake forever preserved. Osborn Cove, then owned by Dave Allen, is also frozen in time. For the first time, on the cove's recurved sand spit, first sketched by R. D. Cutts 90 years before and by H. A. Seran 30 years later, we can see it is covered with a long procession of stable vegetation.

The photograph confirms a vibrant community of marsh cordgrass and bushes of groundsel tree covering the length of the sandy spit, which was probably the same in 1907 and — so far as we know — in 1848.

Allen wanted this Maryland farm to be his permanent residence. He built a big machine shop and squirreled away supplies --boxes of soap, camp-ware, old US Army tents, barrels of sugar, thousands of tools, lubricants and had two old Ford Model-A trucks. He built a pier out of used utility poles around 1942. Preserved with toxic creosote, they would last 60 years.

The cove was next photographed from the air about 1942 by a U.S. Army pilot serving under Air Corps two-star Gen. St. Clair "Bill" Streett, who was trying for an image of the boss's house near Osborn Cove, but missed! In this picture, submerged aquatic vegetation lines the inner shoreline of the cove but, most interesting to me, the vegetated sand spit is still stable. Allen's property was surveyed in 1953 and the team accurately mapped the sand bar. He was carving off a lot across one of the small valleys from the 53 acres he owned for a friend he wanted to have as his neighbor. Within five years the friend died; in 10 years Allen, himself, was dead.

A busy community of estuarine species occupied the spit: thousands of Littorina and Melampus snails and fiddler crabs that were preyed upon by raccoon, otters and shorebirds. Behind the bar was a quiet tidal pond, the nursing ground for small fish, including several species of the killifish, silversides, panfish like white perch, and circling schools of juvenile menhaden. In the soft, silty-sand bottom were scores of benthic infaunal species which most people don't know exist. But most shore dwellers know well the soft– or "steamer" clams the (recently commercially harvested) stout razor clam, and smaller mollusks like Macoma balthica. Great blue and little green herons and belted kingfishers stalked the shallows, occasional horseshoe crabs, diamondback terrapins and huge snapping turtles crawled up on the sandy shorelines to lay their clutches of eggs.

I hesitate to guess at the number of soft and hard crabs William Howard Bean and his son Franklin Gross caught in that tidal pond over their 40 years fishing there. Several decades ago, a man in their family caught 365 one morning and was pleased to sell them in Solomons for $3.65 — a penny apiece.

Since navigation chart resurveying is infrequent, aerial views have become the most effective way to track shoreline change, and in our warming world with sea level rising, this has become a worldwide issue. Osborn Cove has become a small canary in the mine for these issues on the Chesapeake.

The USDA flew the region again Oct. 13, 1957 and their image again provides a clear image of the sand spit, still thoroughly vegetated. There's a boat at Mr. Allen's dock and the field north of his house has been cropped.

My wife Nancy and I moved to Osborn Cove in 1974, and eventually owned Dave Allen's house, shop and the shoreline. As a young scientist working in the Chesapeake, the place quickly became a research interest as well as a home. With help from my then-employer, the Academy of Natural Sciences of Philadelphia, my staff and I did a serious study of the cove, its watershed, hydrography, and the plankton and bacterial life that swarmed in this productive habitat. Our mapping, thanks to biologist Mike Kachur, listed all of the plant species we could find living on this unusual sand spit. I published the story in the journal Marine Biology, vol. 61, 1980 (pp. 53-67). A colleague, Dr. Jerry Smith, flew me over the Cove in 1975, providing yet another image of the vibrant stable plant community residing on that embracing sandbar. What a joy it was to see this treasured place from on high!

My later work at the EPA's Chesapeake Bay Program office of environmental monitoring allowed me to dovetail my personal interest in Osborn Cove's habitat with the new Volunteer Monitoring Program headed by Kathleen K. Ellett at the Alliance for the Chesapeake Bay. I began analyzing data that I'd collected over a decade and found that sea level at the cove was measurably rising.

In 1993, another aerial image showed the vegetation all along the spit to be vibrant. I thought at this time that the bar was actually lengthening, and there was a chance that it might totally enclose the tidal pond. The world's rising oceans, (coupled with a phenomenon called subsidence of the glacial fore-bulge, formed about 12,000 years ago) had other ideas. Comparing the trees visible on the 1938 aerial with present vegetation, I found the stump of a now drowned cedar tree was several feet offshore in the pond, and by 1993, extension of the bar had apparently ceased, but the vegetation was as strong as ever.

As part of my research I'd driven calibrated stakes along the whole sand bar to measure sand movement. It appeared that eroded sediment from the cliff would move by wind, wave and current along the bar. As a matter of principal, I did nothing to prevent this, expecting that we had at least another century before any threat to our home, and I felt responsible for the small ecosystem of the bar and pond, which I could watch from my home office window every day.

I continued measurements at Osborn Cove long after EPA and states had tightened budgets and abandoned volunteer monitoring. I have continued to monitor the site since leaving the EPA 12 years ago.

By 2008, the vegetation structure along the sand spit was breaking up, and, by 2010, most of it had vanished. With wave and power-boat wake action uninhibited, the unprotected sand was spilling over in waves, starting to fill the tidal pond and smother organisms living there. I went about rescuing hundreds of air-breathing marsh periwinkle snails which would otherwise have drowned.

The data set, now covering 38 years, and the record of the sand spit stretching back 165 years, is remarkable. My former NOAA colleague Marcia Olson has analyzed the entire dataset and demonstrated that sea level has risen about 5.5 inches, or 139 mm, which is roughly consistent with sea-level changes reported for Baltimore and Solomons Island, MD. This has been of immense significance for the millions of creatures depending on the sand spit and tidal pond.

The supply of sediment which has fed this system for hundreds of years is certainly not decreasing. It's the inability of the marsh plants, with their stabilizing peat formation, to keep pace with the increasing rate of sea level rise. This is true along marshes and shorelines bordering much of Chesapeake. The problem in Osborn Cove is only a microcosm of what's happening Bay wide. The increasing frequency of collapses from my erodible cliff could now threaten our home in my lifetime.

A descendant of Mr, Allen after visiting Osborn Cove wrote me in 2005 exclaiming at the amount of cliff erosion since the 1950s.

There are many who would have us believe that climate change science and rising sea level are not science at all. I find this thinking hard to reconcile with the change occurring inexorably outside my window every day.