|
Plumb Beach on the Move
Ecological Changes at Plumb Beach
If you are not a south Brooklyn resident, it is quite likely that you have never even heard of that small part of the Gateway National Recreation Area called Plumb Beach. It is a strip of beach less than a mile long with dunes and a tidal lagoon and marsh at the eastern end. It is adjacent to Sheepshead Bay bordering the eastbound lanes of the Belt Parkway. For reasons having to do with overlapping jurisdictions of New York City Department of Parks and the Department of Transportation, the National Park Service has virtually disowned Plumb Beach. If you were to drive into the Plumb Beach parking lot, you might see the flag of the New York City Parks and Recreation department along side of the American flag. There is no National Park Service flag or sign and national park service rangers are nowhere to be seen.
When Plumb Beach first became a part of Gateway, the National Park Service conducted regular nature walks along the beach especially during the season when horseshoe crabs lay their eggs. The park rangers would introduce the horseshoe crab as a living fossil whose ancestors roamed the bottom of Silurian seas. The rangers admonished the public to let these harmless creatures alone as they come ashore to deposit and fertilize their eggs. They also described how migrating shorebirds have come to depend upon the horseshoe crab eggs as a very nourishing food source that will help prepare them for the journey to their breeding grounds in the arctic tundra. The rangers reassured their touring groups that since most of the eggs were buried; the loss of horseshoe crab eggs to feeding birds was not significant. Although Plumb Beach doesn't compare to Delaware Bay as an important shorebird stopover, it is a very accessible object lesson in ecology and wildlife conservation for the Gateway visitor.
There is an equally important lesson in ecology to be learned from Plumb Beach 25 years later, but no one in the Park Service is going to tell you about it. Along our shorelines, there is a relentless struggle between man-made structures including filled land, and tidal and littoral currents of the sea. That struggle gets headlines when powerful storms tear away parts of barrier islands and beaches destroying and threatening houses and roads.
In the early 1990’s those inexorable forces of tidal currents and wind created severe erosion on Plumb Beach. A bicycle path runs along the Belt Parkway, as it parallels Plumb Beach. The erosion undermined the bicycle path and small brick building near the Plumb Beach parking lot. The part of the bicycle path that curved away from the Belt Parkway towards the water’s edge collapsed onto the beach. At one point along the beach the high tide came within 25 feet of the Belt Parkway. One prolonged storm combined with high tides could have undermined the parkway. To prevent the loss of this important artery, the decision was made to nourish the beach.
In 1992, thousands of cubic yards of sand dredged from the bottom of Rockaway Inlet were pumped onto Plumb Beach while earth-moving machines created massive artificial dunes where there had been a gently sloping beach. A contractor and volunteers planted dune grass and installed snow fencing to prevent wind erosion and trampling of these fragile plantings. At the edge of the Belt Parkway a steel road barrier was installed, which protected the natural dunes and marshes east of the beach from destructive incursions by off-the-road vehicles.
As a result of all the new sand pumped onto the central section of Plumb Beach, much of the former mud and sand flats that had been frequented by shorebirds was replaced by relatively sterile sand mixed with clamshells. (Nevertheless, seven years later, the mud and sand flats have been re-colonized with much of the tidal zone life that again provides food for migratory shore birds in the fall.) The tidal currents and wind began to work on the newly installed dunes. It was not long before the highest tides of each month were lapping at the base of the man-made dunes creating steep bluffs where there had been a slope. By 1998, large portions of the dunes were gone. Where did the sand go? One would expect it to slump out onto the sand flats immediately opposite the eroding dunes. Some portion of the sand may be going there but much of it is drifting eastward along the beach probably driven by strong northwesterly winter winds. Since 1992 the dry beach has extended more than fifty yards to the east into the marsh and the tidal sand flats have extended even further. The drifting of all the excess sand has caused some major ecological changes.
The most obvious changes in the beach topography have taken place a half mile east of the artificially created dunes. The eastward extension of the dry beach blocked a natural channel between a tidal lagoon and the sea. This water channel acted as a natural barrier between the dry beach and Plumb Beach Marsh, protecting the wading birds, shorebirds and waterfowl in the marsh from human disturbance. Now the extended beach permits people with their unleashed dogs to walk well into the formerly isolated marsh. Sand flats, which were formerly 18 inches below the level of the marsh, now smother about one quarter of the marsh. Extensive mussel beds that bordered the marsh were buried under the drifting sand.
A new channel from the tidal lagoon now extends eastward across the marsh into Gerritsen Inlet. Before 1993, during the horseshoe crab egg-laying season, the tidal lagoon had been teaming with their activity. In the spring of 1999, there was very little horseshoe crab activity in that lagoon. Egg-laying horseshoe crabs are also missing from the scene along the length of Plumb Beach along with the shorebirds that feed on their eggs. Most of the horseshoe crab egg-laying seems to be confined to the shallow water in and around the marsh. It is speculated that the slope of a beach may be a factor in the selection of breeding sites by horseshoe crabs. The steeper slope created at Plumb Beach by the beach nourishment may have created an impediment to horseshoe crab breeding.
In noting the topographical and ecological changes at Plumb Beach, it has to be recognized that the beach nourishment by the U.S. Army Corp of Engineers in 1992 was an emergency action required to prevent the severing of an arterial highway, the Belt Parkway. In the creation of the Belt Parkway many marshes were buried and a major part of the Jamaica Bay ecosystem was disrupted. In order to protect our infrastructure the whole process of beach nourishment will very likely have to be repeated and further damage and disruption of the Plumb Beach wildlife habitat will occur.
Ronald Bourque August 29, 1999
Post script, 2005: The dry beach has now extended 890 feet eastward over the salt marsh. About 4 acres of beach have replaced that much marsh. There is irony in the attempts to restore salt marsh Islands in Jamaica Bay with sand nourishment while Plumb Beach marsh is being buried under sand. See annotated April 3, 2005 photograph of advanced Plumb Beach dune erosion. Compare the width of dune with October 2004 photographed the same area.
In late summer of 2004, common and least terns were feeding their fledglings on the new extension of the beach. There is no evidence that they were breeding there but this new habitat will be monitored for tern and/or plover breeding activity.
Because of the severe erosion that threatened the Belt Parkway, the bicycle path and this maintenance building, beach nourishment was quickly implemented by the U.S Army Corp of Engineers.
In 1990 the beach erosion began to undermine the bicycle path along the Belt Parkway. Concrete rubble (at left) was placed there to slow the progress of erosion.
This 1986 aerial photograph of Plumb Beach shows the generally stable state of the beach, dunes, salt marsh and lagoon that existed for more than 25 years before the 1992 beach nourishment. The erosion of the central section of the beach (Bicycle path interrupted by erosion - arrow ) was the unstable part of the beach that threatened a pipeline and the Belt Parkway.
This 2001 aerial photograph shows a radically altered Plumb Beach topography with the dry beach extending 890 feet (2004) beyond the old lagoon channel eastward to Gerritsen Inlet. The lagoon channel now cuts through the marsh to the eastward to Gerritsen Inlet. (Note: North is at the bottom of the photograph.)
This 2005 oblique aerial photograph shows the new dune formation spreading northward into the marsh. If the tongue of sand - lower right - continues to move northward, it could cut off the tidal flow into the salt marsh and lagoon. The ecological functions of the marsh and lagoon and marsh would be lost. The flooded tidal lagoon is used by least terns to hunt fish to feed their young. The marsh itself supports breeding clapper rails.
Wind erosion appears to be the major mechanism for the movement of sand that extended the dry beach over the salt marsh. Westerly winds blow in dry weather easily moving the dry sand to the east. Easterly winds tend to be associated with wet weather anchoring the sand against drifting westward.
At High tide, wave action eats away the base of the dunes creating steep unstable bluffs. Every day more sand is carried away by littoral currents and wind.
The dunes shown here are less than one fourth their width when they were established during the 1992 nourishment. The dunes then extended well past the surf line you see the in the background. Photograph taken in October 2004.
This March, 2005 photograph taken in the same area of Plumb Beach dunes as previous photograph, illustrates the considerable dune loss since the fall of 2004. Marine Parkway Bridge in the background.
Compare this photo to the previous one taken in March 2005. This very close to that remnant dune area that measures 40 feet from the bluff edge to the Belt Parkway. Subtract 10 feet of buffer for this photo.
Storm water runoff combined with the wave action of the April 14th - 15th nor'easter has exposed the edge bicycle path. The rubble and gravel were the foundations of the bicycle path that was rebuilt after the last major storm undermined it.
This one of the two gullies formed by the action of storm water runoff. Evidence of the water flowing of the bicycle path is visible at the left edge of the gully.
|
