New York's Staten Island has many millionaire-mansions built with profits from the oyster trade. That borough is not the only part of greater New York City that once focused on the tasty filter-feeders to the point of over-harvesting. Historically, the Lower Hudson River Estuary had 350 square miles of oyster beds, but that abundance fell victim to sewage pollution, landfill and the aforesaid over-consumption. The last New York oyster bed closed in 1927.
Oysters and their shells piled in massive beds had served a major purpose: a buffer against storms. A new study is the first to provide a scientific link between the loss of ancient oyster beds from overconsumption by European settlers and a lapse in coastal walls against storm waves and flooding.
The University of Massachusetts Amherst-led study included researchers from Stevens Institute of Technology and Woods Hole Oceanographic Institute (WHOI). In it, the scientists applied learnings from sediment models from coastal ponds, and simulations of hydrodynamics, to demonstrate that the first breakdown of harbor oyster buffers after European settlement was aligned with "a significant increase in wave-derived overwash deposition" at the field sites.
"We initially set out to investigate what Hurricane Sandy's resultant sand deposit looked like in coastal ponds on Staten Island, a location in outer New York Harbor that is occasionally exposed to ocean swells. These sites were flooded severely during the event and we were curious how this Sandy deposit compared to sediments deposited by earlier flood events. An event layer from Hurricane Sandy was clearly present at all our sites, as well as older storm deposits that dated to historical floods," geoscientist Jonathan Woodruff at UMass Amherst said. Just to fill in, an "event layer" is when sediment leaves traces of past events. For instance, Sandy deposited dense, coarse-grained red sediment.
In the study, the researchers learned that storm deposits such as that went away in the period 1600 to 1800. "If it were just one site it would have been one thing, but at every site we saw the same: no storm deposits for thousands of years before European settlement and then after colonization, storm waves start to become more and more effective in transporting sand inland to our field sites. Something the early colonists did seemed to increase storm-induced overwash at the study sites. The million dollar question was what," noted Woodruff.
The study authors initially thought that sea-level rise might have been the cause -- or changes in storm activity, or clearing of land. However, none of these possibilities was consistent with what was being observed in the experiments. The researchers reached dead ends until they hit upon the decimation of New York Harbor's oyster beds. When Europeans arrived, the oysters covered possibly 220,000 acres of the Hudson and Raritan Rivers' estuary. They were a staple of settlers' diets and provided lime for agricultural fields and construction mortar.
Between those significant years, 1600 and 1800, much of the overharvesting took place.
The hypothesis was tested using a model that simulated circulation and waves -- it reconstructed wave heights and elevations of storm surges for two historic storms. One of those was Sandy, in 2012, and the other was a serious 1992 winter storm.
The team also gathered core sediment samples from New York City coastal areas about 16 to 21 feet deep, which went back about 3,000 years. They used these to examine layers from storms, and other features.
Both storm simulations involved control cases with and without oyster beds. The finding in the report was that "reefs provided significant coastal protection from waves prior to their disturbance between 1600 and 1800."
It's also important to note that the study found that that area of New York Harbor now experiences about 30 percent to 200 percent higher-elevation wave energy from heavy storms than in the long-ago past. This ramped-up vulnerability to storms is likely shared by other coastal areas now missing their natural oyster beds," said the study authors in their report.
The findings were published in the online issue of Earth Surface Processes and Landforms.
