Rising seas present hidden dangers to Sandy Hook’s ecology, report says

Increased sea-level rise — even at levels less than a foot — will reconfigure Gateway National Recreation Area Sandy Hook’s delicate fresh-groundwater system, which sustains one of the last two old-growth American Holly maritime forests in the country, according to a new study by the U.S. Geological Survey.

The study, recently released, modeled different scenarios. Researchers looked at sea-level changes of 0.66, 1.3 and 1.97 feet above the current level and investigated increases and declines in groundwater due to shifts in precipitation and storm frequency. Their models also included one that combines the high-end rise projection and more rainfall.

“This report attempts to quantify those impacts on (groundwater resources) in a way that hasn’t been looked at closely before in this area,” Matthew Pajerowski, a supervisory hydrologist for the agency said in an email. Pajerowski coordinated the Sandy Hook study with two similar models at Fire Island, New York, and Assateague Island, Maryland.

According to the latest assessment by the United Nations’ Intergovernmental Panel on Climate Change, released earlier this week, average global temperature will increase by 1.5 degrees Celsius within the next two decades. That uptick will trigger a rise in sea level of 1 to 2 feet by the end of this century. If warming surpasses 1.5 C, however, the ice sheets at Earth’s poles could further destabilize, forcing even more sea level rise.

The Geological Survey study offers a different perspective on the impact of sea-level rise on New Jersey’s coastlines: Reports like the latest from the United Nations tend to focus on the encroachment of water on land. This one, however, examines the trouble that could come from beneath.

At Sandy Hook, fresh groundwater sits just below the soil, in a contact-lens-shaped pocket that rests atop a deeper layer of salty groundwater. As sea level rises, the saltwater presses upward and from the ocean and bay sides, which causes a thinning of the freshwater “lens.”

The recreation area’s unique Bayside Holly maritime forest, along with other areas of vegetation throughout the 6-mile, 27,000-acre park, rely on that already narrow substratum of freshwater to survive. If saltwater creeps in and more frequently inundates the land from the surface, flora with the deepest roots — like the American Holly — cannot survive. Such a phenomenon can now be seen in other coastal areas of the state. The same is true along the southern Atlantic coast and Delaware Bayshore, for example, where saltwater intrusion has killed off swaths of cedar trees.

Subterranean stress

The Geological Survey study also points out that the subterranean stress brought on by sea-level rise will force a more rapid rate of “evapotranspiration,” the evaporation of water from the soil, due to the rising saltwater table’s pressing the freshwater lens up against the ground surface. This, too, will cause the roots of trees, shrubs and grasses to absorb more saltwater than they can handle.

“The important findings of this study show that sea-level rise can pose risks to the shallow groundwater system,” Pajerowski said. “Particularly at barrier-beach islands that have saltwater bodies on either side of a relatively narrow body of land.”

Not surprisingly, the three sea-level rise scenarios the Geological Survey modeled showed significant upland portions of the park transitioning to wetlands — an “increase in area at the expense of other ecosystems” in the park, as the study’s authors put it, “particularly the Bayside Holly Forest.”

Under the low-end sea-level rise projection of 0.66 feet, the study found some 34 acres of “emerging wetlands” will develop. In the worst-case scenario — 1.97 feet of rise — just over 143 acres of land will transition to wetlands.

Source