N.J. coastal wetlands moderated some of Hurricane Sandy’s fury

between flooding, vegetation growth and sediment deposits in wetland ecosystems — either temporarily or long-term.

The release notes that this is where the bad news comes in. As she works through the data analysis this fall, Quirk said she has not found much sign of sediment deposits, before or after the hurricane struck.

Sandy had the potential to deposit a lot of sediments, fast, which would have been good for building up wetlands. Hurricane Irene in 2011 had been associated with a bump up in wetland accretion by several millimeters at a number of locations in the region — a bonus growth equivalent to the amount that typically accrues in an entire year.

“Sediment-limited systems like coastal lagoon marshes largely depend on deposition by storms to vertically adjust elevation, so they don’t sink relative to sea level,” Quirk said. “In places where we have ongoing monitoring, the evidence suggests that some sites are subsiding — sinking below the surface —rather than increasing elevation at a rate similar to local sea level rise. Surface deposition would be a good thing for these marshes.”

Any number of reasons could explain why those hoped-for sediment deposits did not materialize, she said. Maybe the unusually high tide during Hurricane Sandy caused less suspension of sediments in the storm-surge waters. Or maybe the storm water did carry sediments and plant debris, but dropped them on the barrier island or inland along the tree line and not at her sampling sites in the marsh interior.

Whatever the reason, Quirk’s findings point to cause for continued concern over the coastal marshes’ future.

“These salt marshes provide a number of extremely valuable ecosystem services and benefits to society,” she said. Storm surge protection is just one of these. Coastal marshes also provide excellent habitat for commercially and recreationally important fish and shellfish, especially as a nursery ground for these animals. They are also important for storing, transforming and removing nutrients that can be harmful to the aquatic ecosystems.

The areas of tidal wetlands remaining in New Jersey have been sharply reduced in proportion to the past, with surrounding areas built up with bulkheads and other development — making the remaining wetlands all the more crucial to protect because they cannot shift inland.

“With accelerating sea level rise, it is unknown how many of these marshes are going to be able to keep up because they are dependent on plant growth, which is a slow process,” Quirk said.

“Since 2010, the northern area of Barnegat Bay and the marsh on the bayside of the barrier island at Island Beach State Park is converting before our eyes from marsh to open water.”