Habitats
November 7, 2008Coastal Wetlands
In 2004, the Narragansett Bay Estuary Program published several major reports on status, trends and restoration opportunities for Narragansett Bay coastal wetlands. The study mapped about 3300 acres of tidal marshes on Narragansett Bay, of which a majority have been impacted by human activity, such as ditching for drainage or mosquito control. The study included an examination of Bay shorelines, finding that about a quarter of the Bay’s shores-about 130 miles along the Bay’s 540-mile shoreline-are “hardened,” that is, protected by bulkheads, revetments, and seawalls. These manmade features protect coastal property at the expense of coastal habitat.
The NBEP studies found that from the 1950s to the 1990s, the Narragansett Bay estuary experienced a net loss of 548 acres (1%) of tidal habitat including coastal wetlands and waters. The losses concentrated on intertidal habitats with a net loss of 306 acres (10%) of estuarine marshes and a net loss of 205 acres (11%) of beaches and other intertidal nonvegetated wetlands (unconsolidated shores). Almost 110 acres (0.1%) of coastal waters were lost. The studies found that these changes were caused by coastal erosion, sea level rise, residential development and other factors, and suggested that some of the losses documented may result from climate change (NBEP 2004).
Calf Pasture Point in North Kingstown, R.I., provides an example of anthropogenic impacts on coastal wetland habitats. Until 1939, the area was a coastal salt pond system with fringing wetlands, connected to Narragansett Bay via a tidal inlet or breachway. Protected shallow-water areas such as this serve as important habitat and spawning refuges for many species of estuarine fish, shellfish and birds.
At the onset of World War II, the salt pond was used as a disposal site for dredged material from the development of Allen Harbor, part of the Quonset Point naval base. Later, the Navy used the area as a dumpsite for hazardous waste. Today, after some cleanup, the Town of North Kingstown is in the process of redeveloping the site for recreational use. However, the historic salt pond habitat is permanently lost.
[insert calf pasture map here]
Town Pond in Portsmouth, R.I. was similarly filled. Around 1950, this historic salt pond was used as a disposal site for dredged material from the Mount Hope Bay shipping channel. The filling converted about 40 acres of shallow-water tidal habitat into a mud flat; over time, the area was colonized by the invasive reed Phragmites australis, a plant characteristic of disturbed habitats.
Beginning about 2000, the U.S. Army Corps of Engineers, R.I. Dept. of Environmental Management, Narragansett Bay Estuary Program and other partners began a project to restore tidal habitat at Town Pond. In 2008 the $6 million project was completed, creating more than 20 acres of salt pond habitat. The original footprint of the pond couldn’t be fully replicated, due to the location of new infrastructure such as roads and powerlines which were built since 1950, as well as the difficulty and cost of removing fill material from the site, necessitating a “net zero removal” restoration design.
[insert Town Pond maps here]
Sea Grass Beds
Sea grass beds are a critically important coastal habitat, serving as spawning areas and refugia for a wide variety of estuarine creatures, from bay scallops and blue crabs to tautog and winter flounder. In the Northeast, the dominant species of sea grass is eelgrass, Zostera marina. Eelgrass was once widespread throughout the shallower waters of Narragansett Bay and the South Shore coastal ponds—nautical charts of Providence River from the 1860’s show “grass beds” along the edges of the channel. 150 years later, eelgrass grows only in lower Narragansett Bay, no further north than Prudence Island. Nitrogen pollution is widely considered to be a principal factor in the decline of eelgrass. Short et al. (1996), for example, demonstrated a strong relationship between eutrophication of Ninigret Pond on Rhode Island’s South Shore, driven by housing development, and decline of eelgrass beds there.
After many decades of decline, there is preliminary evidence that eelgrass may be increasing in Narragansett Bay. A 2006 survey by URI, NBNERR and Save The Bay found more than 400 acres of eelgrass in Narragansett Bay, of which just over 100 acres were in well-flushed areas along the southern edges of the Bay (southern Newport and Little Compton, R.I.) Nearly 300 acres were well within the Bay estuary. The report found that, even accounting for differences in mapping techniques since the last survey (1996), the extent of eelgrass had increased; at two sites analyzed in detail (T-Wharf at Prudence Island and Potters Cove in Jamestown), the eelgrass beds had doubled in size over ten years (Bradley et al. 2007)
Freshwater Wetlands
(working)