4.2 Tidal Wetlands. Phragmites Australis

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1 4.2 Tidal Wetlands Few topics elicit such strong emotions in Guilford as the current state of salt marshes. These marshes, more broadly known as tidal wetlands, are undergoing a transformation as sea level rise, erosion, altered tidal flushing, invasive species, and sudden marsh dieback collectively work toward degrading the marshes from all sides. The Town of Branford's regulations describe the importance of tidal wetlands well: "Tidal wetlands are areas of high nutrient and biological productivity which improve water quality by trapping sediments and nutrients, reducing turbidity, restricting the passage of toxins and heavy metals, decreasing biological oxygen demand, and buffering storm and wave energy. Due to their transitional location between upland areas and coastal waters, tidal wetlands are sensitive to disturbance." Some of the notable tidal wetland systems in Guilford include Leete's marsh, Great Harbor salt marsh, Long Cove, the Chaffinch Island marshes, the West River complex, Sluice Creek, Grass Island, the East River complex, and the Sanctuary in the upper East River area. Numerous pockets of marshes are located throughout Little Harbor, Sachems Head, Vineyard Point, Mulberry Point, and near the marina. Refer to Map 4-1 for locations of the major tidal wetland systems in Guilford. Tidal wetlands at Spencer's Creek Preserve Phragmites Australis One of the primary threats facing tidal wetlands is the invasion of Phragmites australis, also known as the Common Reed. Phragmites is an invasive species that often colonizes salt marshes upon human development or alteration of the landscape at or surrounding the site. Undersized culverts, tide gates, and other factors may effectively limit tidal flow, allowing for the invasion of Phragmites to take place as the decrease in salinities and tidal flooding duration allows for the low-saline tolerant plant to survive. Consequently, Phragmites is often removed by restoring the natural conditions of the location before being impeded in some way. Locations suggested for Phragmites removal include properties along Seaside Road, Chittenden Beach,

2 and Old Quarry. If solutions such as increased tidal flushing are possible, then the long-term elimination of Phragmites is possible. Without solutions like those described above, only short-term solutions such as cutting and spraying Phragmites will be possible. Tide Gates Tide gates were designed and installed at locations across the northeast in the early first-half of the 20 th century. They were used for mosquito control, which was successful to a certain point. On the other hand, they were detrimental to tidal flushing and significantly altered flow regimes, sediment transport and species distribution. A number of questions surround the issue of whether tide gates should be open, partly open, or closed for optimal environmental health. Ultimately, tide gate management must be accomplished case-by-case with the priority objective in mind, whether it is flood control, Phragmites removal, water quality improvement, etc.

3 Map 4-1

4 Erosion of Marshes Significant erosion of tidal wetland salt marshes is occurring around Grass Island, east and west of the mouth of the West River, and near Trolley Road and Great Harbor. Additionally, the marshes are sinking/collapsing in many locations, most notable the Leete's marsh north of Shell Beach Road. Erosion events in a coastal setting are dependent upon many factors including sea level rise, surrounding conditions, storm events, and human alteration of drainage and currents. "Natural erosion," such as the case at the Grass Island salt marsh, calls for solutions such as soft armoring and beach nourishment which may slow erosion. However, depending upon the location, implementation of any given solution may reduce erosion at one location but increase erosion at another. The footpaths that have developed at Trolley Road and Chaffinch Island are reportedly eroding the salt marshes. A solution to this problem is to post signs and control foot access. However, these are intensely-used areas and deterrence of foot traffic will be difficult. Construction of elevated boardwalks is one solution that has been suggested for protecting the marshes. Boardwalk installation could occur in concert with advertisements of locations throughout the Town where the public can go and view or walk close to the salt marsh without damaging the ecosystem. It should be noted that boardwalk construction is locally controversial and many residents are not in favor of it, believing that it will increase traffic and ultimately damage marshes anyway. Sea Level Rise Tidal wetland marshes are eroding at the edge of open water In its landmark 2001 report, the Intergovernmental Panel on Climate Change (IPCC) estimated that global sea level will rise 9 to 88 centimeters during the 21st century. According to the much-publicized February 2007 report by IPCC, these predictions have been somewhat refined using six models to predict a more narrow range of sea level rise of 28 to 43 cm (11 to 16.9 inches) in the 21st century. Some coastal states have reported subsidence or drowning of tidal wetlands because they can no longer accumulate peat fast enough to stay above sea level. In Connecticut, the effect depends on location. According to Mr. Ron Rozsa, Ecologist with the DEP's OLISP, sea level rise appears to be altering the zonation of plant communities in southeastern Connecticut, where the tidal range averages

5 0.75 meters. Studies have documented that at least two marsh systems are currently not keeping up with sea level rise. On Connecticut's western shore, with a tidal range of up to two meters, extensive areas of low marsh vegetation have drowned, including marshes in Norwalk. Another ramification of sea level rise is the tendency for marsh systems to migrate landward. As sea level rises, marshes which are able to stay above the rising water level will tend to move inland. For developed areas where seawalls, lawns and other structures or fill material are at the edge of the marsh, landward movement is limited. Sudden Marsh Dieback The salt marshes of the entire Eastern seaboard have been faced with a dilemma that is currently being termed by some scientists as "sudden wetland dieback." Although there is dispute between scientists surrounding what exactly is occurring, recent studies have suggested that marsh dieback may be connected to a 20-year tidal cycle. It is known that the health of salt marshes and the zonation of the vegetation which resides within the marshes are threatened. Results of salt marsh dieback include the development of tidal flats and pockets of holes in the absence of the various salt marsh grasses. The contributing factors which bring about these results are not fully known and include many possibilities. For example, it is believed that the loss of peat has caused the subsidence in Leete's marsh, but this is not the cause of dieback in other locations.