Salt Marsh Restoration in Connecticut: 20 Years of Science and Management

Abstract

In 1980 the State of Connecticut began a tidal marsh restoration program targeting systems degraded by tidal restrictions and impoundments. Such marshes become dominated by common reed grass ( Phragmites australis ) and cattail ( Typha angustifolia and T. latifolia ), with little ecological connection to Long Island Sound. The management and scientific hypothesis was that returning tidal action, reconnecting marshes to Long Island Sound, would set these systems on a recovery trajectory. Specific restoration targets (i.e., predisturbance conditions or particular reference marshes) were considered unrealistic. However, it was expected that with time restored tides would return ecological functions and attributes characteristic of fully functioning tidal salt marshes. Here we report results of this program at nine separate sites within six marsh systems along 110 km of Long Island Sound shoreline, with restoration times of 5 to 21 years. Biotic parameters assessed include vegetation, macroinvertebrates, and use by fish and birds. Abiotic factors studied were soil salinity, elevation and tidal flooding, and soil water table depth. Sites fell into two categories of vegetation recovery: slow, ca. 0.5%, or fast, more than 5% of total area per year. Although total cover and frequency of salt marsh angiosperms was positively related to soil salinity, and reed grass stand parameters negatively so, fast versus slow recovery rates could not be attributed to salinity. Instead, rates appear to reflect differences in tidal flooding. Rapid recovery was characterized by lower elevations, greater hydroperiods, and higher soil water tables. Recovery of other biotic attributes and functions does not necessarily parallel those for vegetation. At the longest studied system (rapid vegetation recovery) the high marsh snail Melampus bidentatus took two decades to reach densities comparable with a nearby reference marsh, whereas the amphipod Orchestia grillus was well established on a slow-recovery marsh, reed grass dominated after 9 years. Typical fish species assemblages were found in restoration site creeks and ditches within 5 years. Gut contents of fish in ditches and on the high marsh suggest that use of restored marsh as foraging areas may require up to 15 years to reach equivalence with reference sites. Bird species that specialize in salt marshes require appropriate vegetation; on the oldest restoration site, breeding populations comparable with reference marshland had become established after 15 years. Use of restoration sites by birds considered marsh generalists was initially high and was still nearly twice that of reference areas even after 20 years. Herons, egrets, and migratory shorebirds used restoration areas extensively. These results support our prediction that returning tides will set degraded marshes on trajectories that can bring essentially full restoration of ecological functions. This can occur within two decades, although reduced tidal action can delay restoration of some functions. With this success, Connecticut...

Early Ecological Responses to Hydrologic Restoration of a Tidal Pond and Salt Marsh Complex in Narragansett Bay, Rhode Island

“…Both of these parameters decrease sharply as salinities exceed 26 ppt (WARREN et al, 2002), and this level was achieved on average in the Upper Impoundment of Potter Pond after tidal restoration. As live P. australis was lost in the Upper Impoundment, it was replaced by an increasing area of open water habitat that was rapidly used by highly mobile nekton such as F. heteroclitus and Palaemonetes spp.…”

Guidelines, processes and tools for coastal ecosystem restoration, with examples from the United States

“…True functional equivalency with a reference system may take decades or longer (Zedler & Callaway 1999). For example, a program begun in 1980 to restore tidal action to marshes off Long Island Sound in Connecticut and evaluated 20 years later by comparing restoration and reference sites found highly variable rates of recovery within and among marshes and that recovery of animal populations took up to two decades or more (Brawley et al 1998, Warren et al 2002. Therefore, to make time-frame criteria more meaningful, performance criteria should be stated in terms of trends as well as target ranges.…”

Invertebrate Community Composition Across Inundation Regimes and Its Potential to Reduce Plant Stress

“…Many of these invertebrates are often prey organisms for higher trophic level marsh animals. High tide predators such as fish and crustaceans, and low tide predators like wading and shore birds, depend on the abundance and diversity of invertebrates that occupy the sediments across a range of marsh elevations (MacKenzie et al 2015, Warren et al 2002.…”

“…Support for this has been reported by Fell et al (2000), Burdick et al (1997), andRozsa (1995b) who found that characteristic salt marsh invertebrate communities similar to nearby reference communities established when tidal hydrology was restored. An important qualifier for restored tidal hydrologic connectivity to drive invertebrate community assembly is an adequate supply of propagules, primarily planktonic larvae, and sediment conditions suitable for subsequent survival (Warren et al 2002).…”

“…The general process for plant succession involves a rapid die off of terrestrial plants above the impoundment due to their low salinity stress tolerance (Warren et al 2002). This die off event opens space for pioneer species, those species that are able to tolerate frequent salt water inundation, to establish.…”