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Chapter 2 - Coastal EcosystemsIn recognition of the importance of barrier beaches to thetidal wetlands and lagoons behind them, many states havetaken action to protect their barrier beaches by preventingadditional structures that might impede their naturalaccretion or migration (e.g. Massachusetts Barrier BeachInventory and Executive Order restricting further buildingon barrier beaches).Longitudinal upstream connectivityAs sea level rises the salt wedge will intrude farther upstreamin coastal rivers (Najjar et al. 2000). Thus, wherenow there may be fringing salt marshes at the seawardend of estuaries and brackish and then freshwater tidalwetlands fringing farther upstream, in the future all thesemay become salt (if they remain elevated enough to bevegetated at all.) However, in some larger coastal riversthere is plenty of longitudinal space for these fringingtidal marshes to migrate upstream as the sea level risesand tidal influence and salt intrude farther. On the otherhand, where coastal river continuity is truncated by naturalfalls, dams, or restricting culverts that would preventa tidal wetland from moving upstream, it is likely thatthe freshwater and brackish tidal wetlands will disappearand/or become entirely saline. Note however, that modelingsuch changes specifically is complicated by the need totake into account changes in the river’s hydrology due topotential changes in the rates and volumes of freshwaterflow.Rate of accretion/erosionTidal wetlands and other shorefront habitats can persist inthe face of moderate rates of sea level rise through accretion,supported by sedimentation and organic matter accumulation(Chmura et al. 2003). However, if relative sealevel change exceeds net elevation change (the net effect ofaccretion and compaction), wetlands and beaches will beinundated and ultimately lost (Peterson et al. 2008). Ingeneral, over the last century, salt marshes have accretedsediment at a rate to keep up with rising seas (Hartig et al.2002; Najjar et al. 2000; Roman et al. 1997). Recently,however, several authors have predicted that salt marsheswill not be able to accrete fast enough to keep up withpredicted sea level rise and the result will be outrightinundation in some cases or at the least major losses ofSpartina patens dominated marsh and expansion of Spartinaalterniflora dominated marsh (Gornitz et al. 2004; Morriset al. 2005).Not all tidal wetlands accrete at the same rates. Some,such as freshwater tidal wetlands that may have sparseplant cover but harbor many rare plant species, are moredependent for accretion on sediment input from riversthan salt marshes (Neubauer 2008). Salt marshes aremore dependent on vegetative accretion than sedimentinputs and the vegetative production may be dependenton the stimulus of flooding (Nyman et al. 2006). Insome areas warmer temperatures associated with climatechange may increase marsh productivity and subsequentlyincrease organic sediment accretion rates (Langley et al.2009). However, this effect may be more pronounced infreshwater than saltwater systems and background accretionand erosion rates are a fairly site-specific phenomenon,depending on a variety of local factors not easilypredicted without detailed studies. Titus (2008) has compiledmaps that depict site-specific scenarios for wetlandaccretion along the Mid-Atlantic coast from New York toVirginia. Other authors have determined accretion ratesin other states (e.g., CT: Orson et al. 1998; Warren andNiering 1993; RI: Bricker-Urso et al. 1989).Potential Resilience Attributes to be Assessedat Regional ScalesGiven data gaps and data resolution, comparative resilienceis probably best addressed at an estuary or CSUlevel, rather than at a beach by beach or marsh by marshlevel (EPA 2008). A logical start would be to build fromsome of the following system-specific attributes.BeachesSizeThe area of all beach and dune systems in the NorthwestAtlantic has been calculated using GIS data from TNC’sNorthern Appalachian and North Atlantic Coastecoregional plans and generated for Chesapeake Baybased on the NWI, ESI, and National Land CoverDataset (NLCD). It would be advisable to update these2-50Northwest Atlantic Marine Ecoregional Assessment • Phase 1 Report