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Chapter 2 - Coastal EcosystemsRiver Dominated areas include river channels, drownedriver valleys, deltaic estuaries, salt wedge estuaries, andtidal fresh marshes. This class of estuary tends to be linearand seasonally turbid, especially in upper reaches, andcan be subjected to high current speeds. These estuariesare sedimentary and depositional, and can be associatedwith a delta, bar, or barrier island and other depositionalfeatures. These estuaries also tend to be highly flushed,with a wide and variable salinity range, and seasonallystratified. They have moderate surface to volume ratios,high watershed to water area ratios, and can have very highwetland to water area ratios as well. These estuaries areoften characterized by a V-shaped channel configurationand a salt wedge.Coastal lagoon areas include lagoons, sloughs, barrierisland estuaries, bar-built estuaries, and tidal inlets. Thisclass of estuary tends to be shallow and highly enclosed,with reduced exchange with the ocean. They often experiencehigh evaporation, and are quiescent in terms ofwind, current, and wave energy. They tend to have a veryhigh surface to volume ratio, low to moderate watershed towater area ratios, and can have a high wetland to water ratio.Note that the length of the outer barrier beaches thatform the lagoons was included in the CSU characterizationsbelow.Coastal embayments include bays, sounds, and coastalbights. This class of estuary is loosely bounded by landforms,open to marine exchange, and has moderate to highsalinities. They are well-flushed, often deep, and subjectto potentially high energy input from tides, winds, wavesand currents. These estuaries can range from very low tovery high in terms of surface area to volume, watershed towater area, and wetland to water ratio.at the seaward end formed by glacial action. However,the fjords of the Gulf of Maine (sometimes referred to as“fjards” – see Pettigrew et al. 1997) lack the topographicand benthic constrictions of true fjords and are generallywell mixed.Delineating CSU BoundariesFour project sub-teams made CSU delineations basedupon continuity of processes and natural breaks. The teamcollectively reviewed and approved a final set of 62 delineations,shown in Figure 2-8.To the extent possible, areas were delineated at oceanographicdiscontinuities such as large-scale oceanic currents.Estuarine circulation models and tidal maps ofdiscontinuities (i.e. where currents move in oppositedirections) were consulted. These delineations were thencompared with information on the biogeography of marineinvertebrates (Wigley and Theroux 1981). The subteamsattempted to avoid crossing over watersheds andconsolidating areas with very different freshwater inputs.In Maine, focus area boundaries already delineated byMaine’s Beginning with Habitat program were considered(BwH 2009). Generally, islands along the Mainecoast were included in their most immediate nearby CSU.Riverine CSUs were separated for midsize to large tributariesby intuitive natural features. In general, strings ofbarrier island lagoons are presented as single CSUs. Unitboundaries were sometimes extended beyond a particularfeature or estuarine unit so that the coast would be dividedinto a contiguous string of CSUs. (For some partsof the region where this delineation resulted in relativelylarge units, subunits were also delineated based on coastalecology and locally accepted delineations for planning andmanagement purposes.)Fjords, glacially carved embayments that are drowned bythe sea, are deep, seasonally cold-water estuaries with lowto moderate riverine inputs found at mid to high latitudes.This class of estuary has relatively complex, usually rockyshorelines and bottoms and is partially enclosed, sometimesby mountainous landforms. The waters of fjords aretypically stratified, often due to a geologic sill formation2-20Northwest Atlantic Marine Ecoregional Assessment • Phase 1 Report