High brackish riverbank marsh (S1S2)
High brackish riverbank marshes typically occur as fairly narrow zones in brackish water settings along the upper reaches of tidal river estuaries, almost always in association with low brackish riverbank marsh. They have a similar tidal flood frequency as high salt marshes, but contain plants that require more fresh water influence, such as mudwort, eastern lilaeopsis, and false water pimpernel. This community differs from its low marsh counterpart primarily in that is dominated by salt-meadow cordgrass. The transition between high and low brackish riverbank marsh occurs approximately at the mean high water mark; from here this community stretches landward to the upper reaches of spring tides.
Brackish riverbanks are flooded by seawater pushing in from the tides that is diluted by freshwater flowing in from the watershed above. Fresh water can form a lens on top of the sea water, causing the salinity to fluctuate widely with the tides. Where slopes are gentler, the marsh may cover broader areas.
Substrates below most brackish marshes are generally sulfihemist soils with low surface salt content. Substrates of smaller brooks near the upper reaches of tidal influence are often composed of gravelly or cobbly material. Soil water salinity generally ranges from greater than 0.5 parts per thousand (ppt) to less than 18 ppt (oligo- to mesohaline).
Characteristic vegetation: This community is characterized by a variable mix of graminoids and forbs including stout bulrush (Bolboschoenus robustus), New York aster (Symphyotrichum novi-belgii), salt-meadow cordgrass (Spartina patens), salt marsh rush (Juncus gerardii), narrow-leaved cattail (Typha angustifolia), fresh-water cordgrass (Spartina pectinata), common creeping bentgrass (Agrostis stolonifera), chaffy salt sedge (Carex paleacea), seaside goldenrod (Solidago sempervirens), and three-square rush (Schoenoplectus pungens). One or more of these species may be locally dominant.
Less frequent species include halberd-leaved orach (Atriplex prostrata), beach umbrella sedge (Cyperus filicinus), silverweed (Argentina anserina), water parsnip (Sium suave), hedge bindweed (Calystegia sepium), shore rush (Juncus arcticus var. balticus), curly dock (Rumex crispus), common plantain (Plantago major), spike grass (Distichlis spicata), salt marsh water hemp (Amaranthus cannabinus), smooth cordgrass (Spartina alterniflora), Virginia wild rye (Elymus virginicus), Kentucky bluegrass (Poa pratensis), poison ivy (Toxicodendron radicans), switch grass (Panicum virgatum), necklace sedge (Carex hormathodes), vanilla grass (Hierochloe odorata), purple loosestrife (Lythrum salicaria), and seabeach sand spurrey (Spergularia salina).
Rare plants that occur here and distinguish this community from high salt marshes that have equivalent flood regime include Atlantic mudwort (Limosella australis), eastern lilaeopsis (Lilaeopsis chinensis), pygmy weed (Crassula aquatica), and false water pimpernel (Samolus valerandi ssp. parviflorus). These rare species can also occur in the low brackish riverbank marsh. Atlantic mudwort may also be found on brackish intertidal flats.
Good examples of this community occur along the upper tidal reaches of the Lamprey, Cocheco, Bellamy, Squamscott, and
High brackish riverbank marshes often occur as part of larger brackish tidal riverbank marsh systems.
High brackish riverbank marsh (right) along Garvin Brook (photo by Bill Nichols)