Low brackish riverbank marsh (S1S2)
Low brackish riverbank marshes occur in fairly narrow zones along the upper reaches of tidal river estuaries where the salinity of the river is less than it is downstream in salt marsh systems. Brackish riverbanks and streambanks are flooded by seawater pushing in from tides that is diluted by freshwater flowing in from the watershed above. The hydroperiod (the duration and frequency of tidal flooding) roughly corresponds to that found in the similar low salt marsh community, whereas soil water salinity is more equivalent to brackish marshes (0.5-18 ppt). Fresh water can form a lens on top of the seawater, causing salinity to fluctuate widely with the tides.
This is a narrowly defined tidal community, but it may grade into intertidal flat communities and subtidal systems toward the channel and high brackish riverbank marsh (which it is nearly always found in association with) landward. It often occurs as a narrow band, but where slopes are gentler the marsh may cover broader areas. Several rare plants are restricted to brackish riverbank marshes in
Sulfihemist soils with low surface salt content likely underlie this community (Breeding et al. 1974). Substrate of smaller brooks near the upper reaches of the tidal influence are often gravelly or cobbly. Soil water salinity generally ranges from greater than 0.5 parts per thousand (ppt) to less than 18 ppt (oligo- to mesohaline).
Characteristic vegetation: Smooth cordgrass (Spartina alterniflora) typically dominates this physically stressful low marsh community. As salinity decreases, stout bulrush (Bolboschoenus robustus) and narrow-leaved cattail (Typha angustifolia) may become more prominent and dominate in some examples. Associated vascular plants in low abundance may include salt marsh water hemp (Amaranthus cannabinus), halberd-leaved orach (Atriplex prostrata), small spike-rush (Eleocharis parvula), salt-loving spike-rush (Eleocharis uniglumis), three-square rush (Schoenoplectus pungens), saltmarsh bulrush (Bolboschoenus maritimus ssp. paludosus), common glasswort (Salicornia depressa), and sea lavender (Limonium carolinianum). Rare plants that occur here and distinguish this community from low salt marsh include mudwort (Limosella australis), eastern lilaeopsis (Lilaeopsis chinensis), pygmy weed (Crassula aquatica), and false water pimpernel (Samolus valerandi ssp. parviflorus), though these rare species can also occur in the high brackish riverbank marsh, and 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
Low brackish riverbank marshes occur as part of larger brackish tidal riverbank marsh systems.
Low brackish riverbank marsh along the Cocheco River (photo by Bill Nichols)
Low brackish riverbank marsh along Garvin Brook (photo by Bill Nichols)