Brackish Marsh (S2S3)
Brackish marshes are transitional between freshwater and salt marsh communities. They form occasionally along the upland edge of salt marshes and tidal riverbanks where freshwater runoff or groundwater dilutes the salinity of the high marsh surface. This allows a mix of fresh and salt marsh species intolerant of higher or lower salinity to coexist along with species restricted to brackish conditions. They are only flooded during spring tides and storm surges. Dominant plant species and growth forms vary widely depending on local hydrology and salinity levels.
Some brackish marshes are dominated by the non-native and invasive narrow-leaved cattail (Typha angustifolia), particularly in coves or other protected areas with restricted spring-tide “sheet flow” (bi-monthly or less frequent tidal flooding events) and with significant freshwater input.
Characteristic vegetation: A few common species in this community are stout bulrush (Bolboschoenus robustus), chaffy salt sedge (Carex paleacea), common creeping bentgrass (Agrostis stolonifera), salt marsh rush (Juncus gerardii), seaside goldenrod (Solidago sempervirens), and New York aster (Symphyotrichum novi-belgii). Several rare plant species are restricted to this community.
Variants: Several variants are described, with reasonably distinct plant associations distributed along a hydrology and salinity gradient.
1. Short graminoid variant:
This variant supports a high diversity of plants and is generally flooded less frequently than the other variants. It is slightly higher in elevation, receives more freshwater input, and experiences less frequent tidal flooding than the high salt marsh community. It is characterized by a mix of graminoids including common creeping bentgrass (Agrostis stolonifera), salt-meadow cordgrass (Spartina patens), and salt marsh rush (Juncus gerardii). One or more of these species may be locally dominant.
2. Medium graminoid variant:
This variant is dominated by chaffy salt sedge (Carex palacea), but is otherwise floristiclly similar to the short graminoid variant. The hydroperiod appears to be slightly wetter. Common associates include stout bulrush (Bolboschoenus robustus), common creeping bentgrass (Agrostis stolonifera), salt-meadow cordgrass (Spartina patens), salt marsh rush (Juncus gerardii), seaside goldenrod (Solidago sempervirens), and fresh-water cordgrass (Spartina pectinata).
3. Tall graminoid variant:
This variant occurs along the upland edge of salt marshes in shallow, less frequently flooded depressions (compared to other variants). Three-square rush (Schoenoplectus pungens), narrow-leaved cattail (Typha angustifolia), chaffy salt sedge (Carex paleacea), common reed (Phragmites australis), and fresh-water cordgrass (Spartina pectinata) are characteristic.
Brackish marsh community at Wallis Sands estuary (photo by Ben Kimball)
Brackish marsh community at Bellamy River Wildlife Sanctuary (photo by Ben Kimball)
Brackish marsh community at Great Bay National Wildlife Refuge (photo by Ben Kimball)