High marsh

High marsh is a tidal marsh zone located above the Mean Highwater Mark (MHW) which, in contrast to the low marsh zone, is inundated infrequently during periods of extreme high tide and storm surge associated with coastal storms. This zone is impacted by spring tides, which is a bi-monthly lunar occurrence where the high marsh experiences higher inundation levels. The high marsh is the intermittent zone between the low marsh and the uplands, an entirely terrestrial area rarely flooded during events of extreme tidal action caused by severe coastal storms. The high marsh is distinguished from the low marsh by its sandy soil and higher elevation. The elevation of the high marsh allows this zone to be covered by the high tide for no more than an hour a day. With the soil exposed to air for long periods of time, evaporation occurs, leading to high salinity levels, up to four times that of sea water. Areas of extremely high salinity prohibit plant growth altogether. These barren sandy areas are known as "salt pans". Some cordgrass plants do survive here, but are stunted and do not reach their full size.

The high marsh depends on regular tidal activity and inundation to deposit sediments.^[1] Sediment deposition facilitates mineral and organic matter buildup and sediment accretion. The minerals and organic matter promote vegetation growth and the sediment accretion promotes heightened elevation growth.^[2]

The high marsh is also important to many habitat specialists such as the Saltmarsh Sparrow, Black Rail, American Black Duck, saltmarsh spike-grass, and salt-hay. These specialists rely on the high marsh ecosystem to provide for their biological needs to ensure stable productivity and abundance.^[3][4] Among these biological needs are foraging, mating, nesting, incubation, and brooding.

The Clean Water Act of 1972 was the first act to protect these ecosystems but, due to the absence of protection, many wetlands were converted into farmland and residential land.