Natural Communities of NH -- Photo Guide

Coastal salt pond marsh  (S1)



Coastal salt pond marshes
are a broadly defined community type with vegetation zones distributed along hydrologic and salinity gradients. They are wetlands lying beyond the upper reach of spring tides but periodically infused with salt water during storm events. Basins are typically seasonally to semi-permanently flooded. They support a greater number of freshwater shallow emergent marsh species closer to their upper margins and medium-depth emergent marsh species tolerant of wetter, more brackish conditions in lower areas. Salinities fluctuate seasonally and yearly in response to freshwater input, evaporation, and periodic infusion with salt water.

In New Hampshire, this only known occurrence of this community is at Odiorne Point State Park in Rye. During a 1997 field survey at this site, water chemistry is characterized by a brackish to slightly brackish salinity and an average pH of 8.2. The marsh is separated from the coastal shoreline by a cobble ridge rising up to 12 ft. above mean sea level. The northern end of this ridge drops to approximately 7.5 ft. above mean sea level and shows recent evidence of wave action overtopping the barrier and depositing salt water and small amounts of sand into the marsh. The southern end of the cobble ridge is slightly higher (9-10 ft. above mean sea level) and has several furrows on its backside formed by breaching storm waves. The seasonally flooded soils consist of a 25 cm thick O horizon overlying a gravelly silt loam containing scattered coarse sand. Depth to bedrock (Rye Formation) in one soil pit was 35 cm. Scattered outcrops are exposed in the marsh. As of 2010, the vegetation composition of this community was heavily impacted by non-native invasive species .

Characteristic vegetation: Vegetation appears to be zonally distributed along hydrologic gradients (flood and saturation duration and salinity). The marsh is dominated by clonal stands of narrow-leaved cattail (Typha angustifolia) and softstem bulrush (Scirpus tabernaemontanii). Lower areas exposed later in the growing season after draw-down are dominated by small spike-rush (Eleocharis parvula), in association with salt-loving spike-rush (E. halophila), olive-brown spike-rush (E. flavescens), saltmarsh bulrush (Scirpus maritimus), and  three-square rush (S. pungens). Fresh-water cord-grass/slough-grass (Spartina pectinata) is abundant on higher ground along the basin edge. Other rare plants occurring in this marsh include coast-blite goosefoot (Chenopodium rubrum) and horned pondweed (Zannichellia palustris).

Other characteristic brackish marsh species include salt marsh plantain (Plantago maritima),  seaside goldenrod (Solidago sempervirens), common reed (Phragmites australis), marsh creeping bent-grass (Agrostis stolonifera), and New York aster (Aster novi-belgii). Many of these species occur in either or both fresh water and brackish habitats, but when found together, they indicate brackish conditions. Several other species found only in freshwater habitats are restricted to higher ground along the basin edge where plant diversity is highest. The uncommon hyssop-leaved loosestrife (Lythrum hyssopifolia) and marsh cord-grass (Spartina caespitosa) also occur here.



Coastal salt pond marsh at Odiorne Point State Park (photo by Ben Kimball for the NH Natural Heritage Bureau)
Coastal salt pond marsh at Odiorne Point State Park (photo by Ben Kimball)

Coastal salt pond marsh at Odiorne Point State Park (photo by Ben Kimball for the NH Natural Heritage Bureau)
Coastal salt pond marsh at Odiorne Point State Park (photo by Ben Kimball)

Aerial photo showing the salt pond marsh at Odiorne Point State Park (source: 2003 color aerials)
Aerial photo showing the salt pond marsh at Odiorne Point State Park (source: 2003 color aerials) 

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