Natural Community Systems -- Photo Guide

Salt marsh system

salt marsh system in Hampton Harbor, NH (photo by Ben Kimball for the NH Natural Heritage Bureau)
Salt marsh system in Hampton Harbor (photo by Ben Kimball)

 Salt marsh system along the edge of Great Bay (photo by Ben Kimball for the NH Natural Heritage Bureau)
Salt marsh system at Great Bay National Wildlife Refuge (photo by Ben Kimball)

DescriptionSalt marsh systems include upper and middle intertidal areas corresponding to high and low salt marsh, respectively, with an intermittent brackish marsh border along upland edge.  Small salt pannes and pools are common, particularly in the high marsh.  Salt marsh soil water salinity roughly corresponds to polyhaline levels (18–30 ppt).  In pannes and pools, evaporation may increase salinity above polyhaline levels.  Salt marshes grow atop fibrous marine peat.  The transition between high and low salt marsh occurs approximately at the mean high water mark; from here high salt marsh stretches landward to the upper reaches of spring tides.  Brackish marshes occur where freshwater runoff along the upland border reduces salt concentrations to meso-haline levels.

Low salt marshes are dominated by Spartina alterniflora (smooth cord-grass) and occur between mean sea level and mean high tide in areas protected from high-energy wave action.  Other vascular halophytes occur in low abundance.  Macroalgae (seaweed) may also be present.  High salt marshes are strongly dominated by Spartina patens (salt-meadow cord-grass), with lesser amounts of other graminoids. Brackish marshes are often indicated by Scirpus robustus (stout bulrush), Carex paleacea (chaffy salt sedge), and Typha angustifolia (narrow-leaved cattail), among other species.  Salt pannes and pools (pools are deeper) are low wet areas isolated from tidal creeks that occur in both saline and brackish marshes where they form fine-scale natural communities (less than 1m2 to over 100 m2).  Salinity levels in pannes found in the high salt marsh are typically in the range of 40–50(-60) ppt.  Species composition varies with salinity, hardness of substrate, elevation, soil oxygen, hydroperiod, and other factors.

The ability of individual plant species to tolerate the unique combination of stresses in salt marshes dictate which plant species grow where.  There are numerous factors that affect plant distribution: hydroperiod (duration and frequency of tidal flooding), soil salinity, soil oxygen, nutrient availability, elevation of substrate, concentration of growth inhibitors, storms, ice-scouring, land use history, and competitive interactions and biological facilitation between and among species.  Many of these factors and processes are interrelated, but vary along gradients at different rates or in different quantities.

Between the time of European settlement until recently, salt marshes were routinely drained by farmers to increase the productivity of salt-meadow cord-grass and spike-grass for hay, pasture, mulch, and in an effort to reduce salt marsh mosquito (Aedes sollicitans) populations.  The ecological impacts of ditching include reduced flood duration and lowered water table and changes in species composition across many groups of species in the marsh (insects, mollusks, crustaceans, shorebirds, waterfowl, and plants).

Diagnostic natural communities: 

      • Low salt marsh (S3)

      • High salt marsh (S3)

      • Salt pannes and pools (S3)

Peripheral or occasional natural communities:

      • Brackish marsh (S2S3)

      • Coastal salt pond marsh (S1)

      • Marsh elder shrubland (S1)

Landscape settings: intertidal coastal embayments

Soils: marine peat; organic materials 16 to 50" thick overlying sandy materials (low marsh); organic materials >50" over sand, silt, or bedrock (high marsh); shallow peats (<16") are occasional in areas towards outer limits of salt marsh (seaward and inland); poly-haline (18–30 ppt), strongly minerotrophic

Spatial pattern: large patch, narrow-linear to irregularly linear (<1–100+ acres); narrow to broad linear bands fringing coastal shorelines, with scattered orbicular patches: linear bands of low salt marsh; broad-linear patches of high salt marsh; intermittent strands of brackish marsh along upland border; small orbicular patches of pannes and pools

Physiognomy: primarily herbaceous

Distribution: occurs at Great Bay, in the Blackwater River estuary, and in other coastal embayments

Characteristic species:

Low salt marsh:
Abundant species:
   Spartina alterniflora (smooth cordgrass)
Occasional to locally abundant:
   Salicornia europaea (common glasswort)
   Atriplex spp. (orachs)
   Eleocharis parvula (small spike-rush)
   Suaeda spp. (sea blites)
   Spergularia marina (seabeach sand-spurrey)
   Ascophyllum nodosum (a seaweed)
   Fucus spp. (rockweeds)

High salt marsh:
   Spartina patens (salt-meadow cord-grass)
Occasional species:
   Spartina alterniflora (smooth cord-grass; short form)
   Distichlis spicata (spike-grass)
   Juncus gerardii (salt marsh rush)

Brackish marsh:
   Scirpus robustus (stout bulrush)
   Carex paleacea (chaffy salt sedge)
   Typha angustifolia (narrow-leaved cattail)

Salt pannes and pools:
   Triglochin maritimum (arrow-grass)
   Spartina alterniflora (smooth cord-grass; short form)
   Ruppia maritima (widgeon-grass)
   Scirpus maritimus (saltmarsh bulrush)
   Potamogeton pectinatus (sago pondweed)
   Zannichellia palustris (horned pondweed)

Associated natural community systems:  Salt marsh systems transition to brackish tidal riverbank marsh system upstream and sparsely vegetated intertidal system towards the subtidal zone.

estuarine bay natural communities

high and low salt marsh in a small cove at at Adams Point on Great Bay (photo by Ben Kimball)
salt marsh system in a small cove at at Adams Point on Great Bay. Spartina patens lies down in the
high salt marsh in the foreground, while the taller Spartina alterniflora of the low salt marsh rises
behind it (photo by Ben Kimball).

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