Baccharis Consulting LLC

Location of Reed Tidal Marsh

Location of Reed Tidal Marsh

There are six main factors that affect Reed Tidal Marsh location.  These include:

  • Water Salinity
  • Water Level/Elevation
  • Impoundments
  • Disturbance
  • Reed Grass Spraying Efforts
  • Marsh Fires
Water Salinity

Reed grass (Phragmites australis) can handle water salinity up to roughly 25 ppt.  This leads it to find a location where the water salinity is less than or equal to 25 ppt.  In the Inland Bays and lower Delaware Bay that have higher water salinity, reed grass will locate on the edges of marshlands.  In the upper parts of Delaware Bay and Delaware River, where water salinity is lower, Reed Tidal Marsh can locate throughout a marsh.

Picture of Reed Tidal Marsh on edge of marsh

Reed Tidal Marsh at the edges of marshland in Rehoboth Bay watershed, high salinity water

Picture of Low density Dirty Cotton Marsh

Low density Reed Tidal Marsh that covers a large area of marsh (outlined in blue), low salinity water

Water Level/Elevation

Reed Tidal Marsh generally grows just above the elevation of North Atlantic Low Salt Marsh (dominated by salt marsh cordgrass (Spartina alterniflora)).   This is often the same elevation as North Atlantic High Salt Marsh (dominated by salt meadow hay (Spartina patens)).  This is a detriment to North Atlantic High Salt Marsh and is leading in part to losses in high marsh.  The slightly higher elevation allows the reed grass to avoid some of the higher salinity in the marsh.



Impoundments provide a multitude of disturbances and ample area for reed grass to colonize.  Any impoundment along the coast will reveal plenty of Reed Tidal Marsh.  The impoundments in some case freshen the water providing a ripe medium for the reed grass.  However, in some rare cases it can work the other way and raise water salinity through evaporation.  An impoundment breach at Prime Hook National Wildlife Refuge led to a sudden increase in water salinity.  The resulting conditions wiped out Eastern Reed Marsh (non-tidal reed type) growing in the impoundment.



Disturbance is a driving mechanism and clarion call for an invasion of reed grass.  Most undisturbed marshes do not have much reed grass.  Some examples would be the marshes of Bombay Hook and Great Marsh near Lewes.  After the breach of the Prime Hook National Wildlife Refuge impoundment, reed grass grew back after about a year.


Reed Grass Spraying Efforts

Delaware has an active program to spray reed grass in an effort to eliminate it from the marshes.  The Little Creek Wildlife Area report shows that these efforts can bring back North Atlantic High Salt Marsh.  The spraying efforts or lack thereof can determine the distribution of reed grass or affect densities.


Marsh Fires

Marsh fires set either naturally or by humans can wipe swathes of Reed Tidal Marsh or other marshes.  In some cases, such as Army Creek marsh, controlled burns as used to eliminate reed grass .  In other cases the fires wipe out large areas of marsh (see picture below).

Picture of Burnt Marsh

              Burnt marsh (dark area to left of creek) in Blackbird Creek watershed

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