About Port Royal Sound

The Port Royal Sound system is unique compared to other coastal areas in North America because it is a large embayment dominated by expansive salt marshes and an area with high salinity water.  An embayment was created when rising sea levels submerge valleys along the coast.   The net result was and is that Port Royal Sound represents a marine habitat that extends inland for 10 miles.  Half of Beaufort County’s land area is actually under marine waters.

Port Royal Sound has these conditions because of three factors:  (1) It does not have any freshwater rivers of significant size entering it; (2) It has an exceptionally high tidal amplitude (see Section 5.4); and (3) Its low lying topography was submerged by rising sea level.   

The absence of freshwater rivers influences this coastal area in two ways.  First, there was no source of sediment to fill in low-lying areas as the sea level rose.  This lack of sediment migration explains why sections of the Sound are over 40 feet deep and most of its tidal creeks are 10 or more feet deep.  Second, the lack of freshwater resulted in there being little or no brackish marsh in the Port Royal Sound system.  Since the sound has an average tidal amplitude of 8.5 feet and little freshwater inflow, the net result is the sound’s salinity is influenced primarily by tidal waters from the ocean rather than freshwater from the upland.  The lack of brackish marsh illustrates how limited this freshwater input is. 

The impact of a rising sea level on the region is obvious - half of Beaufort County is now at or below sea level.   Even though the maps show names like the Broad River and the May River, these “rivers” are actually salt water “fingers” extending inland because most of their flow comes from the ocean in the form of tides, rather than from the uplands in the form of runoff.

The net result is that Spartina alterniflora and salt marshes dominate the local landscape and extend far inland. Not surprisingly, half of all South Carolina’s salt marsh occurs in Beaufort County.  The exceptionally large tidal amplitude maintains a high flow rate to flush them out and keep them healthy. 

The Port Royal Sound system does receive some freshwater runoff from inland areas including adjacent sections of Hampton and Jasper counties.  The importance of this freshwater runoff is significant to certain aquatic species.  This relationship is best illustrated during drought periods when blue crab and shrimp production decline dramatically.  Female blue crabs do not breed in high salinity waters and therefore are absent during severe droughts when salinity of Port Royal Sound’s salt marshes may even exceed the salinity of the ocean (because of evaporation).  During severe droughts, shrimp larvae survival also declines dramatically, presumably because as less nutrients are washed into the marsh from upland areas the results is less plankton production and less food.

For more information, please visit the following websites:

http://www.targetglobalwarming.com

http://www.cleanenergy.org