THE BARNSTABLE MARSH 



by 



Alfred C. Redfield 

 Woods Hole Oceanographic Institution 



The Barnstable Marsh is a favorable place to examine the formation and 

 development of the New England type of salt marsh. Two -thirds of the enclos- 

 ure protected by the sand spit is occupied by mature high marsh. The surface 

 is at high water level and is vegetated with Spartina patens , the dwarf form of 

 S. alterniflora, and Distichlis maritima, which form a firm turf punctuated 

 with characteristic pond holes. The deepest peat has an age greater than 

 5,000 years. In contrast, near the terminus of the sand spit early stages in 

 the colonization of recently formed foreshore may be observed. The open 

 waters of the harbor are occupied by sand flats on which S. alterniflora grows, 

 forming nnarshy islands in various stages of development, where even the elev- 

 ation is sufficient. See Figure 8. 



The development of the marsh may be interpreted by a combination of 

 ideas originally suggested by Shaler (1886) and Mudge (1858), namely by the 

 interaction of the accumulation of sediment and a rising sea level.* These to- 

 gether determine the depth of water on the foreshore and thus whether the 

 marsh plants can grow. The high marsh vegetation is limited to a range close 

 to mean high water. S. alterniflora, however, can grow over the upper 2/3 of 

 of the intertidal zone or at Barnstable to 5 or 6 feet below the high marsh level. 



If sediments accumulate more rapidly than sea level rises, S. alterniflora 

 will be able to grow out over greater areas as the water over the sand flats be- 

 comes more shallow. The advancing front will mark the contour at which the 

 substratum of sand is at the lower level of Spartina growth. Behind this front, 

 peat will be found at increasing depths, having been formed at a lower stage of 

 sea levels. Thus, the depth of the peat layer will vary with the age of the de- 

 posits, as scaled by the chronology of rising sea levels. See Figure 9. 



Locally and from time to time the relations of sedimentation to sea levels 

 may change, either by the shifting of channels in the sand flats, or by the cutting 

 off of the sources of sediment. This may check the advance of the marsh, lead 

 to its erosion, and cause masses of "dead" peat to become exposed at depths too 

 great for the growth of Spartina. 



*Dr. V. J. Chapman has informed the author that he has developed a 

 similar combination of the Shaler and Mudge theories of salt marsh forma- 

 tion which is set forth in his book on the salt marshes of the world, pres- 

 ently in press . 



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