the marsh surface in the 17th century. 

 The wood had rotted, the marsh surface had 

 risen about 30 cm keeping up with the 

 change in sea level, but the stones 

 remained in place. 



As one would expect from the way 

 marshes grow, coarser sediments are found 

 at the growing edges of the marsh and on 

 the adjacent flats, while finer particles 

 penetrate further into the grasses. This 

 picture varies depending on the particular 

 site and its proximity to the sediment 

 source. In New England, the newly forming 

 parts of the marsh typically have a sand 

 sediment which changes to silty muds 

 further into the marsh. Farther south, 

 where a more abundant sediment supply 

 comes down the rivers, marsh substrates 

 contain less sand and more silts and 

 clays. This general pattern is modified 

 by processes, such as changes in the 

 seaward barrier, that mobilize sand and 

 allow it to be carried into the marsh by 

 flood tides. This results in sandy 

 sediments well within the marsh. 



Storms cause masses of sand to be 

 carried over the barrier and onto the 

 marsh, where the sand may be deposited on 

 a large area of marsh surface (called a 

 washover). Wind-blown sand can have a 

 similar result. Niering et al. (1977) 

 found that severe storms of the past few 

 decades could be recognized in Connecticut 

 marsh cores by the sand layers they 

 deposited (Figure 3). The sand layers on 

 the marsh surface were subsequently buried 

 as sea level and the marsh surface rose. 



In New England, sand is also carried 

 onto the marsh surface by "ice rafting." 

 Ice rafting occurs when ice forms on a 

 beach or sand flat; a subsequent high tide 

 lifts the ice mass including this layer of 

 sand, and wind and currents carry the mass 

 into the marsh where it becomes stranded. 

 On melting, a layer of sand remains on the 

 marsh surface, raising the local 

 elevation. The mosaic pattern of tiny 

 changes in elevation and vegetation that 

 can form the boundary between high and low 

 marshes is at least partly formed in this 

 manner. 



Pieces of low marsh can also be 

 stranded by ice rafting. This can occur 

 when a block of marsh is frozen into the 



ice. The tide lifts the ice and marsh 

 block, and carries it up onto some other 

 part of the salt marsh. The result is 

 mounds of S. alterni flora sticking above 

 the marsh surface in either high or low 

 marsh. The Spartina usually dies and the 

 sediment mound either erodes or becomes a 

 site for the growth of marsh edge plants 

 like Lva. It may take several years 

 before the spot returns to its former 

 elevation. 



Low spots can also be found in the 

 marsh. These low spots, if they become 

 permanently filled with water, are called 

 pannes. Pannes may result from having 

 marsh growth occur all around a spot on a 

 tidal flat (Redfield 1972). This area is 

 isolated from the sediment supply in the 

 flooding water by the surrounding new 

 marsh. It cannot fill with sediment or 

 drain, so it remains below the local 

 surface level, water-filled all the time. 

 Low spots on the marsh may also be 

 associated with patches of wrack stranded 

 on the marsh. The wrack covers and kills 

 the grass and a low spot may result. 



2.2 TIDAL CIRCULATION 



Marshes are flooded and drained 

 through characteristic, meandering tidal 

 creeks. In the process of formation, the 

 marshes fill up the basins in which they 

 form and numerous tidal creeks of 

 sufficient size always remain to carry the 

 tidal waters that cover the marshes at the 

 highest tides. This equilibrium condition 

 is modified as the creeks erode the 

 outside back of their bends, while 

 depositing sediments on the inside bank. 

 The positions of the creeks change 

 slightly with time, but the total 

 watercourse area, which is determined by 

 the marsh elevation in relation to sea 

 level, remains approximately the same. 

 Marsh vegetation plays a considerable role 

 in stabilizing the position of the creeks. 



Garofalo (1980) found that the bank 

 of a freshwater stream migrated 0.32 m/yr, 

 while a comparable salt marsh stream 

 migrated only two-thirds as much because 

 the peat sediment bound by the fibrous 

 grass roots resisted erosion. Another 

 indication of the erosion protection 

 provided by Spartina can be seen in the 



