Patterns of development in the creekbank region of a barrier island Spartina alterniflora marsh

Physical factors, such as local geomorphology and hydrology, are the primar y determinants of biological pattern and process in a salt marsh. The incre ased topographic relief associated with the creekbank region is thought to control the unique chemistry and productivity found there. This study was d esigned to examine the role that tidal creeks play-during the natural devel opment of a barrier island Spartina alterniflora marsh ecosystem on the Eas tern Shore of Virginia, USA. A salt marsh chronosequence, resulting from a 1962 overwash event, was used as a 'space-for-time' substitution in order t o define the changes that take place within this marsh over a successional time scale. The chronosequence of marshes is largely attributed to the vari ation in elevation across the overwash platform: younger marshes are higher relative to sea level. We used a principal components analysis on a suite of physico-chemical and biological variables. A single principle component explained 53% of the variability in the data and is used to describe the fu nctional trajectory along which these marshes develop. This component is as sociated with an increase in sediment organic matter and nitrogen content ( %N), porewater nutrients, S. alterniflora height, weight, %flowering and %N , and a decrease in grain size and redox potential. The factor scores from this analysis, which were used as a proxy for the functional maturity of th e marsh, increased from creek edge to interior marsh for young marsh sites. Thus, the marsh nearest the creek most resembles the mature marsh. The tem poral patterns of creek-water physico-chemistry vary between different aged creeks, suggesting that due to their small size and shallow depth younger creeks act to retain nutrients and particulates within the marsh. The hydro logical, chemical and biological processes within the creeks themselves and at the creekbank are important in controlling the overall rate of marsh de velopment. While creeks act to accelerate the rate of maturation, our resul ts also indicate that not all marshes follow the same developmental traject ory and that the regional landscape may be a more important factor. With th e increased interest in marsh restoration and creation for the mitigation o f coastal wetland loss, there is a need for a greater functional understand ing of the factors that control marsh development. The results of this stud y suggest that increasing creek frontage will increase the rate at which cr eated marshes achieve functional equivalence with mature marshes.