ABSTRACT
Physical forces, such as geomorphology and hydrology, are the primary factors
controlling pattern and process in a salt marsh. This study was designed
to examine how these controlling factors operate during the natural development
of a barrier island salt marsh ecosystem. A particular emphasis was placed
on the creekbank zone because of the increased topographic relief associated
with the morphology of the creek. A chronosequence of marshes was employed
to define the changes that take place within the marsh on a successional
time scale. There are predictable changes that take place in the physico-chemical
variables associated with the substrate, and in the productivity, growth
form, and tissue element composition of Spartina alterniflora. The
processes associated with the interaction between biotic and abiotic factors
appears to be driving the observed changes. In all of the young marshes,
the zone closest to the creekbank exhibited values of physico-chemistry
and productivity representative of an older marsh, such that the marsh
near the creek appears more mature. This implies that the physical forces
associated with the regional morphology are driving the process of succession
at a faster rate in this zone.
This chronosequence
contained two young creeks of similar age which exhibited significantly
different rates of primary production. While these two young creeks were
similar in their local morphology, they differed in their regional morphology.
One creek received drainage from a large upland catchment area, and the
other received drainage from a small catchment which contains a salt flat.
The inflow of large quantities of fresh groundwater from the upland catchment
produced lower salinities, and led to greater S. alterniflora
production. The other creek had no significant upland drainage, and
therefore had high salinities and low macrophyte production. When there
is lower production, the processes linked to the interaction between biotic
and abiotic factors is diminished, and the maturation process is slowed.
Thus, the regional geomorphology, which determines the local hydrology,
controls the patterns and processes associated with the ecological development
of the marsh. This study suggests that the geomorphology, on both a local
and a regional scale, is important in controlling the developmental processes
which result in the observed patterns of physico-chemistry and productivity
in a salt marsh.
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