ROLES AND PATTERNS OF HURRICANE SEDIMENTATION IN AN ESTUARINE MARSH LANDSCAPE

The passage of hurricane Andrew across the Louisiana coastal zone in 1992 was used to study the effects of hurricane sedimentation on estuarine marshes. (1) The thickness and nutrient content of hurricane sediments, (2) the composition of hurricane sediments relative to pre-existing sediments, and (3) the relationship between hurricane sedimentation and small-scale heterogeneity in the emergent plant community were investigated. Vertical accretion resulting from the hurricane was 4-11 times greater than the long-term (30 year) annual rate. The hurricane sediments will be within the root zone of emergent vegetation for 35-50 years, depending on the local marsh vertical accretion rate. Element concentration, organic matter content, and texture of hurricane sediments varied over a wide area, which suggested that hurricane sediments did not originate from a common sediment pool. The concentration of most elements analysed did not differ between hurricane sediments and pre-existing sediments, which suggested that hurricane sediments originated primarily from the same local bays and lakes that provide material for other sedimentation events. Hurricane sediments were thicker in Juncus roemerianus stands than in surrounding Spartina alterniflora stands. Greater hurricane sedimentation in J. roemerianus stands was attributed to greater stem density there and may help maintain plant community heterogeneity if J. roemerianus is less flood-tolerant than S. alterniflora, as previous work suggests. Previous studies have noted the effect of environmental gradients on plant species distribution, but our data indicate that plant species can also generate different environmental conditions associated with their distribution.