ROLES AND PATTERNS OF HURRICANE SEDIMENTATION IN AN ESTUARINE MARSH LANDSCAPE

The passage of hurricane Andrew across the Louisiana coastal zone in 1 992 was used to study the effects of hurricane sedimentation on estuar ine marshes. (1) The thickness and nutrient content of hurricane sedim ents, (2) the composition of hurricane sediments relative to pre-exist ing sediments, and (3) the relationship between hurricane sedimentatio n and small-scale heterogeneity in the emergent plant community were i nvestigated. 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 35-5 0 years, depending on the local marsh vertical accretion rate. Element concentration, organic matter content, and texture of hurricane sedim ents varied over a wide area, which suggested that hurricane sediments did not originate from a common sediment pool. The concentration of m ost elements analysed did not differ between hurricane sediments and p re-existing sediments, which suggested that hurricane sediments origin ated primarily from the same local bays and lakes that provide materia l for other sedimentation events. Hurricane sediments were thicker in Juncus roemerianus stands than in surrounding Spartina alterniflora st ands. Greater hurricane sedimentation in J. roemerianus stands was att ributed to greater stem density there and may help maintain plant comm unity heterogeneity if J. roemerianus is less flood-tolerant than S. a lterniflora, as previous work suggests. Previous studies have noted th e effect of environmental gradients on plant species distribution, but our data indicate that plant species can also generate different envi ronmental conditions associated with their distribution.