Abstract: The Impact of Hurricane Andrew: Changes in the Texture and Chemistry of Barataria Estuary Bottom Sediments

G. C. Flowers, L. V. Koplitz, G. L. McPherson

In 1993, approximately one year after the passage of Hurricane Andrew, bottom sediment samples were taken from 97 locations in the Barataria Estuary, which is located near Grand Isle, Louisiana. Bottom sediments of the Barataria Estuary are enriched in sand relative to other southeastern Louisiana estuaries (e.g., Lakes Pontchartrain and Maurepas). The sand content of bottom sediments is comparable to that of Perdido Bay and other estuaries along the Mississippi-Alabama-Florida coast, but this has not always been the case. Comparison of sand-silt-clay diagrams for 1969 and 1993 indicates that a significant change in bottom sediment texture has occurred over the past 24 years. In 1969, the bottom of Barataria Estuary consisted predominantly of sandy and clayey silts; prese tly, sand-silt-clay is the most abundant sediment type. Presumably, the passage of eight hurricanes near the estuary, including Hurricane Andrew in 1992, caused the relative increase in sand content of the bottom sediments.

Bottom sediments of the estuary contain an average of approximately 5µmoles/g acid volatile sulfide (AVS), which is considerably lower than averages for the Hudson River (12.6 µmoles/g) and Long Island Sound (15.9 µmoles/g). AVS content, unlike metal concentration, does not correlate positively with the clay content of the sample. Assuming the sediment AVS is due to the presence of monosulfides, the average scavenging capacity of bottom sediments is approximately 5 µomoles divalent heavy metal/g. The Barataria Estuary, therefore, has a limited capacity to absorb heavy metals via exchange reactions with sediment AVS. Fortunately, recoverable metal data for Barataria Estuary bottom sediments indicate that heavy metal contamination is not a problem in this estuary. Be ause bulk metal content is controlled largely by sediment texture, low metal concentrations are expected in a bay containing relatively coarse-grained bottom sediments. In the case of a major metal spill, water quality in the Barataria Estuary would be impacted more than an estuary containing fine sediments.

AAPG Search and Discovery Article #90955©1995 GCAGS 45th Annual Meeting and Gulf Section SEPM, Baton Rouge, Louisiana