EFFECT OF HYDROLOGIC MANAGEMENT ON MARSH SURFACE SEDIMENT DEPOSITION IN COASTAL LOUISIANA

High rates of coastal land loss in Louisiana have prompted efforts to maintain or restore coastal wetland habitats, and structural managemen t of marsh hydrology is one of a number of approaches that has been ad opted. The aim of this study was to determine the effect of hydrologic management measures on marsh-surface sediment deposition in the Missi ssippi deltaic plain. Four impoundments, ranging in size from 50 ha to 177 ha and similarly sized control sites were included in the study. At each site, marsh-surface sediment traps were collected approximatel y biweekly for 3.5 yr to measure changes in sediment deposition. There was no significant difference in sediment deposition between any of t he impoundment and control sites during the premanagement period. The results show no significant difference in marsh-surface sediment depos ition between management year 1992-1993 and management year 1994-1995, but management year 1993-1994 had significantly lower sediment deposi tion than either the first or the last year of the study. Management y ear 1992-1993 showed the highest sediment deposition when it was asses sed across all basins, areas, and sites, and this high rate of deposit ion is accounted for by the impact of Hurricane Andrew. For all manage ment years there were significant differences between impoundment and control sites, with control sites showing higher rates of marsh surfac e sediment deposition than impoundments. No clear pattern was identifi ed concerning the influence of various types of hydrologic management on rates of sediment deposition. This reduction in sediment deposition indicated that the areas under management in this study are receiving insufficient inorganic sediment deposition to keep pace with sea-leve l rise.