Patterns and Pathways of Wetland Sedimentation and Landscape Change in Coastal Louisiana
Coastal Louisiana wetlands exist in a dynamic physical environment and retracted dramatically in the last century. Here I examine the spatial and temporal variability of this landscape with an emphasis on the interactions between anthropogenic landscape modifications and geological processes. The Mississippi River watershed underwent drastic changes during the past 200 years, beginning with widespread land clearing and, later, large-scale reservoir construction. These modifications caused increases in suspended sediment concentrations, then sharp decreases, and have remained relatively stable since 1960. I show how changes in land area of the Mississippi River birdfoot delta reflect these fluctuations, and that they are distinct from the timing of land losses elsewhere along the coast. The deposition of inorganic sediments elsewhere along the coast is driven primarily by marine processes. I quantified the total amount and spatial distribution of mineral sediment following recent hurricanes and found that Hurricanes Katrina, Rita, and Gustav deposited an estimated 68, 48, and 21 million metric tons (MMT), respectively. I used the observed sediment deposition patterns away from the coast and storm track to estimate a long-term tropical cyclone sedimentation rate (5.6 MMT/yr) for coastal Louisiana wetlands, which accounts for the majority of inorganic sediments in soils of the abandoned delta lobes and chenier plain. I applied geographically weighted regression as a supplement to a traditional regression of geological and anthropogenic factors to further explore patterns of landscape variability. I found that the patterns of interior wetland loss are strongly related to the density of dredged canals, and that this relationship varies spatially. Canals closer to the coast, for example, are more strongly correlated to land loss than those found further inland. The research presented here raises new questions about how physical, chemical, and biological systems interact and regulate coastal systems, and how these driving factors can vary considerably over relatively short distances. The success of coastal restoration in Louisiana and elsewhere will be greatly aided if this spatial variability and remaining scientific uncertainties are included in planning and implementation schemes.
sediment, spatial analysis, landscape ecology, delta, hurricane, canal
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