Identifier

etd-10012007-155906

Degree

Doctor of Philosophy (PhD)

Department

Oceanography and Coastal Sciences

Document Type

Dissertation

Abstract

Channel networks in tidal marshes serve as conduits for the exchange of water between the estuary and the marsh surface and form the spatial structure that regulates the flow of organisms, materials, and energy throughout the marsh system. Canal dredging creates channels with distinct linear shapes, and the artificial levee created from the dredged material creates ‘spoil banks’ along either side of the channel edge. Differences in morphology and adjacent marsh surface elevation between natural and dredged channel systems have not been well quantified, but may have important implications for the functioning of tidal channels as habitat for marsh-dependent species. I used GIS methods commonly applied to terrestrial landscape patterns, Light Detection and Ranging (LiDAR) data, and aerial orthophotographs to examine differences in the shape complexity of natural and dredged channel networks and to compare the elevation of the marsh adjacent to natural and dredged channels and productive and non-productive oil and gas wells in a tidal salt marsh in Louisiana. I examined the distribution of Spartina alterniflora, Geukensia demissa demissa, and Littoraria irrorata in relation to channel morphology, soil properties and elevation of the marsh edge at natural creeks, dredged canals, and open bay edges in order to correlate landscape patterns with ecological processes. Dredged canal networks were significantly less complex in shape. The elevation of the marsh within 30 m of the channel edge was highest along dredged channels. The marsh at distances greater than 30 m from dredged canals appears to be more broken up, but not lower in elevation than in natural systems. Densities of S. alterniflora and G. demissa were lower, and soil and leaf nitrogen were less in marsh adjacent to dredged canals. The age distribution of G. demissa populations provided evidence that structural differences between natural creeks and dredged canal systems influence the recruitment, growth, and mortality of mussels. This work demonstrates that landscape scale changes to tidal marshes have the potential to alter ecological processes at the microhabitat scale. Dredged canals may reduce the growth and productivity of plants and animals that are critical to maintaining coastal Louisianans marshes.

Date

2007

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

R. Eugene Turner

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