Date of Award

Spring 2003

Project Type

Dissertation

Program or Major

Earth and Environmental Science

Degree Name

Doctor of Philosophy

First Advisor

David M Burdick

Abstract

Anthropogenic alterations that restrict tidal flows negatively impact 20% of New England salt marshes, but management attempts to restore tides to these sites can be met with unexpected or less than optimal results. Restoration planners may be hindered by a lack of synthesized information regarding important biotic and abiotic factors that determine the distribution of dominant salt marsh plants and invasive species. An ecosystem model was developed to better predict salt marsh habitat response to hydrologic modification as a synthesis of existing models for biomass production, marsh elevation, tidal hydrology, and plant succession. A field experiment was conducted to provide the ecological basis for estimating plant responses to physical stresses and interspecific competition. Six plant species common to New England salt marshes were examined: halophyte species Spartina alterniflora, Spartina patens, and Juncus gerardii, and brackish invasive species Phragmites austrahs, Typha angustifolia, and Lythrum salicaria .

The model was applied to spatial grids representing marsh area at four salt marsh sites with past or current impacts due to restricted tidal flows. At each site, field data for model parameterization was acquired according to a regional data-collection protocol. To assess model performance, the spatial distribution of marsh plants was predicted using specifications from past hydrologic and ecological conditions at two sites. Aggregated model predictions of halophyte-dominated and invasive-dominated marsh areas were within 4% of observed totals. The model was then run for each of the four study sites to generate 20-year simulations of plant composition changes resulting from current and possible hydrologic scenarios. Scenarios included changes in culvert shape, dimensions, and placement. Model simulations in response to tidally-restricted conditions predicted gradual replacement of halophytes by brackish invasive species, especially P. australis. Simulations involving tidal restoration strongly favored halophyte species. Based on spatial model outputs, realistic visualizations of marsh scenario results were designed and rendered. Use of this technology may provide new ways for resource managers to assess potential restoration outcomes, and to communicate the expected results of marsh improvement projects to non-technical audiences.

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