The subject of my Ph. D. dissertation was the modern evolution of river-mouth tidal freshwater deltas. These deltas have the highest plant diversity of all coastal wetland types and consequently provide a wide array of nutrient-rich aquatic and riparian habitats. Paleoecological studies of tidal freshwater wetlands carried out by Professor Grace Brush and her associates have shown that the dominant factor in habitat change has been changes in sediment accretion, and that changes are sudden and interspersed with periods of stability. Since the sediments in a river-mouth tidal freshwater wetland come from the associated upland watershed, these systems provide a unique perspective on the downstream impacts of human acitvities (e.g. deforestation, agriculture, and urban development) on wetland plant associations and wildlife habitats. The roles of climate, watershed hydrology, and sediment transport, which mediate the impacts of human acitivties on tidal freshwater deltas, were also investigated.

My research of tidal freshwater deltas has involved a combination of field monitoring at two wetlands to establish the relationships between important system variables and computer modeling to simulate wetland evolution under different anthropogenic, hydrologic, and ecologic regimes. Some of the variables I monitored from 1993-1997 include precipitation, river discharge, wetland water levels, bi-weekly sedimentation rates, patterns of grain size distributions, sediment inorganic geochemistry, animal activity, and plant associations. These variables have been analyzed using standard statistical methods as well as GIS-based spatial algorithms applied to a GIS database of the Otter Point Creek tidal freshwater system that I have developed.

The computer modeling has involved two distinct approaches in order to characterize a system whose controlling influences depend on the time scale of investigation. At a high resolution time scale, an integrated assessment approach is taken so that seasonal and interannual subestuarine hydrology, sediment transport, and sediment deposition processes can be simulated. At a lower resolution, a diffusion-based model of delta progradation is employed to assess the long term trends in sediment accumulation and habitat distributions under changing land use conditions.

By quantifying the influence of the dominant controlling processes on sediment supply and removal through changes in water levels it has been possible to predict which activities in the wetland and in the watershed will contribute new habitats or destroy existing ones. This information will allow managers to evaluate proposed restoration projects with regard to their longevity and effectiveness. The model could also be used by managers to regulate land use changes upstream in order to prevent desirable existing habitats from becoming unstable... but most importantly, the research will provide fundamentally new insights into the basic functioning of tidal freshwater wetlands.