In order to design a management program that will successfully restore and maintain tidal freshwater wetland habitats, it is necessary to understand the physical processes of wetland evolution, because these processes determine the response of natural habitats to restoration efforts. Gosselink and Turner (1978) demonstrated the importance of hydrology in controlling the spatial heterogeneity of wetlands, but very little is known about the evolution of tidal freshwater wetlands, and how stable the spatial heterogeneity is through time. Hydrologic and geomorphic processes are manifest through patterns and rates of sediment accumulation as well as spatial and temporal distributions of vegetation. Thus, baseline studies of the historic and present configurations of these characteristics will provide important information on the functioning of tidal freshwater wetlands.

Recently, Hilgartner (1995) and Pasternack (1998) used a combination of paleoecological methods, field monitoring, and computer modeling to reconstruct the history and quantify the physical processes of evolution in a Chesapeake Bay tidal freshwater wetland. Their research showed that wetland habitat conditions are intimately linked with watershed fluxes of sediment, nutrients, and heavy metals (Pasternack et al., 1997; Knight and Pasternack, 1998). Also, they found that tidal freshwater wetland evolution does not follow a classic successional sequence such as any of those proposed by Cowles (1899), Clements (1916), or Redfield (1972). Instead, natural and anthropogenic disturbances drive habitat evolution.

The general objective of this study is to determine the geomorphic potential of the site to revert back to a functional tidal freshwater marsh with an array of beneficial aquatic and riparian habitats. Specific objectives include a) assessing the stability of the physical structure of the system in the past, b) determining the amount and direction of energy driving changes in sediment patterns in the system, c) quantifying the relative proportion of vertical accretion due to watershed influx of inorganic sediment versus in situ biomass accumulation, and d) characterizing the spatio-temporal distributions of habitats within each site.

The approach proposed to meet the objective of this study is to reconstruct and compare the historical environmental conditions on McCormack-Williamson Tract and in a nearby reference tidal freshwater wetland. Since the reference wetland has been functioning more or less continuously over time, it should have a complete record of the environmental conditions experienced by this type of system in the Sacramento-San Joaquin Delta. The method for reconstructing environmental conditions involves characterizing the general lithological and stratigraphic framework using a large number of cores taken from the field sites and then selecting a subset of those cores for radiocarbon dating and detailed paleoenvironmental analysis.

During summer-autumn 2000, 12 long sediment cores were collected on the McCormack Williamson Tract.

Since December we have been processing cores in the laboratory. The first step is to cut a core open, photo-document it, describe its stratigraphy (i.e. visual variations in color, texture, patterns, etc.), and subsample layers.

Cores appear to contain a wide range of fossil materials indicative of a surprising array of ancient habitats.

Along with a wide range of physical, chemical, and isotpic parameters, core sediments will be assayed for their pollen content, which will be indicative of pre-historic and historic environmental conditions, including climate and land use changes.