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Wetland Development: Are There Ecological Assembly Rules?EPA Grant Number: U915886
Title: Wetland Development: Are There Ecological Assembly Rules?
Investigators: Weilhoefer, Christine L.
Institution: Portland State University
EPA Project Officer: Boddie, Georgette
Project Period: January 1, 2001 through January 1, 2004
Project Amount: $100,195
RFA: STAR Graduate Fellowships (2001) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Aquatic Ecosystems , Fellowship - Aquatic Ecology and Ecosystems
The objectives of this research project are to: (1) reconstruct the historic condition of the Willamette River Basin based on fossil diatoms in floodplain wetland sediment; and (2) better understand diatom ecology in wetlands. Several preliminary steps that build on the current knowledge of river-floodplain ecology are required before it will be possible to complete a paleoreconstruction of conditions in this system. First, the spatial patterns of wetland diatom assemblages need to be explored. Wetlands are highly variable habitats, and a sampling method that best captures this heterogeneity is needed to accurately characterize their diatom assemblages. To use floodplain wetlands for paleoecology, a chronological profile of diatom fossils in the sediment is required. The strong seasonal patterns of inundation and fluctuating water levels in floodplain wetlands may preclude their functioning as long-term diatom fossil depositories. A pilot study examining the patterns of diatom species along various wetland environmental gradients may establish the best way to characterize their diatom assemblages. In addition, the examination of changes in the diatom sequence over time in a dated sediment core may provide evidence as to whether a chronological diatom profile is preserved in these wetlands.
Once it has been established how to best characterize the floodplain wetland diatom assemblage, the linkage between a large river and its floodplain wetlands needs to be described. It is known that floodwater serves as a sediment and nutrient source, but patterns and timing of flood effects on the wetland biological community need to be examined. For example, is the river’s signal rapid, coming and going with flood waters, or do the physical and chemical changes that the floodwaters cause have a more lasting effect on the wetland biota? An indepth study of the annual cycle of algae in a wetland and its associated river may demonstrate the river flood signal on the wetland biota and whether this signal is reflected in the wetland’s diatom assemblage. The current diatom assemblage in a floodplain wetland is influenced by a combination of local wetland conditions (i.e., light levels, surrounding land use) and the large river watershed condition (i.e., geology, flood dynamics). The relative importance of these two major types of factors varies on both temporal and spatial scales. During baseflow periods, local wetland conditions may be more important in shaping the wetland algal assemblage. While during flood periods, large river watershed conditions tend to dominate. In addition, the importance of flooding influences may vary depending on the spatial position of the wetland within the floodplain. The final step in understanding the linkage between floodplain wetlands and a large river is to determine the environmental factors that influence the wetland algal assemblage. To accomplish this step, wetland diatom assemblages will be examined along flood frequency, and bathymetric and surrounding land-use gradients. The optima and tolerances of diatom species to various measured environmental variables then may be used as a calibration set to infer past environmental conditions.
With the knowledge gained from the above steps, it may be possible to utilize floodplain wetland diatom assemblages to reconstruct changes in the Willamette River Basin. First, a persistent wetland that has historically been periodically flooded by the Willamette River must be located. Changes in the diatom assemblages in this wetland should reflect changes in the Willamette River Basin over time. Dating the sediment sequence will provide information about when these changes actually occurred and might provide information about what forces were behind them. This information may provide evidence for how the functioning of the Willamette River Floodplain system has changed over time.