PNW 98 Session - Full Abstracts

Full Abstract

LIZBETH SEEBACHER(1)
Lizbeth Seebacher

(1) University of Washington

Restoration of Coastal Estuarine Habitats Within Previously Diked Wetlands in the South Slough National Estuarine Research Reserve, Charleston, Oregon

The diking and filling of tidal wetlands for both agriculture and pastureland has caused significant damage along the coast of Oregon. The Coos Bay area has suffered an estimated 90 percent loss of the salt marshes present only 100 years ago.

The primary purpose of this study was to determine what factors may be contributing to the inhibition of vegetation recruitment as well as what factors may aid in accelerating vegetation establishment on a previsouly diked and breached estuarine marsh within the South Slough National Estuarine Research Reserve (SSNERR) near Coos Bay, Oregon.

Most of the wetlands at the SNNERR were diked, drained and filled around the turn of the century and are in varying stages of successional recovery following breaching of the dikes by natural processes. Several factors may contribute to the inhibition of emergent vegetation establishment in a previously diked and breached marsh. These potential factors include: inappropriate marsh surface elevations, restricted tidal circulation and prolonged inundation periods, high interstitial soil salinity from evaporation, an adverse effect of increased algal mat growth and the lack of a viable salt marsh seed supply. These factors were tested in this research project.

The tidal inundation periods for the experimental marsh were determined to rise and fall in unity inside and outside of the dike. The restricted opening of the dike did not seem to cause prolonged inundation periods. The act of shading the soil to reduce evaporation and therefore reduce soil salinity proved to have a negative impact on vegetation recruitment as well as algae growth. The removal of the algal mat as to mitigate the possibility of the mat smothering new seedlings was determined to be unsuccessful as well. The final treatment, was the addition of viable seed. This proved to be an unsuccessful method of revegetation with a lack of significant statistical results. Additional experiments were tested; these included transplanting containerized seedlings using various erosion control methods and a soil chemical analysis. Additional data collected and analyzed included: a sediment accretion analysis, a soil core analysis, and historical precipitation and slough water salinity data.