The overriding goal of this study was to provide first order estimates of dilution and tidal flushing of waste discharges released hypothetically into various Oregon estuaries during critical low flows and tides. Causal relationships between discharged wastes and subsequent estuarine response were studied. Various approaches to determine the assimilative capacity of tidal estuaries were described and applied to ten of Oregon's estuaries for which limited hydraulic flow information was available. This study mainly focused on the well-mixed condition common to most of Oregon's estuaries. The characteristics of the estuary used in the calculations were: tidal volumes, river flow, topography, and salinity information. Comparison of results from the modified tidal prism method and fraction of freshwater method for determining tidal flushing was made. Stommel's and Thomann's one-dimensional model was used to predict the spatial pollutant distribution from a waste outfall discharging into an estuary. Flushing rates in an overmixed estuary were determined using Gibson's method as well as flushing times calculation for a marina-like small basin. / Graduation date: 1976

Graduation date: 1976

During 1973 data was collected to analyze the seasonal variations of the tidal dynamics, water quality and sediments of the Alsea Estuary. A summary of historical information with a list of all known alterations to the estuary was made. A complete physical description, including the geographical setting and mixing classification of the estuary, was done. Times of high and low water and tidal ranges at three locations were measured. Tide measurements made at Waldport indicated that the published tide predictions for that location were reliable. At a location upstream of the estuary embayment noticeable damping of the tidal wave amplitude was detected during periods of high river flow and high tidal range. High water lag times were found to decrease during periods of high river flow, but low water lag times were unaffected by river flow. The tide motion was found to be a damped, partially standing wave, which altered its behavior according to the volume of water in the estuary. The high and low tide water quality parameters of salinity, temperature, dissolved oxygen, turbidity and pH were measured at 10 to 18 locations during each season to determine any seasonal changes in them. The parameters at a given location were found to be a function of river flow and tidal range. Winter and summer sediment samples were analyzed for grain size distribution, volatile solids and porosity. The sediments from the main channel exhibited characteristics of a high velocity regime and those of the north channel, a low velocity regime. / Graduation date: 1975

xviii, 160 p. : ill. (some col.) / Salt marshes are intertidal communities dominated by halophytic vascular plants that are subjected periodically to tidal inundation. These species have developed various adaptations to this stress, including tolerances of fluctuating salinity, extended periods of inundation and intervals of anoxic conditions. The marshes are divided into zones of different plant communities based on species' tolerances of ambient estuarine conditions. Abiotic stresses change along the estuarine salinity gradient (marine to riverine), potentially altering development and composition of plant communities. Abiotic gradients associated with tides are not the only factors that contribute to development of plant community composition in salt marshes. Both negative (competition) and positive (facilitation) biological interactions are also important. Factors that influence community structure in salt marshes, particularly on the eastern North American seaboard, have been well studied. In contrast, salt marshes along the Oregon coast are smaller and more discrete and have received comparatively little attention. The community structure and seed bank composition of six marshes along an estuarine salinity gradient were evaluated. Four major community types dominated marshes that varied in the salinity of inundating tidal waters. Community types were relatively consistent throughout the estuary despite the distances between the marshes. Unlike the emergent plant communities, marsh seed bank composition was more similar within a marsh than within a community type. The low and high marsh community types were separated by a distinct boundary in the marine marshes. Although abiotic factors influence the physical separation of communities, competitive interactions commonly determine the upper limit of a species. In Metcalf marsh, however, the upper boundary for two dominant low marsh species was not determined by competition with the high marsh dominant species. Positive biotic interactions between seedlings and existing vegetation in a community are important factors in determining species distributions, particularly in stressful estuarine environments. In salt marshes, where abiotic stress can be harsh, presence of existing vegetation can ameliorate these conditions and enhance germination and seedling establishment. However, interaction between seedlings and the emergent marsh community was highly competitive, though germination of one species was enhanced in the presence of existing vegetation. This dissertation includes un-published co-authored material. / Committee in charge: Dr. Scott Bridgham, Chairperson; Dr. Richard Emlet, Advisor; Dr. Steven Rumrill, Member; Dr. Alan Shanks, Member; Dr. Gregory Retallack Outside Member

Typescript. Includes vita and abstract. Bibliography: Includes bibliographical references (leaves 283-301). Description: xxx, 301 leaves : ill. ; 29 cm.