The probable pollution distribution and flushing times have been calculated for the Columbia River Estuary, a coastal plain estuary. The pollution distribution was determined by the fresh water fraction and by the diffusion equation. The flushing times were calculated by the modified tidal prism method and by the fraction of fresh water, These methods are explained and discussed in the study. The widely varying river flow and resulting salt water intrusion were considered, as well as the varying semi-diurnal tidal range. These changing factors cause a complex variation in estuarine classification from well-mixed to stratified. The data used was taken principally from the U. S. Corps of Engineers current measurement program of 1959. The data show a stronger flow on the north side of the estuary during flood tide and a stronger flow on the south side during ebb tide. Due to this fact, the estuary was also treated as two separate channels in calculating the pollution distribution. The results of the various calculations for combinations of conditions are given in this study. A comparison of the different methods is also summarized. The estuary has been found to have a relatively short flushing time, even under low river flow conditions. The variation in strength of flow from the north side to the south side has been shown to produce pollution distributions not normally expected in an estuary. / Graduation date: 1965

Levels of ⁶⁵Zn in water, sediments, plants, and animals in Alder Slough, a small ecosystem in the Columbia River Estuary, were determined periodically during a one year period. Concentrations of total Zn in organisms were also measured to permit computation of specific activities (μCi⁶⁵Zn/g total Zn). Temporal fluctuations in the activities of ⁶⁵Zn and the concentrations of total Zn occurred in all components of the ecosystem. Activities of ⁶⁵Zn and concentrations of total Zn varied among individual fish from the study area. Pooled estimates of population standard deviations of these values in all samples of two fish species taken during the year amounted to about 20% of their grand means. Usually, individuals with high ⁶⁵Zn activities also proved to have high total Zn concentrations, hence specific activities were less variable than either ⁶⁵Zn or total Zn. The nuclear reactors at Hanford, Washington, the source of most of the ⁶⁵Zn in the Columbia River, were shut down for approximately 45 days during this study. This event presented the opportunity to investigate the response of various components of the ecosystem to reduced ⁶⁵Zn input. The rates of ⁶⁵Zn specific activity decline in several organisms were measured following reactor shutdown. The time required for specific activity of an organism to be reduced by one-half under the conditions prevailing is termed "ecological half-life". The "ecological half-life" differs from the biological half-life of an organism because: 1. it is defined in terms of specific activity 2. it reflects the continued addition of radioactivity to the organism from its food web and water. "Ecological half-lives" vary with the trophic levels of the organisms and with changes in prevailing ecological conditions. / Graduation date: 1968