The benthic microalgae of sediments of the two tidal flats in Yaquina Bay, Oregon were investigated to determine the environmental factors limiting the abundance and the horizontal and vertical distribution of these organisms. The Southbeach tidal flat which is under the marine realm of deposition consists of fine to medium grained sand. The Sally's Bend tidal flat is under the fluviatile realm of deposition and consists of silt. Measurements were made of interstitial temperatures, movements of sand, turbidity, pH, salinity, depth of light penetration through the sediments, and the water content of the substrate. Samples of the benthic microalgal community were collected by using a piston corer. Sections of the cores were used for estimating the biomass: (1) by making direct counts of live microalgae, (2) by estimating chlorophyll a concentration and (3) by measuring ash-free dry weight. The greatest biomass of microalgae was found to be in cores from the lower intertidal zone while cores from the upper intertidal zone had the lowest biomass. This distribution probably results from the greater fluctuations in temperature, salinity, water content, and oxygen content, which are more variable in the upper intertidal zone. The greater biomass in cores from the lower intertidal zone may be the result of less fluctuation in environmental factors as well as the fact that this area is exposed to nutrient-laden water for longer periods of time than the upper intertidal zone. The greatest biomass of microalgae was found in the upper centimeter of cores collected at all levels of the intertidal zone, because light can penetrate no more than a few millimeters through sediment. Occurrence of algae below the photic zone is thought to result from vertical migration, sedimentation, or the activity of burrowing animals. It was found that the Southbeach tidal flat had a significantly greater biomass than Sally's Bend at all intertidal levels and in the various layers of the cores. This was attributed to differences in environmental conditions peculiar to each tidal flat which is the result of the hydrography of the bay. Estimates of the rates of potential gross production were made using a Gilson Differential Respirometer. The community from the Southbeach tidal flat had a greater potential gross rate of production than the Sally's Bend community. This was partially the result of high rates of bacterial respiration in cores from the Sally's Bend tidal flat. This tidal flat had significantly greater amounts of organic matter than Southbeach and the abundance of bacteria in sediment is related to the amount of organic matter. Measurements of the concentrations of chlorophyll a were corrected for the percentage of pheophytin present. Significantly greater amounts of pheophytin were found in cores from the Sally's Bend tidal flat which probably resulted from the large amounts of allochthonous detrital chlorophyll deposited in these sediments. The microflora consisted almost exclusively of diatoms. One hundred and fifty-four species and varieties were identified. Most of the species found in the lower intertidal zone were found in the mid and upper intertidal zones as well. Many of the species identified have never been reported from Oregon prior to this investigation. / Graduation date: 1969

Thesis (M.S.)--Rhodes University, 2005. / Title from PDF t.p. (viewed on Apr. 15, 2007). Includes bibliographical references (p. 131-152).

Thesis (M.C.E.)--University of Delaware, 2006. / Principal faculty advisors: Dominic M. Di Toro and James T. Kirby, Dept. of Civil & Environmental Engineering. Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (leaves 228-246).

Graduation date: 1987

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The Pitt Water Estuary is a shallow, barrier estuary, with typically normal marine salinity, which has been subject to considerable anthropogenic modification. Modern seafloor environments were described using the distribution of sedimentary facies and foraminiferal and ostracod assemblages, examined from surficial sediment samples. Ten sedimentary facies were identified by grouping sediment samples using particle-size distribution data and lithic sand content. Faunal assemblages were identified by cluster analysis, with twelve sample, and eight species associations defined by foraminifera, and eight sample, and six species associations defined by Ostracoda. The distribution of sedimentary facies varies, firstly, with the upstream change in relative current energy (tidal versus fluvial) as reflected by the relative proportion of quartzose to lithic sand in sediment; and, secondly, with the water depth variation in current strength, as reflected by the sand grain size and mud content. The distribution and composition of foraminiferal and ostracod assemblages is determined mainly by average salinity and pH. The position of species along the axis of the estuary correlates with the altered salinity profile inferred to occur during floods, with tolerance to lowered salinity being greater further upstream. Low pH conditions are widely distributed (due to the anoxia of stagnant, nutrient-enriched waters), causing calcareous test dissolution which, in some areas, totally excludes calcareous foraminifera and ostracods. Illumination is also important in controlling ostracod distribution, being lowest in widespread turbid waters. Additional factors controlling foraminiferal and ostracod distribution include: substrate mobility, nutrients, seagrass distribution, tidal exposure, and tolerance to varying temperature. Recent seafloor environments were described using the distribution of sediments, foraminifera and ostracods in short cores and previous spatial surveys. They have changed considerably since the late 19th century, mainly as a result of human activities which continue to affect the estuary. During periods of increased agricultural activity (1920’s-1940s; 1960’s-present), greater land clearance, cultivation and fertiliser usage within the catchment area lead to increased sediment and nutrient loading of fluvial waters entering the estuary. This lead to increased sedimentation, mud accumulation, turbidity, and lowered dissolved oxygen and pH within the estuary, causing the demise of dense clam and oyster beds, reduced distribution of ostracods and calcareous foraminifera, increased distribution of agglutinated foraminifera, and increased faunal abundance within nutrient-enriched sediments. Dam construction and irrigation activities during the 20th century, reduced rainfall over the last thirty years, and causeway construction during the 1870’s, have all contributed to increased water stagnation, reduced flushing, and more upstream penetration of the estuary by marine waters.