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Sediment samples were collected from eight sampling sites along the Yaquina Estuary, Oregon from Yaquina Bay to Elk City near the head of the estuary. Samples were collected in November 1973, February 1974, May 1974 and August 1974 from two or three intertidal levels depending on the magnitude of the intertidal area exposed at low tide. Concurrent sediment and water samples were obtained for the determination of water temperature, salinity, sediment size, and percentage of organic carbon and cabonate in each sample. Incident light and exposure period data were obtained for the sampling year. A total of 36,564 diatoms identified and counted in 71 samples was separated into 390 taxa (species or varieties). Of the 390 taxa, 31%, representing 30% of the total cell count, could not be identified from available literature. The relative abundance values of the taxa were utilized for the comparisons of several community composition parameters (the Information measure, Simpson's diversity index, redundancy, niche breadth, and a measure of similarity) which were used for comparisons of spatial and temporal distributions of sediment-associated diatom assemblages within the estuary. Multivariate analyses (clustering, disciminant analysis, principal components, canonical correlation) of species and environmental data were employed to analyze the distribution of sediment-associated diatom assemblages relative to the sampling strategy and to environmental gradients. The distribution of sediment-associated diatoms in Yaquina Estuary was regulated primarily by mean salinity and characteristics of the sediment. Above Yaquina Bay the prominent taxa exhibited overlapping distributions along the salinity gradient to a location in brackish water where the mean salinity was approximately 5°/oo. Here, a relatively sharp discontinuity in the diatom flora existed which appeared to be the product of the biochemical and biophysical mechanisms involved in osmotic regulation of mesohalobian and oligohalobian assemblages. Relatively large disparities in the structure of sediment-associated diatom assemblages were found within relatively small local areas of Yaquina Bay. These differences were attributed to the properties of the sediment, Responses of the diatom assemblages to light intensity, temperature and exposure to intertidal emergence were not obvious. Approximately one-half of the numerical variation in the diatom flora apparently was related to factors other than the physical and chemical variables considered in this study. Comparisons of previous distributional surveys in Yaquina Estuary indicated that the diatom flora associated with the sediments was dissimilar in species composition to proximal epilithic, epiphytic and planktonic diatom assemblages. Species diversity was generally high throughout the intertidal sediments, irrespective of tidal height and season, while redundancy was generally low. High diversity values may represent contamination of samples, behavioral-physiological adaptations of the sediment flora, or the spatial heterogeneity of intertidal sediments. / Graduation date: 1977

We investigate the silicon (Si) cycle in the Southern Ocean through two isotopic approaches: (1) 30Si-incubation experiments and (2) natural silicon isotopic composition (ä30Si). 30Si-spiked incubation allows to discriminate the short-term (~ 1 day) net Si-uptake flux in bSiO2 production and dissolution. ä30Si of both biogenic silica and dissolved silicon integrates at seasonal/annual scale bSiO2 production or dissolution and mixing. (1) A new mass spectrometer method (HR-SF-ICPMS) has been developed for 30Si-isotopic abundance measurements. This methodology is faster and easier than the previous available methodologies and has the same precision. A complete set of incubation was coupled with parallel 32Si-incubations and the two methodologies give not significantly different bSiO2 production rates. In the Southern Ocean, especially in the southern Antarctic Circumpolar Current, the large silicic acid concentration degrades the sensitivity of the method with Si dissolution fluxes staying generally below the detection limit. In contrast, the 28Si-isotopic dilution was sensitive enough to assess low biogenic silica dissolution rates in silicic acid poor waters of the northern ACC. We show that large accumulation of detrital dissolving biogenic silica after productive period implies really efficient silicon loop with integrated (euphotic layer) dissolution:production ratio equal or larger than 1. (2) We largely expand the silicic acid isotopic data in the open ocean. Relatively simple mass and isotopic balances have been performed in the Antarctic Zone and have allowed to apply for the first time ä30Si in a quantitative way to estimate regional net silica production and quantify source waters fueling bSiO2 productivity. We observe that at the end of the productive period as suggested with 30Si-incubation, large accumulation of detrital biogenic silica in the surface waters increase the D:P ratio and subsequently dampens the bSiO2 production mediated isotopic fractionation with residual biogenic silica carrying heavier ä30Si than expected. Seasonal isotopic evolution is simulated and seems in agreement with our observations. These simulations strongly suggest working with non-zero order equations to fully assess the seasonal expression of the different processes involved: mixing, uptake, dissolution. Si-isotopes are also tracking the origin and fates of the different ACC pools across the Southern Ocean meridional circulation. Moreover during the circumpolar eastward pathway, the bSiO2 dissolution in deep water decreases the corresponding ä30Si values and this imprint is further transmitted via the upper limb of the meridional circulation in the intermediate water masses.

The objective of this study has been to investigate whether epilithic diatoms could be used as a tool for assessing the condition of small to medium sized Arizona streams. Eighty-four perennial streams throughout the state were sampled during spring months of 1993, 1994 and 1995. One hundred and ninety-five samples were collected from 115 sites for water chemistry, epilithic diatoms, and stream characteristics. Exploratory analysis techniques were employed to determine if unique diatoms assemblages could be associated with any physical stream characteristics or water chemistry constituents. Multivariate and univariate analysis techniques failed to uncover any relationships between diatom species and environmental variables. Samples were dominated by species having ubiquitous distributions and wide environmental tolerance.

The uncertainty surrounding the impact of future changes in climate and water resources has created renewed interest on how lakes have responded to drought in the past. There is a need to determine potential future available water by understanding past changes in water levels; the underlying ecological characteristics of using diatoms as a proxy for lake-level reconstructions is the basis of this thesis. By integrating knowledge from past water-level fluctuation studies and theories, along with developing a better understanding of diatom ecology in lake systems, more effective techniques are being developed to improve water-depth reconstructions. Diatom assemblages were examined from eight lakes in northwestern Ontario collected in surface sediments along a depth gradient at ~1-m water-depth intervals. Three major zones, based on the composition of diatom assemblages in each lake were consistently identified in all lakes: i) a near-shore assemblage of Achnanthes (sensu lato) species and other benthic taxa (Nitzschia, Cymbella); ii) a mid-depth small Fragilaria (sensu lato)/ small Aulacoseira zone with various Navicula taxa, and iii) a deep-water planktonic zone. The depths at which transitions between these zones are located varied among lakes, and the depth of the transition between the planktonic and benthic zones was consistent with water chemistry variables (e.g. DOC, TP) that are related to light attenuation. Deeper pelagic to benthic transitions occurred in lakes with the lowest DOC and TP (i.e. generally more light attenuation in lakes with higher concentrations of TP or DOC). Other findings included a decrease in species evenness and numbers with depth, along with an increase in scaled chrysophyte relative to diatoms. / Thesis (Master, Biology) -- Queen's University, 2010-07-23 12:36:01.347

The Winnipeg River Drainage Basin (WRDB), located in the boreal forest region of Canada, is a pivotal region of focus for the assessment of water availability to determine susceptibility to drought in the past. To date, there have been relatively few paleolimnological studies focusing on how lake levels have changed in the past and whether these changes have been synchronous in the WRDB. This study investigates temporal patterns in effective moisture from Little Raleigh Lake over the last two millennia. Analyses are based on diatoms from two near-shore sediment cores from different locations and water depth in Little Raleigh Lake. Changes in diatom assemblages are used to reconstruct quantitative estimates of effective moisture in the past through the calibration of a diatom-inferred depth model developed from diatom assemblages in surficial sediments along a depth transect in Little Raleigh Lake. Declines of ~1-3m occurred during the late Holocene, with prolonged periods of aridity consistent with the timing of the Medieval Climate Anamoly (~950-1250AD) and the Little Ice Age (~1650-1750AD). The nearshore core retrieved closer to the present-day ecotone between the benthic and planktonic diatom assemblages was more sensitive to tracking water level changes in the lake than the deeper core. Conditions during the last two millennia can be used for the assessment of water availability in the past, and may offer insight on future conditions under increasing temperatures. / Thesis (Master, Biology) -- Queen's University, 2011-07-29 17:09:49.155

Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 48-50). Also available on the World Wide Web.