No description available.

Redshank selected low tide feeding sites on the Ythan Estuary in a manner consistent with the "Ideal Free" model (Fretwell and Lucas 1970). Predictions derived from the "Despotic" (Fretwell 1972) model were contravened. Redshank feeding rates were independent of the density in the mud of their major prey species, Corophium volutator, the size of prey available however, was crucial in determining food intake. High densities of Corophium too small to be taken had an apparent confusing effect, resulting in increased search costs. The shift in the Redshank distribution towards the mouth of the estuary in late autumn, previously associated with decreasing daylength (Joffe 1978), was consistent with a change in the cue, from energy intake per unit time to energy intake per unit feeding cost, used by Redshank to select their lowtide feeding sites. Increase in the proportion of Redshank feeding at low tide, the switch from roosting to feeding in agricultural land at high tide, increase in the degree of fidelity to low tide sites and decrease in the amount of movement about the estuary at low tide all indicate an increase in the pressure on Redshank to feed efficiently. Although no significant turnover in the winter population was detected, a PASCAL simulation revealed that turnover of 3 0% of the population size, or higher, would have gone undetected. Significant turnover was noted during the autumn period. Lower quality Redshank, e.g. juveniles and light birds, were predominant among the autumn emigrants. Severe weather conditions in 1981/82 resulted in a 22% reduction in the winter population, almost entirely through increased mortality. Juveniles and, despite the "Ideal Free" distribution, Redshank on the lower section of the estuary, the least preferred in autumn, were apparently more vulnerable to severe weather conditions.

Thesis advisor: Gail C. Kineke / To determine the role of cohesive suspended particle characteristics on sediment transport patterns in an energetic estuary floc size, density, and settling velocity were investigated in the Connecticut River estuary over three years spanning varying fluvial discharge regimes. Concurrent measurements of in-situ floc size, flow, bed stress, salinity and suspended-sediment concentration (SSC) were used to identify primary influences on floc size variability. Water discharge ranged from 202 to 910 m³/s between the three sampling campaigns, and the timing of major sediment discharge events preceding measurement periods from 23 to 162 days. Two distinct particle populations were observed under high and low sediment discharge regimes. With abundant fluvial sediment input, flocculation occurred resulting in large, loosely-packed flocs dominating the suspended signal (median sizes of 194-209 µm; median excess densities of 13-17 kg/m³). Following an extended period of low sediment discharge, small, dense aggregates resuspended from the bed were observed throughout the water column (median size of 171 µm and excess density of 60 kg/m³). The timing of and partial decoupling of water and sediment discharge led to inter-annual patterns of cohesive particle characteristics controlled by fresh sediment supply. The large, light flocs with lower settling velocities characteristic of high sediment supply regimes likely bypass the estuary. Smaller compact aggregates dominated the low-sediment discharge regimes. However, the similar disaggregated size distribution of the two regimes suggests the same fine source material is reintroduced to the estuary with the intrusion of the salt wedge, which extends farther up-estuary during low discharge regimes and ultimately supplies the off-channel bays and coves. / Thesis (MS) — Boston College, 2017. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

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

The sedimentary sulfur cycle is one of the main components of estuarine biogeochemical systems. It is initiated by the oxidation of organic matter via sulfate reducing bacteria which produce hydrogen sulfide (H2S). The S(II) then reacts via both abiotic and biotic pathways to form sulfur with other oxidation states. The three most widely-studied “operationally”–defined components of the sedimentary sulfur system are total reduced (inorganic) sulfur (TRS), acid volatile sulfide (AVS), and dissolved (=filter-passing) sulfide. This study focused on several parameters that are widely held to be important in determining TRS in sediments and the relative proportions of TRS, AVS and dissolved S(II) forms. The formation of iron sulfide minerals requires metabolizable organic matter and SO4 2- to produce S(II) and “reactive”-Fe as a source for the iron in iron sulfide minerals. One of these components is generally the limiting factor in TRS formation (e.g., Berner 1970). Nine different sites from three locations on the Central Texas coast were studied for a variety of parameters including organic matter, sulfate concentrations, sulfate reduction rate, solid “reactive” and dissolved iron, and grain size, as well as TRS, AVS, and ΣH2S. At each site five sediment cores were taken to a depth of 20 cm whenever possible. The cores were sectioned in 2 cm intervals. The porewater was extracted and both solid and dissolved components were analyzed using a variety of methods, including carbon and sulfur coulometry, acid extraction, chromium extraction, and drying the sediment. The results of he analyses showed that the central Texas coast is a widely diverse system. Some sites were very sandy while others were fine-grained. This variety was especially true for the Nueces Bay and Baffin Bay sites. The East Matagorda Bay sites showed more homogeneity in almost all analysis. While the heterogeneity of locations along the Central Texas coast makes it difficult to make a definitive statement about the controls on TRS in this area, most sites are controlled by the low amounts of iron in the system, which limits the amount of iron sulfide that can form. Low reactive iron concentrations and high degrees of pyritization (DOPs) support this argument. Exceptions exist for low-salinity (sulfate-limited) or very fine-grained (organic matter limited) sites.

The overarching aim of this thesis was to describe the ecology of the assemblages of free-living nematodes in the sediments of nearshore marine and estuarine waters on the microtidal lower west coast of Australia. The thesis also provides descriptions of ten previously undescribed species as well as develops and tests a habitat classification scheme for the Swan River Estuary using these biotic assemblages. The first section of my thesis has determined the ways in which the characteristics of the nematode assemblages in nearshore marine waters along the microtidal lower west coast of Australia are related to habitat type, time of year and shore-perpendicular zones. Three habitat types, which had previously been identified on the basis of a suite of enduring environmental characteristics, could be broadly described as highly sheltered from wave activity and containing dense seagrass (habitat type 1), moderately sheltered from wave activity and with sparse seagrass (habitat type 2) and relatively exposed to wave activity and with no seagrass (habitat type 6). Sampling in five consecutive seasons yielded > 15 000 nematodes, representing 75 species. The number of species and densities in habitat type 1, and particularly those in its subtidal zone, were far greater than those in the other two habitat types. Both of these biotic variables underwent marked seasonal changes, declining to low levels during winter. The compositions of the assemblages differed significantly among the three habitat types, with the differences between habitat types 1 and 6 being particularly marked. Paracomesoma sipho, Dichromadora sp., Marylynnia annae and Pomponema sp., which, on the basis of their buccal cavity morphology, are assumed to feed primarily on benthic diatoms, were particularly abundant at the most sheltered habitat type, whereas Gonionchus australis, Theristus sp. and Bathylaimus australis, which are assumed to be deposit feeders, were relatively abundant at the most highly exposed habitat type. The compositions of the assemblages differed among seasons and were most discrete in spring, due to marked increases in the densities of certain species. However, differences in the compositions in the different zones of each habitat type were relatively small, presumably reflecting the influence of the small tidal regime of this region. The second component of this thesis has determined the ways in which the density, number of species, species composition and trophic structure of free-living nematode assemblages in the subtidal waters of a large microtidal estuary change spatially and temporally, and has explored whether those four biotic characteristics are related to certain environmental factors. Based on data derived from samples collected seasonally at 12 sites throughout the estuary, the densities and number of species of nematodes decreased progressively with distance from estuary mouth, to reach a minimum at sites where salinities were most variable, and then increased slightly in the uppermost part of the estuary where salinities were least. Densities were also generally greatest in spring, due largely to increases in the abundance of epistrate-grazing species at the time when the amount of primary food (microphytobenthos) peaked. The spatial distribution of the composition of the nematode assemblages was closely correlated with salinity and, to a lesser extent, grain-size composition and amount of particulate organic material in the sediment (%POM). Although species composition changed sequentially along the estuary, the change was particularly pronounced between sites above and below the area where salinities started to decline markedly and become more variable and %POM increased markedly. This reflected, in particular, far greater abundances of Spirinia parasitifera at the six downstream sites, and of Theristus sp. 1 at the six sites further upstream. Species composition underwent pronounced seasonal cyclical changes at all sites, presumably reflecting interspecific differences in the timing of peak reproduction and thus of recruitment. The trophic structure of the nematode assemblages changed both spatially and temporally in relation to the relative abundance of different food sources. Thus, for example, non-selective deposit feeders, such as Theristus sp. 1, dominated samples in the upper estuary, where %POM was by far the greatest, and was rare or absent at downstream sites. Conversely, epistrate grazers, such as species of the Chromadoridae, were most abundant at downstream sites in spring, when the density of the microphytobenthos reached its maximum. The data for the nematode assemblages in nearshore subtidal marine sediments of the lower west coast of Australia were compared with those in nearshore subtidal sediments in the upper and lower regions of the Swan River Estuary. The densities and average species richness in cores from the marine environment were much lower than in cores from both estuarine regions. However, the total number of species found in the marine environment was much greater than in the estuary. The compositions of the nematode assemblages were more variable in marine than estuarine sediments. The assemblages from the two estuarine regions were far more similar to each other than to those from the marine region at a species level, and also, but to a lesser extent, at the generic and family levels. While the trophic compositions of the nematode assemblages in the upper estuarine region was dominated by non-selective deposit feeding species and those of the lower estuarine region were dominated by epistrate grazing species during spring and non-selective deposit feeding species in other seasons, the dominant functional feeding groups varied among the sites representing the marine region. That variability presumably reflects differences in the relative contributions of the different potential food sources. Surprisingly, the trophic composition in the upper estuarine region, i.e. comprising predominantly non-selective deposit feeders, was similar to that at the very different environment of the most exposed marine site. The dominance of this feeding group at the marine site is assumed to be attributable to the fact that the only food source of any note is POM and, even then, it occurs in only small amounts. Taxonomic descriptions have been produced for ten new species of nematodes found during the ecological studies of the free-living aquatic nematofaunas of south-western Australia. These species were chosen because they were members of families for which the other species had been described and, in a number of cases, were important for distinguishing between the compositions of a priori groups. They comprised four species of Axonolaimidae, representing the genera Ascolaimus, Parascolaimus, Odontophora and Parodontophora, and six species of Desmodoridae, representing single species of Bolbonema, Eubostrichus, Catanema and Leptonemella and two species of Onyx. As a complement to the nematological study of the Swan River Estuary, a novel habitat classification system was developed and then applied in this environment. This system was based on enduring environmental characteristics and employed the relatively new multivariate statistical routines SIMPROF and LINKTREE. The applicability of habitat types produced by this classification system to biotic assemblages was tested using the data for the estuarine nematode assemblages described above. The results demonstrate that the compositions of the assemblages differed significantly among each of the habitat types defined by the classification system. While there were also significant differences between the compositions of the nematofaunas at sites belonging to the same habitat type, the extent of these differences were generally less than those between habitat types. A significant and strong correlation was also found between the spatial pattern exhibited by the environmental characteristics used to define habitat types, and that of the nematofauna.

THE THESIS This thesis describes the investigation of an estuarine front, the 'tidal-intrusion front, which was initially found in the Seiont estuary, North Wales but has subsequently been observed at other locations. In the Seiont, the front forms after low water, moves a considerable distance into the estuary to an upstream limit, retreats from the estuary and finally weakens, all within the duration of the flooding tide. It separates mixed from stratified regimes and is characterised by its surface appearance; inside the estuary, the front is 'V'-shaped with its apex directed towards the estuary head. Associated convergent flows include collection of all surface buoyant material at the apex of the V. Following a considerable field investigation of the front in the Seiont, two short periods were spent studying a similar feature in Loch Creran, Scotland. In the process of investigating other sites to determine the range of estuarine parameters appropriate to a stable tidal-intrusion front, an alternative estuarine convergence was discovered in the Conwy estuary, North Wales. The Conwy shows similar frontal behaviour to the Seiont during the early part of the flood tidal phase, but increased flood currents subsequently break down stratification producing an estuary of the 'well-mixed' class. 5 Throughout the remainder of the flood tide an axial line of debris forms along a substantial proportion of the estuary length. The persistence of the line indicates a secondary circulation which includes surface convergence towards the estuary axis. However, the line disperses at high water and no similar system is apparent during the ebb. The specific aims of the thesis may be summarised with respect to: a) the tidal-intrusion or T.I. front; i) to understand the parameters which govern the movements of the front. ii) to explain and/or reproduce by modelling, the three-dimensional aspects of the 'V'-shaped frontal boundary. b) the axial convergence or A.C. i) to detrmine the nature of the secondary circulation in the Conwy i.e. the pattern of cross-sectional secondary velocities. ii) to determine a mechanism which accounts for both the production of a sustained secondary circulation and its existence only during the flood phase of the tide. and finally, we attempt to define the stable parameter ranges for both types of convergence.

No description available.

x, 106 leaves : ill., maps ; 29 cm Notes Typescript Thesis (Ph. D.)--University of Oregon, 1986 Includes vita and abstract Bibliography: leaves 98-106 Another copy on microfilm is located in Archives

Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: The investigation of the interrelationship of the fluvial morphology and the salinity of the Great Fish River Estuary was performed by the combination of a two-dimensional morphological model and a one dimensional advection dispersion module. Two scenarios were defined for investigation, namely Scenarios A and B. Model bathymetry and grid/network for each model and scenario was compiled from topographical information obtained from aerial photos, SRTM data, LIDAR and 24 measured river cross sections of the area from the river mouth up to 27km upstream of the river mouth. Model boundary conditions were developed from empirical formulas and measured data from the Department of Water and Sanitation (DWS). Both models were calibrated with results obtained during field measurement conducted from 5 – 7 May 2012. Scenario A consisted of a long term 5 year morphological simulation (1 May 2007 to 30 May 2012) with manual mouth closure events for identified river low flow periods. Water levels upstream of the river mouth were extracted from the two-dimensional morphological module and used as the downstream boundary condition of the one-dimensional advection dispersion (salinity) model. For scenario B floods with return periods between 1:2 and 1:100 years were simulated in the morphological model. The resultant bathymetries were then used to compile the network and bathymetry of the one dimensional advection dispersion (salinity) model. The different flood resultant bathymetries were then used with equal boundary conditions (representative of the average flow in the river) in the one dimensional salinity model. The predicted salinity was compared for each bathymetry used. From model results distinct trends were observed. During low flow conditions the estuary basin fills with sediments and during floods the sediments are flushed out of the estuary. Large magnitude floods greatly erode the estuary especially in the middle reach, during floods the tidal inlet experiences overtopping and subsequent erosion, the constriction at the tidal inlet is completely destroyed during larger floods. The estuary mouth in its closed state experiences slight overtopping and the mouth is breached during periods of high river flows. The magnitude of salt intrusion depends mainly on the size (the constriction) of the river mouth (tidal inlet). During periods of mouth closure the average salinity in the estuary decreases, average salinity increases if the tidal inlet area is increased. The extent of salt intrusion is approximately 10 km upstream of the river mouth when the mouth is open and the intrusion length increases during spring tides. / AFRIKAANSE OPSOMMING: Die verwantskap tussen die Groot Vis Rivier Estuarium morfologie en sout toestand is ondersoek deur die kombinasie van ‘n twee dimensionele morfologiese model en ‘n een dimensionele sout model. Twee toestande is gedefinieer vir ondersoek naamlik Scenario A en Scenario B. Die area vanaf die rivier mond tot 27 km stroomop van die rivier mond is deur die modelle gesimuleer. Die gemodeleerde area stem ooreen met die area waar gemete rivier-snit diepte metings beskikbaar was, onbrekende data is aangevul met behulp van lugfotos, LIDAR- en SRTM- data. Die model grens toestande is bepaal met empiriese vereglykings asook gemete data vanaf die Departement Waterwese. Beide numeriese modelle was gekalibreer met veld data verkry vanaf 5 tot 7 Mei 2012. Scenario A het behels ‘n langtermyn 5 jaar morfologiese modellering (1 Mei 2007 tot 30 Mei 2012) met toemond toestande gedurende gedefinieerde rivier vloei toestande. Die watervlakke van die twee dimensionele morfologiese model stroomop van die mond is gebruik as die stroomaf grenstoestand van die een dimnesionele model om die effek van die morfologiese veranderinge te inkorporeer in die sout model. Scenario B het behels die simulering van rivier vloede met herhaal periodes tussen 1:2 en 1:100 jaar in die morfologiese model. Die rivier-bodem vlakke verkry van laasgenoemde simulasiesis toe gebruik in die een dimensionele sout model met dieselfde grenstoestande wat ooreenstem met die gemiddelde toestande in die Groot Vis Rivier. Aangesien die grenstoestande dieselfde was en net die rivier-bodem vlakke gevarieer is, kon die effek van vloede op die souttoestand in die estuarium bepaal word. Uit die model resultate kon duidelike tendense waargeneem word. Gedurende lae rivier vloei toestande is die estuarium gevul met sediment en tydens vloede het die sediment weer ge-erodeer en gedeponeer in die oseaan. Groot vloede veroorsaak baie erosie in die estuarium veral in die middel bereik en by die riviermonding. Indien die vloed groot genoeg is word die riviermond vernouing totaal uitgespoel. Die riviermonding in die geslote staat ondervind effense oorstroming en word oopgespoel indien die rivier vloei groot genoeg is. Die graad van die sout indringing in die estuarium hang hoofsaaklik af van die grootte (die vernouing) van die rivier mond. Gedurende toe mond toestande is die gemiddelde sout vlakke in die estuarium laer, wanner die rivier monding groter raak, word die gemiddelde sout vlakke in die estuarium meer. Die omvang van die sout indringing strek tot ongeveer 10 km stroomop van die rivier mond wanneer die mond oop is en die indringing afstand neem toe gedurende spring getye.