Estuaries, the regions where runoff of fresh water, soil, and contaminants first encounter the ocean, are also primary fishing and recreation areas. It is therefore important to understand the dynamics associated with mixing and currents within these bodies of water. Pollutants and fresh water from river runoff flow out to sea in the upper layer, while nutrient-carrying oceanic water returns beneath. While there have been many studies of the processes involved in this exchange flow, the dynamics and vertical structure of transverse flows are much less understood, despite the role these currents play in redistributing water properties and momentum throughout the estuary. One such estuary, Juan de Fuca Strait, is an ideal location in which to study estuarine exchange and the resulting cross-channel flows induced by internal friction, primarily because its length and smooth topography reduce the topograpic steering of currents. Historical current meter data from a number of deployments in Juan de Fuca Strait reveal that, while mean along-channel currents are roughly consistent with the thermal wind equation, cross-channel flows are not, particularly at mid-depths where transverse currents are largest. A momentum balance using historical sea level and current meter data suggests that the vertical eddy viscosity Aᵥ ≈ 0.02 m²s⁻¹ at interfacial depths in May. The mean circulation in Juan de Fuca Strait-depths is highly seasonal in nature, however, and larger values may be more appropriate in summer when the estuarine exchange peaks due to the freshet. Stronger friction is in turn associated with elevated mixing rates and increased transverse velocities. An Acoustic Doppler Current Profiler deployed in Juan de Fuca Strait in the summer of 1996 resolved the vertical structure of these velocities. Concurrent Current-Temperature-Depth data reveal that neither the along- nor the cross-channel currents are in geostrophic balance with the hydrographic structure, suggesting that the physical processes associatd with these currents are more localised than the five kilometre scales over which the hydrography was measured. Zooplankton within Juan de Fuca Strait comprise a significant part of the scattering cross-section upon which the ADCP depends. During their dusk migration into the euphotic zone to feed and dawn descent to escape predation, they do not act as passive backscatter targets for the Acoustic Doppler Current Profiler. Vertical migration velocities, measured from the backscatter intensity record, reached 0.03 m s⁻¹, suggesting that significant biases in the measured vertical velocity could be introduced. Little effect was actually seen in the velocity fields, however, even though the cross-sectional fraction of the zooplankton was an order of magnitude larger than the background. Mean currents in Juan du Fuca Strait reveal strong transverse flows at mid-depths, suggestive of interfacial Ekman layers. The along-channel estuarine exchange is significantly enhanced at neap tide, consistent with weaker mixing upstream. The cross-channel flows at interfacial depths are also substantially larger during neap tide, implying a fortnightly modulation of mixing rates within the strait. The ADCP was also used to measure the Reynolds stresses directly. These were found to be more than an order of magnitude larger at neap tide than during spring tide and were consistent with changes in the mean current over the spring-neap cycle. Reynolds stresses were maximal at mid-depth on the transition from ebb to flood, at which time the gradient Richardson numbers were smallest, suggesting that critical layer absorption of internal waves are important dynamically. / Graduate

Studies were undertaken for estuarine stocking of mulloway Argyrosomus japonicus to develop efficient marking techniques; to identify key habitats and migratory patterns of stocked fish; to evaluate the diet and growth of stocked fish and recruitment to commercial fisheries; and to develop a numerical model to estimate optimal stocking density from the predatory impact of stocked fish. The 10-step responsible approach to marine stock enhancement (Blankenship and Leber 1995) was reviewed for four Australian species, and Argyrosomus japonicus and Lates calcarifer were found to be the best candidates for stocking in Australia. Immersion of mulloway in an oxytetracycline-undiluted seawater solution produced poor quality marks, whilst oxytetracycline-diluted seawater solutions and alizarin complexone-seawater solutions produced high quality marks in otoliths and fin spines. These techniques were applied to produce double marks, and in batch mode at fish densities of 30 kg m-3. Key habitats for mulloway were identified as discrete holes or basins up to 20 m deep. Hatchery-reared fish initially had significantly greater movements (greater than 10 km in 3 d) when released in shallow water, compared to hatchery-reared fish released directly over deep holes. Such targeted release strategies could revolutionise stocking of depleted fisheries in estuarine and aquatic habitats, and even oceans. Stomach content analysis of mulloway captured from a coastal lagoon and riverine estuary revealed ontogenetic changes in major prey of mysid shrimp, prawns and forage fish. Comparison between benthic resources and dietary composition in these two estuaries revealed that mulloway consume prey resources in proportion to those in the environment, and do not actively select prey. Simulations of a novel Predatory Impact Model were run for part of the Georges River Recreational Fishing Haven, Sydney, to evaluate appropriate stocking density and associated predatory impact. The 15 km stretch of the Georges River contained c. 361,000 m2 of key mulloway habitat, and 10% of mysid shrimp production within this habitat was assigned to support stocked fish. Given these values, this section of river could support c. 4,000 stocked 8 cm mulloway. Over the 4 y during which mulloway are resident in the estuary, these fish will have a maximum yearly predatory impact of 6.7 t y-1 forage fish, 1.8 t y-1 school prawns and 2.2 t y-1 cephalopods, which represents 48%, 17% and 127% of former commercial fishery in the Georges River respectively.

Thesis (MSc)--University of Stellenbosch, 2007 / Bibliography. Also available via the Internet.

<p>If an estuarine system is to be investigated using an oceanographic modeling approach, a decision must be made whether to use a simple and robust framework based on e.g. mass-balance considerations, or if a more advanced process-resolving three-dimensional (3-D) numerical model are necessary. Although the former are straightforward to apply, certain fundamental constraints must be fulfilled. 3-D modeling, even though requiring significant efforts to implement, generates an abundance of highly resolved data in time and space, which may lead to problems when attempting to specify the "representative state" of the system, a common goal in estuarine studies.</p><p>In this thesis, different types of models suitable for investigating estuarine systems have been utilized in various settings. A mass-balance model was applied to investigate potential changes of water fluxes and salinities due to the restoration of a mangrove estuary in northern Colombia. Seiches, i.e. standing waves, in the Baltic Sea were simulated using a 2-D shallow-water model which showed that the dominating harmonic oscillation originates from a fjord seiche in the Gulf of Finland rather than being global. Another study pertaining to the Gulf of Finland used velocity-fields from a 3-D numerical model together with Lagrangian-trajectory analyses to investigate the mixing dynamics. The results showed that water from the Baltic proper is mixed with that from the river Neva over a limited zone in the inner parts of the Gulf. Lagrangian-trajectory analysis was finally also used as a tool to compare mass-balance and 3-D model results from the Gulf of Riga and the Bay of Gdansk, highlighting when and where each method is applicable.</p><p>From the present thesis it can be concluded that the above described estuarine-modeling approaches not only require different levels of effort for their implementation, but also yield results of varying quality. If oceanographic aspects are to be taken into account within Integrated Coastal Zone Managment, which most likely should be the case, it is therefore important to decide as early as possible in the planning process which model to use, since this choice ultimately determines how much information about the physical processes characterizing the system the model can be expected to provide.</p>

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

A digital computer model was developed to simulate the time and space distribution of a dissolved pollutant in an estuary. The program is basically a one-dimensional finite-difference model, but two dimensions can be represented by attaching together several one-dimensional channels. The influence of convection, dispersion and decay are included in the model. The time scale is based on increments of less than one tidal cycle so that intertidal velocities are represented. A sensitivity analysis was conducted on the convection portion of the model and several tables and graphs are included to indicate the nature and magnitude of numerical errors associated with the model. A method for correcting these errors is also presented. A tracer study was conducted on the Yaquina Estuary, Newport, Oregon and results are compared with two computer model simulations. / Graduation date: 1971

If an estuarine system is to be investigated using an oceanographic modeling approach, a decision must be made whether to use a simple and robust framework based on e.g. mass-balance considerations, or if a more advanced process-resolving three-dimensional (3-D) numerical model are necessary. Although the former are straightforward to apply, certain fundamental constraints must be fulfilled. 3-D modeling, even though requiring significant efforts to implement, generates an abundance of highly resolved data in time and space, which may lead to problems when attempting to specify the "representative state" of the system, a common goal in estuarine studies. In this thesis, different types of models suitable for investigating estuarine systems have been utilized in various settings. A mass-balance model was applied to investigate potential changes of water fluxes and salinities due to the restoration of a mangrove estuary in northern Colombia. Seiches, i.e. standing waves, in the Baltic Sea were simulated using a 2-D shallow-water model which showed that the dominating harmonic oscillation originates from a fjord seiche in the Gulf of Finland rather than being global. Another study pertaining to the Gulf of Finland used velocity-fields from a 3-D numerical model together with Lagrangian-trajectory analyses to investigate the mixing dynamics. The results showed that water from the Baltic proper is mixed with that from the river Neva over a limited zone in the inner parts of the Gulf. Lagrangian-trajectory analysis was finally also used as a tool to compare mass-balance and 3-D model results from the Gulf of Riga and the Bay of Gdansk, highlighting when and where each method is applicable. From the present thesis it can be concluded that the above described estuarine-modeling approaches not only require different levels of effort for their implementation, but also yield results of varying quality. If oceanographic aspects are to be taken into account within Integrated Coastal Zone Managment, which most likely should be the case, it is therefore important to decide as early as possible in the planning process which model to use, since this choice ultimately determines how much information about the physical processes characterizing the system the model can be expected to provide.

Thesis (Ph. D.)--University of Queensland, 2002. / Includes bibliographical references.

An understanding of the reactivity of hydrophobic organic micropollutants (HOMs) is of paramount importance to water quality managers because of their toxicity, persistence, and liability to bioaccumulate. In this study, the role played by the main estuarine variables (organic matter, suspended particulate matter [SPM], particle type and salinity) on HOM behaviour was investigated by employing samples from estuaries with different geochemical signatures (Chupa, Russia, and the Dart, Plym, Beaulieu and Carnon, U K ) . A laboratory-based technique was developed for the determination of the solubility and sorptive behaviour of HOMs using 14C-labelled, beta-emitting organic compounds (2,2\5,5'-tetrachlorobiphenyl (2,2’5,5'-TCB), bis(2-ethylhexyl)phthalate ester (DEHP), and benzo[a]pyrene (BaP)) coupled with liquid scintillation counting. The results indicate that relative solubility is mainly dependent upon the type of dissolved organic carbon (DOC) present, not its concentration, and is reduced with increasing salinity. The uptake of 2,2’5,5'-TCB and BaP by particles is time dependent with a system response time (the time required to achieve 63% of the new equilibrium) of about 0.37 hours for 2,2',5,5’-TCB and 0.02 hours for BaP. The adsorption, expressed as particle-water partition coefficients, KDS, is to a varying extent dependent on DOC, salinity and particle characteristics (iron/manganese hydroxides, particulate carbon and specific surface area). Adsorption is best defined by a linear isotherm and is enhanced in sea water compared with river water owing to a reduction in charge on particle surfaces at high ionic strengths. This effect has been quantified using an adsorption salting constant, Gp, whose values are typically in the range 0.4-2 L mol-2 The inverse relationship between KD and SPM concentration, an effect well documented in the literature, has been defined by a simple power law (KD = a SPM-b where a and b are site and compound-specific constants). Typical values for a and b are approximately 4x10^ and 0.6 for 2,2',5,5'- TCB, 50x105 and 1.0 for DEHP, and 2x105 and 0.5 for BaP, respectively. Empirical parameterisation of these effects are extremely useful for encoding into numerical transport and distribution models, and their application is demonstrated in this thesis by calculating the retention of HOMs by estuaries.

Thesis (Ph. D.)--University of California, Santa Cruz, 2001. / Includes bibliographical references (leaves 167-174).