Eddy Educed Entrainment

River morphodynamics and sediment transportMechanics of sediment transpor

Exchange flow between open water and floating vegetation

This study describes the exchange flow between a region with open water and a region with a partial-depth porous obstruction, which represents the thermally-driven exchange that occurs between open water and floating vegetation. The partial-depth porous obstruction represents the root layer, which does not penetrate to the bed. Initially, a vertical wall separates the two regions, with fluid of higher density in the obstructed region and fluid of lower density in the open region. This density difference represents the influence of differential solar heating due to shading by the vegetation. For a range of root density and root depths, the velocity distribution is measured in the lab using PIV. When the vertical wall is removed, the less dense water flows into the obstructed region at the surface. This surface flow bifurcates into two layers, one flowing directly through the root layer and one flowing beneath the root layer. A flow directed out of the vegetated region occurs at the bed. A model is developed that predicts the flow rates within each layer based on energy considerations. The experiments and model together suggest that at time- and length-scales relevant to the field, the flow structure for any root layer porosity approaches that of a fully blocked layer, for which the exchange flow occurs only beneath the root layer.National Science Foundation (U.S.) (grant EAR0509658

Development of large fish farm numerical modeling techniques with in situ mooring tension comparisons

Author Posting. © Elsevier B.V., 2006. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Aquacultural Engineering 36 (2007): 137-148, doi:10.1016/j.aquaeng.2006.10.001.A study is conducted to validate a numerical model for calculating mooring system tensions of a large fish farm containing 20 net pens in the absence of waves. The model is forced using measured current velocity values obtained outside of the farm. Mooring line tensions calculated with the numerical model are compared with load cell field data sets. The approach considers current velocity reduction and load characteristics that occur through the net pen system for both clean and fouled net conditions. Without accounting for the reduction, the numerical model produces excessively conservative results. With reduction, a substantial improvement occurs. Understanding these differences will help to establish appropriate safety factors when designing large marine fish farms using the model. Additional validation studies should be conducted with wave and current forcing to investigate the modeling large fish farms for exposed or open ocean sites.The authors would also like to express sincere thanks the National Oceanic and Atmospheric Administration for funding this project through the Saltonstall-Kennedy program under Grant NAO3NMF4270183

Intangible Barriers to the Diagnosis & Treatment of Emotionally Disturbed Students: Reformulated School Psychologist Roles

The special education category of emotional disturbance (ED) allows for the provision of special education services for students who struggle with mental and emotional disorders (MED). Outcome studies for ED/MED students in school and after completing compulsory education are discouraging. At the same time, the literature indicates that certain intervention efforts can be effective with this population. Why is there disparity between what is known about efficacious treatment for ED students and the dismal outcome data? This doctoral project posits that long-standing, tenacious and intangible barriers impede the diagnosis and treatment of ED students. These barriers exist in and outside of the school proper. School districts need staff on site who have a degree of expertise in mental and emotional disorders; i.e. a school staff member well versed in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR). The school staff member potentially suited to fill that role is the school psychologist. The controversial and unorthodox role of DSM-expert is posited as the core role to address these barriers to ED identification and treatment. Building on this central function, the school psychologist can provide linkage for the team to the DSM-IV-TR, MED literature and between the extended team members (e.g. linking school staff, parents, and community providers). Implications for training are discussed as well

Effects of Organic Particle Deposition on Porewater Oxygenation and Oxygen Exchange in Cohesive Sediment

This ex situ study utilised oxygen microprofiling and whole-core incubations to investigate potential changes in oxygenation of cohesive sediments resulting from open-ocean fin-fish farming. We examined oxygen conditions in sediments subjected to potential moderate depositional loads (1.1, 2.2, and 3.2 g C m⁻² d⁻¹) of organic farm particles from mariculture expected to settle in dispersive environments. White biofilms formed over particulates that accumulated on the sediment surface after 7 d of at least 2.2 g C m⁻² d⁻¹. Diffusive oxygen uptake (DOU) rates were estimated from sediment microprofiles taken in cores following total oxygen uptake (TOU) determination from whole-core incubations. DOU closely aligned with TOU (DOU:TOU ≈ 1) in cores where biofilms did not develop on the sediment surface (<1.1 g C m⁻² d⁻¹); however, the development of biofilms reduced the DOU:TOU ratio (<1), suggesting the biofilms were responsible for non-diffusive oxygen transport in the TOU. It was speculated that ‘vents’ in the biofilms may have enhanced the solute exchange rates in those cores. The presence of biofilms enhanced benthic TOU, reducing oxygen penetration depths in sediments adjacent to the biofilms by approximately 1 mm compared to unenriched cores. However, these sediments adjacent to biofilms still had an average oxygen penetration of ~2.5 mm, suggesting the patchy accumulation of organic farm particles and development of biofilms on the sediment surface are enhancing the structural heterogeneity of the seafloor and increasing the availability of organic carbon for higher trophic consumers in an otherwise organically deplete system

Interactions between the mat-forming alga Didymosphenia geminata and its hydrodynamic environment

Algae require dissolved nutrients to grow, but nutrient concentrations are often very low in unpolluted streams and rivers. The supply of dissolved nutrients to benthic (bottom-dwelling) algae increases with increasing river flow, but higher flows also produce drag forces that can damage the algae. To persist under high-flow, low-nutrient conditions, benthic algae must balance the conflicting requirements of minimal drag (to minimize detachment risks) and maximal exposure to turbulent flow (to maximize nutrient supplies). We explored flow-algae interactions using the freshwater alga Didymosphenia geminata. D. geminata forms dense mats in swift, nutrient-poor rivers, and is of particular interest because it is a highly invasive species in North American and New Zealand. To identify the properties that help D. geminata grow rapidly and resist detachment, we transplanted cobbles with attached D. geminata mats from a river to a laboratory flow chamber and measured flow properties above and within the mats. We then removed the mats from the cobbles and repeated the measurements. We found that water flow near the streambed is strongly altered in the presence of D. geminata mats. The dense, interwoven D. geminata stalks produce high friction and reduce flow fluctuations around and within the mats. The reduction in flow fluctuations around mats may reduce the risk of detachment and help retain dissolved nutrients within mats. We also found that D. geminata mats increase the roughness of riverbeds relative to bare cobbles, which may increase the rate of nutrient supply from the water to mat surfaces. Benthic autotrophs in oligotrophic rivers must adapt to and modify their hydrodynamic environment to balance the conflicting requirements of minimal drag (to minimize detachment risks) and maximal exposure to turbulent flow (to maximize nutrient acquisition). We explored flow–organism interactions using the benthic, freshwater alga Didymosphenia geminata. D. geminata forms large mats in swift, oligotrophic alluvial rivers. The physical properties that allow D. geminata to resist detachment and proliferate under these harsh conditions are unknown. We transplanted cobbles with attached D. geminata mats from a riverbed to a flume and used velocimetry and microelectrode profiling to measure hydrodynamic and transport conditions above and within the mats over a wide range of flows. We then removed the mats from the cobbles and repeated the velocimetry measurements. Experiment results indicated that D. geminata mats reduce form-induced stresses and near-bed turbulent velocity fluctuations, which may reduce the risk of detachment. D. geminata mats also increase turbulent shear stress just above mat surfaces, which may enhance water column–mat solute exchange. High friction associated with flow at mat surfaces leads to very low velocities and predominantly diffusive transport within mats, which may in turn favor the retention of solutes derived from organic matter within and below mats. Enhanced mass transfer at mat surfaces and effective solute retention in mat matrices suggest a mechanism by which D. geminata cells acquire nutrients from different sources: advection-dominated transport of water-column nutrients to cells at mat surfaces, and diffusion-dominated transport from decomposing organic matter within mats, with minimal advective losses