http://hdl.handle.net/1903/2749 2013-06-19T08:05:02Z http://hdl.handle.net/1903/13870 Title: Morphology in Urbanized Streams of the Puget Sound Lowland Region Authors: Boyle, Pamela Abstract: The purpose of this research is to evaluate the effects of urbanization on channel morphology. Three hypotheses are tested: 1) Channel morphology measured from one cross section is not similar to reach-averaged values, 2) Channel shear stress ratios and erosivity increase with urbanization, and 3) Channel morphological complexity decreases with urbanization increases. Results indicate that single cross-section data do not adequately describe channel morphology. Shear stress and bed mobility did not increase with urbanization, perhaps due to the presence of large bed grain sizes that adjust to increases in flow. Similarly, channel complexity did not decrease with increased urbanization. These data indicate that channel changes resulting from urbanization are influenced by sediment supply as well as discharge, and that this should be taken into consideration in restoration design. 2004-01-01T00:00:00Z http://hdl.handle.net/1903/13840 Title: The importance of female phenotype in determining reproductive potential and recruitment in Atlantic coast striped bass (Morone saxatilis) Authors: Peer, Adam Christopher Abstract: The influence of female phenotype on the reproductive potential of Atlantic coast striped bass is addressed in three key areas of research. The importance of the environment in shaping maternal phenotype was evaluated using a spawning stock time-series to evaluate possible environmental drivers of female migration timing in the Chesapeake Bay. Results showed that local and recent water temperature was the primary factor influencing timing of movement onto spawning grounds, with higher temperatures resulting in early movements. Next, two approaches were used to evaluate the influence of female energetic condition on reproductive potential. First, a field approach was used to test the hypothesis that relative total female condition (hereafter condition) has a positive influence on pre-fertilized indicators of reproductive potential (i.e., probability of spawning, relative fecundity, and relative oocyte volume). Results indicated that condition had a positive influence on residual fecundity, residual oocyte volume and indirectly on the probability of spawning. In the second approach, a laboratory experiment was conducted to test the hypothesis that female condition has a positive effect on offspring size, growth and survival. The null hypothesis that the maternal influences on offspring phenotype did not differ in the Chesapeake Bay and Roanoke River populations also was tested. In contrast to the effects of female condition on pre-fertilized indicators of reproductive potential, condition had no influence on offspring phenotype in either population. Instead, post-spawn gutted weight alone had the greatest influence on offspring phenotype, although to a lesser and potentially insignificant degree in the Roanoke River. Finally, a preliminary field evaluation was conducted in the Patuxent River, MD to determine whether maternal influences can lead to disproportionate numbers of mothers contributing to juvenile recruitment. Specifically, this study evaluated whether the variance in the distribution of half-sibling families was greater than expected by random reproductive success (i.e., Poisson process). If true, it was expected that the effective population size would be orders of magnitude smaller than the census size. Results provide preliminary evidence for higher than expected variance in reproductive success; however, methodological improvements will be necessary to confirm these results in the future 2012-01-01T00:00:00Z http://hdl.handle.net/1903/13821 Title: IMPACTS OF WINDS AND RIVER FLOW ON ESTUARINE DYNAMICS AND HYPOXIA IN CHESAPEAKE BAY Authors: Li, Yun Abstract: In the stratified rotating estuary of Chesapeake Bay, the driving mechanisms of wind-induced lateral circulation are examined using a three-dimensional hydrodynamic model (ROMS). A new approach based on the streamwise vorticity dynamics is developed, and the analysis reveals a balance among three terms: the conversion of the planetary vorticity by along-channel current shear, baroclinicity due to cross-channel density gradient, and turbulent diffusion. It is found that the lateral flow in the Bay is mainly driven by the Ekman forcing, but the lateral baroclinicity creates asymmetry in the streamwise vorticity between down- and up-estuary winds. The traditional view of wind-driven circulation in estuaries ignores the lateral circulation, but wind-induced lateral flows can affect subtidal estuarine circulation and stratification. Coriolis acceleration associated with the lateral flows is of first-order importance in the along-channel momentum balance, with the sign opposite to the stress divergence in the surface layer and the pressure gradient in the bottom layer, thereby reducing the shear in the along-channel current. Moreover, the lateral straining of the density field by lateral circulation offsets the along-channel straining to control the overall stratification. Regime diagrams are constructed using the dimensionless Wedderburn (<italic>W</italic>) and Kelvin (<italic>Ke</italic>) numbers to clarify the net wind effects. A coupled hydrodynamic-biogeochemical model is developed to simulate the seasonal cycle of dissolved oxygen in Chesapeake Bay and investigate key processes which regulate summer hypoxia in the estuary. Diagnostic analysis of the oxygen budget for the bottom water reveals a balance between physical transport and biological consumption. In addition to the vertical diffusive flux, the along-channel and cross-channel advective fluxes are found to be important contributors in supplying oxygen to the bottom water. While the vertical diffusive oxygen flux varies over the spring-neap tidal cycle and is enhanced during wind events, the advective oxygen fluxes show long-term averages due to the gravitational estuarine circulation but display strong oscillations due to wind-driven circulations. It is found that water column respiration comprises about 74% of the total consumption and sediment oxygen demand contributes 26%. Sensitivity-analysis model runs are conducted to further quantify the effects of river flow, winds, water column respiration and sediment oxygen demand on the hypoxic volume in the estuary. 2012-01-01T00:00:00Z http://hdl.handle.net/1903/13801 Title: REACTIVATION OF PLASTICITY BY DARK EXPOSURE PROMOTES ANATOMICAL AND PHYSIOLOGICAL RECOVERY FROM CHRONIC MONOCULAR DEPRIVATION IN ADULTS Authors: Montey, Karen Abstract: Chronic monocular deprivation, initiated early in postnatal life and maintained until adulthood, causes severe amblyopia, characterized by a significant decrease in strength and selectivity of visual cortical responses evoked by stimulation of the deprived eye. Amblyopia is highly resistant to reversal in adulthood, but binocular visual deprivation through dark exposure can be used to promote recovery from chronic monocular deprivation. To identify the locus of the changes in excitatory synaptic transmission that accompany the response to, and recovery from chronic monocular deprivation, I quantified the density of dendritic spines throughout the depth of the primary visual cortex. I demonstrate that chronic monocular deprivation induces a significant loss of dendritic spine density in all cortical laminae. Importantly, recovery of visual responses induced by dark exposure followed by reverse deprivation is accompanied by a significant recovery of dendritic spine density. As the majority of excitatory synaptic transmission is mediated by spine synapses, this suggests significant loss and recovery of excitatory synaptic density during loss and recovery of vision. The observation that mid cortical laminae, which are enriched for thalamocortical synapses, participates in the recovery from chronic monocular deprivation in adulthood was unexpected, given that plasticity at thalamorecipient synapses has been demonstrated to be constrained very early in postnatal life. Isolation of the thalamocortical component of the visually evoked potential via cortical silencing confirmed an experience-dependent strengthening during the recovery from amblyopia. This work further supports the hypothesis that dark exposure in adulthood returns the visual cortex to a "juvenile" state, capable of expressing plasticity at thalamocortical synapses. Severe amblyopia is characterized by a loss of the strength and selectivity of visually evoked activity in primary visual cortex. The reduction in visually evoked responses recovers completely when dark exposure is followed by reverse deprivation (open deprived eye, close nondeprived eye). However, the recovery of spatial acuity, measured by performance in a spatial frequency discrimination task, is incomplete. Therefore, I designed a strategy to promote the strengthening of synapses serving the deprived eye that utilizes tetanic visual stimulation. Dark exposure followed by visual tetanus induced a significant strengthening of synapses serving the deprived eye. Importantly, the potentiation of visual responses generalized to novel stimuli without modifying stimulus selectivity. Subsequent repetitive performance of a two-choice spatial frequency discrimination task, promoted a recovery of orientation selectivity and spatial acuity. The combination of dark exposure (to reactivate plasticity), visual tetanus (to promote synaptic strength) and perceptual learning (to promote neuronal stimulus selectivity) may accelerate and enhance recovery of visual functions, thereby optimizing the recovery from severe amblyopia. 2012-01-01T00:00:00Z