Seasonal observations of surface waters in two Gulf of Maine estuary-plume systems: Relationships between watershed attributes,optical measurements and surface pCO2

The partial pressure of carbon dioxide (pCO₂) in estuary-plume systems is related to the internal processes of net organic metabolism and physical mixing, but is also strongly influenced by biogeochemical inputs from the land and ocean. Surface layer pCO₂, stimulated fluorescence of chlorophyll (f-chl) and colored organic matter (f-com), and beam attenuation at 660 nm (c-660) were measured during three seasonal surveys of the Kennebec (ME) and Merrimack (MA) estuary-plume systems. These estuaries are both supplied by large New England Rivers and separated by less than 150 km, but significant differences were often observed in the distributions of surface pCO₂ and optical variables. High pCO₂ concentrations were generally associated with high f-com, while lower pCO₂ concentrations were associated with high f-chl and c-660. Using simple regression models, optical measurements were used to estimate chlorophyll and total organic carbon concentrations. Results suggest that labile riverine carbon is responsible for sustaining supersaturated pCO₂ conditions and that phytoplankton productivity, likely driven by inputs of riverine dissolved inorganic nitrogen, is responsible for pCO₂ undersaturation. Although optical variables are often related to surface pCO₂, the results suggest that efforts to retrieve pCO₂ in complex waters using optical data may be enhanced using a site-specific, multivariate approach.     

A comparison of two numerical models for the prediction of vibrations from underground railway traffic

Two prediction models for calculating vibration from underground railways are developed: the pipe-in-pipe model and the coupled periodic finite element–boundary element (FE–BE) model.The pipe-in-pipe model is a semi-analytical three-dimensional model that accounts for the dynamic interaction between the track, the tunnel and the soil. The continuum theory of elasticity in cylindrical coordinates is used to model two concentric pipes: an inner pipe to represent the tunnel wall and an outer pipe to represent the surrounding soil. The tunnel and soil are coupled accounting for equilibrium of stresses and compatibility of displacements at the tunnel–soil interface. This method assumes that the tunnel is invariant in the longitudinal direction and the problem is formulated in the frequency–wavenumber domain using a Fourier transformation. A track, formulated as an Euler–Bernoulli beam, is then coupled to this model. Results are transformed to the space domain using the inverse Fourier transform.The coupled periodic FE–BE model is based on a subdomain formulation, where a boundary element method is used for the soil and a finite element method for the tunnel. The Craig–Bampton substructuring technique is used to efficiently incorporate the track in the tunnel. The periodicity of the tunnel is exploited using the Floquet transformation to formulate the track–tunnel–soil interaction problem in the frequency–wavenumber domain and to compute the wave field radiated into the soil.An invariant concrete tunnel, embedded in a homogeneous full space is analyzed using both approaches. The pipe-in-pipe model offers an exact solution to this problem, which is used to validate the coupled periodic FE–BE model. The free field response due to a harmonic load in the tunnel is predicted and results obtained with both models are compared. The advantages and limitations of both models are highlighted. The coupled periodic FE–BE model has a greater potential as it can account for the complex periodic geometry of the tunnel and the layering in a soil medium. The effect of coupling a floating slab to the tunnel–soil system is also studied with both models by calculating the insertion gain.     

Effects Of Changing Surface Heat Flux On Atmospheric Boundary-Layer Flow Over Flat Terrain

We examine the unsteady response of a neutral atmospheric boundary layer (ABL) of depth h and friction velocity u _* when a uniform surface heat flux is applied abruptly or decreased rapidly over a time scale t<inf>θ</inf> less than about h /(10u _*). Standard Monin–Obukhov (MO) relationships are used for the perturbed eddy viscosity profile in terms of the changes to the heat flux and mean shear. Analytical solutions for changes in temperature, mean wind and shear stress profile are obtained for the surface layer, when there are small changes in h /|L_MO| over the time scale t_MO~|L _MO|/(10u_*) (where L _MO and t _MO are the length and time scales, respectively). They show that a maximum in the wind speed profile occurs at the top of the thermal boundary layer for weak surface cooling, i.e. a wind jet, whereas there is a flattening of the profile and no marked maximum for weak surface heating. The modelled profiles are approximately the same as those obtained from the U.K. Met Office Unified Model when operating as a mesoscale model at 12-km horizontal resolution. The theoretical model is modified when strong surface heating is suddenly applied, resulting in a large change in h /|L _MO| (>>1), over the time scale t _MO. The eddy structure is predicted to change significantly and the addition of convective turbulence increases the shear turbulence at the ground. A low-level wind jet can form, with convective turbulence adding to the mean momentum of the flow. This was verified by our laboratory experiment and direct numerical simulations. Additionally, it is shown that the effects of Coriolis acceleration diminish (rather than as suggested in the literature, amplify) the formation of the wind jets in the situations considered here. Hence, only when the surface heat flux changes over time scales greater than 1/f (where f is the Coriolis parameter) does the ABL adjust monotonically between its equilibrium states. These results are also applicable to the ABL passing over spatially varying surface heat fluxes.     

Regional-scale Proterozoic IOCG-mineralized breccia systems: examples from the Wernecke Mountains, Yukon, Canada

A large scale Proterozoic breccia system consisting of numerous individual breccia bodies, collectively known as Wernecke Breccia, occurs in north-central Yukon Territory, Canada. Breccias cut Early Proterozoic Wernecke Supergroup sedimentary rocks and occur throughout the approximately 13 km thick deformed and weakly metamorphosed sequence. Iron oxide–copper–gold ± uranium ± cobalt mineralization is associated with the breccia bodies and occurs as veins and disseminations within breccia and surrounding rocks and locally forms the breccia matrix. Extensive sodic and potassic metasomatic alteration occurs within and around breccia bodies and is overprinted by pervasive calcite and dolomite/ankerite, and locally siderite, alteration, respectively. Multiple phases of brecciation, alteration and mineralization are evident. Breccia bodies are spatially associated with regional-scale faults and breccia emplacement made use of pre-existing crustal weaknesses and permeable zones. New evidence indicates the presence of metaevaporitic rocks in lower WSG that may be intimately related to breccia formation. No evidence of breccia-age magmatism has been found to date.

Research, Extension and Industry – Working Together Can Achieve Results

Over recent decades, research has been directed to assessing the impacts of land uses on valuable natural assets, such as the Great Barrier Reef. Land managers in adjacent areas are expected to adopt practices to minimize any adverse affects on downstream environments. Conversely, researchers are being pressed to provide answers to the problems. In response, researchers and environmental managers are bombarding land managers with information regarding the potential environmental implications of their practices. Is this an effective mode to achieve on-ground change?

Collaboration between all groups – research, industry and extension – may be more effective in developing and implementing practical solutions to these more complex issues. A change from the research and extension models currently used may be needed to achieve positive resource management outcomes.

Research, development and extension initiatives underway in the Australian sugar industry to improve farm practice and reduce the potential for adverse impacts on downstream environments are discussed. Case studies provide some insights into how science and extension skills work best together and how an industry group can respond to a community concern.     

Site‐scale variability of streambank fluvial erodibility parameters as measured with a jet erosion test

The erosion rate of cohesive streambanks is typically modelled using the excess shear stress equation, dependent on two erodibility parameters: critical shear stress and erodibility coefficient. The jet erosion test (JET) has become the most common method for estimating these erodibility parameters in situ. Typically, results from a few JETs are averaged to acquire a single set of parameters for characterizing a streambank layer; however, this may be inadequate for accurately characterizing erodibility. The research objectives were to investigate the variability of JET results from assumed homogeneous streambank layers and to estimate the number of JETs required to accurately characterize erodibility for use in predictive models. On three unique streambanks in Oklahoma and across a range of erodibility, 20 to 30 JETs were conducted over a span of three days at each site. Unique to this research, each JET was analysed using the Blaisdell, scour depth and iterative solutions. The required sample size to accurately estimate the erodibility parameters depended on the JET solution technique, the parameter being estimated, and the degrees of precision and confidence. Conducting three to five JETs per soil layer on a streambank typically provided an order of magnitude estimate of the erodibility parameters. Because the parameters were log‐normally distributed, using empirical equations to predict erosion properties based on soil characteristics will likely contain high uncertainty and thus should be used with caution. This study exemplifies the need to conduct in situ measurements using the JET to accurately characterize streambank resistance to fluvial erosion. Copyright © 2015 John Wiley & Sons, Ltd.