A summary of environmental issues and findings: Tennessee-Tombigbee Waterway   总被引：1，自引：0，他引：1  

Nathaniel D. McClure IV 《Environmental Geology》1985,7(1-2):109-124

The enactment of the National Environmental Policy Act (NEPA) had a substantial influence on the manner in which the Tennessee-Tombigbee Waterway (Tenn-Tom) was constructed The interdisciplinary approach, including a board of outside consultants functioning as environmental advisors, played a valuable role toward meeting the objectives of minimizing adverse impacts and maximizing the positive environmental aspects Several of the key environmental issues associated with the Tenn-Tom are addressed and the findings are presented impacts addressed include aquifer drawdown, waterlogging, water quality, interbasin transfer, mixing of species, endangered species, erosion, sedimentation, and loss of wildlife habitat Additional discussion is also presented to explain the findings and place the identified impacts into perspective While implementation of the Tenn-Tom involved losses and resource tradeoffs, measures have been incorporated into the project to mitigate for significant resource losses The evaluation, planning, and design process for the Tenn-Tom can serve as a model approach for compliance with NEPA and other environmental statutes  相似文献   

The Economic Contributions of Agricultural Tourism in Michigan          下载免费PDF全文

Gregory Veeck  Lucius Hallett IV  Deborah Che  Ann Veeck 《Geographical review》2016,106(3):421-440

Family farms have long generated income from agricultural tourism including U‐picks, wagon rides, corn mazes and petting zoos, but contemporary agricultural tourism reflects much greater sophistication in terms of product variety, services, activities, and marketing. In Michigan, farm operators have moved beyond classic products and activities and the traditional consumer base. New sources of revenue derive from classes on beer, cider, mead and wine making, yarn spinning, perfume/soap‐making, farm markets, fishing, educational classes, school tours and hospitality including weddings and on‐farm restaurants. This case study of Michigan agricultural tourism reports results from a systematic survey of 154 agritourism operations conducted throughout the state during summer and fall of 2013 with a focus on the economic benefits of the fast‐changing sector. This study summarizes tax revenues, sales and employment trends for the farm operations participating in the survey but also quantitatively assesses the contribution of agricultural tourism to Michigan's economy through an extrapolation of the sample to estimate state‐wide totals. Results from OLS multivariate regression analysis intended to identify relationships between employment, advertising and scale to gross sales per day are also reported. These analyses show the importance of agricultural tourism to rural and peri‐urban places in Michigan and throughout the nation, while raising concerns about a growing division between large and small operators and what this growing gap may mean for the future of the sector.  相似文献   

Policy options to streamline the carbon market for agricultural nitrous oxide emissions     

Meredith T. Niles  Hannah Waterhouse  Robert Parkhurst  Eileen L. McLellan  Sara Kroopf 《Climate Policy》2019,19(7):893-907

The majority of emissions of nitrous oxide – a potent greenhouse gas (GHG) – are from agricultural sources, particularly nitrogen fertilizer applications. A growing focus on these emission sources has led to the development in the United States of GHG offset protocols that could enable payment to farmers for reducing fertilizer use or implementing other nitrogen management strategies. Despite the development of several protocols, the current regional scope is narrow, adoption by farmers is low, and policy implementation of protocols has a significant time lag. Here we utilize existing research and policy structures to propose an ‘umbrella’ approach for nitrogen management GHG emissions protocols that has the potential to streamline the policy implementation and acceptance of such protocols. We suggest that the umbrella protocol could set forth standard definitions common across multiple protocol options, and then modules could be further developed as scientific evidence advances. Modules could be developed for specific crops, regions, and practices. We identify a policy process that could facilitate this development in concert with emerging scientific research and conclude by acknowledging potential benefits and limitations of the approach.

Key policy insights

• Agricultural greenhouse gas market options are growing, but are still underutilized

• Streamlining protocol development through an umbrella process could enable quicker development of protocols across new crops, regions, and practices

• Effective protocol development must not compromise best available science and should follow a rigorous pathway to ensure appropriate implementation

  相似文献   

翼龙类和驰龙类尾的前关节突和脉弧棒的趋同演化及翼龙类和鸟类尾部肌肉退化的平行模式     

W. Scott PERSONS  IV 《地球学报》2010,31(Z1):54-54

The caudal morphology of dromaeosaurid dinosaurs and most “rhamphorhynchoid” pterosaurs is a striking example of convergent evolution. In both groups, all but the most anterior five to seven caudal vertebrae have postzygopophyses that are elongate, equaling or exceeding the corresponding centra in length, and have bifurcating rod-shaped prezygopophyses that extend as much as seven times the length of the corresponding centra.  相似文献   

轨道高程控制网优化设计及应用   总被引：1，自引：0，他引：1  

李建平  吕豆豆  宗婷婷  张届 《测绘科学》2014,39(9)

文章分析了《高速铁路工程测量规范》(TB10601-2009)中推荐的轨道高程控制网矩形法的特点及其在实践中的应用方式,指出其优缺点,并以实践为基础提出Z型法测量方式.通过对Z型法的相邻点高差中误差、每千米高差全中误差的估算及工程实践检验,认为Z型法无论在工作效率还是观测成果的精度方面,都优于矩形法,认为其可以成为轨道高程控制网的建网方法.Z型法的提出,对施工单位轨道高程网测量的效率及精度提升具有重要参考价值.  相似文献   

Geology and tectonics of Neoproterozoic salt diapirs and salt sheets in the eastern Willouran Ranges,South Australia          下载免费PDF全文

Thomas E. Hearon IV  Mark G. Rowan  Timothy F. Lawton  Patrick T. Hannah  Katherine A. Giles 《Basin Research》2015,27(2):183-207

Allochthonous salt structures and associated primary and secondary minibasins are exposed in Neoproterozoic strata of the eastern Willouran Ranges, South Australia. Detailed geologic mapping using high‐quality airborne hyperspectral remote‐sensing data and satellite imagery, combined with a qualitative structural restoration, are used to elucidate the evolution of this complex, long‐lived (>250 Myr) salt system. Field observations and interpretations at a resolution unobtainable from seismic or well data provide a means to test published models of allochthonous salt emplacement and associated salt‐sediment interaction derived from subsurface data in the northern Gulf of Mexico. Salt diapirs and sheets are represented by megabreccias of nonevaporite lithologies that were originally interbedded with evaporites that have been dissolved and/or altered. Passive diapirism began shortly after deposition of the Callanna Group layered evaporite sequence. A primary basin containing an expulsion‐rollover structure and megaflap is flanked by two vertical diapirs. Salt flowed laterally from the diapirs to form a complex, multi‐level canopy, now partly welded, containing an encapsulated minibasin and capped by suprasalt basins. Salt and minibasin geometries were modified during the Late Cambrian–Ordovician Delamerian Orogeny (ca. 500 Ma). Small‐scale structures such as subsalt shear zones, fractured or mixed ‘rubble zones’ and thrust imbricates are absent beneath allochthonous salt and welds in the eastern Willouran Ranges. Instead, either undeformed strata or halokinetic drape folds that include preserved diapir roof strata are found directly below the transition from steep diapirs to salt sheets. Allochthonous salt first broke through the diapir roofs and then flowed laterally, resulting in variable preservation of the subsalt drape folds. Lateral salt emplacement was presumably on roof‐edge thrusts or, because of the shallow depositional environment, via open‐toed advance or extrusive advance, but without associated subsalt deformation.  相似文献   

MODFLOW as a Configurable Multi-Model Hydrologic Simulator     

Christian D. Langevin  Joseph D. Hughes  Alden M. Provost  Martijn J. Russcher  Sorab Panday 《Ground water》2024,62(1):111-123

MODFLOW 6 is the latest in a line of six “core” versions of MODFLOW released by the U.S. Geological Survey. The MODFLOW 6 architecture supports incorporation of additional hydrologic processes, in addition to groundwater flow, and allows interaction between processes. The architecture supports multiple model instances and multiple types of models within a single simulation, a flexible approach to formulating and solving the equations that represent hydrologic processes, and recent advances in interoperability, which allow MODFLOW to be accessed and controlled by external programs. The present version of MODFLOW 6 consolidates popular capabilities available in MODFLOW variants, such as the unstructured grid support in MODFLOW-USG, the Newton-Raphson formulation in MODFLOW-NWT, and the support for partitioned stress boundaries in MODFLOW-CDSS. The flexible multi-model capability allows users to configure MODFLOW 6 simulations to represent the local-grid refinement (LGR) capabilities available in MODFLOW-LGR, the multi-species transport capabilities in MT3DMS, and the coupled variable-density capabilities available in SEAWAT. This paper provides a new, holistic and integrated overview of simulation capabilities made possible by the MODFLOW 6 architecture, and describes how ongoing and future development can take advantage of the program architecture to integrate new capabilities in a way that is minimally invasive and automatically compatible with the existing MODFLOW 6 code.  相似文献   

Hydraulic-Head Formulation for Density-Dependent Flow and Transport     

Christian D. Langevin  Sorab Panday  Alden M. Provost 《Ground water》2020,58(3):349-362

Density-dependent flow and transport solutions for coastal saltwater intrusion investigations, analyses of fluid injection into deep brines, and studies of convective fingering and instabilities of denser fluids moving through less dense fluids typically formulate the groundwater flow equation in terms of pressure or equivalent freshwater head. A formulation of the flow equation in terms of hydraulic head is presented here as an alternative. The hydraulic-head formulation can facilitate adaptation of existing constant-density groundwater flow codes to include density-driven flow by avoiding the need to convert between freshwater head and hydraulic head within the code and by incorporating density-dependent terms as a compartmentalized “correction” to constant-density calculations already performed by the code. The hydraulic-head formulation also accommodates complexities such as unconfined groundwater flow and Newton-Raphson solution schemes more readily than the freshwater-head formulation. Simulation results are presented for four example problems solved using an implementation of the hydraulic-head formulation in MODFLOW.  相似文献   

Using qPCR Assays to Predict Rates of Cometabolism of TCE in Aerobic Groundwater     

John T. Wilson  James C. Mills IV  Barbara H. Wilson  Mark L. Ferrey  David L. Freedman  Dora Taggart 《Ground Water Monitoring & Remediation》2019,39(2):53-63

Monitored natural attenuation (MNA) is commonly used as a remedy for trichloroethene (TCE) in anaerobic groundwater; however, MNA has not been applied to TCE contamination in aerobic groundwater. Under aerobic conditions, bacteria initiate the degradation of many organic substances with oxygenase enzymes. Several of these enzymes are known to degrade TCE through a fortuitous reaction known as cometabolism. There are commercially available qPCR assays that can determine the number of gene copies of these enzymes. If the qPCR assay could be used to predict the first-order rate constant for cometabolism of TCE, the qPCR assay could be used to screen sites to determine whether MNA was a plausible remedy for TCE contamination. This study reevaluated data from water samples that were collected from 19 wells on five sites in Minnesota, New York, and Utah. Data had previously been published on the rate constant for cometabolism of TCE in the water samples as determined by a ¹⁴C-assay and the abundance of gene copies for five enzymes that cometabolize TCE as determined using a qPCR assay. The Michaelis-Menten (Haldane) kinetic parameters for cometabolism of TCE and the abundance of DNA for the five oxygenase enzymes were used to predict the rate constant for cometabolism of TCE. The predicted rate constants were evaluated and validated by comparing them to the rate constants derived from the ¹⁴C-assay. For predicted rate constants greater than 0.003 per year, the predicted rate constants agreed with the measured rate constants within a factor of three. The qPCR assay serves as a convenient screening tool to determine whether MNA is a plausible remedy for an aerobic plume of TCE.  相似文献   

Supersonic jet formation and propagation in x-pinches     

D. M. Haas  S. C. Bott  J. Kim  D. A. Mariscal  R. E. Madden  Y. Eshaq  U. Ueda  G. Collins IV  K. Gunasekera  F. N. Beg  J. P. Chittenden  N. Niasse  C. A. Jennings 《Astrophysics and Space Science》2011,336(1):33-40

Observations of supersonic jet propagation in low-current x-pinches are reported. X-pinches comprising of four 7.5 ??m diameter tungsten wires were driven by an 80 kA, 50 ns current pulse from a compact pulser. Coronal plasma surrounding the wire cores was accelerated perpendicular to their surface due to the global J×B force, and traveled toward the axis of the x-pinch to form an axially propagating jet. These jets moved towards the electrodes and, late in time (??150 ns), were observed to propagate well above the anode with a velocity of 3.3±0.6×10⁴ m/s. Tungsten jets remained collimated at distances of up to 16 mm from the cross point, and an estimate of the local sound speed gives a Mach number of ??6. This is the first demonstration that supersonic plasma jets can be produced using x-pinches with such a small, low current pulser. Experimental data compares well to three-dimensional simulations using the GORGON resistive MHD code, and possible scaling to astrophysical jets is discussed.  相似文献