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971.
Sean Michael Earley Matthew Neal Waters Donald Thieme Joseph McDonald Smoak 《Journal of Paleolimnology》2017,57(4):295-306
Many freshwater resources receive materials from human development causing a decrease in ecological services when compared to pre-disturbance periods. As a result, the understanding of eutrophication and limnological change has increased, but less attention has been given to systems under intense human impact that have not eutrophied so that drivers precluding eutrophication can be documented. The primary objective of this research was to reconstruct allochthonous inputs and in-lake processes for Long Pond, Georgia, USA from the mid Holocene to present and link them to primary producer community changes. Long Pond is a mesotrophic lake located in a highly altered watershed from agricultural and municipal land use and housing developments. A 5 m sediment core was collected from Long Pond, and organic matter, nutrients (C, N, P), metals (Al, Fe, Cu), and photosynthetic pigments were measured. Long Pond existed in three limnological states spanning the past ~6000 years. Prior to modern lacustrine conditions, Long Pond was a wetland/peat system that experienced the highest primary producer abundance recorded in the core. The modern lacustrine state began in the late Holocene and was characterized by increased connectivity with the surrounding watershed and low productivity. Human impacts began around 1900 AD and included high levels of phosphorus and metal deposition but moderate levels of primary producer abundance. As a result, in-lake dynamics are believed to be regulating the trophic status of Long Pond. Low concentrations of available phosphorus in the water column combined with high concentrations of sedimentary phosphorus may imply the binding of phosphorus to the sediments by certain materials such as aluminum and iron. Long Pond serves as an example of the complex in-lake processes that can occur from allochthonous inputs and autochthonous responses in lake systems thus complicating management decisions. 相似文献
972.
Philip A. Allen Nikolaos A. Michael Mitchall D’Arcy Duna C. Roda‐Boluda Alexander C. Whittaker Robert A. Duller John J. Armitage 《Basin Research》2017,29(2):180-202
Sediment is fractionated by size during its cascade from source to sink in sediment routing systems. It is anticipated, therefore, that the grain size distribution of sediment will undergo down‐system changes as a result of fluvial sorting processes and selective deposition. We assess this hypothesis by comparing grain size statistical properties of samples from within the erosional source region with those that have undergone different amounts of transport. A truncated Pareto distribution describes well the coarser half of the clast size distribution of regolith, coarse channel bed sediment and proximal debris flows (particularly their levees), as well as the coarser half of the clast size distribution of gravels that have undergone considerable amounts of transport in rivers. The Pareto shape parameter a evolves in response to mobilization, sediment transport and, importantly, the selective extraction of particles from the surface flow to build underlying stratigraphy. A goodness of fit statistic, the Kolmogorov–Smirnov vertical difference, illustrates the closeness of the observed clast size distributions to the Pareto, Weibull and log‐normal models as a function of distance from the depositional apex. The goodness of fit of the particle size distribution of regolith varies with bedrock geology. Bedload sediment at catchment outlets is fitted well by the log‐normal and truncated Pareto models, whereas the exponential Weibull model provides a less good fit. In the Eocene Escanilla palaeo‐sediment routing system of the south‐central Pyrenees, the log‐normal and truncated Pareto models provide excellent fits for distances of up to 80 km from the depositional apex, whereas the Weibull fit progressively worsens with increasing transport distance. A similar trend is found in the Miocene–Pliocene gravels of the Nebraskan Great Plains over a distance of >300 km. Despite the large fractionation in mean grain size and gravel percentage from source region to depositional sink, particle size distributions therefore appear to maintain log‐normality over a wide range of transport distance. Use of statistical models enables down‐system fractionation of sediment released from source regions to be better understood and predicted and is a potentially valuable tool in source‐to‐sink approaches to basin analysis. 相似文献
973.
974.
Joseph veverka Michael Noland Carl Sagan James Pollack Lynn Quam Robert Tucker Botand Eross Thomas Duxbury William Green 《Icarus》1974,23(2):206-289
This paper contains a complete set of the best enhancements of Mariner 9 high resolution television pictures of Phobos and Deimos, consisting of 27 different views of Phobos, and 9 of Deimos. Pertinent data about the pictures are arranged in convenient tabular and graphical form. 相似文献
975.
Michael J. Price 《Icarus》1973,20(4):455-464
New measurements of the equivalent widths of the 4-0 S(0) and S(1) H2 quadrupole lines in the Uranian spectrum have been obtained using high dispersion (4.12 Å/mm) image-tube spectrography. The measured equivalent widths are for the S(0) and S(1) lines, respectively. Curve-of-growth analysis in terms of a reflecting layer model yields an H2 column-density of 780?330+940km amagat and a temperature of 78?24+80°K. Interpretation using a semi-infinite, homogeneous, isotropically scattering model for line formation yields a scattering mean free path at λ6400 Å of 550 ± 250 km amagat. Quoted errors for both the H2 column-density and the scattering mean free path include the effect of uncertainty in the choice of atmospheric temperature. The results are discussed in terms of current models for the Uranian atmosphere. 相似文献
976.
Anders Bryn Geir-Harald Strand Michael Angeloff Yngve Rekdal 《Norsk geografisk tidsskrift. Norwegian journal of geography》2018,72(3):131-145
The Norwegian area frame survey of land cover and outfield land resources (AR18X18), completed in 2014, provided unbiased statistics of land cover in Norway. The article reports the new statistics, discusses implications of the data set, and provides potential value in terms of research, management, and monitoring. A gridded sampling design for 1081 primary statistical units of 0.9 km2 at 18?km intervals was implemented in the survey. The plots were mapped in situ, aided by aerial photos, and all areas were coded following a vegetation type system. The results provide new insights into the cover and distribution of vegetation and land cover types. The statistic for mire and wetlands, which previously covered 5.8%, has since been corrected to 8.9%. The survey results can be used for environmental and agricultural management, and the data can be stratified for regional analyses. The survey data can also serve as training data for remote sensing and distribution modelling. Finally, the survey data can be used to calibrate vegetation perturbations in climate change research that focuses on atmospheric–vegetation feedback. The survey documented novel land cover statistics and revealed that the national cover of wetlands had previously been underestimated. 相似文献
977.
978.
Economic‐Development Stakeholder Perspectives on Boomtown Dynamics in the Eagle Ford Shale,Texas 下载免费PDF全文
Unconventional oil and gas production in the United States reversed a decades‐old trend of rising oil imports, provided an argument for lifting the U.S. crude oil export ban and motivated the development of domestic natural gas export facilities. But the most visible impact of unconventional‐hydrocarbon extraction is the creation of boomtowns in rural regions. Despite widespread media coverage, scholarly analysis of boomtowns is restricted to regional econometric studies with little attention to how economic stakeholders understand and respond to booming economies. Here we analyze interviews with key economic stakeholders in the Eagle Ford Shale in Texas. Respondents consider their community's economic success relative to the price of oil and indicate concerns about the deterioration of roads, high housing demand, and skyrocketing wages. We also re‐examine John Gilmore's foundational work on boomtowns in the 1970s in the context of contemporary unconventional extraction. 相似文献
979.
980.
Tracking embodied carbon flows in the Belt and Road regions 总被引:3,自引:1,他引:2
In the past few decades, economic globalization has driven rapid growth of cross-border trade and a new international division of labor, leading to increasing inter- country embodied carbon flows. Multi-region input-output (MRIO) analysis is used to identify embodied carbon flows between major world regions, including seven regions along the Belt and Road (BR), and the spatial distribution of production- and consumption-based carbon intensities. The results show that current embodied carbon flows are virtually all from BR regions to developed countries, with more than 95% of world net embodied carbon exports coming from BR regions. Consumption in the United States and European Union countries induce about 30% of the carbon emissions in most BR regions, indicating that the former bear a high proportion of consumers’ responsibility for the carbon emitted in the latter. For this reason, measuring environmental responsibilities from consumption rather than a production- based perspective is more equitable, while developing countries should be given a louder voice in the construction through dialogue and cooperation, in part in the context of the Belt and Road Initiative, of an inclusive global climate governance system. 相似文献