Temporal trends in water clarity and land-use/land-cover (LULC), as well as the relationship between changes in water clarity and LULC, were analyzed using water clarity values extracted from Landsat images from 1986 to 2008, acquired for east-central Maine. Of 40 lakes identified using satellite imagery, our analysis found one lake with a significant decrease in water clarity. In a second data-set, with 99 lakes, we identified two lakes with a significant increase in water clarity. Analyses of the relationship between temporal changes in the water clarity and LULC did not identify any clear, consistent, relationships between changes in the water quality variables and LULC. Overall, the results of this study aid in the identification of the relationship between water clarity and LULC, and identify temporal changes in water clarity. The findings of this study support the previous research that demonstrates the ability of satellite imagery to be used in assessments of water clarity, thus enabling evaluation at broader spatial scales and longer temporal scales than assessments that rely solely on ground-based data. 相似文献
Very little is currently known about the globalization of the temporary staffing industry, a strategically significant sector given its role in promulgating wider labor market flexibility. This article starts to rectify this research lacuna in four ways: by conceptualizing the international expansion of temporary staffing and comparing it to other business service sectors, by identifying and mapping the top twenty transnational staffing agencies, by offering a typology of the leading transnational agencies based on their functional and geographic characteristics, and by charting a research agenda for future work on this sector. 相似文献
The Irish Sea, like many marine areas, is threatened by anthropogenic activities. In particular the Pisces Reef system, a series of smothered rocky reefs are subject to fishing pressures as a result of their position within a Nephrops norvegicus fishery. In an area of sediment deposition and retention the reefs modify the environment by increasing the energy of near-bottom currents which results in localised scouring. This is the first study to attempt to characterise and investigate the ecological functioning of the Pisces Reef system. A multidisciplinary approach was essential for accurate investigation of the area. To facilitate more effective management of the benthic habitats of the Reef system, this study integrates acoustic, seismic, grab sampling and video ground-truthing methods for benthic habitat discrimination. Orientation of the scour hollows also suggest that seabed features could be used to infer dominant flow regimes such as the Irish Sea Gyre. The data revealed significant geology–benthos relationships. A unique biotope was described for the reef habitat and it was demonstrated that scouring may influence community composition through disturbance mechanisms. This study provides preliminary information required for management of a unique habitat within a uniform region. 相似文献
Springs in karstic carbonate rocks frequently carry a sediment load as well as a dissolved load. Analysis of morphology and
mineralogy of suspended sediment from three contrasting karst springs reveals a suite of clastic particles that reflect both
source areas and processes that take place within the aquifer. Nolte Spring in Lancaster County, Pennsylvania, USA, discharges
sediment of apparently precipitated calcite, indicating that at some point in the aquifer or vadose zone, water exceeds saturation
with respect to calcite. Sediment morphologies and chemical conditions in the aquifer point to two different scenarios for
this precipitation. The other two springs, Arch Spring in Blair County, Pennsylvania and Bushkill Spring in Northampton County,
Pennsylvania, show no evidence of calcite precipitation. Arch Spring discharges mainly layer silicates, while Bushkill Spring
discharges mainly silica.
Resumen Los manantiales en rocas carbonatadas karstficadas tienen frecuentemente una carga de sedimentos y de sólidos disueltos. Los
análisis de la morfología y mineralogía de los sedimentos suspendidos de tres manantiales kársticos contrastados revela un
conjunto de partículas clásticas que reflejan ambas áreas fuente y los procesos que tienen lugar dentro del acuífero. Nolte
Spring en el Condado de Lancaster, Pennsylvania, USA, descarga sedimento de calcita aparentemente precipitada indicando que
en cierto punto del acuífero o en la zona vadosa, el agua supera la saturación con respecto a la calcita. La morfología de
los sedimentos y las condiciones químicas en el acuífero apuntan a dos escenarios diferentes para esta precipitación. Los
otras dos manantiales, Arch Spring en el Condado de Blair, Pennsylvania y Bushkill Spring en el Condado de Norhtampton, Pennsylvania,
no muestran evidencia de precitación de calcita. Arch Spring descarga principalmente filosilicatos mientras que Bushkill Spring
descarga fundamentalmente Sílice.
Résumé Les sources situées en contexte carbonaté karstique charrient fréquemment, outre les matières dissoutes, une charge solide.
La morphologie et la minéralogie des sédiments en suspension issus de trois sources karstiques de caractéristiques distinctes
ont été analysées : une série de particules clastiques, reflétant à la fois les secteurs des sources et les processus internes
de l’aquifère, en ressort. Les sédiments issus de Nolte Spring (Comté de Lancaster, Pennsylvanie, Etats-Unis) sont constitués
de calcite apparemment précipitée: ceci indique que l’eau atteint la sursaturation vis-à-vis de la calcite à un certain point
de l’aquifère ou de la zone non-saturée. La morphologie des sédiments et les conditions chimiques au sein de l’aquifère mènent
à deux scénarii différents pour expliquer cette précipitation. Les deux autres sources, Arch Spring (Comté de Blair, Pennsylvanie)
et Bushkill Spring (Comté de Northampton, Pennsylvanie), ne présentent aucun indice de précipitation de calcite. Arch Spring
exporte essentiellement des phyllosilicates, alors que la silice est majoritaire à Bushkill Spring.
Major transformation of the global energy system is required for climate change mitigation. However, energy demand patterns and supply systems are themselves subject to climate change impacts. These impacts will variously help and hinder mitigation and adaptation efforts, so it is vital they are well understood and incorporated into models used to study energy system decarbonisation pathways. To assess the current state of understanding of this topic and identify research priorities, this paper critically reviews the literature on the impacts of climate change on the energy supply system, summarising the regional coverage of studies, trends in their results and sources of disagreement. We then examine the ways in which these impacts have been represented in integrated assessment models of the electricity or energy system.Studies tend to agree broadly on impacts for wind, solar and thermal power stations. Projections for impacts on hydropower and bioenergy resources are more varied. Key uncertainties and gaps remain due to the variation between climate projections, modelling limitations and the regional bias of research interests. Priorities for future research include the following: further regional impact studies for developing countries; studies examining impacts of the changing variability of renewable resources, extreme weather events and combined hazards; inclusion of multiple climate feedback mechanisms in IAMs, accounting for adaptation options and climate model uncertainty. 相似文献
Records from lake sediment cores are critical for assessing the relative stability of climate and ecosystems over the Holocene.
Duck Lake in south-central Lower Michigan, USA, was the focus of a study that identified how changes in the geochemical variables
in lake sediments relate to variations in regional climate and local land use during the Holocene. More than 8.5 m of lacustrine
sediment were recovered using Livingston and freeze corers and analyzed for organic carbon, inorganic (carbonate) carbon,
total nitrogen, and trace metals. Repeating packages of sediment (1–10 cm thick) that grade from light (inorganic carbon-rich)
to dark (organic carbon-rich) were found from the surface to a depth of about 8 m. Variations in the high-resolution gray
scale data from core X-radiographs are highly correlated to the relative amount of inorganic carbon. Geochemical analyses
of the upper 8.5 m of sediment revealed a wide range of values: 0.05–10.6% for inorganic carbon (i.e. 0.5–89% calcium carbonate)
and 1.1–28% for organic carbon (i.e. 2.7–70% organic matter). Organic carbon to nitrogen ratios indicate that most of the
sediment organic matter is produced within the lake. A core chronology based on eight AMS radiocarbon dates shows low sediment
accumulation rates (0.05 cm/year) from 10,000 to 3,800 cal year BP and higher sediment accumulation rates (0.1–0.3 cm/year)
from 3,800 cal year BP to present. We suggest that carbonate accumulates during relatively dry times, whereas organic matter
accumulation dominates when nutrient input to the lake is enhanced by wetter climate. The Duck Lake core records a distinct
low point in inorganic carbon deposition that may be related to the 8.2 ka cooling event now documented from several sites
in North America. Spectral analysis of gray scale values shows significant ~200-year periodicities over the past 8,000 years,
hypothesized to result from climate changes induced by solar forcing. Concentrations of trace metals (e.g. lead, iron, copper,
zinc) indicate the onset of regional anthropogenic influence about 150 cal year BP. 相似文献
Journal of Paleolimnology - We developed a portable extruder for precise and accurate high-resolution subsampling of unconsolidated sediment cores. This extruder is capable of producing subsamples... 相似文献
Prediction of true classes of surficial and deep earth materials using multivariate spatial data is a common challenge for geoscience modelers. Most geological processes leave a footprint that can be explored by geochemical data analysis. These footprints are normally complex statistical and spatial patterns buried deep in the high-dimensional compositional space. This paper proposes a spatial predictive model for classification of surficial and deep earth materials derived from the geochemical composition of surface regolith. The model is based on a combination of geostatistical simulation and machine learning approaches. A random forest predictive model is trained, and features are ranked based on their contribution to the predictive model. To generate potential and uncertainty maps, compositional data are simulated at unsampled locations via a chain of transformations (isometric log-ratio transformation followed by the flow anamorphosis) and geostatistical simulation. The simulated results are subsequently back-transformed to the original compositional space. The trained predictive model is used to estimate the probability of classes for simulated compositions. The proposed approach is illustrated through two case studies. In the first case study, the major crustal blocks of the Australian continent are predicted from the surface regolith geochemistry of the National Geochemical Survey of Australia project. The aim of the second case study is to discover the superficial deposits (peat) from the regional-scale soil geochemical data of the Tellus Project. The accuracy of the results in these two case studies confirms the usefulness of the proposed method for geological class prediction and geological process discovery.
Exploration and development of offshore hydrocarbon resources has advanced into remote deepwater regions over the last decade and poses significant technical challenges for the design and installation of wells and facilities at extreme water depths. Seafloor and shallow subsurface processes and conditions in these areas are complex and generally poorly understood, and the geohazards to development are larger scale and fundamentally different to those encountered onshore; consequently the geohazard risk to deepwater development projects is potentially significant and requires careful evaluation and mitigation during the front-end planning and engineering design stages of projects. There are no established industry standards or methods for the assessment of geohazards and engineering-quality geophysical data at the scale of development. The paper describes an integrated and systematic map-based approach for the assessment and mitigation of seabed geohazards and risk to proposed deepwater development. The approach employs a multi-disciplinary team working with engineering-quality field calibrated data to accurately map and assess seafloor ground conditions and ensure that development proposals are not exposed to intolerable geohazard risk. The approach taken is very similar to the practice of establishing geological models for land-based engineering projects, in which the complete geological history of the site is used to characterise and predict the performance of the ground. Such an approach is routine for major projects on land but so far does not seem to be common practice in the offshore industry. The paper illustrates the seafloor geomophological mapping approach developed. The products are being used to optimise development layouts to avoid geohazards where possible and to support site-specific engineering design of facilities based on a detailed understanding of the potential geohazard loadings and associated risk. 相似文献
The past 12 years have seen significant steps forward in the science and practice of coastal flood analysis. This paper aims to recount and critically assess these advances, while helping identify next steps for the field. This paper then focuses on a key problem, connecting the probabilistic characterization of flood hazards to their physical mechanisms. Our investigation into the effects of natural structure on the probabilities of storm surges shows that several different types of spatial-, temporal-, and process-related organizations affect key assumptions made in many of the methods used to estimate these probabilities. Following a brief introduction to general historical methods, we analyze the two joint probability methods used in most tropical cyclone hazard and risk studies today: the surface response function and Bayesian quadrature. A major difference between these two methods is that the response function creates continuous surfaces, which can be interpolated or extrapolated on a fine scale if necessary, and the Bayesian quadrature optimizes a set of probability masses, which cannot be directly interpolated or extrapolated. Several examples are given here showing significant impacts related to natural structure that should not be neglected in hazard and risk assessment for tropical cyclones including: (1) differences between omnidirectional sampling and directional-dependent sampling of storms in near coastal areas; (2) the impact of surge probability discontinuities on the treatment of epistemic uncertainty; (3) the ability to reduce aleatory uncertainty when sampling over larger spatial domains; and (4) the need to quantify trade-offs between aleatory and epistemic uncertainties in long-term stochastic sampling. 相似文献