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111.
112.
This paper presents the development of a Regional Neural Network for Water Level (RNN_WL) predictions, with an application to the coastal inlets along the South Shore of Long Island, New York. Long-term water level data at coastal inlets are important for studying coastal hydrodynamics sediment transport. However, it is quite common that long-term water level observations may be not available, due to the high cost of field data monitoring. Fortunately, the US National Oceanographic and Atmospheric Administration (NOAA) has a national network of water level monitoring stations distributed in regional scale that has been operating for several decades. Therefore, it is valuable and cost effective for a coastal engineering study to establish the relationship between water levels at a local station and a NOAA station in the region. Due to the changes of phase and amplitude of water levels over the regional coastal line, it is often difficult to obtain good linear regression relationship between water levels from two different stations. Using neural network offers an effective approach to correlate the non-linear input and output of water levels by recognizing the historic patterns between them. In this study, the RNN_WL model was developed to enable coastal engineers to predict long-term water levels in a coastal inlet, based on the input of data in a remote NOAA station in the region. The RNN_WL model was developed using a feed-forwards, back-propagation neural network structure with an optimized training algorithm. The RNN_WL model can be trained and verified using two independent data sets of hourly water levels.The RNN_WL model was tested in an application to Long Island South Shore. Located about 60–100 km away from the inlets there are two permanent long-term water level stations, which have been operated by NOAA since the1940s. The neural network model was trained using hourly data over a one-month period and validated for another one-month period. The model was then tested over year-long periods. Results indicate that, despite significant changes in the amplitudes and phases of the water levels over the regional study area, the RNN_WL model provides very good long-term predictions of both tidal and non-tidal water levels at the regional coastal inlets. In order to examine the effects of distance on the RNN_WL model performance, the model was also tested using water levels from other remote NOAA stations located at longer distances, which range from 234 km to 591 km away from the local station at the inlets. The satisfactory results indicate that the RNN_WL model is able to supplement long-term historical water level data at the coastal inlets based on the available data at remote NOAA stations in the coastal region. 相似文献
113.
A survey of the modern physical setting of Lake El’gygytgyn, northeastern Siberia, is presented here to facilitate interpretation
of a 250,000-year climate record derived from sediment cores from the lake bottom. The lake lies inside a meteorite impact
crater that is approximately 18 km in diameter, with a total watershed area of 293 km2, 110 km2 of which is lake surface. The only surface water entering the lake comes from the approximately 50 streams draining from
within the crater rim; a numbering system for these inlet streams is adopted to facilitate scientific discussion. We created
a digital elevation model for the watershed and used it to create hypsometries, channel networks, and drainage area statistics
for each of the inlet streams. Many of the streams enter shallow lagoons dammed by gravel berms at the lakeshore; these lagoons
may play a significant role in the thermal and biological dynamics of the lake due to their higher water temperatures (>6°C).
The lake itself is approximately 12 km wide and 175 m deep, with a volume of 14.1 km3. Water temperature within a column of water near the center of this oligotrophic, monomictic lake never exceeded 4°C over
a 2.5 year record, though the shallow shelves (<10 m) surrounding the lake can reach 5°C in summer. Though thermally stratified
in winter, the water appears completely mixed shortly after lake ice breakup in July. Mean annual air temperature measured
about 200 m from the lake was −10.3°C in 2002, and an unshielded rain gage there recorded 70 mm of rain in summer of 2002.
End of winter snow water equivalent on the lake was approximately 110 mm in May 2002. Analysis of NCEP reanalysis air temperatures
(1948–2002) reveals that the 8 warmest years and 10 warmest winters have occurred since 1989, with the number of days below
−30°C dropping from a pre-1989 mean of 35 to near 0 in recent years. The crater region is windy as well as cold, with hourly
wind speeds exceeding 13.4 m s−1 (30 mph) typically at least once each month and 17.8 m s−1 (40 mph) in winter months, with only a few calm days per month; wind may also play an important role in controlling the modern
shape of the lake. Numerous lines of evidence suggest that the physical hydrology and limnology of the lake has changed substantially
over the past 3.6 million years, and some of the implications of these changes on paleoclimate reconstructions are discussed.
This is the second in a series of eleven papers published in this special issue dedicated to initial studies of El'gygytgyn Crater Lake and
its catchment in NE Russia. Julie Brigham-Grette, Martin Melles, Pavel Minyuk were guest editors of this special issue. 相似文献
114.
Mountain regions are subject to a variety of hazardous processes. Earthquakes, landslides, snow avalanches, floods, debris
flows, epidemics and fires, among other processes, have caused injury, death, damage and destruction. They also face challenges
from increased populations, and expansion and intensification of␣activities, land uses and infrastructure. The combination
of a dynamic bio- geophysical environment and intensified human use has increased the vulnerability of mountain social–ecological
systems to risk from hazards. The ability of social–ecological systems to build resilience in the context of hazards is an
important factor in their long-term sustainability. The role of resilience building in understanding the impact of hazards
in mountain areas is examined and illustrated, in part, through examples from Canada and India. Resilient social–ecological
systems have the ability to learn and adjust, use all forms of knowledge, to self-organize and to develop positive institutional
linkages with other social–ecological systems in the face of hazards. The analysis suggests that traditional social–ecological
systems built resilience through avoidance, which was effective for localized hazards. The more recent development and implementation
of cross-scale institutional linkages is shown to be a particularly effective means of resilience building in mountain social–ecological
systems in the face of all hazards. 相似文献
115.
Ali Polat Peter W.U. Appel Robert Frei Yuanming Pan Yldrm Dilek Juan C. Ordez-Caldern Brian Fryer Julie A. Hollis Johann G. Raith 《Gondwana Research》2007,11(1-2):69
The Mesoarchean (ca. 3075 Ma) Ivisaartoq greenstone belt in southern West Greenland includes variably deformed and metamorphosed pillow basalts, ultramafic flows (picrites), serpentinized ultramafic rocks, gabbros, sulphide-rich siliceous layers, and minor siliciclastic sedimentary rocks. Primary magmatic features such as concentric cooling-cracks and drainage cavities in pillows, volcanic breccia, ocelli interpreted as liquid immiscibility textures in pillows and gabbros, magmatic layering in gabbros, and clinopyroxene cumulates in ultramafic flows are well preserved in low-strain domains. The belt underwent at least two stages of calc-silicate metasomatic alteration and polyphase deformation between 2963 and 3075 Ma. The stage I metasomatic assemblage is composed predominantly of epidote (now mostly diopside) + quartz + plagioclase ± hornblende ± scapolite, and occurs mainly in pillow cores, pillow interstitials, and along pillow basalt-gabbro contacts. The origin of this metasomatic assemblage is attributed to seafloor hydrothermal alteration. On the basis of the common presence of epidote inclusions in diopside and the local occurrence of epidote-rich aggregates, the stage I metasomatic assemblage is interpreted as relict epidosite. The stage II metasomatic assemblage occurs as concordant discontinuous layered calc-silicate bodies to discordant calc-silicate veins commonly associated with shear zones. The stage II metasomatic assemblage consists mainly of diopside + garnet + amphibole + plagioclase + quartz ± vesuvianite ± scapolite ± epidote ± titanite ± calcite ± scheelite. Given that the second stage of metasomatism is closely associated with shear zones and replaced rocks with an early metamorphic fabric, its origin is attributed to regional dynamothermal metamorphism. The least altered pillow basalts, picrites, gabbros, and diorites are characterized by LREE-enriched, near-flat HREE, and HFSE (especially Nb)-depleted trace element patterns, indicating a subduction zone geochemical signature. Ultramafic pillows and cumulates display large positive initial εNd values of + 1.3 to + 5.0, consistent with a strongly depleted mantle source. Given the geological similarities between the Ivisaartoq greenstone belt and Phanerozoic forearc ophiolites, we suggest that the Ivisaartoq greenstone belt represents Mesoarchean supra-subduction zone oceanic crust. 相似文献
116.
In this paper, we map the gendered contours of contemporary water management in order to demonstrate that regimes for individual ownership of water rights, markets, and the productive use of water simply reinscribe and simultaneously submerge in their apparent gender-neutrality a normative masculinity that underpins economic globalization and fortifies existing power relations. Not only do such arrangements disadvantage reproductive values and non-consumptive users; more generally, they also lack the capacity to ensure water’s sustainable development. Consequently, new management institutions for sustainability are demanded and, in making a case for equity-enhancing and adaptive institutions that better reflect water’s materiality, its multiple values and emerging water scarcity, we argue the need to invoke the conserving and ecologically protective feminine principle. To support our reasoning, we analyse water reform processes instituted in Australia and specifically by the State of Tasmania, referring to the latter jurisdiction to illustrate the gendered nature of resource management and to underscore tensions between economic globalization and sustainability, concluding that the tensions between the two agendas are probably irresolvable. We position our work in the borderlands among gender studies, feminist geography and philosophy, and political ecology, drawing together insights about the construction of resource management, the possibilities of the feminine care ethic, and ideas about the characteristics of institutional systems that could ensure equitable allocation and sustainable use of the planet’s resources. 相似文献
117.
Mechanisms controlling soil carbon turnover and their potential application for enhancing carbon sequestration 总被引:6,自引:0,他引:6
In addition to increasing plant C inputs, strategies for enhancing soil C sequestration include reducing C turnover and increasing
its residence time in soils. Two major mechanisms, (bio)chemical alteration and physicochemical protection, stabilize soil organic C (SOC) and thereby control its turnover. With (bio)chemical alteration, SOC is transformed by biotic
and abiotic processes to chemical forms that are more resistant to decomposition and, in some cases, more easily retained
by sorption to soil solids. With physicochemical protection, biochemical attack of SOC is inhibited by organomineral interactions
at molecular to millimeter scales. Stabilization of otherwise decomposable SOC can occur via sorption to mineral and organic
soil surfaces, occlusion within aggregates, and deposition in pores or other locations inaccessible to decomposers and extracellular
enzymes. Soil structure is a master integrating variable that both controls and indicates the SOC stabilization status of
a soil. One potential option for reducing SOC turnover and enhancing sequestration, is to modify the soil physicochemical
environment to favor the activities of fungi. Specific practices that could accomplish this include manipulating the quality
of plant C inputs, planting perennial species, minimizing tillage and other disturbances, maintaining a near-neutral soil
pH and adequate amounts of exchangeable base cations (particularly calcium), ensuring adequate drainage, and minimizing erosion.
In some soils, amendment with micro- and mesoporous sorbents that have a high specific surface – such as fly ash or charcoal
– can be beneficial.
All authors contributed equally to this article. 相似文献
118.
A paleolimnological investigation of post-European sediments in a Lake Michigan coastal lake was used to examine the response of Lower Herring Lake to anthropogenic impacts and its role as a processor of watershed inputs. We also compare the timing of this response with that of Lake Michigan to examine the role of marginal lakes as early warning indicators of potential changes in the larger connected system and their role in buffering Lake Michigan against anthropogenic changes through biotic interactions and material trapping. Sediment geochemistry, siliceous microfossils and nutrient-related morphological changes in diatoms, identified three major trophic periods in the recent history of the lake. During deforestation and early settlement (pre-1845–1920), lake response to catchment disturbances results in localized increases in diatom abundances with minor changes in existing communities. In this early phase of disturbance, Lower Herring Lake acts as a sediment sink and a biological processor of nutrient inputs. During low-lake levels of the 1930s, the lake goes through a transitional period characterized by increased primary productivity and a major shift in diatom communities. Post-World War II (late 1940s–1989) anthropogenic disturbances push Lower Herring Lake to a new state and a permanent change in diatom community structure dominated by Cyclotella comensis. The dominance of planktonic summer diatom species associated with the deep chlorophyll maximum (DCM) is attributed to epilimnetic nutrient depletion. Declining Si:P ratios are inferred from increased sediment storage of biogenic silica and morphological changes in the silica content of Aulacoseira ambigua and Stephanodiscus niagarae. Beginning in the late 1940s, Lower Herring Lake functions as a biogeochemical processor of catchment inputs and a carbon, nutrient and silica sink. Microfossil response to increased nutrients and increased storage of biogenic silica in Lower Herring Lake and other regional embayments occur approximately 20–25 years earlier than in a nearby Lake Michigan site. Results from this study provide evidence for the role of marginal lakes and bays as nutrient buffering systems, delaying the impact of anthropogenic activities on the larger Lake Michigan system. 相似文献
119.
Regional-scale Proterozoic IOCG-mineralized breccia systems: examples from the Wernecke Mountains, Yukon, Canada 总被引:1,自引:0,他引:1
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.
相似文献
Julie HuntEmail: |
120.
Jean-Philippe Boulanger Julie Leloup Olga Penalba Matilde Rusticucci Florence Lafon Walter Vargas 《Climate Dynamics》2005,24(4):393-413
The Paraná-Plata basin is the second largest hydrological basin in South America and is of great importance for the countries of the region (Argentina, Bolivia, Brazil, Paraguay and Uruguay). The present study focuses on the long-term trends in basin-scale precipitation with special emphasis on the role of distribution changes in extreme large-scale precipitation events and on the characteristics and evolution of ENSO teleconnections over the last 50 years. First, we defined a Paraná-Plata basin total precipitation index (PTPI) as the precipitations spatially averaged over the hydrological basin. On interannual time scales, such an index is mainly representative of anomalous monsoon precipitations in the northern part of the basin and large convective precipitation anomalies in the center of the basin (Paraguay-southern Brazil-Uruguay-northern Argentina) typical of the canonical ENSO teleconnection pattern. Our major findings clearly highlight a positive trend in yearly averaged PTPI mainly from the late 1960s to the early 1980s with a strong dependence from month-to-month. The largest precipitation increase is observed from November to May in southern Brazil and Argentina. A close examination of PTPI distributions during the two halves of the period 1950–2001 shows that the changes in the mean state from 1950–1975 to 1976–2001 result from significant changes in each calendar month mean state and in the tails of the PTPI anomaly distributions in May with lesser and weaker large-scale dry events and stronger large-scale wet events. Further studies will be needed to assess whether the observed trend in large-scale extreme precipitation conditions can be related to natural climate variability or anthropogenic activities and whether it is associated to changes in local/regional extreme events. The stronger wet conditions in different months seem to be associated to changes in ENSO characteristics (amplitude, propagation, spatial structure, ...) since the 1982–1983 El Niño. Indeed, spatial ENSO teleconnections (stronger in November and April–May) have greatly evolved from 1950–1975 to 1976–2001. Moreover, we demonstrate that there is a strong modulation and displacement of the teleconnection patterns from one event to another, impeding the definition of robust statistical relationship between ENSO and precipitation in the Paraná-Plata basin (except maybe over a very limited area near the common border between Paraguay, Argentina and Brazil). Finally, the non-antisymmetrical patterns of precipitation between El Niño and La Niña conditions and the non-linear relationship between precipitation and either Niño3.4 or Niño1+2 sea surface temperature indices show that linear statistical forecast systems are actually of very limited use for impact predictions on society on a local or regional scale. 相似文献