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111.
Natural Hazards - Assessment of susceptibility to torrential flows at the catchment scale is a necessary step for prioritising zones that can be identified by hazard and risk maps. In the Andean... 相似文献
112.
Jessica Silva Lomba Maria Isabel Fraga Alves 《Stochastic Environmental Research and Risk Assessment (SERRA)》2020,34(3):465-491
In extreme value analysis, sensitivity of inference to the definition of extreme event is a paramount issue. Under the peaks-over-threshold approach, this translates directly into the need of fitting a Generalized Pareto distribution to observations above a suitable level that balances bias versus variance of estimates. Selection methodologies established in the literature face recurrent challenges such as an inherent subjectivity or high computational intensity. We suggest a truly automated method for threshold detection, aiming at time efficiency and elimination of subjective judgment. Based on the well-established theory of L-moments, this versatile data-driven technique can handle batch processing of large collections of extremes data, while also presenting good performance on small samples. The technique’s performance is evaluated in a large simulation study and illustrated with significant wave height data sets from the literature. We find that it compares favorably to other state-of-the-art methods regarding the choice of threshold, associated parameter estimation and the ultimate goal of computationally efficient return level estimation. 相似文献
113.
Inmaculada Rodríguez Santalla María Jos Snchez García Isabel Montoya Montes David Gmez Ortiz Tomas Martín Crespo Jordi Serra Raventos 《Geomorphology》2009,104(3-4):238-252
This paper presents an analysis of the dune field dynamics of El Fangar Spit in the Ebro Delta (Spain), associating it with the internal structure of dunes carried out with ground-penetrating radar and supported by data from topographic DGPS. These analyses are of great importance to ascertain the state of the internal structure of dunes as an important element in their stability and, therefore in their evolution. The internal structure shows accretion and progradation sequences of dunes over beach deposits, which depend on dune morphology (height, crest orientation) and location, as well as the processes acting on them. 相似文献
114.
115.
The efficiency of the biological removal of carbon and nitrogen from leachates is determined by the activity of microbial populations present in biological reactors. In this work, a complete characterization of bacterial communities revealed by personal genome machine sequencing (PGM) has been carried out from different points of a nitrification–denitrification process operated in an urban landfill. The leachate fed to the treatment is a mixture of young leachate, old leachate, and effluent from an anaerobic digestion process, in a volume ratio of 1:0.9:0.12, respectively. The anoxic and oxic reactors are followed by an ultrafiltration step. Samples are taken from different points of the process. Results reveal the microbial diversity of the samples, which include detection of minority populations that are difficult to explore by other methods. Bacteria belonging to Bacteroidetes and Proteobacteria are dominant in all the samples analyzed. Proteobacteria represents more than 50% of the total population in all cases. Samples taken after the biological treatment show a significant reduction in the relative abundance of Firmicutes, Tenericutes, and Lentisphaerae phyla in comparation with the initial leachate. The relative abundance of the classes is also studied and the most abundant in the samples are β‐Proteobacteria and Flavobacteria. 相似文献
116.
Water concentrates from Turia river (1.5 mg L−1 total organic C) obtained by nanofiltration (membrane mass cut-off 90 Da) were fractioned by non-ionic Amberlite resins (DAX8 and XAD4) to afford three samples termed as hydrophobic acid (50%), transphilic acid (24%) and hydrophobic neutral (12%). If a nanofiltration membrane 270 Da mass cut-off is used then about 50% of dissolved organic matter is not retained. These three fractions were characterized by analytical and spectroscopic techniques (1H NMR, MALDI–TOF-MS, ESI–API-MS, ESI–MS/MS). Overall, these data are compatible with the presence of oligosaccharides, oligopeptides and fatty acids as the main components of dissolved organic matter. Particularly revealing was the information from MALDI–TOF-MS and ESI–MS/MS where series of compounds differing in the number of hexose units were identified. The three fractions have many spectroscopic similarities and, particularly the hydrophobic and transphilic ones, are really almost identical. This similarity in the fraction composition shows that the conventional fractionation procedure is inefficient as a standard general method for separation of different compound types. The composition of dissolved organic matter was confirmed, and some individual organic compounds identified, by GC–MS analysis of the silylated derivatives obtained by reacting the fractions with a mixture of N,O-bis(trimethylsilyl)trifluoroacetamide with trimethylchlorosilane (10%). Thus, rather surprisingly, the dissolved organic matter of this natural raw water is predominantly composed of a relatively simple mixture of a few types of compounds with molecular weights well below 1100 Da (about six hexose units). These results, particularly the absence of detectable amounts of high molecular weight humic acids and low molecular weight phenolic compounds indicates that trihalomethanes formed in the water disinfection process by Cl2 really derive from oligosaccharides and oligopeptides. Also, the data suggests alternative strategies to effect a more efficient fractionation of the dissolved organic matter. 相似文献
117.
Inmaculada de Vicente Eva Ortega-Retuerta Ignacio P. Mazuecos Michael L. Pace Jonathan J. Cole Isabel Reche 《Aquatic Sciences - Research Across Boundaries》2010,72(4):443-453
In inland waters, transparent exopolymer particles (TEP) can affect carbon export and sequestration in sediments with consequences
for lake C budgets. We measured TEP concentration in 32 lakes from two contrasting lake districts covering wide ranges in
biological and chemical characteristics. North temperate lakes, located in a wet region, have low to moderate ionic strength
and low to high dissolved organic carbon with corresponding variation in color (light absorbance). Mediterranean lakes located
in a semiarid region were characterized by high ionic strength and high concentrations of dissolved organic carbon but low
color. TEP concentrations were large relative to the living portion of the particulate organic carbon pool in both Mediterranean
(36%) and north temperate (33%) lakes. TEP concentrations ranged from 36 to 1,462 μg [as Gum Xanthan equivalents (GX eq)] L−1 in north temperate lakes. In the Mediterranean lakes, concentrations were higher that previously reported for other systems
and ranged from 66 to 9,038 μg GX eq L−1. TEP concentration was positive and significantly related to chlorophyll a (chl a) in north temperate lakes and in the entire data set. Although a significant and positive relationship between TEP and chl
a was also detected in the Mediterranean lakes, bacterial abundance was most strongly related to TEP. In contrast with the
positive influence of phytoplankton and bacteria on TEP, there were weaker relationships between TEP and the chemical variables
tested. We observed a significant and positive relationship between pH and TEP (for all lakes) but this relationship was indirectly
driven by a co-variation of pH with phytoplankton biomass based on multiple regression analysis. For the Mediterranean lakes,
the negative (but not significant) trends between TEP and both conductivity and divalent cations suggest thresholds above
which TEP will likely be destabilized. Under these conditions, TEP may flocculate or disperse in the water column. 相似文献
118.
María Isabel Arce María del Mar Sánchez-Montoya María Rosario Vidal-Abarca María Luisa Suárez Rosa Gómez 《Aquatic Sciences - Research Across Boundaries》2014,76(2):173-186
Most streams draining to the Mediterranean basin are temporary. As a result of their hydrological regime, temporary streams are affected by drying and rewetting periods. Drying can alter in-stream nitrogen (N) availability and reduce N processing rates and subsequent retention after re-wetting. We sought to determine if hydrologic drying modifies reach-scale sediment chemical properties and constrains the response of N processing to rewetting. We compared different abiotic characteristics of sediments and nitrification and denitrification rates between a perennial and intermittent reach in the same stream over a wet period, when surface water flowed in both reaches, and a dry period, when the intermittent reach dried up. We analyzed N processing rates by incubating sediments with stream water, thereby simulating a rewetting when sediments from the intermittent reach were dry. We found that drying increased the sediment nitrate (NO3 ?) content. Conversely, drying did not reduce the recovery of N processing rates to pre-dry levels after simulated flooding conditions. Our results suggest that dry reaches may act as a potential NO3 ? source by releasing downstream NO3 ? pulses after stream flow recovery. Given the European Water Framework Directive requirements to assess stream ecological status, these N pulses following rewetting should be considered when designing management plans in temporary streams. Our study highlights the rapid response of in-stream N processing to rewetting period following a drought. This high resilience to process N should be seen as a vital ecosystem service provided by temporary streams despite annual dry periods. 相似文献
119.
Natalia Pardo Shane Cronin Alan Palmer Jonathan Procter Ian Smith 《Bulletin of Volcanology》2012,74(5):1161-1185
New tephro-stratigraphic studies of the Tongariro Volcanic Centre (TgVC) on the North Island (New Zealand) allowed reconstruction of some of the largest, andesitic, explosive eruptions of Mt. Ruapehu. Large eruptions were common in the Late Pleistocene, before a transition to strombolian-vulcanian and phreatomagmatic eruptive styles that have predominated over the past 10,000?years. Considering this is the most active volcano in North Island of New Zealand and the uppermost hazard limits are unknown, we identified and mapped the pyroclastic deposits corresponding to the five largest eruptions since ~27?ka. The selected eruptive units are also characterised by distinctive lithofacies associations correlated to different behaviours of the eruptive column. In addition, we clarify the source of the ~10–9.7?ka Pahoka Tephra, identified by previous authors as the product of one of the largest eruptions of the TgVC. The most common explosive eruptions taking place between ~13.6 and ~10?ka?cal?years BP involved strongly oscillating, partially collapsing eruptive columns up to 37?km high, at mass discharge rates up to 6?×?108?kg/s and magnitudes of 4.9, ejecting minimum estimated volumes of 0.6?km3. Our results indicate that this volcano (as well as the neighbouring andesitic Mt. Tongariro) can generate Plinian eruptions similar in magnitude to the Chaitén 2008 and Askja 1875 events. Such eruptions would mainly produce pyroclastic fallout covering a minimum area of 1,700?km2 ESE of the volcano, where important touristic, agricultural and military activities are based. As for the 1995/1996 eruption, our field data indicate that complex wind patterns were critical in controlling the dispersion of the eruptive clouds, developing sheared, commonly bilobate plumes. 相似文献
120.
Unusually severe or prolonged drought ranks among the most devastating and calamitous of all extreme climate events, contributing
to wildfires, crop failure, livestock death, food shortages and famine. The response of human activities and the natural environment
to such historical weather perturbations provides a guide to where the most critical sensitivities to future climate changes
may lie (McCarthy et al., 2001, ‘Climatic change 2001: Impact adaptation, and vulnerability’, from 3rd Assesment Report of
IPCC). The reconstruction of regional climatic histories and investigations of the impacts of – and social response to – extreme
droughts in history are thus of crucial significance if we are to understand and anticipate the potential repercussions of
future events (Wigley, 1985, Nature 316, 106–107; Grove and Conterio, 1995, Clim. Change 30, 223).
Chihuahua, in the arid Northwest of Mexico, is one of the most seriously and frequently drought affected regions of the country
(Garcia, 2000, available at www.sequia.edu.mx/proyectos/vulnera.html). Prolonged drought in the 1930s, 1950s and 1990s contributed
to water scarcity, harvest failure, illness, livestock disease, abandonment and water conflict and served to highlight the
particular vulnerability of agrarian society in this region to climatic variability (Sandoval, 2003, Ingeneria Hidraulica en Mexico 18(2), 133–155). Recent investigations using tree ring analysis have identified several phases of such prolonged drought over
the last seven centuries. In this paper we use archival documents to investigate the impacts of such periods in late colonial
Chihuahua and to explore how society in the region responded to and coped with them. 相似文献