Decadal-scale changes in suspended wood after riparian recruitment in managed stands in headwater streams of coastal British Columbia,Canada     

Felipe Rossetti de Paula  John S. Richardson  Alex C.Y. Yeung  Stephen J. Mitchell  Devesh Bahuguna 《地球表面变化过程与地形》2020,45(9):1974-1989

Large wood (LW) affects several ecological and hydrogeomorphic processes in streams. The main source of LW is riparian trees falling inside channels. However, in confined valley floors, falling trees are more likely to be suspended above the channel. Eventually, these suspended trees will decompose and break to finally fall into the channel to better provide functions for streams. We evaluated changes in wood decay, length, diameter, and suspended status (suspended or non-suspended) 17 years post-harvest and nine years after the first sampling occurred in 2006 in 12 headwater streams of coastal British Columbia, Canada. We also evaluated whether changes differed among riparian management treatments (no-harvest buffers of 10 and 30 m in width, thinning, and unharvested reference sites), and identified the factors affecting wood changes and suspended status. Wood pieces advanced in decay, became shorter, and 34% of them (n = 108) changed status from suspended to non-suspended. Non-suspended wood pieces were more decayed and shorter than suspended wood. Suspended wood was longer, thicker, less decayed, and represented 46.5% (n = 147) of the wood sampled in 2006. Our findings revealed limited influences of riparian management on many aspects of wood changes considered in this study. Changes in wood characteristics were more likely for pieces that were smaller in diameter, longer, and suspended closer to the water. The transition from suspended to non-suspended LW can be a long-term process that can increase wood residence time and reduce LW in-stream functions particularly in confined stream valleys. The suspended stage is also an important mechanism underlying time lags in stream ecosystem responses to riparian tree fall. © 2020 John Wiley & Sons, Ltd.  相似文献   

Forecasting annual precipitation to improve the operation of dams in the Comahue region,Argentina     

Paula Elisa Romero  Alfredo Luis Rolla  Fernando Losano 《水文科学杂志》2020,65(11):1974-1983

ABSTRACT

This paper attempts to design statistical models to forecast annual precipitation in the Neuquen and Limay river basins in the Comahue region of Argentina. These forecasts are especially useful as they are used to better organize the operation of hydro-electric dams, the agriculture in irrigated valleys and the safety of the population. In this work, multiple linear regression statistical models are built to forecast mean annual rainfall over the two river basins. Since the maximum precipitation occurs in the winter (June–August), forecasting models have been developed for the beginning of March and for the beginning of June, just before the rainy season starts. The results show that the sea-surface temperatures of the Indian and Pacific oceans are good predictors for March models and explain 42.8% of the precipitation index variance. The efficiency of the models increases in June, adding more predictors related to the autumn circulation.  相似文献   

The interplay between the viscosity and EUV radiation on the dispersal of protoplanetary discs     

J. C. Vallejo  A. I. Gómez de Castro 《Astrophysics and Space Science》2018,363(12):246

A key issue in the evolution of protostellar discs is the analysis of the mechanisms by which the disc is eventually dispersed and the time-scales involved in this process. The photoevaporation is very likely an important process in dispersing discs material and for explaining the observational time-scales needed for reaching a discless status. We analyze the role of the EUV radiation on a variety of disc models when different viscosity values are used. Our analysis focus on the changes of different diagnostic indicators commonly used for comparison of discs models and observed systems.  相似文献   

Artificial intelligence applied to floating boom behavior under waves and currents     

G. Iglesias  A. Castro  J.A. Fraguela 《Ocean Engineering》2010,37(17-18):1513-1521

Floating containment booms are an essential device in the fight against coastal pollution, allowing to contain the pollutant prior to its recovery. An Artificial Intelligence model is developed with the focus on the effective draft, or draft available for containment that a floating boom will provide in open waters. The dataset is obtained through an extensive laboratory campaign in which seven model booms are subjected to numerous wave and current combinations. This dataset is randomly divided into two subsets, one for training, the other for testing or validating the model. Input and output variables are selected based on dimensional analysis and laboratory results. The AI technique chosen for the model is multilayer feedforward artificial neural networks trained with the back-propagation algorithm, for their capability to apprehend higher-order patterns from the training examples and subsequently generalize them to other (validation) cases. In order to find an efficient network architecture, a comparative study involving 640 neural networks is carried out. Having selected the best performing architecture, the model is successfully validated; it is a virtual laboratory allowing to determine the effective draft that a certain boom design will provide under given wave and current conditions.  相似文献   

Photoionization of cool MHD disk winds     

A.I. Gómez de Castro  C. Ferro-Fontán 《Astrophysics and Space Science》2003,287(1-4):31-34

Recent ultraviolet observations point out that there is hot, dense plasma associated with the optical jet in some T Tauri stars. In this contribution, cool MHD disk wind physics is reviewed by means of a self-similar analytical model to analyze whether hot (Te ? 80,000 K) and dense (n_e ? 10⁹ cm^-3) plasma can be produced in disk winds. It is shown that these high densities can only be achieved at the base of the wind where the stellar X-rays radiation field is strong. The propagation of the X-rays radiation through the disk wind is analyzed: a cocoon of photoionized gas is generated around the star. However, it is difficult to foresee how temperatures as high as ～ 5 × 10⁴ can be reached unless a significant fraction of the X-rays radiation is produced by magnetic reconnection at the boundary between the stellar magnetosphere and the accretion disk.  相似文献   

Anurans from the Candeleros Formation (?Cenomanian-Turonian) of west-central Argentina: new evidence for pipoid evolution     

Ana M. Bez  Paula Muzzopappa  Laura Nicoli 《Cretaceous Research》2007,28(6):1005-1016

The fluvio-lacustrine deposits of the ?Cenomanian-Turonian Candeleros Formation in the northwestern fringe of Patagonia have yielded numerous remains of vertebrates, including anurans. A new, partially articulated immature specimen of a small pipimorph pipoid from the upper part of this unit is described herein. Although incompletely preserved, the morphology and proportions of the skeleton are strongly reminiscent of corresponding elements of the holotype of Avitabatrachus uliana from the lower section of the same formation at a nearby locality, thus suggesting that these specimens might represent the same, or a closely related, taxon. The new specimen is a metamorphosing individual: it has a zygapophyseal articulation between the sacrum and the neural arch of a postsacral vertebra that bears conspicuous transverse processes, and four pairs of ribs. These traits are not present in the available material of A. uliana, but they might have occurred within the normal range of variation of a single species. Although the generic and specific allocation of the new material is uncertain, a parsimony analysis performed to clarify the relationships of A. uliana supports a phylogenetic placement of this taxon outside the crown Pipidae. The evidence provided by the Candeleros anurans confirms the presence of stem pipids in Patagonia in the early Late Cretaceous.  相似文献   

Net aboveground primary production and soil properties of floating and attached freshwater tidal marshes in the Río de la Plata estuary,Argentina     

Paula Pratolongo  Patricia Kandus  Mark M. Brinson 《Estuaries and Coasts》2007,30(4):618-626

In the lower delta of the Paraná River, at the head of the Río de la Plata estuary (Argentina), we compared net aboveground primary production (NAPP) and soil properties of the dominant macrophyteScirpus giganteus (Kunth) in a floating and an attached marsh community. Both marshes are tidally influenced but in different ways. The floating marsh site is relatively isolated from tidal influences because its ability to float makes it resistant to overland flow and to sediment inputs from the estuary. The attached marsh lacks the capacity to float and receives sediment supplies from the estuary through overland flow. These hydrologic differences are reflected in lower mineral content in sediments of the floating marsh. Using a leaf tagging technique, estimated NAPP was 1,109 ± 206 g m⁻² yr⁻¹ for the floating marsh and 1,866 ±258 g m⁻² yr⁻¹ for the attached marsh. We attribute the lower NAPP of the floating marsh to isolation from sediment input from overland flow.  相似文献   

Effects of local site and building parameters on damage distribution in Angra do Heroísmo—Azores     

Paula Teves-Costa  Carlos S. Oliveira  M. Luisa Senos 《Soil Dynamics and Earthquake Engineering》2007,27(11):986-999

During the M_w=6.9 January 1, 1980 earthquake in the Azores, the damage distribution in the town of Angra do Heroísmo, in Terceira Island, had a non-homogeneous spatial character. In order to understand the observed pattern of damage a microtremor survey was carried out, using ambient vibrations, and the data were analysed with the J-Sesame software, following the H/V Nakamura methodology. The results are in good agreement with the surface geology and they show a good correlation with the observed damages. Two building surveys were performed, in 1980 on damage evaluation and in 2000 on characterization of few building parameters. With all these elements (surface geology type, soil peak frequency, building type, number of stories and damage level) for 2111 buildings it was possible to perform several interparameter analysis, which enabled the identification of indicators that could be used to improve the damage estimation for future events.  相似文献   

On the individual calibration of hailpads     

Covadonga Palencia  Claude Berthet  Marta Massot  Amaya Castro  Jean Dessens  Roberto Fraile   《Atmospheric Research》2007,83(2-4):493-504

This paper is a comparative study between the two most common hailpad calibration systems: one annual calibration of a whole consignment of material, and the individual calibration of each plate after a hailfall. Individual calibration attempts to minimize errors due to differences in sensitivity to the impact of hailstones between plates from the same consignment, or due to differences in the inking process before the actual measurement.The comparison was carried out using calibration data from the past few years in the hailpad network in south-western France, and data from an individual calibration process on material provided by the hailpad network in Lleida (Spain). The same type of material was used in the two cases.The results confirm that the error in measuring hailstone sizes is smaller in the case of an individual calibration of hailpads than when one single calibration process was carried out for a whole consignment. The former is approximately 80% of the latter. However, this error could have been higher if it had not been the same person carrying out the single calibration process and the measuring of the dents: it has been found that differences in the inking process may account for up to 20% of the error in the case of small hailstones. Calibration errors affecting other variables, e.g. energy or parameter λ of the exponential size distribution are generally higher (5% and 18%, respectively) than errors due to the spatial variability of the hailstones. However, the calibration method does not influence the maximum size, since the relative error attributed to the spatial variability is about 8 times the calibration error.In conclusion, if errors in determining energy or parameter λ are to be reduced to a minimum, it is highly advisable to be consistent in applying the measuring procedure (if possible with the same person carrying out the measurements all the time), and even to use individual calibration on each plate, always bearing in mind that technicians have to be trained appropriately in order to achieve the highest possible degree of uniformity.  相似文献   

The use of a climate-type classification for assessing climate change effects in Europe from an ensemble of nine regional climate models     

M. de Castro  C. Gallardo  K. Jylha  H. Tuomenvirta 《Climatic change》2007,81(1):329-341

Making use of the Köppen–Trewartha (K–T) climate classification, we have found that a set of nine high-resolution regional climate models (RCM) are fairly capable of reproducing the current climate in Europe. The percentage of grid-point to grid-point coincidences between climate subtypes based on the control simulations and those of the Climate Research Unit (CRU) climatology varied between 73 and 82%. The best agreement with the CRU climatology corresponds to the RCM “ensemble mean”. The K–T classification was then used to elucidate scenarios of climate change for 2071–2100 under the SRES A2 emission scenario. The percentage of land grid-points with unchanged K–T subtypes ranged from 41 to 49%, while those with a shift from the current climate subtypes towards warmer or drier ones ranged from 51 to 59%. As a first approximation, one may assume that in regions with a shift of two or more climate subtypes, ecosystems might be at risk. Excluding northern Scandinavia, such regions were projected to cover about 12% of the European land area.  相似文献