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991.
Rethinking the longitudinal stream temperature paradigm: region‐wide comparison of thermal infrared imagery reveals unexpected complexity of river temperatures 下载免费PDF全文
Aimee H. Fullerton Christian E. Torgersen Joshua J. Lawler Russell N. Faux E. Ashley Steel Timothy J. Beechie Joseph L. Ebersole Scott G. Leibowitz 《水文研究》2015,29(22):4719-4737
Prevailing theory suggests that stream temperature warms asymptotically in a downstream direction, beginning at the temperature of the source in the headwaters and levelling off downstream as it converges to match meteorological conditions. However, there have been few empirical examples of longitudinal patterns of temperature in large rivers due to a paucity of data. We constructed longitudinal thermal profiles (temperature vs distance) for 53 rivers in the Pacific Northwest (USA) using an extensive data set of remotely sensed summertime river temperatures and classified each profile into one of five patterns of downstream warming: asymptotic (increasing then flattening), linear (increasing steadily), uniform (not changing), parabolic (increasing then decreasing), or complex (not fitting other classes). We evaluated (1) how frequently profiles warmed asymptotically downstream as expected, and (2) whether relationships between river temperature and common hydroclimatic variables differed by profile class. We found considerable diversity in profile shape, with 47% of rivers warming asymptotically and 53% having alternative profile shapes. Water temperature did not warm substantially over the course of the river for coastal parabolic and uniform profiles, and for some linear and complex profiles. Profile classes showed no clear geographical trends. The degree of correlation between river temperature and hydroclimatic variables differed among profile classes, but there was overlap among classes. Water temperature in rivers with asymptotic or parabolic profiles was positively correlated with August air temperature, tributary temperature and velocity, and negatively correlated with elevation, August precipitation, gradient and distance upstream. Conversely, associations were less apparent in rivers with linear, uniform or complex profiles. Factors contributing to the unique shape of parabolic profiles differed for coastal and inland rivers, where downstream cooling was influenced locally by climate or cool water inputs, respectively. Potential drivers of shape for complex profiles were specific to each river. These thermal patterns indicate diverse thermal habitats that may promote resilience of aquatic biota to climate change. Without this spatial context, climate change models may incorrectly estimate loss of thermally suitable habitat. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
992.
In this study, uncertainty in model input data (precipitation) and parameters is propagated through a physically based, spatially distributed hydrological model based on the MIKE SHE code. Precipitation uncertainty is accounted for using an ensemble of daily rainfall fields that incorporate four different sources of uncertainty, whereas parameter uncertainty is considered using Latin hypercube sampling. Model predictive uncertainty is assessed for multiple simulated hydrological variables (discharge, groundwater head, evapotranspiration, and soil moisture). Utilizing an extensive set of observational data, effective observational uncertainties for each hydrological variable are assessed. Considering not only model predictive uncertainty but also effective observational uncertainty leads to a notable increase in the number of instances, for which model simulation and observations are in good agreement (e.g., 47% vs. 91% for discharge and 0% vs. 98% for soil moisture). Effective observational uncertainty is in several cases larger than model predictive uncertainty. We conclude that the use of precipitation uncertainty with a realistic spatio‐temporal correlation structure, analyses of multiple variables with different spatial support, and the consideration of observational uncertainty are crucial for adequately evaluating the performance of physically based, spatially distributed hydrological models. 相似文献
993.
The seismic behaviour of a wide variety of structures can be characterized by the rocking response of rigid blocks. Nevertheless, suitable seismic control strategies are presently limited and consist mostly on preventing rocking motion all together, which may induce undesirable stress concentrations and lead to impractical interventions. In this paper, we investigate the potential advantages of using supplemental rotational inertia to mitigate the effects of earthquakes on rocking structures. The newly proposed strategy employs inerters, which are mechanical devices that develop resisting forces proportional to the relative acceleration between their terminals and can be combined with a clutch to ensure their rotational inertia is only employed to oppose the motion. We demonstrate that the inclusion of the inerter effectively reduces the frequency parameter of the block, resulting in lower rotation seismic demands and enhanced stability due to the well-known size effects of the rocking behaviour. The effects of the inerter and inerter-clutch devices on the response scaling and similarity are also studied. An examination of their overturning fragility functions reveals that inerter-equipped structures experience reduced probabilities of overturning in comparison with uncontrolled bodies, while the addition of a clutch further improves their seismic stability. The concept advanced in this paper is particularly attractive for the protection of rocking bodies as it opens the possibility of nonlocally modifying the dynamic response of rocking structures without altering their geometry. 相似文献
994.
The links between entrance geometry,hypsometry and hydrodynamics in shallow tidally dominated basins
Peter J. de Ruiter Julia C. Mullarney Karin R. Bryan Christian Winter 《地球表面变化过程与地形》2019,44(10):1957-1972
Geomorphological characteristics of tidal basins control hydrodynamics and sediment transport potential within such basins, for example, by adjusting the balance in tidal asymmetry. In this study we examine the effects of entrance geometry on tidal velocity asymmetry, slack water asymmetry, bed shear stress patterns and hypsometric profile shapes by comparison of six shallow meso-tidal basins of Tauranga Harbour, New Zealand. Numerical model results show how tidal distortion increases with distance from a basin entrance. A simple ratio between basin width and entrance width defines levels of basin dilation. Sub-basins with a constricted geometry and deep entrance channels are associated with small bed shear stress values and high rates of flood-directed tidal velocity asymmetry in the sheltered basin centres, indicating a large potential for sediment deposition of larger particles. Moreover, slack water asymmetry within these basins is weakly ebb-directed, indicating a small potential for transport of fine sediments out of the basins. The constricted depositional basins are characterized by convex hypsometric profiles with elevated intertidal regions. Unconstricted geometries are associated with larger bed shear stress values and more ebb-directed tidal velocity asymmetry within basin centres, suggesting limited potential for overall sediment deposition. The slack tide duration asymmetry is weakly flood-dominant indicating that limited input of fine sediment into the basins is possible. The comparatively high-energy conditions within these exposed basins are associated with a less convex hypsometric intertidal profile. The ability to estimate tidal asymmetries is advantageous when developing management strategies related to ecosystem functioning, navigability or coastal protection in specific geomorphic settings. © 2019 John Wiley & Sons, Ltd. 相似文献
995.
Michel Ritz William L. Brown Christian Moreau Daniel Ohnenstetter 《Journal of Applied Geophysics》1996,34(4):229-236
Three radial audiomagnetotelluric (AMT) sounding profiles were carried out across the narrow, 65-km diameter troctolitic Meugueur-Meugueur ring structure, central Aïr, Niger, to study its electrical configuration; one profile extended across the bedrock into the large Ofoud complex situated slightly off geographical centre within the ring. Apparent resistivity data from 27 sites ranged from isotropic to strongly anisotropic. In nearly all soundings, one- and two-dimensional modelling indicated the presence of a major zone of low resistivity (60–600 Ωm), about 200 m thick, dipping steeply inwards at an angle of 65–80° and extending to a depth of at least 2–5 km. This layer, overlain and underlain by rocks of higher resistivities in excess of 5000 Ωm, is taken to be the outer contact. A highly resistive body, about 200 m in width, dipping inwards to a depth of at least 4 km is taken to be the Meugueur-Meugueur intrusion, which is thus interpreted to be a cone sheet. 相似文献
996.
On the potential of plant species invasion influencing bio‐geomorphologic landscape formation in salt marshes 下载免费PDF全文
Christian Schwarz Tom Ysebaert Wouter Vandenbruwaene Stijn Temmerman LiQuan Zhang Peter M. J. Herman 《地球表面变化过程与地形》2016,41(14):2047-2057
Species invasions are known to change biotic and abiotic ecosystem characteristics such as community structure, cycling of materials and dynamics of rivers. However, their ability to alter interactions between biotic and abiotic ecosystem components, in particular bio‐geomorphic feedbacks and the resulting landscape configuration in tidal wetlands, such as tidal channels have not yet been demonstrated. We studied the impact of altered bio‐geomorphic feedbacks on geomorphologic features (i.e. tidal wetland channels), by comparing proxies for channel network geometry (unchanneled flow lengths, fractal dimension) over time between non‐invaded and invaded salt marsh habitats. The non‐invaded habitats (the south of eastern Chongming Island, Yangtze estuary, China) show little change in network geometry over time with a tendency for an increased drainage density. The invaded site (salt marshes in the north of eastern Chongming Island invaded by the exotic plant species Spartina alterniflora) showed a decreasing tendency in channel drainage density throughout and after the species invasion. This suggests that species invasions might not only affect biotic ecosystem characteristics, but also their ability to change bio‐geomorphic feedback loops, potentially leading to changes in existing geomorphologic features and therefore landscape configuration. Our results further suggest that the species invasion also altered sediment composition. Based on observations we propose a mechanism explaining the change in channel drainage density by an alteration in plant properties. The physical and physiological characteristics of the invading species Spartina alterniflora clearly differ from the native species Scirpus mariqueter, inducing different bio‐geomorphic feedback loops leading to the observed change in salt marsh channel configuration. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
997.
998.
Pumping test in a confined aquifer under tidal influence 总被引:2,自引:0,他引:2
In a coastal environment, tide-induced head fluctuations can complicate the interpretation of drawdown data from pumping tests. For confined aquifers and sinusoidal tides, the superposition principle can be used to obtain a closed-form solution. After subtracting the net tidal effects, the drawdown data become amenable to the standard analyses. Numerical simulations have shown that the method is reliable when the distance of the monitoring well to the well does not exceed 10% of the distance between the well and the tidal boundary. 相似文献
999.
Mercury flux to estuarine sediments, derived from Pb-210 and Cs-137 geochronologies (Guaratuba Bay, Brazil) 总被引:1,自引:0,他引:1
A sediment core from Guaratuba Bay was used to indicate possible Hg modifications to this coastal environment brought about by growing agricultural activity. Sedimentation rates were estimated to be 6.1 mm/year and 5.2 mm/year through 210Pb and 137Cs geochronologies, respectively. Mercury concentrations and organic matter ratios in the surface layers are greater than in the older sediments, supporting the hypothesis of anthropogenic enrichment. Results show that the Hg flux has raised more than twofold during the second half of the 20th century. These results point to the need for further studies to substantiate the hypothesis of anthropogenic enrichment and to quantify point sources of Hg to this estuary. 相似文献
1000.
Jens Christian Refsgaard Jeroen P. van der Sluijs James Brown Peter van der Keur 《Advances in water resources》2006
Although uncertainty about structures of environmental models (conceptual uncertainty) is often acknowledged to be the main source of uncertainty in model predictions, it is rarely considered in environmental modelling. Rather, formal uncertainty analyses have traditionally focused on model parameters and input data as the principal source of uncertainty in model predictions. The traditional approach to model uncertainty analysis, which considers only a single conceptual model, may fail to adequately sample the relevant space of plausible conceptual models. As such, it is prone to modelling bias and underestimation of predictive uncertainty. 相似文献