Hillslope response under variable microclimate     

Netra R. Regmi  Eric V. McDonald  Craig Rasmussen 《地球表面变化过程与地形》2019,44(13):2615-2627

Solar radiation-controlled microclimatic variation has been considered a major force on hillslope evolution via feedback among geomorphology, vegetation, soil and hydrology. In this study, we investigate the influence of solar radiation on hillslope dynamics on Santa Catalina Island, CA by comparing hillslope morphology and frequency–magnitude relationships of shallow landslides, rills and gullies on slopes receiving low annual solar radiation (LSR) and high annual solar radiation (HSR), which were found equivalent to north- and south-facing slopes, respectively. LSR slopes on Santa Catalina Island were found more vegetated compared to HSR slopes. LiDAR elevation-derived hillslope morphology showed LSR slopes steeper, rougher and more concave than HSR slopes. Similarly, frequency–magnitude plots showed larger relative frequency of high-magnitude shallow landslides, rills and gullies on LSR slopes, and low-magnitude shallow landslides, rills and gullies on HSR slopes. We argue that the morphology, mass movement and erosion characteristics of LSR and HSR slopes reflect the process–response of microclimate-controlled variation in type and density of vegetation cover, soil physical properties – including moisture, texture, structure, infiltration and erodibility – and surface and subsurface hydrology. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.  相似文献   

A Coupled Groundwater–Surface Water Modeling Framework for Simulating Transition Zone Processes          下载免费PDF全文

Pradeep Mugunthan  Kevin T. Russell  Binglei Gong  Michael J. Riley  Arthur Chin  Blair G. McDonald  Linda J. Eastcott 《Ground water》2017,55(3):302-315

There is an identified need for fully representing groundwater–surface water transition zone (i.e., the sediment zone that connects groundwater and surface water) processes in modeling fate and transport of contaminants to assist with management of contaminated sediments. Most existing groundwater and surface water fate and transport models are not dynamically linked and do not consider transition zone processes such as bioturbation and deposition and erosion of sediments. An interface module is developed herein to holistically simulate the fate and transport by coupling two commonly used models, Environmental Fluid Dynamics Code (EFDC) and SEAWAT, to simulate surface water and groundwater hydrodynamics, while providing an enhanced representation of the processes in the transition zone. Transition zone and surface water contaminant processes were represented through an enhanced version of the EFDC model, AQFATE. AQFATE also includes SEDZLJ, a state‐of‐the‐science surface water sediment transport model. The modeling framework was tested on a published test problem and applied to evaluate field‐scale two‐ and three‐dimensional contaminant transport. The model accurately simulated concentrations of salinity from a published test case. For the field‐scale applications, the model showed excellent mass balance closure for the transition zone and provided accurate simulations of all transition zone processes represented in the modeling framework. The model predictions for the two‐dimensional field case were consistent with site‐specific observations of contaminant migration. This modeling framework represents advancement in the simulation of transition zone processes and can help inform risk assessment at sites where contaminant sources from upland areas have the potential to impact sediments and surface water.  相似文献   

Lithological controls on hillslope sediment supply: insights from landslide activity and grain size distributions   总被引：1，自引：0，他引：1       下载免费PDF全文

Duna C. Roda‐Boluda  Mitch D'Arcy  Jordan McDonald  Alexander C. Whittaker 《地球表面变化过程与地形》2018,43(5):956-977

The volumes, rates and grain size distributions of sediment supplied from hillslopes represent the initial input of sediment delivered from upland areas and propagated through sediment routing systems. Moreover, hillslope sediment supply has a significant impact on landscape response time to tectonic and climatic perturbations. However, there are very few detailed field studies characterizing hillslope sediment supply as a function of lithology and delivery process. Here, we present new empirical data from tectonically‐active areas in southern Italy that quantifies how lithology and rock strength control the landslide fluxes and grain size distributions supplied from hillslopes. Landslides are the major source of hillslope sediment supply in this area, and our inventory of ~2800 landslides reveals that landslide sediment flux is dominated by small, shallow landslides. We find that lithology and rock strength modulate the abundance of steep slopes and landslides, and the distribution of landslide sizes. Outcrop‐scale rock strength also controls the grain sizes supplied by bedrock weathering, and influences the degree of coarsening of landslide supply with respect to weathering supply. Finally, we show that hillslope sediment supply largely determines the grain sizes of fluvial export, from catchments and that catchments with greater long‐term landslide rates deliver coarser material. Therefore, our results demonstrate a dual control of lithology on hillslope sediment supply, by modulating both the sediment fluxes from landslides and the grain sizes supplied by hillslopes to the fluvial system. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Soil macroporosity and infiltration characteristics of a forest podzol     

J. M. Buttle  D. J. McDonald 《水文研究》2000,14(5):831-848

Spatial distribution of soil macroporosity was determined for a forest podzol from tension infiltrometer measurements at the soil surface. Surface‐derived macroporosity values were compared with point infiltration characteristics obtained from soil water content and soil water chemistry measurements during an experimental irrigation, and with parameters of a kinematic wave model applied to soil water content data. Macroporosity estimated by the tension infiltrometer ranged from 0·00087 to 0·0219% of soil volume, and infiltration at these two sites was dominated by propagation of a well‐defined wetting front through the soil profile and bypass flow via soil macropores, respectively. Infiltration at sites with intermediate macroporosities reflected a combination of these two processes, although results were inconclusive at one site owing to lateral flow at the base of the soil profile. There was no agreement between macroporosities estimated by the tension infiltrometer and the kinematic wave model. The maximum soil conductance parameter within the profile at a site, however, was related directly to the surface‐derived macroporosity. The partial agreement between surface‐derived macroporosity estimates and point infiltration characteristics shown here supports the use of tension infiltrometry as a rapid, non‐destructive method of assessing spatial variations in the relative contribution of macropore flow to the infiltration process. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

Geochemistry of a confirmed Precambrian impact ejecta deposit: The Grænsesø spherule layer,South Greenland     

Matthew S. Huber  Christian Koeberl  Frank C. Smith  Billy P. Glass  Roland Mundil  Iain McDonald 《Meteoritics & planetary science》2019,54(10):2254-2272

Samples from a single outcrop of the Graenseso spherule layer, Midternaes, South Greenland, consist of a spherule‐bearing dolomixtite with matrix‐supported intraclasts up to 1 m in size. In addition to field observations, we performed mineralogical and whole rock geochemical analysis, including electron microprobe, neutron activation analysis, X‐ray fluorescence, and mass spectrometry of the horizon and the overlying and underlying strata. We show that the spherules are petrographically similar to those in the Zaonega spherule layer, Karelia, Russia. Our petrographic and chemical results are consistent with the previous suggestion that the Grænsesø layer correlates with the Zaonega layer, and it is possible that both layers are related to the Vredefort impact event. The samples containing spherules, as well as the overlying rocks, have elevated REEs compared to the underlying pre‐impact layer, suggestive of a new continental source of sediment that may be coincident with the impact event. Zircons separated from the lower part of the Grænsesø spherule layer display complex age patterns suggesting that they have genetically different origins based on distinctly different Th/U ratios. Crystallization ages of all groups are ≥ 2.8 Ga, with ~2.8 Ga representing a time of major crustal growth globally. Therefore, we cannot conclusively determine in this study if the zircons are locally derived or if they are transported with the ejecta. The spherule layer was deposited by a high‐energy, subaqueous debris flow, an origin that is consistent with the hypothesis that the layer was deposited by impact‐induced waves and/or currents.  相似文献   

Studies of a regulated dryland river: surface–groundwater interactions     

Alyson K. McDonald  Zhuping Sheng  Charles R. Hart  Bradford P. Wilcox 《水文研究》2013,27(12):1819-1828

Unlike rivers in humid regions, dryland rivers typically exhibit reduced flow in the downstream direction as a result of transmission losses, which include seepage of streamflow into the aquifer, evaporation, and transpiration. However, much remains to be learned about the nature of the exchange between surface water and groundwater in these landscapes, especially in terms of spatial and temporal variability. Our study focused on streambank seepage and groundwater flow in the alluvial aquifer, specifically on answering questions such as: Is there seasonal variability in seepage losses? Is seepage permanently lost? Can losses be reduced by killing riparian vegetation? To better understand the magnitude, variability, and fate of streambank seepage, we assessed river stages, groundwater hydraulic gradients, and groundwater flow paths at two sites along a reach of the Pecos River, a dryland perennial river in West Texas. We found that along this reach the river was losing water to the aquifer even under low‐flow conditions; but seepage was controlled by a number of different mechanisms. Seepage increased not only during high‐flow events but also when the groundwater level was declining owing to long periods of no irrigation release. Tamarix (saltcedar) control did not affect hydraulic gradients nor reduce streambank seepage and given that this reach of the Pecos River is a losing one, streamflow will not be enhanced by controlling saltcedar. These findings can be used to improve basic conceptual models of dryland river systems and to predict hydrologic responses to changes in the timing and magnitude of streamflows and to riparian vegetation management. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Platinum-group minerals in the Limoeiro Ni–Cu–(PGE) sulfide deposit,Brazil: the effect of magmatic and upper amphibolite to granulite metamorphic processes on PGM formation     

J. Mota-e-Silva  H. M. Prichard  C. F. Ferreira Filho  P. C. Fisher  I. McDonald 《Mineralium Deposita》2015,50(8):1007-1029

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Intrinsic bioremediation of a petroleum-impacted wetland   总被引：4，自引：0，他引：4  

Mills MA  Bonner JS  McDonald TJ  Page CA  Autenrieth RL 《Marine pollution bulletin》2003,46(7):887-899

Following the 1994 San Jacinto River flood and oil spill in southeast Texas, a petroleum-contaminated wetland was reserved for a long-term research program to evaluate bioremediation as a viable spill response tool. The first phase of this program, presented in this paper, evaluated the intrinsic biodegradation of petroleum in the contaminated wetland. Sediment samples from six test plots were collected 11 times over an 11-month period to assess the temporal and spatial petroleum concentrations. Petroleum concentrations were evaluated using gas chromatography-mass spectrometer analyses of specific target compounds normalized to the conservative biological marker, C(30)17alpha,21beta(H)-hopane. The analyses of specific target compounds were able to characterize that significant petroleum biodegradation had occurred at the site over the one-year period. Total resolved saturate and total resolved aromatic hydrocarbon data indicated the petroleum was degraded more than 95%. In addition, first-order biodegradation rate constants were calculated for the hopane-normalized target compounds and supported expected biodegradation patterns. The rapid degradation rates of the petroleum hydrocarbons are attributed to conditions favorable to biodegradation. Elevated nutrient levels from the flood deposition and the unconsolidated nature of the freshly deposited sediment possibly provided a nutrient rich, oxic environment. Additionally, it is suggested that an active and capable microbial community was present due to prior exposure to petroleum. These factors provided an environment conducive for the rapid bioremediation of the petroleum in the contaminated wetland.  相似文献   

Principal component analysis and neural networks for detection of amino acid biosignatures     

Evan D. Dorn  Gene D. McDonald  Kenneth H. Nealson 《Icarus》2003,166(2):403-409

We examine the applicability of Principal Component Analysis (PCA) and Artificial Neural Network (ANN) methods of data analysis to biosignature detection. These techniques show promise in classifying and simplifying the representation of patterns of amino acids resulting from biological and non-biological syntheses. PCA correctly identifies glycine and alanine as the amino acids contributing the most information to the task of discriminating biotic and abiotic samples. Trained ANNs correctly classify between 86.1 and 99.5% of a large set of amino acid samples as biotic or abiotic. These and similar techniques are important in the design of automated data analysis systems for robotic missions to distant planetary bodies. Both techniques are robust with respect to noisy and incomplete data. Analysis of the performance of PCA and ANNs also lends insight into the localization of useful information within a particular data set, a feature that may be exploited in the selection of experiments for efficient mission design.  相似文献   

Clearwater East impact structure: A re‐interpretation of the projectile type using new platinum‐group element data from meteorites     

Iain McDonald 《Meteoritics & planetary science》2002,37(3):459-464

Abstract— Platinum‐group element (PGE) concentrations and ratios obtained from samples of the Clearwater East impact melt have been used along with other siderophile element ratios to classify the impacting projectile as a carbonaceous chondrite. This is at odds with recent chromium isotope analyses that suggest ordinary chondrite‐type material is present. The present study reviews and reinterprets the available PGE data in the light of new PGE data from meteorites and concludes that the PGE ratios in the impact melt are most consistent with ordinary (possibly type‐L) chondrite source material, not carbonaceous chondrites. Therefore the structure was most probably formed by the impact of an asteroid composed of material similar to ordinary chondrites.  相似文献