Seasonal connections between meteoric water and streamflow generation along a mountain headwater stream     

Sam J. Leuthold  Stephanie A. Ewing  Robert A. Payn  Florence R. Miller  Stephan G. Custer 《水文研究》2021,35(2):e14029

In snowmelt-driven mountain watersheds, the hydrologic connectivity between meteoric waters and stream flow generation varies strongly with the season, reflecting variable connection to soil and groundwater storage within the watershed. This variable connectivity regulates how streamflow generation mechanisms transform the seasonal and elevational variation in oxygen and hydrogen isotopic composition (δ¹⁸O and δD) of meteoric precipitation. Thus, water isotopes in stream flow can signal immediate connectivity or more prolonged mixing, especially in high-relief mountainous catchments. We characterized δ¹⁸O and δD values in stream water along an elevational gradient in a mountain headwater catchment in southwestern Montana. Stream water isotopic compositions related most strongly to elevation between February and March, exhibiting higher δ¹⁸O and δD values with decreasing elevation. These elevational isotopic lapse rates likely reflect increased connection between stream flow and proximal snow-derived water sources heavily subject to elevational isotopic effects. These patterns disappeared during summer sampling, when consistently lower δ¹⁸O and δD values of stream water reflected contributions from snowmelt or colder rainfall, despite much higher δ¹⁸O and δD values expected in warmer seasonal rainfall. The consistently low isotopic values and absence of a trend with elevation during summer suggest lower connectivity between summer precipitation and stream flow generation as a consequence of drier soils and greater transpiration. As further evidence of intermittent seasonal connectivity between the stream and adjacent groundwaters, we observed a late-winter flush of nitrate into the stream at higher elevations, consistent with increased connection to accumulating mineralized nitrogen in riparian wetlands. This pattern was distinct from mid-summer patterns of nitrate loading at lower elevations that suggested heightened human recreational activity along the stream corridor. These observations provide insights linking stream flow generation and seasonal water storage in high elevation mountainous watersheds. Greater understanding of the connections between surface water, soil water and groundwater in these environments will help predict how the quality and quantity of mountain runoff will respond to changing climate and allow better informed water management decisions.  相似文献   

Modelling the effect of changing precipitation inputs on deep soil water utilization          下载免费PDF全文

Ji Qi  Daniel Markewitz  David Radcliffe 《水文研究》2018,32(5):672-686

Forests in the Southeastern United States are predicted to experience future changes in seasonal patterns of precipitation inputs as well as more variable precipitation events. These climate change‐induced alterations could increase drought and lower soil water availability. Drought could alter rooting patterns and increase the importance of deep roots that access subsurface water resources. To address plant response to drought in both deep rooting and soil water utilization as well as soil drainage, we utilize a throughfall reduction experiment in a loblolly pine plantation of the Southeastern United States to calibrate and validate a hydrological model. The model was accurately calibrated against field measured soil moisture data under ambient rainfall and validated using 30% throughfall reduction data. Using this model, we then tested these scenarios: (a) evenly reduced precipitation; (b) less precipitation in summer, more in winter; (c) same total amount of precipitation with less frequent but heavier storms; and (d) shallower rooting depth under the above 3 scenarios. When less precipitation was received, drainage decreased proportionally much faster than evapotranspiration implying plants will acquire water first to the detriment of drainage. When precipitation was reduced by more than 30%, plants relied on stored soil water to satisfy evapotranspiration suggesting 30% may be a threshold that if sustained over the long term would deplete plant available soil water. Under the third scenario, evapotranspiration and drainage decreased, whereas surface run‐off increased. Changes in root biomass measured before and 4 years after the throughfall reduction experiment were not detected among treatments. Model simulations, however, indicated gains in evapotranspiration with deeper roots under evenly reduced precipitation and seasonal precipitation redistribution scenarios but not when precipitation frequency was adjusted. Deep soil and deep rooting can provide an important buffer capacity when precipitation alone cannot satisfy the evapotranspirational demand of forests. How this buffering capacity will persist in the face of changing precipitation inputs, however, will depend less on seasonal redistribution than on the magnitude of reductions and changes in rainfall frequency.  相似文献   

Jurassic igneous rocks of the central Sanandaj–Sirjan zone (Iran) mark a propagating continental rift,not a magmatic arc     

Hossein Azizi  Robert J. Stern 《地学学报》2019,31(5):415-423

Jurassic igneous bodies of the Sanandaj–Sirjan zone (SaSZ) in SW Iran are generally considered as a magmatic arc but critical evaluation of modern geochronology, geochemistry and radiogenic isotopes challenges this conclusion. There is no evidence for sustained igneous activity along the ~1,200 km long SaSZ, as expected for a convergent plate margin; instead activity was brief at most sites and propagated NW at ~20 mm/a. Jurassic igneous rocks define a bimodal suite of gabbro‐diorite and granite. Chemical and isotopic compositions of mafic rocks indicate subcontinental lithospheric mantle sources that mostly lacked subduction‐related modifications. The arc‐like features of S‐type granites reflect massive involvement of Cadomian crust and younger sediments to generate felsic melts in response to mafic intrusions. We conclude that Jurassic SaSZ igneous activity occurred in a continental rift, not an arc. SaSZ igneous rocks do not indicate that subduction along the SW margin of Eurasia began in Jurassic time.  相似文献   

HP special issue: Canadian geophysical union 2016          下载免费PDF全文

William Quinton  Daniel L. Peters 《水文研究》2018,32(4):459-461

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Wetlands and low-gradient topography are associated with longer hydrologic transit times in Precambrian Shield headwater catchments     

Daniel Lane  Colin P.R. McCarter  Murray Richardson  Chris McConnell  Tim Field  Huaxia Yao  George Arhonditsis  Carl P.J. Mitchell 《水文研究》2020,34(3):598-614

The estimation of hydrologic transit times in a catchment provides insights into the integrated effects of water storage, mixing dynamics, and runoff generation processes. There has been limited effort to estimate transit times in southern boreal Precambrian Shield landscapes, which are characteristically heterogeneous with surface cover including till, thin soils, bedrock outcrops, and depressional wetland features that play contrasting hydrologic roles. This study presents approximately 3.5 years of precipitation and streamflow water isotope data and estimates mean transit times (MTTs) and the young water fraction (p_y) across six small catchments in the Muskoka-Haliburton region of south-central Ontario. The main objectives were to define a typical range of MTTs for headwater catchments in this region and to identify landscape variables that best explain differences in MTTs/p_y using airborne light detection and ranging and digital terrain analysis. Of the transit time distributions, the two parallel linear reservoir and gamma distributions best describe the hydrology of these catchments, particularly because of their ability to capture more extreme changes related to events such as snowmelt. The estimated MTTs, regardless of the modelling approach or distribution used, are positively associated with the percent wetland area and negatively with mean slope in the catchments. In this landscape, low-gradient features such as wetlands increase catchment scale water storage when antecedent conditions are dryer and decrease transit times when there is a moisture surplus, which plausibly explains the increases in MTTs and mean annual runoff from catchments with significant coverage of these landscape features.  相似文献   

In Situ Remediation of Contaminated Ground Water: The Funnel-and-Gate System   总被引：6，自引：0，他引：6  

Robert C. Starr  John A. Cherry 《Ground water》1994,32(3):465-476

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What the Sunspot Record Tells Us About Space Climate   总被引：1，自引：0，他引：1  

David H. Hathaway  Robert M. Wilson 《Solar physics》2004,224(1-2):5-19

The records concerning the number, sizes, and positions of sunspots provide a direct means of characterizing solar activity over nearly 400 years. Sunspot numbers are strongly correlated with modern measures of solar activity including: 10.7-cm radio flux, total irradiance, X-ray flares, sunspot area, the baseline level of geomagnetic activity, and the flux of galactic cosmic rays. The Group Sunspot Number provides information on 27 sunspot cycles, far more than any of the modern measures of solar activity, and enough to provide important details about long-term variations in solar activity or “Space Climate.” The sunspot record shows: 1) sunspot cycles have periods of 131± 14 months with a normal distribution; 2) sunspot cycles are asymmetric with a fast rise and slow decline; 3) the rise time from minimum to maximum decreases with cycle amplitude; 4) large amplitude cycles are preceded by short period cycles; 5) large amplitude cycles are preceded by high minima; 6) although the two hemispheres remain linked in phase, there are significant asymmetries in the activity in each hemisphere; 7) the rate at which the active latitudes drift toward the equator is anti-correlated with the cycle period; 8) the rate at which the active latitudes drift toward the equator is positively correlated with the amplitude of the cycle after the next; 9) there has been a significant secular increase in the amplitudes of the sunspot cycles since the end of the Maunder Minimum (1715); and 10) there is weak evidence for a quasi-periodic variation in the sunspot cycle amplitudes with a period of about 90 years. These characteristics indicate that the next solar cycle should have a maximum smoothed sunspot number of about 145 ± 30 in 2010 while the following cycle should have a maximum of about 70 ± 30 in 2023.  相似文献   

The baryonic mass–velocity relation: clues to feedback processes during structure formation and the cosmic baryon inventory     

Lucio Mayer  Ben Moore 《Monthly notices of the Royal Astronomical Society》2004,354(2):477-484

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Evidence in a glassy cosmic spherule from Antarctica for grazing incidence encounters with the Earth's atmosphere     

Matthew J. GENGE  Monica M. GRADY  Robert HUTCHISON 《Meteoritics & planetary science》1996,31(5):627-632

Abstract— Cosmic dust accreted by the Earth can be extensively reprocessed during atmospheric encounters. The textures and compositions of reprocessed material provide important constraints by which the processes affecting extraterrestrial matter in the Earth's atmosphere can be better understood. Here we report results on an unusual Antarctic glassy cosmic spherule that demonstrates strong textural evidence for at least two grazing incidence encounters with the Earth's atmosphere prior to final reentry. The particle consists of a central glassy core with four peripheral glass lobes that transect a silicate particle rim. The texture of the particle confirms previous theoretical speculations that some high velocity, low incidence angle interplanetary particles experience numerous encounters with the Earth's atmosphere and also indicates that micrometeorites demonstrating multiple melting episodes should be interpreted with caution.  相似文献   

A plume tectonics model for the Tharsis province, Mars     

Daniel Mège  Philippe Masson 《Planetary and Space Science》1996,44(12):1499-1546

Morphological and structural data from the whole Tharsis province suggest that a number of shallow grabens radially oriented about the Tharsis bulge on Mars are underlain by dykes, which define giant radiating swarms similar to, e.g. the Mackenzie dyke swarm of the Canadian shield. Mechanisms for graben formation are proposed, and the depth, width, and height of the associated dykes are estimated. Structural mapping leads to define successive stages of dyke emplacement, and provide stress-trajectory maps that indicate a steady source of the regional stress during the whole history of the Tharsis province. A new tectonic model of Tharsis is presented, based on an analogy with dyke swarms on the Earth that form inside hot spots. This model successfully matches the following features: (1) the geometry of the South Tharsis Ridge Belt, which may have been a consequence of the compressional stress field at the boundary between the uplifted and non-uplifted areas in the upper part of the lithosphere at the onset of hot spot activity; (2) extensive lava flooding, interpreted as a consequence of the high thermal anomaly at the onset of plume (hot spot) activity; (3) wrinkle ridge geometry in the Tharsis hemisphere, the formation of which is interpreted as a consequence of buoyant subsidence of the brittle crust in response to the lava load; (4) Valles Marineris limited stretching by preliminary passive rifting, and uplift, viewed as a necessary consequence of adiabatic mantle decompression induced by stretching. The geometrical analysis of dyke swarms suggests the existence of a large, Tharsis-independent extensional state of stress during all the period of tectonic activity, in which the minimum compressive stress is roughly N---S oriented. Although magmatism must have loaded the lithosphere significantly after the plume activity ceased and be responsible for additional surface deformations, there is no requirement for further loading stress to explain surficial features. Comparison with succession of magmatic and tectonic events related to hot spots on the Earth suggests that the total time required to produce all the surface deformation observed in the Tharsis province over the last 3.8 Ga does probably not exceed 10 or 15 Ma.  相似文献