Modelling how vegetation cover affects climate change impacts on streamflow timing and magnitude in the snowmelt‐dominated upper Tuolumne Basin,Sierra Nevada          下载免费PDF全文

Nicoleta C. Cristea  Jessica D. Lundquist  Steven P. Loheide II  Christopher S. Lowry  Courtney E. Moore 《水文研究》2014,28(12):3896-3918

We investigated, through hydrologic modelling, the impact of the extent and density of canopy cover on streamflow timing and on the magnitude of peak and late summer flows in the upper Tuolumne basin (2600–4000 m) of the Sierra Nevada, California, under current and warmer temperatures. We used the Distributed Hydrology Soil Vegetation Model for the hydrologic modelling of the basin, assuming four vegetation scenarios: current forest (partial cover, 80% density), all forest (uniform coverage, 80% density), all barren (no forest) and thinned forest (partial cover, 40% density) for a medium‐high emissions scenario causing a 3.9 °C warming over a 100‐year period (2001–2100). Significant advances in streamflow timing, quantified as the centre of mass (COM) of over 1 month were projected for all vegetation scenarios. However, the COM advances faster with increased forest coverage. For example, when forest covered the entire area, the COM occurred on average 12 days earlier compared with the current forest coverage, with the rate of advance higher by about 0.06 days year^?1 over 100 years and with peak and late summer flows lower by about 20% and 27%, respectively. Examination of modelled changes in energy balance components at forested and barren sites as temperatures rise indicated that increases in net longwave radiation are higher in the forest case and have a higher contribution to melting earlier in the calendar year when shortwave radiation is a smaller fraction of the energy budget. These increases contributed to increased midwinter melt under the forest at temperatures above freezing, causing decreases in total accumulation and higher winter and early spring melt rates. These results highlight the importance of carefully considering the combined impacts of changing forest cover and climate on downstream water supply and mountain ecosystems. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Dispersal of Mississippi and Atchafalaya sediment on the Texas-Louisiana shelf: Model estimates for the year 1993   总被引：1，自引：0，他引：1  

Kehui Xu  Courtney K. HarrisRobert D. Hetland  James M. Kaihatu 《Continental Shelf Research》2011,31(15):1558-1575

A three-dimensional coupled hydrodynamic-sediment transport model for the Texas-Louisiana continental shelf was developed using the Regional Ocean Modeling System (ROMS) and used to represent fluvial sediment transport and deposition for the year 1993. The model included water and sediment discharge from the Mississippi River and Atchafalaya Bay, seabed resuspension, and suspended transport by currents. Input wave properties were provided by the Simulating WAves Nearshore (SWAN) model so that ROMS could estimate wave-driven bed stresses, critical to shallow-water sediment suspension. The model used temporally variable but spatially uniform winds, spatially variable seabed grain size distributions, and six sediment tracers from rivers and seabed.At the end of the year 1993, much of the modeled fluvial sediment accumulation was localized with deposition focused near sediment sources. Mississippi sediment remained within 20-40 km of the Mississippi Delta. Most Atchafalaya sediment remained landward of the 10-m isobath in the inner-most shelf south of Atchafalaya Bay. Atchafalaya sediment displayed an elongated westward dispersal pattern toward the Chenier Plain, reflecting the importance of wave resuspension and perennially westward depth-averaged currents in the shallow waters (<10 m). Due to relatively high settling velocities assumed for sediment from the Mississippi River as well as the shallowness of the shelf south of Atchafalaya Bay, most sediment traveled only a short distance before initial deposition. Little fluvial sediment could be transported into the vicinity of the “Dead Zone” (low-oxygen area) within a seasonal-annual timeframe. Near the Mississippi Delta and Atchafalaya Bay, alongshore sediment-transport fluxes always exceeded cross-shore fluxes. Estimated cumulative sediment fluxes next to Atchafalaya Bay were episodic and “stepwise-like” compared to the relatively gradual transport around the Mississippi Delta. During a large storm in March 1993, strong winds helped vertically mix the water column over the entire shelf (up to 100-m isobath), and wave shear stress dominated total bed stress. During fair-weather conditions in May 1993, however, the freshwater plumes spread onto a stratified water column, and combined wave-current shear stress only exceeded the threshold for suspending sediment in the inner-most part of the shelf.  相似文献   

Archaeal lipids record paleosalinity in hypersaline systems   总被引：2，自引：0，他引：2  

Courtney Turich  Katherine H. Freeman 《Organic Geochemistry》2011,42(9):1147-1157

We present an ecologically based biomarker method for estimating past salinity, especially in hypersaline conditions. The relative amounts of acyclic diether and tetraether membrane lipids synthesized by Archaea correlate with salinity from 0–250 practical salinity units (psu) in modern settings. We examined the preservation of this lipid biomarker–salinity relationship in ancient sedimentary organic matter using samples from two sequences of marls and diatomites deposited just prior to the Messinian Salinity Crisis. Salinity estimates were consistent with expected absolute salinity, as well as the amplitude of variations leading up to the Messinian Salinity Crisis. This lipid biomarker approach to salinity reconstruction complements existing paleosalinity proxies because (i) Archaea survive and thrive over a broad salinity range, well beyond that of haptophyte algae and other plankton which form the microfossil record and (ii) it provides fine salinity resolution for the wide range broadly defined as hypersaline. With the proxy, there is the potential to provide novel insights into salinity variation within desiccating basins in climatically sensitive seas (e.g. Dead Sea, Permian Delaware Basin), evolution of brines, timing of onset of hypersaline conditions and evaporite deposition.  相似文献   

Aqueous Carbon Monoxide Cycling in a Fjord-Like Estuary     

Courtney E. Schmidt  Brian G. Heikes 《Estuaries and Coasts》2014,37(3):751-762

Dissolved carbon monoxide, [CO], was measured in oxic surface waters and in the anoxic layer of the Pettaquamscutt River, Rhode Island, from March to August 2008. Samples were collected at near-shore locations to examine spatial and seasonal changes at solar noon. Each month, a set of diel samples was collected at the surface stations to evaluate photoproduction and biological processing. In July and August, anoxic samples from depths >6 m were collected to examine the presence of an active anaerobic CO metabolism. The surface [CO] decreased from 65 to 5 nmol kg^?1 from spring to summer, which was attributed to a decline in dissolved organic matter. Diel [CO] showed a strong mid-afternoon maximum with a late evening and early morning minimum. Inferred first-order loss rates, attributed to biological processing, ranged from 0.1–0.6 h^?1 without a clear seasonal pattern. [CO] saturation ratios were typically >200 at mid-day, >7 in morning/late evening, and never below 1, implying the river is always a net source of CO to the atmosphere. [CO] in the anoxic layer averaged 2 nmol kg^?1.  相似文献   

Spatial variability of recent macroscopic charcoal deposition in a small montane lake and implications for reconstruction of watershed-scale fire regimes     

Colin J. Courtney Mustaphi  Emma L. Davis  Joelle T. Perreault  Michael F. J. Pisaric 《Journal of Paleolimnology》2015,54(1):71-86

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Ecological Entrepreneurship Support Networks: Roles and functions for conservation organizations     

Courtney E. Kimmel  R. Bruce Hull 《Geoforum》2012,43(1):58-67

Changing social and economic drivers of land use require a more integrated approach to land conservation that addresses both the land and the socio-economic context of land use. Technical and legal conservation focused at the single-parcel scale is insufficient. This research examines ecological entrepreneurship, discussed by Marsden and Smith (2005), as an integrated conservation strategy that targets environmental as well as economic goals. Specifically, we explore the roles and functions that must be provided by Ecological Entrepreneurship Support Networks (EESNs). In particular, we look at land trusts engaging in these efforts. Through a series of case studies, we examine the roles and functions, as well as motivations and challenges faced by land trusts involved in EESNs. The lessons learned through these case studies are intended to inform broader sustainable development efforts.  相似文献   

A note on the effects of abnormally low temperature on the Carolina marsh clam     

Courtney T. Hackney 《Estuaries and Coasts》1985,8(4):394-395

Populations of the Carolina Marsh Clam,Polymesoda caroliniana, suffered high mortality in southeastern North Carolina during the winters of 1983–84 and 1984–85. Adult populations in brackish marshes in the Cape Fear estuary suffered 33% mortality in 1983 and 38% in 1985. Some data suggest that more flooded areas suffered less mortality. A laboratory experiment found that some clams died after only 4 h exposure to 0 to ?1°C. LT₅₀ occurred after only 6.3 h and no individuals survived 24 h exposure. Cold intolerance is suggested as the primary limiting factor in its northern distribution.  相似文献   

Small towns as ‘sub-poles’ in English rural development: Investigating rural–urban linkages using sub-regional social accounting matrices     

Paul Courtney  Lucy Mayfield  Richard Tranter  Philip Jones  Andrew Errington   《Geoforum》2007,38(6):1219-1232

This paper uses spatial economic data from four small English towns to measure the strength of economic integration between town and hinterland and to estimate the magnitude of town–hinterland spill-over effects. Following estimation of local integration indicators and inter-locale flows, sub-regional social accounting matrices (SAMs) are developed to estimate the strength of local employment and output multipliers for various economic sectors. The potential value of a town as a ‘sub-pole’ in local economic development is shown to be dependent on structural differences in the local economy, such as the particular mix of firms within towns. Although the multipliers are generally small, indicating a low level of local linkages, some sectors, particularly financial services and banking, show consistently higher multipliers for both output and employment.  相似文献   

A Synthetic Haematite Reference Material for LA‐ICP‐MS U‐Pb Geochronology and Application to Iron Oxide‐Cu‐Au Systems     

Liam Courtney‐Davies  Sarah E. Gilbert  Cristiana L. Ciobanu  Simon R. Tapster  Marcus W. Richardson  Nigel J. Cook  Benjamin P. Wade  Max R. Verdugo‐Ihl  Kathy Ehrig  Daniel J. Condon 《Geostandards and Geoanalytical Research》2021,45(1):143-159

In both nature and synthetic experiments, the common iron oxide haematite (α‐Fe₂O₃) can incorporate significant amounts of U into its crystal structure and retain radiogenic Pb over geological time. Haematite is a ubiquitous component of many ore deposit types and, therefore, represents a valuable hydrothermal mineral geochronometer, allowing direct constraints to be placed on the timing of ore formation and upgrading. However, to date, no suitable natural haematite reference material has been identified. Here, a synthetic haematite U‐Pb reference material (MR‐HFO) is characterised using LA‐ICP‐MS and ID‐TIMS. Centimetre‐scale ‘chips’ of synthesised α‐Fe₂O₃ were randomly microsampled via laser ablation‐extraction and analysed using ID‐TIMS. Reproducible U/Pb and Pb/Pb measurements were obtained across four separate chips (n = 13). Subsequently, an evaluation of the suitability MR‐HFO in constraining U‐Pb data via LA‐ICP‐MS is presented using a selection of natural samples ranging from Cenozoic to Proterozoic in age. The MR‐HFO normalised U‐Pb ratios are more concordant and ages more accurate versus the same LA‐ICP‐MS spot analyses normalised to zircon reference material, when compared with independently acquired ID‐TIMS data from the same natural haematite grains. Results establish MR‐HFO as a suitable reference material for LA‐ICP‐MS haematite U‐Pb geochronology.  相似文献   

Evolution of an englacial volcanic ridge: Pillow Ridge tindar, Mount Edziza volcanic complex, NCVP, British Columbia, Canada   总被引：2，自引：1，他引：1  

Benjamin R. Edwards  Ian P. Skilling  Barry Cameron  Courtney Haynes  Alex Lloyd  Jefferson H.D. Hungerford 《Journal of Volcanology and Geothermal Research》2009,185(4):251

Glaciovolcanic deposits are critical for documenting the presence and thickness of terrestrial ice-sheets, and for testing hypotheses about inferred terrestrial ice volumes based on the marine record. Deposits formed by the coincidence of volcanism and ice at the Mount Edziza volcanic complex (MEVC) in northern British Columbia, Canada, preserve an important record for documenting local and possibly regional ice dynamics. Pillow Ridge, located at the northwestern end of the MEVC, formed by ice-confined, fissure-fed eruptions. It comprises predominantly pillow lavas and volcanic breccias of alkaline basalt composition, with subordinate finer-grained volcaniclastic deposits and dykes. The ridge is presently  4 km long,  1000 m in maximum width, and  600 m high. Fifteen syn- and post-eruptive lithofacies are recognized in excellent exposures along the glacially dissected western side of the ridge. We recognize five lithofacies associations: (1) poorly sorted tuff breccia and dykes, (2) proximal pillow lava, dykes and tuff breccia, (3) distal pillow lava, poorly sorted conglomerate and well-sorted volcanic sandstone, (4) interbedded tuff, lapilli tuff, and tuff breccia units, and (5) heterolithic volcanogenic conglomerate and sandstone. Given the abundance of pillow lavas and the lack of surrounding topographic barriers capable of impounding water, we agree with Souther [Souther, J.G., 1992. The late Cenozoic Mount Edziza volcanic complex. Geol. Soc. Can. Mem., vol. 420. 320 pp] that the bulk of the edifice formed while confined by ice, but have found evidence for a more complex and variable eruption history than that which he proposed. Preliminary estimates of water-ice depths derived from FTIR analyses of H₂O give ranges of 300 to 680 m assuming 0 ppm CO₂, and 857 to 1297 m assuming 25 ppm CO₂. Variations in depth estimates among samples may indicate that water/ice depths changed during the evolution of the ridge, which is consistent with our interpretations for the origins of different lithofacies associations. Given that the age of the units are likely to be ca. 0.9 Ma [Souther, J.G., 1992. The late Cenozoic Mount Edziza volcanic complex. Geol. Soc. Can. Mem., vol. 420. 320 pp], Pillow Ridge may be the best documentation of a regional high stand of the Cordilleran Ice Sheet (CIS) in the middle Pleistocene, and an excellent example of the lithofacies and stratigraphic complexities produced by variations in water levels during a prolonged glaciovolcanic eruption.  相似文献