Investigating the influence of hydrogeomorphic setting on the response of lake sedimentation to climatic changes in the Uinta Mountains, Utah, USA     

Lee B. Corbett  Jeffrey S. Munroe 《Journal of Paleolimnology》2010,44(1):311-325

Reader Lake and Elbow Lake, two high-altitude lakes in the Uinta Mountains of Utah, are located approximately 2 km apart, at similar elevations, and within identical vegetation communities. Loss on ignition, carbon to nitrogen ratios, biogenic silica, and sediment grain size were analyzed throughout percussion cores retrieved from both lakes to construct continuous time series spanning 14 to ca. 2 ka BP. Given the proximity of the lakes, it is assumed that both were subjected to the same climatic forcing over this time. Accordingly, the first goal of this study was to consider these two multiproxy datasets in concert to yield an integrated paleoclimate record for this region. Close inspection of the records identified discrepancies indicating that the lakes responded to climate changes in different ways despite their proximity and similar setting. Clarifying these differences and understanding why the two lakes behaved differently at certain times was the second goal of this study. Overall, the paleoclimatic records document lake formation in the latest Pleistocene following glacier retreat. Buried glacier ice at the location of Reader Lake may have persisted through the Younger Dryas. Both lakes became biologically productive ca. 11.5 ka BP, and the first appearance of conifer needles indicates that trees had replaced alpine tundra in these watersheds by 10.5 ka BP. The interval from 10 to 6 ka BP was marked by a dramatic increase in precipitation, perhaps related to enhanced monsoonal circulation driven by the insolation maximum. The two lakes recorded this event in notably contrasting ways given their differing hydrogeomorphic settings. Precipitation decreased from 6 to 4 ka BP, and low water levels and drought conditions marked the interval from 4.0 to 2.7 ka BP. The integrated paleoclimate record developed from these cores provides a useful point of comparison with other records from the region. The differences between the records from these closely spaced lakes underscore the need to consider hydrogeomorphic setting when evaluating the suitability of a lake for a paleolimnological study.  相似文献   

Carbon dioxide fluxes and DOC concentrations of eroding blanket peat gullies   总被引：1，自引：0，他引：1  

Gareth D. Clay  Simon Dixon  Martin G. Evans  James G. Rowson  Fred Worrall 《地球表面变化过程与地形》2012,37(5):562-571

UK peatlands are affected by severe gully erosion with consequent impacts on ecosystem services from these areas. Incision into the peat can damage the vegetation and hydrology and lead to increases in carbon loss and sediment transfer downstream. Gullies represent then a conduit for and a hotspot of carbon loss but the relatively high water tables of gullies have meant that they have been identified as areas with a high restoration potential because of easily restored peat‐forming conditions. This study uses a series of gully sites, subject to different restoration interventions, to investigate differences in carbon pathways (DOC, CO₂) and hydrology between restoration strategies and gully position. The results show that the position within the gully (interfluve, gully side, or gully floor) does not significantly affect water quality but that it plays a significant role in CO₂ exchange. Gully floors are areas of high photosynthesis and ecosystem respiration, though net ecosystem exchange is not significantly different across the gully. While gully position plays a role in the cycling of some carbon species, this study highlights the importance of vegetation as a key control on carbon cycling. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Topographic,pedologic and climatic interactions influencing streamflow generation at multiple catchment scales   总被引：1，自引：0，他引：1  

Geneviève Ali  Doerthe Tetzlaff  Chris Soulsby  Jeffrey J. McDonnell 《水文研究》2012,26(25):3858-3874

Dominant flow pathways (DFPs) in mesoscale watersheds are poorly characterized and understood. Here, we make use of a conservative tracer (Gran alkalinity) and detailed information about climatic conditions and physical properties to examine how temporally and spatially variable factors interact to determine DFPs in 12 catchments draining areas from 3.4 to 1829.5 km² (Cairngorms, Scotland). After end‐member mixing was applied to discriminate between near surface and deep groundwater flow pathways, variation partitioning, canonical redundancy analyses and regression models were used to resolve: (i) What is the temporal variability of DFPs in each catchment?; (ii) How do DFPs change across spatial scales and what factors control the differences in hydrological responses?; and (iii) Can a conceptual model be developed to explain the spatiotemporal variability of DFPs as a function of climatic, topographic and soil characteristics? Overall, catchment characteristics were only useful to explain the temporal variability of DFPs but not their spatial variation across scale. The temporal variability of DFPs was influenced most by prevailing hydroclimatic conditions and secondarily soil drainability. The predictability of active DFPs was better in catchments with soils supporting fast runoff generation on the basis of factors such as the cumulative precipitation from the seven previous days, mean daily air temperature and the fractional area covered by Rankers. The best regression model R² was 0.54, thus suggesting that the catchments’ internal complexity was not fully captured by the factors included in the analysis. Nevertheless, this study highlights the utility of combining tracer studies with digital landscape analysis and multivariate statistical techniques to gain insights into the temporal (climatic) and spatial (topographic and pedologic) controls on DFPs. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Fluvial carbon flux from headwater peatland streams: significance of particulate carbon flux   总被引：1，自引：0，他引：1  

R. R. Pawson  M. G. Evans  T. E. H. A. Allott 《地球表面变化过程与地形》2012,37(11):1203-1212

The extensive blanket peatlands of the UK uplands account for almost half of total national terrestrial carbon storage. However, much of the blanket peat is severely eroded so that the contemporary role of the peatland system in carbon sequestration is compromised by losses of organic carbon in dissolved (DOC) and particulate (POC) form in the fluvial system. This paper presents the first detailed assessment of dissolved and organic carbon losses from a severely eroded headwater peatland (River Ashop, South Pennines, UK). Total annual fluvial organic carbon losses range from 29–106 Mg C km,^‐2 decreasing from the headwaters to the main catchment outlet. In contrast to less eroded systems fluvial organic carbon flux is dominated by POC. POC:DOC ratios decrease from values of 4 in the headwaters to close to unity at the catchment outlet. These results demonstrate the importance of eroding headwater sites as sources of POC to the fluvial system. Comparison with a range of catchment characteristics reveals that drainage density is the best predictor of POC:DOC but there is scatter in the relation in the headwaters. Steep declines in specific POC yield from headwater catchments are consistent with storage of POC within the fluvial system. Key to the significance of fluvial carbon flux in greenhouse gas budgets is understanding the fate of fluvial carbon. Further work on the fate of POC and the role of floodplains in fluvial carbon cycling is urgently required. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Glacier retreat and landform production on an overdeepened glacier foreland: the debris‐charged glacial landsystem at Kvíárjökull,Iceland     

Georgina L. Bennett  David J. A. Evans 《地球表面变化过程与地形》2012,37(15):1584-1602

Glacier recession and landform development in a debris‐charged glacial landsystem characterized by an overdeepening is quantified using digital photogrammetry, digital elevation model (DEM) construction and mapping of the Icelandic glacier Kvíárjökull for the period 1945–2003. Melting of ice‐cores is recorded by surface lowering rates of 0·8 m yr^–1 (1945–1964), 0·3 m yr^–1 (1964–1980), 0·015 m yr^–1 (1980–1998) and 0·044 m yr^–1 (1998–2003). The distribution/preservation of pushed and stacked ice‐cored moraine complexes are determined by the location of the long‐term glacial drainage network in combination with retreat from the overdeepening, into which glacifluvial sediment is being directed and where debris‐rich ice masses are being reworked and replaced by esker networks produced in englacial meltwater pathways that bypassed the overdeepening and connected to outwash fans prograding over the snout. Recent accelerated retreat of Kvíárjökull, potentially due to increased mass balance sensitivity, has made the snout highly unstable, especially now that the overdeepening is being uncovered and the snout flooded by an expanding pro‐glacial, and partially supraglacial, lake. This case study indicates that thick sequences of debris‐charged basal ice/controlled moraine have a very low preservation potential but ice‐cored moraine complexes can develop into hummocky moraine belts in de‐glaciated terrains because they are related to the process of incremental stagnation, which at Kvíárjökull has involved periodic switches from transport‐dominant to ablation‐dominant conditions. Glacier recession is therefore recorded temporally and spatially by two suites of landforms relating to two phases of landform production which are likely typical for glaciers occupying overdeepenings: an early phase of active, temperate recession recorded by push moraines and lateral moraines and unconfined pro‐glacial meltwater drainage; and a later phase of incremental stagnation and pitted outwash head development initiated by the increasing topographic constraints of the latero‐frontal moraine arc and the increasing importance of the overdeepening as a depo‐centre. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Electrical Resistivity Imaging of a Permanganate Injection During In Situ Treatment of RDX‐Contaminated Groundwater     

Todd Halihan  Jeffrey Albano  Steve D. Comfort  Vitaly A. Zlotnik 《Ground Water Monitoring & Remediation》2012,32(1):43-52

Groundwater beneath the former Nebraska Ordnance Plant (NOP) is contaminated with the explosive hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine (RDX) and trichloroethene (TCE). Previous treatability experiments confirmed that permanganate could mineralize RDX in NOP aquifer material. The objective of this study was to determine the efficacy of permanganate to transform RDX in the field by monitoring a pilot‐scale in situ chemical oxidation (ISCO) demonstration. In this demonstration, electrical resistivity imaging (ERI) was used to create two‐dimensional (2‐D) images of the test site prior to, during, and after injecting sodium permanganate. The ISCO was performed by using an extraction‐injection well configuration to create a curtain of permanganate. Monitoring wells were positioned downgradient of the injection zone with the intent of capturing the permanganate‐RDX plume. Differencing between ERI taken preinjection and postinjection determined the initial distribution of the injected permanganate. ERI also quantitatively corroborated the hydraulic conductivity distribution across the site. Groundwater samples from 12 downgradient wells and 8 direct‐push profiles did not provide enough data to quantify the distribution and flow of the injected permanganate. ERI, however, showed that the permanganate injection flowed against the regional groundwater gradient and migrated below monitoring well screens. ERI combined with monitoring well samples helped explain the permanganate dynamics in downgradient wells and support the use of ERI as a means of monitoring ISCO injections.  相似文献   

Improved statistical prediction of surface currents based on historic HF-radar observations     

Sergey Frolov  Jeffrey Paduan  Michael Cook  James Bellingham 《Ocean Dynamics》2012,62(7):1111-1122

Accurate short-term prediction of surface currents can improve the efficiency of search-and-rescue operations, oil-spill response, and marine operations. We developed a linear statistical model for predicting surface currents (up to 48?h in the future) based on a short time history of past HF-radar observations (past 48?h) and an optional forecast of surface winds. Our model used empirical orthogonal functions (EOFs) to capture spatial correlations in the HF-radar data and used a linear autoregression model to predict the temporal dynamics of the EOF coefficients. We tested the developed statistical model using historical observations of surface currents in Monterey Bay, California. The predicted particle trajectories separated from particles advected with HF-radar data at a rate of 4.4?km/day. The developed model was more accurate than an existing statistical model (drifter separation of 5.5?km/day) and a circulation model (drifter separation of 8.9?km/day). When the wind forecast was not available, the accuracy of our model degraded slightly (drifter separation of 4.9?km/day), but was still better than existing models. We found that the minimal length of the HF-radar data required to train an accurate statistical model was between 1 and 2?years, depending on the accuracy desired. Our evaluation showed that the developed model is accurate, is easier to implement and maintain than existing statistical and circulation models, and can be relocated to other coastal systems of similar complexity that have a sufficient history of HF-radar observations.  相似文献   

Scales and structure of frontal adjustment and freshwater export in a region of freshwater influence     

Joanne Hopkins  Jeffrey A. Polton 《Ocean Dynamics》2012,62(1):45-62

Sea surface temperature satellite imagery and a regional hydrodynamic model are used to investigate the variability and structure of the Liverpool Bay thermohaline front. A statistically based water mass classification technique is used to locate the front in both data sets. The front moves between 5 and 35 km in response to spring–neap changes in tidal mixing, an adjustment that is much greater than at other shelf-sea fronts. Superimposed on top of this fortnightly cycle are semi-diurnal movements of 5–10 km driven by flood and ebb tidal currents. Seasonal variability in the freshwater discharge and the density difference between buoyant inflow and more saline Irish Sea water give rise to two different dynamical regimes. During winter, when cold inflow reduces the buoyancy of the plume, a bottom-advected front develops. Over the summer, when warm river water provides additional buoyancy, a surface-advected plume detaches from the bottom and propagates much larger distances across the bay. Decoupled from near-bed processes, the position of the surface front is more variable. Fortnightly stratification and re-mixing over large areas of Liverpool Bay is a potentially important mechanism by which freshwater, and its nutrient and pollutant loads, are exported from the coastal plume system. Based on length scales estimated from model and satellite data, the erosion of post-neap stratification is estimated to be responsible for exporting approximately 19% of the fresh estuarine discharge annually entering the system. Although the baroclinic residual circulation makes a more significant contribution to freshwater fluxes, the episodic nature of the spring–neap cycle may have important implications for biogeochemical cycles within the bay.  相似文献   

Initiation conditions for debris flows generated by runoff at Chalk Cliffs, central Colorado   总被引：7，自引：1，他引：6  

Jeffrey A. Coe  David A. Kinner  Jonathan W. Godt 《Geomorphology》2008,96(3-4):270

We have monitored initiation conditions for six debris flows between May 2004 and July 2006 in a 0.3 km² drainage basin at Chalk Cliffs; a band of hydrothermally-altered quartz monzonite in central Colorado. Debris flows were initiated by water runoff from colluvium and bedrock that entrained sediment from rills and channels with slopes ranging from about 14° to 45°. The availability of channel material is essentially unlimited because of thick channel fill and refilling following debris flows by rock fall and dry ravel processes. Rainfall exceeding I = 6.61(D)^− 0.77, where I is rainfall intensity (mm/h), and D is duration (h), was required for the initiation of debris flows in the drainage basin. The approximate minimum runoff discharge from the surface of bedrock required to initiate debris flows in the channels was 0.15 m³/s. Colluvium in the basin was unsaturated immediately prior to (antecedent) and during debris flows. Antecedent, volumetric moisture levels in colluvium at depths of 1 cm and 29 cm ranged from 4–9%, and 4–7%, respectively. During debris flows, peak moisture levels in colluvium at depths of 1 cm and 29 cm ranged from 10–20%, and 4–12%, respectively. Channel sediment at a depth of 45 cm was unsaturated before and during debris flows; antecedent moisture ranged from 20–22%, and peak moisture ranged from 24–38%. Although we have no measurements from shallow rill or channel sediment, we infer that it was unsaturated before debris flows, and saturated by surface-water runoff during debris flows.Our results allow us to make the following general statements with regard to debris flows generated by runoff in semi-arid to arid mountainous regions: 1) high antecedent moisture levels in hillslope and channel sediment are not required for the initiation of debris flows by runoff, 2) locations of entrainment of sediment by successive runoff events can vary within a basin as a function of variations in the thickness of existing channel fill and the rate of replenishment of channel fill by rock fall and dry ravel processes following debris flows, and 3) rainfall and simulated surface-water discharge thresholds can be useful in understanding and predicting debris flows generated by runoff and sediment entrainment.  相似文献   

Elementary forms for land surface segmentation: The theoretical basis of terrain analysis and geomorphological mapping   总被引：10，自引：0，他引：10  

Jozef Minr  Ian S. Evans 《Geomorphology》2008,95(3-4):236-259

Land surface morphology is fundamental to geomorphological mapping and many GIS applications. Review and comparison of various approaches to segmentation of the land surface reveals common features, and permits development of a broad theoretical basis for segmentation and for characterization of segments and their boundaries. Within the context of defining landform units that maximise internal homogeneity and external differences, this paper introduces the concept of elementary forms (segments, units) defined by constant values of fundamental morphometric properties and limited by discontinuities of the properties. The basic system of form-defining properties represents altitude and its derivatives, constant values of which provide elementary forms with various types of homogeneity. Every geometric type of elementary form can be characterized by a defining function, which is a specific case of the general polynomial fitted function. Various types of boundary discontinuity and their connections and transformations into other types of morphological unit boundaries are analysed.The wealth of types of elementary forms and their boundaries is potentially unbounded and thus is sufficient to cover the real variety of landforms. Elementary forms in the basic set proposed here have clear potential for genetic and dynamic interpretation. A brief worked example documents the possibility of analytical computation of various models of ideal elementary forms for particular segments of landform. Ideal elementary forms can be considered as attractors, to which the affinity of surface segments can be measured by multivariate statistical methods. The use of the concept of elementary forms in landscape segmentation is promising and it could be adapted for elementary segmentation of various other spatial fields.  相似文献