High-frequency monitoring of hydrological and biogeochemical fluxes in forested catchments of southern Chile     

Cristián Frêne  Juan J. Armesto  Freddy Véliz  Fernando D. Alfaro  Kathleen C. Weathers 《水文研究》2021,35(5):e14175

The variability of rainfall-dependent streamflow at catchment scale modulates many ecosystem processes in wet temperate forests. Runoff in small mountain catchments is characterized by a quick response to rainfall pulses which affects biogeochemical fluxes to all downstream systems. In wet-temperate climates, water erosion is the most important natural factor driving downstream soil and nutrient losses from upland ecosystems. Most hydrochemical studies have focused on water flux measurements at hourly scales, along with weekly or monthly samples for water chemistry. Here, we assessed how water and element flows from broad-leaved, evergreen forested catchments in southwestern South America, are influenced by different successional stages, quantifying runoff, sediment transport and nutrient fluxes during hourly rainfall events of different intensities. Hydrograph comparisons among different successional stages indicated that forested catchments differed in their responses to high intensity rainfall, with greater runoff in areas covered by secondary forests (SF), compared to old-growth forest cover (OG) and dense scrub vegetation (CH). Further, throughfall water was greatly nutrient enriched for all forest types. Suspended sediment loads varied between successional stages. SF catchments exported 455 kg of sediments per ha, followed by OG with 91 kg/ha and CH with 14 kg/ha, corresponding to 11 rainfall events measured from December 2013 to April 2014. Total nitrogen (TN) and phosphorus (TP) concentrations in stream water also varied with rainfall intensity. In seven rainfall events sampled during the study period, CH catchments exported less nutrients (46 kg/ha TN and 7 kg/ha TP) than SF catchments (718 kg/ha TN and 107 kg/ha TP), while OG catchments exported intermediate sediment loads (201 kg/ha TN and 23 kg/ha TP). Further, we found significant effects of successional stage attributes (vegetation structure and soil physical properties) and catchment morphometry on runoff and sediment concentrations, and greater nutrients retention in OG and CH catchments. We conclude that in these southern hemisphere, broad-leaved evergreen temperate forests, hydrological processes are driven by multiple interacting phenomena, including climate, vegetation, soils, topography, and disturbance history.  相似文献   

Terrestrial LiDAR monitoring of coastal foredune evolution in managed and unmanaged systems     

I. Conery  K. Brodie  N. Spore  J. Walsh 《地球表面变化过程与地形》2020,45(4):877-892

Coastal dunes provide essential protection for infrastructure in developed regions, acting as the first line of defence against ocean-side flooding. Quantifying dune erosion, growth and recovery from storms is critical from management, resiliency and engineering with nature perspectives. This study utilizes 22 months of high-resolution terrestrial LiDAR (Riegl VZ-2000) observations to investigate the impact of management, anthropogenic modifications and four named storms on dune morphological evolution along ~100 m of an open-coast, recently nourished beach in Nags Head, NC. The influences of specific management strategies – such as fencing and plantings – were evaluated by comparing these to the morphologic response at an unmanaged control site at the USACE Field Research Facility (FRF) in Duck, NC (33 km to the north), which experienced similar environmental forcings. Various beach-dune morphological parameters were extracted (e.g. backshore-dune volume) and compared with aeolian and hydrodynamic forcing metrics between each survey interval. The results show that LiDAR is a useful tool for quantifying complex dune evolution over fine spatial and temporal scales. Under similar forcings, the managed dune grew 1.7 times faster than the unmanaged dune, due to a larger sediment supply and enhanced capture through fencing, plantings and walkovers. These factors at the managed site contributed to the welding of the incipient dune to the primary foredune over a short period of less than a year, which has been observed to take up to decades in natural systems. Storm events caused alongshore variable dune erosion primarily to the incipient dune, yet also caused significant accretion, particularly along the crest at the managed site, resulting in net dune growth. Traditional empirical Bagnold equations correlated with observed trends of backshore-dune growth but overpredicted magnitudes. This is likely because these formulations do not encompass supply-limiting factors and erosional processes. © 2019 John Wiley & Sons, Ltd.  相似文献   

The Atlas of Ancient Rome: Biography and Portraits of the City     

Alexander J. Kent 《The Cartographic journal》2020,57(1):88-89

  相似文献   

Updated Characterization of Dorowa Phosphate Rock Mined in Zimbabwe     

Tumbure  Akinson  Bretherton  Mike R.  Bishop  Peter  Hedley  Mike J. 《Natural Resources Research》2020,29(3):1561-1570

Natural Resources Research - The physical and chemical characteristics of mined phosphate rock will vary temporally as the location and nature of the ore body changes and as the type of equipment...  相似文献   

Appraisal of Hydraulic Flow Units and Factors of the Dynamics and Contamination of Hydrogeological Units in the Littoral Zones: A Case Study of Akwa Ibom State University and Its Environs,Mkpat Enin L.G.A,Nigeria     

George  Nyakno J. 《Natural Resources Research》2020,29(6):3771-3788

Natural Resources Research - Borehole-controlled one-dimensional geo-electric data were integrated with water samples obtained from boreholes drilled near the vertical electrical sounding at 12...  相似文献   

Extension of the effective modal seismic design method to generally irregular RC wall structures     

Philip J. Wilkinson  Oren Lavan 《Bulletin of Earthquake Engineering》2018,16(11):5341-5370

Structural irregularity in new buildings is sometimes desired for aesthetic reasons. Often it is unavoidable due to different uses in adjacent spaces within the building. The seismic behaviour of irregular structures is harder to predict than that of regular buildings. More comprehensive analysis techniques are often required to achieve adequate accuracy. Designing irregular structures poses additional challenges as the structural characteristics are unknown. There is a lack of practical design methods that reliably produce economic and seismically robust design solutions for highly irregular RC structures. This paper presents an extension of the Effective Modal Design (EMD) method from asymmetric-plan RC wall buildings to vertically setback asymmetric-plan RC wall buildings. EMD is a generalization of the Direct Displacement-Based Design method for highly irregular ductile uncoupled RC wall structures. EMD reverse engineers a multi-degree of freedom Equivalent Linear System to produce the most economic design solution that achieves the target performance levels. The utility of EMD is verified for a wide range of setback asymmetric-plan reinforced concrete wall structures using nonlinear time history analysis of reasonably realistic 3D structural models. Advantages of EMD include explicit consideration of nonlinear, torsional and ‘higher mode’ effects. The method produces capacity-designed design actions for all reinforced concrete walls in the seismic structural system. EMD only requires three response spectrum type analyses. It does not require time history analysis or pushover analysis. EMD is a practical seismic design method for generally irregular RC wall buildings that uses analysis techniques that most engineering practitioners are familiar and confident with. It was found that for over 95% of the structures considered, EMD achieved critical mean peak responses between ??20 and +?15% of the target response values, with a median of ??5%. This significant improvement in design accuracy and reliability (compared to traditional force based design) was achieved at the relatively small additional computational effort of two Response Spectrum Analyses. This demonstrates the value that the proposed Effective Modal Design method adds to the current spectrum of seismic design methods for irregular ductile RC wall structures.  相似文献   

Nonlinear dynamics of long-wave perturbations of the Kolmogorov flow for large Reynolds numbers     

Maxim Kalashnik  Michael Kurgansky 《Ocean Dynamics》2018,68(8):1001-1012

The nonlinear dynamics of long-wave perturbations of the inviscid Kolmogorov flow, which models periodically varying in the horizontal direction oceanic currents, is studied. To describe this dynamics, the Galerkin method with basis functions representing the first three terms in the expansion of spatially periodic perturbations in the trigonometric series is used. The orthogonality conditions for these functions formulate a nonlinear system of partial differential equations for the expansion coefficients. Based on the asymptotic solutions of this system, a linear, quasilinear, and nonlinear stage of perturbation dynamics is identified. It is shown that the time-dependent growth of perturbations during the first two stages is succeeded by the stage of stable nonlinear oscillations. The corresponding oscillations are described by the oscillator equation containing a cubic nonlinearity, which is integrated in terms of elliptic functions. An analytical formula for the period of oscillations is obtained, which determines its dependence on the amplitude of the initial perturbation. Structural features of the field of the stream function of the perturbed flow are described, associated with the formation of closed vortex cells and meandering flow between them. As a supplement, an asymptotic analysis of nonlinear dynamics of long-wave perturbations superimposed on a damped by small viscosity Kolmogorov flow (very large, but finite Reynolds numbers) is made. It is strictly shown that all velocity components of the perturbed flow remain bounded in this case.  相似文献   

Low‐P and high‐T metamorphism of basalts: Insights from the Sudbury impact melt sheet aureole and thermodynamic modelling     

Taus R. C. Jrgensen  Douglas K. Tinkham  C. Michael Lesher 《Journal of Metamorphic Geology》2019,37(2):271-313

Low‐pressure and high‐temperature (LP–HT) metamorphism of basaltic rocks, which occurs globally and throughout geological time, is rarely constrained by forward phase equilibrium modelling, yet such calculations provide valuable supplementary thermometric information and constraints on anatexis that are not possible to obtain from conventional thermometry. Metabasalts along the southern margin of the Sudbury Igneous Complex (SIC) record evidence of high‐grade contact metamorphism involving partial melting and melt segregation. Peak metamorphic temperatures reached at least ~925°C at ~1–3 kbar near the SIC contact. Preservation of the peak mineral assemblage indicates that most of the generated melt escaped from these rocks leaving a residuum characterized by a plagioclase–orthopyroxene–clinopyroxene–ilmenite‐magnetite±melt assemblage. Peak temperatures reached ~875°C up to 500 m from the SIC lower contact, which marks the transition to metabasalts that only experienced incipient partial melting without melt loss. Metabasalts ~500 to 750 m from the SIC contact are characterized by a similar two‐pyroxene mineral assemblage, but typically contain abundant hornblende that overgrew clino‐ and orthopyroxene along an isobaric cooling path. Metabasalts ~750 to 1,000 m from the SIC contact are characterized by a hornblende–plagioclase–quartz–ilmenite assemblage indicating temperatures up to ~680°C. Mass balance and phase equilibria calculations indicate that anatexis resulted in 10–20% melt generation in the inner ~500 m of the aureole, with even higher degrees of melting towards the contact. Comparison of multiple models, experiments, and natural samples indicates that modelling in the Na₂O–CaO–FeO–MgO–Al₂O₃–SiO₂–H₂O–TiO₂–O₂ (NCFMASHTO) system results in the most reliable predictions for the temperature of the solidus. Incorporation of K₂O in the most recent amphibole solution model now successfully predicts dehydration melting by the coexistence of high‐Ca amphibole and silicate melt at relatively low pressures (~1.5 kbar). However, inclusion of K₂O as a system component results in prediction of the solidus at too low a temperature. Although there are discrepancies between modelling predictions and experimental results, this study demonstrates that the pseudosection approach to mafic rocks is an invaluable tool to constrain metamorphic processes at LP–HT conditions.  相似文献   

Late Quaternary sea‐level change and evolution of Belfast Lough,Northern Ireland: new offshore evidence and implications for sea‐level reconstruction     

Ruth M. K. Plets  S. Louise Callard  J. Andrew G. Cooper  Joseph T. Kelley  Daniel F. Belknap  Robin J. Edwards  Antony J. Long  Rory J. Quinn  Derek W. T. Jackson 《第四纪科学杂志》2019,34(4-5):285-298

The interplay of eustatic and isostatic factors causes complex relative sea‐level (RSL) histories, particularly in paraglacial settings. In this context the past record of RSL is important in understanding ice‐sheet history, earth rheology and resulting glacio‐isostatic adjustment. Field data to develop sea‐level reconstructions are often limited to shallow depths and uncertainty exists as to the veracity of modelled sea‐level curves. We use seismic stratigraphy, 39 vibrocores and 26 radiocarbon dates to investigate the deglacial history of Belfast Lough, Northern Ireland, and reconstruct past RSL. A typical sequence of till, glacimarine and Holocene sediments is preserved. Two sea‐level lowstands (both max. ?40 m) are recorded at c. 13.5 and 11.5k cal a bp . Each is followed by a rapid transgression and subsequent periods of RSL stability. The first transgression coincides temporally with a late stage of Meltwater Pulse 1a and the RSL stability occurred between c. 13.0 and c. 12.2k cal a bp (Younger Dryas). The second still/slowstand occurred between c. 10.3 and c. 11.5k cal a bp . Our data provide constraints on the direction and timing of RSL change during deglaciation. Application of the Depth of Closure concept adds an error term to sea‐level reconstructions based on seismic stratigraphic reconstructions.  相似文献   

Shalstab mathematical model and WorldView-2 satellite images to identification of landslide-susceptible areas     

König  Téhrrie  Kux  Hermann J. H.  Mendes  Rodolfo M. 《Natural Hazards》2019,97(3):1127-1149

Natural Hazards - Natural hazards, occurring all over the world, may become a disaster when humans and nature interact. In Brazil, landslides triggered by heavy rainfall are the most common...  相似文献