Application of microcosm experiments for quantifying lateral flow and evapotranspiration on recovering bog ecotypes     

Michael M. Swenson  Shane Regan  Laurence W. Gill 《水文研究》2020,34(22):4211-4225

The importance of characterizing the ecohydrological interactions in natural, damaged/drained, and restored bogs is underscored by the importance of peatlands to global climate change and the growing need for peatland restoration. An understudied aspect of peatland ecohydrology is how shallow lateral flow impacts local hydrological conditions and water balance, which are critical for peatland restoration success. A novel method is presented using microcosms installed in the field to understand the dynamics of shallow lateral flow. Analysis of the difference in water table fluctuation inside and outside the microcosm experimental areas allowed the water balance to be constrained and the calculation of lateral flow and evapotranspiration. As an initial demonstration of this method, a series of four microcosm experiments were set up in locations with differing ecological quality and land management histories, on a raised bog complex in the midlands of Ireland. The timing and magnitude of the lateral flow differed considerably between locations with differing ecological conditions, indicating that shallow lateral flow is an important determining factor in the ecohydrological trajectory of a recovering bog system. For locations where Sphagnum spp. moss layer was present, a slow continuous net lateral input of water from the upstream catchment area supported the water table during drought periods, which was not observed in locations lacking Sphagnum. Consistent with other studies, evapotranspiration was greater in locations with a Spaghnum moss layer than in locations with a surface of peat soil.  相似文献   

Numerical modelling of SH L_g waves in and near continental margins     

J. Regan  D. G. Harkrider 《Geophysical Journal International》1989,98(1):107-130

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Decomposition of mineral absorption bands using nonlinear least squares curve fitting: Application to Martian meteorites and CRISM data     

Mario Parente  Heather D. Makarewicz  Janice L. Bishop 《Planetary and Space Science》2011,59(5-6):423-442

This study advances curve-fitting modeling of absorption bands of reflectance spectra and applies this new model to spectra of Martian meteorites ALH 84001 and EETA 79001 and data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). This study also details a recently introduced automated parameter initialization technique. We assess the performance of this automated procedure by comparing it to the currently available initialization method and perform a sensitivity analysis of the fit results to variation in initial guesses. We explore the issues related to the removal of the continuum, offer guidelines for continuum removal when modeling the absorptions and explore different continuum-removal techniques. We further evaluate the suitability of curve fitting techniques using Gaussians/Modified Gaussians to decompose spectra into individual end-member bands. We show that nonlinear least squares techniques such as the Levenberg–Marquardt algorithm achieve comparable results to the MGM model (Sunshine and Pieters, 1993, Sunshine et al., 1990) for meteorite spectra. Finally we use Gaussian modeling to fit CRISM spectra of pyroxene and olivine-rich terrains on Mars. Analysis of CRISM spectra of two regions show that the pyroxene-dominated rock spectra measured at Juventae Chasma were modeled well with low Ca pyroxene, while the pyroxene-rich spectra acquired at Libya Montes required both low-Ca and high-Ca pyroxene for a good fit.  相似文献   

Numerical simulations of the Lyman α forest – a comparison of gadget-2 and enzo     

John A. Regan  Martin G. Haehnelt  Matteo Viel 《Monthly notices of the Royal Astronomical Society》2007,374(1):196-205

We compare simulations of the Lyman α forest performed with two different hydrodynamical codes, gadget-2 and enzo . A comparison of the dark matter power spectrum for simulations run with identical initial conditions show differences of 1–3 per cent at the scales relevant for quantitative studies of the Lyman α forest. This allows a meaningful comparison of the effect of the different implementations of the hydrodynamic part of the two codes. Using the same cooling and heating algorithm in both codes, the differences in the temperature and the density probability distribution function are of the order of 10 per cent. The differences are comparable to the effects of box size and resolution on these statistics. When self-converged results for each code are taken into account, the differences in the flux power spectrum – the statistics most widely used for estimating the matter power spectrum and cosmological parameters from Lyman α forest data – are about 5 per cent. This is again comparable to the effects of box size and resolution. Numerical uncertainties due to a particular implementation of solving the hydrodynamic or gravitational equations appear therefore to contribute only moderately to the error budget in estimates of the flux power spectrum from numerical simulations. We further find that the differences in the flux power spectrum for enzo simulations run with and without adaptive mesh refinement are also of the order of 5 per cent or smaller. The latter require 10 times less CPU time making the CPU time requirement similar to that of a version of gadget-2 that is optimized for Lyman α forest simulations.  相似文献   

A plutonic brother from another magma mother: Disproving the Eocene Foraker‐McGonagall pluton piercing point and implications for long‐term slip on the Denali Fault     

Sean P. Regan  Jeffrey A. Benowitz  Mark E. Holland 《地学学报》2020,32(1):66-74

The Denali Fault is an active strike‐slip fault system responsible for the highest topography in North America, yet there are conflicting constraints on the fault's Cenozoic slip history. The long‐term slip rate constraint of the eastern Denali Fault is ~400 km since 57 Ma. In apparent conflict, the long‐term slip rate of the western Denali Fault is 38 km since 38 Ma based on the reconstruction of the Foraker and McGonagall plutons. Tests of the genetic relationship of the plutons with bulk rock geochemical and paired U‐Pb and Hf zircon analysis suggest a disparate origin. The McGonagall pluton, despite having a lower SiO₂, has lower ε_Hf values inconsistent with chemical and isotopic variations between the two being the result of contamination. The Denali Fault is a highly strain partitioned system, but the amount of Cenozoic slip dispersed east to west is likely significantly less than the previous ~360 km constraint.  相似文献   

Late Holocene paleohydrology of Kluane Lake, Yukon Territory, Canada     

Janice Brahney  John J. Clague  Thomas W. D. Edwards  Brian Menounos 《Journal of Paleolimnology》2010,44(3):873-885

We have gained new insight into the dynamic late Holocene paleohydrology and paleolimnology of Kluane Lake by reconstructing lakewater δ¹⁸O using sediment cellulose as an oxygen-isotope archive. Our data suggest that the lake was regularly open hydrologically between 5000 and 1000 cal year BP, although with substantially lower water levels and with greater evaporative loss in relation to inflow than under contemporary conditions. During part of this period the lake was meromictic and may have undergone intermittent hydrologic closure, but southward drainage to the Pacific Ocean via the Alsek River system was generally maintained. Isotopic evidence confirms that Kluane Lake underwent complete hydrologic closure 430–300 cal year BP (AD 1520–1650) after a major advance of Kaskawulsh Glacier blocked southward drainage. Closure persisted as the lake overtopped the Duke River fan, initiating northward drainage to the Bering Sea via the Yukon River system. Although incision of the new outlet channel led to a rapid decline in lake level, northward discharge via the Kluane River has been maintained for the past three centuries because of abundant inflow from the Slims River. Substantial quantities of glacial meltwater and seasonal runoff continue to drain via the Slims River from Kaskawulsh Glacier and its catchment in the St. Elias Mountains. During this period Kluane River has also become an important route for migrating anadromous salmon. The modern isotope hydrology of Kluane Lake confirms that its current positive water balance is highly dependent on discharge from Slims River. Declining glacial meltwater contributions to Slims River will likely lead to lower water levels in Kluane Lake over the coming decades and possible re-establishment of intermittent or perennial hydrologic closure.  相似文献   

Life in the last lane: star formation and chemical evolution in an extremely gas rich dwarf     

Ayesha Begum  Jayaram N. Chengalur  Robert C. Kennicutt  Igor D. Karachentsev  Janice C. Lee † 《Monthly notices of the Royal Astronomical Society》2008,383(2):809-816

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