Influence of landscape position and vegetation on long-term weathering rates at the Hubbard Brook Experimental Forest, New Hampshire, USA     

Carmen A. Nezat  Joel D. Blum  Chris E. Johnson 《Geochimica et cosmochimica acta》2004,68(14):3065-3078

The spatial variability of long-term chemical weathering in a small watershed was examined to determine the effect of landscape position and vegetation. We sampled soils from forty-five soil pits within an 11.8-hectare watershed at the Hubbard Brook Experimental Forest, New Hampshire. The soil parent material is a relatively homogeneous glacial till deposited ∼14,000 years ago and is derived predominantly from granodiorite and pelitic schist. Conifers are abundant in the upper third of the watershed while the remaining portion is dominated by hardwoods. The average long-term chemical weathering rate in the watershed, calculated by the loss of base cations integrated over the soil profile, is 35 meq m⁻² yr⁻¹—similar to rates in other ∼10 to 15 ka old soils developed on granitic till in temperate climates. The present-day loss of base cations from the watershed, calculated by watershed mass balance, exceeds the long-term weathering rate, suggesting that the pool of exchangeable base cations in the soil is being diminished. Despite the homogeneity of the soil parent material in the watershed, long-term weathering rates decrease by a factor of two over a 260 m decrease in elevation. Estimated weathering rates of plagioclase, potassium feldspar and apatite are greater in the upper part of the watershed where conifers are abundant and glacial till is thin. The intra-watershed variability across this small area demonstrates the need for extensive sampling to obtain accurate watershed-wide estimates of long-term weathering rates.  相似文献   

Lead and strontium isotopes as monitors of experimental granitoid mineral dissolution     

Yigal Erel  Joel D. Blum  Jiwchar Ganor 《Geochimica et cosmochimica acta》2004,68(22):4649-4663

Flow-through dissolution experiments were carried out on crushed granitoid rock (the Elat Granite) and three mineral separates (plagioclase, perthite, and biotite + chlorite) from this rock at pH 1 and 25°C. Major element concentrations were combined with Pb and Sr isotopic analyses of starting materials and output solutions and together enabled us to elucidate several important mechanisms related to granitoid rock weathering. We observed an initial stage of rock dissolution (<200 hours of reaction) that was characterized by elemental release from traces of calcite and/or apatite and to a lesser extent from the interlayer sites of biotite. Dissolution in the interval of 200 to 400 h was dominated by the release of elements from the interlayer sites of biotite, and at 400 to 1000 h of reaction the chemistry of output solutions was dominated by the release of elements from tetrahedral and octahedral sites of biotite as well as from plagioclase. After 1000 h, the dissolution of plagioclase, and to a lesser extent biotite, dominated the composition of elements released by the rock. We demonstrate that Pb and Sr isotope ratios in the output solutions can be used to identify each of these stages of dissolution. By comparing our experimental results on the release of Pb and Sr isotopes with field measurements of Pb and Sr isotopes in soil chronosequences from the Wind River and the Sierra Nevada Mountains (USA), we are able to show that similar isotopic patterns appear in both the pH 1 experiments and in soils formed under natural conditions at higher pH. By combining these experimental results with previous field studies, we are able to estimate the duration of most of these stages of granitoid weathering under natural conditions in temperate climates. In soils older than a few hundred years and younger than 10,000 yr the release of elements from interlayer sites of biotite controls the weathering flux. Soils between 10,000 and 100,000 yr old are dominated by biotite and plagioclase weathering, with biotite weathering controlling the first part of this period and plagioclase dominating the later part. After more than 100,000 yr, plagioclase, and to a lesser degree biotite, dominate the weathering flux within these granitoid soils.  相似文献   

Variability of rainfall over Lake Kariba catchment area in the Zambezi river basin,Zimbabwe     

Shepherd Muchuru  Joel O. Botai  Christina M. Botai  Willem A. Landman  Abiodun M. Adeola 《Theoretical and Applied Climatology》2016,124(1-2):325-338

  相似文献   

Estimating Pile Set-up Using 24-h Restrike Resistance and Computed Static Capacity for PPC Piles Driven in Soft Lousiana Coastal Deposits   总被引：1，自引：0，他引：1  

Jay X. Wang  Neha Verma  Eric J. Steward 《Geotechnical and Geological Engineering》2016,34(1):267-283

In this paper, the CPT-based predicted ultimate pile resistances (R_p) were compared with the measured pile resistances (R_m) at different elapsed time for the piles driven into saturated soft clays where piles displayed significant set-up effect. The measured pile resistances were based on 115 restrike records collected from 95 production piles, and 74 records of 9 tested piles. The predicted ultimate pile resistances were calculated from the LCPC, the Schmertmann, and the de Ruiter–Beringen methods, respectively. With the significant pile set-up effect taken into account, the relationship between measured resistances and predicted capacities at different times after pile installation were investigated. The ratios of the measured pile resistances to the predicted capacities scattered in a large spectrum. The ratios fluctuated and stayed within a range of 0.6–1.6 for different CPT methods since end of initial driving until more than 2 months after pile installation. Plots of the ratios versus the predicted pile capacities using different CPT methods have revealed that the ratio (R_m/R_p) presented a strong dependence on the predicted capacities. Great research efforts have been devoted to the analyses of the ratios of the 24-h measured resistance to the predicted capacity based on different CPT methods, in an attempt to find a feasible empirical correlation. It is found that a simple linear relationship exists between the quad root of the ratio and the predicted capacity. The developed empirical equations will give pile foundation engineers an insight into the ultimate resistances of driven piles demonstrating significant pile set-up effects. Pile set-up makes pile resistances grow with time, and it might be one of the reasons that cause the frequently reported large discrepancy between calculated static capacity and measured resistance at a certain time after pile installation.  相似文献   

Groundwater potential assessment in a sedimentary terrain,southwestern Nigeria     

Ahzegbobor P. Aizebeokhai  Kehinde D. Oyeyemi  Emmanuel S. Joel 《Arabian Journal of Geosciences》2016,9(7):496

Geoelectrical resistivity techniques are increasingly being applied in addressing a wide range of hydrological, environmental, and geotechnical problems. This is due to their effectiveness in near-surface characterization. In the present study, a suite of vertical electrical soundings (VESs) was integrated with 2D geoelectrical resistivity and time-domain induced polarization (IP) imaging to characterize the near-surface and delineate the underlying aquifer in a sedimentary terrain. The geophysical survey was conducted as part of preliminary studies to evaluate the potential of groundwater resource in Iyana-Iyesi and Canaan Land area of Ota, southwestern Nigeria. A high-yield confined sandy aquifer overlain by a low-yield aquitard was delineated; overlying the aquitard is a very resistive and thick layer that is predominantly composed of kaolinitic swelling clay intercalated with phosphate mineral.  相似文献   

When hazard avoidance is not an option: lessons learned from monitoring the postdisaster Oso landslide,USA     

Reid  Mark E.  Godt  Jonathan W.  LaHusen  Richard G.  Slaughter  Stephen L.  Badger  Thomas C.  Collins  Brian D.  Schulz  William H.  Baum  Rex L.  Coe  Jeffrey A.  Harp  Edwin L.  Schmidt  Kevin M.  Iverson  Richard M.  Smith  Joel B.  Haugerud  Ralph A.  George  David L. 《Landslides》2021,18(9):2993-3009

On 22 March 2014, a massive, catastrophic landslide occurred near Oso, Washington, USA, sweeping more than 1 km across the adjacent valley flats and killing 43 people. For the following 5 weeks, hundreds of workers engaged in an exhaustive search, rescue, and recovery effort directly in the landslide runout path. These workers could not avoid the risks posed by additional large-scale slope collapses. In an effort to ensure worker safety, multiple agencies cooperated to swiftly deploy a monitoring and alerting system consisting of sensors, automated data processing and web-based display, along with defined communication protocols and clear calls to action for emergency management and search personnel. Guided by the principle that an accelerating landslide poses a greater threat than a steadily moving or stationary mass, the system was designed to detect ground motion and vibration using complementary monitoring techniques. Near real-time information was provided by continuous GPS, seismometers/geophones, and extensometers. This information was augmented by repeat-assessment techniques such as terrestrial and aerial laser scanning and time-lapse photography. Fortunately, no major additional landsliding occurred. However, we did detect small headscarp failures as well as slow movement of the remaining landslide mass with the monitoring system. This was an exceptional response situation and the lessons learned are applicable to other landslide disaster crises. They underscore the need for cogent landslide expertise and ready-to-deploy monitoring equipment, the value of using redundant monitoring techniques with distinct goals, the benefit of clearly defined communication protocols, and the importance of continued research into forecasting landslide behavior to allow timely warning.

  相似文献   

Paper 5. climate change impacts on the energy sector and possible adjustments in the mink region     

Joel Darmstadter 《Climatic change》1993,24(1-2):117-129

The discussion reviews the prevailing pattern of energy demand and supply in the MINK states, speculates on the region's long-term energy future in the absence and presence of greenhouse warming, and, in the latter case, considers energy sector adaptation to such a prospect. Climate-sensitive energydemand is dominated by heating and cooling in various sectors of the regional economy (around 20% of regional energy consumption) and by such agricultural applications as irrigation pumping and crop drying (around 5%). A climate-sensitive energysupply issue of some importance is the region's partial dependence on hydroelectric capacity in the upper Missouri river basin. The analysis finds that, unlike the rather significant impacts likely to be experienced by other sectors of the regional economy, the hypothesized warming trend will translate into only small net increases in energy demand; and that technological possibilities and policy measures are available to mute any serious climatic effects on the energy sector.  相似文献   

Multilevel Slug Tests with Comparisons to Tracer Data     

Joel G. Melville  Fred J. Molz  Oktay Güven  Mark A. Widdowson 《Ground water》1991,29(6):897-907

  相似文献   

Reconstruction of seasonal temperatures in Central Canada since A.D. 1700 and detection of the 18.6- and 22-year signals     

Joel Guiot 《Climatic change》1987,10(3):249-268

This paper presents an attempt to summarize various sparse proxy series into continuous and exhaustive climatic data. Freeze-up and break-up dates, early meteorological records and tree-ring data have been combined for the Hudson Bay region and 22 continuous proxy series extending from 1700 to 1979 have been deduced. These new series in term provided the basis for a regressive reconstruction of six seasonal temperature series. Verification tests are successful mainly for the high frequencies components. The low frequencies variability is better estimated by a best analogues method. Both kinds of reconstructions have been combined to improve the results. The main characteristic of the reconstructions is a warming trend beginning at the end of the 19th century. Evidence for a beat wave resulting from 22-year solar and 18.6-year lunar nodal tidal cycles is presented. A phase analysis showed results consistent with other studies of summer temperature variability: temperature maxima correspond to sunspot minima ending an even cycle and are emphasized by the lunar maxima. Different phenomena are pointed out for autumn and winter temperatures: their maxima coincide to sunspot even maxima amplified by lunar minima. In spring, the transition season, these signals are not apparent.  相似文献   

A modified parameterization of flux-profile relationships in the surface layer using different roughness length values for heat and momentum   总被引：1，自引：0，他引：1  

Patrick Mascart  Joel Noilhan  Hervé Giordani 《Boundary-Layer Meteorology》1995,72(4):331-344

The surface-layer flux-profile formulae of Louis (1979), used in many atmospheric models, are modified in a simple way to allow for different values of the roughness lengths for heat and momentum. The modified set of formulae simplifies the calculation of surface-layer fluxes over most natural land surfaces, where the roughness length for momentum can be almost an order of magnitude greater than that for heat.  相似文献