Modeling alternative paths of chemical evolution of Na-HCO3-type groundwater near Oak Ridge, Tennessee, USA   总被引：2，自引：0，他引：2  

Laura E. Toran  James A. Saunders 《Hydrogeology Journal》1999,7(4):355-364

 This paper demonstrates that both cation exchange, a commonly invoked mechanism, and silicate hydrolysis, which is less commonly considered, can produce Na-HCO₃-type water in sedimentary rocks. Evolution of Na-HCO₃ groundwater beneath the Oak Ridge Reservation, Tennessee, USA, was studied by comparing observed end-member groundwater composition from multiport samplers to compositions generated by reaction-path geochemical models. Observed groundwater compositions could be reproduced by either the silicate-hydrolysis model or the cation-exchange model. Secondary minerals precipitated in the silicate-hydrolysis model are similar to those present along fractures in the shale and carbonate host rocks, and observed molar Sr²⁺/Ca²⁺ ratios more closely resemble evolution from shale weathering. Both mechanisms should be considered to understand the evolution of Na-HCO₃ groundwater. Received, April 1998 · Revised, January 1999 · Accepted, March 1999  相似文献   

Measurements of the Henry's Law Coefficients of 2-Methyl-3-buten-2-ol, Methacrolein, and Methylvinyl Ketone   总被引：1，自引：0，他引：1  

Laura T. Iraci  Bradly M. Baker  Geoffrey S. Tyndall  John J. Orlando 《Journal of Atmospheric Chemistry》1999,33(3):321-330

Using an equilibrium headspace technique, Henry's law coefficients were measured for methacrolein (H = 6.5 ± 0.7 M atm-1) and methylvinyl ketone (41 ± 7.0 M atm-1) in water at 25 °C. In addition, 2-methyl-3-buten-2-ol was studied at 30 °C in water and in an aqueous ionic solution representative of plant tissue. Similar values were found in deionized water (65 ± 3.5 M atm-1) and in a 0.05 mol kg-1 Ca2+, K+, NO3-, SO42- solution (62 ± 0.8 M atm-1). These Henry's Law coefficients are too small to allow for significant partitioning of methacrolein, methylvinyl ketone or methylbutenol into cloud water under equilibrium conditions.  相似文献   

Numerical experiments on the Rayleigh-Ritz method when applied to doubly connected plates in the case of free edge holes     

P. A. A. Laura  D. R. Avalos  H. A. Larrondo  R. E. Rossi 《Ocean Engineering》1998,25(7)

Numerical experiments are performed on the determination of the fundamental frequency of transverse vibration of simply supported rectangular plates having rectangular holes with free edges. This constitutes a rather common technological situation since holes are present in plates or slabs due to operational conditions, namely passage of conduits or ducts, electric conductors, etc., Satisfying exactly the governing natural boundary conditions at the hole edges is practically an impossible task. This study reviews numerical experiments where the displacement function is expanded into a double Fourier series which constitutes the exact solution when the plate is simply connected. Satisfactory convergence is achieved when the plate is doubly connected.  相似文献   

Quantifying Annual Nitrogen Loss to Groundwater Via Edge-of-Field Monitoring: Method and Application     

Michael Cardiff  Laura Schachter  Jake Krause  Madeline Gotkowitz  Brian Austin 《Ground water》2023,61(1):21-34

Increased nitrate concentrations in groundwater and surface waters represent one of the most widespread and acute impacts of modern agriculture on the environment. However, there is often a fundamental gap in understanding how individual agricultural fields and practices contribute to this broad-scale issue. To practically address nutrient dynamics at individual agricultural sites, methods for assessing nitrogen loss to groundwater that are minimally invasive and thus can encourage farmer “buy in” are necessary. We present an approach that uses edge-of-field monitoring at multilevel samplers along with a once-per-year tracer application (bromide) to calculate nitrogen loss on an annual basis. Using appropriate spatio-temporal integrals of measured concentrations, a net loss of nitrogen to groundwater (per field area) can be calculated. This approach directly measures impacts of nitrogen leaching below the water table, while avoiding permanent in-field installations that can interfere with farm operations. We present an application of this technique to assess nitrogen loss to groundwater over 5 years for a commercial agricultural field in Sauk County, WI. Results from Field 19 indicate that nitrogen losses are similar to (or slightly below) previously reported values for corn and potato crops. In all years, however, we estimate that more than 25% (>60 kg/ha) of nitrogen applied leached as nitrate to groundwater. Use of this mass flux estimation method was most reliable when: (1) tracer is injected directly at the water table, limiting “smearing” within the vadose zone; and (2) nitrate concentrations from laboratory analysis were obtained, rather than using ion-selective electrodes or nitrate test strips.  相似文献   

Biodiversity Conservation in the REDD   总被引：1，自引：0，他引：1  

Gary D Paoli  Philip L Wells  Erik Meijaard  Matthew J Struebig  Andrew J Marshall  Krystof Obidzinski  Aseng Tan  Andjar Rafiastanto  Betsy Yaap  JW Ferry Slik  Alexandra Morel  Balu Perumal  Niels Wielaard  Simon Husson  Laura D'Arcy 《Carbon balance and management》2010,5(1):1-9

Background

Forests occur across diverse biomes, each of which shows a specific composition of plant communities associated with the particular climate regimes. Predicted future climate change will have impacts on the vulnerability and productivity of forests; in some regions higher temperatures will extend the growing season and thus improve forest productivity, while changed annual precipitation patterns may show disadvantageous effects in areas, where water availability is restricted. While adaptation of forests to predicted future climate scenarios has been intensively studied, less attention was paid to mitigation strategies such as the introduction of tree species well adapted to changing environmental conditions.

Results

We simulated the development of managed forest ecosystems in Germany for the time period between 2000 and 2100 under different forest management regimes and climate change scenarios. The management regimes reflect different rotation periods, harvesting intensities and species selection for reforestations. The climate change scenarios were taken from the IPCC's Special Report on Emission Scenarios (SRES). We used the scenarios A1B (rapid and successful economic development) and B1 (high level of environmental and social consciousness combined with a globally coherent approach to a more sustainable development). Our results indicate that the effects of different climate change scenarios on the future productivity and species composition of German forests are minor compared to the effects of forest management.

Conclusions

The inherent natural adaptive capacity of forest ecosystems to changing environmental conditions is limited by the long life time of trees. Planting of adapted species and forest management will reduce the impact of predicted future climate change on forests.  相似文献   

Dynamics of dissolved major (Na,K, Ca,Mg, and Si) and trace (Al,Fe, Mn,Zn, Cu,and Cr) elements along the lower Orinoco River          下载免费PDF全文

Abrahan Mora  Jürgen Mahlknecht  Juan Carlos Baquero  Alain Laraque  Juan A. Alfonso  Daniel Pisapia  Laura Balza 《水文研究》2017,31(3):597-611

This study addresses the changes in dissolved major and trace element concentrations along the Orinoco River, including the mixing zone between the Orinoco and Apure Rivers. Water samples from the Apure and Orinoco Rivers were collected monthly in four sectors over a period of 15 months. Auxiliary parameters (pH, dissolved oxygen, conductivity, and temperature), total suspended sediments, dissolved organic carbon (DOC), and major (Na, K, Ca, Mg, and Si) and trace (Al, Fe, Mn, Zn, Cu, and Cr) element concentrations were measured in all sectors. The relative contribution of both rivers after the Apure–Orinoco confluence was determined using Ca as a tracer. Moreover, a mixing model was developed to determine whether dissolved species exhibit a conservative behavior during mixing. The results indicate that DOC is removed from waters during the Apure–Orinoco mixing, probably due to absorption of DOC on mineral phases supplied by the Apure River. Dissolved Na, Ca, and Mg behave conservatively during the mixing processes, and their concentrations are controlled by a dilution process. The anomaly in the temporal pattern of K in the Orinoco is caused by the input of biogenic K originating from the Apure River during the high‐water stage. The loss of dissolved Si during the low‐water stage can be explained by the uptake of Si by diatoms. Dissolved Mn, Zn, Al, and Fe showed a non‐conservative behavior during the Apure–Orinoco mixing. The removal of Mn and Zn from the dissolved phase can be explained by the formation of Mn‐oxyhydroxides and the scavenging of Zn onto Mn oxides. Dissolved Fe is controlled by redox processes, although the removals of Fe and Al due to the preferential adsorption of large organometallic complexes by mineral surfaces after the Apure–Orinoco confluence can affect the mobility of both elements during transport. The conservative behavior shown by Cu and Cr can be related to the tendency of both elements to be complexed with small organic colloids, which are not preferentially adsorbed by clays.  相似文献   

Individual and population indicators of Zostera japonica respond quickly to experimental addition of sediment-nutrient and organic matter     

Qiuying Han  Laura M. Soissons  Dongyan Liu  Marieke M. van Katwijk  Tjeerd J. Bouma 《Marine pollution bulletin》2017,114(1):201-209

A manipulative field experiment was designed to investigate the effects of sediment-nutrients and sediment-organic matters on seagrasses, Zostera japonica, using individual and population indicators. The results showed that seagrasses quickly responded to sediment-nutrient and organic matter loading. That is, sediment-nutrients positively impacted on seagrasses by increasing N content of leaves and roots, leaf length and belowground biomass. Sediment-organic matter loading lowered N content of seagrass leaves and belowground biomass. Negative effects of organic matter loading were aggravated during nutrient loading, by decreasing N content of leaves, P content of roots, leaf width, shoot number in the middle period of the experiment, increasing C/N ratio of leaves, C/P and N/P ratio of roots and above to belowground biomass ratio of seagrasses. Consequently, Z. japonica could be considered as a fast indicator to monitor seagrass ecosystem status in the eutrophic areas and facilitate to interpreting the response of seagrasses to multiple stressors.  相似文献   

New evidence of sea‐level lowstands and paleoenvironment during MIS 6 and 4 in the Cantabrian coastal karst: the Cobiheru cave (North Iberia)          下载免费PDF全文

Daniel Ballesteros  Laura Rodríguez‐Rodríguez  Saúl González‐Lemos  Santiago Giralt  Diego Jaime Álvarez‐Lao  Luna Adrados  Montserrat Jiménez‐Sánchez 《地球表面变化过程与地形》2017,42(11):1704-1716

The geomorphological evolution of the Cobiheru Cave shows the influence of the non‐carbonate coastal mountain ranges on coastal karst evolution, as well as the temporal distribution of the cold‐adapted fauna sites in the Cantabrian Coast. Geomorphological observation and uranium/thorium (U/Th) dating lead to the construction of an evolution model. The model comprises two episodes of cave deposition occurring at c. 60–70 and 130–150 ka, linked to cold climate conditions, global sea‐level lowstands and the erosion of alluvial fans that covered the karst. Moreover, the comparison between the Cobiheru record and some raised beaches identified in previous studies sets the beginning of the sea‐level lowering in the Cantabrian Sea during the marine isotope stages (MIS) 5–4 transition. Two palaeoenvironments are inferred based on finding Equus ferus and Elona quimperiana. A wet deciduous forest would have developed on the emerged marine terrace of the Cobiheru Cave since at least the Middle Pleistocene, and an open landscape with scarce vegetation would have been present at c. 65 ka. The erosional event identified in the Cobiheru Cave helps to understand the temporal distribution of cold‐adapted mammals located in the Asturias region. The probable sites of cold‐adapted fauna developed in caves and alluvial fans would have disappeared after 65 ka. Therefore, palaeontological and palaeoclimate research based on cold‐adapted mammals suggests the occurrence of an hiatus in the palaeontological record prior to 50 ka. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

The importance of wind forcing in fjord wave modelling     

Christakos  Konstantinos  Furevik  Birgitte R.  Aarnes  Ole Johan  Breivik  Øyvind  Tuomi  Laura  Byrkjedal  Øyvind 《Ocean Dynamics》2020,70(1):57-75

Ocean Dynamics - Accurate predictions of surface ocean waves in coastal areas are important for a number of marine activities. In complex coastlines with islands and fjords, the quality of wind...  相似文献   

Stratospheric entry point for upper-tropospheric air within the Asian summer monsoon anticyclone     

QiuJun Fan  JianChun Bian  Laura L. Pan 《中国科学:地球科学(英文版)》2017,60(9):1685-1693

The Asian summer monsoon (ASM) anticyclone isolates upper-tropospheric air within the interior of the anticyclone from the outside. Forward trajectory simulations in previous studies have shown that much of the air within the ASM anticyclone can be trapped for up to two or three weeks, not only laterally but also vertically. Here, we investigate the locations of exit points for upper-tropospheric air trapped within the ASM anticyclone, especially the preferred tropopause-crossing locations, using a 3-dimensional trajectory model. Forward trajectory calculations show two-thirds of the air crosses the tropopause at the southern part of the anticyclone via upward diabatic transport. Furthermore, some air crosses at northern and eastern parts via isentropic shedding, but air crosses rarely through the center of the anticyclone. However, calculations also show that many stratospheric parcels within the anticyclone are traceable from the upper-tropospheric anticyclone. This implies they cannot break through the tropopause directly overhead but instead enter the stratosphere via other entry points.  相似文献