Steady-State Soil Vapor Extraction from a Pressure-Controlled or Flow-Controlled Well     

Tomas Perina  Tien-Chang Lee 《Ground Water Monitoring & Remediation》2005,25(3):63-72

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Inferring the location of catchment characteristic soil moisture monitoring sites. Covariance structures in the temporal domain     

Tomas K. Thierfelder  Rodger B. Grayson  Dietrich von Rosen  Andrew W. Western 《Journal of Hydrology》2003,280(1-4):13-32

Information shortage is a fundamental constraint in catchment hydrology that severely affects the possibilities for secure inference of the generic hydrologic landscape, as well as for secure validation of physically deduced distributed models. The introduction of databases with high enough spatiotemporal resolution to properly reflect generic hydrological catchment characteristics may therefore be considered as an inferential breakthrough. The work presented here is part of a project where observations from such an Australian catchment (the Tarrawarra) are utilised to estimate the discrepancy for individual soil moisture monitoring sites in reflecting generic catchment characteristics. With low enough discrepancy, observation sites may be considered as catchment characteristic soil moisture monitoring (CASMM) sites, thus capturing unbiased catchment characteristics and being well suited to represent the catchment in a monitoring effort. In this particular study, covariance structures in the temporal domain are inferred in order to enable subsequent enquiries regarding CASMM discrepancies. This is accomplished with ARMAX filters applied to the conditional auto- and cross-covariance structures that connect observations of soil moisture to the temporal variation of meteorology. The results suggest that weekly observations of Tarrawarra soil moisture are quite consistent realisations of first order auto-regressive processes, which means that the present state of soil moisture is generally acquired through the past week. With auto-correlative effects filtered out, cross-correlative meteorological effects on Tarrawarra soil moisture are identified and generally represented by the present week's accumulation of rainfall, the present week's accumulation of global radiation, and the previous week's maximum wind speed. After successive filtering of conditional cross-correlative effects, residual time-series observations may be considered as temporally independent, and therefore are well suited for subsequent inferences regarding covariance structures in the spatial domain. Since the exclusion of auto-correlative effects is necessary for unambiguous model interpretation, the estimated cross-correlative parameters should reflect the true nature of underlying physical processes.  相似文献   

The Influence of Grazing by two Acartia Species on Olisthodiscus luteus CARTER   总被引：2，自引：0，他引：2  

Carmelo  R.Tomas Ellen E.  Deason 《Marine Ecology》1981,2(3):215-223

Abstract. The grazing of Acartia hudsonica and Acartia tonsa was observed on cultures of Olisthodiscus luteus and Dunaliella tertiotecta presented alone and in combination. Feeding on D. lertiolecla by both Acartia species increased directly with concentration but was always lower at equivalent food concentrations when O. luteus was present. In mixed phytoplankton cultures, A. hudsonica fed on both species at low O. luteus concentration, only on D, lertiolecla at intermediate levels and stopped feeding at highest O. luteus concentrations. A. tonsa showed a variable but similar result. These studies indicate the possible role of these dominant herbivores on the dynamics of O. luteus populations.  相似文献   

Phosphorus Cycling in a Freshwater Estuary Impacted by Cyanobacterial Blooms     

Jolita Petkuviene  Mindaugas Zilius  Irma Lubiene  Tomas Ruginis  Gianmarco Giordani  Arturas Razinkovas-Baziukas  Marco Bartoli 《Estuaries and Coasts》2016,39(5):1386-1402

The availability of reactive phosphorus (P) may promote cyanobacterial blooms, a worldwide increasing phenomenon. Cyanobacteria may also regulate benthic P cycling through labile organic input to sediments, favouring reduced conditions and P release, ultimately acting as self-sustainment mechanism for the phytoplankton blooms. To analyse P–cyanobacteria feedbacks and compare external versus internal loads, we investigated P cycling in the Curonian Lagoon, a freshwater estuary with recurrent summer blooms. At two sites representing the dominant sediment types, we characterised P pools and mobility, via combined pore water analysis, calculation of diffusive exchanges and flux measurements via sediment core incubations. Annual P budgets were also calculated, to analyse the whole lagoon role as net sink or source. Muddy sediments, representing nearly 50 % of the lagoon surface, displayed higher P content if compared with sandy sediments, and most of this pool was reactive. The muddy site had consequently higher pore water dissolved inorganic phosphorus (DIP) concentrations maintaining high diffusive gradients. However, measured fluxes suggested that both sediment types were mostly P sinks except for a large DIP regeneration (nearly 30 μmol m^?2 h^?1) recorded at the muddy site during an intense cyanobacteria bloom. Such internal regeneration had the same order of magnitude as the annual external P load and may offset the net annual DIP sink role of the estuary. It may also prolong the duration of the bloom. Our results suggest that positive feedbacks can regulate N-fixing cyanobacteria blooms and internal P recycling, through either diffusive fluxes or sediment settling and resuspension.  相似文献   

Natural attenuation of chlorinated solvents: a comparative study     

Tomas Kuchovsky  Ondra Sracek 《Environmental Geology》2007,53(1):147-157

Sites contaminated by chlorinated solvents have been investigated. Sites Dolni Tresnovec and Zetor located in Czech Republic exhibit relatively reducing conditions. Primary chlorinated solvents are attenuated by reductive dechlorination processes, and plumes have probably reached steady-state at Zetor site. Terminal electron accepting processes (TEAP) are ferric iron reduction and sulfate reduction at respective Dolni Tresnovec and Zetor sites. Source of organic matter at Dolni Tresnovec site is the waste deposited at local landfill. At Zetor site reducing conditions are linked to the petroleum hydrocarbons spill from broken pipeline. In contrast, site Dubnica in Slovak Republic exhibits oxidizing conditions, and natural attenuation of chlorinated solvents occurs mostly by dispersion. Modeling by the program BIOCHLOR indicated formation of steady-state plumes close to source at Zetor site, much longer steady-state plumes at Dolni Tresnovec site, and extremely long plumes at Dubnica site. Results demonstrate an important role of redox conditions in natural attenuation of chlorinated solvents.  相似文献   

Heterogeneous processes of geochemical migration: V. S. Golubev and A. A. Garibyants,Consultant Bureau, 1971, 150 pp. Translated by J. P. Fitzsimmons. $22.50     

Tomas Paces 《Geochimica et cosmochimica acta》1973,37(3):711-712

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Further studies on the Fennoscandian gravity field versus the Moho depth and land uplift     

Lars E. Sjöberg  Huaan Fan  Tomas Nord 《Journal of Geodesy》1994,69(1):32-42

Whether post-glacial rebound or/and crustal variation contributes to the pattern of the Fennoscandian gravity field has been of great interest to geoscientists. Previous numerical studies are based on different Moho maps, different global Earth gravity models and different isostatic models of Pratt type, resulting in quite different conclusions.In this study, we use the improved Moho depth map of Korja et al. (1993), the OSU91A Earth gravity model and a refined modeling of the Moho depth contribution. We conclude that not more than about 40% and 30% of the Fennoscandian geoid and gravity depressions of the orders of -12m and -40 mGal might be caused by crustal thickening, leaving at least -6 m and -28 mGal to be adjusted in accordance with post-glacial rebound.  相似文献   

A simplified approach to analysing historical and recent tritium data in surface waters          下载免费PDF全文

Robert L. Michel  Pradeep Aggarwal  Luis Araguas‐Araguas  Brent D. Newman  Tomas Vitvar 《水文研究》2015,29(4):572-578

Tritium concentrations in river and stream waters from different locations can be compared by normalizing them using the ratio of tritium concentrations in precipitation and surface water (C_p/C_s) in the study area. This study uses these ratios in a hydrological residence time context to make regional‐ and global‐scale comparisons about river basin dynamics. Prior to the advent of nuclear weapons testing, the C_p/C_s ratio was greater than or equal to 1 everywhere because of the decay of tritium in the watershed after it was deposited by precipitation. After an initial increase in the ratios during the bomb peak, the ratio dropped to less than 1 for most surface waters in the following years. This post‐bomb change in the ratio is due to the retention of the bomb‐pulse water in watersheds on timescales that are long relative to the residence time of tritium in the atmosphere. Ratios were calculated for over 6500 measurements of tritium in river and stream waters compiled by the International Atomic Energy Agency. These measurements span the post‐nuclear era (1940s to present) and include many long‐term datasets, which make it possible to examine residence times of waters in watersheds on a global basis. Plotting C_p/C_s versus time shows that ratios tended to reach a minimum in approximately one to two decades after the bomb peak for most locations. This result suggests that changes affecting quantity and quality of river flows need to be assessed on a multi‐decadal timescale. These long lag times have significant implications for assessing climate or land‐use change impacts on a large number of river systems around the world. The continuing value of tritium in studying surface water systems for both the Southern and Northern Hemisphere is also demonstrated. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.  相似文献   

Groundwater hydrochemistry and origin in the south-eastern part of Wadi El Natrun,Egypt     

Hend Ahmed Ibrahim Hussein  Adam Ricka  Tomas Kuchovsky  Maged Mostafa El Osta 《Arabian Journal of Geosciences》2017,10(7):170

The demand for water is rapidly increasing in Egypt, because of high population and agriculture production growth rate, which makes research of water resources necessary. The regional multi-aquifer system of the Miocene–Pleistocene age is discharged in Wadi El Natrun area. Intensive aquifer overexploitation and agricultural development in the area are related to groundwater quality deterioration. Hydrochemical and hydrogeological data was evaluated to determine the groundwater origin and quality in the south-eastern part of wadi, which appears to be more significant for water supply owing to lower groundwater salinity. The dominance of the high mineralised Cl groundwater type was found; however, also less mineralised SO₄ and HCO₃ types were identified there. Based on the ion relations, halite and gypsum dissolution and ion exchange are the most important hydrochemical processes forming the groundwater chemical composition. The Cl dominated groundwater matches the discharge part of the regional hydrogeological system. Contrary, the presence of HCO₃ and SO₄ hydrochemical types corresponds to the infiltration and transferring parts of the hydrogeological system indicating the presence of zones conducting low mineralised groundwater. The discharge area of the over-pumped aquifer in Wadi El-Natrun lies 23 m beneath the sea level with the shoreline being at the distance of 100 km, thus there is a real risk of seawater intrusion. Using the hydrochemical facies evolution diagram, four samples in the centre of the discharge area indicate advanced seawater intrusion. The zones of the highest demand for groundwater quality protection were indicated based on a spatial pattern of hydrogeochemical composition.  相似文献   

Accumulation Rate Measurements at Taylor Dome, East Antarctica: Techniques and Strategies for Mass Balance Measurements in Polar Environments     

David L. Morse  Edwin D. Waddington  Hans-Peter Marshall  Tomas A. Neumann  Eric J. Steig  Jack E. Dibb  Dale P. Winebrenner  & Robert J. Arthern 《Geografiska Annaler: Series A, Physical Geography》1999,81(4):683-694

Accumulation rate measurements on the East Antarctic plateau are challenging due to both spatial and temporal variability. Annual stratigraphy is often not reliably or consistently preserved in the firn, and so accumulation cannot be determined from snow pit stratigraphy. We present a suite of accumulation rate measurements collected over several seasons at Taylor Dome, East Antarctica. We compare net accumulation results from direct burial rate measurements and β -activity firn cores along a 35 km traverse. The two methods are consistent and show that the net accumulation varies from greater than 10 cm a⁻¹ to about 1 cm a⁻¹ (ice equivalent) southwest to northeast across the dome. We map the depth of shallow radar layering to interpolate and extrapolate these point-location measurements and show that considerable variations occur over kilometer scales resulting from subtle surface topography. We also present accumulation rates estimated from concentration of the cosmogenic isotope ¹⁰Be and from activity profiles of ²¹⁰Pb. Finally, satellite passive microwave data are used to estimate spatially averaged accumulation rates on the regional to continental scale to provide a context for these local observations. We show that robust mass balance measurements in this environment must rely on spatial and/or temporal averaging.  相似文献