排序方式： 共有9条查询结果，搜索用时 296 毫秒
1
1.
Simulating Stable Isotope Ratios in Plumes of Groundwater Pollutants with BIOSCREEN‐AT‐ISO 
下载免费PDF全文
下载免费PDF全文 Patrick Höhener Zhi M. Li Maxime Julien Pierrick Nun Richard J. Robins Gérald S. Remaud 《Ground water》2017,55(2):261-267
BIOSCREEN is a well‐known simple tool for evaluating the transport of dissolved contaminants in groundwater, ideal for rapid screening and teaching. This work extends the BIOSCREEN model for the calculation of stable isotope ratios in contaminants. A three‐dimensional exact solution of the reactive transport from a patch source, accounting for fractionation by first‐order decay and/or sorption, is used. The results match those from a previously published isotope model but are much simpler to obtain. Two different isotopes may be computed, and dual isotope plots can be viewed. The dual isotope assessment is a rapidly emerging new approach for identifying process mechanisms in aquifers. Furthermore, deviations of isotope ratios at specific reactive positions with respect to “bulk” ratios in the whole compound can be simulated. This model is named BIOSCREEN‐AT‐ISO and will be downloadable from the journal homepage. 相似文献
2.
Violaine Ponsin Amélie Chablais Julien Dumont Olivier Radakovitch Patrick Höhener 《Ground Water Monitoring & Remediation》2015,35(2):30-38
The objective of this study was to investigate whether 222Rn in groundwater can be used as a tracer for light non‐aqueous phase liquid (LNAPL) quantification at a field site treated by dual‐phase LNAPL removal. After the break of a pipeline, 5 ha of soil in the nature reserve Coussouls de Crau in southern France was contaminated by 5100 m3 of crude oil. Part of this oil seeped into the underlying gravel aquifer and formed a floating oil body of about 3.9 ha. The remediation consists of plume management by hydraulic groundwater barriers and LNAPL extraction in the source zone. 222Rn measurements were performed in 21 wells in and outside the source zone during 15 months. In uncontaminated groundwater, the radon activity was relatively constant and remained always >11 Bq/L. The variability of radon activity measurements in wells affected by the pump‐and‐skim system was consistent with the measurements in wells that were not impacted by the system. The mean activities in wells in the source zone were, in general, significantly lower than in wells upgradient of the source zone, owing to partitioning of 222Rn into the oil phase. The lowest activities were found in zones with high non‐aqueous phase liquid (NAPL) recovery. LNAPL saturations around each recovery well were furthermore calculated during a period of high groundwater level, using a laboratory‐determined crude oil–water partitioning coefficient of 38.5 ± 2.9. This yielded an estimated volume of residual crude oil of 309 ± 93 m3 below the capillary fringe. We find that 222Rn is a useful and cheap groundwater tracer for finding zones of good LNAPL recovery in an aquifer treated by dual‐phase LNAPL removal, but that quantification of NAPL saturation using Rn is highly uncertain. 相似文献
3.
Iron transformations in a calcium carbonate rich fresh-water sediment were studied by analyzing the relevant constituents of both interstitial water and solid matter. Analysis of interstitial water shows that the observed redox sequence NO−3/NH+4, MnO2/Mn(II), FeOOH/Fe(II), SO2−4/S(−II) is roughly in agreement with that predicted by the Gibbs Free Energy for the corresponding reactions. In contrast to marine sediments, these redox transitions occur in the uppermost sediments, i.e., at depths of 0–4 cm.
Deeper in the sedimentary sequence, the depth profile for dissolved iron exhibits a steady non-linear increase up to 400 μmol dm−3. In this anoxic zone, according to thermodynamic predictions, iron (II)-minerals such as iron sulfide, siderite, and vivianite should precipitate while Fe(III) oxides should be completely dissolved. However, microscopic analysis showed that Fe(III) oxides were present throughout the studied sediment. Furthermore, scanning electron microscope/energy dispersive spectroscopy analysis suggests the presence of iron sulfide could be verified but not that of siderite or vivianite. These observations indicate kinetic control of iron transformations.
We have investigated the importance of kinetic control of iron distribution in anoxic sediments using a diagenetic model for dissolved iron(II). A rough estimate of time scales for dissolution and precipitation rates was made by imposing limiting boundary conditions. Using the calculated rate constant, we established that more than 1000 years would be required for the complete dissolution of Fe(III) oxides, which is agreement with our observations and experimental data from the literature. Calculated precipitation rates of Fe(II) for a given mineral phase such as siderite yield a maximum value of 3 μg(FeCO3) g−1(dry sediment) yr−1. Such low rates would explain the absence of siderite and vivianite.
Finally, it can be inferred from the MnT/FeT ratio in the sediments that this ratio depends on the redox conditions of the sediment-water interface at the time of deposition. Thus, this ratio can be used as “paleo-redox indicator” in lacustrine sediments. 相似文献
4.
This work presents analytical models which are able to predict contours of concentrations and isotope ratios of organic pollutants in homogeneous aquifers. Four analytical solutions of the advective–dispersive transport equation for reactive transport from the literature differing in assumptions regarding biodegradation kinetics were used. Stable isotope ratios are computed after modelling the individual reactive transport of isotopic species in the aquifer, which respond differently to fractionation by biodegradation or sorption. The main finding of this study is that the isotope ratios in the plumes are very sensitive to the assumptions underlying the biodegradation kinetics in the models. When biodegradation occurs throughout the core of the plume as first-order reaction, the transversal gradients in isotope ratios are smooth. When biodegradation occurs in a bi-molecular reaction with an electron acceptor (modelled by double-Monod kinetics), steep transversal isotope gradients are predicted. When the reaction rates approach instantaneous reaction along the plume fringes, isotope shifts in the core of the plume disappear. A model incorporating plume and fringe degradation produces the most plausible predictions of isotope ratios in this study. It is shown furthermore that isotope fractionation by sorption causes an even different pattern of isotope ratios, with positive shifts restricted to near the forerunning front of an expanding plume. The models developed in this work can serve for the validation of numerical models and may be incorporated in natural attenuation support systems such as e.g. BIOSCREEN. 相似文献
5.
6.
The sugar factory at Aarberg, Switzerland, has processed about 18×106 metric tons of sugar beets in the last 100 years. This has been accompanied by releases of dissolved organic carbon to the
groundwater, induced both by direct wastewater disposal until 1964 and by ongoing leakage from solid-waste deposits. Downgradient
in the groundwater of the glaciofluvial aquifer, depletion of oxygen concentrations accompanied by low nitrate, high ammonium,
dissolved Mn(II) and Fe(II) concentrations are observed. This study was aimed at developing a quantitative comprehension of
theimpact of the leaking waste deposits on biogeochemical processes in the aquifer and on groundwater quality. The study includes
a review of historical information, a survey of the hydrogeochemistry in the aquifer, the characterisation of river-water
infiltration rates with the radon method, establishment of a mass-balance model based on a numerical flow and transport model,
and application of a stable-carbon-isotope method to show biodegradation of sugar-waste deposits in the aquifer. The investigations
demonstrate that present emissions from waste deposits would not lead to the consumption of all the O2 in the aquifer. The present occurrence of anoxic groundwater conditions is explained as a result of the long history of waste
loading.
Electronic Publication 相似文献
7.
Mean dissolved inorganic nitrogen concentrations ([DIN]) in deep, seasonally stratified lakes with comparable DIN inputs can differ by up to a factor of 3 depending on hydraulic and morphometric properties and/or different trophic states of the lakes. In such lakes, net N sedimentation rates were estimated with two independent methods (sediment core analysis and input-output mass balances). They were higher in eutrophic lakes (Mean: 5.1; SD: ± 1.6 g m–2 yr–1; n = 13) than in oligotrophic lakes (1.6 ± 1.0 g m–2 yr–1; n = 3), but independent of [DIN]. Gaseous N loss rates to the atmosphere, as calculated from combined N- and P-mass balances from selected lakes, ranged from 0.9 to 37.4 g m–2 yr–1 (n = 10) and were positively correlated with [DIN]. Reduction of NO
3
-
to N2 is assumed to be the main cause for gaseous N losses. A simple one-box mass balance model for [DIN], based on DIN input and rates and kinetics of N removal processes (net sedimentation and gaseous N loss) is proposed, and validated with a data base on [DIN] and DIN input in 19 deep, seasonally stratified lakes of central Europe. The model illustrated that the amount of water loading per unit surface area of a lake (called water discharge height q) is the critical parameter determining mean lake [DIN] relative to mean input [DIN]. Lakes with a q > 50 m yr–1 have average [DIN] similar to the [DIN] of the inflows regardless of their trophic states, because input and outflow exceed lake-internal N removal processes. A high primary production favors DIN removal in lakes with q < 50 m yr–1. It is concluded that measures to decrease primary production, e.g. by means of P removal programs, lead to an increase of [DIN] in lakes. 相似文献
8.
P. De Cannière J. SchwarzbauerP. Höhener G. LorenzS. Salah O.X. LeupinP. Wersin 《Applied Geochemistry》2011,26(6):967-979
Data interpretation of the Porewater Chemistry (PC) experiment at the Mont Terri Rock Laboratory has led to unexpected observations of anaerobic microbial processes which caused important geochemical perturbations of the Opalinus Clay water in the borehole. The increases of acetate to 146 mg C/L, of DIC to 109 mg C/L and of CH4 to 0.5 mg C/L were unexpected and could not be explained without the presence of a C source in the system. The organic C fuelling the observed microbial activity was until then unknown. Leaching tests were performed on several polymers used for the fabrication of the PC equipment to identify the source of organic matter (OM). Polyethylene (PE) appears to be very inert and does not release detectable concentrations of dissolved organic C (DOC) (<1 ppb) into the water. Polyurethane (PU) leaches out a dozen different organic compounds accounting for only 13 μg DOC/g PU. Under the conditions of the leaching tests, 1 g of polyamide (PA, Nylon) also releases ∼512 μg of the plasticizer N-Butyl-Benzene-Sulfonamide (NBBS). Soaking tests with polyethylene samples immersed in acetone under conditions similar to those used to remove grease spots on the porous PE filter prior to installation showed that acetone could have been trapped in the PE filter, corresponding to an initial concentration of 1.5 g acetone/L of water. However, the accumulated amount of organic C taken into account from all these components was insufficient to satisfactorily explain the observed microbially mediated reducing perturbation. Finally, large amounts of dissolved organic C were found to be released in the system by the jelly polymer filling the reference compartment of the pH and Eh electrodes permanently installed over 5 years in flow-through cells on the water circulation loop of the PC experiment. Glycerol was further identified by chromatographic analysis as the main organic compound released by the electrodes. From the analysis results, as well as from the geochemical calculations, the most likely primary organic C source fuelling the microbial perturbation was glycerol released from the polymeric gel filling the reference electrodes (1.6 g glycerol/electrode). Other sources, such as acetone, may also have contributed to microbial processes, but only to a minor extent. 相似文献
9.
Nitrogen cycling across the sediment-water interface in an eutrophic,artificially oxygenated lake 总被引：9，自引：0，他引：9
Processes controlling the nitrogen (N) exchange between water and sediment in eutrophic Lake Sempach were studied using three different independent methods: benthic flux chambers, interstitial water data and hypolimnetic mass balances. The sediments released NH
4
+
(1.1–16.1 mmoles m–2 d–1), NO
2
-
(0.1–0.4 mmoles m–2 d–1) and dissolved organic N (<0.25 mmoles m–2 d–1). A net NO
3
-
consumption (2.4–11.1 mmoles m–2 d–1) related to the NO
3
-
concentrations in the overlying water was observed in all benthic chamber experiments. The flux of the reactive species NO
3
-
and NH
4
+
was found to depend on hydrodynamic conditions in the water overlying the sediment. For this reason, benthic chambers overestimated the fluxes of inorganic N compared to the other methods. Thus, in short-term flux chamber experiments the sediment may either become a sink or a source for inorganic N depending on the O2 concentration in the water overlying the sediment and the stirring rate. As demonstrated with a15NO
3
-
experiment, nitrate-ammonification accounted for less than 12% of the total NO
3
-
consumption. After six years of artificial oxygenation in Lake Sempach, a decrease in hypolimnetic total inorganic nitrogen (TIN) was observed in the last two years. The occurrence of dense mats of H2S-oxidizingBeggiatoa sp. indicated micro-aerobic conditions at the sediment surface. Under these conditions, a shorter distance between the ecological niches of nitrifying and denitrifying bacteria, and therefore a faster NO
3
-
-transport, can possibly explain the lowering of TIN by enhanced net denitrification. 相似文献
1