Transport of double-stranded ribonucleic acids (dsRNA) and deoxyribonucleic acids (DNA) in sand and iron oxide-coated sand columns under varying solution chemistries.

Assessing ecological risks associated with the use of genetically modified RNA interference crops demands an understanding of the fate of crop-released insecticidal double-stranded RNA (dsRNA) molecules in soils. We studied the adsorption of one dsRNA and two double-stranded DNA as model nucleic acids (NAs) during transport through sand- and iron oxide-coated sand (IOCS)-filled columns over a range of solution pH and ionic compositions. Consistent with NA-sand electrostatic repulsion, we observed only slight retention of NAs in sand columns.

Oxidation of Reduced Peat Particulate Organic Matter by Dissolved Oxygen: Quantification of Apparent Rate Constants in the Field.

Peat particulate organic matter (POM) is an important terminal electron acceptor for anaerobic respiration in northern peatlands provided that the electron-accepting capacity of POM is periodically restored by oxidation with O during peat oxygenation events. We employed push-pull tests with dissolved O as reactant to determine pseudo-first-order rate constants of O consumption ( k) in anoxic peat soil of an unperturbed Swedish ombrotrophic bog. Dissolved O was rapidly consumed in anoxic peat with a mean k of 2.

High Temporal and Spatial Variability of Atmospheric-Methane Oxidation in Alpine Glacier Forefield Soils.

Glacier forefield soils can provide a substantial sink for atmospheric CH, facilitated by aerobic methane-oxidizing bacteria (MOB). However, MOB activity, abundance, and community structure may be affected by soil age, MOB location in different forefield landforms, and temporal fluctuations in soil physical parameters. We assessed the spatial and temporal variability of atmospheric-CH oxidation in an Alpine glacier forefield during the snow-free season of 2013.

How functional is a trait? Phosphorus mobilization through root exudates differs little between Carex species with and without specialized dauciform roots.

Root structures secreting carboxylates and phosphatases are thought to enhance a plant's phosphorus (P) acquisition. But do closely related species with and without such structures really differ in root exudation, P mobilization, or ecological niche? We investigated this by comparing 23 European Carex species with and without 'dauciform roots' (DRs). Plants grown in pots with sand were screened for DR formation, phosphatase activities, carboxylate exudation, and utilization of various organic and inorganic P compounds.

Quantification of Phenolic Antioxidant Moieties in Dissolved Organic Matter by Flow-Injection Analysis with Electrochemical Detection.

Phenolic moieties in dissolved organic matter (DOM) play important roles as antioxidants in oxidation processes in natural and engineered systems. This work presents an automated and highly sensitive flow injection analysis (FIA) system coupled to both spectrophotometric and electrochemical detection to quantify electron-donating phenolic moieties in DOM by determining the number of electrons that these moieties transfer to an added chemical oxidant, the radical cation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS(•+)). The FIA system was successfully validated using Trolox as a redox standard.

Field-scale tracking of active methane-oxidizing communities in a landfill cover soil reveals spatial and seasonal variability.

Aerobic methane-oxidizing bacteria (MOB) in soils mitigate methane (CH4 ) emissions. We assessed spatial and seasonal differences in active MOB communities in a landfill cover soil characterized by highly variable environmental conditions. Field-based measurements of CH4 oxidation activity and stable-isotope probing of polar lipid-derived fatty acids (PLFA-SIP) were complemented by microarray analysis of pmoA genes and transcripts, linking diversity and function at the field scale.

Physical extraction of microorganisms from water-saturated, packed sediment.

Microbial characterization of aquifers should include samples of both suspended and attached microorganisms (biofilms). We investigated the effect of shear, sonication, and heat on the extraction of microorganisms from water-saturated, packed sediment columns containing established biofilms. Shear was studied by increasing flow velocity of the column eluent, sonication by treating the columns with ultrasound at different power levels, and heat by warming up the column eluent to different temperatures.

Degradation of polar organic micropollutants during riverbank filtration: complementary results from spatiotemporal sampling and push-pull tests.

The fate of polar organic micropollutants (logDOW (pH 7) between -4.2 and +3.5) during riverbank filtration (RBF) at the river Thur was studied using both spatiotemporally resolved sampling and single-well push-pull tests (PPT), followed by LC-MS/MS analysis.

Poly-use multi-level sampling system for soil-gas transport analysis in the vadose zone.

Soil-gas turnover is important in the global cycling of greenhouse gases. The analysis of soil-gas profiles provides quantitative information on below-ground turnover and fluxes. We developed a poly-use multi-level sampling system (PMLS) for soil-gas sampling, water-content and temperature measurement with high depth resolution and minimal soil disturbance.

In-situ sonication for enhanced recovery of aquifer microbial communities.

Sampling methods for characterization of microbial communities in aquifers should target both suspended and attached microorganisms (biofilms). We investigated the effectiveness and reproducibility of low-frequency (200 Hz) sonication pulses on improving extraction efficiency and quality of microorganisms from a petroleum-contaminated aquifer in Studen (Switzerland). Sonication pulses at different power levels (0.

Chemical extraction of microorganisms from water-saturated, packed sediment.

Microbial characterization of aquifers should combine collection of suspended and attached microorganisms (biofilms). This study investigated chemical extraction of microorganisms from water-saturated, packed sediment containing established biofilms. It compares the use of different detachment-promoting agent (DPA) solutions with tap water as eluent in column experiments.

Field-scale labelling and activity quantification of methane-oxidizing bacteria in a landfill-cover soil.

Aerobic methane-oxidizing bacteria (MOB) play an important role in soils, mitigating emissions of the greenhouse gas methane (CH(4)) to the atmosphere. Here, we combined stable isotope probing on MOB-specific phospholipid fatty acids (PLFA-SIP) with field-based gas push-pull tests (GPPTs). This novel approach (SIP-GPPT) was tested in a landfill-cover soil at four locations with different MOB activity.

Structure and function of methanotrophic communities in a landfill-cover soil.

In landfill-cover soils, aerobic methane-oxidizing bacteria (MOB) convert CH(4) to CO(2), mitigating emissions of the greenhouse gas CH(4) to the atmosphere. We investigated overall MOB community structure and assessed spatial differences in MOB diversity, abundance and activity in a Swiss landfill-cover soil. Molecular cloning, terminal restriction-fragment length polymorphism (T-RFLP) and quantitative PCR of pmoA genes were applied to soil collected from 16 locations at three different depths to study MOB community structure, diversity and abundance; MOB activity was measured in the field using gas push-pull tests.

Development and evaluation of micro push-pull tests to investigate micro-scale processes in porous media.

Soils and sediments are porous media characterized by heterogeneities across a wide range of spatial scales. Physical, chemical, and biological properties have been found to show great variation even at subcentimeter scales. Here we present a new micro technique for the in situ study of chemical and microbiological reactions in water-saturated porous media at the mm-scale.

Response of methanotrophic activity and community structure to temperature changes in a diffusive CH/O counter gradient in an unsaturated porous medium.

Microbial methane oxidation is a key process in the global methane cycle. In the context of global warming, it is important to understand the responses of the methane-oxidizing microbial community to temperature changes in terms of community structure and activity. We studied microbial methane oxidation in a laboratory-column system in which a diffusive CH(4)/O(2) counter gradient was maintained in an unsaturated porous medium at temperatures between 4 and 20 degrees C.

Transport of methane and noble gases during gas push-pull tests in variably saturated porous media.

The gas push-pull test (GPPT) is a single-well gas-tracer method to quantify in situ rates of CH4 oxidation in soils. To improve the design and interpretation of GPPT field experiments, gas component transport during GPPTs was examined in abiotic porous media over a range of water saturations (0.0 < or = Sw < or = 0.

Effect of water-table fluctuation on dissolution and biodegradation of a multi-component, light nonaqueous-phase liquid.

Light nonaqueous-phase liquids (LNAPLs) such as gasoline and diesel fuel are among the most common causes of soil and groundwater contamination. Dissolution and subsequent advective transport of LNAPL components can negatively impact water supplies, while biodegradation is thought to be an important sink for this class of contaminants. We present a laboratory investigation of the effect of a water-table fluctuation on dissolution and biodegradation of a multi-component LNAPL (85% hexadecane, 5% toluene, 5% ethylbenzene, and 5% 2-methylnapthalene on a molar basis) in a pair of similar model aquifers (80 cm x 50 cm x 3 cm), one of which was subjected to a water-table fluctuation.

Methanotrophic activity in a diffusive methane/oxygen counter-gradient in an unsaturated porous medium.

Microbial methane (CH4) oxidation is a main control on emissions of this important greenhouse gas from ecosystems such as contaminated aquifers or wetlands under aerobic onditions. Due to a lack of suitable model systems, we designed a laboratory column to study this process in diffusional CH4/O2 counter-gradients in unsaturated porous media. Analysis and simulations of the steady-state CH4, CO2 and O2 gas profiles showed that in a 15-cm-deep active zone, CH4 oxidation followed first-order kinetics with respect to CH4 with a high apparent first-order rate constant of approximately 30 h(-1).

Transport of methane and noble gases during gas push-pull tests in dry porous media.

A field method called the gas push-pull test (GPPT) was previously developed and tested for the in situ quantification of aerobic methane (CH4) oxidation by soil microorganisms. The GPPT consists of an injection followed by extraction of reactant and tracer gases into and out of the soil. Quantification of microbial activities from GPPTs requires insight in the transport of reactant and tracer gases under diverse field conditions.

Models to determine first-order rate coefficients from single-well push-pull tests.

Push-pull tests (PPTs) have been successfully employed to quantify various microbially mediated processes in the subsurface. Current models for determining first-order rate coefficients (k) from PPTs assume complete and instantaneous mixing of injected test solution in the portion of the aquifer investigated by the test, i.e.

Determination of NAPL-water interfacial areas in well-characterized porous media.

The nonaqueous-phase liquid (NAPL)-water interfacial area is an important parameter which influences the rate of NAPL dissolution in porous media. The aim of this study was to generate a set of baseline data for specific interfacial area for a two-phase-entrapped NAPL-water system in well-characterized porous media and subsequently use these data to evaluate two current theoretical models. The first model tested distributes entrapped NAPL over the pore classes based on Land's algorithm and assumes the resulting blobs to be spherical.

Field-scale isotopic labeling of phospholipid fatty acids from acetate-degrading sulfate-reducing bacteria.

Isotopic labeling of biomarker molecules is a technique applied to link microbial community structure with activity. Previously, we successfully labeled phospholipid fatty acids (PLFA) of suspended nitrate-reducing bacteria in an aquifer. However, the application of the method to low energy-yielding processes such as sulfate reduction, and extension of the analysis to attached communities remained to be studied.

Approximate solution for solute transport during spherical-flow push-pull tests.

An approximate analytical solution to the advection-dispersion equation was derived to describe solute transport during spherical-flow conditions in single-well push-pull tests. The spherical-flow case may be applicable to aquifer tests conducted in packed intervals or partially penetrating wells. Using results of two-dimensional numerical simulations, we briefly illustrate the applicability of the derived spherical-flow solution and provide a comparison with its cylindrical-flow counterpart.

New field method: gas push-pull test for the in-situ quantification of microbial activities in the vadose zone.

Quantitative information on microbial processes in the field is important. Here we propose a new field method, the "gas push-pull test" (GPPT) for the in-situ quantification of microbial activities in the vadose zone. To evaluate the new method, we studied microbial methane oxidation above an anaerobic, petroleum-contaminated aquifer.