Transport of Chemicals in the Vadose Zone

Open access

Transport, dispersion, and degradation of nonpoint source contaminants during flood‐managed aquifer recharge

Core Ideas

  • Vadose zone heterogeneity does not induce significant macrodispersion of contaminants mobilized during flood-managed aquifer recharge.
  • Slow wetting front velocities maximize nitrate removal through denitrification and contaminant dispersion.
  • Fast wetting front celerities result in rapid increases in groundwater storage following inundation.
  • Maximizing the celerity:velocity ratio through the vadose zone maximizes water quantity without degrading quality.
  • In general, sites with higher residual water content through the vadose zone should optimize this criterion.

Open access

Quantitative analysis of diurnal CO2 flux variations above an alkaline playa

Core Ideas

  • Magnesium-carbonate playas forming from CO2-rich groundwater show no net emission of CO2.
  • Surficial CO2 exchange is found to be dominated by CO2 solubility from diurnal cycling in temperature.
  • Diurnal fluctuations involve daytime CO2 emissions and CO2 uptake during the night.
  • Radiocarbon signature of CO2 indicates mixing of atmospheric CO2 with a geologic source of carbon from the groundwater.

Open access

Fate of herbicides in cropped lysimeters: 1. Influence of different processes and model structure on vadose zone flow

Core Ideas

  • For effective model description, multi-process modeling must be explored.

  • Mixing processes between immobile and mobile water are of greater importance for finer soils.

  • Evaporation fractionation effects have no clear impact on simulated stable water isotopes in lysimeter drainage.

Open access

Fate of herbicides in cropped lysimeters: 2. Leaching of four maize herbicides considering different processes

Core Ideas

  • Leached herbicide concentrations depend on the soil texture.
  • Concentration peaks of herbicides in lysimeter drainage can be linked with rain events.
  • Solute transport modeling allows us to identify dominant processes affecting herbicide leaching.
  • Stable carbon isotopes measured in drainage can identify biodegradation processes in the unsaturated zone.

Open access

Design of a bioaugmented soil aquifer treatment for efficient removal of p-nitrophenol

Core Ideas

  • The efficiency prediction model of field-scale bioaugmented soil aquifer treatment (SAT) is established.
  • Response surface methodology was implemented for bioaugmented SAT efficiency optimization regulation.
  • The critical bioaugmented SAT parameters were initial concentration, medium thickness, and wet/dry ratio.
  • Alternate wetting–drying conditions improved the reduction of p-nitrophenol.

Open access

Nitrate contamination of urban groundwater and heavy rainfall: Observations from Dakar, Senegal

Core Ideas

  • Soil-water and solute dynamics were assessed by high-frequency monitoring and vadose-zone modelling.
  • High-frequency monitoring was conducted at an experimental site adjacent to a septic tank.
  • Heavy rainfall events (>10 mm hr−1) cause the leaching of wastewater from the septic tank to groundwater.
  • Observations show the contribution of septic systems and rainfall to groundwater contamination by nitrate.

Open access

Colloidal transport of heavy metals in low‐advective‐velocity environmental systems: Reactive transport model on biogeochemical and hydrodynamic impacts

Core Ideas

  • Colloidal transport of Fe (hydr)oxide particles with complex biogeochemical dynamics is presented.
  • Enhanced control of Fe reduction by Fe-reducing bacteria with immobile Fe (hydr)oxide mineral surfaces is observed.
  • Sensitivity of the colloidal transport of contaminants under low-flow-velocity conditions is observed.
  • Absence of colloidal particle transport might underestimate transport of sorbed contaminants.

Open access

Fate and transport of Cryptosporidium parvum oocysts in repacked soil columns: Influence of soil properties and surfactant

Core Ideas

  • Mechanisms governing transport of C. parvum oocysts in soils are influenced by soil types and soil water chemistry.
  • Surfactant affected the transport and retention behaviors of C. parvum oocysts in soils.
  • qPCR was used for the detection and enumeration of C. parvum oocysts in natural soil and water samples.

Open access

Numerical investigation on light non–aqueous phase liquid flow in the vadose zone considering porosity effects on soil hydraulic properties

Core Ideas

  • A new theoretical model is developed, considering porosity effects on soil hydraulic properties.
  • The model capability is verified using the results of a centrifuge test.
  • The results of parametric studies have revealed the importance of porosity effects.

Open access

Phosphate oxygen isotope ratios in vegetated riparian buffer strip soils

Core Ideas

  • Vegetated riparian buffer strips accelerate biological P cycling.
  • Phosphate oxygen isotope values decreased along a vegetated riparian buffer strip to grassland transect.
  • Biogeochemical P cycling varies with soil depth and distance from a stream.
  • Cycling-related changes in isotope values complicate stream P source identification.

Open access

In situ measurement of 3D contact angle in sand based on X‐ray computed tomography

Core Ideas

  • An in situ 3D contact angle method based on X-ray CT is introduced to vadose zone hydrology.
  • Local heterogeneity in equilibrium contact angles is captured and linked to pore-scale features.
  • The method has limited capability to measure dynamic or acute contact angles.

Open access

A device to simulate contaminant transfer and surface and subsurface flow through intact soil monoliths

Core Ideas

  • A device for collecting intact soil and subjecting it to artificial rainfall was developed.
  • The setup allows for high resolution measurement and sampling of drainage and overland flow.
  • It is designed for clean sampling permitting analysis of various contaminants at trace levels.
  • We present an experiment to test the device on transfer of ivermectin from cow dung.

Open access

Precipitation is the key determinant of topsoil δ15N values in southern Patagonia's semiarid rangelands

Core Ideas

  •  Interpretation of δ15N values in soils remains a significant and unresolved challenge.
  •  Precipitation is the main driver of variation in δ15N values in Patagonian soils.
  •  Vadose zone research is needed to better understand the interactive effects of water and N on δ15N in soil.

Open access

Cotransport of titanium dioxide nanoparticles and formaldehyde in saturated and unsaturated columns packed with quartz sand

Core Ideas

  • We study simultaneous transport of titanium dioxide (TiO2) nanoparticles and formaldehyde (FA).
  • The transport of FA in packed columns was hindered in the presence of TiO2 nanoparticles.
  • The solution ionic strength significantly affected TiO2 retention within the porous medium.

Open access

Gas diffusivity‐based characterization of aggregated soils linking to methane migration in shallow subsurface

Core Ideas

  • Aggregated soils have bimodal properties that affect methane migration in soil.
  • Gas diffusivity, water characteristic, and thermal conductivity are bimodal fingerprints.
  • Diffusive CH4 migration is largely controlled by soil moisture than leakage rate.

Open access

Influence of agricultural managed aquifer recharge on nitrate transport: The role of soil texture and flooding frequency

Core Ideas

  • Short-lived Ag-MAR flooding events cause NO3 leaching and organic N mineralization.
  • Soil texture affects the timing of NO3 leaching under Ag-MAR.
  • Soil texture affects the conditions for biogeochemical processes under Ag-MAR.
  • Reducing time between flooding events for Ag-MAR reduces NO3 produced by mineralization.

Open access

Quantifying hydrologic pathway and source connectivity dynamics in tile drainage: Implications for phosphorus concentrations

Core Ideas

  • Hydrograph separation methods are coupled to study tile flow pathway and source connectivity dynamics.
  • Results highlight preferential flow of old and new water, bypass recharge, and diffuse flow to tile drainage.
  • Sources and pathways of subsurface flow improve prediction of nutrient concentrations.

Open access

Water‐dispersible nanocolloids and higher temperatures promote the release of carbon from riparian soil

Core Ideas

  • Mineral nanocolloids protect and facilitate transport of soil organic carbon.
  • Higher sediment specific surface area increases release of organic carbon with nanominerals.
  • From our model, a 1 °C rise in the temperature increases the OC release rate up to 79% over 90 d.

Open access

Role of degradation concepts for adsorbing contaminants in context of wastewater irrigation

Core Ideas

  • Results differ for degradation in solution alone and in both solution and adsorbed phase.
  • Long-term concentration is independent of degradation concept for linear adsorption.
  • Nonlinear adsorption leads to more degradation and lower concentration.
  • Analytical models generally approximate the long-term concentration within 10%.
  • Seasonality is important for drainage and cannot be estimated with annual averages.

Open access

Increased irrigation water salinity enhances nitrate transport to deep unsaturated soil

Core Ideas

  • Water flow and solute transport under an agricultural field were characterized.
  • Measurements were taken using a vadose zone monitoring system.
  • High Cl irrigation resulted in increased NO3 concentrations in deep soil.

Open access

Suction cup system‐dependent variable boundary condition: Transient water flow and multicomponent solute transport

Core Ideas

  • A water flow and solute transport model was combined with a chemical modeling tool.
  • Physical and chemical processes taking place when using suction cups were modeled.
  • A small volume and high initial vacuum least disturbed the carbonate chemistry.
  • For systems in equilibrium, the pH error depends on the initial vacuum applied.
  • A linear relationship between sampled volume and suction cup design is presented.

Open access

Heterogeneity of the peat profile and its role in unsaturated sodium chloride rise at field and laboratory scales

Core Ideas

  • There is a high potential for solute uplift in unsaturated subarctic bog peat.
  • Hydrophysical properties are highly variable in shallow moss-dominant bog peat.
  • Solute is held above the water table where pores are small and disconnected.