Vadose zone oxygen (O2) dynamics during drying and wetting cycles: An artificial recharge laboratory experiment

Vadose zone oxygen dynamics control all subsurface redox reactions and play a decisive role in maintaining groundwater quality. Although drying and wetting events are common in artificial recharge, their effects on subsurface oxygen distribution are poorly documented. We monitored oxygen concentration in the unsaturated zone in a mid-scale (1 m high) laboratory soil lysimeter, which was subjected to short wetting and drying cycles that simulated a highly permeable shallow aquifer recharged by river water. Ten cycles of varying duration were performed for a period of 85 days. Measurements of oxygen in the liquid and the gas phases were recorded every 20 s using non-invasive optical fibers (PreSens). The results provided high-resolution (in time) oxygen concentration maps. The infiltration rate revealed a decreasing trend during wetting cycles associated with biological clogging. Such a decrease with time was accompanied by a depletion of O2 concentration, occurring within the first few hours of the infiltration. During drying, O2 concentrations recovered rapidly at all depths owing to air flushing, resulting in a stratified vertical profile consistent with the biological consumption of O2 along the air infiltration path. Furthermore, drying periods caused a potential recovery of the infiltration capacity while preserving the soil biological activity. Scraping also led to the recovery of the infiltration capacity of the soil but was less effective than drying. Our experiment suggests that the small-scale heterogeneity played a key role in accurately mapping pore-scale O2 concentrations and should be considered in modeling O2 fluxes of unsaturated soils under natural or managed recharge conditions

Advancing measurements and representations of subsurface heterogeneity and dynamic processes: towards 4D hydrogeology

Essentially all hydrogeological processes are strongly influenced by the subsurface spatial heterogeneity and the temporal variation of environmental conditions, hydraulic properties, and solute concentrations. This spatial and temporal variability generally leads to effective behaviors and emerging phenomena that cannot be predicted from conventional approaches based on homogeneous assumptions and models. However, it is not always clear when, why, how, and at what scale the 4D (3D + time) nature of the subsurface needs to be considered in hydrogeological monitoring, modeling, and applications. In this paper, we discuss the interest and potential for the monitoring and characterization of spatial and temporal variability, including 4D imaging, in a series of hydrogeological processes: (1) groundwater fluxes, (2) solute transport and reaction, (3) vadose zone dynamics, and (4) surface–subsurface water interactions. We first identify the main challenges related to the coupling of spatial and temporal fluctuations for these processes. We then highlight recent innovations that have led to significant breakthroughs in high-resolution space–time imaging and modeling the characterization, monitoring, and modeling of these spatial and temporal fluctuations. We finally propose a classification of processes and applications at different scales according to their need and potential for high-resolution space–time imaging. We thus advocate a more systematic characterization of the dynamic and 3D nature of the subsurface for a series of critical processes and emerging applications. This calls for the validation of 4D imaging techniques at highly instrumented observatories and the harmonization of open databases to share hydrogeological data sets in their 4D components

Greenhouse gasses emissions in rivered sediments: a multidisciplinary approach

The following document contains a short summary about some hydrogeological parameters that are important to know the behaviour of groundwater and the main processes involved in the nitrogen and the carbon cycle and its relation with underground stored water. The main thesis part is the explanation of a laboratory experiment done with riverbed sediments. The laboratory experiment tries to control some of the parameters that affect the riverbed soil in an artificial recharge basin in or der to observe how these parameters modify the soil behaviour referring to the microbial growth. Different compounds were added to jars that cointain the riverbed soil and different moisture conditions were performed; then soil and gas samples were taken d uring 50 days at different interval times. These samples were analysed to find how the nitrogen and the carbon was changing in the soil. From the experiment results it is possible to say that, with the conditions applied to the riverbed soil jars, the nitr ogen and carbon family compounds content was no despicable and different biochemical processes occurred in the riverbed soil. Carbon dioxide emissions (and concentrations) showed that the riverbed soil was active during the experiment and some nitrous oxid e and methane was emitted although it is not possible to say that different moisture conditions or different substrate added modifies the soil biochemical response with different compound productio

Diseño de un ensayo hidràulico en un salar

Este trabajo final de máster tiene como objetivo la caracterización hidrodinámica e hidrogeoquímica de un salar. Para ello, se utilizan un conjunto de herramientas de interpretación y modelización numérica con el objetivo último de diseñar un ensayo hidráulico que permita mejorar el conocimiento existente sobre el comportamiento hidráulico del salar. En concreto, intentar delimitar la existencia de zonas kársticas desarrolladas en el salar y conductos preferentes donde se puedan concentrar los flujos y la salmuera

Greenhouse gasses emissions in rivered sediments: a multidisciplinary approach

The following document contains a short summary about some hydrogeological parameters that are important to know the behaviour of groundwater and the main processes involved in the nitrogen and the carbon cycle and its relation with underground stored water. The main thesis part is the explanation of a laboratory experiment done with riverbed sediments. The laboratory experiment tries to control some of the parameters that affect the riverbed soil in an artificial recharge basin in or der to observe how these parameters modify the soil behaviour referring to the microbial growth. Different compounds were added to jars that cointain the riverbed soil and different moisture conditions were performed; then soil and gas samples were taken d uring 50 days at different interval times. These samples were analysed to find how the nitrogen and the carbon was changing in the soil. From the experiment results it is possible to say that, with the conditions applied to the riverbed soil jars, the nitr ogen and carbon family compounds content was no despicable and different biochemical processes occurred in the riverbed soil. Carbon dioxide emissions (and concentrations) showed that the riverbed soil was active during the experiment and some nitrous oxid e and methane was emitted although it is not possible to say that different moisture conditions or different substrate added modifies the soil biochemical response with different compound productio

Diseño de un ensayo hidràulico en un salar

Este trabajo final de máster tiene como objetivo la caracterización hidrodinámica e hidrogeoquímica de un salar. Para ello, se utilizan un conjunto de herramientas de interpretación y modelización numérica con el objetivo último de diseñar un ensayo hidráulico que permita mejorar el conocimiento existente sobre el comportamiento hidráulico del salar. En concreto, intentar delimitar la existencia de zonas kársticas desarrolladas en el salar y conductos preferentes donde se puedan concentrar los flujos y la salmuera

Greenhouse gasses emissions in rivered sediments: a multidisciplinary approach

The following document contains a short summary about some hydrogeological parameters that are important to know the behaviour of groundwater and the main processes involved in the nitrogen and the carbon cycle and its relation with underground stored water. The main thesis part is the explanation of a laboratory experiment done with riverbed sediments. The laboratory experiment tries to control some of the parameters that affect the riverbed soil in an artificial recharge basin in or der to observe how these parameters modify the soil behaviour referring to the microbial growth. Different compounds were added to jars that cointain the riverbed soil and different moisture conditions were performed; then soil and gas samples were taken d uring 50 days at different interval times. These samples were analysed to find how the nitrogen and the carbon was changing in the soil. From the experiment results it is possible to say that, with the conditions applied to the riverbed soil jars, the nitr ogen and carbon family compounds content was no despicable and different biochemical processes occurred in the riverbed soil. Carbon dioxide emissions (and concentrations) showed that the riverbed soil was active during the experiment and some nitrous oxid e and methane was emitted although it is not possible to say that different moisture conditions or different substrate added modifies the soil biochemical response with different compound productio