This study investigates the effects of fire on the chemistry and flux of precipitation diverted to the forest floor as stemflow and throughfall by observing the impact of the June 2013 Thompson Ridge Wildfire in the Jemez River Basin of New Mexico. The loss of canopy cover from wildfire drastically modifies landscapes and alters ecosystems as fire replaces leafy canopies with charred branches and trunks, changes soil composition and erosion processes, and affects hydrologic flow paths and water chemistry. In order to track these changes, throughfall and stemflow collectors were installed beneath burned and unburned canopies in two catchments impacted by the Thompson Ridge Fire. Throughfall, stemflow, and open precipitation samples were analyzed for major cations, anions, dissolved inorganic and organic carbon, trace metals, and rare earth elements to determine how fire affects the chemical composition of the precipitation that interacts with burned canopies. Precipitation samples collected from both burned and unburned sites during the 2014 summer monsoon season show variations across burn severity, specifically in calcium, strontium, phosphate, and dissolved inorganic carbon concentrations, and across collector type with stemflow concentrations generally higher than throughfall and open precipitation concentrations. A stem count model was used to determine tree density for individual plots and catchments from LiDAR images taken before the 2013 fire. The stem count model was used to upscale event and monsoon season solute fluxes from plot to catchment scale. Higher nutrient concentrations combined with higher volumes of precipitation diverted as stemflow in burned forests have a multiplicative effect resulting in greater nutrient fluxes via stemflow creating nutrient hot spots surrounding burned tree trunks. Upscaling these plot scale concentrations and solute fluxes allows this study to represent changes to an entire catchment and quantify effects of wildfire on chemical loads and water chemistry.

A modification in an existing water uptake and solute transport numerical model was implemented in order to allow the model to simulate solute uptake by the roots. The convection-dispersion equation (CDE) was solved numerically, using a complete implicit scheme, considering a transient state for water and solute fluxes and a soil solute concentration dependent boundary for the uptake at the root surface, based on the Michaelis- Menten (MM) equation. Additionally, a linear approximation was developed for the MM equation such that the CDE has a linear and a non-linear solution. A radial geometry was assumed, considering a single root with its surface acting as the uptake boundary and the outer boundary being the half distance between neighboring roots, a function of root density. The proposed solute transport model includes active and passive solute uptake and predicts solute concentration as a function of time and distance from the root surface. It also estimates the relative transpiration of the plant, on its turn directly affecting water and solute uptake and related to water and osmotic stress status of the plant. Performed simulations show that the linear and non-linear solutions result in significantly different solute uptake predictions when the soil solute concentration is below a limiting value (Clim). This reduction in uptake at low concentrations may result in a further reduction in the relative transpiration. The contributions of active and passive uptake vary with parameters related to the ion species, the plant, the atmosphere and the soil hydraulic properties. The model showed a good agreement with an analytical model that uses a linear concentration dependent equation as boundary condition for uptake at the root surface. The advantage of the numerical model is it allows simulation of transient solute and water uptake and, therefore, can be used in a wider range of situations. Simulation with different scenarios and comparison with experimental results are needed to verify model performance and possibly suggest improvements. / Uma modificação em um modelo existente de extração de água e transporte de solutos foi realizada com o objetivo de incluir nele a possibilidade de simular a extração de soluto pelas raízes. Uma solução numérica para a equação de convecção-dispersão (ECD), que utiliza um esquema de resolução completamente implícito, foi elaborada e considera o fluxo transiente de água e solutos com uma condição de contorno à superfície da raiz de extração de soluto dependente de sua concentração no solo, baseada na equação de Michaelis- Menten (MM). Uma aproximação linear para a equação de MM foi implementada de tal forma que a ECD tem uma solução linear e outra não-linear. O modelo considera uma raiz singular com geometria radial sendo sua superfície a condição de contorno (limite) de extração e sendo o limite extremo a meia-distância entre raízes vizinhas, função da densidade radicular. O modelo de transporte de soluto proposto inclui extração de soluto ativa e passiva e prediz a concentração de soluto como uma função do tempo e da distância à superfície da raiz, além de estimar a transpiração relativa da planta, que por sua vez afeta a extração de água e solutos e é relacionado com a condição de estresse da planta. Simulações mostram que as soluções linear e não-linear resultam em predições de extração de solutos significativamente diferentes quando a concentração de solutos no solo está abaixo de um valor limitante (Clim). A redução da extração em baixas concentrações pode resultar em uma redução adicional na transpiração relativa. As contribuições ativa e passiva da extração de solutos variam com parâmetros relacionados à espécie de íon, à planta, à atmosfera e às propriedades hidráulicas do solo. O modelo apresentou uma boa concordância com um modelo analítico que aplica uma condição de contorno linear, à superfície da raiz, de extração de solutos dependente da concentração no solo. A vantagem do modelo numérico sobre o analítico é que ele permite simular fluxos transientes de água e solutos, sendo, portanto, possível simular uma maior gama de situações. Se faz necessário simulações com diferentes cenários e comparações com dados experimentais para se verificar a performance do modelo e, possivelmente, sugerir melhorias.

A modification in an existing water uptake and solute transport numerical model was implemented in order to allow the model to simulate solute uptake by the roots. The convection-dispersion equation (CDE) was solved numerically, using a complete implicit scheme, considering a transient state for water and solute fluxes and a soil solute concentration dependent boundary for the uptake at the root surface, based on the Michaelis- Menten (MM) equation. Additionally, a linear approximation was developed for the MM equation such that the CDE has a linear and a non-linear solution. A radial geometry was assumed, considering a single root with its surface acting as the uptake boundary and the outer boundary being the half distance between neighboring roots, a function of root density. The proposed solute transport model includes active and passive solute uptake and predicts solute concentration as a function of time and distance from the root surface. It also estimates the relative transpiration of the plant, on its turn directly affecting water and solute uptake and related to water and osmotic stress status of the plant. Performed simulations show that the linear and non-linear solutions result in significantly different solute uptake predictions when the soil solute concentration is below a limiting value (Clim). This reduction in uptake at low concentrations may result in a further reduction in the relative transpiration. The contributions of active and passive uptake vary with parameters related to the ion species, the plant, the atmosphere and the soil hydraulic properties. The model showed a good agreement with an analytical model that uses a linear concentration dependent equation as boundary condition for uptake at the root surface. The advantage of the numerical model is it allows simulation of transient solute and water uptake and, therefore, can be used in a wider range of situations. Simulation with different scenarios and comparison with experimental results are needed to verify model performance and possibly suggest improvements. / Uma modificação em um modelo existente de extração de água e transporte de solutos foi realizada com o objetivo de incluir nele a possibilidade de simular a extração de soluto pelas raízes. Uma solução numérica para a equação de convecção-dispersão (ECD), que utiliza um esquema de resolução completamente implícito, foi elaborada e considera o fluxo transiente de água e solutos com uma condição de contorno à superfície da raiz de extração de soluto dependente de sua concentração no solo, baseada na equação de Michaelis- Menten (MM). Uma aproximação linear para a equação de MM foi implementada de tal forma que a ECD tem uma solução linear e outra não-linear. O modelo considera uma raiz singular com geometria radial sendo sua superfície a condição de contorno (limite) de extração e sendo o limite extremo a meia-distância entre raízes vizinhas, função da densidade radicular. O modelo de transporte de soluto proposto inclui extração de soluto ativa e passiva e prediz a concentração de soluto como uma função do tempo e da distância à superfície da raiz, além de estimar a transpiração relativa da planta, que por sua vez afeta a extração de água e solutos e é relacionado com a condição de estresse da planta. Simulações mostram que as soluções linear e não-linear resultam em predições de extração de solutos significativamente diferentes quando a concentração de solutos no solo está abaixo de um valor limitante (Clim). A redução da extração em baixas concentrações pode resultar em uma redução adicional na transpiração relativa. As contribuições ativa e passiva da extração de solutos variam com parâmetros relacionados à espécie de íon, à planta, à atmosfera e às propriedades hidráulicas do solo. O modelo apresentou uma boa concordância com um modelo analítico que aplica uma condição de contorno linear, à superfície da raiz, de extração de solutos dependente da concentração no solo. A vantagem do modelo numérico sobre o analítico é que ele permite simular fluxos transientes de água e solutos, sendo, portanto, possível simular uma maior gama de situações. Se faz necessário simulações com diferentes cenários e comparações com dados experimentais para se verificar a performance do modelo e, possivelmente, sugerir melhorias.

Current treatment of wastewater can effectively remove the contaminants; however, the effluent is still not widely reused because of some undesired substances like pathogens and trace organic chemicals. To promote water reuse, membrane-based technologies have emerged as a robust and more efficient alternative to current treatment practice. Among these membrane processes, forward osmosis (FO) utilizes an osmotic pressure gradient across a semi-permeable membrane to reclaim high-quality water. Still, several key challenges remain to be addressed towards broader FO application, including energy-intensive draw regeneration to yield product water and salinity buildup in the feed solution. To bypass energy-intensive draw regeneration, commercial solid fertilizers was utilized as a regeneration-free draw solute (DS), harvesting fresh water towards direct agricultural irrigation. However, using nutrient-rich fertilizers as DS resulted in an elevated reverse solute flux (RSF). This RSF, known as the cross-membrane diffusion of DS to the feed solution, led to deteriorated solute buildup on the feed side, reduced osmotic driving force, increased fouling propensity, and higher operation cost. To effectively mitigate solute buildup while achieving energy-efficient water reclamation, a parallel electrodialysis (ED) device was integrated to FO for DS recovery in the feed solution. The salinity in the feed solution was consistently controlled below 1 mS cm-1 via the hybrid FO-ED system. Considering solute buildup is merely a consequence of RSF, direct control of RSF was further investigated via operational strategy (i.e., an electrolysis-assisted FO) and membrane modification (i.e., surface coating of zwitterion-functionalized carbon nanotubes). Significantly reduced RSF (> 50% reduction) was obtained in both approaches with minor energy/material investment. With two major bottlenecks being properly addressed for energy-efficient water reclamation, FO was further integrated with a microbial electrolysis cell (MEC) to achieve integrated nutrient-energy-water recovery from high-strength wastewater (i.e., the digestor centrate). The abovementioned research projects are among the earliest efforts to address multiple key challenges of FO during practical application, serving as a cornerstone to facilitate the transformation of current water/wastewater treatment plant to resource recovery hub in order to ensure global food-energy-water security. / Doctor of Philosophy / Exploring alternative water supply, for instance via reusing wastewater, will be essential to deal with the global water crisis. Current wastewater treatment can effectively remove the contaminants; however, the treated wastewater is still not widely reused due to the possible presence of residual contaminants. In recent years, membrane-based technologies have emerged as a promising treatment process to produce clean water. Among all available membrane technologies, forward osmosis (FO) takes advantage of the osmotic pressure difference across a special membrane to extract fresh water from a low-salinity FEED solution (for example, wastewater) to a high-salinity DRAW solution. The reclaimed fresh water can be reused for other applications. Still, the FO process is facing several critical challenges for broader applications. The first challenge is that additional energy is required to separate clean water from the diluted DRAW solution, leading to notably increased energy consumption for the FO process. To bypass this energy-intensive separation, commercial solid fertilizers was utilized as a separation-free DRAW solution for FO process. Once the clean water is extracted to the DRAW solution (fertilizer), the diluted fertilizer solution together with the fresh water can be directly used for agricultural irrigation. The second challenge is that, when fertilizer is applied as the DRAW solution, nutrient rich fertilizers can penetrate the FO membrane and escape to the FEED solution (wastewater). This phenomenon is known as the reverse solute flux (RSF). RSF can result in many adverse effects, such as wastewater contamination and increased operational cost. To prevent this, we used an additional device named electrodialysis to effectively recapture the “escaped” fertilizers in the FEED solution. Besides this indirect approach to recover escaped fertilizers, we also investigated direct approaches to control RSF, including operational strategy and membrane modification. With two major challenges being properly addressed for energy-efficient water reclamation, FO was further combined with a microbial electrolysis cell (MEC) to achieve multiple resource recovery from wastewater, including water, nutrient, and energy components. The above mentioned research projects are among the earliest efforts to address multiple key challenges of FO during water and resource recovery from wastewater to ensure global food-energy-water security.

Ce travail contribue à l'acquisition des connaissances sur les mécanismes et les facteurs contrôlant le transfert des éléments traces dans le système sol-nappes d'eaux souterraines. Le nombre de plus en plus important de sols contaminés par les éléments traces potentiellement toxiques suite aux activités industries a reçu beaucoup d'attention au cours des deux dernières décennies. Les polluants accumulés dans ces sols peuvent alors être transférés dans différents compartiments de l'environnement en fonction de leur origine, leur spéciation et les conditions physico-chimiques et biologiques du milieu. Ainsi, une des problématiques est la pollution des nappes d'eau souterraine par ces éléments traces. Les flux massiques d'éléments traces dans les sols vers les nappes d'eau souterraines sont un paramètre d'entrée important pour prévoir le devenir des pollutions des aquifères et donc à évaluer le potentiel de la contamination des ressources en eau potable. L’objectif de cette thèse a été de proposer une méthode de mesure des flux en laboratoire qui permette de simuler au mieux les conditions naturelles des transferts des éléments traces vers les nappes. Pour cela, nous avons mis au point une colonne de laboratoire non-saturée. Cette colonne a été testée dans différentes conditions de lixiviation, comparée aux méthodes de lixiviations normées et testée en condition d’immobilisation des éléments traces lors de l’apport d’amendements. Dans un premier temps, la colonne de laboratoire permet de diminuer l’erreur sur l’estimation des flux. Elle permet des mettre en évidence des phénomènes de sorption, désorption et complexation des éléments traces sur les substrats, contrôlant ainsi les transferts verticaux.Dans un deuxième temps nous avons évaluer l’effet d’amendements minéraux sur la mobilité des éléments traces sur deux sols contaminés par des extractions chimiques. Nous avons ensuite étudié la lixiviation de ces éléments suite à l’apport d’amendements: de l’hydroxyapatite et de la Grenaille d’acier dans ces deux sols en utilisant les colonnes de sol développés précédemment. L'étude de la localisation des éléments traces sur les minéraux nouvellement formés suite à l'apport de ces amendements minéraux et leur interaction avec les constituants minéraux d'origine des sols (microscopie couplé à des spectromètres de fluorescence X) nous a permis de comprendre et de déterminer les réactions mis en jeu au cours de la lixiviation de ces éléments. Ainsi, l’apport d’hydroxyapatite (HA) et de Grenaille d’acier (GA) ont permis de diminuer significativement les concentrations en Cd, Zn dans les lixiviats. En revanche, l’apport de HA et GA aux sols augmente significativement la libération de As (dans le cas de HA) et Pb suite a l’apport de GA et HA. Les phases minérales porteuses de ces éléments traces, ont pu être caractériser et ainsi les mécanismes responsables de l’immobilisation ou du relargage ont pu être identifiés. / This work contributes to the knowledge of the mechanisms and factors controlling the transfer of trace elements, particularly in the soil- groundwater pathway. Extensive soil contamination with potentially toxic traces elements from various industries has in many industrialized countries received significant attention over the last two decades. Mass fluxes of trace elements in soils to groundwater are important input parameter for predicting the fate of pollution of aquifers and thus to assess the potential for contamination of drinking water resources. The objective of this study was to propose a method for measuring the fluxes in laboratory to simulate the natural conditions. For this, we have developed an unsaturated soil column. This column was then tested in various leaching conditions (compared to standardized leaching methods and tested under conditions of immobilization of trace elements). At first, the laboratory column reduces the error in the estimation of flux. And allows to highlight sorption, desorption and complexation of trace elements on the substrates. In a second step we evaluate the effect of mineral amendments on the mobility of trace elements in two contaminated soils (extraction), the study their location on the newly formed minerals (microscopy coupled with X-ray fluorescence spectrometers) and finally the leaching of these. The addition of hydroxyapatite (HA) and Steel Shot (GA) have significantly reduced the concentrations of Cd, Zn and As (in the case of the contribution of GA). In contrast, the addition of HA and GA in soils significantly increases the release of As (in the case of HA) and Pb following the addition of GA and HA). Mineral phases carrying these trace elements have been well characterized and the mechanisms responsible for the retention or release have been identified.