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A water supply plan approach was used to investigate irrigation application on landscaped areas in Virginia with a focus on turfgrass. The economically-important turfgrass industry in Virginia should be proactive in conserving drinking water supplies to meet human consumption needs, especially in drought times. This thesis investigates current irrigation water supplies, water supply sustainability, and alternative water sources to meet irrigation demands and offers an insight on how potable water is unnecessarily consumed for non-potable irrigation needs. A Virginia evapotranspiration website was developed to offer a scientifically based source for efficient irrigation scheduling. The website was developed using a collaborative and user-centered design method, which included potential users in the process. The final website is hosted on the Virginia Tech website at http://www.turf.cses.vt.edu/Ervin/et_display.html and utilizes data from weather stations throughout the state. Evapotranspiration-based irrigation was tested at three case study sites in Blacksburg, Williamsburg and Norfolk, Virginia to assess potential water conservation. In Williamsburg, a 55% water savings was reported with evapotranspiration-based irrigation. In Blacksburg, slightly more water was applied on research greens irrigated based on evapotranspiration demand. Significantly less water was applied in Norfolk, compared to the evapotranspirationbased irrigated plots. The study also uncovered increased confidence to alter irrigation systems and the need to conduct irrigation audits when irrigating based on evapotranspiration. Evapotranspiration-based irrigation, reclaimed water and harvested rainwater were investigated to determine feasibility for meeting irrigation demands, while reducing potable water consumption at four case study sites in Blacksburg, Fairfax, Williamsburg and Norfolk, Virginia. Due to the limited collection potential at the Blacksburg site, reclaimed water and harvested rainwater was not feasible. However, the on-site weatherstation could offer a unique opportunity to calculate evapotranspiration. In Fairfax, all three alternative water sources could be integrated to supply enough water to irrigate a soccer field and adjacent athletic fields and save an estimated $7,000 per season in potable water costs. Harvested rainwater at the Williamsburg site could supplement the irrigation pond and reduce reliance on groundwater. In Norfolk, reclaimed water use is economically feasible, but rainwater harvesting could meet the irrigation needs, while evapotranspiration-based irrigation is too labor intensive for homeowners. / Ph. D.

The design of wetlands to replace those lost to development requires quantitative understanding of the wetland water budget in order to estimate the amount of water available to the wetland over time. Many methods exist to estimate each component of the wetland water budget. In this study, monthly values of the water budget components namely, precipitation, runoff, evapotranspiration, and groundwater seepage were calculated using a water budget model and compared to on-site field measurements for a wetland in Manassas, Prince William County, VA. The monthly precipitation estimated from a weather station 32.18 km from the site differed from the on-site values by as much as 2.9 times. Runoff estimates calculated by the Soil Conservation Service (SCS) method using antecedent moisture condition (AMC) II underpredicted runoff for every month by as high as 100 percent compared to the on-site measured runoff. The choice of AMC greatly affected the SCS runoff estimates. Runoff was the dominant water budget component at the Manassas wetland. The evapotranspiration (ET) estimates using the Thornthwaite method either over or underestimated ET when compared to ET calculated from diurnal cycles of the water table in the wetland. Groundwater seepage losses were calculated using Darcy's equation with an assumed hydraulic gradient of one, and with gradients measured with nested piezometers. Seepage losses at the Manassas wetland were negligible. Overall, the water budget model provided conservative estimates of the available water in the wetland during the 10-month period of observation. / Master of Science

Earth's near-surface environment sustains nearly all terrestrial life, yet this critical zone is threatened by the environmental migration of new and potentially harmful compounds produced to support a growing human population. Traditional transport equations often fail to capture the environmental behavior of these emerging contaminants due to issues such as flow heterogeneity. Thus, there is a need to better evaluate controls on pollutant partitioning in Earth's critical zone. Our first study investigated the transport and distribution of the neonicotinoid insecticide thiamethoxam (TMX) by growing TMX-coated corn seeds in coarse vs fine-textured soil columns maintained with versus without growing corn plants. Fine-textured soil transported TMX at concentrations that were two orders of magnitude higher than coarse-textured soil, due to preferential flow in the fine-textured soil columns and higher evapotranspiration (ET) concentrating more TMX in the coarse-textured soil. Living plants increased the concentration of TMX at depth, indicating that growing plants may drive preferential transport of neonicotinoids. For the second study we planted TMX-coated corn seeds and maintained field plots with and without viable crops (n = 3 plots per treatment), measuring TMX concentrations in three hydrological compartments (surface runoff, shallow lateral flow, and deep drainage) and soil. TMX was transported in the highest concentrations via surface runoff, while also showing continual migration within the subsurface throughout the growing season. Plants facilitated downward migration of TMX in soil yet restricted losses in drainage. For our final study, we used a simple isotope mixing method to evaluate how preferential flow alters the influence of compound chemical properties on solute transport. We applied deuterium-labeled rainfall to plots containing manure spiked with eight veterinary antibiotics with a range of mobility, and quantified transport to suction lysimeters (30 and 90 cm). We showed that low preferential flow (<20%) eliminates the influence of compound chemical properties and, contrary to conventional understanding, more preferential flow (~ >20%) amplifies these chemical controls, with more mobile compounds appearing in significantly higher concentrations than less mobiles ones. Altogether, we provide a refined understanding of solute partitioning in the critical zone necessary to improve process-based transport modeling. / Doctor of Philosophy / Earth’s near-surface environment sustains nearly all terrestrial life, yet this critical zone is threatened by the environmental migration of new and potentially harmful pollutants produced to support a growing human population. Additionally, traditional mathematical methods fail to accurately describe the behavior of these emerging pollutants in soils due to complex flow patterns. Thus, scientists need to better understand how these pollutants contaminate water bodies in the critical zone. We first conducted a greenhouse experiment to understand and measure the amount of the neonicotinoid insecticide thiamethoxam (TMX) that could move from coated corn seeds through the soil environment. Water draining from fine-textured soil had >100 times more TMX than water draining from course-textured soil, due to commonly occurring fractures/cracks in the finer-particle soil and more evaporation from soil and plant leaves sequestering TMX in the sandy soil. Growing plants amplified TMX movement through soil voids to lower depths. We then conducted a field study to determine how much TMX could move to the surrounding environment throughout the corn growing season. We found that plants aided in downward movement of TMX yet restricted total losses from the plot overall by removing soil water. Our third study investigated the degree to which chemical pollutant properties control movement of solutes when water flows preferentially through soil void space. Common dairy manure was spiked with eight pollutants ranging in chemical attraction to soil and was added to an agricultural field. After irrigation, we found that when total drainage water was less than 20% derived from preferential flow, chemical properties had a negligible effect on the amount of pollutant in draining soil water. Contrary to conventional understanding, when draining water contained more than 20% preferential flow, chemical properties had a strong influence on the amount of pollutant detected. Altogether, we provide new understanding of how solutes move though the critical zone. These findings are necessary to create mathematical tools that more accurately depict pollutant behavior below-ground.

La connaissance du microclimat et de l’évapotranspiration ou flux de chaleur latente qui représente la consommation réelle en eau de la culture à l’échelle des parcelles agricoles est une donnée importante pour comprendre le développement des cultures. La plupart des modèles permettant d’estimer l’évapotranspiration sont utilisés sur des surfaces homogènes sans tenir compte des interactions surface - atmosphère et de la variabilité spatiale du domaine agricole. Nous avons utilisé un modèle de couche limite atmosphérique afin de prendre en compte ces interactions. Une approche dite « patchée » permet d’introduire la variabilité spatiale des surfaces dans le modèle à partir des diverses proportions et des caractéristiques des principaux couverts végétaux qui composent le paysage. Une méthode d’assimilation variationnelle a été implémentée afin d’estimer certains paramètres du modèle difficile à connaître précisément. La méthode est basée sur le calcul de l’adjoint du modèle et utilise une température de surface observée par télédétection. L’approche développée est comparée à des approches plus simples considérant chaque type de surface indépendamment, mettant en évidence le rôle de la prise en compte de la variabilité spatiale de la surface sur la simulation du microclimat et des flux de surface / Knowledge of climate at regional scale and evapotranspiration (or latent heat flux which represents the actual water consumption of culture) is a key to understand the development of crops. Most of the methods aiming at estimating evapotranspiration assume homogeneous or decoupled atmospheric variables over the modelling domain without accounting for the feedback between surface and atmosphere. In order to analyse such dependencies and to predict microclimate and land surface fluxes we have developed a coupled atmospheric boundary layer - land surface model which accounts for the landscape heterogeneity using a tiled approach. We have implemented appropriate procedures (variational data assimilation) for assimilating remote sensing data into the model allowing to retrieve some input parameters difficult to estimate spatially (soil moisture and aerodynamic roughness). The developed method is compared to classical approaches considering each type of surface independently. Results are discussed in this paper

The Tropical savannas of central Brazil (cerrado) and the Everglades wetland (Florida) ecosystems are ideal systems to study landscape spatial mosaics and their interactions. Both ecosystems show a variety of plant physiognomies distributed within small spatial scales and elevation gradients. Such variety of plant physiognomies provide an opportunity to investigate the roles of climate, topography, nutrient availability and water table dynamics as determinants of plant physiognomic distributions, and their role in shaping regional systems. South Florida Wetlands and the tropical savannas of central Brazil are examples of hydrologically-controlled ecosystems. In hydrologically-controlled ecosystems water sources, the availability of nutrients, and the patterns of water movement play important roles in determining vegetation structure and function. The main objective of this study was to understand ecosystem level processes that shape different physiognomies in two hydrologically-controlled ecosystems. I conducted field work at the IBGE ecological reserve, a field experimental station located in Brasilia, Brazil. I also worked at the Everglades National Park in an area located near the south entrance of the Park in Homestead, Florida. I carried out three interconnected studies investigating water and nutrient dynamics: (1) In a Brazilian savanna I manipulated levels of litter input and measured changes to soil properties, organic matter decomposition and tree growth. I found that changes in litter input affect soil physicochemical properties and soil biochemical processes. I also found that litter dynamics influence tree growth through their effects on soil physicochemical properties. (2) I also studied the effect of water table depth and its temporal variation on spatial patterns of vegetation distribution in the cerrado landscape. I monitored diurnal and seasonal changes in water table depth along two tree-density and topographic gradients. In addition, I measured woody species composition, growth rates of four tree species, litter production, soil nutrients, and nutrient resorption efficiency along those two gradients. I found that water table depth has an important role in determining the spatial distribution of cerrado physiognomies; it also affects tree growth, species composition and nutrient resorption efficiency. (3) In the Everglades I studied patterns of underground water uptake by two vegetation types. I monitored seasonal and diurnal changes in water table depth in a Hammock forest, in a stand dominated by the invasive woody species Schinus terebinthifolius, as well as the water level in an adjacent lake. I estimated stand level transpiration using two different approaches: with sap flow measurements and diurnal oscillations in water table levels. Then, I calculated the total quantity of groundwater withdrawn by evapotranspiration for the wet and dry seasons in the Hammocks and in the exotic invaded site and then compared the results. I found that water uptake by Everglades trees is well coupled to diurnal changes in water table depth and that the amount of water withdrawn from the groundwater was larger during the wet season than during the dry season. Finally, I detected hydrological feedbacks between different vegetation types and nearby bodies of water. Results of this study contributes to the current knowledge of ecosystem level processes in tropical and subtropical ecosystems where water circulation and water availability play a dominant role in shaping vegetation structure and function.

Avec l'augmentation des sécheresses dans les forêts tempérées, la gestion sylvicole envisage de réduire la densité des peuplements adultes pour limiter le déficit hydrique. Cependant, la réduction de la canopée arborée augmente le rayonnement dans le sous-bois et permet le développement de la strate herbacée monopoliste. Nos objectifs étaient de caractériser l'évapotranspiration (ETu) de 4 herbacées monopolistes (Molinia caerulea, Calluna vulgaris, Pteridium aquilinum and Rubus sp.) et de quantifier leur impact sur la teneur en eau du sol (SWC) dans des peuplements de Quercus petraea. L’ETu des quatre herbacées cultivées en pot a été quantifiée en conditions semi-contrôlées caractérisées par deux niveaux d’éclairement relatif et 3 niveaux de SWC. In situ, le SWC, le microclimat et l’ETu de P. aquilinum et M. caerulea ont été mesurés sur 20 dispositifs dans les peuplements forestiers de Q. petraea présentant un gradient croissant de LAI. Chaque dispositif était subdivisé en 2 placettes, l’une était désherbée et l'autre enherbée. M. caerulea et C. vulgaris ont une faible régulation de leur ETu alors que P. aquilinum et Rubus sp. ont une stratégie conservatrice face au stress hydrique. SWC diminue plus rapidement quand le LAI de la strate herbacée augmente, ce qui est directement lié à l’ouverture du couvert arboré avec une valeur seuil de LAI de la strate arborée à 2-3, sous laquelle la contribution de la strate herbacée à l’évapotranspiration du peuplement pourrait compenser la diminution de celle de la strate arborée.Ces résultats montrent la nécessité de considérer la végétation du sous-bois dans la gestion sylvicole notamment lorsque la ressource hydrique est limitante. Ainsi, la réduction de la densité de la strate arborée doit être un compromis entre la réduction de la surface foliaire des arbres pour réduire l’ET, et le maintien d’une densité suffisante de la strate arborée pour limiter la croissance et l'ETu de la végétation du sous-bois. / In the context of ongoing increase of drought in temperate forests, forest managers consider the reduction of stand density to limit soil water depletion. The reduction of tree canopy density increases light below canopy and allows the development of monopolistic understorey vegetation. Our objectives were to characterize the evapotranspiration (ETu) of common understorey plants (Molinia caerulea, Calluna vulgaris, Pteridium aquilinum and Rubus sp.) and to quantify their impacts on soil water content (SWC) in mature oak stands (Quercus petraea).A first experiment was set up in a greenhouse where the 4 understorey species were potted and subjected to 2 levels of light transmittance and 3 levels of SWC. Microclimate and ETu were monitored. A second experiment was carried out on 20 plots (10 with M. caerulea and 10 with P. aquilinum) in oak stands with contrasted LAI. On each plot, two circular areas were set up, one weeded and the other untouched. SWC, microclimate and ETu were monitored.M. caerulea and C. vulgaris are more water spenders, whereas P. aquilinum and Rubus sp. are more water savers under water stress. Soil water depletion was faster with increasing understorey vegetation LAI, which was directly linked to tree canopy opening with a threshold of tree LAI of 2-3 below which the understorey contribution could offset the reduction of tree ET. The experimentations showed that the relative contribution of understory vegetation in the ecosystem water balance is significant, and depends on SWC and on the understorey species identity. These results show the necessity to consider understorey vegetation in forest management when water availability is an issue. Lower tree canopy density could increase the understorey ETu and soil water stress for trees. From a management perspective, thinning should be designed as a compromise between the reduction of tree leaf area to reduce ET, and maintaining sufficient tree canopy to restrict the growth and ETu of understorey vegetation.

Au cours des dernières décennies, un type de marais filtrant, généralement planté de saules, a été développé pour opérer un système de traitement d’eau sans effluent, par évapotranspiration. Ces marais à effluent sont généralement utilisés pour le traitement d’eau usée domestique, mais pourraient aussi présenter une alternative intéressante pour d’autres applications, comme le traitement de lixiviat contaminé. Les guides de conception actuellement disponibles ne permettent toutefois pas de concevoir un système flexible qui permettrait de gérer les grandes variations de volume à traiter liées à la nature même des lixiviats (i.e. résultent entièrement des précipitations) et ne tiennent pas compte de la variation inter et intra-annuelle de l’évapotranspiration (ET) du saule. Cette thèse présente d’abord une revue de littérature de ET du genre Salix et de ses facteurs de variation les plus importants. Il apparaît que les conditions de croissance ont plus d’importance que l’identité spécifique et que la disponibilité en eau, la fertilisation et la contamination sont les principaux facteurs dictant l’ET des saules. L’effet de l’âge, du contexte expérimental, de la densité de plant et du type de sol n’a pas pu être clairement démontrés par cette revue. Ensuite, une étude portant sur le potentiel d’ET de S. miyabeana ‘SX67’ est présentée. Il est démontré qu’un modèle basé sur des paramètres foliaires et sur le déficit de pression de vapeur d’eau dans l’air permet de prédire l’ET de S. miyabeana en condition de marais filtrant. Cette étude permettra entre autres d’améliorer les plans de conception d’un éventuel marais de saules à effluent nul. Pour continuer, la réponse de S. miyabeana ‘SX67’ à différentes concentrations de lixiviat et à différents types de substrats a été étudiée. Ce cultivar s’est montré tolérant aux concentrations du lixiviat brut retrouvées sur un site d’entreposage de poteaux de bois traité. Le type de substrat a influencé la réponse du saule et ses performances écophysiologiques, en plus d’affecter la dynamique des contaminants. Finalement, la modélisation hydrologique d’un système à effluent nul par marais de saules permet de proposer une méthode de dimensionnement des différents compartiments du système pour atteindre un objectif d’effluent nul sur une période de 20 ans, ainsi que de proposer des solutions de conception et d’opération optimale. L’application du modèle au cas spécifique d’un site d’entreposage de poteaux de bois traité a permis d’évaluer la faisabilité, d’un point de vue hydrologique, de cette technologie dans le contexte climatique du sud du Québec. Sur la base de cette étude, la principale limite pour l’application des marais à effluent nul au Québec sont la surface de marais et le volume de stockage requis. Dans le cas où une étape de prétraitement efficace précède le marais de saule, la durée de vie du marais ne devrait pas être limitante et dépendra principalement de la durée de vie des végétaux. Cependant, le destin des contaminants dans le système, qu’il s’agisse de la disposition des contaminants accumulés à l’étape de prétraitement ou d’une éventuelle translocation de contaminants dans les parties aériennes des végétaux, devrait être considéré avant d’établir un système à effluent nul. Les résultats de cette recherche permettent, entre autres, de proposer les marais de saules à effluent nul comme une alternative intéressante pour le traitement d’eau contaminée au Québec. / During the last decades, a type of constructed wetlands, usually planted with willows, was developed to operate a water treatment system with zero effluent, by evapotranspiration. These zero liquid discharge wetlands are typically used for domestic wastewater treatment, but could also be an attractive alternative for other applications, such as contaminated leachate treatment. However, the design guidelines currently available do not allow for the design of a flexible system that would manage the large variations of volume to be treated related to the very nature of leachates (i.e. produced entirely from precipitation) and do not take into account inter and intra-annual variation of willows evapotranspiration (ET). This thesis first presents a literature review of ET for the genus Salix and its most important driving factors. It appears that growing conditions are more important than species identity and that water availability, fertilization and contamination are the main factors dictating ET in willow. The effect of age, experimental context, planting density, and soil type could not be clearly demonstrated by this review. Then, a study on the potential ET of S. miyabeana 'SX67' is presented. It is shown that a model based on foliar parameters and on the water vapor pressure deficit in the air makes it possible to predict the ET of S. miyabeana under wetland conditions. This study will, among other things, improve the design plans for a potential zero effluent willow wetland. To continue, the response of S. miyabeana 'SX67' to different leachate concentrations and different types of substrates was studied. This cultivar has been tolerant of raw leachate concentrations found at a treated wood pole storage site. The type of substrate influenced the willow response and ecophysiological performance, and affected the dynamics of the contaminants. Finally, the hydrological modelling of a system with zero effluent by willow bed makes it possible to propose a method of dimensioning for the different compartments of the system in order to reach a zero effluent objective over a period of 20 years, as well as to propose solutions for optimal design and operation. The application of the model to the specific case of a treated wood pole storage site made it possible to assess the hydrological feasibility of this technology in the climate context of southern Quebec. On the basis of this study, the main limit for the application of zero effluent willow bed in Quebec is the wetland area and the storage volume required. In the case where an effective pre-treatment step precedes the willow bed, the life of the wetland should not be limiting and will depend mainly on the lifespan of the plants. However, the fate of the contaminants in the system, be it the disposition of the accumulated contaminants at the pre-treatment stage or a possible translocation of contaminants into the aerial parts of the plants, should be considered before establishing a system with zero effluent. The results of this research make it possible, among other things, to propose zero-effluent willow wetlands as an interesting alternative for the treatment of contaminated water in Quebec.