Large public events, such as concerts, rallies, and festivals, impact turf health when held on natural turfgrass surfaces. The impact associated with these events is due to the placement of physical structures such as stages and seating areas and pedestrian and vehicular traffic on the turf surface. Trafficked turf protection covers, which are field covers meant to be placed directly on the turf surface where pedestrian or vehicular traffic is expected and/or equipment will be placed, can be used to minimize damage to the turf surface. Scientific data on turf response to these covers is lacking. Four cover treatments comprised of a non-covered non-trafficked control, plywood, plywood + Enkamat Plus, and white high-density polypropylene [single sided (Terratile) or double sided (Matrax)] were applied to tall fescue (Festuca arundinacea Schreb.) and effects of light intensity, duration of covering, season and soil moisture were evaluated. Growth chambers and field experiments were conducted in 2010-2011. Tissue samples were taken in growth chambers experiments every four days over the 20-day period to analyze chlorophyll (Chl a, Chl b, Chl a+b) and carotenoids (carot) under split factors of light intensity (12hr, PAR 530 μmol m-2 s-1, 5 μmol m-2 s-1) and soil moisture (50%, 75% of pot soil moisture capacity). Field trial treatment effects were observed every two days and eight days after cover removal in the spring, summer and fall and a normalized difference vegetative index (NDVI) measure was used at the conclusion of each trial period to confirm visual ratings. Covers that allowed light transmission to the canopy provided the best visual retention of percent green cover and higher contents of Chl a, Chl b, Chl a+b and carot. However, when treatments were tested under conditions that simulated low light under a concert stage (PAR 5 μmol m-2 s-1), covers performed similarly. Moderate soil moisture increased Chl b and carot content under covers. Field trials showed that plywood and plywood + Enkamat allowed for acceptable covering periods of six days in spring, four days in fall, and zero days in summer. Summer conditions shortened the number of days (8 -10) thattall fescue could be covered with Matrax and Terratile and still maintain an acceptable level of green cover. Matrax performed the best during high temperatures and did not tend to sink into the turf in saturated soil. All covers exhibited desirable qualities and limitations that should be considered for turf protection during an event. / Master of Science

This thesis estimates the ecosystem evaporation response to two forms of aridity: (1) atmospheric aridity in the form of vapor pressure deficit (Chapter 2), and (2) soil moisture aridity (Chapter 4). We also develop new methods to estimate the ecosystem response to aridity. For the response to atmospheric aridity (Chapter 2), we build a theoretical framework that allows us to derive an analytical expression for the ecosystem evaporation response to vapor pressure deficit with all environmental conditions held fixed (Chapter 2). For the response to soil moisture aridity, we develop a method to estimate the response of evaporation to interventions on soil moisture using only passive data generated in a simulated reality (Chapter 4). To guide the development of this data-driven approach, we review and analyze causal inference’s applications in the Earth system, considering generic scenarios that are applicable to the land-atmosphere system as well as many other subdomains of the Earth system (Chapter 3). The subsections below elaborate more on the contents of each Chapter. Chapter 2: When does vapor pressure deficit drive or reduce evaporation? Increasingvapor pressure deficit increases atmospheric demand for water. While increased evaporation in response to increased atmospheric demand seems intuitive, plants are capable of reducing evaporation in response to increased vapor pressure deficit by closing their stomata. We examine which effect dominates the response to increasing vapor pressure deficit: atmospheric demand and increases in evaporation, or plant response (stomata closure) and decreases in evaporation. We use Penman-Monteith, combined with semi-empirical optimal stomatal regulation theory and underlying water use efficiency, to develop a theoretical framework for assessing evaporation response to vapor pressure deficit. The theory suggests that depending on the environment and plant characteristics, evaporation response to increasing vapor pressure deficit can vary from strongly decreasing to increasing, highlighting the diversity of plant water regulation strategies. The evaporation response varies due to: 1) climate, with tropical and temperate climates more likely to exhibit a positive evaporation response to increasing vapor pressure deficit than boreal and arctic climates; 2) photosynthesis strategy, with C3 plants more likely to exhibit a positive evaporation response than C4 plants; and 3) plant type, with crops more likely to exhibit a positive evaporation response, and shrubs and gymniosperm trees more likely to exhibit a negative evaporation response. These results, derived from previous literature connecting plant parameters to plant and climate characteristics, highlight the utility of our simplified framework for understanding complex land atmosphere systems in terms of idealized scenarios in which evaporation responds to vapor pressure deficit only. This response is otherwise challenging to assess in an environment where many processes co-evolve together. Chapter 3: Causal inference for process understanding in Earth sciences There is growinginterest in the study of causal methods in the Earth sciences. However, most applications have focused on causal discovery, i.e. inferring the causal relationships and causal structure from data. This paper instead examines causality through the lens of causal inference and how expert-defined causal graphs, a fundamental from causal theory, can be used to clarify assumptions, identify tractable problems, and aid interpretation of results and their causality in Earth science research. We apply causal theory to generic graphs of the Earth system to identify where causal inference may be most tractable and useful to address problems in Earth science, and avoid potentially incorrect conclusions. Specifically, causal inference may be useful when: (1) the effect of interest is only causally affected by the observed portion of the state space; or: (2) the cause of interest can be assumed to be independent of the evolution of the system’s state; or: (3) the state space of the system is reconstructable from lagged observations of the system. However, we also highlight through examples that causal graphs can be used to explicitly define and communicate assumptions and hypotheses, and help to structure analyses, even if causal inference is ultimately challenging given the data availability, limitations and uncertainties. Chapter 4: Estimating the ecosystem evaporation response to interventions on soilmoisture: confounding and causal modeling in a simulated world We build a simulated reality using a numerical model designed to represent feedbacks in the land atmosphere system, and observational boundary conditions that are confounded by the real world’s underlying climate state. Although no simulation can reproduce the real land-atmosphere system’s complexity and any simulation’s predictions will deviate from the real world, this simulated reality does share the same characteristics of the real world that make causal inference challenging: it contains feedbacks, non-linearity, and the real world’s confounding-induced covariations between boundary conditions. We use this simulated reality to estimate confounding’s impact on relationships between soil moisture and ecosystem evaporation, and also to validate a method for calculating ecosystem evaporation response to interventions on soil moisture from passive observations. We repeat this analysis at 12 sites spanning a range of humid and arid climates in western North American and Europe, and find that: • Confounding bias is largest at the more humid sites, and lower at the more arid sites where soil moisture limits evaporation and decouples the response from other environmental factors (Section 4.3.1). • At the more humid sites, bias due to confounding is of a larger magnitude than model specification bias, even when the specified model is a linear model applied to a known non-linear process. This highlights the importance of accounting for confounding. (Section4.3.1). • Statistically adjusting for potential sources of confounding improves causal estimates at the highly confounded sites without degrading causal estimates at arid, soil moisture-limited sites characterized by less confounding bias (Section 4.3.2). • The estimated causal effects appear to differentiate true variations in the causal effects across climates and ecosystems. (Section 4.3.2).

<p> This thesis examines the field performance of the water balance and equilibrium evapotranspiration models, and defines the environmental conditions for which they provided accurate estimates of water loss from a corn crop in Southern Ontario.</p> <p> It is shown that the water balance model should be used only when surface runoff is measured and drainage is negligible. An error analysis indicated that soil moisture change could be estimated within 10 percent when measurements were conducted at six sites every eight days.</p> <p> The equilibrium model predicted daily evapotranspiration within 6 percent when the latent heat exchange utilized between 65 and 80 percent of the available energy, indicating that the model can be applied within temperature limits of 17° and 32°C.</p> / Thesis / Doctor of Philosophy (PhD)

Due largely to fire exclusion and land use changes, upland oak ecosystems in the central and eastern U.S. are shifting dominance from fire-tolerant oaks (Quercus spp.) to shade-tolerant, fire-sensitive species (mesophytes). This shift has been hypothesized to occur via a positive feedback loop termed mesophication, where mesophytes create shaded understory that limits oak growth and wetter fuels and soils, decreasing forest flammability. To determine how canopy water partitioning varies between oaks and mesophytes, I measured stemflow, throughfall, and surface soil moisture monthly over a 14-month period for overstory and midstory trees of oaks (Q. alba, Q. falcata) and hypothesized mesophytes (Carya tomentosa, Acer rubrum, Ulmus alata) in northern Mississippi. Overstory oaks partitioned 5.1% of rainwater into stemflow, while mesophytic species partitioned 7.2%, leading to 3.5% wetter soils under mesophytes. The hydrology of mesophyte canopies may reduce forest flammability and promote conditions favorable for mesophyte regeneration, ultimately compromising long-term oak regeneration.

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<p> Peatlands are an important component of the global carbon cycle, storing 23 g C m-2 yr-1 to comprise a global carbon pool of approximately 455 Pg. Peat drainage and harvesting results in removal of surface vegetation, thereby reducing gross photosynthesis to zero. Moreover, lowering the water table increases carbon oxidation. Consequently, peatland drainage and mining can reduce or eliminate the carbon sink function of the peatland. In the first part of this study, net ecosystem CO2 exchange was studied in a natural (NATURAL), two-year (YOUNG) and seven-year (OLD) post cutover peatland near Ste. Marguerite Marie, Quebec during the summer of 1998. Although the NATURAL site was a source of CO2 during the study season, CO2 emissions were 270 to 300% higher in the cutover sites (138, 363, and 399 g CO2-C m-2; NATURAL, YOUNG and OLD, respectively). Active restoration practices and natural re-vegetation of peatlands have the potential to return these ecosystems to net carbon sinks by increasing net ecosystem production (NEP) and therefore decreasing CO2 emissions to the atmosphere. Net ecosystem CO2 exchange in a natural (NATURAL) peatland and a partly restored peatland (REST) near Ste. Marguerite Marie, Quebec, was compared with a naturally re-vegetated peatland (RVEG) near Riviere-du-Loup, Quebec. Ecophysiological parameters indicate that the REST site was more than twice as productive as the natural LAWNS and three times as the RVEG site (GPmax=18.0, 8.3, and 6.5 g CO2 m-2 d-1, respectively). These results indicate that active restoration improves carbon sequestration over natural re-vegetation but that the net carbon sink function at both sites has not been restored. The presence of Sphagnum cover at the RVEG site resulted in a significant decrease in net ecosystem respiration (NER), indicating the potential for decreasing soil respiration at restored cutover sites through increasing the volumetric soil moisture content.</p> / Thesis / Master of Science (MSc)

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Due to inadequate long-term and large-scale observation approach for observation of soil moisture across the globe, this study intends to unveil the importance of using simulated soil moisture fields from land surface models, forced with observed precipitation and near-surface meteorology in monitoring drought and formulating effective water management practices for continued production irrigation applications. This study shows that socio-economic and ecosystem effects can be determined by evaluating spatial-temporal changes in irrigation applications. Thus, it facilitates understanding of the importance of water management and how water, energy, and carbon flows protect our climate and environment. By using Soil Moisture Active Passive (SMAP) in monitoring soil moisture, the information obtained is critical in providing early drought warnings, particularly in those parts of the United States that experience flash agricultural droughts. Further, this study highlights that frequent and reliable soil moisture measurements from SMAP helped improve the predictive capability of weather and climate models.

Free-swelling properties of montmorillonites in water systems were studied using X-ray diffraction techniques. Four specimen type montmorillonites (Wyoming bentonite, Otay bentonite, hectorite and nontronite) and several soil clays were selected. In Phase I of the study the differential swelling properties were related to the type of cation on the exchange complex and to variations in the mineralogical properties of the montmorillonites. / Ph. D.