The influence of soil water repellency (WR) on vegetation recovery after a fire is poorly understood. This dissertation presents strategies to broaden opportunities for enhanced post-fire rangeland restoration and monitoring of burned piñon and juniper (P-J) woodlands by: 1) mapping the extent and severity of critical and subcritical WR, 2) determining the influence of WR on soil ecohydrologic properties and revegetation success, and 3) evaluating the suitability of a wetting agent composed of alkylpolyglycoside-ethylene oxide/propylene oxide block copolymers as a post-fire restoration tool for ameliorating the effects of soil WR and increasing seedling establishment. Results indicate that: • Post-fire patterns of soil WR were highly correlated to pre-fire P-J woodland canopy structure. Critical soil WR levels occurred under burned tree canopies while sub-critical WR extended out to approximately two times the canopy radius. At sites where critical soil WR was present, infiltration rate, soil moisture, and vegetation cover were significantly less than at non-hydrophobic sites. These parameters were also reduced in soils with subcritical WR relative to non-hydrophobic soils (albeit to a lesser extent). Aerial photography coupled with feature extraction software and geographic information systems (GIS) proved to be an effective tool for mapping P-J cover and density, and for scaling-up field surveys of soil WR to the fire boundary scale. • Soil WR impairs seed germination and seedling establishment by decreasing soil moisture availability by reducing infiltration, decreasing soil moisture storage capacity, and disconnecting soil surface layers from underlying moisture reserves. Consequently, soil WR appears to be acting as a temporal ecological threshold by impairing establishment of desired species within the first few years after a fire. • Wetting agents can significantly improve ecohydrologic properties required for plant growth by overcoming soil WR; thus, increasing the amount and duration of available water for seed germination and seedling establishment. Success of this technology appears to be the result of the wetting agent increasing soil moisture amount and availability by 1) improving soil infiltration and water holding capacity; and 2) allowing seedling roots to connect to underling soil moisture reserves.

The need for energy efficient, clean and quiet, energy conversion devices for mobile and stationary applications has presented proton exchange membrane (PEM) fuel cells as a potential energy source. The use of PEM fuel cells for automotive and other transient applications, where there are rapid changes in load, presents a need for better understanding of transient behavior. In particular at low humidity operations; one of the factors critical to the performance and durability of fuel cell systems is water transport in various fuel cell layers, including water absorption in membrane. An essential aspect to optimization of transient behavior of fuel cells is a fundamental understanding of response of fuel cell system to dynamic changes in load and operating parameters. This forms the first objective of the dissertation. An insight in to the time scales associated with various transport phenomena will be discussed in detail. In the second component on the study, the effects of membrane properties on the dynamic behavior of the fuel cells are analyzed with focus on membrane dry-out for low humidity operations. The mechanical behavior of the membrane is directly related to the changes in humidity levels in membrane and is explored as a part third objective of the dissertation. Numerical studies addressing this objective will be presented. Finally, porous media undergoing physical deposition (or erosion) are common in many applications, including electrochemical systems such as fuel cells (for example, electrodes, catalyst layer s, etc.) and batteries. The transport properties of these porous media are a function of the deposition and the change in the porous structures with time. A dynamic fractal model is introduced to describe such structures undergoing deposition and, in turn, to evaluate the changes in their physical properties as a function of the deposition. / Ph. D.

L'augmentation de la décomposition de la matière organique des cryosols arctiques sous l'effet du réchauffement et de la dégradation du pergélisol contribuerait à une rétroaction positive sur les changements climatiques. Nous étudions le fonctionnement biogéochimique de deux Cryosols: un cryosol histique (H) et un cryosol turbique (T), en conditions naturelles et réchauffés. Les profils ont été instrumentés à Salluit (Nunavik, Canada) et les mesures ont été faites pendant les étés 2010 et 2011. Le réchauffement augmente la respiration de l'écosystème (ER) de manière plus intense pour H que pour T, bien que ER pour H soit plus faible. La sensibilité thermique de ER (Q10) est supérieure pour T que pour H et diminue avec le réchauffement. L'étude montre que les cycles journaliers de ER en fonction de la temperature forment des hystérésis. La variance de ER est mieux expliquée en utilisant la température minimale de la journée et la profondeur du front de dégel pour H. Pour T, l'ajout de la vitesse du vent et la radiation solaire améliore l'explication de la variance de ER. Nous montrons trois dynamiques spécifiques aux écosystèmes nordiques: 1) ER dépendant des propriétés du sol et de la solution du sol ; 2) rôle de variables thermo-indépendantes sur ER et 3) variations journalières du Q10 et interannuelles de la respiration basale. La décomposition de la matière organique est la principale source de CO2 pour H alors que les processus végétaux contrôlent ER pour T. Nos résultats contribuent à la compréhension et à l'extrapolation des mesures ponctuelles dans les écosystèmes de toundra, améliorant ainsi la modélisation du cycle du carbone dans les cryosols. / Increased organic mater decomposition rate in Arctic Cryosols due to warming and to permafrost thawing can lead to the release of greenhouse gases, thus potentially creating a positive feedback on climate change. We studied the biogeochemical functioning of two different permafrost-affected soils (i.e. Cryosols): a Histic Cryosol (H) and a Turbic Cryosol (T), both in natural conditions and under an experimental warming. Profiles were instrumented in Salluit (Nunavik, Canada) and monitored during summers 2010 and 2011. The induced warming increased CO2 fluxes in both soils; this impact was however more striking at H even if ER was lower than at T. Temperature sensitivity of ER (Q10) was higher at T than at H and decreased both with warming. We highlighted that diurnal ER cycles as a function of temperature showed hysteretic loops. Linear models performed to explain ER variance were improved adding daily minimum temperature and thaw front depth at H. In contrast at T, adding wind speed and solar radiation in models improved the ER variance explanation. We showed three specific CO2 flux dynamics related to northern ecosystems: 1) the large difference of ER depending on soil properties and soil solution composition; 2) environmental variables strongly alter CO2 fluxes and 3) the diurnal Q10 variations and the inter annual variability of basal respiration. Our results support the assumption that organic matter decomposition might be the major source of CO2 at H while plant-derived processes dominated ER at T. Our results contribute to understand and extrapolate the numerous punctual measurements of CO2 fluxes from tundra ecosystems improving carbon cycle modeling in Cryosols.

Die Anwendbarkeit der Verdünnungsmethode mit Hilfe des Markers Deuteriumoxid (D2O) zur in vivo-Erfassung der sich ändernden Körperzusammensetzung wurde an 53 Ziegenlämmern der Rasse Bunte Deutsche Edelziege im Gewichtsabschnitt von 4 kg bis 20 kg LM überprüft. Bei einer Lebendmasse von 4, 8, 12, 16 bzw. 20 kg wurde den Tieren nach einer 13- bis 18stündigen Nüchterung D2O injiziert und nach weiteren vier bis fünf Stunden Blutproben gezogen. Bei jeweils einem Teil der Tiere erfolgte anschließend die Schlachtung und die chemische Analyse der Körper zur Bestimmung des Ganzkörperwassergehaltes, der Chymusmasse und der Leerkörperzusammensetzung. Die Messungen der D2O-Konzentrationen in den Blutproben und die chemische Analyse der Ganzkörper ergaben eine Überschätzung des Ganzkörperwassergehaltes durch die Verdünnungsmethode um im Mittel 3,99 %. Zwischen dem chemisch bestimmten und dem geschätzten Wert besteht eine enge lineare Beziehung. Die Schätzung des Inhaltes des Gastro-Intestinaltraktes (Chymus) dient zur Schätzung der Leerkörpermasse. Dessen Variabilität lässt sich im Wesentlichen durch die Lebendmasse erklären. Die chemische Analyse der Tierkörper zeigte, dass die Zusammensetzung des fettfreien Leerkörpers im hohen Maß von der Leerkörpermasse abhängt. Anhand von allometrischen Regressionsgleichungen wurden die Bestandteile der fettfreien Leerkörpermasse geschätzt und daraus die Zusammensetzung des fetthaltigen Leerkörpers ermittelt. Der Vergleich der mittels chemischer Analyse bestimmten bzw. der Verdünnungsmethode geschätzten Leerkörperzusammensetzung ergab eine hohe Übereinstimmung beim Wasser-, Rohprotein- und Rohaschegehalt. Der Rohfettgehalt wies dagegen größere Abweichungen auf. Als Ursache wurde die Streuung der geschätzten Chymusmasse bzw. Chymuswassermasse aufgedeckt. Das Fazit ist, dass sich die D2O-Verdünnungsmethode zur in vivo-Bestimmung der sich ändernden Körperzusammensetzung von Ziegenlämmern im Gewichtsabschnitt von 4 kg bis 20 kg LM eignet. / On young goats (breed Bunte Deutsche Edelziege) with a live weight range of 4 kg up to 20 kg the suitability of the dilution method using the marker deuterated water (D2O) was checked in order to measure the changes of body composition during growth on living animals (in vivo). At a live weight of 4, 8, 12, 16 and 20 kg the animals received an intrave¬nous dose of D2O after a fastening time of 13 to 18 hours. Blood samples were taken after a waiting period of 4 to 5 hours. In connection with the last blood sample in each period a part of the animals were slaughtered to determine the total body water content, the digesta mass and the empty body composition by chemical analysis. The determination of the marker concentration in the blood samples and the chemical analysis of the total bodies showed that the dilution method overestimated total body water content by 3,99 %. There is a close linear relationship between the estimated and the chemically determined content of total body water. The estimation of the digesta mass serves for the estimation of the empty body mass. Its variation mainly depends on the live weight. The chemical analysis of the animal bodies revealed that the composition of the fat-free empty body is mainly dependent on the empty body mass. Using allometric equations the components of the fat-free empty body mass were estimated and thus the composition of the empty body could be calculated. The comparison of the chemically determined components with the estimated components of the empty body showed a high agreement concerning the content of water, protein and ash. However estimation of the fat content is less accurate. The reason is the variation of the estimated digesta mass and the digesta water mass. It can be concluded that the dilution technique using deuterated water is a practicable method to determine in vivo the changing body composition of growing kids with a live weight range of 4 kg up to 20 kg.

The Canterbury plains are frequently exposed to summer drought and climate predictions forecast that the severity and frequency of summer drought will increase. The most commonly used pasture grass, perennial ryegrass (Lolium perenne L.), is drought sensitive. One possible method to maintain sward dry matter (DM) production under water stress is to use an alternative grass species such as tall fescue (Festuca arundinacea Schreb.). The objective of this research was to compare summer DM production of monoculture swards of perennial ryegrass and tall fescue under various seasonal drought regimes to study physiological and biochemical drought responses of each species. Data were collected over a period of two-summer seasons, Season One (2006-2007) and Season Two (2007-2008) in an automated rain shelter at Lincoln, Canterbury. Drought treatments included exposure of plants to a spring or autumn drought or a four-weekly "irrigated" drought regime. DM yields of the two species were similar under each watering regime. The control treatment, under non-limiting conditions, has the highest accumulated yield in both Season One and Two for ryegrass (17.1 and 15.7 t DM ha⁻¹) and tall fescue (18.8 and 16.0 t DM ⁻¹) respectively. Spring and autumn drought treatments were similar for the two species in accumulated yield in either season, however the exposure to drought stress returned yields lower than the control. Consistently, the lowest-yielding treatment was the four-weekly irrigated drought, which resulted in an average yield across species in Season One of 10.1 t DM ha⁻¹ and 8.35 t DM ha⁻¹ in Season Two. Growth rates of the swards were calculated using accumulated DM production against accumulated thermal time using a base temperature of 3°C for both species. The control treatments showed a strong linear relationship for both species in both seasons, though Season Two showed a period of approximately 390 °Cd of no growth. Spring growth was similar for all treatments until October when both the spring drought and four-weekly irrigated treatment deviated from the control as water stress commenced. Growth also ceased under autumn drought later in the season. The physiological drought responses between species and among treatments differed. Tall fescue under control conditions had the highest photosynthesis rates of 20.5 µmol CO₂ m⁻² s⁻¹,or 22% higher than ryegrass, whereas the four-weekly irrigated treatment showed no inter-species differences. Differences were also found for other gas exchange parameters. Physiological water use efficiency (phys WUE) in ryegrass was 15% greater than tall fescue in Season Two. Photosynthesis and gas exchange rates against leaf water potential showed declining gas flow in both species across all treatments in response to drying soil conditions and across all irrigation treatments. The osmo-protectant proline was 22% higher in concentration in ryegrass than in tall fescue in Season Two and increased in drought stressed treatments in both seasons. Water stress was found to reduce total chlorophyll concentrations in all treatments and in tall fescue, while little change occurred in the chlorophyll a:b ratio. In conclusion, the findings from this thesis suggest similar DM responses for the two species under drought. The findings suggests that tall fescue performs more as a "water user" under drought conditions, compared with perennial ryegrass, which is more a "water saver." Resonses to the changing environment to a point, before "shuttting up shop" through lower stomatal conductance.

Land application of wastes has become increasingly popular, to promote nutrient recycling and environmental protection, with soil functioning as a partial barrier between wastes and groundwater. Dairy shed effluent (DSE), may contain a wide variety of pathogenic micro-organisms, including bacteria (e.g. Salmonella paratyphyi, Escherichia coli. and Campylobacter), protozoa and viruses. Groundwater pathogen contamination resulting from land-applied DSE is drawing more attention with the intensified development of the dairy farm industry in New Zealand. The purpose of this research was to investigate the fate and transport of bacterial indicator-faecal coliform (FC) from land-applied DSE under different irrigation practices via field lysimeter studies, using two water irrigation methods (flood and sprinkler) with contrasting application rates, through the 2005-2006 irrigation season. It was aimed at better understanding, quantifying and modelling of the processes that govern the removal of microbes in intact soil columns, bridging the gap between previous theoretical research and general farm practices, specifically for Templeton soil. This study involved different approaches (leaching experiments, infiltrometer measurements and a dye infiltration study) to understand the processes of transient water flow and bacterial transport; and to extrapolate the relationships between bacterial transport and soil properties (like soil structure, texture), and soil physical status (soil water potential ψ and volumetric water content θ). Factors controlling FC transport are discussed. A contaminant transport model, HYDRUS-1D, was applied to simulate microbial transport through soil on the basis of measured datasets. This study was carried out at Lincoln University’s Centre for Soil and Environmental Quality (CSEQ) lysimeter site. Six lysimeters were employed in two trials. Each trial involved application of DSE, followed by a water irrigation sequence applied in a flux-controlled method. The soil columns were taken from the site of the new Lincoln University Dairy Farm, Lincoln, Canterbury. The soil type is Templeton fine sandy loam (Udic-Ustochrept, coarse loamy, mixed, mesic). Vertical profiles (at four depths) of θ and ψ were measured during leaching experiments. The leaching experiments directly measured concentrations of chemical tracer (Br⁻ or Cl⁻) and FC in drainage. Results showed that bacteria could readily penetrate through 700 mm deep soil columns, when facilitated by water flow. In the first (summer) trial, FC in leachate as high as 1.4×10⁶ cfu 100 mL⁻¹ (similar to the DSE concentration), was detected in one lysimeter that had a higher clay content in the topsoil, immediately after DSE application, and before any water irrigation. This indicates that DSE flowed through preferential flow paths without significant treatment or reduction in concentrations. The highest post-irrigation concentration was 3.4×10³ cfu 100 mL⁻¹ under flood irrigation. Flood irrigation resulted in more bacteria and Br⁻ leaching than spray irrigation. In both trials (summer and autumn) results showed significant differences between irrigation treatments in lysimeters sharing similar drainage class (moderate or moderately rapid). Leaching bacterial concentration was positively correlated with both θ and ψ, and sometimes drainage rate. Greater bacterial leaching was found in the one lysimeter with rapid whole-column effective hydraulic conductivity, Keff, for both flood and spray treatments. Occasionally, the effect of Keff on water movement and bacterial transport overrode the effect of irrigation. The ‘seasonal condition’ of the soil (including variation in initial water content) also influenced bacterial leaching, with less risk of leaching in autumn than in summer. A tension infiltrometer experiment measured hydraulic conductivity of the lysimeters at zero and 40 mm suction. The results showed in most cases a significant correlation between the proportion of bacteria leached and the flow contribution of the macropores. The higher the Ksat, the greater the amount of drainage and bacterial leaching obtained. This research also found that this technique may exclude the activity of some continuous macropores (e.g., cracks) due to the difference of initial wetness which could substantially change the conductivity and result in more serious bacterial leaching in this Templeton soil. A dye infiltration study showed there was great variability in water flow patterns, and most of the flow reaching deeper than 50 cm resulted from macropores, mainly visible cracks. The transient water flow and transport of tracer (Br⁻) and FC were modelled using the HYDRUS-1D software package. The uniform flow van Genuchten model, and the dual-porosity model were used for water flow and the mobile-immobile (MIM) model was used for tracer and FC transport. The hydraulic and solute parameters were optimized during simulation, on the basis of measured datasets from the leaching experiments. There was evidence supporting the presence of macropores, based on the water flow in the post-DSE application stage. The optimised saturated water content (θs) decreased during the post-application process, which could be explained in terms of macropore flow enhanced by irrigation. Moreover, bacterial simulation showed discrepancies in all cases of uniform flow simulations at the very initial stage, indicating that non-equilibrium processes were dominant during those short periods, and suggesting that there were strong dynamic processes involving structure change and subsequently flow paths. It is recommended that management strategies to reduce FC contamination following application of DSE in these soils must aim to decrease preferential flow by adjusting irrigation schemes. Attention needs to be given to a) decreasing irrigation rates at the beginning of each irrigation; b) increasing the number of irrigations, by reducing at the same time the amount of water applied and the irrigation rate at each irrigation; c) applying spray irrigation rather than flood irrigation.

Worldwide there is considerable concern over the effects of human activities on the quantity and quality of freshwater. Measurement of infiltration behaviour will be important for improving freshwater management. This study identifies that New Zealand has a sporadic history of measuring soil water movement attributes on a limited number of soil types, although the current practical demand should be large for management of irrigation, dairy farm effluent disposal, as well as municipal / domestic waste- and storm-water disposal. Previous research has demonstrated that infiltration behaviour is governed by the interplay between numerous mechanisms including hydrophobicity and preferential flow, the latter being an important mechanism of contaminant leaching for many NZ soils. Future characterisation will need to recognise the dynamic nature of these interactions, and be able to reliably characterise the key infiltration mechanisms. Since macropores are responsible for preferential flow, it is critical that infiltration studies use a representative sample of the macropore network. The aim of this project was to study the mechanisms governing the infiltration behaviour of a layered soil in large (50 x 70 cm) monolith lysimeters, where the connectivity of the macropore network remains undisturbed. Four lysimeters of the Gorge silt loam were collected, a structured soil with four distinct layers. On each lysimeter there were four separate infiltration experiments, with water applied under suctions of 0, 0.5, 1, and 1.5 kPa by a custom-built tension infiltrometer. Each lysimeter was instrumented with 30 tensiometers, located in arrays at the layer boundaries. There was also a field experiment using ponded dye infiltration to visually define preferential flowpaths. Analysis of dye patterns, temporal variability in soil matric potential (Ψm), and solute breakthrough curves all show that preferential flow is an important infiltration mechanism. Preferential flowpaths were activated when Ψm was above -1.5 kPa. During saturated infiltration, at least 97% of drainage was through the ‘mobile’ pore volume of the lysimeter (θm), estimated among the lysimeters at 5.4 – 8.7 % of the lysimeter volume. Early-time infiltration behaviour did not show the classical square-root of time behaviour, indicating sorptivity was not the governing mechanism. This was consistent across the four lysimeters, and during infiltration under different surface imposed suctions. The most likely mechanism restricting sorptivity is weak hydrophobicity, which appears to restrict infiltration for the first 5 – 10 mm of infiltration. Overall, the Gorge soil’s early-time infiltration behaviour is governed by the dynamic interaction between sorptivity, hydrophobicity, the network of air-filled pores, preferential flow and air encapsulation. Long-time infiltration behaviour was intimately linked to the temporal dynamics of Ψm, which was in turn controlled by preferential flow and soil layer interactions. Preferential flowpaths created strong inter-layer connectivity by allowing an irregular wetting front to reach lower layers within 2 – 15 mm of infiltration. Thereafter, layer interactions dominate infiltration for long-time periods, as Ψm in soil layers with different K(Ψm) relationships self-adjusts to try to maintain a constant Darcy velocity. An important finding was that Ψm rarely attained the value set by the tension infiltrometer during unsaturated infiltration. The results show that ‘true’ steady-state infiltration is unlikely to occur in layered soils. A quasi-steady state was identified once the whole column had fully wet and layer interactions had settled to where Ψm changes occurred in unison through each soil layer. Quasi-steady state was difficult to identify from just the cumulative infiltration curve, but more robustly identified as when infiltration matched drainage, and Ψm measurements showed each layer had a stable hydraulic gradient. I conclude that the in-situ hydraulic conductivity, K(Ψm), of individual soil layers can be accurately and meaningfully determined from lysimeter-scale infiltration experiments. My results show that K(Ψm) is different for each soil layer, and that differences are consistent among the four lysimeters. Under saturated flow the subsoil had the lowest conductivity, and was the restricting layer. Most interestingly this pattern reversed during unsaturated flow. As Ψm decreased below -0.5 to -1 kPa, the subsoil was markedly more conductive, and the topsoil layers became the restricting layers. All four soil layers demonstrate a sharp decline in K(Ψm) as Ψm decreases, with a break in slope at ~ -1 kPa indicating the dual-permeability nature of all layers.

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