Soil moisture and ground thaw state are both indicative of a hillslopes ability to transfer water. In cold regions in particular, it is widely known that the wetness of surface soils and depth of ground thaw are important for runoff generation, but the diversity of interactions between surface soil moisture and ground thaw themselves has not been studied. To fill this knowledge gap, detailed shallow soil moisture and thaw depth surveys were conducted along systematic grids at the Baker Creek Basin, Northwest Territories. Multiple hillslopes were studied to determine how the interactions differed along a spectrum of topological, typological and topographic situations (T³ template). Results did not show a simple relationship between soil moisture and ground thaw as was expected. Instead, correlation was a function of wetness such that the correlation between soil moisture and ground thaw improved with site wetness. To understand why differences in soil moisture and ground thaw state arose, water and energy fluxes were examined for these subarctic study sites to discern the key processes controlling the patterns observed. Results showed that the key control in variable soil moisture and frost table interactions among the sites was the presence of surface water. At the peatland and wetland sites, accumulated water in depressions and flow paths maintained soil moisture for a longer duration than at the hummock tops. These wet areas were often locations of deepest thaw depth due to the transfer of latent heat accompanying lateral surface runoff. Although the peatland and wetland sites had large inundation extents, modified Péclet numbers indicated that the relative influence of external and internal hydrological processes at each site were different. Continuous inflow from an upstream lake into the wetland site caused advective and conductive thermal energies to be of equal importance to ground thaw. The absence of continuous surface flow at the peatland and valley sites led to the dominance of conductive thermal energy over advective energy for ground thaw. A quantitative explanation for the shallow soil moisture-ground thaw patterns was provided by linking hydrological processes and hillslope storage capacity with the calculated water and energy fluxes as well as the modified Péclet number. These results suggest that the T³ template and the modified Péclet number could be very useful parameters for differentiating landscape components in modeling soil moisture and frost table heterogeneity in cold regions.

Soil solution samplers have certain inadequacies that limit their range of possible applications. Passive Capillary Samplers (PCAPS), which apply suction to the soil pore-water via a fiber glass wick, have shown promising results in preliminary experiments in regard to collection efficiency of water and of bromide tracers. The objectives of this study were to evaluate PCAPS under non-steady state field conditions with respect to (1) effect of installation procedure and operational characteristics, (2) ability to estimate the soil-water flux, and (3) ability to estimate the mean concentration of agrochemicals. At the same time, samplers were used to (4) evaluate the effect of a cereal rye (Secale cereale (L.)) cover crop on NO₃⁻ leaching. Thirty-two PCAPS and 32 suction cup samplers were installed below the root zone at a depth of 120 cm in a Willamette Variant loam wet soil (fine loamy mixed mesic Pachic Ultic Argixeroll). Samplers were installed in an ongoing cover crop/crop rotation study. Regarding overall performance, flux measurements were within 20 % of the native values as determined by a water balance. The air release from the sample bottles was a point of concern and might have slowed down the sampling rate. The installation procedure introduced bias into volume and concentration measurements of the part of the PCAPS closest to the refilled trench. The leachate concentration as calculated using the arithmetic mean of suction cup sampler measurements holds a significant bias, deviating by up to 97 % for bromide concentrations. Phosphate was not detected by the suction cup samplers indicating that ceramic cups should not be used for phosphate sampling. Matrix and preferential flow could clearly be distinguished using the PCAPS, showing that PCAPS are a valuable tool to assess the hydrology and solute transport mechanisms of a field site. The cover crop reduced NO₃⁻-N leaching significantly at the recommended N rate as evaluated by PCAPS. The cover crop reduced the seasonal mean NO₃⁻-N concentration at the recommended N rate from 13.5 mg LI to 8.1 mg L⁻¹, which is under the E.P.A. drinking water quality standard of 10 mg L⁻¹. The total NO₃⁻-N mass lost under the fallow treatment at the recommended N rate was 48 kg N ha⁻' which compares to 32 kg N ha⁻' under the cover crop treatment. Given the increasing problems with nitrate contamination of ground water, programs to support the cultivation of catch crops in conjunction with nitrogen soil testing should be considered as a relatively easy, effective, and biologically sound means to reduce nitrate concentrations in the recharge to the ground water in agricultural settings. / Graduation date: 1994

Three studies were undertaken from 2006 to 2007 to examine litter (dead plant material) in southwestern Manitoba pastures. First, the relationship between litter and soil microclimate was tested across five pasture sites. The amount of litter biomass was not strongly related to soil moisture, though near-surface soil temperatures were reduced when litter was present. Second, the effect of four simulated grazing strategies on the litter layer was measured in six pastures. It was found that after three years of simulated grazing, litter was present in largest quantities in the least-frequently grazed treatments. Finally, a field survey was conducted assessing the quantity of litter present in native pastures across Manitoba. Litter was quite variable and averaged 1902 kg/ha over two years. This research confirmed the value of litter as an indicator of sustainable pasture management, though it remains unclear whether litter is important to pastures from the perspective of soil microclimate. / October 2008

To assess the accuracy of the second-generation Prairie Agrometeorological Model (PAM2nd) as an agrometeorological model for spring wheat on the Canadian Prairies, a study was conducted to validate the model using field measurements. Results from model validation indicated soil moisture was being overestimated at most sites during the second half of the growing season, while soil moisture was underestimated during periods that experienced consecutive days of rainfall. Modifications to the model were implemented to improve the model's ability to simulate soil moisture. Evapotranspiration estimates from PAM2nd and the FAO56 Penmen-Monteith method were compared to water balance methods. Both models produced estimates that fell within the range of water balance ET measurement error. The similarity in performance of both models to estimate ET compared to the water balance ET means the adoption of either model could be justified. However, PAM2nd would be more appropriate because it requires fewer, more commonly measured, surface weather parameters. / February 2009

This thesis examines the feasibility of assimilating space borne remotely-sensed microwave data into WATClass using the ensemble Kalman filter. WATClass is a meso-scale gridded hydrological model used to track water and energy budgets of watersheds by way of real-time remotely sensed data. By incorporating remotely-sensed soil moisture estimates into the model, the model’s soil moisture estimates can be improved, thus increasing the accuracy of the entire model. Due to the differences in scale between the remotely sensed data and WATClass, and the need of ground calibration for accurate soil moisture estimation from current satellite-borne active microwave remote sensing platforms, the spatial variability of soil moisture must be determined in order to characterise the dependency between the remotely-sensed estimates and the model data and subsequently to assimilate the remotely-sensed data into the model. Two sets of data – 1996-1997 Grand River watershed data and 2002-2003 Roseau River watershed data – are used to determine the spatial variability. The results of this spatial analysis however are found to contain too much error due to the small sample size. It is therefore recommended that a larger set of data with more samples both spatially and temporally be taken. The proposed algorithm is tested with simulated data in a simulation of WATClass. Using nominal values for the estimated errors and other model parameters, the assimilation of remotely sensed data is found to reduce the absolute RMS error in soil moisture from 0.095 to approximately 0.071. The sensitivities of the improvement in soil moisture estimates by using the proposed algorithm to several different parameters are examined.

This thesis examines the feasibility of assimilating space borne remotely-sensed microwave data into WATClass using the ensemble Kalman filter. WATClass is a meso-scale gridded hydrological model used to track water and energy budgets of watersheds by way of real-time remotely sensed data. By incorporating remotely-sensed soil moisture estimates into the model, the model’s soil moisture estimates can be improved, thus increasing the accuracy of the entire model. Due to the differences in scale between the remotely sensed data and WATClass, and the need of ground calibration for accurate soil moisture estimation from current satellite-borne active microwave remote sensing platforms, the spatial variability of soil moisture must be determined in order to characterise the dependency between the remotely-sensed estimates and the model data and subsequently to assimilate the remotely-sensed data into the model. Two sets of data – 1996-1997 Grand River watershed data and 2002-2003 Roseau River watershed data – are used to determine the spatial variability. The results of this spatial analysis however are found to contain too much error due to the small sample size. It is therefore recommended that a larger set of data with more samples both spatially and temporally be taken. The proposed algorithm is tested with simulated data in a simulation of WATClass. Using nominal values for the estimated errors and other model parameters, the assimilation of remotely sensed data is found to reduce the absolute RMS error in soil moisture from 0.095 to approximately 0.071. The sensitivities of the improvement in soil moisture estimates by using the proposed algorithm to several different parameters are examined.

Soil moisture and ground thaw state are both indicative of a hillslopes ability to transfer water. In cold regions in particular, it is widely known that the wetness of surface soils and depth of ground thaw are important for runoff generation, but the diversity of interactions between surface soil moisture and ground thaw themselves has not been studied. To fill this knowledge gap, detailed shallow soil moisture and thaw depth surveys were conducted along systematic grids at the Baker Creek Basin, Northwest Territories. Multiple hillslopes were studied to determine how the interactions differed along a spectrum of topological, typological and topographic situations (T³ template). Results did not show a simple relationship between soil moisture and ground thaw as was expected. Instead, correlation was a function of wetness such that the correlation between soil moisture and ground thaw improved with site wetness. To understand why differences in soil moisture and ground thaw state arose, water and energy fluxes were examined for these subarctic study sites to discern the key processes controlling the patterns observed. Results showed that the key control in variable soil moisture and frost table interactions among the sites was the presence of surface water. At the peatland and wetland sites, accumulated water in depressions and flow paths maintained soil moisture for a longer duration than at the hummock tops. These wet areas were often locations of deepest thaw depth due to the transfer of latent heat accompanying lateral surface runoff. Although the peatland and wetland sites had large inundation extents, modified Péclet numbers indicated that the relative influence of external and internal hydrological processes at each site were different. Continuous inflow from an upstream lake into the wetland site caused advective and conductive thermal energies to be of equal importance to ground thaw. The absence of continuous surface flow at the peatland and valley sites led to the dominance of conductive thermal energy over advective energy for ground thaw. A quantitative explanation for the shallow soil moisture-ground thaw patterns was provided by linking hydrological processes and hillslope storage capacity with the calculated water and energy fluxes as well as the modified Péclet number. These results suggest that the T³ template and the modified Péclet number could be very useful parameters for differentiating landscape components in modeling soil moisture and frost table heterogeneity in cold regions.

The overarching goal of this dissertation project was to address several fundamental aspects of applying site-specific crop management for fiber quality in cotton production. A two-year (2005 and 2006) field study was conducted at the IMPACT Center, a portion of the Texas A&M Research farm near College Station, Texas, to explore the spatial variability of cotton fiber quality and quantify its relationship with in-season soil moisture content. Cotton samples and in-situ soil moisture measurements were taken from the sampling locations in both irrigated and dry areas. It was found that generally low variability (CV < 10%) existed for all of the HVI (High Volume Instrument) fiber parameters under investigation. However, an appreciable level of spatial dependence among fiber parameters was discovered. Contour maps for individual fiber parameters in 2006 exhibited a similar spatial pattern to the soil electrical conductivity map. Significant correlations (highest r = 0.85) were found between most fiber parameters (except for micronaire) and in-season soil moisture in the irrigated areas in 2005 and in the dry area in 2006. In both situations, soil moisture late in the season showed higher correlation with fiber parameters than that in the early-season. While this relationship did not hold for micronaire, a non-linear relationship was apparent for micronaire in 2006. This can be attributed to the boll retention pattern of cotton plants at different soil moisture levels. In addition, a prototype wireless- and GPS-based system was fabricated and developed for automated module-level fiber quality mapping. The system is composed of several subsystems distributed among harvest vehicles, and the main components of the system include a GPS receiver, wireless transceivers, and microcontrollers. Software was developed in C language to achieve GPS signal receiving, wireless communication, and other auxiliary functions. The system was capable of delineating the geographic boundary of each harvested basket and tracking it from the harvester basket to the boll buggy and the module builder. When fiber quality data are available at gins or classing offices, they can be associated with those geographic boundaries to realize fiber quality mapping. Field tests indicated that the prototype system performed as designed. The resultant fiber quality maps can be used to readily differentiate some HVI fiber parameters (micronaire, color, and loan value) at the module level, indicating the competence of the system for fiber quality mapping and its potential for site-specific fiber quality management. Future improvements needed to make system suitable for a full-scale farming operation are suggested.

The Carrizo-Wilcox aquifer is a valuable groundwater resource, situated in a semi-arid landscape of Southwest Texas, where over-use by dependent farming practices has lowered aquifer levels. In semi-arid regions, rates of groundwater recharge are predominantly low due to high potential evapotranspiration rates; however, least understood is the role that vegetation plays in soil-plant-water dynamics. Vegetation management potentially plays a major role in countering the loss to recharge because evapotranspiration (ET) varies with vegetation type and cover. The conversion from shrubland to grassland likely reduces rooting depths and total plant cover. Subsequently, deep drainage (percolation below the root zone) will likely increase and lead to groundwater recharge, at least temporarily. The primary aims of the study were to identify those biotic and abiotic factors facilitating deep drainage and to examine differences in recharge for the years following clearing of natural shrub vegetation. Soil chloride was examined to estimate long-term recharge rates, since its concentration in the soil is influenced by the movement of water. Short-term soil moisture trends were also monitored for any water movement deep in the soil profile in response to individual rain events. Rooting depths decreased following removal of vegetation; yet root biomass unexpectedly increased due to successful grass establishment during the first five years after treatment. Soil properties did not vary between treatments, indicating that the majority of chloride differences seen were a consequence of vegetation change. Peak and total soil chloride concentrations were expected to decrease and occur deeper in the soil profile 15-30 years following the clearing of woody vegetation. Total chloride decreased by up to 65% after 30 years and resulted in an estimated 14.9 mm/yr more recharge compared to adjacent untreated controls. Evidence in this study suggest that much of this chloride is leached during the first five years following treatment and that more leaching occurs in especially wet periods. During the wet 2007 growing season, soil moisture below the root zone increased by up to 17% after vegetation clearing. The results of this study indicate that hydrologic changes following brush removal were evident in this system and are likely to positively influence groundwater recharge in the long-term.

Thesis (doctoral)--Swiss Federal Institute of Technology, Zurich, 1997. / Vita. Includes bibliographical references (p. 121-128).