Peatlands are carbon sinks and occupy approximately 13% of Canada’s terrestrial surface of which 0.02% have been harvested for horticultural peat. The extraction of peat from natural peatlands alters the hydrology which affects the growth and survival of Sphagnum the primary peat forming vegetation. Ericaceous shrubs do not require specific water content and soil water pressure conditions for their existence and in cutover peatlands they occupy more than 70% of the surface. Rainfall interception, transpiration and root water uptake and redistribution are processes that alter water availability at the soil surface. The high abundance of shrubs at cutover peatlands will influence the surface water balance and more importantly soil water availability and, inevitably determine the success of Sphagnum reestablishment at the site. This study seeks to understand the role that ericaceous shrubs play in the surface hydrological balance at a cutover site and how these changes impact Sphagnum development. Rainfall interception, transpiration, litter layer evaporation and soil water flux was investigated in the field and lab. Approximately 334 mm of rainfall was measured over the season. The shrub canopy and litter had a maximum storage capacity of 4 and 1.2 mm respectively and intercepted ca. 36.7% (120 mm) of rainfall over the season. The effects of rainfall intensity and duration were more important than gross rainfall in determining the amount of water intercepted by the canopy, while the thickness and mass of the litter layer largely determined the storage capacity. Evapotranspiration from shrubs averaged 2.5 mm day-1 with a total of 211 mm over the season. Transpiration was 68% (142 mm) of total evapotranspiration losses, and represented the greatest water loss from the shrub canopy. From these analyses only 22% (72 mm) of rainfall is available for other soil processes and moss development. The evaporation under a litter cover is lower than bare peat and in the field represents water storage of 17 mm over the season. Reduced water input by litter interception is offset by the increased water storage under the litter. Laboratory analyses of soil water flux under ericaceous shrubs show that water loss under the shrubs was greater than bare peat. Water use under the shrubs was highest between -10 and -30 cm and was ca. 2 times greater than bare peat at the same levels. Volumetric water content (θ) decreased throughout the day and water use by shrubs during the day was twice that at night. The shrubs also maintained θ and soil water pressure (ψ) above the threshold values of 50% and -100 cm, respectively, needed for Sphagnum survival. Based on these analyses the shrubs will be beneficial to Sphagnum reestablishment and survival once the primary water losses have been compensated. I recommend raising the water table above -20 cm. In peatland restoration activities, at this level, water used between -10 and -30 cm can quickly be recharged and surface moisture maintained above threshold by capillary rise helping to offset water loss by interception and transpiration through capillary rise.

<p>Drylands, comprising arid and semi-arid areas and the dry subtropics, over some 40% of the world's land area and support approximately 2 billion people, including at least 1 billion who depend on dryland agriculture and grazing. 10-20% of drylands are estimated to have already undergone degradation or desertification, and lack of monitoring and assessment remains a key impediment to preventing further desertification. Change in vegetation cover, specifically in the spatial organization of vegetation may occur prior to irreversible land degradation, and can be used to assess desertification risk. Coherent spatial structures arise in the distribution of dryland vegetation where plant growth is localized in regular spatial patterns. Such "patterned vegetation" occurs across a variety of vegetation and soil types, extends over at least 18 million ha, occurs in 5 continents and is economically and environmentally valuable in its own right.</p> <p>Vegetation patterning in drylands arises due to positive feedbacks between hydrological forcing and plant growth so that the patterns change in response to trends in mean annual rainfall. Mathematical models indicate that vegetation patterns collapse to a desertified state after undergoing a characteristic set of transformations so that the condition of a pattern at any point in time can be explicitly linked to ecosystem health. This dissertation focuses on the mathematical description of vegetation patterns with a view to improving such predictions. It evaluates the validity of current mathematical descriptions of patterning for the specific case of small-scale vegetation patterns and proposes alternative hypotheses for their formation. It assesses the significance of seed dispersal in determining pattern form and dynamics for two cases: vegetation growing on flat ground with isotropic patterning, and vegetation growing on slopes and having anisotropic (i.e. directional) patterning. Thirdly, the feedbacks between local biomass density and infiltration capacity, one of the positive feedbacks believed to contribute to patterning, are quantified across a wide range of soil and climatic conditions, and new mathematical descriptions of the biomass-infiltration relationship are proposed. Finally the influence of land surface microtopography on the partitioning of rainfall into infiltration and runoff is assessed.</p> / Dissertation

In dryland regions, where water is a limited resource, land use/land cover has undergone and continues to undergo significant change mainly due to human activities. The nature of runoff from dryland regions and the influence of land use/land cover change are largely not quantified. The objective of this study is to examine runoff dynamics and the influence of land cover in drylands of western Texas across multiple spatial and temporal scales. The study consists of four major components: (1) an experimental study at Honey Creek upland catchment (19 ha) to assess vegetation treatment effects on runoff by hydrometric and isotopic methods; (2) a hydrochemical evaluation of hydrologic linkage between the upland and bottomland at the second-order Honey Creek watershed; (3) a detailed precipitation-streamflow analysis at North Concho River basin to assess long-term and large-scale precipitation-streamflowvegetation dynamics; and (4) a comparison of streamflow in North, Middle, and South Concho River basins and a regional streamflow trend analysis for the entire western Texas. The study indicates runoff production in the drylands of western Texas is dominated by a few large runoff-producing events. The small catchment experiment indicated that runoff increased about 40 mm per year when 60% of woody plants were removed. This effect may relate to the presence of a baseflow component, but was not verified in regional trend analysis for the Edwards Plateau region where most rivers are spring-fed. The decrease in streamflow in North Concho River basin after the 1950's is in large part related to the enhanced infiltration capacity from reduced grazing pressure and improved vegetation cover. Regional streamflow trend analysis suggests some headwater areas outside the Edwards Plateau region experienced patterns of streamflow change similar to those in North Concho River basin, although artificial impoundments complicated the analysis. The study has broader application in ecohydrological research beyond specific geographic areas and specific vegetation types when evaluating the impact of ecosystem structure change on hydrology and water resources.

The first objective of this study was to investigate the role of an invasive grass species, Arundo donax (L.), on the hydrologic cycle. At a site on the Rio Grande in South Texas, we measured the gas exchange of carbon dioxide and water vapor at the leaf scale and structural characteristics, such as leaf area and shoot density, at the stand scale. In order to assess the effect of water availability, this study was conducted along transects perpendicular to the edge of the river along a potential moisture gradient. The second objective was to quantify the effect of two herbivores, an armored scale, Rhizaspidiotus donacis (Leonardi), and a stem-galling wasp, Tetramesa romana (Walker),on the photosynthetic and transpiration rates of A. donax. Leaf gas exchange measurements were made to determine the direction and magnitude of the effect on physiological processes and by what mechanisms any effects arose. Stands of A. donax used approximately 9.1 � 1.1 mm of water per day. This rate of water use was at the high end of the spectrum for plants. The major controls on stand scale transpiration were evaporative demand, leaf area index, and water availability. During two summer seasons, stand scale transpiration varied greatly, following the pattern of variability in precipitation, suggesting that recent rainfall constituted a significant proportion of the water taken up by this species. Herbivory by a stem-galling wasp and a sap-feeding scale, both separately and together, reduced the rates of leaf scale physiological processes in A. donax. The efficacy of the wasp was density dependent, and this herbivore reduced the carboxylation rate of Rubisco. The effect of the scale took approximately five months to manifest, which coincided with generation time. Scale reduced photosynthesis by decreasing the maximum rate of electron transport. When the two insects were both present, the effect of their herbivory seemed to be additive. These results will assist the responsible management agencies in evaluating the propriety of using one or both of the insect herbivores as biological control agents.

<p>Seasonally dry ecosystems cover large areas over the world, have high potential for carbon sequestration, and harbor high levels of biodiversity. They are characterized by high rainfall variability at timescales ranging from the daily to the seasonal to the interannual, and water availability and timing play key roles in primary productivity, biogeochemical cycles, phenology of growth and reproduction, and agricultural production. In addition, a growing demand for food and other natural resources in these regions renders seasonally dry ecosystems increasingly vulnerable to human interventions. Compounded with changes in rainfall regimes due to climate change, there is a need to better understand the role of climate variabilities in these regions to pave the way for better management of existing infrastructure and investment into future adaptations. </p><p>In this dissertation, the ecohydrological responses of seasonally dry ecosystem to climate variabilities are investigated under a comprehensive framework. This is achieved by first developing diagnostic tools to quantify the degree of rainfall seasonality across different types of seasonal climates, including tropical dry, Mediterranean, and monsoon climates. This global measure of seasonality borrows from information theory and captures the essential contributions from both the magnitude and concentration of the rainy season. By decomposing the rainfall signal from seasonality hotspots, increase in the interannual variability of rainfall seasonality is found, accompanied by concurrent changes in the magnitude, timing, and durations of seasonal rainfall, suggesting that increase in the uncertainty of seasonal rainfall may well extend into the next century. Next, changes in the hydrological partitioning, and the temporal responses of vegetation resulting from these climate variabilities, are analyzed using a set of stochastic models that accounts for the unpredictability rainfall as well as its seasonal trajectories. Soil water storage is found to play a pivotal role in regulating seasonal soil water hysteresis, and the balance between seasonal soil water availability and growth duration is found to induce maximum plant growth for a given amount of annual rainfall. Finally, these methods are applied in the context of biodiversity and the interplay of irrigation and soil salinity, which are prevailing management issues in seasonally dry ecosystems.</p> / Dissertation

<p>Tropical Cyclones (TCs) intensity and frequency are expected to be impacted by climate change. Despite their destructive potential, these phenomena, which can produce heavy precipitation, are also an important source of freshwater. Therefore any change in frequency, seasonal timing and intensity of TCs is expected to strongly impact the regional water cycle and consequently the freshwater availability and distribution. This is critical, due to the fact that freshwater resources in the US are under stress due to the population growth and economic development that increasingly create more demands from agricultural, municipal and industrial uses, resulting in frequent over-allocation of water resources. </p><p>In this study we concentrate on monitoring the impact of hurricanes and tropical storms on vegetation activity along their terrestrial tracks and investigate the underlying physical processes. To characterize and monitor the spatial organization and time of recovery of vegetation disturbance in the aftermath of major hurricanes over the entire southeastern US, a remote sensed framework based on MODIS enhanced vegetation index (EVI) was developed. At the SE scale, this framework was complemented by a water balance approach to estimate the variability in hurricane groundwater recharge capacity spatially and between events. Then we investigate the contribution of TCs (season totals and event by event) to the SE US annual precipitation totals from 2002 to 2011. A water budget approach applied at the drainage basins scale is used to investigate the partitioning of TCs' precipitation into surface runoff and groundwater system in the direct aftermath of major TCs. This framework allows exploring the contribution of TCs to annual precipitation totals and the consequent recharge of groundwater reservoirs across different physiographic regions (mountains, coastal and alluvial plains) versus the fraction that is quickly evacuated through the river network and surface runoff. </p><p>Then a Land surface Eco-Hydrological Model (LEHM), combining water and energy budgets with photosynthesis activity, is used to estimate Gross Primary Production (GPP) over the SE US The obtained data is compared to AmeriFlux and MODIS GPP data over the SE United States in order to establish the model's ability to capture vegetation dynamics for the different biomes of the SE US. Then, a suite of numerical experiments is conducted to evaluate the impact of Tropical Cyclones (TCs) precipitation over the SE US. The numerical experiments consist of with and without TC precipitation simulations by replacing the signature of TC forcing by NARR-derived climatology of atmospheric forcing ahead of landfall during the TC terrestrial path. The comparison of these GPP estimates with those obtained with the normal forcing result in areas of discrepancies where the GPP was significantly modulated by TC activity. These areas show up to 10% variability over the last decade.</p> / Dissertation

No description available.

<p>The research was driven by a need to increase the knowledge base concerning wetland ecological responses, as well as to identify and evaluate the factors driving the functioning of the Franschhoek Trust Wetland. An ecohydrological study was undertaken in which vegetation cover, depth to groundwater, water and soil chemistry were monitored at 14 sites along three transects for a 12 month period. The parameters used include temperature, pH, electrical conductivity (EC), sodium, potassium, magnesium, calcium, iron, chloride, bicarbonate, sulphate, total nitrogen, ammonia, nitrate, nitrite and phosphorus. T-tests and Principal Component Analysis (PCA) were used to analyze trends and to express the relationship between abiotic factors and vegetation.</p>

Anthropogenically-induced climate change has the potential to have serious implications on aquatic ecosystems and may ultimately affect the supply and quality of freshwater lakes and rivers throughout the world. As a class of ecosystems, inland waters are vulnerable to climatic change and other pressures, due to their small size and their position in the landscape. There is therefore a need to assess the impact of projected climatic change on aquatic ecosystems. Owing to this need, ecological indicators have been developed as a method of quantifying, identifying, monitoring and managing the ecological integrity of aquatic environments. The aim of this research was to develop techniques in order to conceptualise the higher order impacts of projected climate change on environmentally related streamflows and water temperature in South Africa, and to simulate these using an appropriate hydrological model. For this dissertation the downscaled daily climate output from the ECHAM5/MPI-OM General Circulation Model (GCM) was used as an input into the daily time step conceptualphysical ACRU Agrohydrological Modelling System in order to simulate the impacts of projected climate change on selected eco-hydrological indicators at the Quinary Catchment spatial scale. In this research these indicators were grouped into two broad categories: 1. Ecological Flow Indicators and 2. Water Temperature Indicators. The results of this research took the form of maps and time series graphs. The ecological flow indicator results investigate the magnitude and duration of flow events and were analysed spatially for the 5 838 hydrologically interlinked and cascading Quinary Catchments constituting the southern Africa study region. The ECHAM5/MPI-OM GCM projects the magnitude and duration of both annual subcatchment runoff and accumulated streamflows to increase in the eastern parts of southern Africa for the intermediate future climate scenario (2046 - 2065), with this trend strengthening in the distant future climate scenario (2081 - 2100). The computationally intensive water temperature indicator results were analysed spatially at the scale of the Thukela Catchment. The Thukela catchment was selected as a case study area because of its diversity - in altitude, rainfall, soils and ecological regions, as well as in its population geography and levels of education and employment. This diversity presents a challenge to studies of impacts of projected climate change, including its potential impacts on water temperatures. The spatial analyses indicate that subcatchment runoff, accumulated streamflows and mixed maximum water temperature are all likely to increase under projected future climate conditions. A temporal investigation, in the form of time series analyses, focused on four water temperature indicators and was performed for 15 selected Quinary Catchments, located within the Thukela Catchment. These temporal analyses indicate that the absolute variability (i.e. standard deviation) of both individual subcatchment runoff and accumulated catchment streamflows, are projected to increase in the future, while the relative variability (i.e. coefficient of variation) is likely to remain much the same or even decrease slightly over time period. These temporal analyses also indicate that there is a noticeable difference in the mixed maximum water temperature within a single Quaternary Catchment due to hydrological flow routing, with an increase in water temperatures as the water cascades downstream from the upper Quinaries to the Quinaries at lower altitudes. The techniques developed and used in this research could aid decision makers involved in ecological and water management planning. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.

Thesis (Ph. D.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 116-126). Also available on the World Wide Web.