Thesis (M.S.)--Missouri State University, 2008. / "August 2008" Includes bibliographical references (leaves 27-30). Also available online.

Indiana University-Purdue University Indianapolis (IUPUI) / I examined interactions between plants and the environment they live in along the soil-plant-atmospheric continuum and addressed the effects of drought and acid deposition on plant water use. Using a novel stable isotope technique, I showed that plant water source utilization can be modulated in some species based on the soil and atmospheric conditions they experience, whereas others only access a single subsurface water source. By modeling cuticular conductance in multiple plant species, I showed that the variability of cuticular conductance across species is largely related to the changes in leaf water potentials between pre-dawn and midday measurements collected in field studies. I also assessed the individual and combined effects of soil water stress and atmospheric water stress on plant productivity by developing a new methodology, which can be used across scales. In doing so, I found that in deciduous broad-leaf forests, periods of high vapor pressure deficit caused sufficient hydraulic stress to reduce plant productivity more than low soil water content alone, and often reduced productivity to levels equal to periods of both low soil water stress and high vapor pressure deficit. Utilizing historical data from a whole forest acidification experiment, I was able to link the stress of nutrient deficiencies caused by acid deposition (specifically calcium) to increases in plant water utilization. This was the first observation of such an effect at the ecosystem scale and could have significant implications for understanding water availability in the future. Finally, I assessed a common method for extracting cellulose from tree rings for isotope analyses, which is often used to determine the historical water use efficiency of plants. I was able to determine chemical alteration to the cellulose molecule using stable isotope measurements and spectroscopy. The chemical modification seems to be systemic and therefore could be addressed through mathematical corrections to existing data. Having accurate values of plant water use efficiency is extremely important for understanding how different stressors in the past changed the way plants used their water resources. My series of studies provide new insights and tools to evaluate the plant-environment interactions in current and future environments.

To investigate the prevalence and magnitude of hydrophobicity in near-surface peat, a poor fen was characterized into four main post-fire microforms: i) severely burned hollows (SB-H), ii) severely burned Sphagnum fuscum hummocks (SB-Sf), iii) lightly burned S. fuscum hummocks (LB-Sf) and, iv) lightly burned feathermoss lawns (LB-F). The SB-H possessed the most hydrophobicity at the surface (85 ± 20 s) and increased at the 2 cm depth (183 ± 35 s). In comparison, the LB-F experienced an increase in hydrophobicity from the surface (44 ± 10 s) to 5 cm (323 ± 32 s) and remained high to the 10 cm depth (211 ± 31 s). Results on Sphagnum recovery show that only LB-Sf are recovering and the SB-H show marginal recovery of pioneer species such as Ceratodon purpureus and Polytrichum strictum. Moreover, S. fuscum had a mean surface cover of 56 ± 5.9% in the LB-Sf and both pioneer species together possessed a total cover of 15 ± 4.4% in the SB-H. While the vascular cover was correlated with increased transplant productivity which in conjunction with moisture availability (preference for hydrophilic substrate), transplant size (15cm diameter preferred over smaller colonies), and transplant location (SB-H preferred over LB-F) should all lead to decreased mortality in treatments. However, each species possesses slightly different characteristics that may be more desirable under reclamation conditions. Species that typically form hummock microform types like Sphagnum fuscum, Sphagnum magellanicum, and to some extent Sphagnum angustifolium can retain moisture under dry conditions (Clymo and Hayward, 1982; Andrus, 1986) and may be optimal for areas experiencing droughts or water limitations. Areas that are commonly inundated with water may benefit from a species that grows through lateral expansion such as Sphagnum angustifolium, Sphagnum riparium, or Sphagnum squarrosum (Andrus, 1986). With S. angustifolium possibly being the best generalist due to its ability to remain photosynthetically active throughout a large range of moisture contents, tolerate desiccation, and grow rapidly (Silvola and Aaltonen, 1984; Andrus, 1986). / Thesis / Master of Science (MSc)

Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 116-124). Also available on the World Wide Web.

Peatlands are unique and important landscape systems, providing valuable ecosystem services such as water and carbon storage, water supply and flood attenuation. They are known to account for more than 10% of the world’s terrestrial carbon store and represent 50 – 70% of the global wetland resource. The UK government’s decision to support the IUCN, UK Peatland Program Commission of Inquiry on Peatlands, recognises the importance and urgency with which action is needed to understand and restore damaged peatland landscapes, and their associated ecosystem services. To meet this need, it is recognised that peatlands in the South West of the UK are important as bio-climatically and functionally marginal peatlands that are undergoing extensive restoration to reinstate key ecological and hydrological function. This thesis aims to improve understanding of the temporal and spatial variability of the ecohydrological structure and function of peatland ecosystems in the South West UK, and will provide the first baseline for the spatially distributed extrapolation of change across larger landscape extents. The research seeks to characterise the structure and function of peatland ecohydrology across multiple spatial and temporal scales. This is accomplished by bringing together remote sensing analyses of ecohydrological structure and function coupled with an integrated and high resolution hydrological monitoring system to characterise the spatial and temporal variability of runoff production and water storage across two headwater catchments. Key outcomes of this research are: 1. The development of novel methods to assess the spatial distribution of near surface hydrology in upland ecosystems using airborne thermal imaging data, 2. Improved understanding of how laser altimetry data can be used to measure the ecohydrology of landscapes more appropriately. 3. An empirical understanding of both the spatial and temporal variability of hydrology across representative sites within the moorlands of the South West UK. The high-resolution monitoring data are the first to describe the hydrological processes operating in these peatlands systems effectively, and provide an insight into how these processes are controlled by the anthropogenic drainage networks that are present throughout this shallow marginal peatland system.

Peatland ecosystems in the eastern Georgian Bay, Ontario, region often provide overwintering habitat for the eastern massasauga rattlesnake (Sistrurus c. catenatus), a species considered at-risk across its range. Suitable overwintering habitat requires a resilience zone with peat temperatures above 0°C and a water table position sufficient to provide moisture without risk of flooding and these ecohydrological conditions commonly occur in raised peatland microforms (hummocks). Due to a changing climate, these peatlands are at risk of increased wildfire frequency and burn severity which may threaten overwintering habitat availability and suitability. In 2018, a wildfire burned over 11,000 ha of the eastern Georgian Bay landscape which serves as critical habitat for the massasauga. We monitored water table position, snow depth, rainfall, and peat thermal dynamics in hummocks in three burned and three unburned peatlands to assess the potential impacts of wildfire on massasauga overwintering habitat. We found that hummocks were able to provide unfrozen and unflooded habitat regardless of peat burn severity and that surface complexity and peatland-scale characteristics provided the greatest control on microhabitat suitability. This research highlights the importance of conserving peatland ecosystems that provide resilient species at risk habitat. / Thesis / Master of Science (MSc) / The eastern massasauga rattlesnake is a species at risk native to Ontario and parts of the USA. In the eastern Georgian Bay region, massasaugas overwinter in wetlands for up to half the year. This is a sensitive period because flooding or freezing within the hibernacula can be fatal. Due in part to climate change, wetlands in this region are at increased wildfire risk which may threaten the quality of massasauga overwintering habitat. In 2018, a wildfire burned over 11,000 ha of land along eastern Georgian Bay, some of which was massasauga habitat. We monitored the water table position and soil temperature in potential massasauga overwintering habitat to assess its quality after wildfire. We found that wetlands provide unflooded and unfrozen habitat even when burned, and that wetland surface complexity is likely an important regulator of overwintering habitat quality. This research highlights the importance of identifying and protecting wetland ecosystems that provide resilient habitat in the face of a disturbance.

M.Sc Thesis / Northern peatlands are able to persist on the landscape and continue to accumulate carbon in the long-term thanks to a suite of ecohydrological feedbacks that confer resilience to disturbance such as the drier and warmer conditions associated with climate change. One feedback of particular interest operates between peat pore-water residence time and chemistry, whereby changes in hydraulic structure with depth restrict turnover in deeper layers, allowing decay end-products to accumulate and thermodynamically suppress decomposition. In this way, the burial of peat facilitates its continued recalcitrance. While this feedback has been observed in more extensive northern peatlands, at least on the side of carbon dynamics and geochemistry, there has been no observational study of profiles of pore-water residence time nor has it been assessed in smaller peat-forming systems. The peat-filled bedrock depressions of the Canadian Shield offered a unique opportunity to study this feedback in systems where primary peat formation occurs under geological constraints on growth in the form of the largely impermeable bedrock. These systems play important hydrological, biogeochemical and ecological roles on the landscape. Understanding their resilience on the landscape may reveal key insights into their evolution and their response to disturbance, which is increasing in the eastern Georgian Bay region. These systems have previously exhibited a hydrological feedback between water table depth and specific yield that varies with depression size. To assess the hydraulic structure that constrains pore-water transport to support continued recalcitrance, profiles of hydrophysical properties and pore-water residence time in four deep (>0.4 m mean depth) and five intermediate (<0.4 m) depressions. Hydraulic structure varied by depression size and depth in the profile, with very low hydraulic conductivities measured in the catotelms of deep sites. The two classes of depressions exhibited distinct hydrology, in the form of dampened water table fluctuations and hydraulic gradients in the deeper sites. Stable isotope analysis of δ2H and δ18O was used to estimate relative pore-water residence times using the simplified inverse transit time proxy (ITTP) for samples collected from May-August 2017. These estimates were observed to have similar controls to hydraulic structure and a close relationship with depth-averaged conductivity on a whole-site basis. While it was hypothesized that the catotelms of deeper depressions would have less pore-water turnover than that of shallower depressions, the ITTP was only able to differentiate between catotelm-acrotelm and deep-intermediate individually. The relative residence time of pore-water in deep catotelms based on δ2H was longer than in intermediate catotelms, but not significantly. These results broadly supported previous pore-water residence time work despite the likely ubiquitous promotion of turnover in the wetter-than-average study period. Carbon accumulation was quantified from extracted peat cores and pore-water chemistry was assessed as dissolved organic matter (DOM) quality using fluorescence spectrometry of monthly pore-water samples. Fluorescence and absorption indices varied by the same depression characteristics as hydraulic structure of site size and depth, but only the humification index exhibited significant temporal variation. Characterization of pore-water DOM was somewhat unclear across the seven indices calculated, although the DOM of intermediate sites appeared to be less humified, more recently produced and autochthonous in nature compared to deep sites Carbon accumulation was predominantly driven by the waterlogged, relatively stable carbon stored deep in the catotelm. Total carbon accumulated in the profile, and even more so the amount stored in the catotelm, were strongly related to depression depth. The thickness and carbon storage of the acrotelm was insensitive to depression morphology, with some intermediate sites being considered all acrotelm based on their water table behaviour. Overall, deeper peat-filled depressions showed stronger signs of the pore-water residence time-chemistry feedback, suggesting the carbon stored in their deep peat layers is more resilient to decay, by way of less conductive deep peat, longer relative pore-water residence times and more humified, less biologically active DOM. In order to comprehensively assess this feedback, longer stable isotope records are essential to ensure robust residence time estimates through differing moisture conditions, and a greater variety of depression sizes may allow for elucidation of threshold depression sizes where hydrological behaviours diverge. This study, at least on a categorical basis, can be used to inform conservation strategies of the relative vulnerability of these important reptile habitats and carbon stores, as well as guide restoration efforts to construct sufficiently deep, resilient systems. / Thesis / Master of Science (MSc)

Indiana University-Purdue University Indianapolis (IUPUI) / Water is fundamental for plant growth, and vegetation response to water availability influences water, carbon, and energy exchanges between land and atmosphere. Vegetation plays the most active role in water and carbon cycle of various ecosystems. Therefore, comprehensive evaluation of drought impact on vegetation productivity will play a critical role for better understanding the global water cycle under future climate conditions. In-situ meteorological measurements and the eddy covariance flux tower network, which provide meteorological data, and estimates of ecosystem productivity and respiration are remarkable tools to assess the impacts of drought on ecosystem carbon and water cycles. In regions with limited in-situ observations, remote sensing can be a very useful tool to monitor ecosystem drought status since it provides continuous observations of relevant variables linked to ecosystem function and the hydrologic cycle. However, the detailed understanding of ecosystem responses to drought is still lacking and it is challenging to quantify the impacts of drought on ecosystem carbon balance and several factors hinder our explicit understanding of the complex drought impacts. This dissertation addressed drought monitoring, ecosystem drought responses, trends of vegetation water constraint based on in-situ metrological observations, flux tower and multi-sensor remote sensing observations. This dissertation first developed a new integrated drought index applicable across diverse climate regions based on in-situ meteorological observations and multi-sensor remote sensing data, and another integrated drought index applicable across diverse climate regions only based on multi-sensor remote sensing data. The dissertation also evaluated the applicability of new satellite dataset (e.g., solar induced fluorescence, SIF) for responding to meteorological drought. Results show that satellite SIF data could have the potential to reflect meteorological drought, but the application should be limited to dry regions. The work in this dissertation also accessed changes in water constraint on global vegetation productivity, and quantified different drought dimensions on ecosystem productivity and respiration. Results indicate that a significant increase in vegetation water constraint over the last 30 years. The results highlighted the need for a more explicit consideration of the influence of water constraints on regional and global vegetation under a warming climate.

The Southwest United States (SWUS) is facing an ongoing drought which has led to water short- ages, in addition to forest mortality due to wildfire and bark beetle outbreaks associated with increased temperatures. This region has a population of 9.6 million people and is one of the fastest growing parts of the United States, and pressure on its resources can be expected to increase in the future. The SWUS is also projected to become more arid in the coming century under greenhouse gas induced climate change, which will impact its environmental, economic and social vitality. This thesis explores the climate dynamics which control water availability, streamflow, and vegetation green-up in the SWUS, in order to constrain our understanding of the mechanisms controlling the ecohydrology of the region, and to inform projections for the 21st century. Chapters 1 and 2 investigate the climate drivers responsible for producing the observed vari- ability in streamflow for the Gila River, a tributary of the Colorado, and the upper Rio Grande. The Gila is the southernmost snowfed river in the SWUS, and has a spring streamflow peak that responds to melting of the snowpack at its headwaters in New Mexico. The Gila is also sufficiently south so that it has a secondary streamflow peak in the summer which is fed by rains from the North American Monsoon (NAM). On interannual timescales, the Gila’s spring peak is primarily influenced by natural variability associated with Pacific sea surface temperature (SST), while the summer peak apparently does not respond to interannual variability. The upper Rio Grande is fur- ther north and east in the SWUS, and only has one streamflow peak occurring in spring-summer which is influenced by both tropical Pacific SST and Atlantic SST. Spring streamflow has also declined in each river post-1998, and this is due to a shift in the tropical Pacific leading to negative precipitation anomalies and drying in the SWUS. Chapter 2 assess a region of the SWUS that receives both winter storm track precipitation and NAM, and therefore has two periods of vegetation green-up annually with an intervening spring dry season. The first peak in vegetation occurs during the spring, and is influenced by the magnitude of winter precipitation and snowmelt, which gradually adds water to the soils. The second peak in vegetation follows the spring dry season when soil moisture recovers with the arrival of the NAM. A climatic shift in the tropical Pacific occurred in 1997/98 and produced a shift to an earlier and more severe spring dry season, and reduced vegetation green-up. An earlier extended dry period in the mid-century (1948 to 1966) also was influenced by a cool phase of the tropical Pacific, which led to a reduction in precipitation of a similar magnitude as the recent drought. However, the recent drought is more severe - and temperatures also have been greater during the recent period. Using a decomposition of the impact of precipitation and potential evapotranspiration (PET) on soil moisture, we found that PET contributed 39% to the negative soil drying anomalies in the recent post-1998 drought, compared to 8% during the earlier extended dry period. This indicates an increased role of temperature during the recent drying. In Chapter 4 we evaluated 18 CMIP5 models based on comparisons with observations of pre- cipitation, net ecosystem exchange, leaf area index and soil moisture from land surface model output. Following our evaluation, we selected three models which best simulated the bimodal region: CanEMS2, GFDL-ESM2G and GFDL-ESM2M. These models indicate that overall this region will be drier in the 21st century; runoff is projected to decrease, particularly in the spring, soil moisture is reduced, and snow fall declines. The variability in projected precipitation, how- ever, is large, and we find that for the most part does not exceed what can be expected from model natural climate variability. The multi-model ensemble from the rest of the CMIP5 models indicate an overall decline in annual precipitation by the end of the 21st century, particularly during the spring. The three models also project an increase in net primary productivity in both the spring and summer growing seasons due to the effects of CO2 fertilization. Enhanced vegetation growth is likely to further exacerbate drying of the soils as vegetation draws down moisture, and enhances water losses via evapotranspiration. The fertilization process is, however, still uncertain and fur- ther studies are needed on the representation of CO2 enhanced vegetation growth in the SWUS to constrain this result. The findings of this thesis have contributed enhanced our knowledge of how climate dynamics, natural variability, and recent warming have influenced the ecohydrology of the SWUS, and also inform future climate projections. Constraining our understanding of this region is of importance given the growing populations, mounting pressures on natural resources, and anthropogenically induced climate change which is expected to affect this region in the 21st century.

Increasing atmospheric carbon dioxide (CO₂) leads to global warming. This can have several impacts on climate and on plant biodiversity, and has been the topic of many studies. The objective of this thesis was to understand the effects of higher atmospheric CO₂ on soil moisture dynamics in the grasslands of central Minnesota using detailed hydrologic modeling to explain previous experimental observations at the BioCON site, a free-air CO₂ enrichment experiment. The hydraulic properties and texture of soils collected from BioCON were determined in the laboratory through grainsize analysis and continuous evaporative drying to determine soil moisture retention curves and hydraulic conductivities. These results were used as input for numerical soil water flow and energy balance models. The models showed that vegetation presence and atmospheric CO₂ concentrations significantly affected the soil moisture dynamics. Summer evapotranspiration (ET) had a higher variation for bare plots than for vegetated plots. This likely occurred because the vegetation provided a buffer against the variations in weather conditions. Vegetation not only retains part of the precipitation on its leaves, it also retains water in its structure and transpires while carrying out photosynthesis. Higher water content was also seen for the bare plots than for the vegetated soils. For some vegetated plots, there were differences between simulated and observed soil moisture. This could have been caused by a difference in plant composition and could suggest that different plant species can respond differently to varying CO₂ atmospheric concentrations leading to different soil moisture dynamics. In addition to this, smaller ET values and higher soil water content values at vegetated elevated CO₂ conditions than at ambient CO₂ conditions were simulated. This was expected, as higher atmospheric CO₂ is linked to higher plant water efficiency and larger biomass. For the simulations, higher values for stomatal resistance and higher plant and plant residue biomass were used. If increasing CO₂ conditions in fact decreases ET, regional weather patterns could be affected as less ET could delay the speed that water flows through the water cycle. / text