第23回名古屋大学年代測定総合研究センターシンポジウム平成22(2010)年度報告

Thesis (M.S.)--Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution, 2001. / Bibliography: p. 65-67.

Thesis (M.S.)--East Carolina University, 2009. / Presented to the faculty of the Department of Geological Sciences. Advisor: D. Reide Corbett. Title from PDF t.p. (viewed May 3, 2010). Includes bibliographical references.

Master's thesis. / Format: PDF. Bibl.

Thesis (Ph. D.)--University of California, Davis and San Diego State University, 2003. / Includes bibliographical references (leaves 95-101). Also available via the World Wide Web. (Restricted to UC campuses).

Thesis (M. Sc.)--York University, 2002. Graduate Programme in Biology. / Typescript. Includes bibliographical references (leaves 155-164). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ71590.

Competition over freshwater resources is increasing at local and global scales. Growing urban and suburban centers utilize surface and groundwater resources to meet municipal, industrial, and agricultural demands, often at the expense of riparian ecosystems. Paradoxically, those same urban centers produce a significant volume of treated effluent that can be reused to restore and sustain riparian systems. Use of effluent as a source of water for the environment raises important questions about the benefits and impacts of effluent on riparian functions and ecosystem services, particularly in the context of climate change and drought conditions. This dissertation addresses knowledge gaps surrounding riparian change and resilience along the effluent-dominated Upper Santa Cruz River in southern Arizona. Appendix A investigates whether the Netleaf hackberry (Celtis laevigata var. reticulata) tree can provide accurate information on historic changes in climatic and hydrological conditions. Results indicate that hackberry trees do record climate-related stress in annual ring-width patterns and can therefore provide a historic frame of reference against which to compare current and future changes in riparian conditions. Appendix B documents spatial and temporal patterns of effluent uptake by Fremont cottonwood trees (Populus fremontii) through development of a new application for dendrochronology, specifically dendrochemistry. Results show that annual tree rings contain temporally variable concentrations of a micropollutant found only in effluent and may have the potential to record spatial and temporal patterns of effluent dispersion in riparian ecosystems. Appendix C investigates the complex interactions of ecohydrological conditions that led to a riparian mortality event along the Upper Santa Cruz River in 2005. Effluent is shown to contribute to riparian vegetation expansion, but also, due to its consistent delivery of nutrients and water, homogenize the system and ultimately diminish its resilience to perturbations and stress. Results highlight the paradoxical nature of effluent as both a contributor to riparian growth and a potential impediment to riparian function. This paradox can be resolved through a well-defined effluent impact monitoring and assessment program that incorporates historic information as well as current trends to detect significant changes in ecosystem functions and services.

Precipitation, more than any other environmental factor, controls patterns of ecosystem production and biogeochemical cycling in arid and semiarid environments. Growing-season rains in these regions are highly unpredictable as they come in intermittent pulses varying in size, frequency and spatial extent, thereby producing unique hydrological patterns that constrain the location and residence time of soil water available for biological activity. In order to understand how arid and semiarid ecosystems respond to inputs of precipitation within the context of ecosystem science and global change studies, knowledge is needed on how plants and other organisms respond as an integrated system to such environmental control. The focus of my research was to understand how the distribution of precipitation events influences the dynamics of carbon cycling in semiarid ecosystems. At a semiarid riparian woodland, measurements of CO2 exchange and evapotranspiration revealed that following precipitation events occurring soon after prolonged dry periods the efficiency of rain-use (amount of carbon gain per unit of precipitation over a specific period time) was low. Precipitation did not readily stimulate primary productivity, water was mainly lost as soil evaporation and large respiratory CO2 effluxes were observed. This commonly observed features in seasonally dry ecosystems might have profound consequences for the seasonal and annual carbon balance. In this woodland, 47% of the precipitation within a single growing season (May-October) was returned to atmosphere as soil evaporation and the CO2 efflux observed just during the first rainy month (July) was equivalent to almost 50% of the net carbon gain observed over the six-month growing season. Results from experimental irrigations in understory plots of riparian mesquite woodland revealed that the magnitude and duration of the large CO2 fluxes occurring soon after rainfall was higher in plots located under tree canopies where, relative to intercanopy plots, the amount of plant litter was higher, soil evaporation and plant photosynthetic rates were lower. Efficiency of rain-use in semiarid ecosystems during the growing season apparently was determined by the degree of coupling between gross photosynthesis and ecosystem respiration, by the fraction of precipitation lost as soil evaporation and by the water-use efficiency of the component vegetation.

Tropical agroforestry systems are perceived to have the capacity to be resilient to future changes in climate. This study quantifies the response of two tropical agroforestry tree seedlings; Gliricidia sepium (Jacq.) Walp and Cedrela odorata L. to increases in atmospheric concentrations of carbon dioxide (CO2) (800 ppm), temperature (+2°C daytime and +3°C nighttime) and the combined conditions. As well, this study analyzes the microbial community structure and nutrient concentration in response to elevated concentrations of CO2 on tropical silvopastoral soil, conventional pastoral soil and a regenerated forest soil. Both tree species demonstrated very individual responses to the different climate scenerios. While no significant CO2 fertilizer effect was observed in either species the combined treatment demonstrated a significant increase in seedling height for both species. The response of G. sepium to the combined treatment was similar to its response to the temperature treatment which could be a result of achieving the optimal range in temperature for growth. As well, an increase in C:N ratio from G. sepium seedling leaves under the combined treatment indicates the possibility of the nutrient concentration diminishing thereby reducing the role of this species as a provider of high nutrient biomass. The soil microbial community showed very little change in response to elevated concentrations of CO2 and differences in community structure between sites were also negligible. Soil nutrient concentration maintained the best balance over the course of both twelve week incubations for the regenerated forest site followed by the silvopastoral site and lastly the conventional pasture site. The response of soil nutrient concentration to elevated concentrations of CO2 was negligible reflecting the response of the soil microbial community.

Groundwater dependent ecosystems (GDEs), including wetlands and river baseflow systems, are a topic of substantial scientific study. The degradation of GDEs due to urbanization has been well documented. An altered hydrologic regime, through increased impervious area resulting in a flashier hydrologic regime with lower troughs, higher peaks, and quicker changes, has been recognized as a main factor affecting ecological condition. Yet studies on GDEs rarely include a hydrologic modelling component. In this study, the conjunctive hydrologic model MIKE SHE was used to simulate the Lovers Creek subwatershed near Barrie, ON. The hydrologic regime was simulated for pre-development (natural), current (urbanized), and various low-impact development (LID) land use scenarios. The results were linked to the ecological condition via the TQmean metric, which has been used in the literature to relate the hydrologic and ecological conditions of streams. The highest percentage LID scenario restored, on average, 11% of the reduction in TQmean that occurred from pre-development to urbanized conditions, indicating that LID has the potential to protect GDEs in urbanized watersheds. It is expected that the effect of LID would be amplified if considered on a more local scale within a predominantly high density urban area. Recommendations for future modelling efforts to evaluate GDEs and represent LID are made.