Until the 1930s, flows of the Colorado River maintained approximately 781,060 hectares of wetlands in its delta. These wetlands provided important feeding and nesting grounds for resident and migratory birds as well as spawning and protection habitat for many fish and other invertebrate species. However, the Delta's wetlands started to disappear as water was used for agricultural and urban uses in the United States and Mexico. The 1944 United States-Mexico water treaty, which allocates 1.8 million m��/year to Mexico, did not define a minimum flow to maintain the Delta's ecosystems. The resulting degraded Delta lead to the perception in the 1980s that the Delta was a dead ecosystem. This study investigates whether this "dead Delta" perception is valid. Its central hypothesis is that regenerated vegetation in riparian and flood plain zones is associated with surplus river flows during the 1990s. A vegetation analysis, using satellite imagery and field methods, shows that native trees have regenerated during the last 20 years, and now account for 23% of vegetation in a 100 km, non-perennial, stretch of river below the United States-Mexico border. A spatial trend analysis using multi-temporal data on percent vegetation cover indicates that there are 6,320 hectares that show a significant increasing trend (p-value<0.05) in vegetation cover, with the Delta's riparian zone having at least 18% of its area showing this trend. The study estimates that once in four years February to April flow of 300 million m�� (at 80-120 m��/s) is sufficient to germinate and establish new cohorts of native trees, and highlights the need for smaller but more periodic flows in order to maintain wetland areas. It is concluded that there is clear evidence of the resilience of the Delta's ecosystems and that the "dead Delta" perception is no longer valid. There exist critical habitat in the Delta that needs to be protected, while there also exist short and long term opportunities to ecologically enhance and expand current habitat. Hydrological and ecological studies are needed to estimate specific water requirements for these areas in order to efficiently target them for immediate and long term conservation actions. / Graduation date: 2003

This thesis combines detailed analyses of living plant communities with paleolimnological methods to develop the use of plant macrofossils as an effective tool to track hydroecological changes in ponds of the Slave River Delta (SRD), N.W.T. Several approaches were used to develop an understanding of the relationships between hydrolimnological conditions, living plant communities, and the composition of sedimentary macrofossil remains across spatial and temporal scales. A spatial survey approach was used to assess the relationships between the composition of plant macrofossil assemblages contained in the surface sediments and the hydrological and limnological conditions of 40 SRD basins that span a broad range of hydrological settings in the delta. Results show that there are strong relationships between the prevailing hydrolimnological conditions in the SRD and the composition of sedimentary macrofossil remains, and subsequently indicator macrofossil taxa were identified to distinguish between sites with high river influence (flood-dominated sites: ostracode shells, Daphnia ephippia, Chara oospores; exchange-dominated sites: Myriophyllum winter-bud scales, Daphnia ephippia) and sites with low river influence (evaporation-dominated: Ceratophyllum leaves, Lemna leaves, Drepanocladus leaves). In light of the strong connection between spring flood events and the hydrolimnological conditions of SRD ponds, and growing concerns that the frequency of spring floods have declined in recent decades, paleolimnological investigations were initiated at a pond (SD2) adjacent to the Slave River to construct a record of flood events in the SRD. Prior to analysis of macrofossil assemblages from sediment cores, a detailed study of the living plant community was conducted at SD2, and results were compared to the distributions of surficial sedimentary plant macrofossil assemblages to assess how representative surficial sediment assemblages are of the living plant community. This study indicates distinct patch-scale (or quadrat-scale)similarity between the living vegetation and sedimentary remains in the central basin, as well as distinct similarity between the living aquatic macrophytes and sedimentary remains at a pond-scale, suggesting there is excellent potential to track changes in the composition and percent cover of aquatic macrophytes in pond sediment cores using plant macrofossil assemblages. Additionally, this study indicates that influence of long-distance transport of macrofossils during the 2005 flood event was minor at this pond, and may not be an important factor affecting paleolimnological reconstructions of plant communities. With contemporary studies as a framework, an ~90-year record of ice-jam flood frequency was reconstructed from a sediment core collected from pond SD2. Multi-proxy analyses indicated decadal-scale oscillations in flood frequency at this site, with at least three multi-year periods of low river influence. Beginning in ~1943, an 18-year period of particularly low river influence and greatly reduced water levels was indicated by abundant macrofossils of Sagittaria cuneata and represents the driest period over the past ~90-years. Similarities between the flood history of SD2 and upstream sites in the Peace-Athabasca Delta suggest that spring discharge generated from headwaters and major contributing rivers plays a key role in the frequency and magnitude of spring flood events of both deltas.

This thesis combines detailed analyses of living plant communities with paleolimnological methods to develop the use of plant macrofossils as an effective tool to track hydroecological changes in ponds of the Slave River Delta (SRD), N.W.T. Several approaches were used to develop an understanding of the relationships between hydrolimnological conditions, living plant communities, and the composition of sedimentary macrofossil remains across spatial and temporal scales. A spatial survey approach was used to assess the relationships between the composition of plant macrofossil assemblages contained in the surface sediments and the hydrological and limnological conditions of 40 SRD basins that span a broad range of hydrological settings in the delta. Results show that there are strong relationships between the prevailing hydrolimnological conditions in the SRD and the composition of sedimentary macrofossil remains, and subsequently indicator macrofossil taxa were identified to distinguish between sites with high river influence (flood-dominated sites: ostracode shells, Daphnia ephippia, Chara oospores; exchange-dominated sites: Myriophyllum winter-bud scales, Daphnia ephippia) and sites with low river influence (evaporation-dominated: Ceratophyllum leaves, Lemna leaves, Drepanocladus leaves). In light of the strong connection between spring flood events and the hydrolimnological conditions of SRD ponds, and growing concerns that the frequency of spring floods have declined in recent decades, paleolimnological investigations were initiated at a pond (SD2) adjacent to the Slave River to construct a record of flood events in the SRD. Prior to analysis of macrofossil assemblages from sediment cores, a detailed study of the living plant community was conducted at SD2, and results were compared to the distributions of surficial sedimentary plant macrofossil assemblages to assess how representative surficial sediment assemblages are of the living plant community. This study indicates distinct patch-scale (or quadrat-scale)similarity between the living vegetation and sedimentary remains in the central basin, as well as distinct similarity between the living aquatic macrophytes and sedimentary remains at a pond-scale, suggesting there is excellent potential to track changes in the composition and percent cover of aquatic macrophytes in pond sediment cores using plant macrofossil assemblages. Additionally, this study indicates that influence of long-distance transport of macrofossils during the 2005 flood event was minor at this pond, and may not be an important factor affecting paleolimnological reconstructions of plant communities. With contemporary studies as a framework, an ~90-year record of ice-jam flood frequency was reconstructed from a sediment core collected from pond SD2. Multi-proxy analyses indicated decadal-scale oscillations in flood frequency at this site, with at least three multi-year periods of low river influence. Beginning in ~1943, an 18-year period of particularly low river influence and greatly reduced water levels was indicated by abundant macrofossils of Sagittaria cuneata and represents the driest period over the past ~90-years. Similarities between the flood history of SD2 and upstream sites in the Peace-Athabasca Delta suggest that spring discharge generated from headwaters and major contributing rivers plays a key role in the frequency and magnitude of spring flood events of both deltas.

River deltas are dynamic ecosystems of environmental, ecological, and societal importance. In coastal Louisiana, land loss and increased nutrient loading are altering the eco-geomorphic equilibrium, raising concern for the environmental concerns associated with climate and anthropogenic change. Over the last 100 years, nearly 5000 km2 of wetlands have been submerged due to a variety of environmental and anthropogenic forces. Wetland drowning and costal retreat is predicted to continue, threatening both human and environmental interests. As a result, mitigation efforts in the form of planned river diversions designed to build new land by natural delivering sediment to the once-leveed floodplains have been proposed. Denitrification in coastal wetlands has the potential to limit the risks of hypoxia and related eco-geomorphic issues by reducing the nitrogen export to receiving waters. The goal of this research project is to understand and quantify to propagation of environmental fluxes through a delta distributary system. Water fluxes in the delta distributary network are not solely propagated within the distributary channels and interdistributary areas, taking the form of inundated island interiors surrounded by subaerial levees, are hydrologically important. At Wax Lake Delta (WLD) in coastal Louisiana, roughly 50% of the flow is exchanged to the island swamps, suggesting that significant portions of nutrients are transported to the island interiors. The hydraulic residence times (HRTs) of the islands are estimated to be 15 – 29 hours and 11 – 18 hours on Mike and Pintail Islands, respectively; both being well below HRT estimates for significant denitrification. Spatial variability in network structure, specifically channel width and frequencies of confluences and bifurcations, influences the transport dynamics within the delta. However, flow partitioning in major distributary channels at WLD is relatively constant with time, supporting the hypothesis that network structure controls flux dynamics. / text

published_or_final_version / Industrial and Manufacturing Systems Engineering / Doctoral / Doctor of Philosophy

During the past decade, the high-speed rail (HSR) has got momentum in China, and a number of lines have been put into operation. However, it is noted that the HSR development in China is quite different from that in other regions. The discrepancies are mainly embodied in the duality of HSR types, the diversity of station locations, and the mixed-speed and cross-rail-type train running scheme. These characteristics have considerable impacts on the HSR stations in terms of the external accessibility in the HSR network as well as the internal accessibility in the cities. Based on the comparative study on the accessibility of main HSR stations in Yangtze River Delta, it is discovered that compared with the conventional rail (CR), the HSR has significantly improved the external accessibility of various cities. It is also found that the HSR has further enhanced the hub status of big cities in the rail network, while the differences among the other cities have been reduced, since the small cities have benefited much more from the HSR than the medium cities. Besides, introducing a new HSR line would improve the external accessibility of cities not only in the HSR network but also in the CR network, due to substantial increases in the efficiency of the whole rail system. In terms of the internal accessibility, it is found that the location choice of stations has significant impacts on the accessibility of HSR stations in cities, and the newly built stations have much lower accessibility due to their remote locations and the under-developed transport facilities and services connecting to them. Overall, for a complete journey by the HSR, the improvement in the external accessibility has made the internal accessibility of HSR stations more critical and sensitive. In this sense, more efforts should be paid to improve the urban transport system so as to fully utilize the positive effects brought about by the HSR. / published_or_final_version / Transport Policy and Planning / Master / Master of Arts in Transport Policy and Planning

published_or_final_version / Chinese / Master / Master of Philosophy

Against the background of a rapidly collapsing socialist empire in Eastern Europe and the former Soviet Union, socialist China has since the late 1970s consciously endeavored to develop a "socialist market economy with Chinese characteristics." This thesis assesses the process of economic and spatial transformation in the Zhujiang (Pearl River) Delta, one of the fastest growing economic regions in China. The purposes are to identify the general pattern of economic and spatial changes, to determine the key forces responsible for such changes, and to explore the theoretical implications of these changes in the broader context of interpretation about the operating mechanism of regional development. The overall objective is to understand how a regional economy under socialism is transformed after the intrusion of global market forces. My analyses of regional data and indepth case studies reveal that the Zhujiang Delta has since 1979 moved away from the previous impasse of involutionary growth or growth without development and entered a new era of real transformative development in which dramatic growth has occurred not only in agricultural and industrial output but also in labour productivity, per capita income, and employment. The take-off of the delta's regional economy has owed little to the expansion of state-run modern manufacturing, but has been fueled primarily by numerous small-scale, labour-intensive, and rural-base industries. The spatial outcome of this rural industrialization has been a rapid urbanization of the countryside, especially of the area adjacent to and between major metropolitan centres. There has been no increasing concentration of population in large cities as the conventional wisdom of urban transition might have predicted. Regional development in the Zhujiang Delta during the 1980s was not an outcome of any active state involvement. It was instead a result of relaxed control by the socialist central state over the delta's regional economy. Local governments, along with the collective and private sectors, are found to be the chief agents responsible for the transformation of the peasant economy and the development of the transport infrastructure. The penetration of global market forces via Hong Kong into the Zhujiang Delta has significantly facilitated the process of economic, spatial, and social transformation. This study of the operating mechanism of regional development in the Zhujiang Delta presents a dialectical model of local-global interaction to combat the two prevailing schools of exogenism and endogenism. It also suggests that previous theories on Chinese regional development, which assumed a strong socialist central state monopolizing local economic affairs, might need fundamental modifications. For the Zhujiang Delta, the development of which is still in the early take-off stage, the establishment of a modern transport infrastructure has shown remarkable effects, leading to rather than following the growth of the delta's economy. Finally, the relocation of transnational capital and manufacturing production from Hong Kong to the Zhujiang Delta has not displayed a spatial tendency of high concentration in the primate city as the conventional theory of globalization would suggest. Non-economic factors such as historical, cultural, and social linkages between investors and their target regions are found to have played a major role which should not be overlooked in understanding the mechanism and spatial patterns of the internationalization of production.

Thesis (Ph. D. - Geosciences)--University of Arizona, 1987. / Includes bibliographical references (leaves 321-348).

Thesis (M.S.)--Utah State University. Dept. of Civil Engineering, 1965. / Includes bibliographical references.