• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 271
  • 51
  • 21
  • 6
  • 4
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 1
  • 1
  • 1
  • Tagged with
  • 404
  • 404
  • 141
  • 72
  • 72
  • 65
  • 60
  • 51
  • 45
  • 43
  • 42
  • 36
  • 35
  • 31
  • 31
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
231

Vegetation Dynamics Over the Northeast Region of Brazil and Their Connections With Climate Variability During the Last Two Decades of the Twentieth Century.

Barbosa, Humberto. January 2004 (has links)
The spatial and temporal responses of natural landscape ecosystems in the Northeast region of Brazil (NEB) to changes in rainfall conditions over the last two decades of the 20th century have not been fully examined. The NEB ecosystems are highly dynamic landscape responding to weather conditions, of which rainfall is the most important variable. The research described in this dissertation was conducted to test whether or not the impact of rainfall fluctuations on the vegetation dynamics can be spatially and temporally differentiated within the NEB ecosystems. This was achieved in two phases: In phase one, the spatial and temporal consistency of the response of monthly normalized difference vegetation index (NDVI) derived from Advanced Very High Resolution Radiometer (AVHRR) data records to monthly rain gauge data records for the period 1982-1993 was assessed. This assessment of the spatial and temporal responses of the NDVI time series data to rainfall time series data tested the hypotheses that responses of NEB ecosystems to rainfall conditions can occur with different time lags and can be spatially heterogeneous. This was achieved by using correlation coefficients with different time lags and by applying factor analysis through the use of Varimax rotation. In phase two, the spatial and temporal variability of the NDVI responses to NEB land surface conditions for the period 1982-2001 was quantified. This quantification of temporal and spatial variability in NDVI across the NEB ecosystems tested the hypothesis that responses of NDVI variability to land surface conditions of the NEB can be temporally and spatially heterogeneous by combining statistical parameters of monthly series of NDVI (minimum, mean, maximum, anomalies and coefficient of variation) and by using annual NDVI images. The results of phase one of this research showed that the direct response (i.e., no lagged response) of the NEB ecosystems to rainfall was associated with different land cover types. A strong positive relation was found in rainfall-limited NEB ecosystems that are associated with Caatinga biome. Particularly, the disturbance of the landscape reduced the significance of the relationship. Over the Cerrado biome and Atlantic rain forest (evergreen tropical forest), significant negative relations between NDVI and rainfall were found where there are no moisture availability constraints. However, the NDVI responses of the NEB ecosystems to changing rainfall conditions were found to be strongly positive for the correlation of NDVI with rainfall in the concurrent plus one previous month. This was demonstrated for most of the NEB ecosystems, except for the southeastern NEB that is formed by the Atlantic rain forest that, in certain areas, has been converted to cropland. In general, there is a good spatial agreement between the NEB ecosystems and the patterns of NDVI variability on both the annual basis and the interannual basis as the temporal responses of the NEB ecosystems are affected by both positive and negative correlations with rainfall. In phase two, the results show clear indications that, for the inter-annual NDVI variability in the interval between 20% and 45% variability a positive response of ND VI to changes in rainfall exist for most of NEB ecosystems where main annual rainfall amounts vary from 300 to 750 mm. A strong decrease of response was found in the monthly NDVI anomalies trend over the period of September 1988 to August 1997. The decrease might be interpreted as a response of NEB ecosystems caused by the impact of enhanced aridity over the 1990s. Overall, in the first phase, it was observed that responses of different land cover types of the NEB to rainfall conditions appeared to occur with different time lags and appeared to be spatially heterogeneous. In the second phase, the inter-annual NDVI variability in the NEB ecosystems to land surface variations appeared to be temporally and spatially heterogeneous. These results suggest that vegetation responses over the NEB ecosystems to changing rainfall conditions, as measured by changes in NDVI to rainfall fluctuations, may have a potential for predicting the impact of rainfall conditions on the NEB landscape dynamics.
232

Eastern watershed analysis of alternate approaches to delineation in Austin, TX

Vermillion, Elizabeth Lauren, 1982- 24 November 2010 (has links)
Drainage area is a measure of the number of acres feeding into a creek. Drainage area threshold is the amount of acreage required for the creek to be included on a map. Watersheds mapped according to higher drainage area thresholds will show creek systems that are shorter and concentrated at the bottom of the watershed. Watersheds mapped according to lower drainage area thresholds show creek systems that are longer and extend further up the watershed. Since all watersheds are subject to different land uses, soil types, geology, etc., they should be mapped according to different drainage area thresholds. Headwaters are where creeks begin. There is empirical evidence that properly functioning headwaters significantly reduce erosion, improve water quality, slow stormwater flows, and provide habitat. If municipalities use lower drainage area thresholds to define their creeks, they can include more headwaters in their creek setback requirements. This professional report identifies the Harris Branch watershed as being under relatively more pressure to develop and exhibiting more environmental risk than other watersheds in Austin, Texas’ Desired Development Zone. Creeks in the watershed are redrawn according to reduced drainage area thresholds using a simple ArcGIS analysis. The analysis reveals a critical mass where creek setbacks appear to be too extensive. If creeks with a drainage area of 5 acres are protected by development code, the setbacks created have excessive branching that could be too restrictive for development. A critical mass ratio should be considered when determining which drainage area threshold is most appropriate for a watershed. The critical mass ratio is equal to the number of branches allowed per a specified distance of creek centerline. The process of identifying this critical mass ratio can help growing cities find a balance between the need to encourage development in designated areas and the need to protect natural creek systems everywhere. I recommend that municipalities review the effects of reducing drainage area threshold for each watershed, and then identify the drainage area threshold that, when protected by setback requirements, allows for extended and connected greenways as well as an increase in density. / text
233

Integrated watershed management planning for St. Lucia

Cox, Christopher Anthony January 2003 (has links)
A decision support framework (DSF) to guide watershed management planning in St. Lucia was developed. The DSF, supported by three components, integrated physiographic criteria in spatially defining sustainable land management regimes, crop suitability based on agro-ecologic zoning criteria, and water quality modelling tools. / In the first component, a methodology for agricultural and forestry land management zoning based on decision-rule frameworks was developed, employing GIS-based spatial multiple-criteria integration techniques. Land capability, recommended land management regimes, crop suitability and broad agricultural/forestry land utilization type zones were derived for the country. Sixteen broad agricultural and forestry land utilization types (LUTs) based on FAO agro-ecologic zoning guidelines were spatially defined over the island. These LUT zones represent relative suitability for rain-fed annual and perennial crop production, grazing and forestry. / In the second component, field research to quantify rainfall, runoff and erosion from two small watersheds under contrasting land management regimes was undertaken. Over the study period the erosion rate from an intensively cultivated, degraded agricultural watershed was 20 times that of a completely forested watershed. SCS curve numbers were evaluated for both watersheds based on rainfall-runoff relationships. / The third component demonstrated the application of a distributed-parameter hydrologic/water quality model, AnnAGNPS, in land management scenario evaluation, in terms of runoff and soil erosion. Data from the second component were used to calibrate and validate the model in simulation of daily runoff and erosion losses from the two watersheds over the study period. The model generally performed better in runoff simulation for the agricultural watershed compared to the forested watershed. Average annual erosion rates under current land management regimes were estimated at 73.3 and 7.2 t/ha for the agricultural and forested watersheds respectively. The model was applied to simulate runoff and erosion losses from the agricultural watershed under alternative sustainable land management regimes derived in the first component. Simulated average annual erosion losses were reduced to 9.2 t/ha. / This study demonstrated the application of efficient and powerful computer-based tools in the development of a decision support framework for watershed management planning for small islands.
234

A comparative assessment of stormwater runoff from a coastal and interior log yard

Fikart, Alena 11 1900 (has links)
Stormwater runoff from log yards in different BC regions can affect aquatic habitats to varying degrees given differences in weather, water quality and tree species. The objective of this thesis was to compare runoff quality and total runoff loadings from a coastal and interior log yard. Chemical analyses, toxicity tests and treatments were conducted. Data were compared to criteria, statistically compared between sites and assessed for seasonal trends. Export coefficients (ECs) were compared between sites. Relationships between toxicological and chemical variables were explored statistically. Runoff toxicity was similar between sites and fairly low. LC50s for 48-hour Ceriodaphnia dubia tests ranged from 32.95 to > 100 and 58.70 to > 100 for coastal and interior runoff, respectively. Microtox ®.5 minute EC50s ranged from 27.12 to > 100 for coastal runoff and 22.22 to > 100 for interior runoff. Several metals and dehydroabietic acid (DHA) exceeded criteria in runoff from both sites. Biochemical oxygen demand, alkalinity, pH and metals were significantly higher (p < 0.05) at the interior site. Sodium and conductivity were higher at the coastal site. No seasonal differences in runoff quality were observed. Therefore, acute effects would occur during periods of high runoff, during autumn at the coastal site and late winter at the interior site. The unpaved interior site generated less runoff per square meter due to ground infiltration. ECs were comparable to the paved coastal site. Exceptions to this include tannins and lignin (11 fold higher at the coastal site) and DHA (9 fold higher at the interior site). C. dubia toxicity was partially associated with TSS for both sites. Tannins and lignins were correlated (r² =0.91) with C. dubia toxicity for coastal runoff. Tannin and lignin concentrations ranged from 45 to 263 mg/L and 43 to 75 mg/L in coastal and interior samples, respectively. Since results suggest that TSS is partially responsible for toxicity, and since contaminants are often bound to TSS, source control and treatment options for TSS should be implemented.
235

A framework for effective urban stream corridor management : a case study of Pietermaritzburg. Component A.

De Lange, Marthinus Arnoldus. January 2003 (has links)
Not only does urbanisation have a negative impact on the establishment of natural open space areas but also has serious implications for urban stream corridors (USCs), the focus of this study. For the purpose of this study USCs are defined as the aquatic, the riparian and the terrestrial zone. The principle objective of this study is to develop a set of policies, based on international and local experiences (Pietermaritzburg Metropolitan Open Space System) to guide municipalities in implementing effective USC management practices. The literature review lead to the identification of both the value of USCs and the threats thereto. The value of USCs includes habitat and biodiversity, purification, amenity, cultural, recreational and eductional valueas well as flood attenuation value. Conversely, threats to USCs include the impacts of urbanisation on stream hydrology, erosion, decline in water quality, loss of natural open space (NOS), alien infestation, littering and unnatural fence barriers. Urban stream corridor management is subject to specific legislation, municipal capacity and importantly, public involvement, which were also evaluated. This process lee;td to the establishment of a conceptual framework containing the critical considerations associated with USC management such as the value of USCs for nature and man, the need for public involvement, effective implementation structures supported by implementation policies and the integration of use management in urban planning. Key to the success of USC management is public involvement. As a consequence, the methodology included a survey to be undertaken with 40 urban riparian households along two streams in Pietermaritzburg to establish their opinion regarding natural open spaces (NOSs) and USC management. A reconnaissance survey of two streams was undertaken to inform the questionnaire and later debate on the issue. The results from this exercise together with the findings of the interviews with stakeholders in the USC management process will form the basis for the establishment of an USC management policy, which will be contained in a separate report (Component B). / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2003.
236

Erosion control alternatives which promote native landscape types in the Old Woman Creek watershed, Erie County, Ohio

Ribble, Steven W. January 1996 (has links)
This project recommends an appropriate land cover master plan for the lower portion of the west fork of Old Woman Creek. The project utilizes the various vegetative treatments, or measures available, to lessen storm water induced sediment concentration levels within the agricultural study site. The over riding design principle is that a return to a more native landscape through the addition of native-like plant species, en mass or as a hedgerow around agricultural fields, will improve the bio-filtering of sediment from runoff as it has in other locations. (Ingles 6/11/96) Suggestions for other erosion control alternatives such as `alternative crops' are also presented. The completion of the master plan is accomplished through identifying those areas in greatest need for erosion control enhancement, suggesting suitable amelioration responses for those areas and illustrating the landscape patterns which would result from the implementation of the project findings. / Department of Landscape Architecture
237

Spatial decision support system for evaluation of land use plans based upon storm water runoff impacts : a theoretical framework

Nodine, Dewayne J. January 1996 (has links)
All land uses affect storm water runoff However, different uses of the same site generate varying amounts of runoff Many communities have come to rely upon detention and/or retention basins for controlling the additional runoff resulting from land development. It is argued that this incremental approach to storm water management must be replaced with a more proactive long-term view.To achieve this, more user-friendly software capable of modeling the effect long-range land use plans have on the volume and behavior of storm water runoff is needed. This software, called a Spatial Decision Support System (SDSS), must be capable of guiding the user, who may not be an expert at runoff analysis, through the process and also capable of generating output in various formats understandable by lay persons. This study utilizes a systems analysis technique to develop a theoretical framework for the Storm Water SDSS. / Department of Urban Planning
238

Assessing the Role of Phosphorus as a Source Water and Treatment Vulnerability Indicator: Implications for Planning, Management and Operations

Chik, Ho Shing (Alex) January 2013 (has links)
Source water protection (SWP) refers to the pressing global need to address the combination of issues affecting water supply and treatment: water quality, water quantity and timing of availability. Although SWP has been increasingly advocated by drinking water professionals, tools to relate upstream land-use impacts to downstream water treatability are lacking. Treatment water quality metrics can seldom be used to decouple the cumulative water quality impacts of natural and anthropogenic land-use disturbances; moreover, some changes in source water quality that potentially compromise the effectiveness of treatment are not reflected by changes in magnitude of these treatment water quality metrics. This underscores the need for an effective vulnerability indicator: a metric for monitoring and assessing the susceptibility of a system to harm arising from source water quality changes. In this research, a proof-of-concept approach was used to evaluate phosphorus as an indicator for linking source water and treatment vulnerabilities in a forested watershed in Alberta, Canada. Relationships between phosphorus and various water quality parameters were assessed using historical Elbow River discharge and Glenmore Reservoir water quality data from 2000 to 2010 to elucidate source water vulnerabilities. The results showed that allochthonous inputs from the Elbow River were the primary drivers of source water quality in the reservoir during significant hydrological events. Autochthonous processes such as dilution and deposition of allochthonous inputs in reservoir bottom sediments buffered water quality changes within the reservoir. Carbon:nitrogen:phosphorus (C:N:P) nutrient ratios observed in the reservoir were indicative of severe-to-moderate phosphorus-limitation for primary production. Although total phosphorus (TP) concentrations reached threshold levels for supporting mesotrophic to eutrophic conditions, primary production was limited. Consistently low reservoir chlorophyll-a levels and low dissolved phosphorus concentrations suggest that drinking water treatment impacts are unlikely to be confounded by the presence of algal matter. The impacts of source water quality changes to drinking water treatability were inferred using historical source water quality data and treatment performance metrics at the Glenmore Water Treatment Plant (WTP) using forward-stepwise multiple linear regression. Raw water TP and total organic carbon (TOC) concentrations explained 78.8% of the coagulant dose variation used in coagulation and flocculation processes (n = 22). Additional plant water quality data and treatment performance metrics were collected in 2012 to confirm these observations. Plant raw water UV-absorbance at 254 nm (UVA254) and TP concentrations described 98.3% of the alum coagulant dose variation used in the newly-installed Actiflo© ballasted-sand flocculation process (n = 26). SUVA and TP together explained 91.2% of the polymer dose variation (n = 26). The inclusion of TP as a significant predictor of coagulant and polymer doses, coupled with a review of literature, suggest that TP is a more sensitive indicator of waterborne particle concentrations present in the raw water than turbidity. Accordingly, TP may play a role in the critical drinking water treatment processes of coagulation, flocculation and clarification which has direct implications for process optimization, chemical coagulant costs, sludge production and impacts to subsequent treatment processes. Scenario building based on anticipated land-uses and impacts from catastrophic landscape disturbances using the coagulant regression models was used to explicitly link potential source water quality impacts to drinking water treatability. The innovative approach of estimating land-use TP loading, steady state reservoir TP concentrations and coagulant dosing requirements at the WTP provides a framework that enables the development and coordination of land-use planning, reservoir management and drinking water treatment operations strategies respectively. Total phosphorus provides a common vulnerability metric relevant to both land-use and water managers for developing and assessing integrated land-use management and SWP strategies.
239

Bacterial source tracking and survival of Escherichia coli

Meays, Cynthia L. 10 February 2006 (has links)
Surface water is used for drinking by many people around the world. E. coli is the most frequently used bacterial indicator used for assessing water quality. The survival, sources, and concentrations of E. coli were examined through a series of experiments that investigated the survival of beef cattle E. coli on land and in water, and used bacterial source tracking (BST) to determine the sources of fecal contamination diurnally and annually in multiple watersheds in British Columbia. A fecal pat experiment was conducted to examine the survival of E. coli under 4 levels of solar exposure. E. coli survived longer with increasing shade. Age of fecal pats, as well as exposure to solar radiation negatively influenced the survival of E. coli. The survival of E. coli in stream water was examined in filtered and unfiltered stream water at 3 different temperatures (6, 20 and 26 ºC). There was no significant difference in the survival of E. coli in filtered versus non-filtered stream water. Lower water temperatures (6 ºC) increased the survival of E. coli. The addition of manure to the water substantially increased the nutrient concentrations and organics. BST is a rapidly growing area of research and technology development and many methods are being developed and tested. The choice of method used for BST depends on: question(s) to be answered, scale of identification needed, available expertise, cost of analysis, turnaround time, and access to facilities. The spatial, diurnal, and annual sources and concentrations of E. coli were investigated in several watersheds in British Columbia. Fecal coliforms and E. coli concentrations varied throughout the day, as well as by site, month and year. Ribotyping identified many different sources of E. coli within the watersheds. The majority of E. coli isolates classified were from wildlife sources in each watershed even though they had different land-use.
240

Mapping riparian vegetation functions using remote sensing and terrain analysis

Lymburner, Leo January 2005 (has links)
Land use practices over the last 200 years have dramatically altered the distribution and amount of riparian vegetation throughout many catchments in Australia. This has lead to a number of negative impacts including a decrease in water quality, an increase in sediment transport and a decrease in the quality of terrestrial and aquatic habitats. The task of restoring the functions of riparian zones is an enormous one and requires spatial and temporal prioritisation. An analysis of the existing and historical functions of riparian zones and their spatial distribution is a major aid to this process and will enable efficient use of remediation resources. The approach developed in this thesis combines remote sensing, field measurement and terrain analysis to describe the distribution of five riparian zone functions: sediment trapping, bank stabilization, denitrification, stream shading and large woody debris production throughout a large semi-arid catchment in central Queensland.

Page generated in 0.0885 seconds