1,721,041 research outputs found
Stream hydrologic characterizations across time and space
No full textIncludes bibliographical references (pages 113-120)
Temporal Dynamics in Surface Water – Groundwater Interactions Inferred From High-Resolution Observations in Streambank Wells
Full text linkGains in streamflow from groundwater and, conversely, losses of streamflow to groundwater, have wide-ranging implications for water quantity and quality. Studies have revealed the potential for stream water levels and adjacent nearby groundwater elevations to be used in conjunction for studying this phenomenon across vast spatial scales based on inferred lateral hydraulic gradients. However, previous studies have used only snapshots in time of these elevations, which may not capture the temporal variability of these processes. This study uses high-resolution observations of stream and nearby groundwater elevations from multiple years across 5 snowmelt-dominated watersheds in the intermountain west to study the seasonal changes in gradients between surface water and groundwater. We found that at every site there were substantial changes in the magnitude and direction of these gradients at seasonal to weekly timescales, usually corresponding to times when stream elevations are changing greatly, such as during snowmelt runoff. This shows that while individual measurements can be useful in revealing these dynamics, high temporal resolution observations are required to capture them accurately. This method further shows the utility of collecting paired surface and groundwater elevations. We also developed a simple metric using the change in surface water and groundwater elevations to evaluate stream-aquifer response to watershed scale processes.</p
Comparison of Dams and Diversions On Downstream Water Quality and Ecosystem Processes
Full text linkWater resources infrastructure, such as impoundments and diversions, is expected to expand in order to supply water for an increasing population living in a drier west. River impoundments and diversions, termed discontinuities, are known to disrupt natural gradients and processes, causing a shift in the balance between water rescources supply and riverine ecosystem services. Deep-release reservoirs and their effects on river processes have been well-studied, but few studies quantify the effects of diversions and surface-release impoundments on water quality and ecosystem processes. Due to the effects of seasonal and climatic variations on river hydrographs, it is important to understand the impacts of discontinuities within the same basin and temporals scale. I deployed sensors upstream and downstream of two deep-release impoundments, one surface- release impoundment, one hydroelectric diversion (power diversion), and one irrigation diversion to understand the relative effects of these projects on river dissolved oxygen (DO), DO saturation, temperature, and specific conductivity (SpC) as well as these water quality relationships with discharge and temperature. Impoundments had an overall greater effect on downstream water quality than diversions. Additionally, water-quality-discharge relationships became weaker downstream of both deep-release impoundments while these relationships did not shift as significantly downstream of the surface-release impoundment and diversions. The irrigation diversion had a larger effect on temperature, DO, and metabolism at lower flows. Combined with model results of downstream temperature changes, this suggests that my results do not capture the largest effect of the irrigation downstream water quality. This combined with a correlation between temperature and DO saturation at low flow suggest that the irrigation diversion has the potential to stimulate ecosystem activity at low flows, especially if they occurred during the predicted warmer temperatures in the future. Adding additional infrastructure to provide water sustainability will exacerbate the compounding effects of these discontinuities within the river network require strategic monitoring and adaptive management in order to maintain ecosystem services provided by rivers.</p
Temporal Dynamics in Surface Water – Groundwater Interactions Inferred From High-Resolution Observations in Streambank Wells
Full text linkGains in streamflow from groundwater and, conversely, losses of streamflow to groundwater, have wide-ranging implications for water quantity and quality. Studies have revealed the potential for stream water levels and adjacent nearby groundwater elevations to be used in conjunction for studying this phenomenon across vast spatial scales based on inferred lateral hydraulic gradients. However, previous studies have used only snapshots in time of these elevations, which may not capture the temporal variability of these processes. This study uses high-resolution observations of stream and nearby groundwater elevations from multiple years across 5 snowmelt-dominated watersheds in the intermountain west to study the seasonal changes in gradients between surface water and groundwater. We found that at every site there were substantial changes in the magnitude and direction of these gradients at seasonal to weekly timescales, usually corresponding to times when stream elevations are changing greatly, such as during snowmelt runoff. This shows that while individual measurements can be useful in revealing these dynamics, high temporal resolution observations are required to capture them accurately. This method further shows the utility of collecting paired surface and groundwater elevations. We also developed a simple metric using the change in surface water and groundwater elevations to evaluate stream-aquifer response to watershed scale processes.</p
Comparison of Dams and Diversions On Downstream Water Quality and Ecosystem Processes
Full text linkWater resources infrastructure, such as impoundments and diversions, is expected to expand in order to supply water for an increasing population living in a drier west. River impoundments and diversions, termed discontinuities, are known to disrupt natural gradients and processes, causing a shift in the balance between water rescources supply and riverine ecosystem services. Deep-release reservoirs and their effects on river processes have been well-studied, but few studies quantify the effects of diversions and surface-release impoundments on water quality and ecosystem processes. Due to the effects of seasonal and climatic variations on river hydrographs, it is important to understand the impacts of discontinuities within the same basin and temporals scale. I deployed sensors upstream and downstream of two deep-release impoundments, one surface- release impoundment, one hydroelectric diversion (power diversion), and one irrigation diversion to understand the relative effects of these projects on river dissolved oxygen (DO), DO saturation, temperature, and specific conductivity (SpC) as well as these water quality relationships with discharge and temperature. Impoundments had an overall greater effect on downstream water quality than diversions. Additionally, water-quality-discharge relationships became weaker downstream of both deep-release impoundments while these relationships did not shift as significantly downstream of the surface-release impoundment and diversions. The irrigation diversion had a larger effect on temperature, DO, and metabolism at lower flows. Combined with model results of downstream temperature changes, this suggests that my results do not capture the largest effect of the irrigation downstream water quality. This combined with a correlation between temperature and DO saturation at low flow suggest that the irrigation diversion has the potential to stimulate ecosystem activity at low flows, especially if they occurred during the predicted warmer temperatures in the future. Adding additional infrastructure to provide water sustainability will exacerbate the compounding effects of these discontinuities within the river network require strategic monitoring and adaptive management in order to maintain ecosystem services provided by rivers.</p
Increased Stream Temperature in Response to Extreme Precipitation Events
Full text linkAquatic ecosystem temperature regulation is essential to the survival of riverine fish species restricted to limited water temperature ranges. Thermal effluent regulations in place to protect these ecosystems restrict thermoelectric power generation when water temperatures are too warm. Climate change projections forecast increased precipitation intensities, a trend that has already been observed in the past century. Though extreme events are becoming more common, the stream temperature response to high-intensity rainfall is not yet well understood. Precipitation (33) and stream temperature records (52) from gages in the Upper Midwestern United States were analyzed to determine whether there exists a positive relationship between high-intensity rainfall and warming stream temperature response. This region was chosen for its already observed trends in increasing precipitation intensity, and both urban and rural gages were used in order to account for the effect of impervious surfaces on runoff amounts and temperature. Days with recorded precipitation were divided by an intensity threshold and classified as either high-intensity or moderate-intensity days. While the effects of rain events on stream temperature are variable, increases in stream temperature in response to high-intensity rainfall were observed. For some basins, daily maximum rates of stream temperature increase were, on average, greater for higher intensity events. Similarly, the daily maximum rate of temperature increase was higher in most streams on days of high-intensity precipitation, compared to days of moderate-intensity events. Understanding the effect of increasing precipitation intensity in conjunction with rising air temperatures will provide insight into the future of aquatic ecosystems and their adaptation to climate change
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Increased Stream Temperature in Response to Extreme Precipitation Events
Full text linkAquatic ecosystem temperature regulation is essential to the survival of riverine fish species restricted to limited water temperature ranges. Thermal effluent regulations in place to protect these ecosystems restrict thermoelectric power generation when water temperatures are too warm. Climate change projections forecast increased precipitation intensities, a trend that has already been observed in the past century. Though extreme events are becoming more common, the stream temperature response to high-intensity rainfall is not yet well understood. Precipitation (33) and stream temperature records (52) from gages in the Upper Midwestern United States were analyzed to determine whether there exists a positive relationship between high-intensity rainfall and warming stream temperature response. This region was chosen for its already observed trends in increasing precipitation intensity, and both urban and rural gages were used in order to account for the effect of impervious surfaces on runoff amounts and temperature. Days with recorded precipitation were divided by an intensity threshold and classified as either high-intensity or moderate-intensity days. While the effects of rain events on stream temperature are variable, increases in stream temperature in response to high-intensity rainfall were observed. For some basins, daily maximum rates of stream temperature increase were, on average, greater for higher intensity events. Similarly, the daily maximum rate of temperature increase was higher in most streams on days of high-intensity precipitation, compared to days of moderate-intensity events. Understanding the effect of increasing precipitation intensity in conjunction with rising air temperatures will provide insight into the future of aquatic ecosystems and their adaptation to climate change
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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