1,720,998 research outputs found
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
Freshwater ecosystem monitoring using satellite remote sensing and field surveys
No full textThesis (Ph.D.)--University of Washington, 2021Freshwater ecosystems transfer and transform energy, nutrients and carbon. The color of lakes and rivers, as observed from space, can provide clues to their ecological function and response to anthropogenic activities. Despite this, remote sensing science has been slower to mature for freshwaters relative to terrestrial and marine ecosystems. This research pairs physical and biogeochemical measurements collected during field campaigns with airborne and satellite remote sensing to improve our understanding of the links between color and chemistry in lakes and rivers. Using remote sensing, we mapped over 3,000 river miles in order to better understand uncertainties introduced to remote sensing retrievals during atmospheric correction of satellite imagery. Building from this work, we then conducted remote sensing analysis of ~500,000 lakes combined with a subset of intensive field surveys to (1) establish the relationship between color and gross primary productivity in shallow arctic-boreal lakes, (2) quantify multi-decadal trends in lake color across arctic-boreal North America, and (3) evaluate the effect of climate variability on arctic-boreal lake color trends. We found that atmospheric correction can bias model results by 3 – 59% for estimates of chlorophyll-a and turbidity derived from Landsat-8 and Sentinel-2 for three large river systems: the Columbia, Amazon and Mississippi. We also discovered the green band (reflectance ~ 560 nm) was the least impacted by uncertainties from processor or sensor choice, implying that the green band is most suitable for historical or cross-sensor analysis. This chapter has been published in Remote Sensing of the Environment. Applying this framework in the high northern latitudes, moderate resolution (30m) satellite and high resolution (5 m) hyperspectral airborne remote sensing imagery were used to infer gross primary productivity rates from arctic-boreal lakes within the NASA Arctic-Boreal Experiment (ABoVE) domain. This study was published in Environmental Research Letters. We then use the Landsat archive to map annual growing season greenness from 1985 – 2019 for lakes throughout the entire ABoVE domain. Over a quarter of lakes showed significant color change. Declining greenness was the dominant trend and was most common in areas also undergoing warming and precipitation increases. This finding, which has been submitted to Proceedings of the National Academy of the Sciences, provides evidence in support of the hypothesis that warming is restructuring arctic-boreal lake ecological dynamics because of changes, in part due to changing hydrologic connectivity. Collectively, these studies have advanced our understanding of the ecological significance of lake and river color, including opportunities to uncover new relationships between lake color and chemistry by combining novel geochemistry data with remote sensing
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Seasonality and Discharge as Key Drivers of Headwater Stream Carbon Dioxide Emissions in the Landscape Carbon Budget
No full textThesis (Ph.D.)--University of Washington, 2025Quantifying carbon losses from inland waters has emerged as an uncertainty in our understanding of the global carbon cycle. Streams and rivers are of particular interest because of their potential to emit carbon dioxide (CO2) to the atmosphere with some estimates predicting riverine carbon emissions will alter the calculation of terrestrial net ecosystem exchange (NEE), the balance between how much carbon land ecosystems absorb and how much they release. Headwater streams, small tributaries of rivers at the highest end of a watershed, are especially important when quantifying these CO2 emissions and carbon losses because of their tight coupling to the terrestrial environment and high turbulence. Heterogeneity within headwater stream networks, both spatially and temporally, makes measuring and upscaling these emissions challenging because measurements of carbon dioxide in streams are often limited to a few monitoring points. In this dissertation, we sought to fill knowledge gaps regarding spatial and temporal variability in CO2 emissions across a range of biomes. In Chapter 2, we demonstrated how under high flow conditions, a stream network in the Pacific Northwest, can have much greater total carbon emissions than during low flow conditions (1.22 Mg C day−1 vs. 0.034 Mg C day−1). Increased stream network area, higher gas exchange, and greater terrestrial connectivity all contributed to these increased emissions in our stream network model. We found these carbon emissions during high flow in November accounted for a much larger percentage of NEE than during base flow in August (54% vs. 0.62%), emphasizing the need to better quantify carbon emission during flow events. In Chapter 3, we expanded this analysis by modeling carbon emissions from five headwater stream networks in different biomes, incorporating stream network extent to account for dynamic flow and a stream network model to account for spatial and temporal variations in CO2 emissions on an annual scale. We found that while accounting for the extent of the stream network due to drying does not change modeled annual emissions substantially (0.06-4.3%), it does change the timing and spatial distribution of emissions and CO2 concentrations. We found discharge was the main driver of emissions at all sites, with 50% of carbon emissions occurring in the top 3-29% of discharge conditions. Spatially, our analysis highlighted that first-order streams consistently produced higher areal emissions compared to higher-order streams, attributed to steeper slopes and connectivity to the source of pCO2, terrestrial soils and groundwater. Finally, in Chapter 4, we estimated CO2 emissions from a stream in an agricultural catchment, an understudied biome in regards to carbon dynamics. We found that in this low-lying catchment with high nutrient and organic matter inputs, the expected coupling between discharge and CO2 emissions was dampened because of a weaker relationship between slope and gas exchange velocity. Instead, we found the hydrologic regime regulated the magnitude of emissions by regulating the source, namely the higher in-stream metabolism contribution (46%) to emissions at a site with high nutrient and organic matter inputs. Across the three chapters, we demonstrate how the hydrologic regime of a stream network governs the timing, source, and magnitude of CO2 emissions. We also show that carbon dynamics in headwater streams vary across networks, influenced by differences in biome, topography, land use, and geology, highlighting the complexity of accurately quantifying carbon losses from these systems
Riverine Biogeochemical Exports from Major Watersheds to the Northwest Patagonian Estuarine Network
No full textThesis (Master's)--University of Washington, 2025River runoff linking terrestrial and marine ecosystems is a significant driver of marine processes (Lewis & Cook, 2023). The effect of river runoff on marine ecosystems is determined by variability in its timing, quality, and quantity. Human watershed perturbations – both direct, e.g. land-use change, and indirect, e.g. climate change – alter all three of these properties. Measuring baseline variability of these properties is crucial to quantifying the effects of human perturbations, which is necessary for tailoring watershed management to limit disruption of marine ecosystem health. This is particularly important in Northwest Chilean Patagonia (NCP), where a semi-enclosed estuarine system highly influenced by river runoff supports much of Chile's $7+ billion fisheries industry. Thanks to a citizen-science effort of unprecedented scale, we were able to characterize baseline inputs of key nutrients to the NCP marine environment for the 2022-2023 water year from the region's five largest watersheds: the Puelo, Yelcho, Palena, Cisnes, and Aysen, from North to South, respectively. Given the pristine nature of NCP's watersheds, these estimates represent one of the world's first regional characterizations of freshwater nutrient inputs to a temperate fjord system in the absence of extensive human intervention. Across all five rivers, we found freshwater concentrations of total nitrogen (TN), total phosphorus (TP), and dissolved organic carbon (DOC) to be lower than those of the receiving subantarctic marine waters, and well below global averages for comparable coastal temperate rainforest (CTR) ecosystems. (For the purposes of this paper, the metrics TN, TP, and DOC will be considered proxies for nitrogen (N), phosphorus (P), and carbon (C).) Conversely, large watersheds were found to be significant contributors of iron (Fe) and dissolved silica (dSi), collectively discharging ~ 79.9 and 291 metric tons during the 2022-23 water year. Taken together, these results indicate a net regulating function of NCP's five largest rivers on marine ecosystems, possibly inhibiting harmful algal blooms by favoring diatoms over dinoflagellates. The results suggest the importance of large watersheds in regulating marine ecosystems, highlight the potential value of watershed conservation for retaining ecosystem services of TN and TP dilution, and provide a baseline characterization of land-sea linkages in a temperate coastal system
Backcountry Recreation Modeling and the Extent of Human and Canine Fecal Markers in Subalpine Lakes of Mount Rainier National Park
No full textThesis (Master's)--University of Washington, 2022Alpine lakes are some of the most fragile ecosystems in our national parks and forests and a focal point of backcountry visitation. As a result of climate change, access to these ecosystems is increasing due to annual reductions in snow cover. This projected extension of shoulder seasons from warming and the increased public interest in national parks and forests creates a confluence of conditions creating concern among land managers. Because of this concern evaluating tools capable of quantifying basin-level visitation and capturing its direct consequence has garnered [more recent] interest. One impact of concern is the infiltration of fecal matter into aquatic systems from unburied waste and leaking privies, which conflicts with principles outlined in the Organic Act of 1916 and the Wilderness Act of 1964. In this study, we sought to evaluate the plausibility of models, parameterized on existing data from Mount Baker-Snoqualmie National Forest (MBS), in estimating basin-level visitation in Mount Rainier National Park (MORA) and, as a consequence of visitation, detect putative human and canine fecal markers in subalpine lakes using microbial source tracking (MST) methods. In MORA, we examined the transferability of a visitation model developed by Wood et al., 2020, and employed MST methods to detect the possible presence of the human-specific and canine-specific Bacteroides (Bacteroidales) markers in 11 subalpine lakes. Here we show that visitation models derived from data outside of MORA lacked transferability compared to the original Wood et al., 2020 study and did not explain enough variation in weekly on-site visitation for accurate estimation in MORA. Though no human-specific marker was detected during the sampling period, these findings do not preclude their presence in the subalpine lakes. Finally, the presence of a canine-specific marker in Upper Deadwood Lake suggests further application of MST methods has value in understanding the pervasion of fecal markers in protected alpine waterway
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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