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Effect of Tides and Currents on UAV-Based Detection of Giant Kelp Canopy
Full text linkSatellite and aerial imagery have been used extensively for mapping the abundance and distribution of giant kelp (Macrocystis pyrifera) in southern California. While tides and currents have been shown to affect the amount of floating kelp canopy on the water surface, there have been no quantifications of how these processes can bias remotely sensed kelp estimates in this region. We used unmanned aerial vehicles (UAVs) to map fine-scale changes in canopy area due to tidal height and current speed at both Palos Verdes, CA and Santa Barbara, CA. Additionally, we collected a biweekly time series of kelp canopy area in Palos Verdes over the course of a year to monitor fine-scale, intra-seasonal changes in canopy coverage. Our automated method for detecting kelp canopy in color and multispectral UAV imagery was highly accurate (over 84% and 98%, respectively) in classifying exemplary kelp and water pixels across a range of weather, ocean, and illumination conditions. Increases in tidal height of 1 m reduced the amount of floating kelp canopy by 15% to 32%. Current speeds are generally low in southern California and had no statistically significant effect on apparent bed size. However, increases in current speeds of 0.1 m/s reduced the amount of floating kelp canopy by over 31%. Tidal height and current speed can introduce significant variability to estimates of kelp abundance, but the magnitude of this variability is region specific. The biweekly time series displayed intra-annual variability typical of giant kelp, with a relatively gradual decline in kelp canopy in late summer corresponding with high sea surface temperatures, a rapid decline in the winter associated with wave disturbance, and a gradual recovery in the spring of the following year. The time series was also able to capture intra-seasonal changes in kelp canopy area that would have gone undetected in an annual or quarterly dataset, namely an increase in area to about half of the maximum in the late fall before wave events began
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Using Isotopes to Explore Global Peat Carbon Dynamics
Full text linkThis dissertation investigates the role of peatlands as critical carbon (C) reservoirs that sequester approximately 600 gigatons of C globally, effectively acting as a significant buffer against climate change. Despite their limited geographic extent—covering only 3% of the Earth's surface—peatlands store nearly twice the C of all global forests combined. This exceptional C storage potential is largely due to the waterlogged, anoxic conditions in these ecosystems that inhibit microbial decomposition and allow organic matter to accumulate over millennia. However, peatlands are highly vulnerable to both natural and anthropogenic pressures, including climate change, land-use modifications, and direct human disturbances, all of which threaten their capacity to serve as long-term C sinks. This dissertation leverages isotopic analysis to examine peatland C dynamics across diverse regions and contexts by exploring the mechanisms driving C dynamics in tropical, boreal, and temperate peatlands, focusing on both surface-derived and deep peat C emissions and accumulation. Tropical peatlands, which differ from boreal and temperate peatlands due to consistently warm temperatures and seasonal rainfall, contain highly dense C deposits but are also at heightened risk of C release under changing rainfall patterns. One case study examines tropical peatlands in Central America, where consistently warm temperatures and seasonal rainfall create dense C deposits. These tropical systems are especially susceptible to C loss with changing rainfall patterns, potentially releasing stored C from deep peat layers. In boreal regions, experimental warming simulates future climate conditions, assessing how elevated temperatures and CO₂ concentrations affect C storage across peat depths. Additionally, this dissertation uses global radiocarbon data to analyze peat accumulation and stability across climates, providing insights into regional differences in peatland resilience under environmental changes. These studies together highlight the significant impact of environmental variables such as precipitation, temperature, and proximity to coastlines on peatland C dynamics, as well as the potential influence of human activities like agriculture drainage and peat extraction on C loss. Findings underscore the importance of conserving and protecting pristine peatlands, which, as natural C sinks, are vital for mitigating greenhouse gas emissions.
Overall, this dissertation underscores the critical importance of peatlands in global C cycling and climate regulation. The research highlights the necessity of conservation efforts to protect these ecosystems from degradation, as their disruption could lead to substantial greenhouse gas emissions and further accelerate climate change. By examining the complex interactions between environmental conditions, C sequestration, and human impacts, this dissertation contributes to a deeper understanding of peatlands' vulnerability and resilience, informing strategies for their preservation in a rapidly changing world
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Imaging Spectroscopy Applications for Mapping and Monitoring Environmental Change in Louisiana’s Coastal Wetlands
Full text linkLouisiana’s coastal wetlands are continually threatened by anthropogenic disturbances and relative sea level rise (RSLR), factors which have caused widespread degradation and loss. This region has historically been a productive ecosystem with high carbon sequestration capacity that offers important ecological benefits to neighboring communities. The region’s “blue carbon” stocks and ecosystem services are now severely degrading with the coastal wetlands’ ongoing submergence resulting from RSLR. Accretion is the trapping of sediments and deposition of organic matter resulting in the buildup of the soil surface, and wetlands will submerge if the factors governing accretion do not sufficiently account for RSLR. Remote sensing offers data that can be applied to wetland ecology to assess ecological processes relating to RSLR and accretion at a regional scale. Imaging spectroscopy, specifically, enables sophisticated modeling techniques that may improve remote sensing applications in wetland regions. This project applies imaging spectroscopy to Louisiana’s coastal wetlands, developing applications for Airborne Visible/Infrared Imaging Spectrometer-Next Generation (AVIRIS-NG) data that include image processing algorithms, environmental parameter retrievals, and assessment of vegetation growth patterns and changes. The study’s first chapter addresses image processing methods for correcting bidirectional reflectance distribution function (BRDF) effects that inhibit image mosaicking. We developed a new empirical algorithm—the adaptive reflectance geometric correction—and applied it to imagery collected around the Atchafalaya and Wax Lake deltas to produce optimized surface reflectance mosaics. The second chapter sees the estimation and mapping of hydrologic suspended solids in from those AVIRIS-NG mosaics with an independently validated and transferable algorithm. The third chapter integrates the AVIRIS-NG data with simultaneously collected data from the Uninhabited Airborne Vehicle Synthetic Aperture Radar (UAVSAR) to estimate aboveground biomass (AGB) in Louisiana’s Wax Lake Delta (WLD). The fourth chapter uses the AVIRIS-NG data to map the WLD’s vegetation species distribution, then compares the results to published data from five years prior to assess extent changes for key vegetation types. It further employs the AGB dataset to examine key species’ growth patterns across elevational gradients and zones. The methods and results developed herein will enable future efforts to model accretion and predict wetland loss at regional scales
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Spatial Patterns in the Response of California’s Kelp Forests to Climate Variability and Extremes
Full text linkKelp forests, like many marine ecosystems, are being exposed to more frequent and intense disturbances. Marine heatwaves are major drivers of widespread and sustained kelp forest losses, as temperature directly affects the distribution and persistence of populations. Heatwave effects have been examined on large scales using satellite-derived data, but there is also variability in kelp responses on local to regional scales, driven by marine microclimates such as localized upwelling. Field and drone-based monitoring efforts have been employed along the California coastline to capture local dynamics, but these surveys only cover spatially discrete samples from selected kelp beds. Consequently, field and drone-based datasets represent one end of the spatial spectrum for observing kelp canopy response and recovery after disturbance events, while satellite observations represent the other end. Neither method alone can fully resolve both local and regional to global-scale dynamics.The development of CubeSat constellations has enabled a workaround for these trade-offs, with global imagery available near-daily at meter-scale. In my first chapter, I develop methods to create spatially continuous time series of California kelp population dynamics from high-resolution CubeSat data. In my second chapter, I employ these time series to highlight local-scale variability in California kelp populations that have been impacted by marine heatwave events, helping to better identify areas of concern and understand the drivers of heatwave-mediated loss and stability. In my third chapter, I scale these methods to effectively map kelp canopy across the state of California. I develop deep learning models for estimating kelp canopy presence and apply these models to a time series of CubeSat data.
My findings contribute new perspectives for addressing and understanding kelp forest disturbance regimes. Mapping kelp populations with CubeSat constellation data allowed for the identification of areas of vulnerability, providing utility in prioritizing areas for strategic protection and restoration. Classifying sections of coastline that supported kelp forests amidst marine heatwave events showed the presence of refugia, where subpopulations have been able to persist in habitats that are buffered from disturbance. Further, mapping these populations across California will allow for the development of new indicators of ecosystem functioning and health
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The Effect of Climate Change and Anthropogenic Activities on Mangrove Ecosystems
Full text linkMangroves are critical tropical coastal ecosystems and provide essential ecological and societal services. Mangroves have been rapidly changing over the last fifty years, and geospatial technologies provide a tool to measure such changes around the world. As a response to climate change and rising temperatures, mangroves have been encroaching into salt marshes at many mangrove-salt marsh ecotones in sub-tropical areas, rapidly shifting their distributions poleward. Although mangroves have faced substantial degradation and deforestation due to human activity, we have seen a rise in anthropological efforts towards their preservation and reforestation in recent years. This dissertation examines both climatic and anthropogenic drivers of change for mangrove ecosystems, using a combination of remote sensing, climate modeling, and manipulative experiments. First, we investigate mangrove range limit dynamics on the Atlantic and Pacific coasts of North America, where the same three species of mangroves are found. Using gridded climate data, remote sensing and manipulative experiments, we compared the realized and fundamental niches of the Atlantic and Pacific mangroves, and found notably different responses to environmental conditions, resulting in contrasting range dynamics. We then focused specifically on the Pacific range limit, where further manipulative experiments on cold water temperatures and aridity highlighted the fact that mangroves’ response to changes in climate is highly species- and location-specific. Therefore, aspects particular to each range population must be taken into consideration to best understand and predict mangrove response to climate change. Lastly, we focused on anthropogenic impacts on mangrove ecosystems. Using the island of Madagascar - a major biodiversity hotspot - as a case study, we conducted a remote sensing analysis of mangrove dynamics over fifty years. Results show that mangroves have faced considerable loss. However, recent awareness arising over the last twenty years has led to better conservation and preservation efforts, resulting in an increase in overall mangrove cover during this period
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
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
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