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Wilson, David

Publications and source records attributed to Wilson, David.

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Functional traits driving species role in the structure of terrestrial vertebrate scavenger networks

Abstract Species assemblages often have a non‐random nested organization, which in vertebrate scavenger (carrion‐consuming) assemblages is thought to be driven by facilitation in competitive environments. However, not all scavenger species play the same role in maintaining assemblage structure, as some species are obligate scavengers (i.e., vultures) and others are facultative, scavenging opportunistically. We used a database with 177 vertebrate scavenger species from 53 assemblages in 22 countries across five continents to identify which functional traits of scavenger species are key to maintaining the scavenging network structure. We used network analyses to relate ten traits hypothesized to affect assemblage structure with the “role” of each species in the scavenging assemblage in which it appeared. We characterized the role of a species in terms of both the proportion of monitored carcasses on which that species scavenged, or scavenging breadth (i.e., the species “normalized degree”), and the role of that species in the nested structure of the assemblage (i.e., the species “paired nested degree”), therefore identifying possible facilitative interactions among species. We found that species with high olfactory acuity, social foragers, and obligate scavengers had the widest scavenging breadth. We also found that social foragers had a large paired nested degree in scavenger assemblages, probably because their presence is easier to detect by other species to signal carcass occurrence. Our study highlights differences in the functional roles of scavenger species and can be used to identify key species for targeted conservation to maintain the ecological function of scavenger assemblages.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Network structure of vertebrate scavenger assemblages at the global scale: drivers and ecosystem functioning implications

The organization of ecological assemblages has important implications for ecosystem functioning, but little is known about how scavenger communities organize at the global scale. Here, we test four hypotheses on the factors affecting the network structure of terrestrial vertebrate scavenger assemblages and its implications on ecosystem functioning. We expect scavenger assemblages to be more nested (i.e. structured): 1) in species-rich and productive regions, as nestedness has been linked to high competition for carrion resources, and 2) regions with low human impact, because the most efficient carrion consumers that promote nestedness are large vertebrate scavengers, which are especially sensitive to human persecution. 3) We also expect climatic conditions to affect assemblage structure, because some scavenger assemblages have been shown to be more nested in colder months. Finally, 4) we expect more organized assemblages to be more efficient in the consumption of the resource. We first analyzed the relationship between the nestedness of the scavenger assemblages and climatic variables (i.e. temperature, precipitation, temperature variability and precipitation variability), ecosystem productivity and biomass (i.e. NDVI) and degree of human impact (i.e. human footprint) using 53 study sites in 22 countries across five continents. Then, we related structure (i.e. nestedness) with its function (i.e. carrion consumption rate). We found a more nested structure for scavenger assemblages in regions with higher NDVI values and lower human footprint. Moreover, more organized assemblages were more efficient in the consumption of carrion. However, our results did not support the prediction that the structure of the scavenger assemblages is directly related to climate. Our findings suggest that the nested structure of vertebrate scavenger assemblages affects its functionality and is driven by anthropogenic disturbance and ecosystem productivity worldwide. Disarray of scavenger assemblage structure by anthropogenic disturbance may lead to decreases in functionality of the terrestrial ecosystems via loss of key species and trophic facilitation processes.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Using the Monte Carlo Method to Evaluate the Reliability of Screening Multifamily Housing for Radon

When screening for radon in a multifamily housing complex using a fixed sample density (e.g., testing 1 in 10 (10%) or 1 in 4 units (25%)), the statistical confidence is dependent upon the assumed elevated radon frequency. For example, testing 25% of units in a complex estimated to have eight units with elevated radon levels will provide 90% confidence. However, if it is assumed that, in the same complex, there are only three units with elevated radon levels, the confidence drops to around 58% for the same sample density. Furthermore, in the previous example, if elevated radon levels are not found during the screening, all that can be stated is that the screening provides 90% confidence that there are no more than seven units in the complex with elevated radon levels. To more fully illustrate this uncertainty, ten separate multifamily housing radon data sets with 1 to 10 units with radon levels ≥4 pCi/L (Table 1) were selected for analysis using the Monte Carlo statistical method. Unlike other mathematically based statistical approaches, the Monte Carlo statistical method relies on repeated analysis of randomly selected data. from a 100% sampled complex at various sample densities. Success for each simulation is defined as finding at least one unit with elevated radon levels. In this statistical method, confidence in the overarching conclusion can be greatly enhanced by repeating the simulated screening hundreds or even thousands of times. For this study, each of the ten data sets was simulated 1,000 times. For each simulation, the data set was randomized three times before the fixed percentage of data was selected.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
NASA NTRS2019

Air and Water Temperature Relationship and Growth of Hyacinth and Primrose

Temperature is a primary determining factor for plant growth and development so providing an appropriate temperature input is critically important for developing growth models. The Delta Region Areawide Aquatic Weed Project (DRAAWP), a USDA (US Dept. of Agriculture)-sponsored area-wide project including NASA Ames Research Center and State of California Department of Boating and Waterways, uses modeling to assess invasive aquatic plant impacts on ecosystem services in the Delta. Availability of continuous records for monitored temperature is limited and particularly in the case of water temperature the distribution of monitoring is inadequate. This work quantitatively defines the influence of air and water temperature in determining dominant growth rate processes for important floating aquatic invasive plants in the Delta. Since these plants function with portions submerged and above water we wanted to understand the relationship between root zone and shoot zone temperature and ability to use a single temperature inputs in DRAAWP models. Water Hyacinth and Primrose were gown in multiple controlled environment chamber studies with various combinations of root zone and shoot zone temperatures. Long-term growth studies provided integrated response of biomass accumulation and distribution within the canopy. Short-term gas exchange studies provide a time scale for responsiveness to temperature and a short-term study approach to evaluate temperature responses at various stages of canopy development.

Hyacinth↗
NASA NTRS2019

Growth Response of Water Hyacinth to Environmental Ranges in the California Sacramento-San Joaquin River Delta

Management of aquatic weeds in complex watersheds and river systems present many challenges to assessment, planning, and implementation of management for aquatic invasive plants. The Delta Region Areawide Aquatic Weed Project (DRAAWP), a USDA sponsored area-wide project including NASA Ames Research Center and State of California Department of Boating and Waterways, is working to enhance decision-making and operational efficiency of invasive plant management in the California Sacramento-San Joaquin Delta. Expansion of invasive aquatic plants has been detrimental to water management and the ecosystem complex in the San Francisco Bay/California Delta. The portion of DRAAWP reported here focuses on parametrizing the environmental response inputs for the Delta models for prominent invasive aquatic plants. Changing climate, long-term drought, shifts in land use, and variation in water flow and quality from input watersheds lead to wide and unique variation in environmental conditions. Environmental variability occurs across a range of time scales from long-term climate and seasonal trends to short-term water flow mediated variations. Response of invasive aquatic plants are examined using controlled environment growth facilities at time scales of weeks, day, and hours using a combination of study duration and growth assessment techniques to assess water quality, temperature, nutrient, and light effects. These provide response parameters for plant growth models in response to the variation and interact with management and economic models associated with aquatic weed management. Plant growth models are informed by remote sensing and applied spatially across the Delta to balance location and type of aquatic plant, growth response to altered environments and phenology.

Sacramento-San Joaquin River Delta.v↗
DOE OSTI2019

Panel Session 11: Featured Country Canada - Remediation of Contaminated Sites

Canada has several unique sites requiring environmental remediation of radiological contaminants. This panel was designed to outline the remediation of contaminated sites across Canada from several perspectives. Remote legacy uranium mining operations, small scale residential locations, and large impacted soil sites all pose different challenges, however there are some common solutions and keys to success. This panel addressed several of those challenges and provided lessons learned on how to successfully plan and execute large scale environmental remediation in both remote and residential locations. This panel focused on the cleaning up several contaminated sites in Canada and monitoring the long-term performance of sites that have already been remediated. Panelists addressed the technical and social challenges associated with various cleanup initiatives North of the 49. Parallel and the solutions that have been adopted to enable these projects to move forward. The panel offered the perspectives of owners, contractors and regulators on current projects and how they are leveraging past experience and learning from others to ensure future undertakings are successful. Presentations proposed include: 1 - Regulating Environmental Remediation in Canada (Michael Rinker, Canadian Nuclear Safety Commission (Canada)); 2 - Integration of Local Knowledge and Engagement/Capacity Building Legacy Uranium Mine Sites (Joe Muldoon, Saskatchewan Research Council (Canada)); 3 - The Path to Institutional Control - Safe, Secure and Stable (R. Liam Mooney, Cameco Corporation (Canada)); 4 - Port Hope Area Initiative: Project Challenges (Scott Parnell, Canadian Nuclear Laboratories (Canada))

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

A Hamiltonian Surface-Shaping Approach for Control System Analysis and the Design of Nonlinear Wave Energy Converters

The dynamic model of Wave Energy Converters (WECs) may have nonlinearities due to several reasons such as a nonuniform buoy shape and/or nonlinear power takeoff units. This paper introduces the Hamiltonian Surface-Shaping (HSS) approach as a tool for the analysis and design of nonlinear control of WECs. The Hamiltonian represents the stored energy in the system and can be constructed as a function of the WEC’s system states, its position, and velocity. The Hamiltonian surface is defined by the energy storage, while the system trajectories are constrained to this surface and determined by the power flows of the applied non-conservative forces. The HSS approach presented in this paper can be used as a tool for the design of nonlinear control systems that are guaranteed to be stable. The optimality of the obtained solutions is not addressed in this paper. The case studies displayed here cover regular and irregular waves and demonstrate that a nonlinear control system can result in a multiple fold increase in the harvested energy.

16 TIDAL AND WAVE POWER↗
DOE OSTI2018

Categorizing An Explosive Device by its Nuclear Signature (Rev. 1)

This report documents a study to eliminate ambiguity in identifying a very low-yield nuclear detonation in the early stages of the response to such an event. The ambiguity arises from the very similar explosive and radiation effects produced by three categories of explosive devices: An explosively driven radiological dispersal device (RDD) or an accidental explosion in which radiologic material is scattered by chemical explosives. A failed nuclear device in which nuclear material, such as uranium or plutonium, has been scattered by conventional explosives. A nuclear device that, in addition to scattering nuclear material, produced a very low-yield from nuclear fission. The study found that the properties of fission products provide a ready solution to the problem. The radiation dose rate from fission products that were produced in a nearly instantaneous “fission event” decreases extremely rapidly over the first eight hours after that event, whereas nuclear materials and common radiological materials produce an essentially constant dose rate. This contrast provides an unequivocal fission product signature. The measurements required to utilize this signature can be made by first responders with radiation detectors already in the field, on time scales of an hour, although later confirmation using more capable detectors, including spectroscopic capability, is advised. The process of categorizing an explosives-related incident, both pre- and post-detonation, can be represented as a Decision Tree. The Decision Tree illustrates the use of already-fielded radiation detectors to categorize incidents as likely to involve only conventional explosives, an explosively driven RDD, or a nuclear device. The identification of an explosion as a fission event is extremely important to evacuation planners. It has been shown that delayed evacuation after sheltering in place for up to 24 hours after a fission event has the potential to reduce radiation exposure to the affected public and responders by a factor of ten. Traditional evidence collection after a nuclear detonation is likely to be similarly delayed, as the value and urgency of collection efforts must be weighed against radiation and other hazardous exposure of the collectors. The evidence that survives the immediate effects of a nuclear detonation will, in many cases, still be available for collection once radiation levels have diminished to acceptable levels. Certain classes of evidence, notably information stored on digital media, may significantly degrade from exposure to post-detonation radiation fields. Technical nuclear forensics collections will be performed in all events with nuclear yield. Modification of the high-yield collection strategy may be necessary for a very low-yield device.

98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL P↗