A physical model of Titan's aerosols

Microphysical simulations of Titan's stratospheric haze show that aerosol microphysics is linked to organized dynamical processes. The detached haze layer may be a manifestation of 1 cm sec-1 vertical velocities at altitudes above 300 km. The hemispherical asymmetry in the visible albedo may be caused by 0.05 cm sec-1 vertical velocities at altitudes of 150 to 200 km, we predict contrast reversal beyond 0.6 micrometer. Tomasko and Smith's (1982, Icarus 51, 65-95) model, in which a layer of large particles above 220 km altitude is responsible for the high forward scattering observed by Rages and Pollack (1983, Icarus 55, 50-62), is a natural outcome of the detached haze layer being produced by rising motions if aerosol mass production occurs primarily below the detached haze layer. The aerosol's electrical charge is critical for the particle size and optical depth of the haze. The geometric albedo, particularly in the ultraviolet and near infrared, requires that the particle size be near 0.15 micrometer down to altitudes below 100 km, which is consistent with polarization observations (Tomasko and Smith 1982, West and Smith 1991, Icarus 90, 330-333). Above about 400 km and below about 150 km Yung et al.'s (1984, Astrophys. J. Suppl. Ser. 55, 465-506) diffusion coefficients are too small. Dynamical processes control the haze particles below about 150 km. The relatively large eddy diffusion coefficients in the lower stratosphere result in a vertically extensive region with nonuniform mixing ratios of condensable gases, so that most hydrocarbons may condense very near the tropopause rather than tens of kilometers above it. The optical depths of hydrocarbon clouds are probably less than one, requiring that abundant gases such as ethane condense on a subset of the haze particles to create relatively large, rapidly removed particles. The wavelength dependence of the optical radius is calculated for use in analyzing observations of the geometric albedo. The lower atmosphere and surface should be visible outside of regions of methane absorption in the near infrared. Limb scans at 2.0 micrometers wavelength should be possible down to about 75 km altitude.     

Fluoride in Nebraska's Ground Water

Fluoride concentrations in ground water are generally low but play an important role in dental health. This study evaluates the vertical and spatial distribution of fluoride in Nebraska's ground water and examines the geological and geochemical processes that control its concentration. Data from 1794 domestic wells sampled by the Nebraska Department of Health and Human Services. Regulation, and Licensure (NDOH) had a range of fluoride concentrations from <0.1 to 2.6 mg/L. and a median concentration of 0.3 mg/L. The median fluoride concentrations for Nebraska's 13 ground water regions varied from 0.2 to 0.7 mg/L. In each of these regions, individual wells may have either insufficient or overabundant F concentrations; we recommend that individual private water systems be tested for fluoride. Based on these data, system-specific recommendations can be made regarding the necessity for fluoridation.
Geochemical data indicated that the majority of fluoride occurs as F. Dissolution of F-bearing minerals controls fluoride occurrence. Apatite plus minor amounts of fluorite along with significant ground water residence times are the primary factors controlling F in the water from the Dakota Formation in Knox County, as well as in other parts of northeastern Nebraska. In western and southwestern Nebraska, dissolution of volcanic glass is the most probable source of F Long residence times plus fluorite also may contribute to the F concentrations in the Chadron Formation.     

A risk assessment approach to contaminants in Port Curtis, Queensland, Australia

Port Curtis is one of Australia's leading ports for which substantial industrial expansion is proposed over the next decade. However, there has been little attempt to date to assess the extent of contamination in waters, sediments and biota or to characterize the potential impacts of contaminants on aquatic biota. Contaminants of potential concern to biota and human health were investigated in the Port Curtis estuary using a screening-level risk assessment approach. Dissolved metal concentrations in waters were below [ANZECC/ARMCANZ, 2000. Australian and New Zealand Guidelines for Fresh and Marine Water Quality, Vol. 1. The Guidelines, Australian and New Zealand Environment and Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand] trigger values, suggesting low risk of these contaminants. In sediments, arsenic, nickel and chromium concentrations exceeded interim sediment quality guidelines-low (ISQG-low), but were also high in the reference zone suggesting a natural origin. Historical data on naphthalene in Harbour sediments showed that it was also of potential concern. Bioaccumulation of contaminants in a range of biota was also used as an indicator of contaminant exposure. Biota were generally enriched in metals and tributyltin, which was also elevated in water and sediments. Although not unique to Port Curtis, mercury in barramundi was identified as a potential risk to human health.     

Need and opportunity for a North American caribou knowledge cooperative

The importance of migratory caribou ( Rangifer tarandus ) to northerners, the increasing pressure to extract non-living resources, and predicted global climate change have led researchers, managers and resource users alike to focus on how to improve our knowledge of this unique northern ungulate. Unprecedented threats to caribou sustainability, along with the increasingly acknowledged value of indigenous hunters'contribution to caribou research, pose the additional challenge to innovate research methods that accommodate differing cultural perspectives and facilitate communication among groups. This paper surveys the state of scientific knowledge of the eleven major northern mainland herds of North America. We recommend an approach to improve our working knowledge of barren-ground caribou in order to assess better future impacts. The transfer of knowledge gained from years of research and indigenous experience on many aspects of caribou ecology should be evaluated and, where applicable, transferred to herds with more modest databases. The establishment of a North American Caribou Monitoring and Assessment System, based on a synthesis of local knowledge and research-based science, is recommended as a tool for improved communication and collective learning.     

Out‐of‐plane seismic response of vertically spanning URM walls connected to flexible diaphragms

A simplified numerical model was used to investigate the out‐of‐plane seismic response of vertically spanning unreinforced masonry (URM) wall strips. The URM wall strips were assumed to span between two flexible diaphragms and to develop a horizontal crack above the wall mid‐height. Three degrees of freedom were used to accommodate the wall displacement at the crack height and at the diaphragm connections, and the wall dynamic stability was studied. The equations of dynamic motion were obtained using principles of rocking mechanics of rigid bodies, and the formulae were modified to include semi‐rigid wall behaviour. Parametric studies were conducted that included calculation of the wall response for different values of diaphragm stiffness, wall properties, applied overburden, wall geometry and earthquake ground motions. The results of the study suggest that stiffening the horizontal diaphragms of typical low‐rise URM buildings will amplify the out‐of‐plane acceleration demand imposed on the wall and especially on the wall–diaphragm connections. It was found that upper‐storey walls connected to two flexible diaphragms had reduced stability for applied earthquake accelerograms having dominant frequency content that was comparable with the frequency of the diaphragms. It was also found that the applied overburden reduced wall stability by reducing the allowable wall rotations. The results of this study suggest that the existing American Society of Civil Engineers recommendations for assessment of vertically spanning walls overestimate the stability of top‐storey walls in multi‐storey buildings in high‐seismic regions or for walls connected to larger period (less stiff) diaphragms. Copyright © 2015 John Wiley & Sons, Ltd.     

Quantitative evaluation of the performance of a permit auction system in reducing bycatch of sea turtles in the Hawaii Swordfish longline fishery

Many authors have suggested the use of a cap and trade auction system to help reduce bycatch—the incidental take of species by fishing gear targeting other species—of sea turtles in the Hawaii-based swordfish longline fishery. However, we know of no quantitative evaluations of the method. We present a simple mathematical model to serve as a framework to evaluate bycatch auction systems quantitatively. We conclude that cap and trade auction systems have the potential to reduce sea turtle bycatch by creating a financial incentive, while keeping permit costs down to 2–3% of total revenues. While stringent regulations aimed at conserving endangered sea turtles would still be essential, implementation of an auction for issuing transferable bycatch permits would likely enhance the economic efficiency of the fleet. Sea turtle mortality could be reduced further if a shrinking cap on total turtle mortality was introduced, taking advantage of the incentives for reducing turtle mortality that are introduced by the cap and trade auction system.     

Factors influencing landscape pattern of the seagrass Halophila decipiens in an oceanic setting

The scale of landscape pattern formation of an ecological community may provide clues as to the processes influencing its spatial and temporal dynamics. We conducted an examination of the spatial organization of an annual seagrass (Halophila decipiens) in an open ocean setting at two spatial scales and growing seasons to identify the relative influence of external (hurricanes) versus internal (clonal growth) factors. Visual surveys of seagrass cover were conducted over 2 years within three replicate 1 km² study areas each separated by ∼25 km in an inshore–offshore transect along the southwest coast of Florida at depths between ∼10 and 30 m. A towed video sled allowed observations of seagrass cover of 1 m² areas approximately every 6 m over thousands of meters of evenly spaced transects within the study areas (coarse scale). The towed video revealed that 17.5% of the seafloor was disturbed irrespective of location or sample time. Randomly selected 10 × 10 m quadrats within the larger, 1 km² study areas were completely surveyed for seagrass cover by divers at 0.625 m² resolution (fine scale). The coarse-scale observations were tested using both conventional geostatistics and an application of a time-series technique (Runs test) for scale of seagrass cover contiguity. Fine-scale observations were examined using conventional geostatistics and a least squares approach (cumulative logistic).     

Changes in European temperature extremes can be predicted from changes in PDF central statistics

Although uncertainties are still large, many potentially dangerous effects have already been identified concerning the impacts of global warming on human societies. For example, the record-breaking 2003 summer heat wave in Europe has given a glimpse of possible future European climate conditions. Here we use an ensemble of regional climate simulations for the end of the twentieth and twenty-first centuries over Europe to show that frequency, length and intensity changes in warm and cold temperature extremes can be derived to a close approximation from the knowledge of changes in three central statistics, the mean, standard deviation and skewness of the Probability Distribution Function, for which current climate models are better suited. In particular, the effect of the skewness parameter appears to be crucial, especially in the case of cold extremes, since it mostly explains the relative warming of these events compared to the whole distribution. An application of this finding is that the future impacts of extreme heat waves and cold spells on non-climatological variables (e.g., mortality) can be estimated to a first-order approximation from observed time series of daily temperature transformed in order to account for simulated changes in these three statistics.     

New metrics for managing and sustaining the ocean's bounty

Policies are arising around the world, most recently in the United States, that mandate the implementation of marine spatial planning as a practical pathway towards ecosystem-based management. In the new United States ocean policy, and several other cases around the globe, ecosystem services are at the core of marine spatial planning, but there is little guidance on how ecosystem services should be measured, making it hard to implement this new approach. A new framework is shown here for practical, rigorous ecosystem service measurement that highlights contributions from both natural and social systems. The novel three-step framework addresses traditional shortcomings of an ecosystem services approach by giving managers and scientists the tools to assess and track: (1) the condition of the ecosystem (supply metrics), (2) the amount of ocean resources actually used or enjoyed by people (service metrics), and (3) people's preference for that level of service (value metrics). This framework will allow real world progress on marine spatial planning to happen quickly, and with a greater chance for success.