Mercury in Florida Bay fish: spatial distribution of elevated concentrations and possible linkages to Everglades restoration

Health advisories are now posted in northern Florida Bay, adjacent to the Everglades, warning of high mercury concentrations in some species of gamefish. Highest concentrations of mercury in both forage fish and gamefish have been measured in the northeastern corner of Florida Bay, adjacent to the dominant freshwater inflows from the Everglades. Thirty percent of spotted seatrout (Cynoscion nebulosus Cuvier, 1830) analyzed exceeded Florida’s no consumption level of 1.5 μg g−1 mercury in this area. We hypothesized that freshwater draining the Everglades served as the major source of methylmercury entering the food web supporting gamefish. A lack of correlation between mercury concentrations and salinity did not support this hypothesis, although enhanced bioavailability of methylmercury is possible as freshwater is diluted with estuarine water. Stable isotopes of carbon, nitrogen, and sulfur were measured in fish to elucidate the shared pathways of methylmercury and nutrient elements through the food web. These data support a benthic source of both methylmercury and nutrient elements to gamefish within the eastern bay, as opposed to a dominant watershed source. Ecological characteristics of the eastern bay, including active redox cycling in near-surface sediments without excessive sulfide production are hypothesized to promote methylmercury formation and bioaccumulation in the benthos. Methylmercury may then accumulate in gamefish through a food web supported by benthic microalgae, detritus, pink shrimp (Farfantepenaeus duorarum Burkenroad, 1939), and other epibenthic feeders. Uncertainty remains as to the relative importance of watershed imports of methylmercury from the Everglades and in situ production in the bay, an uncertainty that needs resolution if the effects of Everglades restoration on mercury levels in fish are to be modeled and managed

A generalized model of mutation-selection balance with applications to aging

A probability model is presented for the dynamics of mutation-selection balance in a haploid infinite-population infinite-sites setting sufficiently general to cover mutation-driven changes in full age-specific demographic schedules. The model accommodates epistatic as well as additive selective costs. Closed form characterizations are obtained for solutions in finite time, along with proofs of convergence to stationary distributions and a proof of the uniqueness of solutions in a restricted case. Examples are given of applications to the biodemography of aging, including instabilities in current formulations of mutation accumulation.Comment: 20 pages Updated to include more historical comment and references to the literature, as well as to make clear how our non-linear, non-Markovian model differs from previous linear, Markovian particle system and measure-valued diffusion models. Further updated to take into account referee's comment

The Age-Specific Force of Natural Selection and Walls of Death

W. D. Hamilton's celebrated formula for the age-specific force of natural selection furnishes predictions for senescent mortality due to mutation accumulation, at the price of reliance on a linear approximation. Applying to Hamilton's setting the full non-linear demographic model for mutation accumulation of Evans et al. (2007), we find surprising differences. Non-linear interactions cause the collapse of Hamilton-style predictions in the most commonly studied case, refine predictions in other cases, and allow Walls of Death at ages before the end of reproduction. Haldane's Principle for genetic load has an exact but unfamiliar generalization.Comment: 27 page

A Study Comparing the Educational Proficiency of Students from High Schools with Eight or Less Teachers, Nine to Sixteen Teachers, and Over Sixteen Teachers Who Attended South Dakota State College as Freshmen During the School Year of 1940-1941

Considerable attention has been given to a study of the effect of certain factors in the high-school background on achievements in college of those persons who attend an institution of higher learning. One of the factors that has been given only limited attention is the size of the high school from which the student enters college

Coping with Poorly Understood Domains: the Example of Internet Trust

The notion of trust, as required for secure operations over the Internet, is important for ascertaining the source of received messages. How can we measure the degree of trust in authenticating the source? Knowledge in the domain is not established, so knowledge engineering becomes knowledge generation rather than mere acquisition. Special techniques are required, and special features of KBS software become more important than in conventional domains. This paper generalizes from experience with Internet trust to discuss some techniques and software features that are important for poorly understood domains

Resonant Orbits in Triaxial Galaxies

Box orbits in triaxial potentials are generically thin, that is, they lie close in phase space to a resonant orbit satisfying a relation of the form l\omega_1 +m\omega_2+n\omega_3=0 between the three fundamental frequencies. Resonant orbits are confined to a membrane; they play roughly the same role, in three dimensions, that closed orbits play in two. Stable resonant orbits avoid the center of the potential; orbits that are thick enough to pass near the center are typically stochastic. Very near the center, where the gravitational potential is dominated by the black hole, resonant orbits continue to exist, including at least one family whose elongation is parallel to the long axes of the triaxial figure.Comment: 20 Latex pages, 11 Postscript figures. Submitted to The Astronomical Journa

Predicting The Effect of Moisture Content On The Flexural Properties of Douglas-Fir Dimension Lumber

Current procedures for adjusting estimates of the mechanical properties of lumber for changes in moisture content are based on trends in the observed means. The present study was initiated to develop analytical procedures for adjusting estimates of the flexural properties of 2-inch-thick Douglas-fir dimension lumber that would be applicable to all levels of the flexural properties. Equations are derived for adjusting modulus of rupture (MOR), modulus of elasticity (MOE), moment capacity (RS = MOR x section modulus), and flexural stiffness (EI = MOEX moment of inertia) for changes in moisture content. The best of these equations are found to be significantly more accurate than current procedures for adjusting estimates of strength properties such as MOR and RS. Because MOE and EI are less affected by changes in moisture content, most of the equations work well for these properties

Durability of Structural Lumber Products at High Temperatures. Part I. 66°C at 75%RH and 82°C at 30%RH

Background. The effect of temperature on properties can be separated into reversible and permanent effects. The National Design Specification (NDS) provides factors (Ct) for reducing properties for reversible effects but provides little guidance on permanent effects.Objectives. The primary objective of this paper is to evaluate the effect of prolonged heating (permanent effect) on the flexural properties of solid-sawn and composite lumber products exposed at 66°C and 75% relative humidity (RH) and at 82°C and 30% RH. A second objective is to determine how to estimate total effects.Procedures. Solid-sawn lumber, laminated veneer lumber (LVL), and laminated strand lumber (LSL) were heated continuously for up to 6 years. After each exposure period, the lumber was conditioned to room temperature at the specified RH and then tested on edge in third-point bending. Some lumber was also tested hot at 66°C after 48 h of exposure and after 3 years of exposure.Results. After 3 years of continuous exposure at 66°C and 75% RH, solid-sawn Spruce-Pine-Fir (SPF) and Douglas-fir retained about 72% of their original modulus of rupture (MOR) and southern pine about 47%. For the first 2 to 3 years of exposure, changes in MOR of LVL were similar to that of solid-sawn SPF and Douglas-fir. After almost 6 years of exposure, SPF retained about 67% MOR and LVL 26% to 49%. The MOR of LSL was more sensitive to duration of exposure than was the MOR of either solid-sawn lumber or LVL, with a residual MOR of 47% after 28 months. After 21 months at 82°C and 30% RH, solid-sawn lumber retained 50% to 55% MOR, LVL 41%, and LSL 45%. For all products, modulus of elasticity was less sensitive to thermal degradation than was MOR.Conclusions. The effect of temperature on MOR of solid-sawn lumber is independent of grade. Composite lumber is more sensitive than solid-sawn to change in strength due to thermal degradation. The difference in MOR between species and product types may be less at low humidity levels than at high. The total effect of temperature on MOR can be estimated by adding the reversible plus the permanent effects. Available literature suggests that the wood used in attics of residential construction is not likely to experience significant accumulation of exposure at temperatures ≥66°C over the life of the structure