Modeling Mercury Fluxes and Concentrations in a Georgia Watershed Receiving Atmospheric Deposition Load from Direct and Indirect Sources

Abstract

This paper presents a modeling analysis of airborne mercury (Hg) deposited on the Ochlockonee River watershed located in Georgia. Atmospheric deposition monitoring and source attribution data were used along with simulation models to calculate Hg buildup in the subwatershed soils, its subsequent runoff loading and delivery through the tributaries, and its ultimate fate in the mainstem river. The terrestrial model calculated annual watershed yields for total Hg ranging from 0.7 to 1.1 μg/m². Results suggest that approximately two-thirds of the atmospherically deposited Hg to the watershed is returned to the atmosphere, 10% is delivered to the river, and the rest is retained in the watershed. A check of the aquatic model results against survey data showed a reasonable agreement. Comparing observed and simulated total and methylmercury concentrations gave root mean square error values of 0.26 and 0.10 ng/L, respectively, in the water column, and 5.9 and 1 ng/g, respectively, in the upper sediment layer. Sensitivity analysis results imply that mercury in the Ochlockonee River is dominated by watershed runoff inputs and not by direct atmospheric deposition, and that methylmercury concentrations in the river are determined mainly by net methylation rates in the watershed, presumably in wetted soils and in the wetlands feeding the river.     

Weapons or mating signals? Claw shape and mate choice in a fiddler crab

Males often possess traits, such as horns, claws, and tusks, which are used during male–male combat. Studies suggest that selection has fine tuned these weapons to improve their effectiveness and that the shape of these weapons provides cues for males to assess the strength of rivals. Similarly, females might also assess a male’s weaponry to determine his value as a mate. The largest weapon relative to body size is the major claw of male fiddler crabs (genus: Uca). Males use their claws both as a weapon and as a courtship signal, waving it to attract females. We used robotic crabs in two-choice experiments to test female mating preferences based on male claw shape in Uca mjoebergi. First, females did not prefer conspecific claws over any of three alternatively shaped stimuli matched for color and for the rate and pattern of waving. The alternative stimuli were two different heterospecific claws and a plain rectangular shape. Second, females significantly preferred the alternative stimuli when they were presented at a faster wave rate. We conclude that claw shape in U. mjoebergi has not evolved under sexual selection imposed by female mating preferences and is more likely to have evolved under selection for effectiveness during male–male competition.     

Nonstructural Urban Stormwater Quality Measures: Building a Knowledge Base to Improve Their Use

This article summarizes a research project that investigated the use, performance, cost, and evaluation of nonstructural measures to improve urban stormwater quality. A survey of urban stormwater managers from Australia, New Zealand, and the United States revealed a widespread trend of increasing use of nonstructural measures among leading stormwater management agencies, with at least 76% of 41 types of nonstructural measures being found to be increasing in use. Data gathered from the survey, an international literature review, and a multicriteria analysis highlighted four nonstructural measures of greatest potential value: mandatory town planning controls that promote the adoption of low-impact development principles and techniques; development of strategic urban stormwater management plans for a city, shire, or catchment; stormwater management measures and programs for construction/building sites; and stormwater management activities related to municipal maintenance operations such as maintenance of the stormwater drainage network and manual litter collections. Knowledge gained on the use and performance of nonstructural measures from the survey, literature review, and three trial evaluation projects was used to develop tailored monitoring and evaluation guidelines for these types of measure. These guidelines incorporate a new evaluation framework based on seven alternative styles of evaluation that range from simply monitoring whether a nonstructural measure has been fully implemented to monitoring its impact on waterway health. This research helps to build the stormwater management industry’s knowledge base concerning nonstructural measures and provides a practical tool to address common impediments associated with monitoring and evaluating the performance and cost of these measures.     

Population growth rate and carrying capacity for springtails Folsomia candida exposed to ivermectin.

Forecasting the effects of stressors on the dynamics of natural populations requires assessment of the joint effects of a stressor and population density on the population response. The effects can be depicted as a contour map in which the population response, here assessed by population growth rate, varies with stress and density in the same way that the height of land above sea level varies with latitude and longitude. We present the first complete map of this type using as our model Folsomia candida exposed to five different concentrations of the widespread anthelmintic veterinary medicine ivermectin in replicated microcosm experiments lasting 49 days. The concentrations of ivermectin in yeast were 0.0, 6.8, 28.8, 66.4, and 210.0 mg/L wet weight. Increasing density and chemical concentration both significantly reduced the population growth rate of Folsomia candida, in part through effects on food consumption and fecundity. The interaction between density and ivermectin concentration was "less-than-additive," implying that at high density populations were able to compensate for the effects of the chemical. This result demonstrates that regulatory protocols carried out at low density (as in most past experiments) may seriously overestimate effects in the field, where densities are locally high and populations are resource limited (e.g., in feces of livestock treated with ivermectin).     

Profiles of cuticular hydrocarbons mediate male mate choice and sexual isolation between hybridising <Emphasis Type="Italic">Chrysochus</Emphasis> (Coleoptera: Chrysomelidae)

Summary. Chemical signals frequently underlie sexual isolation between insect species. Our understanding of the evolutionary forces influencing these signaling systems is known for very few systems, challenging both our efforts to understand insect speciation, and our ability to predict long-term changes in the chemical communication systems of insects. Thus, we are in need of more systems in which both the chemical signals causing sexual isolation and the evolutionary forces driving sexual isolation are understood. Sexual isolation in the hybrid zone between Chrysochus cobaltinus and C. auratus has apparently increased in response to natural selection against hybridisation (i.e. reinforcement). Previous experiments suggested that this isolation was due, at least in part, to male preferences for conspecific females. Here, we confirm this role of male choice, and document that male mate choice in this system is influenced by cuticular hydrocarbon (CHC) profiles. Specifically, male C. cobaltinus responses to control cadavers and conspecific female cadavers painted with different cuticular hexane extracts, together with analyses of the composition of those extracts, revealed that male mate choice is governed by CHC profiles. Multivariate analyses of GC profiles demonstrated that those profiles are indeed both sex- and species-specific. Although GC-MS enabled identification and quantification of the specific cuticular hydrocarbons, we have not yet determined which individual compounds govern mate choice. Having established that CHCs influence sexual isolation in this system, we can now assess the evolutionary lability of these cues, which will inform both our understanding of speciation, and of the conditions under which the chemical signaling systems that influence mate choice in insects can evolve.     

Teenage driving after using marijuana or drinking and traffic accident involvement

Anonymous random digit dialing telephone surveys of nearly 6000 16–19 year old respondents were conducted in Massachusetts and Upstate New York in 1979–1981. These surveys explored frequency of driving after using marijuana, driving after drinking, respondent accident involvement in the year prior to the interview, and a variety of other respondent characteristics. Frequency of driving after using marijuana and after drinking were each associated with greater accident involvement. To isolate the accident risk of driving after marijuana use, respondents who drove after drinking were excluded from a logistic regression analysis. This analysis also controlled for the distance respondents drove and several respondent demographic characteristics. Compared to respondents who did not drive after marijuana use, teenageers who drove after smoking marijuana on at least 6 occasions per month were 2.4 times more likely to be involved in traffic accidents. Those who drove after marijuana use on at least 15 occasions per month were 2.9 times more likely to have an accident.     

In Situ solidification—A case study at a former manufactured gas plant in Macon,Georgia

In situ solidification (ISS) is a reliable, EPA‐recognized technology for the treatment of industrial and waste sites. ISS was employed at a former manufactured gas plant (MGP) site in Macon, Georgia, for the treatment of approximately 33,000 cubic yards of coal tar residues in the saturated zone soil. The site is regulated by the Georgia Environmental Protection Division (EPD) under the Hazardous Site Rehabilitation Act (HSRA) and is located approximately four blocks from downtown Macon. This article will review the technical and regulatory basis for the successful use of this technology, provide an overview of the treatability and pilot testing used to develop the design and implementation of the treatment process, and present the results of the application of ISS to an MGP site. The results of groundwater monitoring, pre and postremediation, will also be discussed. © 2004 Wiley Periodicals, Inc.     

'Biohyets': a method for displaying the extent and severity of environmental impacts

Bioindicators are often more sensitive indicators of both biodiversity and environmental change than abiotic pollution parameters. The responses of selected plants and animals to anthropogenic insults can be used to assess environmental responses at a variety of spatial and temporal scales. This study maps the response of key reptile, mammal, bird and plant species to airborne contaminants around a large mine and mineral processing operation at Olympic Dam in arid Australia. The responses of different bioindicators should ideally be integrated in order to comprehend overall trends in biological integrity adjacent to pollution sources. Assimilation of different bioindicator responses allows greater precision and geographic coverage of the monitored region and reduces potential distortion from unrelated biological or monitoring responses of individual indicator groups. A single, integrated measure of ecosystem health that overlays the responses of otherwise incompatible datasets, is also of more value to industrial operators and environmental regulators than several disparate responses. Biohyets, which are the contours of bioindicator index values derived from multiple biotic measurements, are here used to map variability in ecosystem health and to identify regions, response variables and disturbance parameters for more rigorous analysis.