The effects of salt exclusion during ice formation on circulation in lakes

Laboratory experiments have been performed to investigate the effects of salt exclusion on the behaviour of lakes with salinities up to 8 g L^?1. At these salinities the freezing temperature is less than the temperature of maximum density and, unlike sea-ice, a reverse temperature stratification forms beneath the ice that can support at least some of the excluded salt. Temperature time series at four depths showed that salt exclusion drives cascades of localised overturning, while the persistence of reverse temperature stratification indicated that mixing was not complete. While our array of temperature sensors had insufficient spatial resolution to provide full details of the flow, we hypothesize that: at salinities of 1 and 2 g L^?1  salt is released relatively uniformly and forms a layer of elevated salinity immediately below the ice, which supports double-diffusive salt-fingering; and at salinities of 4 and 8 g L^?1, salt plumes penetrate the reverse stratification. After the ice melted, a relatively fresh surface layer formed above a more saline layer, sufficient to suppress spring turnover. Our measurements compare favourably with field observations from lakes, and highlight the importance of salt exclusion on biogeochemical processes in lakes.     

Sensitivity Analysis of Land Unit Suitability for Conservation Using a Knowledge-Based System

The availability of spatially continuous data layers can have a strong impact on selection of land units for conservation purposes. The suitability of ecological conditions for sustaining the targets of conservation is an important consideration in evaluating candidate conservation sites. We constructed two fuzzy logic-based knowledge bases to determine the conservation suitability of land units in the interior Columbia River basin using NetWeaver software in the Ecosystem Management Decision Support application framework. Our objective was to assess the sensitivity of suitability ratings, derived from evaluating the knowledge bases, to fuzzy logic function parameters and to the removal of data layers (land use condition, road density, disturbance regime change index, vegetation change index, land unit size, cover type size, and cover type change index). The amount and geographic distribution of suitable land polygons was most strongly altered by the removal of land use condition, road density, and land polygon size. Removal of land use condition changed suitability primarily on private or intensively-used public land. Removal of either road density or land polygon size most strongly affected suitability on higher-elevation US Forest Service land containing small-area biophysical environments. Data layers with the greatest influence differed in rank between the two knowledge bases. Our results reinforce the importance of including both biophysical and socio-economic attributes to determine the suitability of land units for conservation. The sensitivity tests provided information about knowledge base structuring and parameterization as well as prioritization for future data needs.     

Land changes and their driving forces in the Southeastern United States

The ecoregions of the Middle Atlantic Coastal Plain, Southeastern Plains, Piedmont, and Blue Ridge provide a continuum of land cover from the Atlantic Ocean to the highest mountains in the East. From 1973 to 2000, each ecoregion had a unique mosaic of land covers and land cover changes. The forests of the Blue Ridge Mountains provided amenity lands. The Piedmont forested area declined, while the developed area increased. The Southeastern Plains became a commercial forest region, and most agricultural lands that changed became forested. Forests in the Middle Atlantic Coastal Plain declined, and development related to recreation and retirement increased. The most important drivers of land conversion were associated with commercial forestry, competition between forest and agriculture, and economic and population growth. These and other drivers were modified by each ecoregion’s unique suitability and land use legacies with the result that the same drivers often produced different land changes in different ecoregions.     

Linking biomarkers to reproductive success of caged fathead minnows in streams with increasing urbanization

Reproductive and oxidative stress biomarkers have been recommended as tools to assess the health of aquatic organisms. Though validated in the laboratory, there are few studies that tie a change in gene expression to adverse reproductive or population outcomes in the field. This paper looked at 17 streams with varying degrees of urbanization to assess the use of biomarkers associated with reproduction or stress in predicting reproductive success of fathead minnows. In addition, the relationship between biomarkers and water quality measures in streams with varying degrees of urbanization was examined. Liver vitellogenin mRNA was correlated with reproduction within a period of 11 d prior to sampling irrespective of habitat, but its correlation with egg output declined at 12 d and beyond indicating its usefulness as a short-term biomarker but its limits as a biomarker of total reproductive output. Stress biomarkers such as glutathione S-transferase may be better correlated with factors affecting reproduction over a longer term. There was a significant correlation between GST mRNA and a variety of anthropogenic pollutants. There was also an inverse correlation between glutathione S-transferase and the amount of the watershed designated as wetland. Egg production over the 21-d was negatively correlated with the amount of urbanization and positively correlated to wetland habitats. This study supports the development of multiple biomarkers linking oxidative stress and other non-reproductive endpoints to changes in aquatic habitats will be useful for predicting the health of fish populations and identifying the environmental factors that may need mitigation for sustainable population management.     

Searching for evidence of acid-catalyzed enhancement of secondary organic aerosol formation using ambient aerosol data

Laboratory experiments suggest that strong acids promote formation of enhanced levels of secondary organic aerosol (SOA), and organic aerosols may contribute to the health impacts of fine PM. We report results from examining hourly speciated fine particle data for evidence of ambient aerosol acidity-catalyzed SOA formation, as indicated by larger increases in the concentrations of organic aerosol mass occurring on days and in locations where more acidic aerosol (lower NH₄⁺/SO₄⁼ molar ratios) exists. Data sets from the southeastern U.S. were examined for which hourly acidity of PM_2.5 aerosols could be estimated, and for which hourly organic carbon (OC) content had been measured simultaneously. Within-day organic aerosol changes during selected periods were statistically related to concurrent aerosol acidity levels estimated from nitrate-corrected ammonium-to-sulfate ratios. Data from the Look Rock, TN, TVA/IMPROVE site for mid-July to mid-August 2004 showed average compositions frequently as acidic as NH₄HSO₄, however, no apparent increases in OC levels with increasing aerosol acidity were observed, even when [OC] changes were compared with time-delayed aerosol acidity estimates. SEARCH network data (2003–2004) for rural Centreville, AL (CTR) and Yorkville, GA (YRK) sites were also examined. Warm-season acidity levels were higher at CTR than at YRK, and daytime levels exceeded those at night at both sites. At the YRK site no consistent positive correlations were found between changes in OC or TC levels and aerosol acidity, even with time lags up to 6 h. Aerosol acidity at this site, however, is relatively low due to nearby agricultural sources of NH₃. In contrast, during selected periods from April to October 2004, at CTR, 6-h lagged OC changes were weakly correlated with daytime, nitrate-corrected NH₄⁺/SO₄⁼ molar ratios, but distinguishing this apparent relationship from meteorological effects on measured OC levels is challenging.     

Situational Waste in Landscape Watering: Residential and Business Water Use in an Urban Utah Community1

Abstract: Landscape water conservation is an important issue for municipalities throughout the Western United States, and especially in Utah as rapid growth strains existing water supplies. We conducted interdisciplinary research in Layton, Utah, that aimed at understanding patterns of landscape water use among households and businesses. The research project involved three basic tasks. First, a landscape “water budget” was developed by producing a calibrated and classified mosaic of landscape type and area from airborne multispectral digital imagery, integrating this information with Layton City parcel boundary data to determine landscape vegetated areas per lot, and estimating irrigation needs derived from reference evapotranspiration (ETo) obtained using weather data for the Salt Lake City metropolitan region. Second, utilizing Layton water billing data, water use for each household and business was identified and categorized as “conserving,”“acceptable” or “wasteful” by determining how much the water applied varied from actual landscape plant need. Third, surveys were administered to a random stratified sample of households and businesses in the study area to investigate various factors that were hypothesized to be predictive of wasteful watering practices. This paper primarily focuses on analysis of the household and business survey data, which explores factors affecting urban landscape water use from a human behavioral perspective. We found that the most significant factors predicting actual water use were the type of irrigation system and whether the location was a household or business. Attitudinal and motivational characteristics were not consistently associated with water use. We found that wasteful watering is the result of many factors embedded in the complex context of urban landscapes. This implies that water conservation programs should identify potential wasteful users through analyses of water billing data and direct water conservation measures at these users by focusing on site‐specific evaluations and recommendations. Water audits or water checks are one such tool that some communities have employed to help people understand and assess the quantity of water needed by and applied to their landscapes. This approach provides an opportunity to evaluate situational constraints at particular locations and design appropriate strategies for reducing water waste.     

The primary aerobic biodegradation of biodiesel B20

We describe the primary aerobic biodegradation of a B20 fuel (20% soybean fatty acid methyl esters, 80% petroleum diesel) by unacclimated inocula from a rainwater detention pond. Biodegradation was rapid and essentially complete, with an overall median 'half-life', at approximately 100 ppm B20, of 6.8 days (n=34). Using purge-and-trap and extraction methodologies, both coupled to GC/MS, and hexachloroethane and hexachlorobenzene as conserved internal markers in the B20, we followed the biodegradation of total detectable material, 76 individual analytes and eight undifferentiated groups of isomers, and calculated their half-lives under these conditions. The fatty acid methyl esters, n-alkanes and iso-alkanes, and simple and alkylated aromatic compounds were the most readily degraded compounds, followed by the naphthenes. The last (identified) compounds to be degraded were ethylalkanes, trisubstituted cyclohexanes and decalins, but even these disappeared with an apparent 'half-life' of <30 days.     

Factors influencing acquisition of ecological and exposure information about hazards and risks from contaminated sites

Considerable research indicates that a wide range of socio-economic factors influence attitudes and perceptions about environmental hazards and risks, and that social trust in those who manage a hazard is strongly correlated to judgements about risks and benefits. We suggest that there are three steps that lead to environmental risk perceptions: acquisition of information, interpretation and synthesis of different pieces of information, and understanding of that information in light of previous knowledge, perceptions, or attitudes. In this study we presented 211 college students in the sciences and non-sciences with ecological and exposure information using text, tables and maps to examine the factors that affect information acquisition and interpretation concerning ecological issues at a fictitious hazardous waste site. Students were allowed about an hour to read the materials and answer questions. The percent of students answering each question correctly varied from 4 to 82%, indicating that some questions were extremely difficult to answer. We attributed these differences to variations in the number of places information was presented (in text, tables, maps, or a combination) and the complexity of the information (how many pieces of information were required to answer the question correctly). The correlation between the number of students answering each question correctly and these combined measures (frequency, complexity) was −0.72. Thus, although there were differences in accuracy concerning ecological information as presented in this study, the major differences were accounted for by how the information was presented, and how much information was required. This suggests that risk communicators should carefully determine which ecological information is critical for the target audience, and ensure that it is presented several times (in different forms). That a lower percentage of people correctly answered questions that required synthesizing several pieces of information suggests that this complexity should be reduced where possible, or that the pieces of information should be tied clearly to the conclusion. Self-declaration of effort and perceptions of safety of the site did not markedly influence the relationship between accuracy, difficulty of finding information, and complexity of information. Other possible confounding variables (i.e., science vs non-science major) only accounted for about 27% of the variation in student’s overall score on ecological questions; age, ethnicity, and gender did not enter as significant variables. We cannot manage environmental hazards with appropriate stakeholder input unless we understand how to present environmental information to achieve a full understanding. Protection of human health and the environment requires that people understand ecological and exposure information, particularly on buffer lands.