Persistence of LNAPL sources: relationship between risk reduction and LNAPL recovery

Light nonaqueous phase liquids (LNAPLs), such as fuels, are the source of much soil and groundwater contamination. Though the mobility of LNAPLs is limited in many environments, dissolved-phase components, such as benzene, can produce groundwater plumes that are more mobile than the LNAPL source. In such a setting, it is commonly assumed that recovery of the LNAPL will result in a reduction in risk associated with the dissolved phase. This paper synthesizes several existing multiphase and chemical transport solutions into a single linked methodology that predicts concentrations of soluble constituents within and downgradient of LNAPL source zones from dissolution of those constituents into groundwater flowing through and below LNAPL sources. This approach has been applied to a variety of LNAPL spill conditions. For biodegradable compounds, these analyses show that the period of time where the dissolved-phase plume is expanding is very small compared to the duration of most LNAPL sources, and that the downgradient extent is generally less than about 100 m for BTEX compounds. Therefore, the risk to receptors, as measured by the maximum downgradient extent of dissolved-phase plume or the maximum concentration of these compounds at a downgradient receptor, is generally unrelated to the longevity of the LNAPL sources. The maximum downgradient extent of the dissolved-phase plume is determined almost entirely by the groundwater velocity and the biodegradation rate. These analyses further demonstrate that recovery of LNAPL by hydraulic methods is often ineffective at reducing risk. Except in coarse-grained soils or intermediate soils with significant LNAPL saturations, free-product recovery approaches do not result in significant reductions in the longevity of downgradient dissolved-phase contamination. Further, for biodegradable constituents, remediation does not result in a near-term decrease in the downgradient extent of contamination. Cleanup methods that act to change the composition of the LNAPL source are more effective at reducing the downgradient concentrations, particularly for fine-grained soils or when LNAPL saturations are low.     

A closer look at detectability

Environmental and Ecological Statistics - The theory underlying line transect and variable circular plot surveys—distance sampling—begins with an assumed detectability function, giving...     

Reclamation techniques in southwestern wyoming

Bridger Coal Company operates a 5.8 million tpy surface coal mine thrity five miles northeast of Rock Springs. Wyoming. Approximately 20.000 acres are under permit, with disturbance over the life of the mine projected to reach 10,000 acres. Located on the western rim of the continental divide, the mine receives less than 8.5 inches of precipitation annually. Soils in the area are coarse-textured. and problems associated with elevated salinity and sodicity arc encountered. A variety of common reclamation techniques have been modified to reflect these conditions. Soil horizons are segregated during salvage operations (the surface six inches as topsoil and the balance as subsoil). Unsuitable materials are not salvaged. Direct application of soil is used (over 130 acres in 1983) to maximize native plant regeneration and conserve soil fertility. Inter-seeding of seeding failures has proven to be significantly more successful than chisel plowing and reseeding. Broadcast seeding has been ineffective because of strong winds, and a no till drill has been modified to handle diverse seed mixes and rock conditions. The utility of fertilization under typically xeric moisture regimes is being evaluated. A research project has been initiated to assess establishment of a predominately native, diverse seed mix under irrigation, as well as to determine irrigation rates and duration.     

Conditional and unconditional estimators of population size

Estimators for the population sizes of animal species are similar to Horvitz-Thompson estimators — they involve dividing counts of detected animals by the probabilities of detection. Knowing detection probabilities for different subpopulations allows one to estimate each sub-population size with such an estimator, and to add the results for an estimator of the total population. In the case where the proportions of animals belonging to the different sub-populations are also known, this paper shows that using those proportions to arrive at a common average detection probability will, when used in conjunction with the total number of animals detected, result in a better estimator. We provide two examples where the inferior estimator may seem sensible.     

Scale Perspectives on Avian Diversity in Western Riparian Ecosystems

Conservation of riparian vegetation in western North America has, in part, emphasized providing habitats for a locally diverse avifauna. Site diversity, especially relative to the number of species present, is generally high within riparian avifaunas. Between-habitat diversity changes across a watershed, with riparian species assemblages differing most from upland assemblages at the highest and lowest elevations. This pattern can be attributed to enhanced avian movements within the riparian vegetation. The corridors for bird movements, in turn, facilitate faunal mixing on a broader scale, influencing regional diversity within landscapes. Riparian ecosystems are viewed as connectors of forests across fragmented landscapes. In western settings, however, they are highly linearized forests transecting watersheds between upland associations of high elevations and very different associations at lower elevations. Regionally, riparian vegetation represents linear islands that are internally both floristically and faunistically dynamic rather than mere bridges of homogeneous vegetation in landscape networks. The significance of riparian vegetation as habitat for western birds has been defined primarily at the local level. Conservation activities favoring site diversity are short-sighted, however, and could have severe consequences for unique elements of riparian avifaunas. Conservation actions must evaluate how local activities alter potential dispersal opportunities for ecological-generalist versus riparian-obligate species. Maintaining the character and integrity of riparian avifaunas requires planning from regional and continental perspectives.     

Mating system and mating success of the desert spider Agelenopsis aperta

Field studies of the desert spider Agelenopsis aperta revealed a primarily monogamous mating system. However polygyny, polyandry and polygynandry were superimposed upon the primary system, with 9% of the marked males and 11% of the marked females in a field population mating more than once. In the laboratory males commonly mated multiply with fertile offspring resulting, while females were less likely than males to mate multiply. Monogamy under field conditions was enforced by two factors: (1) high travel costs to males, and (2) a significant decline in female receptivity after the first mating. Heavy males were more likely to be accepted by females both in the field, and in female choice experiments conducted in the laboratory. Finally, male weight determined the outcome of male-male agonistic interactions over females. One possible explanation for female choice in this system which lacks male parental investment is that females may be using male size as an indicator of future success of their offspring.     

Dominance rank,resource availability,and reproductive maturation in female savanna baboons

Summary Ten years of data collected from a population of savanna baboons, Papio cynocephalus anubis, residing near Gilgil, Kenya were analyzed to ascertain the extent to which social and ecological factors influence reproductive maturation in females. First sexual swelling occurred at an average age of 4.79 years and first birth occurred at an average age of 6.92 years. Age at first menses was significantly correlated with age at first sexual swelling, but age at first sexual swelling was not a good predictor of age at first birth. The amount of rainfall in the 6 months preceding first sexual swelling and resource availability were significantly correlated with age at first sexual swelling. When ecological factors were taken into account, dominant females had an earlier age at onset of puberty, but not an earlier age at first birth, than did subordinate females. We suggest that nutritional and social stress operate at the same physiological level to disrupt GnRH pulsatility and retard reproductive maturation in some females. Given that socioecological variables modify the timing of life history events related to fitness in female baboons, the task for the future is to unravel how socioecological factors influence different life history components and generate variation in lifetime reproductive success. Correspondence to: F.B. Bercovitch     

Motivation and vector navigation in honey bees

Animals that forage from a central place can keep track of their displacement relative to home through a process called "path integration." During a study of the stability of homing information over time, we noticed that honey bees held at a feeding place for several hours sometimes headed not in the homeward compass direction on their release, but in the reverse compass direction. This behavior suggested that the path integration system had been reset to a state corresponding to an outward flight to the food. Most models of insect navigation assume that it is the experience of reaching home that resets the path integration system, enabling the activation of vectors appropriate for subsequent outbound foraging trips. Here we provide evidence that this resetting can be influenced by motivational cues associated with food deprivation. The effect of food deprivation is independent of any positional cues provided by familiar landmarks or by experience in traveling toward a goal.     

可持续工商教育催生未来商业精英

本文为美国环保署副署长在世界资源研究所BELL会议上的讲话。这次会议召开于1997年，即8年前，但讲话内容并未“过时”。从中我们不仅可以了解贝迩项目的发展历史，而且还对一些环境管理制度有深入的理解。[编者按]     

Adsorption mechanisms of PFOA onto activated carbon anchored with quaternary ammonium/epoxide-forming compounds: A combination of experiment and model studies

When wood-based activated carbon was tailored with quaternary ammonium/epoxide (QAE) forming compounds (QAE-AC), this tailoring dramatically improved the carbon's effectiveness for removing perfluorooctanoic acid (PFOA) from groundwater. With favorable tailoring, QAE-AC removed PFOA from groundwater for 118,000 bed volumes before half-breakthrough in rapid small scale column tests, while the influent PFOA concentration was 200 ng/L. The tailoring involved pre-dosing QAE at an array of proportions onto this carbon, and then monitoring bed life for PFOA removal. When pre-dosing with 1 mL QAE, this PFOA bed life reached an interim peak, whereas bed life was less following 3 mL QAE pre-dosing, then PFOA bed life exhibited a steady rise for yet subsequently higher QAE pre-dosing levels. Large-scale atomistic modelling was used herein to provide new insight into the mechanism of PFOA removal by QAE-AC. Based on experimental results and modelling, the authors perceived that the QAE's epoxide functionalities cross-linked with phenolics that were present along the activated carbon's graphene edge sites, in a manner that created mesopores within macroporous regions or created micropores within mesopores regions. Also, the QAE could react with hydroxyls outside of these pore, including the hydroxyls of both graphene edge sites and other QAE molecules. This latter reaction formed new pore-like structures that were external to the activated carbon grains. Adsorption of PFOA could occur via either charge balance between negatively charged PFOA with positively charged QAE, or by van der Waals forces between PFOA's fluoro-carbon tail and the graphene or QAE carbon surfaces.