RATES OF RECENT SEDIMENTATION IN LAKE PEPIN1

ABSTRACT: Sedimentation rates since 1954 in Lake Pepin, as determined from the content of fallout cesium-137 in the sediment profile, have exceeded 2.5 cm/yr in the upper part of the lake. These rates, although somewhat less than those of the previous half century (1895–1954), are sufficiently large that the upstream portion of Lake Pepin is threatened with conversion to a marsh within a century. The density of the sediments measured increased with depth in the sampled profile from 1.1 to 1.2 g/ml at the sediment surface to 1.4 to 1.5 g/ml at 2- or 3-m depth. There was little or no change in the patterns of textural composition or density of the sediment profile with depth and age over the past 80 to 150 years.     

Turning gap acceptance decision-making: the impact of driver distraction

PROBLEM: A number of studies have found that use of in-car phones by drivers can interfere with the cognitive processing necessary for making appropriate and timely vehicle control decisions. However, the specific linkage between communication-based distraction and unsafe decision-making has not been sufficiently explored. METHOD: In a closed-course driving experiment, 39 subjects were exposed to approximately 100 gaps each in a circulating traffic stream of eight vehicles on an instrumented test track that was wet about half the time. The subjects were at the controls of an instrumented car, which was oriented in a typical left-turn configuration (traffic-crossing situation in North America) and with parking brake on and the transmission in neutral. The subjects were instructed to press on the accelerator pedal when they felt that a gap was safe to accept. Their performances were monitored and incentives were provided for balancing safe decision-making with expeditious completion of the task. For half of the gap exposures (randomly assigned), each subject was required to listen and respond to a complex verbal message. RESULTS: When not distracted, the subjects' gap acceptance judgment was found to be significantly influenced by their age, the gap size, the speed of the trailing vehicle, the level of "indecision," and the condition of the track surface. However, when distracted, the subjects did not factor pavement surface condition into the decision process. On wet pavement, the subjects were judged to have initiated twice the level of potential collisions when distracted by the messages that they did when not distracted. DISCUSSION: Listening/responding to verbal messages may reduce the capacity of drivers to process adequately all the important information necessary for safe decision-making. The effects of the messages in our study seemed to cause the subjects to misjudge gap size and speed information when operating under the additional disadvantage of adverse pavement condition. SUMMARY: Attention to complex messages while making decisions about turning through gaps in an on-coming vehicle stream was associated with significantly increased unsafe decision making by subjects in our experiment when the additional complexity of wet surface condition was introduced. IMPACT ON INDUSTRY: While the results reflected a somewhat artificial situation where the measure was signaled intention to act rather than the act itself, nevertheless, they do strongly suggest a scenario in which mental distraction could contribute to crash risk. With the rapid proliferation of telematics in the vehicle market, even with the laudable objectives represented by the Intelligent Transportation Systems initiative, there is a danger of the primary task of the driver being subordinated to a perceived need to enhance information flow to/from the external "world." Industry and governments need to work together to ensure that apparently desirable in-vehicle communication improvements do not compromise safety.     

ACUTE TOXICITY OF PICRIC ACID AND PICRAMIC ACID TO RAINBOW TROUT,SALMO GAIRDNERI,AND AMERICAN OYSTER,CRASSOSTREA VIRGINICA1

ABSTRACT Picric acid (2,4,6-trinitrophenol) and picramic acid (2-amino-4,6-dinitrophenol) are potential water pollutents due to a variety of industrial and munition uses. The possible impacts of picric and picramic acid to two recreationally and commercially important species, rainbow trout, Salmo gairdneri, and American oysters, Crassostrea virginica, were evaluated. Picramic acid was more toxic than picric acid to both species tested. The 96-h LC50s for picric and picramic acids for rainbow trout were 109.6 and 46.2 mg/1, respectively. The 144-h LC50s for picric and picramic acid for American oysters were 254.9 and 69.8 mg/1, respectively. Sublethal no growth EC50s and shell deposition EC50s for oysters showed that both compounds caused adverse effects at much lower concentrations than indicated by the LC50s. For example, the 144-h shell deposition EC50s were 27.9 mg/1 for picric acid and 5.6 mg/1 for picramic acid. Sediment adsorbtion studies in estuarine water indicated that both compounds are not readily adsorbed which suggests that sediment would not play a major role as a sink in contaminated systems. Oysters, which filter large quantities of particulate matter, would more likely be affected by picric and picramic acids in the water column than by exposure to contaminated sediment.     

Origin of lead associated with different reactive phases in Scottish upland soils: an assessment made using sequential extraction and isotope analysis

Soil samples (0-25 cm) have been taken annually since 1991 from three protected plots set up at an upland location at Glensaugh in Aberdeenshire, Scotland. The soils were analysed using the original BCR sequential extraction procedure and the lead isotopic composition was determined in each of the fractions, as well as the unfractionated soil using thermal ionisation mass spectrometry (TIMS). The lead concentrations in all the soils, including those well away from the road, were much higher than typical background values indicating that the whole area has been subject to deposition of anthropogenic lead. The distribution of lead between the different fractions was similar for the two non-roadside soils with most lead present in the oxidizable fraction. Although most lead in the roadside soil was also present in the oxidizable fraction, a substantial proportion (about 10%) was in the easily soluble fraction suggesting that roadside lead could be more mobile than lead in the other soils. Good reproducibility was obtained for the isotope analyses in all the fractions. The ratios calculated for the bulk soil from the ratios in the individual fractions agreed very closely with those measured directly in the unfractionated soil thereby demonstrating both reproducibilty and accuracy. The lowest (206)Pb/(207)Pb ratios were found in the roadside soil consistent with the recent deposition of petrol lead. The (206)Pb/(207)Pb ratios in all fractions of the other soils fell into a narrow band and it was necessary to use (204)Pb ratios to differentiate between lead in the extractable fractions and lead in the residual component. It is probable that lead in the non-roadside soils was deposited a considerable time ago and is characterised by a relatively high (206)Pb/(207)Pb ratio. Use of the (204)Pb ratios showed that the residual components in each of the three soils were isotopically distinct.     

Prey chemical discrimination in ambush foragers: absence in representatives of two additional iguanian lizard families and probable olfactory mediation in a gekkonine gecko

Summary. Lingually mediated prey chemical discrimination in lizards has evolved in active foragers, been lost in taxa that have reverted to ambush foraging, and has not evolved in taxa that have retained the ancestral ambushing. Previous studies have shown that all families of insectivorous ambushers lack prey chemical discrimination, including most families of iguanian lizards and two gekkonid species. I conducted experimental studies of prey chemical discrimination in representatives of two additional iguanian families and a third gekkonid lizard. An oplurid species, Oplurus cuvieri and a corytophanid, Corytophanes cristatus, did not discriminate among prey chemicals and control substances. Prey chemical discrimination is now known to be absent in insectivorous ambush foragers in all but one of the families in Iguania, one of the two major lizard radiations. Hoplocercidae remains unstudied. Like other ambushing gekkonid lizards, Pachydactylus turneri did not exhibit elevated tongue-flick rates in response to prey chemicals. However, after tongue-flicking or being touched on the labial scales by cotton swabs, these lizards bit swabs bearing prey chemicals more frequently than control stimuli. They also exhibited buccal pulsing more frequently in response to prey chemicals than deionized water, suggesting olfactory sampling. The unusually highly developed olfactory organs of gekkonid lizards and their nocturnal habits suggest that olfaction may be more important to foraging than in other lizards. Further studies are needed to determine relative roles of olfaction and vomerolfaction in selective response to prey chemicals and to ascertain whether and to what extent the tongue may be used to locate and identify prey. Received 30 March 1999; accepted 26 July 1999     

Controls of spatial variation in the prevalence of trematode parasites infecting a marine snail

Geographic variability in abundance can be driven by multiple physical and biological factors operating at multiple scales. To understand the determinants of larval trematode prevalence within populations of the marine snail host Littorina littorea, we quantified many physical and biological variables at 28 New England intertidal sites. A hierarchical, mixed-effects model identified the abundance of gulls (the final hosts and dispersive agents of infective trematode stages) and snail size (a proxy for time of exposure) as the primary factors associated with trematode prevalence. The predominant influence of these variables coupled with routinely low infection rates (21 of the 28 populations exhibited prevalence <12%) suggest broad-scale recruitment limitation of trematodes. Although infection rates were spatially variable, formal analyses detected no regional spatial gradients in either trematode prevalence or independent environmental variables. Trematode prevalence appears to be predominantly determined by local site characteristics favoring high gull abundance.     

Discrimination between related and unrelated individuals in the Australian lizard Egernia striolata

We examined evidence for kin-related signal discrimination in the Australian scincid lizard Egernia striolata, using 41 juvenile lizards from 14 litters from a population in the Mount Lofty Ranges, South Australia. We characterised each juvenile at four polymorphic microsatellite DNA loci, determined genetic relatedness among pairs of juveniles, and assigned for each litter one other litter that was genetically closest and one other litter that was genetically most distant. Lizards responded significantly more strongly, with tongue flicks and time in contact, to skin secretion stimuli from more distant than genetically close, unfamiliar conspecific juveniles. When presented with an intruder, juvenile lizards basked for shorter periods when the intruder was more distantly related, and aggressive lizards directed more aggressive acts towards more distantly related than closely related conspecific intruders. We deduce from these results that there is kin recognition in juvenile E. striolata, and that they are able to discriminate related from unrelated individuals among unfamiliar conspecifics.     

Temperature calibration formula for activated charcoal radon collectors

Radon adsorption by activated charcoal collectors such as PicoRad radon detectors is known to be largely affected by temperature and relative humidity. Quantitative models are, however, still needed for accurate radon estimation in a variable environment. Here we introduce a temperature calibration formula based on the gas adsorption theory to evaluate the radon concentration in air from the average temperature, collection time, and liquid scintillation count rate. On the basis of calibration experiments done by using the 25 m³ radon chamber available at the National Institute of Radiological Sciences in Japan, we found that the radon adsorption efficiency may vary up to a factor of two for temperatures typical of indoor conditions. We expect our results to be useful for establishing standardized protocols for optimized radon assessment in dwellings and workplaces.