Detection of advected, reacting redox fronts from self-potential measurements

We report on an experiment aimed at testing the use of self-potential measurements to monitor the motion and mixing of redox reactants advected through a well-controlled, laboratory-scale, artificial aquifer system. A rectangular, plastic tank was filled up with water-saturated sand and an array of unpolarizable electrodes was installed in the sand body. A nearly uniform, steady-state flow was established by tilting the tank and controlling the water level in reservoirs at both ends. Then, we simultaneously injected a known quantity of KMnO(4) and FeCl(2), respectively, into two separate compartments forming the upstream reservoir. We thus generated two abrupt fronts, one oxidizing and the other reducing, which subsequently travelled in parallel by advection through the sand body. The KMnO(4) and FeCl(2) solutions were in contact and reacted with each other in a region located along the median vertical plane parallel to the flow direction. During flow, the electrical potential differences between each electrode and a reference located in the downstream reservoir were recorded. In the unreacted FeCl(2) region the electric potential showed sudden variations successively occurring at increasing distances in the flow direction, associated with the passage of the FeCl(2) front. These signals essentially corresponded to the junction potential produced by the difference in ionic mobility of Fe(2+) and Cl(-). In the unreacted KMnO(4) region sharp signals, but with much smaller amplitudes, were also observed. Near the vertical median plane on the FeCl(2) side, we observed a second front associated with the spreading of the reaction zone. The shape and evolution of the reaction zone was largely controlled by the precipitation of Fe(OH)(3).     

Incorporating dormancy in dynamic microbial community models

Biogeochemical activity in natural and engineered systems depends on the abundances, functional capabilities and physiological states of the indigenous microorganisms. Typically, only a fraction of the microbial population is active at any given time. As environmental conditions change, previously active microorganisms may switch to an inactive or dormant state, while dormant ones may become active. Here, we present an extended modeling concept for the growth and decay of microorganisms that explicitly accounts for their ability to switch between active and dormant states. The equations describing the switching between physiological states are implemented into a biogeochemical reaction simulator. The model was used to reproduce published data from two laboratory experiments in which microorganisms were subjected to intermittent substrate supply or reactivated after a prolonged period of starvation. Parameter values obtained from the simulation of these experiments were used for subsequent sensitivity analyses and for the simulation of hypothetical scenarios. Results for hypothetical microbial communities consisting of two competing species exposed to periodic feeding imply that, under certain conditions, an effective dormancy-reactivation strategy may have a competitive advantage over a fast growth strategy. That is, organisms that can switch rapidly in response to fluctuations in external conditions may outcompete fast-growing organisms. Furthermore, certain combinations of growth and dormancy strategies may lead to the long-term coexistence of the two competing species. Overall, the simulated population dynamics show that dormancy is an important feature of microbial communities, which can lead to complex responses to environmental fluctuations.     

Herbizide in der aquatischen umwelt

The relevance of artificial pond-systems for the ecotoxicological evaluation of pesticides is discussed. It is the primary advantage of such systems that effects and exposure of a chemical can be examined simultaneously. For the herbicide Metolachlor it was demonstrated that the ecotoxicological evaluation of the herbicid in artificial pond-systems leads to reality-nearer ecotoxicological limits in comparison to “single-species-rests”. Up to a concentration of 500 μg/L, the application of the herbicide had no effects on the physico-chemical parameters and biocoenoses examined, even though the test period was extended over 150 days, which can be regarded as chronic exposure for most of the organisms examined. The results presented indicate once again the importance of pond-studies for a realistic evaluation of pesticides.     

Prenatal molecular diagnosis in hypertrophic cardiomyopathy: report of the first case

Hypertrophic cardiomyopathy (HCM) is an autosomal dominant disease that may cause premature sudden death, especially in teenagers and young adults. The recent progress in the molecular genetics of the disease has made genetic testing sometimes available in clinical practice. We report the case of a couple who still requested prenatal molecular testing after detailed information had been given through a multidisciplinary consultation. Prenatal diagnosis in HCM is associated with complex medical and psychological implications, in addition to general ethical considerations, as the potential value of the diagnosis is counterbalanced by the highly variable expression of the disease and the difficulty in predicting its evolution. The R403L mutation in the MYH7 gene had been previously identified in this family, characterized by a malignant form of HCM. In the specific context of this case, we decided to agree to the request of the parents and performed the prenatal diagnosis. To the best of our knowledge, this is the first report of a prenatal molecular diagnosis performed in the context of HCM. Copyright © 2004 John Wiley & Sons, Ltd.     

Atmospheric photochemistry and secondary aerosol formation of urban air in Lyon, France

Photochemical aging of volatile organic compounds (VOCs) in the atmosphere is an important source of secondary organic aerosol (SOA). To evaluate the formation potential of SOA at an urban site in Lyon (France), an outdoor experiment using a Potential Aerosol Mass (PAM) oxidation flow reactor (OFR) was conducted throughout entire days during January-February 2017. Diurnal variation of SOA formations and their correlation with OH radical exposure (OHexp), ambient pollutants (VOCs and particulate matters, PM), Relative Humidity (RH), and temperature were explored in this study. Ambient urban air was exposed to high concentration of OH radicals with OHexp in range of (0.2–1.2)×10¹² molecule/(cm³?sec), corresponding to several days to weeks of equivalent atmospheric photochemical aging. The results informed that urban air at Lyon has high potency to contribute to SOA, and these SOA productions were favored from OH radical photochemical oxidation rather than via ozonolysis. Maximum SOA formation (36 µg/m³) was obtained at OHexp of about 7.4 × 10¹¹molecule/(cm³?sec), equivalent to approximately 5 days of atmospheric oxidation. The correlation between SOA formation and ambient environment conditions (RH & temperature, VOCs and PM) was observed. It was the first time to estimate SOA formation potential from ambient air over a long period in urban environment of Lyon.     

Strong population differentiation of softshell clams (Mya arenaria) sampled across seven biogeographic marine ecoregions: possible selection and isolation by distance

Twenty-two Mya arenaria samples spanning seven marine ecoregions mostly situated in the Cold Temperate Northwest Atlantic (CTNA) biogeographic province were collected between 2001 and 2010 and genotyped at seven highly polymorphic microsatellite loci to test for population differentiation. Results showed strong regional differentiation with six genetic clusters: (1) Northern Gulf of St. Lawrence (GSL), (2) Magdalen Archipelago, (3) Southern GSL, (4) Lower Atlantic Canada, (5) US Coasts and (6) Northern Europe. Population structure was supported no matter the statistical approach and generally does not reflect the geographical limits of marine ecoregions. A latitudinal cline in allelic richness provides evidence for a northward post-glacial expansion range for this species. While geographical distance explains the genetic variation detected in southern CTNA, increased heterogeneity observed in northern CTNA can be explained by isolation by distance, marine landscaping and presumable selective processes acting at the Mar5 locus. Exclusion of Mar5 from analyses resulted in the detection of three genetic clusters instead of six.     

Flood and avalanche hazard in Colorado: Political implications of the new federalism

This article examines the likely impacts of the United States' new federalism on natural hazard land use management in Colorado. Flood and avalanche hazard programs are the focus of the study Both short- and long-term effects of changes in funding are discussed, and the conclusions summarize probable positive and negative program impacts for the state. These results may help researchers and state authorities mitigate similar effects in their states prior to the enactment of new federalism.