Operator-splitting errors in coupled reactive transport codes for transient variably saturated flow and contaminant transport in layered soil profiles

One possible way of integrating subsurface flow and transport processes with (bio)geochemical reactions is to couple by means of an operator-splitting approach two completely separate codes, one for variably-saturated flow and solute transport and one for equilibrium and kinetic biogeochemical reactions. This paper evaluates the accuracy of the operator-splitting approach for multicomponent systems for typical soil environmental problems involving transient atmospheric boundary conditions (precipitation, evapotranspiration) and layered soil profiles. The recently developed HP1 code was used to solve the coupled transport and chemical equations. For steady-state flow conditions, the accuracy was found to be mainly a function of the adopted spatial discretization and to a lesser extent of the temporal discretization. For transient flow situations, the accuracy depended in a complex manner on grid discretization, time stepping and the main flow conditions (infiltration versus evaporation). Whereas a finer grid size reduced the numerical errors during steady-state flow or the main infiltration periods, the errors sometimes slightly increased (generally less than 50%) when a finer grid size was used during periods with a high evapotranspiration demand (leading to high pressure head gradients near the soil surface). This indicates that operator-splitting errors are most significant during periods with high evaporative boundary conditions. The operator-splitting errors could be decreased by constraining the time step using the performance index (the product of the grid Peclet and Courant numbers) during infiltration, or the maximum time step during evapotranspiration. Several test problems were used to provide guidance for optimal spatial and temporal discretization.     

Motivational factors underlying the intention to drink and drive in young male drivers

Problem: Anyone drinking and driving has a high risk of being involved in an accident. Young male drivers, however, run the highest risk at the same levels of blood alcohol as other candidates, as they have more accidents than any other group. A better understanding of their motivations toward drinking and driving is needed to help create effective prevention. Method: In the present study, 115 male drivers aged 18–24 completed a questionnaire—based on Ajzen's theory of planned behavior—designed to study the motivational factors leading to drinking and driving. Results: Young males' intention to drink and drive is predicted by their attitudes, their perceived behavioral control (PBC), and, to a lesser degree, subjective norms. Impact on Industry: The results showing slightly positive PBC over driving after drinking suggest that work aimed at reducing this perception to a more realistic level is a potential prevention avenue.     

Phaedon cochleariae and Gastrophysa viridula (Coleoptera: Chrysomelidae) produce defensive iridoid monoterpenes de novo and are able to sequester glycosidically bound terpenoid precursors

Summary. Larvae of the chrysomelid beetles Phaedon cochleariae and Gastrophysa viridula use iridoid monoterpenes for defense. The compounds are synthesized de novo in the glandular tissue and the reservoir. However, larvae feeding on leaves impregnated with thioglycosides of early precursors of iridoid biosynthesis such as the thioglycosides of 8-hydroxygeraniol, 8 and 9, rapidly accumulate in their defensive secretion. Thioglycosides combine a unique structural similarity to natural substrates with an exceptional chemical and biological stability against hydrolytic enzymes and can be, therefore, used to study transport phenomena of glycosides. The successful import suggests that the larvae possess, in addition to the de novo biosynthesis, the capability to sequester appropriate glycoside precursors that are transformed to iridoid monoterpenes in the reservoir. The uptake process displays a remarkable substrate selectivity, since the thioglycoside of geraniol 10 is not imported. From the two isomeric thioglycosides of 8-hydroxygeraniol, 8 and 9, the isomer 8 is preferred by a factor of ten. The data clearly support the existence of a highly selective transport system which enables the larvae to utilize plant derived terpenoid precursors in addition to their own de novo biosynthesis of iridoids.     

Downscaling climate models and environmental policy: From global to regional politics

High resolution climate models of regions, or downscaling, promises to be at the forefront of future climate policy research. However, most research in this area is in the natural sciences, and the policy community has not taken full notice of this trend at their doorstep. Downscaling provides more concrete information about local impacts of climate change. This raises several important political issues surrounding extreme events, adaptation, risk and equity and legacy concerns, all of which are briefly addressed. The paper concludes with a call for more social science research on downscaling to accompany the rich geophysical science literature in the topic.     

Comparison of external costs between dry tomb and bioreactor landfills: taking intergenerational effects seriously.

Dry tomb and bioreactor landfills were analyzed with respect to their external costs in an intergenerational cost-benefit analysis in a partial framework which enabled a sounder comparison to be carried out between these two technologies from a socio-economic viewpoint. Obviously, this approach was only a first step for building a comprehensive basis of any environmental as well as fiscal policy in the field of waste management. All external costs are identified and evaluated in three different scenarios, corresponding to a worst case, a best guess and a best case. Obviously, discounting is crucial with respect to an intergenerational perspective. Generation-adjusted discounting (GAD) was applied to take into account equity as well as efficiency criteria, in order to deal with three different types of uncertainties that are decisive in waste policy decisions: a physical uncertainty is captured by introducing our three different scenarios; a macroeconomic uncertainty is taken into consideration by calculating present values using different real growth rates; and a microeconomic uncertainty is taken into account by considering individual peculiarities reflected in their subjective time preference rate. The findings show, that whenever there is a low real GDP growth of less than 1%, the bioreactor is generally superior to the dry tomb (lower present values of external costs). This statement becomes more valid as the growth rate decreases. However, whenever there are high positive growth rates, it is the dry tomb technology which is superior to the bioreactor system.