Predicting nitrous oxide emissions through riverine networks.

Nitrous oxide (N2O) is currently the leading ozone-depleting gas and is also a potent greenhouse gas. Predictions of N2O emissions from riverine systems are difficult and mostly accomplished via regression equations based on dissolved inorganic nitrogen (DIN) concentrations or fluxes, although recent studies have shown that hydromorphological characteristics can influence N2O emissions in riverine reaches. Here, we propose a predictive model for N2O riverine concentrations and emissions at the reach scale. The model is based on Damköhler numbers and captures the primary effects of reach-scale biogeochemical and hydromorphological characteristics in flowing waters. It explains the change in N2O emissions from small streams to large rivers under varying conditions including biome, land use, climate, and nutrient availability. The model and observed data show that dimensionless N2O concentrations and emission rates have higher variability and mean values for small streams (reach width <10 m) than for larger streams due to high spatial variability of stream hydraulics and morphology.

Impact of the spatial structure of the hydraulic conductivity field on vorticity in three-dimensional flows.

A material fluid element within a porous medium experiences deformations due to the disordered spatial distribution of the Darcy scale velocity field, caused by the heterogeneity of hydraulic conductivity. A physical consequence of this heterogeneity is the presence of localized kinematical features such as straining, shearing and vorticity in the fluid element. These kinematical features will influence the shape of solute clouds and their fate. Studies on the deformation of material surfaces highlighted the importance of stretching and shearing, whereas vorticity received so far less attention, though it determines folding, a deformation associated with the local rotation of the velocity field. We study vorticity in a three-dimensional porous formation exploring how its fluctuations are influenced by the spatial structure of the porous media, obtained by immersing spheroidal inclusions into a matrix of constant hydraulic conductivity. By comparing porous formations with the same spatial statistics, we analyse how vorticity is affected by the different shape and arrangement of inclusions, defined as the medium 'microstructure'. We conclude that, as microstructure has a significant impact on vorticity fluctuations, the usual second-order statistical description of the conductivity field is unable to capture local deformations of the plume.

Is climate change a threat for water uses in the Mediterranean region? Results from a survey at local scale.

Water scarcity and water security are linked, not only through the direct effects of water shortages on each water users' access to water, but also because of water conflicts generated. Climate change is predicted to raise temperatures in the Mediterranean region and reduce rainfall, leading to a reduction in water yield and possibly worsening the situation of water resource shortages that Mediterranean regions are already experiencing. In its dissemination strategy, the EU FP7 CLIMB project addressed water security threats through an analysis of water uses and water use rivalries within a few target catchments distributed over the Mediterranean region. The present work explores whether climate change is locally perceived by stakeholders (water users and managers) as a key issue for their water uses and water security. Individual interviews, meetings, and compilation of questionnaires were conducted at five sites located in the Mediterranean region. The methodology permitted an analysis of water use and its evolution in the water management context, an identification of the state of awareness of local stakeholders and of the pressures on water use and water use rivalries, and a prioritization of water uses. Currently, the main response to increasing water demand in the Mediterranean region, while not yet considering climate change as a driving force, is a progressive externalization of water resources, with limits represented by national borders and technological possibilities. Overall, 'climate change' was not mentioned by stakeholders during both interviews and in answers to the questionnaires. Even the prospect of decreasing precipitation was not considered a relevant or threatening issue in the coming 20years. This confirms the need to continue all efforts to disseminate the state of knowledge on climate change impacts in the Mediterranean region, such as water scarcity, especially to local water managers, as initiated by various research programs of the European Commission.

A theoretical framework for modeling dilution enhancement of non-reactive solutes in heterogeneous porous media.

Spatial heterogeneity of the hydraulic properties of geological porous formations leads to erratically shaped solute clouds, thus increasing the edge area of the solute body and augmenting the dilution rate. In this study, we provide a theoretical framework to quantify dilution of a non-reactive solute within a steady state flow as affected by the spatial variability of the hydraulic conductivity. Embracing the Lagrangian concentration framework, we obtain explicit semi-analytical expressions for the dilution index as a function of the structural parameters of the random hydraulic conductivity field, under the assumptions of uniform-in-the-average flow, small injection source and weak-to-mild heterogeneity. Results show how the dilution enhancement of the solute cloud is strongly dependent on both the statistical anisotropy ratio and the heterogeneity level of the porous medium. The explicit semi-analytical solution also captures the temporal evolution of the dilution rate; for the early- and late-time limits, the proposed solution recovers previous results from the literature, while at intermediate times it reflects the increasing interplay between large-scale advection and local-scale dispersion. The performance of the theoretical framework is verified with high resolution numerical results and successfully tested against the Cape Cod field data.

A mathematical model for filtration and macromolecule transport across capillary walls.

Metabolic substrates, such as oxygen and glucose, are rapidly delivered to the cells of large organisms through filtration across microvessels walls. Modelling this important process is complicated by the strong coupling between flow and transport equations, which are linked through the osmotic pressure induced by the colloidal plasma proteins. The microvessel wall is a composite media with the internal glycocalyx layer exerting a strong sieving effect on macromolecules, with respect to the external layer composed by the endothelial cells. The physiological structure of the microvessel is represented as the superimposition of two membranes with different properties; the inner membrane represents the glycocalyx, while the outer membrane represents the surrounding endothelial cells. Application of the mass conservation principle and thermodynamic considerations lead to a model composed of two coupled second-order ordinary differential equations for the hydrostatic and osmotic pressures, one, expressing volumetric mass conservation and the other, which is non-linear in the unknown osmotic pressure, expressing macromolecules mass conservation. Despite the complexity of the system, the assumption that the properties of the layers are piece-wise constant allows us to obtain analytical solutions for the two pressures. This solution is in agreement with experimental observations, which contrary to common belief, show that flow reversal cannot occur in steady-state conditions unless the hydrostatic pressure in the lumen drops below physiologically plausible values. The observed variations of the volumetric flux and the solute mass flux in case of a significant reduction of the hydrostatic pressure at the lumen are in qualitative agreement with observed variations during detailed experiments reported in the literature. On the other hand, homogenising the microvessel wall into a single-layer membrane with equivalent properties leads to a very different distribution of pressure across the microvessel walls, not consistent with observations.

The integrated project AquaTerra of the EU sixth framework lays foundations for better understanding of river-sediment-soil-groundwater systems.

The integrated project "AquaTerra" with the full title "integrated modeling of the river-sediment-soil-groundwater system; advanced tools for the management of catchment areas and river basins in the context of global change" is among the first environmental projects within the sixth Framework Program of the European Union. Commencing in June 2004, it brought together a multidisciplinary team of 45 partner organizations from 12 EU countries, Romania, Switzerland, Serbia and Montenegro. AquaTerra is an ambitious project with the primary objective of laying the foundations for a better understanding of the behavior of environmental pollutants and their fluxes in the soil-sediment-water system with respect to climate and land use changes. The project performs research as well as modeling on river-sediment-soil-groundwater systems through quantification of deposition, sorption and turnover rates and the development of numerical models to reveal fluxes and trends in soil and sediment functioning. Scales ranging from the laboratory to river basins are addressed with the potential to provide improved river basin management, enhanced soil and groundwater monitoring as well as the early identification and forecasting of impacts on water quantity and quality. Study areas are the catchments of the Ebro, Meuse, Elbe and Danube Rivers and the Brévilles Spring. Here we outline the general structure of the project and the activities conducted within eleven existing sub-projects of AquaTerra.

In vivo and in vitro biological activities of two human cell lines derived from anaplastic lung cancers.

Cell lines Lu-65 and SK-Luci-6 were established from two patients with anaplastic (non-oat cell) lung cancers. These cell lines showed in vivo and in vitro functional activities that could explain the paraneoplastic syndromes which were clinically manifested. In both patients, elevated white blood cell counts occurred in the absence of any evidence of sepsis. Tumor fragments taken directly from one patient and transplanted to nude mice produced a progressive leukocytosis in the mice. Tissue culture-derived cells from both cell lines enhanced white blood cell numbers following heterotransplantation to nude mice. Cell-free extracts from both cell lines were found to enhance granulocyte-macrophage colony formation in soft agar. Greater colony formation was consistently found with the cell line (SK-Luci-6) that was derived from the patient manifesting the more marked leukocytosis. These data suggest that the tumor cells release colony-stimulating activities. Coincidently, one cell line (Lu-65) synthesized and released large amounts of prostaglandin E2 with little or no other prostaglandin product; the other cell line produced no prostaglandins. When the tumor cell lines were cocultured with explanted fetal rat bones, enhanced bone resorption with excessive calcium release occurred. Bone-resorbing activity correlated with tumor prostaglandin synthesis for the cell line releasing prostaglandin E2. An osteolytic factor that was neither prostaglandin nor parathyroid hormone was released by the SK-Luci-6 cell line. Hypercalcemia was a persistent feature only in the patient from whom the latter tumor line was derived.

Reaction of a frustrated citizen.

Participation on a board of a Comprehensive Community Mental Health Center is a frustrating, saddening, but occasionally positive experience. The positives can continue to outweigh the negatives only if the partnership between staff and citizen can be strengthened. Continued manipulation by either side of the partnership will in the end only destroy the goals we have worked for. With the reduction of federal commitment and the expiration of grants for most of the centers in the country we must band together to find new and creative ways to stay alive. Community Health Centers have made a real difference in the lives of ordinary citizens and in the lives of those who have served on their boards. Hopefully a renewed effect to bring staff and citizen/consumers together will bring about the new partnership without which there may be no Community in Mental Health Centers.