Coupled Reactive Transport Modeling of Redox Processes in a Nitrate-Polluted Sandy Aquifer

The reactive transport modeling of a complicated suite of reactions apparent in the aquifer during the application of N-containing fertilizers is reported. The unconfined sandy aquifer can be subdivided into an oxic zone which contains groundwater with oxygen and nitrate and an anoxic zone characterized by elevated iron and sulfate concentrations in groundwater. Oxygen and nitrate are being reduced by pyrite and organic matter that commonly apparent in the aquifer. The oxidation of pyrite is modeled using the local equilibrium approach, whereas decomposition of organic matter, with the adoption of kinetic approach. The system is buffered by dissolution of aluminum and iron oxides. The modeling process is a two-step procedure. First, the processes are modeled in the one-dimensional (1D) column using PHREEQC code. Subsequently, the calibrated and verified data were copied and used in two-dimensional (2D) PHAST model. Prior to the performance of reactive transport modeling operations with PHAST, a reliable flow model was executed. Finally, predictions are made for the distribution of water chemistry for the year 2008. Model predicts that sulfate derived from the ongoing pyrite oxidation is reduced by the dissolved organic carbon at the higher depth and forms pyrite by the reaction with iron. The results of this study highlight the importance of understanding the interplay between the transport and chemical reactions that occur during the input of nitrate to the aquifer. Reactive transport modeling incorporating the use of a newly developed code PHAST have proved to be a powerful tool for analyzing and quantifying such interactions.     

Estimating minimum streamflow from measurements at ungauged sites in regions with streamflow‐gauging networks

Estimation of low flows in rivers continues to be a vexing problem despite advances in statistical and process‐based hydrological models. We develop a method to estimate minimum streamflow at seasonal to annual timescales from measured streamflow based on regional similarity in the deviations of daily streamflow from minimum streamflow for a period of interest. The method is applied to 1,019 gauged sites in the Western United States for June to December 2015. The gauges were clustered into six regions with distinct timing and magnitude of low flows. A gamma distribution was fit each day to the deviations in specific discharge (daily streamflow divided by drainage area) from minimum specific discharge for gauges in each region. The Kolmogorov–Smirnov test identified days when the gamma distribution was adequate to represent the distribution of deviations in a region. The performance of the gamma distribution was evaluated at gauges by comparing daily estimates of minimum streamflow with estimates from area‐based regression relations for minimum streamflow. Each region had at least 8 days during the period when streamflow measurements would provide better estimates than the regional regression equation, but the number of such days varied by region depending on aridity and homogeneity of streamflow within the region. Synoptic streamflow measurements at ungauged sites have value for estimating minimum streamflow and improving the spatial resolution of hydrological model in regions with streamflow‐gauging networks.     

Marine-derived C calibration and activity record for the past 50,000 years updated from the Cariaco Basin

An expanded Cariaco Basin ¹⁴C chronology is tied to ²³⁰Th-dated Hulu Cave speleothem records in order to provide detailed marine-based ¹⁴C calibration for the past 50,000 years. The revised, high-resolution Cariaco ¹⁴C calibration record agrees well with data from ²³⁰Th-dated fossil corals back to 33 ka, with continued agreement despite increased scatter back to 50 ka, suggesting that the record provides accurate calibration back to the limits of radiocarbon dating. The calibration data document highly elevated Δ¹⁴C during the Glacial period. Carbon cycle box model simulations show that the majority of observed Δ¹⁴C change can be explained by increased ¹⁴C production. However, from 45 to 15 ka, Δ¹⁴C remains anomalously high, indicating that the distribution of radiocarbon between surface and deep ocean reservoirs was different than it is today. Additional observations of the magnitude, spatial extent and timing of deep ocean Δ¹⁴C shifts are critical for a complete understanding of observed Glacial Δ¹⁴C variability.     

Die Aufnahme von Wasserdampf durch menschliche Haut,Pflanze und Erdboden

Zusammenfassung Laboratoriumsversuche und Feldbeobachtungen zeigen einen unerwartet starken Transport von Wasserdampf in die menschliche Haut, in getrocknete und in lebende Pflanzen und in trockenen Erdboden hinein. Diese Vorg?nge selbst beruhen offenbar auf Diffusion und Sorption. Dabei ist für menschliche Haut und für Pflanzen das Entstehen hoher osmotischer Drucke, d. h. niederer Wasserkonzentration, wahrscheinlich gemacht; doch sind die Ursachen dafür noch unbekannt.

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Summary Laboratory experiments and field observations show surprisingly high amounts of transfer of water vapor into human skin, into dry and living plants, and into dry soil. The processes involved seem to be based on diffusion and sorption. These results may be explained by assuming the existence of high osmotic pressures in skin and in plants; the reason for this concentration is not yet known.

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Résumé Des essais de laboratoire et dans la nature montrent un transport inattendu de vapeur d'eau dans la peau humaine, dans des plantes séchées et vivantes ainsi que dans le sol sec. Les phénomènes reposent apparemment sur la diffusion et sur la sorption. En ce qui concerne la peau humaine et les plantes, il est donc probable qu'elles entretiennent des pressions osmotiques élevées; mais la cause en est encore inconnue.

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Contribution Number 32 of the Department of Meteorology and Climatology, University of Washington.

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Herrn Dr.Anders K. ?ngstr?m zu seinem 70. Geburtstag gewidmet.     

Martian Seasonal CO2 Ice in Polygonal Troughs in Southern Polar Region: Role of the Distribution of Subsurface H2O Ice

The Mars Orbiter Camera onboard the Mars Global Surveyor has obtained several images of polygonal features in the southern polar region. In images taken during the end of the southern spring, when the surrounding surface is free of the seasonal frost, CO₂ ice still appears to be present within the polygonal troughs. In Earth's polar regions, polygons such as these are indicative of water ice in the ground below. We analyzed the seasonal evolution of the thermal state and the CO₂ content of these features. Our 2-D model includes condensation and sublimation of the CO₂ ice, a self consistent treatment of the variations of the thermal properties of the regolith, and the seasonal variations of the local atmospheric pressure which we take from the results of a general circulation model. We find that the residence time of seasonal CO₂ ice in troughs depends not only on atmospheric opacity and albedo of the CO₂ ice, but also and most significantly on the distribution of water ice in the regolith. Optical properties of the atmosphere and surface CO₂ ice can be independently obtained from observations. To date this is not true about the distribution of water ice below the surface. Our analysis quantifies the dependence of the seasonal cycle of the CO₂ ice within the troughs on the assumed distribution of the water ice below the surface. We show that presence of water ice in the ground at a depth smaller than the depth of the troughs reduces winter condensation rate of CO₂ ice. This is due to higher heat flux conducted from the water ice rich regolith toward the facets of the troughs.     

Measuring galaxy potentials using shell kinematics

We show that the kinematics of the shells seen around some elliptical galaxies provide a new, independent means for measuring the gravitational potentials of elliptical galaxies out to large radii. A numerical simulation of a set of shells formed in the merger between an elliptical and a smaller galaxy reveals that the shells have a characteristic observable kinematic structure, with the maximum line-of-sight velocity increasing linearly as one moves inward from a shell edge. A simple analytic calculation shows that this structure provides a direct measure of the gradient of the gravitational potential at the shell radius. In order to extract this information from attainable data, we have also derived a complete distribution of line-of-sight velocities for material within a shell; comparing the observed spectra of a shell to a stellar template convolved with this distribution will enable us to measure the gradient of the potential at this radius. Repeating the analysis for a whole series of nested shells in a galaxy allows the complete form of the gravitational potential as a function of radius to be mapped out. The requisite observations lie within reach of the up-coming generation of large telescopes.