87Rb-86Sr age of rocks from the Apollo 15 landing site and significance of internal isochrons

Internal isochrons for two Apollo 15 rocks give an age of(3.34 ± 0.09)and(3.46 ± 0.04) × 10⁹ years with an identical⁸⁷Sr/⁸⁶Sr initial ratio of 0.69928. Considering the possibility for the line obtained in a⁸⁷Sr/⁸⁶Sr,⁸⁷Rb/⁸⁶Sr diagram to be a mixing line, the significance of these results are discussed.     

The origin of high-amplitude magnetic anomalies at the intersection of the Juan de Fuca ridge and Blanco fracture zone

The intersection of the Juan de Fuca ridge and Blanco fracture zone is characterized by unusually high amplitude magnetic anomalies (over 1500 nT) which appear to be associated with a body roughly 50 km in length and 20 km in width aligned along the fracture zone. Simple three-dimensional magnetic models indicate that this anomaly is probably caused by a highly magnetized block of material situated in the western end of the Blanco fracture zone near its intersection with the Juan de Fuca ridge. Rock magnetization studies of tholeiitic basalts dredged from this area confirm the presence of highly magnetized basalts near the ridge crest/transform fault intersection. These tholeiitic basalts are enriched in iron and titanium relative to “normal” oceanic tholeiites, apparently the result of extensive shallow fractionation involving olivine, plagioclase, and clinopyroxene. Magnetic model studies indicate that an average thickness of no more than 500 m of these iron-rich basalts is necessary to produce the observed anomaly pattern. Comparison of these basalts with samples previously dredged from the Juan de Fuca ridge crest suggests that these Fe-rich, highly magnetized basalts probably “leaked” out of the southernmost portion of the Juan de Fuca ridge.     

Petrogenesis of oceanic granites from the Aves Ridge in the Caribbean Basin

A genetic model proposed for granitic rocks dredged from the Aves Rise involves a sodium-enriched hydrothermal fluid phase, shallow emplacement, and significant derivation of components from the upper mantle. Megascopic observations of serially slabbed sections of the rock samples show that aggregates of plagioclase phenocrysts concentrate into channel-like mats. The presence of a late-stage, hydrothermal fluid is suggested by crystal-lined cavities in the plagioclase aggregates.     

Quasi-geostrophic motions in a galactic flow

Summary We continue the theoretical investigation of geostrophically balanced motions of a star gas in a rotating galaxy. The method of small perturbations is employed to derive a quasi geostrophic vorticity equation suitable for solving initial value problems for slow galactic eddying motions. The results derived for this simple theoretical model are then generalized to obtain approximate geostrophic forecast equations suitable for study of nonlinear galactic motions over a whole disk galaxy. A simple discussion of the stability of our approximate vorticity equation is presented. It is expected that in the absence of rapid gravitational instabilities, actual eddy motions observed in spiral galaxies will be at least approximately of the type of motion discussed in this paper. The Rossby adjustment problem is investigated in this context.     

The role of baseflow in dissolved solids delivery to streams in the Upper Colorado River Basin

Salinity has a major effect on water users in the Colorado River Basin, estimated to cause almost $300 million per year in economic damages. The Colorado River Basin Salinity Control Program implements and manages projects to reduce salinity loads, investing millions of dollars per year in irrigation upgrades, canal projects, and other mitigation strategies. To inform and improve mitigation efforts, there is a need to better understand sources of salinity to streams and how salinity has changed over time. This study explores salinity in the baseflow fraction of streamflow, assessing whether groundwater is a significant contributor of dissolved solids to streams in the Upper Colorado River Basin (UCRB). Chemical hydrograph separation was used to estimate baseflow discharge and baseflow dissolved solids loads at stream gages (n = 69) across the UCRB. On average, it is estimated that 89% of dissolved solids loads originate from the baseflow fraction of streamflow, indicating that subsurface transport processes play a dominant role in delivering dissolved solids to streams in the UCRB. A statistical trend analysis using weighted regressions on time, discharge, and season was used to evaluate changes in baseflow dissolved solids loads in streams (n = 27) from 1986 to 2011. Decreasing trends in baseflow dissolved solids loads were observed at 63% of streams. At the three most downstream sites, Green River at Green River, UT, Colorado River at Cisco, UT, and the San Juan River near Bluff, UT, baseflow dissolved solids loads decreased by a combined 823,000 metric tons (mT), which is approximately 69% of projected basin‐scale decreases in total dissolved solids loads as a result of salinity control efforts. Decreasing trends in baseflow dissolved solids loads suggest that salinity mitigation projects, landscape changes, and/or climate are reducing dissolved solids transported to streams through the subsurface. Notably, the pace and extent of decreases in baseflow dissolved solids loads declined during the most recent decade; average decreasing loads during the 2000s (28,200 mT) were only 54% of average decreasing loads in the 1990s (51,700 mT).     

Effect of Biofuels on Biodegradation of Benzene and Toluene at Gasoline Spill Sites

The risk that benzene and toluene from spills of gasoline will impact drinking water wells is largely controlled by the natural anaerobic biodegradation of benzene and toluene. Benzene and toluene, as well as ethanol and other biofuels, are degraded under anaerobic conditions to the same pool of degradation products. Biodegradation of biofuels may produce concentrations of degradation products that make the thermodynamics for degradation of benzene and toluene infeasible under methanogenic conditions and produce larger plumes of benzene and toluene. This study evaluated the concentrations of fuel alcohols that are necessary to inhibit the anaerobic degradation of benzene and toluene under methanogenic conditions. At two ethanol spill sites, concentrations of ethanol greater ≥42 mg/L inhibited the anaerobic degradation of toluene. The pH and concentrations of acetate, dissolved inorganic carbon, and molecular hydrogen were used to calculate the Gibbs free energy for the biodegradation of toluene. In general, the anaerobic biodegradation of toluene was not thermodynamically feasible in water with ≥42 mg/L ethanol. In a microcosm study, when the concentrations of ethanol were ≥14 mg/L or the concentrations of n‐butanol were ≥16 mg/L, the biodegradation of the alcohols consistently produced concentrations of hydrogen, dissolved inorganic carbon, and acetate that would preclude natural anaerobic biodegradation of benzene and toluene by syntrophic organisms. In contrast, iso‐butanol and n‐propanol only occasionally produced conditions that would preclude the biodegradation of benzene and toluene.     

Permeability of coals and characteristics of desorption tests: Implications for coalbed methane production

Desorption tests, conducted before development drilling, can predict early production rates of coalbed methane wells. In this study, results from 136 desorption tests from 30 coreholes are compared to subsequent production histories of surrounding wells. Coals studied are from the Carboniferous Pottsville Formation in the Black Warrior Basin of Alabama, USA. The investigation indicates that the best predictor for gas production is ‘‘gas yield at 120 days, divided by sample depth'. This quotient has a higher correlation with actual gas production than other variables examined, including original reserves in-place. Gas content of coal generally increases with depth. However, coal permeability, and hence the recovery factor, tends to decrease with depth. Therefore, coalbed methane exploration should focus on finding the optimal balance between gas yield and depth. Commercially successful wells are characterized by coals with high gas yields at shallow depths. Desorption tests, especially of slowly-desorbing coals, should be run for a minimum of 120 days, or else should be extrapolated to that time if tests are terminated earlier.     

Assessment of groundwater vulnerability to pollution in Dire Dawa,Ethiopia using DRASTIC

Assessment of groundwater vulnerability to pollution is an effective tool for the delineation of groundwater protection zones. DRASTIC approach was used to determine vulnerability zones in Dire Dawa groundwater basin, a semiarid region of Ethiopia. Maps of the seven DRASTIC parameters were prepared. GIS-ArcView was used for mapping and performing weighted-overlay analysis. The result of the analysis indicated that eastern part of the study area, in which Dire Dawa town is located, is highly vulnerable. A low aquifer vulnerability class was determined for the western portion of the study area as a result of greater groundwater depths, higher relative soil-clay content, and relatively low recharge rates for this area. The area between the two zones is of medium vulnerability. Observed nitrate concentrations in boreholes are in accordance with the vulnerability map. Some of the boreholes in the Sabian well field (Dire Dawa area) already deliver groundwater with nitrate levels significantly exceeding health standards set by the World Health Organization, while boreholes in the western part (low vulnerability zone) contain almost no nitrate. The result of this study is useful for risk assessments and for the development of effective groundwater management strategies for this region and others like it.