Formation of free amino acids in rhizosphere and nonrhizosphere soil

Includes bibliographical references (page 362).Untreated samples of nonrhizosphere and soybean rhizosphere soils each contained about 15 identified free amino acids totaling 2 to 4 µg. per g. of soil; lysine was the most prevalent amino acid in each preparation. Numerous additional unidentified compounds occurred at concentrations estimated as 0.1 to 0.5 µg. per g. Treatment with glucose and potassium nitrate increased the amount of free amino acids to about 100 µg. per g. after 3 days. Concentrations declined after 3 days but still were 4 to 5 times that of the untreated control after 2 weeks' incubation. Glutamic acid was the dominant amino acid in all treated soils. Rhizosphere soil did not differ quantitatively from nonrhizosphere in samples treated with glucose, although a greater variety of ninhydrin reacting compounds was encountered in rhizosphere soil. Treated soils incubated at 20% field moisture capacity differed little in free amino acids from those held at 30%. The features of the free amino acid fraction are discussed

Twentieth Century Geomorphic Changes of the Lower Green River in Canyonlands National Park, Utah: An Investigation of Timing, Magnitude and Process

Since the early 20th century, the Green River, the longest tributary of the Colorado River, has narrowed, decreasing available riparian and aquatic habitat. Initially, the widespread establishment of non-native tamarisk was considered to be the primary driver of channel narrowing. An alternative hypothesis postulated that changes in hydrology drove narrowing. Reductions in total streamflow and changes to flow regime occurred due to wide-spread water development, decreased snowmelt flood magnitude, and the increased cyclicity of wet and dry years. The two hypotheses agree on channel narrowing, but each influences modern river management differently. A tamarisk-driven model of narrowing implies that modern flow management doesn’t substantially affect channel change. Conversely, channel narrowing driven by changes in hydrology implies that present flow management decisions matter and continued adjustments to flow regime may result in future channel change. To understand the roles of decreasing total annual flow, declining annual peak flood magnitude, and changing vegetation communities on 20th century channel narrowing, we investigated channel narrowing along the lower Green River within Canyonlands National Park (CNP). Previous studies agree that the channel has narrowed, however, the rate, timing and magnitude of documented narrowing are only partially understood. Multiple lines of evidence were used to reconstruct the history of channel narrowing in the lower Green River. This study focuses on channel narrowing, but additionally investigated possible changes to channel depth, identified process, timing and magnitude of floodplain formation. Floodplain formation was described in the field using stratigraphy, sedimentology, and dendrogeomorphology exposed in a floodplain trench. Channel and floodplain surveys were conducted to determine possible changes in bed elevation. Additionally, existing aerial imagery, hydrologic data, and sediment transport data were analyzed. These techniques were applied to determine magnitude, timing and processes of channel narrowing at multiple spatial and temporal scales. The floodplain investigation identified a new period of channel narrowing by vertical accretion after high peak flow years of 1983 and 1984. Narrowing was initiated by vertical accretion in the active channel, deposited by moderate floods exceeded more than 50% of the time. Vertical accretion continued in the early 1990s, converting the active channel into a periodically inundated floodplain surface. Suspended-sediment deposition dominated deposits, resulting in the formation of natural levees and floodplain troughs in both inset floodplains. Rates of deposition were highly variable, ranging from 0.03-0.50 m/yr. The lower Green River within Canyonlands National Park has narrowed substantially since the late 1800s, resulting in a narrower channel. Changes to flood magnitude, rate and timing since 1900, driven by increased water storage and diversion in the Green River basin and declines in annual precipitation, were responsible for inset floodplain formation. Floodplains of the contemporary lower Green River in CNP began forming in the late 1930s and continued to form and vertically aggrade in the 20th century by inset floodplain formation. During this time period, peak flow and total runoff declined due to climatic changes and water development. Analysis of aerial imagery covering 61 kilometers (km) of the Green River in CNP shows that changes to the floodplain identified in the trench are representative of the entire study area. The establishment of non-native tamarisk (Tamarix spp.) did not drive channel narrowing, though dense stands stabilized banks and likely promoted sediment deposition. The lower Green River narrowed 12% from 1940-2014, with the majority of narrowing (10% of all narrowing) occurring from the 1980s to the present. Inset floodplain formation reflects changes to flood magnitude and timing resulting from water development and decreases in natural runoff. Findings suggest that long-term management of the riverine corridor within Canyonlands National Park will require a greater focus on upstream flow contributions and how those flows are currently managed. Recovery of endangered endemic native fishes, the Colorado pikeminnow (Ptychocheilus lucius), and the razorback sucker (Xyrauchen texanus), plays a primary role in determining current flow allocations. Collaboration with upstream stakeholders and managers is necessary to maximize elements of the flow regime that preserve channel width and limit channel narrowing

Measuring the Cosmic Ray Muon-Induced Fast Neutron Spectrum by (n,p) Isotope Production Reactions in Underground Detectors

While cosmic ray muons themselves are relatively easy to veto in underground detectors, their interactions with nuclei create more insidious backgrounds via: (i) the decays of long-lived isotopes produced by muon-induced spallation reactions inside the detector, (ii) spallation reactions initiated by fast muon-induced neutrons entering from outside the detector, and (iii) nuclear recoils initiated by fast muon-induced neutrons entering from outside the detector. These backgrounds, which are difficult to veto or shield against, are very important for solar, reactor, dark matter, and other underground experiments, especially as increased sensitivity is pursued. We used fluka to calculate the production rates and spectra of all prominent secondaries produced by cosmic ray muons, in particular focusing on secondary neutrons, due to their importance. Since the neutron spectrum is steeply falling, the total neutron production rate is sensitive just to the relatively soft neutrons, and not to the fast-neutron component. We show that the neutron spectrum in the range between 10 and 100 MeV can instead be probed by the (n, p)-induced isotope production rates 12C(n, p)12B and 16O(n, p)16N in oil- and water-based detectors. The result for 12B is in good agreement with the recent KamLAND measurement. Besides testing the calculation of muon secondaries, these results are also of practical importance, since 12B (T1/2 = 20.2 ms, Q = 13.4 MeV) and 16N (T1/2 = 7.13 s, Q = 10.4 MeV) are among the dominant spallation backgrounds in these detectors

The Star Formation History of LGS 3

We have determined the distance and star formation history of the Local Group dwarf galaxy LGS 3 from deep Hubble Space Telescope WFPC2 observations. LGS 3 is intriguing because ground-based observations showed that, while its stellar population is dominated by old, metal-poor stars, there is a handful of young, blue stars. Also, the presence of HI gas makes this a possible ``transition object'' between dwarf spheroidal and dwarf irregular galaxies. The HST data are deep enough to detect the horizontal branch and young main sequence for the first time. A new distance of D=620+/-20 kpc has been measured from the positions of the TRGB, the red clump, and the horizontal branch. The mean metallicity of the stars older than 8 Gyr is Fe/H = -1.5 +/- 0.3. The most recent generation of stars has Fe/H ~ -1. For the first few Gyr the global star formation rate was several times higher than the historical average and has been fairly constant since then. However, we do see significant changes in stellar populations and star formation history with radial position in the galaxy. Most of the young stars are found in the central 63 pc (21''), where the star formation rate has been relatively constant, while the outer parts have had a declining star formation rate.Comment: To appear in The Astrophysical Journal, 26 pages, 14 figures, uses AASTe

Riparian vegetation, Colorado River, and climate: Five decades of spatiotemporal dynamics in the Grand Canyon with river regulation

Documentation of the interacting effects of river regulation and climate on riparian vegetation has typically been limited to small segments of rivers or focused on individual plant species. We examine spatiotemporal variability in riparian vegetation for the Colorado River in Grand Canyon relative to river regulation and climate, over the five decades since completion of the upstream Glen Canyon Dam in 1963. Long-term changes along this highly modified, large segment of the river provide insights for management of similar riparian ecosystems around the world. We analyze vegetation extent based on maps and imagery from eight dates between 1965 and 2009, coupled with the instantaneous hydrograph for the entire period. Analysis confirms a net increase in vegetated area since completion of the dam. Magnitude and timing of such vegetation changes are river stage-dependent. Vegetation expansion is coincident with inundation frequency changes and is unlikely to occur for time periods when inundation frequency exceeds approximately 5%. Vegetation expansion at lower zones of the riparian area is greater during the periods with lower peak and higher base flows, while vegetation at higher zones couples with precipitation patterns and decreases during drought. Short pulses of high flow, such as the controlled floods of the Colorado River in 1996, 2004, and 2008, do not keep vegetation from expanding onto bare sand habitat. Management intended to promote resilience of riparian vegetation must contend with communities that are sensitive to the interacting effects of altered flood regimes and water availability from river and precipitation. å©2015. American Geophysical Union. All Rights Reserved

Linking morphodynamic response with sediment mass balance on the Colorado River in Marble Canyon: Issues of scale, geomorphic setting, and sampling design

Measurements of morphologic change are often used to infer sediment mass balance. Such measurements may, however, result in gross errors when morphologic changes over short reaches are extrapolated to predict changes in sediment mass balance for long river segments. This issue is investigated by examination of morphologic change and sediment influx and efflux for a 100 km segment of the Colorado River in Grand Canyon, Arizona. For each of four monitoring intervals within a 7 year study period, the direction of sand-storage response within short morphologic monitoring reaches was consistent with the flux-based sand mass balance. Both budgeting methods indicate that sand storage was stable or increased during the 7 year period. Extrapolation of the morphologic measurements outside the monitoring reaches does not, however, provide a reasonable estimate of the magnitude of sand-storage change for the 100 km study area. Extrapolation results in large errors, because there is large local variation in site behavior driven by interactions between the flow and local bed topography. During the same flow regime and reach-average sediment supply, some locations accumulate sand while others evacuate sand. The interaction of local hydraulics with local channel geometry exerts more control on local morphodynamic response than sand supply over an encompassing river segment. Changes in the upstream supply of sand modify bed responses but typically do not completely offset the effect of local hydraulics. Thus, accurate sediment budgets for long river segments inferred from reach-scale morphologic measurements must incorporate the effect of local hydraulics in a sampling design or avoid extrapolation altogether

Isolating the photovoltaic junction: atomic layer deposited TiO2-RuO2 alloy Schottky contacts for silicon photoanodes

We synthesized nanoscale TiO2-RuO2 alloys by atomic layer deposition (ALD) that possess a high work function and are highly conductive. As such, they function as good Schottky contacts to extract photogenerated holes from n-type silicon while simultaneously interfacing with water oxidation catalysts. The ratio of TiO2 to RuO2 can be precisely controlled by the number of ALD cycles for each precursor. Increasing the composition above 16% Ru sets the electronic conductivity and the metal work function. No significant Ohmic loss for hole transport is measured as film thickness increases from 3 to 45 nm for alloy compositions >= 16% Ru. Silicon photoanodes with a 2 nm SiO2 layer that are coated by these alloy Schottky contacts having compositions in the range of 13-46% Ru exhibit average photovoltages of 525 mV, with a maximum photovoltage of 570 mV achieved. Depositing TiO2-RuO2 alloys on nSi sets a high effective work function for the Schottky junction with the semiconductor substrate, thus generating a large photovoltage that is isolated from the properties of an overlying oxygen evolution catalyst or protection layer