Using hydrogeochemical signatures of stream water to assess pathways for rainfall events: towards a predictive model

Thanks to its simple division into agricultural and forestry land use, the Corbeira catchment (Galicia, Spain) is used as a case study to build a predictive model using hydrogeochemical signatures. Stream data acquired under recessional flow conditions over a one year period were obtained from a sampling station near the downstream end of the catchment, and using principal component analysis, it is shown that some of the analytical parameters are covariant, and some are negatively correlated. These findings support inferences about the pathways of rainfall in the catchment. Specific signatures may be associated with the dominant hydrological source, either surface runoff or subsurface waters: additionally, the dominant land use in that part of the catchment, where the flow originated, can also be predicted. The dominant runoff shows a strong covariance between suspended solids (SS) and particulate phosphorus (PP), with a clear negative correlation with pH. Dissolved organic carbon (DOC) data are associated with this covariant set when these compounds are available in the soils in question. Dissolved phosphorus, total organic nitrogen and dissolved nitrates are also associated with the same covariant set when the runoff flows through areas of extensive agricultural use. The SS ? PP covariance is less significant at lower flows. Typical base flow regimes show a significant covariance between salinity and pH, with a marked negative correlation with SS ? PP set, confirming the dominance of subsurface waters in the baseflow, as expected. Seasonally divergent DOC ? SS behaviour proves to be a useful tracer for rainfall regimes. The DOC trend shows a sinusoidal annual variation in amplitude, determined by the rainfall regime. As a result, flow from the catchment is dominated by surface water whenever there is synchronicity between the peaks of DOC and SS. Copyright © 2013 John Wiley & Sons, Ltd.     

Long-term variability of UV radiation in the spectral range of 300–380 nm in Moscow

The seasonal and interannual variability of global ultraviolet (UV) radiation in the spectral range of 300-380 nm (0380) in Moscow in 1968-2014 is analyzed. The effect of cloudiness on the magnitude of 0380 is assessed. The smallest (-22...-26%) losses due to cloudiness are registered in May-August, and the highest ones (to -45%) are observed in October-November. According to the UV radiation reconstruction model and measurement data, the long-term deviations of 0380 from the average (for 1968-1997) due to clouds can reach + (11-12)%. The statistically significant positive linear trend in total annual 0380 is revealed from the data of both the reconstruction model and observations (about 1.5% per decade for 1968-2014 and 3% per decade for 1979-2014).     

Cross-strata and bedforms of probable transitional dune to upper-stage plane-bed origin from a Late Precambrian fluvial sandstone, northern Norway.

A Late Precambrian fluvial sandstone sequence in northern Norway is dominated by large-scale cross-sets that show either lenticular or tabular geometries in the streamwise sections. The lenticular sets interdigitate and in places show nearly symmetrical formsets. The tabular sets are in places solitary, but are mainly grouped in cosets. In both cross-set types, the cross-strata range from concave-up to sigmoidal in shape, with the latter variety comprising subhorizontal to gently inclined topset strata (with parting lineation) that merge uninterruptedly downflow into the steeper (10–2°) foresets. Within the cross-sets the geometry and dip azimuths of the foresets are conspicuously consistent, although the concave-up and sigmoidal strata commonly alternate downcurrent. The cross-strata characteristics suggest flood stage deposition from relatively high velocity steady currents heavily laden with suspended sand. Both cross-set types are interpreted as representing bedforms generated by flow in the dune to upper-stage plane-bed transition. The lenticular cross-sets probably represent periodic dunes, but it is far less clear whether the long bedforms represented by the tabular sets should be classified as dunes, or rather as solitary to quasi-periodic bars.     

On the utility of identification schemes for digital earth science data: an assessment and recommendations

In recent years, a number of data identification technologies have been developed which purport to permanently identify digital objects. In this paper, nine technologies and systems for assigning persistent identifiers are assessed for their applicability to Earth science data (ARKs, DOIs, XRIs, Handles, LSIDs, OIDs, PURLs, URIs/URNs/URLs, and UUIDs). The evaluation used four use cases that focused on the suitability of each scheme to provide Unique Identifiers for Earth science data objects, to provide Unique Locators for the objects, to serve as Citable Locators, and to uniquely identify the scientific contents of data objects if the data were reformatted. Of all the identifier schemes assessed, the one that most closely meets all of the requirements for an Unique Identifier is the UUID scheme. Any of the URL/URI/IRI-based identifier schemes assessed could be used for Unique Locators. Since there are currently no strong market leaders to help make the choice among them, the decision must be based on secondary criteria. While most publications now allow the use of URLs in citations, so that all of the URL/URI/IRI based identification schemes discussed in this paper could potentially be used as a Citable Locator, DOIs are the identification scheme currently adopted by most commercial publishers. None of the identifier schemes assessed here even minimally address identification of scientifically identical numerical data sets under reformatting.     

Evaluating the impact of data quantity, distribution and algorithm selection on the accuracy of 3D subsurface models using synthetic grid models of varying complexity

Testing the accuracy of 3D modelling algorithms used for geological applications is extremely difficult as model results cannot be easily validated. This paper presents a new approach to evaluate the effectiveness of common interpolation algorithms used in 3D subsurface modelling, utilizing four synthetic grids to represent subsurface environments of varying geological complexity. The four grids are modelled with Inverse Distance Weighting and Ordinary Kriging, using data extracted from the synthetic grids in different spatial distribution patterns (regular, random, clustered and sparse), and with different numbers of data points (100, 256, 676 and 1,600). Utilizing synthetic grids for this evaluation allows quantitative statistical assessment of the accuracy of both interpolation algorithms in a variety of sampling conditions. Data distribution proved to be an important factor; as in many geological situations, relatively small numbers of randomly distributed data points can generate more accurate 3D models than larger amounts of clustered data. This study provides insight for optimizing the quantity and distribution of data required to accurately and cost-effectively interpolate subsurface units of varying complexity.     

The effects of heating on low-temperature susceptibility and hysteresis properties of basalts

The variation of the low-field susceptibility of basalts down to liquid-nitrogen temperature always falls into one of three types that depend on the composition and grain size of the titanomagnetite grains present. Group 1 basalts contain predominantly unoxidised, multidomain homogeneous titanomagnetites having x 0.3. Group 2 basalts contain predominantly titanomagnetite grains with many exsolved ilmenite lamallae that subdivide the grains so that they act similarly to single domains. Group 3 basalts contain predominantly multidomain magnetite or magnetite-rich titanomagnetite having x 0.15. After repeated heating to 615°C, the group 1 basalts gradually oxidise above 300°C to produce the characteristics of group 2 basalts, owing to the exsolution of ilmenite. On the other hand, both group 2 and 3 basalts are stable to oxidation until at least 500°C. They are therefore the most useful material for palaeointensity studies.     

Phase transformations of enstatite in spherical shock waves

The analysis of available theoretical evaluations and experimental data reveals discrepancies and makes it possible to formulate the goals for the comprehensive study of the behavior of enstatite MgSiO₃ in shock isentropic waves of various scale and intensity. The paper presents the layout and results of an explosion experiment on the compression of an enstatite sphere with spherical shock waves and the subsequent recovery of the experimental material and its examination in discrete zones (along the sphere radius) that were produced by shock waves in the material. The latter were examined with the application of scanning electron microscopy, Raman spectroscopy, and X-ray diffraction analysis. The comparison of the systematic variations in the texture, chemistry, and phase composition of enstatite along the sphere radius with calculated pressure P(R, t) and temperature T(R, t) values led us to the following conclusions: enstatite starts melting on an isentrope upon pressure relief after shock wave compression at ?? _xx ?? 80 GPa and melts on the front of the spherically converging shock wave at ?? _xx ?? 160 GPa and T ?? 6300 K. Our laboratory experiments with shock waves were the world??s first in which enstatite was loaded with spherical converging shock isentropic waves and which provided evidence that shock wave-loaded MgSiO₃ shows certain morphological and mineralogical features never before detected in this mineral loaded with plane shock wave of smaller amplitude and duration. Goals are formulated for the further studying of shock wave-loaded materials, and the necessity is discussed for conducting an explosion experiment with a five to seven times greater spherical system in order to increase the duration of the shock wave loading impulse.     

Characterization of Quaternary faults by electric resistivity tomography in the Andean Precordillera of Western Argentina

El río San Juan, situado en la Provincia de San Juan (Argentina) cruza la Precordillera y otras unidades geológicas incluyendo la Depresión de Ullum y la Zona de La Laja, entre las latitudes 31°S y 32°S. El curso del río tiene un cierto caracter antecedente como puede deducirse por sus dos trazas perpendiculares unidas por otra casi paralela a las alineaciones estructurales principales. En la zona de la Precordillera, el valle del río San Juan muestra numerosos abanicos aluviales, situados en las zonas de confluencia entre el río principal y sus tributarios. Las superficies de los abanicos aluviales cuaternarios estan cortadas por una serie de escalones que consideramos como terrazas aluviales generadas por episodios repetitivos de agradación y degradación. El sector estudiado incluye una zona con una importante actividad sísmica reciente(La Laja), otra sin una importante actividad sísmica reciente (Precordillera), y una zona subsidente (Ullum) donde se formó un gran lago natural hace unos 6500 años. El antiguo río San Juan fue capturado por el valle de la Quebrada de Ullum mediante una incisión del orden de 25 m, que implicó una nueva adecuación del gradiente del río mediante los efectos de la erosión remontante. El gradiente del río San Juan muestra algunas irregularidades que, aunque no se presenten relacionadas directamente con las estructuras principales, estan relacionadas con la propia dinámica fluvial que acentúa la diferenciación litológica. La anchura del valle del río principal, la geometria y el gradiente de cada tributario, junto a las litologias del basamento y a las dimensiones de cada area fuente local, son los factores principales que controlan los procesos de la generación de las terrazas aluviales. En la zona de La Laja, donde la terraza mas alta soporta un nivel de travertino, la datación de los depósitos travertínicos proporciona datos como para suponer una tasa de incisión del orden de 0,9–1 mm/año, asociada a la actuación periódica de la falla de La Laja.