Fluvial dynamics and 14C-10Be disequilibrium on the Bolivian Altiplano

Determining sediment transfer times is key to understanding source-to-sink dynamics and the transmission of environmental signals through the fluvial system. Previous work on the Bolivian Altiplano applied the in situ cosmogenic ¹⁴C-¹⁰Be-chronometer to river sands and proposed sediment storage times of ~10–20 kyr in four catchments southeast of Lake Titicaca. However, the fidelity of those results hinges upon isotopic steady-state within sediment supplied from the source area. With the aim of independently quantifying sediment storage times and testing the ¹⁴C-¹⁰Be steady-state assumption, we dated sediment storage units within one of the previously investigated catchments using radiocarbon dating, cosmogenic ¹⁰Be-²⁶Al isochron burial dating, and ¹⁰Be-²⁶Al depth-profile dating. Palaeosurfaces appear to preserve remnants of a former fluvial system, which has undergone drainage reversal, reduction in catchment area, and local isostatic uplift since ~2.8 Ma. From alluvium mantling the palaeosurfaces we gained a deposition age of ~580 ka, while lower down fluvial terraces yielded ≤34 ka, and floodplains ~3–1 ka. Owing to restricted channel connectivity with the terraces and palaeosurfaces, the main source of channel sediment is via reworking of the late Holocene floodplain. Yet modelling a set of feasible scenarios reveals that floodplain storage and burial depth are incompatible with the ¹⁴C-¹⁰Be disequilibrium measured in the channel. Instead we propose that the ¹⁴C-¹⁰Be offset results from: (i) non-uniform erosion whereby deep gullies supply hillslope-derived debris; and/or (ii) holocene landscape transience associated with climate or human impact. The reliability of the ¹⁴C-¹⁰Be chronometer vitally depends upon careful evaluation of sources of isotopic disequilibrium in a wide range of depositional and erosional landforms in the landscape. © 2018 John Wiley & Sons, Ltd.     

Groundwater Pumping Is a Significant Unrecognized Contributor to Global Anthropogenic Element Cycles

Quantifying anthropogenic contributions to elemental cycles provides useful information regarding the flow of elements important to industrial and agricultural development and is key to understanding the environmental impacts of human activity. In particular, when anthropogenic fluxes reach levels large enough to influence an element's overall cycle the risk of adverse environmental impacts rises. While intensive groundwater pumping has been observed to affect a wide-range of environmental processes, the role of intensive groundwater extraction on global anthropogenic element cycles has not yet been characterized. Relying on comprehensive datasets of groundwater and produced water (groundwater pumped during oil/gas extraction) chemistry from the U.S. Geological Survey along with estimates of global groundwater usage, I estimate elemental fluxes from global pumping, consumptive use, and depletion of groundwater. I find that groundwater fluxes appreciably contribute to a number of elements overall cycles and thus these cycles were underestimated in prior studies, which did not recognize groundwater pumping's role. I also estimate elemental loadings to agricultural soils in the United States and find that in some regions, groundwater may provide a significant portion (more than 10%) of crop requirements of key nutrients (K, N). With nearly 40% of globally irrigated land under groundwater irrigation, characterizing nutrient and toxic element fluxes to these soils, which ultimately influence crop yields, is important to our understanding of agricultural production. Thus, this study improves our basic understanding of anthropogenic elemental cycles and demonstrates that quantification of groundwater pumping elemental fluxes provides valuable information about the potential for environmental impacts from groundwater pumping.     

The Space and Time Variations of Water Quality and Water Pollution Dynamics in the Oka Basin

Water Resources - The space–time variations in the Oka basin water chemistry have been considered. The specific features in the river water and groundwater pollution along the Oka channel and...     

Planning of Soil-Pore Water Sampling Campaigns Using Pesticide Transport Modeling

Soil-pore water sampling by suction lysimeters monitors the fate of soil contaminants as a function of depth and time. However, sampling campaigns must be planned to most effectively monitor the migration of contaminants with a minimum expenditure of resources. The vertical migration of pesticides was studied at two sites treated with systemic s-triazine herbicides and equipped with suction lysimeters. The measured concentrations were compared with those calculated by a simulation model. This modeling was based on the processes that control the transport and fate of pesticide within the soil. The usefulness of such a tool was demonstrated by the good approximation obtained for pesticide concentrations and arrival times. Moreover, the significant spatial variability of concentrations observed justifies the use of a stochastic approach in modeling that takes into account the spatial variability of soil parameters. Also, the rapid transformation of herbicides observed in unsaturated soil zones demonstrates the importance of taking into account the sum of the toxic residues when evaluating the fate of s-triazines in soil.     

The solubility mechanisms of volatiles in silicate melts and their relations to crystal-andesite liquid equilibria

The anionic structure of magmatic liquids has been estimated at 1 atm and at pressures corresponding to those of the upper mantle. These estimates are based predominantly on spectroscopic data on binary metal oxide-silica and ternary metal oxide-silica-alumina melts. Structural information on melt compositions in aluminate-silica joins has been used to provide detailed information on the role of Al³⁺ in natural magma at atmospheric and high pressure.Regardless of pressure, andesitic melts may be described as combinations of chain, sheet, and three-dimensional network units. Nearly all Al³⁺ in the magmatic liquid resides in the three-dimensional network units. This Al³⁺ is locally charge-balanced with Na⁺, K⁺, Ca²⁺, and Mg²⁺. In the latter two cases, Al³⁺ and Si⁴⁺ are ordered, whereas for Na⁺ and K⁺, Si⁴⁺ and Al³⁺ are randomly mixed. Solution of water in natural magma results in the formation of new nonbridging oxygens in addition to OH groups attached to Si⁴⁺ and metal cations.On the basis of determined solution mechanisms of CO₂ and H₂O in silicate melts, thermodynamic properties of HO+CO₂, fluids and hydrous silicate melts and melting phase relations in peridotite-H₂O-CO₂, systems, it is found that natural andesitic magma in equilibrium with spinel Iherzolite in the upper mantle (10–20 kbar) must contain at least 5–7 wt.% H₂O. Andesitic magma with 5–7 wt.% H₂O in solution may be described as a mixture of Al-free three-dimensional units, sheets, and chains with a small proportion (less than 10%) of monomers.     

ON THE EFFECTS OF THICKNESS OF THE HALF-PLANE MODEL IN HLEM INDUCTION PROSPECTING OVER SULPHIDE DYKES IN A HIGHLY RESISTIVE MEDIUM1

In the quantitative data interpretation for HLEM induction prospecting, a vertical half-plane model in an insulating medium is widely employed. For this assumption to be valid, the steeply dipping massive sulphide dykes must have large strike lengths and depth extents, but small thickness. We report investigations, using the laboratory scale-modelling method, on the response variation of large vertical conductors as the thickness is varied. We conclude that a steeply dipping large dyke can be approximated by a half-plane model only if its thickness is less than half the skin depth. An inductively thick conductor produces larger amplitudes and relatively higher quadrature compared to a thin conductor, even if both have the same induction number.     

Generalized polarization relationships for acoustic gravity waves in the nonisothermal atmosphere with the wind

The nonlinear equation of the first order of the Riccati type has been obtained for the wave impedance of acoustic gravity waves in the nonisothermal atmosphere. The vertically nonuniform horizontal wind and the effect of viscosity on the horizontal components of the velocity field have been taken into account in the calculations. The boundary-value problem for the Riccati equation is defined by the boundary emission condition at high altitudes. Upon finding the wave impedance along with the generalized polarization relationship, all remaining disturbances of the atmospheric parameters related to acoustic gravity waves are found with the help of a simple integration. The results of using a developed formalism are illustrated by the numerical computation of acoustic gravity wave fields in the atmosphere with real vertical profiles of temperature and horizontal field velocity.     

The characteristics of rain electricity in Nigeria. I — Magnitudes and variations

The characteristics of rain and point charges based on routine measurements extending over four rainy seasons are presented. An average rain current density of (1.0±0.1)×10^–10 A m^–2 and charge per unit volume of rain water of (0.43±0.02)×10^–4 C m^–3 for the locality are obtained, which are compared with data obtained elsewhere by other workers. The point-discharge current measurements lead to a revised estimate of (0.86±0.08)×10^–9 A m^–2 for the average point discharge current below storm clouds.     

Short-Term Forecast of Water Levels in Don Mouth Area Using Hydrodynamic Simulation

Water Resources - The article presents the results of the test operation of a calculation–simulation complex (CSC) for level forecasting in a navigable branch in Don R. mouth area with daily...     

Erratum to: Seasonal Variations in the b-Value of the Reservoir-Triggered Seismicity in the Koyna–Warna Region,Western India

Izvestiya, Physics of the Solid Earth - An Erratum to this paper has been published: https://doi.org/10.1134/S1069351322090014