Acidification processes and soil leaching influenced by agricultural practices revealed by strontium isotopic ratios

In natural river systems, the chemical and isotopic composition of stream- and ground waters are mainly controlled by the geology and water-rock interactions. The leaching of major cations from soils has been recognized as a possible consequence of acidic deposition from atmosphere for over 30 years. Moreover, in agricultural areas, the application of physiological acid fertilizers and nitrogen fertilizers in the ammonia form may enhance the cation leaching through the soil profile into ground- and surface waters. This origin of leached cations has been studied on two small and adjacent agricultural catchments in Brittany, western France. The study catchments are drained by two first-order streams, and mainly covered with cambisoils, issued from the alteration and weathering of a granodiorite basement. Precipitations, soil water- and NH₄ acetate-leachates, separated minerals, and stream waters have been investigated. Chemical element ratios, such as Ba/Sr, Na/Sr and Ca/Sr ratios, as well as Sr isotopic ratios are used to constrain the relative contribution from potential sources of stream water elements.Based on Sr isotopic ratio and element concentration, soil water- and NH₄ acetate leaching indicates (1) a dominant manure/slurry contribution in the top soil, representing a cation concentrated pool, with low ⁸⁷Sr/⁸⁶Sr ratios; (2) in subsoils, mineral dissolution is enhanced by fertilizer application, becoming the unique source of cations in the saprolite. The relatively high weathering rates encountered implies significant sources of cations which are not accessory minerals, but rather plagioclase and biotite dissolution.Stream water has a very different isotopic and chemical composition compared to soil water leaching suggesting that stream water chemistry is dominated by elements issued from mineral and rock weathering. Agriculture, by applications of chemical and organic fertilizers, can influence the export of major base cations, such as Na⁺. Plagioclase dissolution, rather than anthropogenically controlled soil water, seems to be the dominant source of Na⁺ in streams. However, Ca²⁺ in streams is mostly derived from slurries and manures deposited on top soils, and transferred into the soil ion-exchange pool and stream waters. Less than 10% of Na⁺, 5-40% of Sr²⁺ and 20-100% of Ca²⁺ found in streams can be directly derived from the application of organic fertilizers.     

Processes,spatio‐temporal factors and measurements of current erosion in the French Southern Alps: a review

Present erosion in mountainous areas of Western Europe causes land management problems, particularly for areas located downstream of erosion zones. Except for transalpine roads and ski resorts, economic activities no longer require as much space as they did in the past. Therefore, natural reforestation has provided signi?cant protection for alpine hillslopes during the 20th century. However, extreme ?oods continue to cause severe damage in intra‐alpine valleys, as well as in piedmont and surrounding plains, making the study of present water erosion phenomena very important. Many studies have investigated the processes and factors of water erosion on slopes at both the catchment and plot scales. They have focused on rock fragmentation and transportation in different ?elds, the spatial and temporal explanatory variables, the consequences downstream (?ooding, sedimentation, river bed evolution) and the impact of ?oods. In the French Alps, present erosion has been studied in a variety of outcrops, with several recent studies conducted in ?elds such as marls, clayey deposits, molasses and moraines. These kinds of outcrops are found throughout the alpine massif, including an area of special interest on the great Jurassic black marl outcrop where badlands are frequently observable. Geomorphologists and hydrologists have been particularly interested in the strong erosion processes in marls, seeking to determine the main patterns and the impact of spatial and temporal factors on soil loss quantities. The main climatic factors of rock disaggregation were found to be the freeze–thaw and wet–dry cycles, which destroy rock cohesion, and the splash effect of rain. The principal site variables are vegetation cover, exposure and dip–slope angle. Erosion rates are two or three orders of magnitude higher on bare soils than on pastures; northern aspect slopes suffer two to four times as much soil loss as southern aspect slopes. Finally, the angle formed by the slope and the dip also determines different behaviours: erosion rates are higher when slope and dip are perpendicular than when they are parallel. The transportation agents are mostly debris ?ows and runoff caused by intense precipitation. Annual erosion depth in the marls is generally assumed to be substantial, up to 10 mm. The high value can be explained by the severity of the climatic conditions and the brittleness of the lithology, which results in numerous fractures. Copyright © 2003 John Wiley & Sons, Ltd.     

Radar observations of asteroid 1999 JM8

Abstract— We report results of delay‐Doppler observations of 1999 JM8 with the Goldstone 8560 MHz (3.5 cm) and Arecibo 2380 MHz (13 cm) radars over 18 days in July‐August 1999. The images place thousands of pixels on the asteroid and achieve range resolutions as fine as 15 m/pixel. The images reveal an asymmetric, irregularly shaped object with a typical overall dimension within 20% of 7 km. If we assume that 1999 JM8's effective diameter is 7 km, then the absolute magnitude, 15.15, and the average Goldstone radar cross section, 2.49 km², correspond to optical and radar albedos of 0.02 and 0.06, establishing that 1999 JM8 is a dark object at optical and radar wavelengths. The asteroid is in a non‐principal axis spin state that, although not yet well determined, has a dominant periodicity of ?7 days. However, images obtained between July 31 and August 9 show apparent regular rotation of features from day to day, suggesting that the rotation state is not far from principal axis rotation. 1999 JM8 has regions of pronounced topographic relief, prominent facets several kilometers in extent, numerous crater‐like features between ?100 m and 1.5 km in diameter, and features whose structural nature is peculiar. Arecibo images provide the strongest evidence to date for a circular polarization ratio feature on any asteroid. Combined optical and radar observations from April 1990 to December 2000 permit computation of planetary close approach times to within ± 10 days over the interval from 293 to at least 2907, one of the longest spans for any potentially hazardous asteroid. Integration of the orbit into the past and future shows close approaches to Earth, Mars, Ceres, and Vesta, but the probability of the object impacting Earth is zero for at least the next nine centuries.     

Kirchhoff scattering series for sources and receivers located in an elastic medium: Another insight into the concept of virtual events

The convolution-type and correlation-type representation theorems are building blocks of wave-scattering theory whose usefulness expands in many seismological applications. For example, the Kirchhoff scattering series currently used for attenuating free-surface multiples has been derived from the convolution-type representation theorem. The recently introduced concept of virtual events, which allows us to put virtual sources and virtual receivers inside the subsurface based on the data collected at the sea surface, has been derived by a combined use of the convolution-type and correlation-type representation theorems. The formulation of inverse Kirchhoff scattering series and virtual events has been limited so far to the cases in which sources or receivers, or both, are located in the water. Unfortunately, this assumption is not valid, especially in the context of virtual events, in which both sources and receivers will often be located in a solid. We here redescribe the Kirchhoff scattering series and reformulate the concept of virtual events for the cases in which sources and receivers are in a solid. Moreover, we describe a new form of Kirchhoff series based on the correlation-type representation theorem and new formulae for computing virtual events which do not include the complex renormalization operation of the previous formulation.     

Scattering diagrams in seismic imaging: More insights into the construction of virtual events and internal multiples

The key processes in marine seismic imaging include (i) removing from seismic data all seismic events (free-surface multiples and ghosts) which contain at least one reflection at the sea surface in their wave-propagation path, and leaving those with no reflection at the free surface (internal multiples and primaries), (ii) removing events with at least two reflections in the subsurface (internal multiples), and leaving events with only one reflection in the subsurface (primaries), and then (iii) locating the scattering points and reflectors inside the subsurface which are the sources of primaries and internal multiple events. All these processes are here explained, derived, and optimized via scattering diagrams (diagrammatica) in a way similar to the way the quantum field theory is often explained via Feynman diagrams. Our discussion of the removal of events with free-surface reflections from the data will be brief, as the diagrammatica of these events are now well understood.The main focus of this paper is the diagrammatica of internal multiples and primaries. Although these events do not contain any reflection at the sea surface, it is important to reconstruct them with scattering points near the sea surface, where seismic data are recorded. So our diagrammatica of primaries and internal multiples include events which are not directly recorded in seismic data but which can be constructed from seismic data. These events have allowed us to construct scattering diagrams of primaries and internal multiples with scattering points near the sea surface. Furthermore, these new diagrammatica of internal multiples and primaries can be used to remove internal multiples from the data.