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11.
12.
Stephen Foster Antonio Pulido-Bosch Ángela Vallejos Luis Molina Armando Llop Alan M. MacDonald 《Hydrogeology Journal》2018,26(8):2781-2791
Intensive irrigated agriculture substantially modifies the hydrological cycle and often has major environmental impacts. The article focuses upon a specific concern—the tendency for progressive long-term increases in the salinity of groundwater recharge derived from irrigated permeable soils and replenishment of unconfined aquifers in more arid regions. This process has received only scant attention in the water-resource literature and has not been considered by agricultural science. This work makes an original contribution by analysing, from scientific principles, how the salinisation of groundwater recharge arises and identifies the factors affecting its severity. If not proactively managed, the process eventually will impact irrigation waterwell salinity, the productivity of agriculture itself, and can even lead to land abandonment. The types of management measure required for mitigation are discussed through three detailed case histories of areas with high-value groundwater-irrigated agriculture (in Spain, Argentina and Pakistan), which provide a long-term perspective on the evolution of the problem over various decades. 相似文献
13.
Pietro Catania Luigi Badalucco Vito Armando Laudicina Mariangela Vallone 《Environmental Earth Sciences》2018,77(9):348
Tillage, especially in semiarid Mediterranean environment, enhances the mineralization process of soil organic matter (SOM) and, in turn, decreases aggregate stability. Furthermore, continuous tillage leads to the formation of plough pan beneath the tilled layer. In the present study, we investigated the effect of an innovative self-propelled machine (spading machine, SM) for shallow tillage on SOM, water stable aggregates (WSA) and soil penetration resistance (PR). Such effects were compared to those of chisel plough (CP), rotary tiller (RT) and no tillage (NT). Each tilling method was applied up to a depth of 15 cm, whereas in NT only a brush cutter was used for weed control. Soil analyses were performed at the start of the experiment (March 2009, T0), in April 2010 (T1), May 2012 (T3), and June 2014 (T5) at both 0–15 and 15–30 cm. Compared to T0, soil PR increased with time in all the treatments and generally followed the order SM?<?RT?<?CP?<?NT. In soil tilled with the SM, soil PR never exceeded 2.5 MPa that was demonstrated to be a critical value for root elongation, and no evidence of the formation of plough pan beneath the tilled layer was observed. SOC as well as water content and WSA were higher in SM compared with CP and RT. In conclusion, the spading machine was proved to be more efficient in lowering the soil PR and in avoiding the formation of the plough pan. Furthermore, SM increased SOC and WSA. 相似文献
14.
The Patia Valley situated between the Western and Central Cordilleras of the southwest Colombian Andes contains two areas in which Mesozoic basic and ultrabasic rocks crop out in abundance. Late Cretaceous Diabase Group pillow basalts which make up much of the Western Cordillera are at least 81 ± 5 Ma in the E1 Tambo-E1 Peñol area. 105-97 Ma hornblende and whole-rock dates from the ophiolitic Los Azules complex indicate an Albian age of formation, although many dates are lower (65-62 Ma) owing the low-grade ocean-floor metamorphism. The metamorphic age distribution here supports an end of Cretaceous emplacement for the complex rather than the Early-Mid Cretaceous emplacement suggested for North Colombian ophiolites similarly aligned along the Romeral fault system. Tertiary dacites intruding the Low Azules complex are 36-15 Ma. 相似文献
15.
Belowground production of roots and rhizomes in the top 20 cm of soil was 2.2 kg m?2 yr?1 based on a maximum minus minimum estimation procedure in a giant cordgrass (Spartina cynosuroides (L.) Roth) marsh in Mississippi. Approximately 1.9 kg m?2 (86%) of this production occurred in late spring-summer and 0.3 kg m?2 in late fall. This estimate ignores any production below 20 cm depth and is thus an underestimate. Production values increased to 4.0 kg m?2 yr?1 using Smalley’s technique and accounting for decomposition. Aboveground tissues (leaves and stems) were depleted in nitrogen in July which corresponded to peaks in both above- and belowground biomass. The low root/shoot ratio (2.6) on this marsh does not suggest that growth is nutrient limited. Indeed, total productivity (above- and belowground) for this marsh was high (between 4.4 and 6.2 kg m?2 yr?1). 相似文献
16.
To control vertical movements in the Orinoco Oil Belt, a high-precision levelling network was installed in an area of about 100 km2. Links to the National Geodetic Network were established.
A total of 190 BMs with deep pile foundations is already installed and the first measurement campaign was concluded. The accuracies obtained are those of first-order levelling works. 相似文献
17.
Armando Majorana 《Celestial Mechanics and Dynamical Astronomy》1981,25(3):267-270
In this paper we study a particular four-body problem: three bodies revolve around their center of mass in circular orbits under the influence of their mutual gravitational attraction, while a fourth body moves in the plane defined by the three bodies but non influencing their motion. The linear stability of the eight equilibrium points is studied, and it is found that it depends on the values of the masses. 相似文献
18.
Roberto Stanley Molina–Garza Jim Pindell Diego Villagómez 《International Geology Review》2020,62(4):415-420
ABSTRACTWe discuss the 2018 publication that reports petrographic, heavy mineral data, mineral chemistry, and zircon geochronology for Oligocene sandstones in the Cerro Pelón area in southern Mexico Sureste basin. As the title of their paper says, the goal of their study is to establish the source (s) of the voluminous Cenozoic section in this region, reaching several kilometres in thickness and important as a petroleum system. These authors conclude that Oligocene sandstones of La Laja Formation were mostly sourced from eclogite- to greenschist-facies metasedimentary, metaigneous, and ultramafic rocks of the Guatemala suture complex. Minor contributions from the Chiapas Massif Complex, exposed directly to the south ~60 km of the Cerro Pelón area, were also suggested by the authors. They thus conclude that the Palaeogene stratigraphic record in southeastern Mexico was mostly controlled by the development of the Caribbean–North America plate boundary rather than by orogenic processes at the Pacific margin of North America. Presently, we do not agree with the conclusions of Ortega Flores and colleagues who studied the Cerro Pelón section, thus some discussion is required. Serpentinite bearing Nanchital Conglomerate is well exposed in the Cerro Pelón area, and high- to low-grade metamorphic rocks experienced an uplift in the vicinity of the Cerro Pelón area at the time of deposition of the La Laja Formation. We believe the data are better explained by multiple local sources in southern and eastern Oaxaca as well as sources to the south and southwest, which include the Cenozoic coastal batholith, the Grenvillean/Guichicovi basement complexes, the Chiapas Massif, the Mazatlán schist and other units in the Cuicateco Belt, as well as the Mesozoic cover of these areas (Todos Santos Formation, Cretaceous carbonate rocks, and Paleogene strata such as the Soyaló and Bosque Formations). 相似文献
19.
The salinity of interstitial water (i.e., the salinity of the free soil water) was examined at 11 equidistant stations along a transect on a Mississippi tidal marsh dominated byJuncus roemerianus andSpartina cynosuroides. Changes in the nearby surface water (e.g., bay water) were reflected in the changes in interstitial water salinity. The salinity of interstitial water was usually higher, varying between 2.5 and 15.8‰ from February 1975 through January 1976, than the salinity of the nearby surface water which ranged from 0.0 to 11.5‰. Following a long period of high salinity in the bay and sound (exceeding 14‰), the salinity of the interstitial water increased to a maximum of 16.8‰ in October. The salinity increased as the distance of the sampling station from the source of the flood water increased. Mean interstitial wate salinity across the marsh studied was within 10‰ which did not seem to influence the marsh plant zonation occurring on the marsh. 相似文献
20.
Armando Manzali Andrea De Luca Patrizia A. Caraveo 《Astrophysics and Space Science》2007,308(1-4):601-605
We report on our analysis of two XMM-Newton observations of the Vela pulsar performed in December 2000 (total exposure time:
96.5 ks). We succeeded in resolving the pulsar spectrum from the surrounding bright nebular emission taking advantage both
of the accurate calibration of the EPIC point spread function and of the Chandra/HRC surface brightness map of the nebula.
This made it possible to assess to pulsar spectral shape disentangling its thermal and non-thermal components. Exploiting
the photon harvest, we have also been able to perform a phase-resolved study of the pulsar emission.
相似文献