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21.
22.
While many studies of non-native species have examined either soft-bottom or hard-bottom marine communities, including artificial structures at docks and marinas, formal comparisons across these habitat types are rare. The number of non-indigenous species (NIS) may differ among habitats, due to differences in species delivery (trade history) and susceptibility to invasions. In this study, we quantitatively compared NIS to native species richness and distribution and examined community similarity across hard-bottom and soft-sediment habitats in San Francisco Bay, California (USA). Benthic invertebrates were sampled using settlement panels (hard-bottom habitats) and sediment grabs (soft-bottom habitats) in 13 paired sites, including eight in higher salinity areas and five in lower salinity areas during 2 years. Mean NIS richness was greatest in hard-bottom habitat at high salinity, being significantly higher than each (a) native species at high salinity and (b) NIS richness at low salinity. In contrast, mean NIS richness in soft-bottom communities was not significantly different from native species richness in either high- or low-salinity waters, nor was there a difference in NIS richness between salinities. For hard-bottom communities, NIS represented an average of 79% of total species richness per sample at high salinity and 78% at low salinity, whereas the comparable values for soft bottom were 46 and 60%, respectively. On average, NIS occurred at a significantly higher frequency (percent of samples) than native species for hard-bottom habitats at both salinities, but this was not the case for soft-bottom habitats. Finally, NIS contributed significantly to the existing community structure (dissimilarity) across habitat types and salinities. Our results show that NIS richness and occurrence frequency is highest in hard-bottom and high-salinity habitat for this Bay but also that NIS contribute strongly to species richness and community structure across each habitat evaluated. 相似文献
23.
Ingrid M.Nedel Reinhardt A.Fuck Amarildo S.Ruiz Gerardo R.Matos-Salinas Alanielson da C.D.Ferreira 《地学前缘(英文版)》2021,12(6):277-293
We present new U-Pb zircon and monazite ages from the Sunsas belt granitic magmatism in Bolivia,SW Amazonian Craton.The geochronological results revealed four major magmatic events recorded along the Sunsas belt domains.The older igneous event formed a granitic basement coeval to the Rio Apa Terrane(1.95-1.85 Ga)in the southern domain.The second magmatic episode is represented by 1.68 Ga granites associated to the Paraguá Terrane(1.69-1.66 Ga)in the northern domain.The 1.37-1.34 Ga granites related to San Ignacio orogeny represent the third and more pervasive magmatic event,recorded throughout the Sunsas belt.Moreover,magmatic ages of~1.42 Ga revealed that the granitogenesis asso-ciated to the Santa Helena orogeny also affected the Sunsas belt,indicating that it was not restricted to the Jauru Terrane.Lastly,the 1.10-1.04 Ga youngest magmatism was developed during the Sunsas oro-geny and represents the final magmatic evolution related to Rodinia assembly.Likewise,the 1.95-1.85 and 1.68 Ga inherited zircon cores obtained in the~1.3 Ga and 1.0 Ga granite samples suggest strong par-tial melting of the Paleoproterozoic sources.The 1079±14 Ma and 1018±6 Ma monazite crystallization ages can be correlated to the collisional tectono-thermal event of the Sunsas orogeny,associated to reac-tions of medium-to high-grade metamorphism.Thus,the Sunsas belt was built by heterogeneous 1.95-1.85 Ga and 1.68 Ga crustal fragments that were reworked at 1.37-1.34 Ga and 1.10-1.04 Ga related to orogenic collages.Furthermore,the 1.01 Ga monazite age suggests that granites previously dated by zir-con can bear evidence of a younger thermal history.Therefore,the geochronological evolution of the Sunsas belt may have been more complex than previously thought. 相似文献
24.
Wendell A. Duffield Joaquin Ruiz James D. Webster 《Journal of Volcanology and Geothermal Research》1995,69(3-4)
The Bishop Tuff, a well known Quaternary high-silica rhyolite in east-central California, is widely considered the type example of a vertically and monotonically zoned pyroclastic deposit that represents zoning in the source magma reservoir, inverted during the process of pyroclastic emplacement. However, the deposit of plinian pumice, which forms the base of the Bishop Tuff and represents the initial 10% or so of all magma erupted during the event that produced the Bishop Tuff, contains features at odds with monotonie zoning for the reservoir. Relative to overlying ignimbrite, the plinian deposit contains a reversal in trace-element zoning. Moreover, the 87Sr/86Sr is significantly higher than that in overlying ignimbrite (about 0.7084 vs 0.7064), and melt inclusions trapped in quartz phenocrysts exhibit notable variability of trace-element concentrations, even within a single host crystal (e.g., U: 10.77 to 8.91 ppm).These data have been previously interpreted as due to processes of chemical fractionation and evolution operating within a magma system closed to chemical interactions with its roof rocks. For example, the reversal in trace-element zoning has been explained by the first-erupted magma being erupted from somewhat below the top of a monotonically zoned reservoir. However, we submit that the reversed zoning and other above-noted features can be explained equally well as consequences of minor assimilation of roof rocks into a magma reservoir that was erupted from the top down.The basal part of the Bishop Tuff exhibits extreme concentrations and depletions of trace elements, relative to the average composition of crustal rocks. For example, the upward decrease of Sr in the Bishop magma reservoir (downward decrease in the ignimbrite) results in concentrations as low as 2–4 ppm. Because of the attendant ‘chemical leverage’, assimilation of < 1 wt.% of Sierra Nevada batholith rocks typical of the area could readily reverse an ‘uncontaminated’ Sr (and other trace elements) trend of zoning and could also substantially raise 87Sr/86Sr. Small-scale trace-element variability in the uppermost part of the Bishop magma reservoir, as recorded by the above-mentioned melt inclusions, may simply reflect melt heterogeneity produced by the process of assimilation. 相似文献
25.
Ruiz F 《Marine pollution bulletin》2001,42(6):482-490
The impact of river-transported metal pollution and industrial wastes on the metal distribution (Cr, Cu, Zn, Pb) in estuarine sediments was studied in the southwestern Spanish estuaries. Intertidal and subtidal surface sediments of the Tinto-Odiel Estuary are very highly polluted by heavy metals, with geoaccumulation indices up to 4 in the three sedimentary environments studied (channel, channel border and salt marsh). The single exception is the Punta Umbria channel, very protected from the point sources by salt marsh deposits and hydraulic processes. In the remaining two estuaries, pollution (Pb, Cu) was only significant near the harbour situated in the Piedras river mouth, whereas very low values were found in the Guadiana Estuary. In these last rivers, the enrichment factor increases from the channel to the salt marsh sediments. 相似文献
26.
Electro-osmosis (EO), the movement of water through porous media in response to an electric field, offers a means for extracting contaminated ground water from fine-grained sediments, such as clays, that are not easily amenable to conventional pump-and-treat approaches. The EO-induced water flux is proportional to the voltage gradient in a manner analogous to the flux dependence on the hydraulic gradient under Darcy's law. The proportionality constant, the soil electro-osmotic conductivity or keo , is most easily measured in soil cores using bench-top tests, where flow is one-dimensional and interfering effects attributable to Darcy's law can be directly accounted for. In contrast, quantification of EO fluxes and keo in the field under deployment conditions can be difficult because electrodes are placed in ground water wells that may be screened across a heterogeneous mixture of lithologies. As a result, EO-induced water fluxes constitute an approximate radial flow system that is superimposed upon a Darcy flow regime through permeable pathways that may or may not be coupled with hydraulic head differences created by the EO-induced water fluxes. A single well comparative tracer test, which indirectly measures EO fluxes by comparing wellbore tracer dilution rates between background and EO-induced water fluxes, may provide a means for routinely quantifying the efficacy of EO systems in such settings. EO fluxes measured in field tests through this technique at a ground water contamination site were used to estimate a mean keo value through a semianalytic line source model of the electric field. The resulting estimate agrees well with values reported in the literature and with values obtained with bench-top tests conducted on a soil core collected in the test area. 相似文献
27.
The Kamoto deposit consists of two stratiform orebodies separated by a barren sedimentary unit. It is a copper and cobalt deposit, the main features of which are summarized in the first part of the paper. Above the upper orebody, dolostone beds are found, where pyrite is the only sulfide mineral. This pyrite was investigated with the help of a microprobe: all idiomorphic grains were found to be surrounded by a well-defined rim, where the cobalt content reaches 4%; framboidal grains were also found to be heterogeneous with respect to cobalt. The distribution of nickel and copper is described. These observations afford one more evidence that post-depositional events played an important role in the Mine Series of Katanga, especially with regard to heavy metals geochemistry.
Resume Le gisement de Kamoto est constitué de deux corps minéralisés stratiformes séparés par une unité sédimentaire stérile. C'est un gisement de cuivre et de cobalt dont les principales caractéristiques sont brièvement résumées. Audessus du corps minéralisé supérieur, on trouve des couches de dolomie, où la pyrite est le seul sulfure présent. Cette pyrite a été étudiée à l'aide d'une microsonde: tous les grains idiomorphes y sont entourés d'une bordure bien nette, où la teneur en cobalt atteint 4%; les grains d'apparence framboïdale sont également hétérogènes au point de vue de leur teneur en cobalt. La distribution du nickel et du cuivre est décrite. Ces observations apportent um témoignage supplémentaire de l'importance des événements postérieurs au dépôt dans la «Série des Mines» katangaise, tout spécialement en ce qui concerne la géochimie des métaux lourds. Elles démontrent que le «système» constitué par la roche sédimentaire est resté ouvert pendant un certain temps après la sédimentation.相似文献
28.
L.?Rosales HozEmail author A.?Carranza Edwards P.?Carvajal Romero C.?Mendez Jaime M.?E.?Ruiz Santoyo 《Environmental Geology》2003,44(7):790-798
The lower reaches of the Coatzacoalcos River in southeast Mexico is an area of intense industrial development. The physico-chemical characteristics of the area have exhibited differences over the years. Apparently from the associated outcroppings of limestone in the Uxpanapa River Basin, the major elements that are dissolved show higher concentrations of Ca, Mg and HCO3– in the waters supplied by this river. The water in the Calzadas River contains high concentrations of Ca, SO4 and HCO3– that are associated with the saline domes crossed by this river. Due to industrial discharges, the sulfate concentration is very high in the water and air during April. Nitrate concentration diminishes with salinity. Higher nitrate as well as nitrite and ammonia levels are present during flood season. Phosphate concentration, associated with high oxygen levels, is higher in January. Zn, Cu and Cr are higher during the dry season (April) when dilution is minimal and low levels of TOC are present. The smaller concentrations of Zn and Cu observed in January are associated with high TOC values in water. The lower levels of Cr present in August are associated with high amounts of suspended matter. Pajaritos Lagoon and Teapa-L, with large industrial discharges, have the highest nutrient and dissolved metal concentrations in the area. Air particles smaller than 2.5 m contain Fe, V, Ti, Cu, Zn, and high amounts of S. These anomalous concentrations of sulfates and metals are attributed to anthropogenic sources. 相似文献
29.
The proposed existence of magnetic lineations in the Terra Cimmeria and Terra Sirenum regions of Mars was initially explained by Earth-like sea-floor spreading. Here we argue instead that these lineations could have been formed at a convergent plate margin through collision and accretion of terranes. A similar process produced banded magnetic anomalies, similar in geometry and even in size to those in Earth's North American Cordillera. Because only sparse and generally weak anomalies have been detected in the martian northern lowlands, which could constitute an analog to the terrestrial oceanic crust, it is possible that the magnetic field stopped its activity while crustal recycling was still active in Mars. 相似文献
30.
Andrs Folguera Antonio Introcaso Mario Gimnez Francisco Ruiz Patricia Martinez Cynthia Tunstall Ezequiel García Morabito Víctor A. Ramos 《Tectonophysics》2007,439(1-4):129-147
The western retroarc of the Southern Andes between 38° and 40° S is formed by a NNW-elongated ridge not associated with stacked thrust sheets. On the contrary, during the last 4–3 Ma this ridge was affected by extensional deformation, regional uplift and related folding on a very broad scale. Receiver function analysis shows that the drainage divide area and adjacent retroarc lie over an attenuated crust. Expected crustal thickness at these latitudes is around 38 km, whereas in this part of the retroarc the thickness is less than 32 km. The causes for such attenuation have been linked to a moderate steepening of the subducted Nazca plate beneath the South American plate, which is suggested by a westward shift and narrowing of the magmatic arc during the last 4 to 5 Ma. Gravimetric studies show that the upper plate did not react homogeneously to slab steepening, but ancient sutures and lithospheric discontinuities deeply buried under Mesozoic to Cenozoic sequences in the retroarc were locally reactivated. These processes resulted in an asthenospheric anomaly that correlates at the surface with the area of Pliocene to Quaternary doming, widespread extension and three radial troughs. Two of the troughs have accommodated substantial amounts of extension, but the third was probably aborted at an early stage. Moreover, the presence of an anomalous concentration of calderas and large volcanic centers over the proposed asthenospheric anomaly, and their age distribution, may indicate minor migration of the asthenospheric anomaly between 4 and 2 Ma through the western South American plate. 相似文献