Heavy metals in sediments of the Tecate River, Mexico   总被引：1，自引：0，他引：1  

F. T. Wakida  D. Lara-Ruiz  J. Temores-Peña  J. G. Rodriguez-Ventura  C. Diaz  E. Garcia-Flores 《Environmental Geology》2008,54(3):637-642

Ten sites along the Tecate River, Mexico were sampled to evaluate the cadmium, lead, nickel and chromium concentrations in sediments. The result shows contamination for cadmium in most of the sites, where two sites were class 4 (polluted to strongly polluted) according to geoaccumulation index proposed by Muller. Two sites were found polluted for all the heavy metals analyzed (Cr, Cd, Pb and Ni), indicating the effect of anthropogenic activities. A correlation between Ni and Cd concentration had been found indicating a common source. These metals are usually used in electroplating industry. The results of this study can be used for decision makers to prioritize measures to control the pollution for these metals.  相似文献   

The importance of bioturbation to continental slope sediment structure and benthic processes off Cape Hatteras, North Carolina     

Robert J. Diaz  G. Randy Cutter  Donald C. Rhoads 《Deep Sea Research Part II: Topical Studies in Oceanography》1994,41(4-6)

Even though the continental slope off Cape Hatteras has sediment accumulation rates on the order of 1 cm/year, large areas of soft sediment are intensively reworked by infaunal organisms. Primary sedimentary structures have been completely replaced with biogenic structures. Surface sedimentary structures are dominated by the bioturbational activities of a deep burrowing infauna (to at least 30 cm). The layer actively mixed by the benthos, as evidenced by sediment profile and X-ray images, is estimated to range from 5 to 20 cm, with the residence time for particles within the surface mixed layer ranging from about 4.5 to 18 years. The biological mixing parameter (G) ranges from 0.4 to 5.5, which indicates moderate to strong biological mixing relative to accumulation and strata formation. Bioturbation contributes to the dynamic forces affecting the surface sediments by decreasing compaction of sediment layers and dilating sediment fabrics by sediment mixing, and introducing large water-filled burrows and voids to subsurface sediments. The sediment profile images captured numerous subsurface feeding voids, and worms in the process of making deep burrows, many of which extended below the 5 to 10 cm average depth of the apparent color redoxpotential discontinuity layer. High rates of accumulation of organic-rich sediment lead to high standing stocks of benthos and intensive feeding/burrowing activity that result in organic rich stratagraphic sequences that are thoroughly mixed. Cape Hatteras is a apparent focusing point for the transport of shallow water sediments to the deep sea. Sediments across other areas of the continental slope just 100's of kilometers south of Cape Hatteras are not as thoroughly mixed or biologically active.  相似文献   

Foraminifera from the continental slope off Cape Hatteras, North Carolina     

G. Randy Cutter Jr  Robert J. Diaz  John Lee 《Deep Sea Research Part II: Topical Studies in Oceanography》1994,41(4-6)

The recent benthic meiofaunal foraminiferal assemblage from the continental slope (590-2 003 m) off Cape Hatteras, North Carolina exhibits high species richness and evenness, moderate diversity values, and lacks numerically dominant species. The preserved planktic assemblage has relatively low species richness, high evenness, low diversity, and a few numerically dominant species. Approximately 9% of the benthic species are those that typically live within continental shelf depth ranges. The benthic assemblage abundances and diversities do not follow depth patterns or geophysical characteristics. No biogeographic boundary can be described within the study area for meiofaunal foraminifera. Oxygen limitation does not appear to be a factor affecting the benthos of the North Carolina continental slope based upon the community structure of the benthic foraminifera, if total assemblage is assumed to reflect the recently living community. The high carbonate content of sediments in the area may be explained by foraminiferal tests. Within the study area, the foraminiferal assemblages are uniform, and probably reflect relative consistency of primary environmental variables as well as dynamic downslope transport and high influx of material from the water column in the vicinity where the Gulf Stream and the Western Boundary Undercurrent cross.  相似文献   

An analysis of the time scales of variability in centuries-long enso-sensitive records in the last 1000 years   总被引：2，自引：0，他引：2  

Henry F. Diaz  Roger S. Pulwarty 《Climatic change》1994,26(2-3):317-342

We document the characteristic time scales of variability for seven climate indices whose time-dependent behavior is sensitive to some aspect of the El Niño/Southern Oscillation (ENSO). The ENSO sensitivity arises from the location of these long-term records on the periphery of the Indian and Pacific Oceans. Three of the indices are derived principally from historical sources, three others consist of tree-ring reconstructions (one of summer temperature, and the other two of winter rainfall), and one is an annual record of oxygen isotopic composition for a high-elevation glacier in Peru. Five of the seven indices sample at least portions of the Medieval Warm Period (~ A.D. 950 to 1250).Time series spectral analysis was used to identify the major time scales of variability among the different indices. We focus on two principal time scales: a high frequency band (~ 2–10 yr), which comprises most of the variability found in the modern record of ENSO activity, and a low frequency band to highlight variations on decadal to century time scales (11 <P < 150 yr). This last spectral band contains variability on time scales that are of general interest with respect to possible changes in large-scale air-sea exchanges. A technique called evolutive spectral analysis (ESA) is used to ascertain how stable each spectral peak is in time. Coherence and phase spectra are also calculated among the different indices over each full common period, and following a 91-yr window through time to examine whether the relationships change.In general, spectral power on time scales of ~ 2–6 yr is statistically significant and persists throughout most of the time intervals sampled by the different indices. Assuming that the ENSO phenomenon is the source of much of the variability at these time scales, this indicates that ENSO has been an important part of interannual climatic variations over broad areas of the circum-Pacific region throughout the last millennium. Significant coherence values were found for El Niño and reconstructed Sierra Nevada winter precipitation at ~ 2–4 yr throughout much of their common record (late 1500s to present) and between 6 and 7 yr from the mid-18th to the early 20th century.At decadal time scales each record generally tends to exhibit significant spectral power over different periods at different times. Both the Quelccaya Ice Cap ¹⁸O series and the Quinn El Niño event record exhibit significant spectral power over frequencies ~ 35 to 45 yr; however, there is low coherence between these two series at those frequencies over their common record. The Sierra Nevada winter rainfall reconstruction exhibits consistently strong variability at periods of ~ 30–60 yr.  相似文献   

Contens of Volume 59     

Henry F. Diaz  Jon K. Eischeid  Chris Duncan  Raymond S. Bradley 《Climatic change》2003,59(3):417-418

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Deep seismic exploration of the Iberian Microplate     

Juvenal Andres  David Marti  Ignacio Marzan  Imma Palomeras  Puy Ayarz  Fernando Simancas  DavidMartinez-Poyatos  Antonio Azor  Francisco Gonzalez-Lodeiro?  Jordi Diaz  Ramon Carbonel 《《地质学报》英文版》2018,92(Z1):11-11

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Secondary production within a seagrass bed (Zostera marina andRuppia maritima) in lower Chesapeake Bay     

Thomas J. Fredette  Robert J. Diaz 《Estuaries and Coasts》1990,13(4):431-440

Monthly sampling of a 140-ha seagrass bed in the lower Chesapeake Bay, Virginia, revealed that 13 numerically and trophically important species, representing about 20% of the total community densities over the year-long study period, accounted for the production of ≈42 g dry wt m^?2 yr^?1. This estimate is likely conservative due to our assumptions on voltinism and fixed size at maturity regardless of season for the species studied. The isopodErichsonella attenuata accounted for 17.6 g dry wt m^?2 yr^?1 or 42% of the calculated total production, while the portunid decapodCallinectes sapidus and the amphipodGammarus mucronatus each accounted for 7.7 g dry wt m^?2 yr^?1. The 10 remaining species (4 peracarids, 4 molluscs, and 2 decapods) each produced less than 2 g dry wt m^?2 yr^?1. Total seagrass-associated secondary production was estimated to equal or exceed 200 g dry wt m^?2yr^?1. By applying this estimate to the entire 140-ha grassbed, we projected that, on average, 4.8 metric tons dry wt of invertebrate standing stock and 55.9 metric tons of invertebrate production occur over the year.  相似文献   

Effects of hopper dredging and sediment dispersion,chesapeake bay   总被引：5，自引：0，他引：5  

Maynard Nichols  Robert J. Diaz  Linda C. Schaffner 《Environmental Geology》1990,15(1):31-43

Hopper dredging operations release suspended sediment into the environment by agitation of the bed and by discharge of overflow slurries. Monitoring of turbidity and suspended sediment concentrations in central Chesapeake Bay revealed two plumes: (1) an upper plume produced by overflow discharge and (2) a near-bottom plume produced by draghead agitation and rapid settling from the upper plume. The upper plume dispersed over 5.7 km² extending 5,200 meters form the discharge point. Redeposited sediment accumulated on channel flanks covering an area of 6.4 km² and reached a thickness of 19 cm. Altogether dredging redistributed into the environment an estimated 100,000 tons of sediment or 12 percent of the total material removed.Near-field concentrations of suspended sediment, less than 300 m from the dredge, reach 840 to 7,200 mg/L or 50 to 400 times the normal background level. Far-field concentrations (>300 m) are enriched 5 to 8 times background concentrations and persist 34 to 50 percent of the time during a dredging cycle (1.5 to 2.0 h). The overflow discharge plume evolves through three dispersion phases: (1) convective descent, (2) dynamic collapse, and (3) long-term passive diffusion (Clark and others 1971). The bulk of the material descends rapidly to the bottom during the convective descent phase, whereas the cloud that remains in suspension is dispersed partly by internal waves. Although suspended sediment concentrations in the water column exceed certain water quality standards, benthic communities survived the perturbation with little effect.  相似文献   

The eclogitized pillows of the Betic Ophiolitic Association: relics of the Tethys Ocean floor incorporated in the Alpine chain after subduction   总被引：1，自引：0，他引：1  

E. Puga  A. Diaz de  Federico A. Demant 《地学学报》1995,7(1):31-43

In the volcanic sequence of the Betic Ophiolitic Association (BOA) volcanic structures and textures are preserved in spite of being metamorphosed to the edogite facies. The original quenched glassy margins of the pillows and lava flows are still recognizable by the darker colour, fine-grained textures and scarcity of phenocrysts. The BOA eclogitized pillows have chemical compositions very similar to the basalts enriched in LIL elements erupted nowadays at the mid-oceanic ridges. Magmatism which generated the BOA most likely began under continental rift conditions at the Triassic-Jurassic boundary and continued under ocean-floor extensional conditions during the lower and middle Jurassic. In age and petrological characteristics this magmatism is equivalent to that of the western Tethys ophiolites. During the Late Cretaceous, due to the collision of African and Iberian Plates, the BOA ophiolites were subducted and underwent a metamorphism in the eclogite fades whose climax in the Lugros outcrop can be estimated at 650–700°C and about 20 kb.  相似文献   

A Method for Obtaining the Nuclear Component in Active Galaxies     

Miguel Sanchez Portal  Angeles I Diaz Beltran 《Astrophysics and Space Science》1998,263(1-4):119-122

We present a new method for the obtention of the nuclear component of active galatic nuclei, that relies on the convolution of a two-dimensional model of the host galaxy, based on seeing-free morphological parameters, with the seeing PSF. The procedure overcomes some limitations of the methods currently in use and does not assume that the nucleus is unresolved. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献