Studies of a contaminated brackish marsh in the Hackensack Meadowlands of Northeastern New Jersey: benthic communities and metal contamination     

Weis JS  Skurnick J  Weis P 《Marine pollution bulletin》2004,49(11-12):1025-1035

Cores taken from 16 stations within Eight Day Swamp, a highly contaminated marsh in the Hackensack Meadowlands, were analyzed for metal concentrations and for benthic community structure. Metal levels were compared with the benchmark ERM values, and expressed in terms of toxic units. Mercury was the most important metal in all the samples in terms of its contribution to the total toxic units. The overall abundance and taxa richness in the benthic community were associated with the height of the location relative to the tidal cycle, but were generally not significantly correlated with metal concentrations at the sites. Ordination of the communities showed that the communities that were low-lying (on the mudflat) were most similar to one another, and those that were higher up on the marsh were most similar to one another. However, diversity indices (Shannon-Wiener H' and Simpson's) were significantly associated with concentrations of the metals (except As) and with the sum of the toxic units at a station.  相似文献   

Conduit-vent structures and related proximal deposits in the Las Cañadas caldera, Tenerife, Canary Islands     

Carles Soriano  Inés Galindo  Joan Martí  John Wolff 《Bulletin of Volcanology》2006,69(2):217-231

The Las Cañadas caldera wall and the outer slopes of the caldera provide three-dimensional exposures of numerous proximal-welded fallout deposits and have been mapped in detail. As a result, some parts of the Ucanca and Guajara Formations of the stratigraphy of Martí et al. (1994) have been divided into members that correspond to individual eruptions. Mapping has also revealed the occurrence of conduit-vent structures associated with proximal-welded fallout deposits. Conduit-vent structures consist of an upper flaring area and a lower narrow conduit. Conduit-vent geometry and dimensions include cylindrical plugs and eruptive fissures steeply dipping towards the caldera depression and elongated vents. The flaring area can be rather asymmetric and is usually filled by down-vent rheomorphic flow of the proximal fallout deposit. The lower conduits are filled by lava plug, agglutination of juveniles onto conduit walls and dyke intrusion with eventual dome extrusion. The eruption dynamics of welded fallout deposits and magma fragmentation within the conduit are consistent with an evolution from explosive to effusive. In this context conduit flow regimes evolve from turbulent to annular flow in which the conduit is progressively choked, and laminar flow leading to the final conduit closure.  相似文献   

Injection and arrest of dykes: implications for volcanic hazards     

Agust Gudmundsson  Laura B. Marinoni  Joan Marti 《Journal of Volcanology and Geothermal Research》1999,88(1-2)

Dykes are the principal channels through which magma reaches the surface in volcanic eruptions. For this reason dykes observed in the field are commonly assumed to be feeders to lava flows. The actual proportion of dykes reaching the surface is, however, poorly known. In order to develop models for the purpose of estimating volcanic hazard, this proportion must be known. This follows because such models should not only consider the probability of dykes being injected from magma chambers during periods of unrest in the associated volcanoes, but also the probability of the injected dykes being arrested. This paper presents field data on several thousand dykes from Iceland and Tenerife (Canary Islands) indicating that many, and probably most, dykes become arrested at various crustal levels and never reach the surface to feed eruptions. Using the results of analytical and numerical models, it is shown that, for common loading conditions, the stress field in the vicinity of a magma chamber may favour the injection and propagation of dykes while the stress field at a certain distance from the chamber favours dyke arrest. This means that many dykes that are injected from the chamber propagate only for a very limited distance from the chamber to the point where they become arrested. The implication is that during periods of unrest in volcanoes, the probability of volcanic eruption is only a small fraction of the probability of dyke injection from the source magma chamber.  相似文献   

Intercomparison of the LASCO-C2, SECCHI-COR1, SECCHI-COR2, and Mk4 Coronagraphs     

Richard A. Frazin  Alberto M. Vásquez  William T. Thompson  Russell J. Hewett  Philippe Lamy  Antoine Llebaria  Angelos Vourlidas  Joan Burkepile 《Solar physics》2012,280(1):273-293

In order to assess the reliability and consistency of white-light coronagraph measurements, we report on quantitative comparisons between polarized brightness [pB] and total brightness [B] images taken by the following white-light coronagraphs: LASCO-C2 on SOHO, SECCHI-COR1 and -COR2 on STEREO, and the ground-based MLSO-Mk4. The data for this comparison were taken on 16?April 2007, when both STEREO spacecraft were within 3.1^° of Earth??s heliographic longitude, affording essentially the same view of the Sun for all of the instruments. Due to the difficulties of estimating stray-light backgrounds in COR1 and COR2, only Mk4 and C2 produce reliable coronal-hole values (but not at overlapping heights), and these cannot be validated without rocket flights or ground-based eclipse measurements. Generally, the agreement between all of the instruments?? pB values is within the uncertainties in bright streamer structures, implying that measurements of bright CMEs also should be trustworthy. Dominant sources of uncertainty and stray light are discussed, as is the design of future coronagraphs from the perspective of the experiences with these instruments.  相似文献   

Topographical controls on small‐volume pyroclastic flows     

Joan Martí  Domenico M. Doronzo  Dario Pedrazzi  Ferran Colombo 《Sedimentology》2019,66(6):2297-2317

Emplacement of small‐volume (<0·1 km³) pyroclastic flows is significantly influenced by topography. The Arico ignimbrite on Tenerife (Canary Islands) is a characteristic small‐volume pyroclastic flow deposit emplaced on high relief topography. The pyroclastic flow flowed down pre‐existing valleys on the southern slopes of the island. In proximal areas deep (up to 100 m) valleys acted as efficient conduits for the pyroclastic flow, which was mostly channelled; in this particular area the ignimbrite corresponds to a homogeneous, moderately welded deposit, consisting of flattened pumices in an abundant ashy matrix with a relatively low lithic fragment content. In intermediate zones significant changes occur in the steepness of the slope and, although still channelled, here the pyroclastic flow was influenced by hydraulic jumps. In this area, two different units can be clearly distinguished in the ignimbrite: the lower unit is composed of a lithic‐rich ground‐layer deposit that formed at the turbulent, highly concentrated head of the flow; the upper unit consists of a well welded pumice‐rich deposit that occasionally reveals a basal layer formed by shearing with the lower part. This division into two units is maintained as far as distal areas near the present‐day coastline, where the slope is very gentle or null and the ignimbrite is not channelled. The ground layer is not found in distal areas. The ignimbrite here only consists of the upper unit, which is occasionally repeated due to a surging process provoked by the lower flow speed, as the pyroclastic flow spread out of the channelled zone. A theoretical model on how topography controlled the deposition of the Arico ignimbrite is derived by interpreting the observed lithological and sedimentological variations in terms of changes in topography and bedrock morphology. This new model is of general applicability and will help to explain other deposits of similar characteristics.  相似文献   

Subsidence and thermal history of an inverted Late Jurassic‐Early Cretaceous extensional basin (Cameros,North‐central Spain) affected by very low‐ to low‐grade metamorphism          下载免费PDF全文

Silvia Omodeo‐Salé  Ramon Salas  Joan Guimerà  Robert Ondrak  Ramon Mas  José Arribas  Isabel Suárez‐Ruiz  Luis Martinez 《Basin Research》2017,29(Z1):156-174

The Cameros Basin (North Spain) is a Late Jurassic‐Early Cretaceous extensional basin, which was inverted during the Cenozoic. It underwent a remarkable thermal evolution, as indicated by the record of anomalous high temperatures in its deposits. In this study, the subsidence and thermal history of the basin is reconstructed, using subsidence analysis and 2D thermal modelling. Tectonic subsidence curves provide evidence of the occurrence of two rapid subsidence phases during the syn‐extensional stage. In the first phase (Tithonian‐Early Berriasian), the largest accommodation space was formed in the central sector of the basin, whereas in the second (Early Barremian‐Early Albian), it was formed in the northern sector. These rapid subsidence phases could correspond to relevant tectonic events affecting the Iberian Plate at that time. By distinguishing between the initial and thermal subsidence and defining their relative magnitudes, Royden's (1986) method was used to estimate the heat flow at the end of the extensional stage. A maximum heat flow of 60–65 mW/m² is estimated, implying only a minor thermal disturbance associated with extension. In contrast with these data, very high vitrinite reflectance, anomalously distributed in some case with respect to the typical depth‐vitrinite reflectance relation, was measured in the central‐northern sector of the basin. Burial and thermal data are used to construct a 2D thermal basin model, to elucidate the role of the processes involved in sediment heating. Calibration of the thermal model with the vitrinite reflectance (%Ro) and fluid inclusion (FI) data indicates that in the central and northern sectors of the basin, an extra heat source, other than a typical rift, is required to explain the observed thermal anomalies. The distribution of the %Ro and FI values in these sectors suggests that the high temperatures and their distribution are related to the circulation of hot fluids. Hot fluids were attributed to the hydrothermal metamorphic events affecting the area during the early post‐extensional and inversion stages of the basin.  相似文献   

The Beach Crowding Index: A Tool for Assessing Social Carrying Capacity of Vulnerable Beaches     

David Serrano Giné  Joan Jurado Rota  María Yolanda Pérez Albert  Carla Bonfill Cerveró 《The Professional geographer》2018,70(3):412-422

The aim of this article is to introduce the Beach Crowding Index (BCI), a procedure to assess the social carrying capacity of vulnerable beaches. The study uses the people at one time (PAOT) approach and data gathered weekly throughout the bathing season regarding the number of beachgoers in 100 m² cells of the beach to assess how many beachgoers it can comfortably hold. The procedure is based on fieldwork, interviews with beachgoers, and geographic information system (GIS) analysis and has been tested on four beaches in protected areas on the Spanish Mediterranean coast. On a scale from 0 to 4, minimum scores throughout the bathing season are 0.7 and maximum 3.7, although results showed wide variation between the beaches, the section of the beach, and the time of day. This study suggests that determining the location of beachgoers and collecting a long-term series of data is fundamental to assessing social carrying capacity and that the BCI procedure can be used for a large number of applications.  相似文献   

Heavy metals in particulate matter and sediments in the southern Barcelona sedimentation system (North-western Mediterranean)     

Pere Puig  Albert Palanques  Joan A. Sanchez-Cabeza  Pere Masqu 《Marine Chemistry》1999,63(3-4)

Concentrations of selected heavy metals (Cr, Cu, Ni, Pb and Zn) from surface sediments, suspended particulate matter and settling particles in the southern Barcelona continental margin were studied in order to evaluate the environmental impact of the anthropogenic metals discharged by the Llobregat River in this Mediterranean area. The temporal variation of heavy metals discharged by this river onto the continental shelf is clearly related to the river water flow. Part of the fine sediment and associated heavy metals transported by the Llobregat River during periods of low river flow accumulate on the river bed, and they are totally removed and discharged onto the Barcelona continental shelf during sporadic river water flow increases. Metals produce significant anomalies of chromium (×2.5), copper (×3.4) and zinc (×3.7) in the surface sediments of the Llobregat prodelta and tend to be transported along the continental shelf following the mean flow. Metals associated with the finest suspended flocs transferred to the slope are controlled by the shelf-slope density front and are transported along slope by the general geostrophic current, instead of accumulating and becoming concentrated in the slope bottom sediments. Settling particulate matter collected in sediment traps on the Barcelona continental slope offshore of the shelf-slope front shows low heavy metal concentrations except in a few sediment trap samples that are significantly metal-enriched in chromium (×4.5) and zinc (×6.8). This enrichment is associated with very short and sporadic river flow increases and is only recorded inside the Foix submarine canyon, which acts as a preferential conduit for the shelf-slope sediment transfer.  相似文献   

Effect of storms during drought on post‐wildfire recovery of channel sediment dynamics and habitat in the southern California chaparral,USA          下载免费PDF全文

Joan L. Florsheim  Anne Chin  Alicia M. Kinoshita  Samira Nourbakhshbeidokhti 《地球表面变化过程与地形》2017,42(10):1482-1492

Current global warming projections suggest a possible increase in wildfire and drought, augmenting the need to understand how drought following wildfire affects the recovery of stream channels in relation to sediment dynamics. We investigated post‐wildfire geomorphic responses caused by storms during a prolonged drought following the 2013 Springs Fire in southern California (USA), using multi‐temporal terrestrial laser scanning and detailed field measurements. After the fire, a dry‐season dry‐ravel sediment pulse contributed sand and small gravel to hillslope‐channel margins in Big Sycamore Creek and its tributaries. A small storm in WY 2014 generated sufficient flow to mobilize a portion of the sediment derived from the dry‐ravel pulse and deposited the fine sediment in the channel, totaling ~0.60 m³/m of volume per unit length of channel. The sediment deposit buried step‐pool habitat structure and reduced roughness by over 90%. These changes altered sediment transport characteristics of the bed material present before and after the storm; the ratio of available to critical shear stress (τ_o/τ_c) increased by five times. Storms during WY 2015 contributed additional fine sediment from tributaries and lower hillslopes and hyperconcentrated flow transported and deposited additional sediment in the channel. Together these sources delivered sediment on the order of six times that in 2014, further increasing τ_o/τ_c. These storms during multi‐year drought following wildfire transformed channel dynamics. The increased sediment transport capacity persisted during the drought period characterized by the longer residence time of relatively fine‐grained post‐fire channel sedimentation. This contrasts with wetter years, when post‐fire sediment is transported from the fluvial system during the same season as the post‐fire sediment pulse. Results of this short‐term study highlight the complex and substantial effects of multi‐year drought on geomorphic responses following wildfire. These responses influence pool habitat that is critical to longer‐term post‐wildfire riparian ecosystem recovery. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Combining EGM2008 and SRTM/DTM2006.0 residual terrain model data to improve quasigeoid computations in mountainous areas devoid of gravity data   总被引：6，自引：4，他引：2  

C. Hirt  W. E. Featherstone  U. Marti 《Journal of Geodesy》2010,84(9):557-567

A global geopotential model, like EGM2008, is not capable of representing the high-frequency components of Earth’s gravity field. This is known as the omission error. In mountainous terrain, omission errors in EGM2008, even when expanded to degree 2,190, may reach amplitudes of 10 cm and more for height anomalies. The present paper proposes the utilisation of high-resolution residual terrain model (RTM) data for computing estimates of the omission error in rugged terrain. RTM elevations may be constructed as the difference between the SRTM (Shuttle Radar Topography Mission) elevation model and the DTM2006.0 spherical harmonic topographic expansion. Numerical tests, carried out in the German Alps with a precise gravimetric quasigeoid model (GCG05) and GPS/levelling data as references, demonstrate that RTM-based omission error estimates improve EGM2008 height anomaly differences by 10 cm in many cases. The comparisons of EGM2008-only height anomalies and the GCG05 model showed 3.7 cm standard deviation after a bias-fit. Applying RTM omission error estimates to EGM2008 reduces the standard deviation to 1.9 cm which equates to a significant improvement rate of 47%. Using GPS/levelling data strongly corroborates these findings with an improvement rate of 49%. The proposed RTM approach may be of practical value to improve quasigeoid determination in mountainous areas without sufficient regional gravity data coverage, e.g., in parts of Asia, South America or Africa. As a further application, RTM omission error estimates will allow refined validation of global gravity field models like EGM2008 from GPS/levelling data.  相似文献