Hydrogeochemical characteristics of central Jianghan Plain, China   总被引：2，自引：0，他引：2  

Yu Zhou  Yanxin Wang  Yilian Li  François Zwahlen  Julie Boillat 《Environmental Earth Sciences》2013,68(3):765-778

The central Jianghan Plain is the semi-closed basin in the middle reaches of Yangtze River. A total of 78 water samples targeting groundwater were collected from 75 sites in this study site, the area between Yangtze River and Han River, including rivers and lakes for temperature, pH, electrical conductivity (EC), total dissolved solids (TDS) and ion composition measurements. Correlation matrix was used to assess the geochemical and anthropogenic processes. The most confined groundwater was grouped into HCO₃–Ca–Mg, while phreatic groundwater and surface water had a more diversified hydrochemistry. The spatial variation in overall water quality as well as comparison with WHO (World Health Organization) standards for drinking water is illustrated. Mn, As and NO₃ ^? concentrations were found to exceed the allowable limits for drinking water of WHO guidelines, and they also show remarkable spatial variations. Abnormally high nitrate concentration, up to 150–190 mg/l, was found only in phreatic groundwater, which suggested that the nitrate pollution might be caused by agricultural activities. The present study may be helpful in further studies concerning water quality issues in this area where groundwater is a vital source for drinking and other activities.  相似文献   

Simulation of the 1980 eruption of Mount St. Helens using the ash-tracking model PUFF     

Julie Fero  Steven N. CareyJohn T. Merrill 《Journal of Volcanology and Geothermal Research》2008

The dispersal of volcanic ash from the May 18, 1980 eruption of Mount St. Helens (MSH) has been simulated using the Lagrangian ash-tracking model PUFF. Previous applications of the model were limited to smaller, short-lived eruptions with ash dispersal occurring mainly within the troposphere. Two high-resolution atmospheric reanalysis datasets (ERA-40 and NCEP/NCAR-40) allowed MSH ash cloud dispersal to be simulated up to 30 km elevation. The 1980 eruption was divided into two distinct eruptive phases, (1) an initial, relatively short-lived blast/surge phase that injected ash up to 30 km and (2) a subsequent nine-hour plinian phase that maintained an average eruption column height of 16 km. Using PUFF, the two phases of the MSH eruption were modeled separately based on a range of individual input parameters and then combined to produce an integrated simulation of the entire eruption. The trajectory and areal extent of the modeled atmospheric ash cloud best match the actual distribution of MSH ash when input parameters are set to values inferred from satellite and radar data collected on May 18, 1980. The prevailing wind field exerts the strongest control on the advection and ultimate position of the modeled ash cloud, making the maximum column height and the vertical distribution of ash the most sensitive of the PUFF input parameters for this event. The results indicate that the PUFF model works well at simulating the dispersal of ash injected well into the lower stratosphere from a moderate, relatively long-lived eruption, such as MSH. However, attempts to use PUFF to recreate some granulometric aspects of the MSH fallout deposit, such as the maximum particle size as a function of distance from source, were not successful. PUFF consistently predicts much greater fallout distances for small ash particles (< 500 µm) than actually observed in the MSH deposit. The effective settling velocities used by the PUFF model appear to be too slow to accurately predict fallout distances of small ash particles. As a consequence the PUFF model may overestimate the duration of ash loading in the atmosphere associated with the distal fine ash component of explosive eruptions.  相似文献   

Hydrochemical behaviour of dissolved nitrogen and carbon in a headwater stream of the Canadian Shield: relevance of antecedent soil moisture conditions     

Julie M. L. Turgeon  François Courchesne 《水文研究》2008,22(3):327-339

This paper examines the impact of contrasting antecedent soil moisture conditions on the hydrochemical response, here the changes in dissolved nitrogen (NO₃^?, NH₄⁺ and dissolved organic nitrogen (DON)) and dissolved organic carbon (DOC) concentrations, of a first‐order stream during hydrological events. The study was performed in the Hermine, a 5 ha forested watershed of the Canadian Shield. It focused on a series of eight precipitation events (spring, summer and fall) sampled every 2 or 3 h and showing contrasted antecedent moisture conditions. The partition of the eight events between two groups (dry or wet) of antecedent moisture conditions was conducted using a principal component analysis (PCA). The partition was controlled (first axis explained 86% of the variability) by the antecedent streamflow, the streamflow to precipitation ratio Q/P and by the antecedent groundwater depth. The mean H⁺, NO₃^?, NH₄⁺, total dissolved nitrogen and DOC concentrations and electrical conductivity values in the stream were significantly higher following dry antecedent conditions than after wetter conditions had prevailed in the Hermine, although the temporal variability was high (17 to 138%). At the event scale, a significantly higher proportion of the changes in DON, NO₃^?, and DOC concentrations in the stream was explained by temporal variations in discharge compared with the seasonal and annual scales. Two of the key hydrochemical features of the dry events were the synchronous changes in DOC and flow and the frequent negative relationships between discharge and NO₃^?. The DON concentrations were much less responsive than DOC to changes in discharge, whereas NH was not in phase with streamflow. During wet events, the synchronicity between streamflow and DON or NO₃^? was higher than during dry events and discharge and NO₃^? were generally positively linked. Based on these observations, the hydrological behaviour of the Hermine is conceptually compatible with a two‐component model of shallow (DON and DOC rich; variable NO₃^?) and deep (DON and DOC poor; variable NO₃^?) subsurface flow. The high NO₃^? and DOC levels measured at the early stages of dry events reflected the contribution from NO₃^?‐rich groundwaters. The contribution of rapid surface flow on water‐repellent soil materials located close to the stream channel is hypothesized to explain the DOC levels. An understanding of the complex interactions between antecedent soil moisture conditions, the presence of soil nutrients available for leaching and the dynamics of soil water flow paths during storms is essential to explain the fluxes of dissolved nitrogen and carbon in streams of forested watersheds. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Bacterial dominance of phototrophic communities in a High Arctic lake and its implications for paleoclimate analysis   总被引：1，自引：1，他引：0  

Dermot Antoniades  Julie Veillette  Marie-Josée Martineau  Claude Belzile  Jessica Tomkins  Reinhard Pienitz  Scott Lamoureux  Warwick F. Vincent 《Polar Science》2009,3(3):147-161

The phototrophic communities in meromictic, perennially ice-covered Lake A, on Ellesmere Island in the Canadian High Arctic, were characterized by pigment analysis using high performance liquid chromatography. Samples were taken to determine the vertical changes down the water column as well as a variation between years. These analyses showed that Lake A had distinct phototrophic communities in its oxic and anoxic layers. The pigment analyses indicated that phototrophic biomass in the upper, oxic waters was dominated by picocyanobacteria, while in the lower, anoxic layer photosynthetic green sulphur bacteria were dominant. Interannual variation in pigment concentrations was related to the penetration of photosynthetically active radiation in the water column, suggesting that light availability may be limiting the net accumulation of photosynthetic bacterial biomass in Lake A. Pigment analysis of the surface sediments indicated that deposition was dominated by the photosynthetic sulphur bacterial contribution. The sedimentary record of bacterial pigments in polar meromictic lakes offers a promising tool for the reconstruction of past changes in ice cover and therefore in climate.  相似文献   

On harbour siltation in the fresh-salt water mixing region     

Michel A.J. de Nijs  Johan C. Winterwerp  Julie D. Pietrzak 《Continental Shelf Research》2009

In this paper a novel series of field measurements are presented, which are the first to elucidate the processes influencing siltation in Botlek Harbour. Botlek Harbour is situated at the limit of saline water intrusion in the Rotterdam Waterway. Normally, after the ebb tide fresher river waters are found in the Rotterdam Waterway at the location of Botlek Harbour. On the flooding tide, the tip of the salt wedge is advected along the Rotterdam Waterway towards the mouth of Botlek Harbour. Hence on flood, a lock-exchange mechanism operates between Botlek Harbour and the Rotterdam Waterway. On the flood tide, when there is a supply of suspended particulate matter (SPM) associated with the presence of the estuarine turbidity maximum (ETM) at the mouth of the harbour, the survey data show exchange of SPM into the harbour. This lock-exchange process is found to be the dominant cause for SPM transport into the harbour. This is further substantiated by an analysis of the mass transport mechanisms. In this analysis, the vertical profiles of the instantaneous velocity, salinity and SPM concentration fields, recorded during the surveys, were decomposed into advective and dispersive transport components. The results of this analysis indicate that the correlation between the lock-exchange mechanism on the flood tide with the availability of SPM for exchange and efficient trapping, dominate the total exchange of SPM (97%). Hence, the increase in measured near-bed SPM concentration within the harbour is ascribed to tidal advection of saline water and the ETM along the Rotterdam Waterway. Tidal advection controls the density difference between the estuary and harbour, as well as the availability of SPM for exchange at the entrance to Botlek Harbour. The location of the ETM at the tip of the salt wedge is a key factor in supplying SPM to Botlek Harbour. Consequently the timing of the availability of SPM at the mouth of the harbour needs to be considered in siltation studies. The survey data suggest that Botlek Harbour basin has a 100% trapping efficiency. Analysis of 5 months of data, from a measuring rig located within the harbour, show excursions of the limit of the salt wedge and ETM. These excursions are likely to affect siltation of upstream harbours. Salinity-induced density gradients control the transport and subsequent trapping of SPM in the estuary in close proximity to the harbour entrance, the exchange of SPM between the estuary and harbour, and the trapping of SPM in the harbour basin.  相似文献   

Isotopic and geochemical characterization of salinization in the shallow aquifers of a reclaimed subsiding zone: The southern Venice Lagoon coastland   总被引：3，自引：0，他引：3  

Julie C. Gattacceca  Christine Vallet-Coulomb  Adriano Mayer  Christelle Claude  Olivier Radakovitch  Enrico Conchetto  Bruno Hamelin   《Journal of Hydrology》2009,378(1-2):46-61

The coastal plain bordering the southern Venice Lagoon is a reclaimed lowland characterized by high subsidence rate, and ground level and water-table depth below sea level. In this agricultural region, where the surface hydrologic network is entirely artificially controlled by irrigation/drainage canals, salinization problems have long been encountered in soils and groundwaters. Here we use isotopic and geochemical tracers to improve our understanding of the origin of salinization and mineralization of the semi-confined aquifer (0–40 m), and the freshwater inputs to this hydrological system. Water samples have been collected at different seasons in the coastal Adriatic Sea, lagoon, rivers and irrigation canals, as well as in the semi-confined aquifer at depths between 12 and 35 m (14 boreholes), and in the first confined aquifer (three boreholes drilled between 40 and 80 m depth). Stable isotopes (δ¹⁸O and δD) and conductivity profiles show that direct saline intrusion from the sea or the lagoon is observed only in a restricted coastal strip, while brackish groundwaters are found over the entire topographic and piezometric depression in the centre of the study area. Fresh groundwaters are found only in the most western zone. The sharp isotopic contrast between the western and central regions suggests disconnected hydrological circulations between these two parts of the shallow aquifer. The border between these two regions also corresponds to the limits of the most strongly subsiding zone.Our results can be interpreted in terms of a four end-member mixing scheme, involving (1) marine water from the lagoon or the open sea, (2) alpine and pre-alpine regional recharge waters carried either by the main rivers Adige, Bacchiglione and Brenta (irrigation waters) or by the regional groundwater circulation, (3) local precipitation, and (4) evaporated waters infiltrated from the surface. Infiltration from the surface is also revealed by the stratification of the electrical conductivity profiles, showing that the brackish groundwaters are overlain by a shallow layer of less saline water all over the central depression. In the first confined aquifer, the groundwaters have isotopic compositions similar to the deep groundwaters of the Venetian confined aquifers (40–400 m depth). The isotopic data and the Br/Cl ratio show that the origin of the salinization of the phreatic aquifer can be ascribed to seawater intrusion alone, with no indication of the involvement of deep brines (identified at 450 m depth) in the process.The chemical composition of the saline and brackish groundwaters is characterized by an excess of sodium and a deficit of calcium compared to conservative mixing between fresh groundwaters and seawater. This suggests that the phreatic aquifer is progressively freshening, as a consequence of the beneficial influence of the extensive irrigation/drainage network, including raised canals acting as a hydraulic barrier along the coast. This freshening tendency may have been lasting since the reclamation in the mid-twentieth century, and has probably been accelerated by the ban on groundwater abstraction since the 1970s.  相似文献   

<Emphasis Type="Italic">Clostridium difficile</Emphasis> infection incidence prediction in hospitals (CDIIPH): a predictive model based on decision tree and fuzzy techniques     

Gyan?Chhipi-ShresthaEmail author  Julie?Mori  Kasun?Hewage  Rehan?Sadiq 《Stochastic Environmental Research and Risk Assessment (SERRA)》2017,31(2):417-430

Several risk factors associated with the increased likelihood of healthcare-associated Clostridium difficile infection (CDI) have been identified in the literature. These risk factors are mainly related to age, previous CDI, antimicrobial exposure, and prior hospitalization. No model is available in the published literature that can be used to predict the CDI incidence using healthcare administration data. However, the administrative data can be imprecise and may challenge the building of classical statistical models. Fuzzy set theory can deal with the imprecision inherent in such data. This research aimed to develop a model based on deterministic and fuzzy mathematical techniques for the prediction of hospital-associated CDI by using the explanatory variables controllable by hospitals and health authority administration. Retrospective data on CDI incidence and other administrative data obtained from 22 hospitals within a regional health authority in British Columbia were used to develop a decision tree (deterministic technique based) and a fuzzy synthetic evaluation model (fuzzy technique based). The decision tree model had a higher prediction accuracy than that of the fuzzy based model. However, among the common results predicted by two models, 72 % were correct. Therefore, this relationship was used to combine their results to increase the precision and the strength of evidence of the prediction. These models were further used to develop an Excel-based tool called C. difficile Infection Incidence Prediction in Hospitals (CDIIPH). The tool can be utilized by health authorities and hospitals to predict the magnitude of CDI incidence in the following quarter.  相似文献   

One Million Years tephra record at IODP Sites U1436 and U1437: Insights into explosive volcanism from the Japan and Izu arcs          下载免费PDF全文

Julie Christin Schindlbeck  Steffen Kutterolf  Susanne M. Straub  Graham D. M. Andrews  Kuo‐Lung Wang  Maryline J. Mleneck‐Vautravers 《Island Arc》2018,27(3)

The 1 Myr tephra records of IODP (International Ocean Discovery Program) Holes U1436A and U1437B in the Izu‐Bonin fore‐ and reararc were investigated in order to assess provenance and eruptive volumes, respectively. In total, 304 tephra samples were examined and 260 primary tephra layers were identified. Tephra provenance was determined by means of major and trace element compositions of glass shards and distinguished between Japan and Izu‐Bonin arc origin of the tephra layers. A total of 33 marine tephra compositions were correlated to the Japan arc and 227 to the Izu arc. Twenty marine tephra layers were correlated between the two drilling sites. Additionally, we defined eleven correlations of marine tephra deposits to major widespread Japanese eruptions; from the 1.05 Ma Shishimuta‐Pink Tephra to the 30 ka Aira‐Tn Tephra, both from Kyushu Island. These eruptions provide independent time markers within the sediment record and six correlations were used to date tephra layers from Japan in Hole U1436A to establish an alternative age model for this hole. Furthermore, the minimum distal tephra volumes of all detected events were calculated, which enabled the comparison of the tephra volumes that derived from the Japan and the Izu‐Bonin arcs. For some of the major Japanese eruptions these are the first volume estimations that also include distal deposits. All of the Japanese tephras derived from events with eruption magnitude M_v ≥ 5.6 and three of the investigated eruptions reach magnitudes M_v ≥ 7. Volcanic events of the Izu‐Bonin arc have mostly eruption magnitudes M_v ≤ 5.  相似文献   

Source and supply of sediment to a shoreline salient in a fringing reef environment     

Michael V.W. Cuttler  Jeff E. Hansen  Ryan J. Lowe  Julie A. Trotter  Malcolm T. McCulloch 《地球表面变化过程与地形》2019,44(2):552-564

Reef-associated landforms are coupled to the health of the reef ecosystem which produces the sediment that forms and maintains these landforms. However, this connection can make reef-fronted coastlines sensitive to the impacts of climate change, given that any decline in ecosystem health (e.g. decreasing sediment supply) or changes to physical processes (e.g. sea level rise, increasing wave energy) could drive the sediment budgets of these systems into a net erosive state. Therefore, knowledge of both the sediment sources and transport mechanisms is required to predict the sensitivity of reef-associated landforms to future climate change. Here, we examine the benthic habitat composition, sediment characteristics (composition, texture, and age), and transport mechanisms and pathways to understand the interconnections between coastal morphology and the reef system at Tantabiddi, Ningaloo Reef, Western Australia. Benthic surveys and sediment composition analysis revealed that although live coral accounts for less than 5% of the benthic cover, coral is the dominant sediment constituent (34% on average). Sediment ages (²³⁸U/²³⁰Th) were mostly found to be thousands of years old, suggesting that the primary sediment source is relic reef material (e.g. Holocene reef framework). Sediment transport across the lagoon was quantified through measurements of ripple migration rates, which were found to be shoreward migrating and responsible for feeding the large shoreline salient in the lee of the reef. The derived sediment fluxes were comparable with previously measured rates of sediment production by bioerosion. These results suggest that sediment budgets of systems dependent on old (>10³ years) source materials may be more resilient to climate change as present-day reef health and community composition (i.e. sources of ‘new’ carbonate production) have limited influence on sediment supply. Therefore, the vulnerability of reef-associated landforms in these systems will be dictated by future changes to mechanisms of sediment generation (e.g. bioerosion) and/or physical processes. © 2018 John Wiley & Sons, Ltd.  相似文献   

A 180 ka record of environmental change at Erdut (Croatia): a new chronology for the loess–palaeosol sequence and its implications for environmental interpretation     

Kaja Fenn  Julie A. Durcan  David S. G. Thomas  Adriano Banak 《第四纪科学杂志》2020,35(4):582-593

While there are numerous thick loess–palaeosol sequences preserved across the Carpathian Basin, well dated sites that provide terrestrial palaeoenvironmental records extending beyond last glacial–interglacial cycle are scarce. Robust chronologies are essential for correlations of loess with other long-term Quaternary records and to further understanding of the palaeoenvironment and climate of this important region beyond the last 125 ka. Here a new geochronology based on 13 post-infrared infrared stimulated luminescence ages focused on the lower part of the loess–palaeosol sequence at Erdut is presented. The results show that the lower part of the Erdut profile spans the penultimate glacial cycle (MIS 7 to MIS 5). The considerable sediments overlaying the investigated part of the profile suggest that this section spans two glacial cycles, rather than the previously suggested one. The most likely source of the discrepancy is the use of uncorrected infrared stimulated luminescence signal, which can cause age underestimation if not accounted for. This study demonstrates the need to revisit sites such as Erdut, re-date them using updated measurement protocols, and update existing palaeoenvironmental interpretations.  相似文献