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141.
Isabel Dyck 《The Professional geographer》1999,51(2):243-253
As medical geography reinvents itself as health geography, the linkages between social theory and the deconstruction of central categories organizing its medical orientation are being explored. This paper discusses the contribution of qualitative research to this process. In providing access to alternative ways of understanding health concerns, and emphasizing issues of power in the production of knowledge, qualitative methodology carries the potential for reconceptualizing key issues framing investigation of the relationships between place, people, and their health. In pursuing current issues in social theory, qualitative research also contributes to the blurring of the subdiscipline's boundaries and revitalizes its agenda. 相似文献
142.
Ana I. Sousa Ana I. Lillebø Miguel A. Pardal Isabel Caçador 《Estuarine, Coastal and Shelf Science》2010
This study aimed to assess the contribution of different salt marsh halophytes (Spartina maritima, Scirpus maritimus, Halimione portulacoides, Sarcocornia fruticosa, and Sarcocornia perennis) to nutrient cycling and sequestration in warm-temperate salt marshes. Carbon, nitrogen and phosphorus concentration in plant organs and rhizosediment, as well as plant biomass were monitored every two months during one year. Results show that the C retained in the rhizosediment does not seem to be species or site specific. However, some halophytes seem to have a higher contribution to retain C from external sources, namely S. perennis and S. maritima. Regarding N, halophytes colonizing the upper and middle marsh areas had the highest NBPP (net belowground primary production) as well as the retention of N in the rhizosediment. Yet, excluding S. maritimus, all halophytes seem to contribute to the retention of N from external sources. The P retained in the rhizosediment does not seem to be species or site specific. Still, only S. maritima colonizing the lower marsh areas, which also had comparatively lower NBPP, seem to have a higher contribution to retain P from external sources. Additionally, it seems that there is no relation between plants sequestration capacity for nutrients and plant photosynthetic pathway. This work shows that nutrient cycling and accumulation processes by salt marsh halophytes contribute to reduce eutrophication (N and P retention) and also to reduce atmospheric CO2 (C retention), highlighting salt marsh ecosystems services and the crucial role of halophytes in maintaining ecosystem functions and health. 相似文献
143.
Chemical availability of arsenic and heavy metals in sediments from abandoned cinnabar mine tailings
Raquel Larios Rodolfo Fernández-Martínez Verónica Silva Isabel Rucandio 《Environmental Earth Sciences》2013,68(2):535-546
The understanding of the solid-phase speciation of arsenic in soils and sediments is important in the evaluations of its potential mobility and availability in the environment. The spoil heaps of abandoned mercury mines contain waste materials with high arsenic and heavy metals concentrations. The weathering of these tailings can cause their mobilization to the surroundings. In this work, the mobility and availability of arsenic and some heavy metals were evaluated in sediments from two heavily polluted mercury mining districts in Asturias (NW Spain). For this purpose, a slightly modified version of the Bureau Community of Reference sequential extraction scheme was applied to sediments. The total contents in the operationally defined fractions were analysed by inductively coupled plasma-atomic emission spectrometry. Extremely high total arsenic concentrations were found in all sediments ranging from 4,000 to 24,800 mg kg?1. High easily mobilizable arsenic contents were found in the first mining area, related to the solubilization of Ca-bearing phases, supported by extracts analyses, X-ray diffraction results and the positive correlation found among the As and Ca fractionations. Ni and Zn were the most mobile among heavy metals, being Cr the least mobile, suggesting an anthropogenic origin due to the metallurgical processes, transport or dispersion generated from neighbour spoil heaps. In the second mining area, the bulk of As was concentrated in the residual phase, as well as Cr, Cu, Fe, Pb, Ti, indicating a mineralogical origin and the low availability of these elements. The strong correlations established between As and Fe and Ti distributions support the hypothesis that As is mainly associated to structural mineral phases in these sediments. 相似文献
144.
Paulo Valladares Soares Sueli Yoshinaga Pereira Silvio Jorge C. Simoes George de Paula Bernardes Sérgio Augusto Barbosa Isabel Cristina B. Trannin 《Environmental Earth Sciences》2012,67(6):1685-1694
This work describes the methodological approach used for mapping the potential infiltration areas of the Guaratinguetá watershed (160?km2), situated in Southeastern Brazil. The method is considered a qualitative approach, which takes into account thematic maps (geology, pedology, geomorphology, and land use/land cover) and the precipitation spatial distribution. A group of experts in Earth Sciences and Geotechnical Engineering has applied an infiltration potential scale factor that ranges from 5 (highest influence) to 1 (lowest influence). The final infiltration map was produced using several ArcGIS? tools. The results showed that the most suitable (very high) infiltration areas represent only around 7% of the watershed area, which are associated with smooth and gentle hills, fluvial Tertiary sediments and yellow oxisols. However, growing impacts caused by land farming and urban developments require urgent planning for this region. Areas with high to moderate capacity of infiltration represent around 56% of the watershed and are found in the domain of igneous-metamorphic rocks associated with steep hill-slopes and relatively well-preserved forest fragments. This region requires a land-use strategy, such as reforestation programs, in order to increase the infiltration capacity of the watershed. 相似文献
145.
Péter árkai Isabel Abad Fernando Nieto Tibor Németh Péter Horváth Viktória K. Kis Katalin Judik Juan Jiménez-Millán 《Swiss Journal of Geoscience》2012,105(2):263-282
Frequently, at temperatures lower than the metamorphic peak conditions, slates undergo mineral transformations, usually mediated by fluids. We have studied core material of an epizonal slate series (Szendr? Mountains, NE-Hungary) to reconstruct the post-metamorphic lower-T hydrothermal alterations using petrographic, X-ray diffraction, electron microprobe methods, and transmission electron microscopy. The borehole crosscuts an upper part of the ca. 600?C800?m Lower-Carboniferous flysch-like Szendr? Phyllite Formation. The samples were metamorphosed reaching epizonal conditions with a mineral assemblage characterized by quartz, muscovite, chlorite and albite. Even in the freshest samples, break-up and loosening of the regional metamorphic structure was observed, with cracks parallel to or crossing the cleavage. In the upper part, chlorite and albite are almost absent, while the presence of paragonite, mixed Na?CK mica, and mixed-layered minerals with smectitic component are characteristic. Goethite, halloysite, and subordinate kaolinite are present in the most altered sample (13.0?m in the profile) which may indicate the position of the fissures in which the circulation of the post-metamorphic fluids was the most intense. Muscovite is the only mica from the lower part of the profile and chlorite becomes a significant constituent, whereas paragonite, halloysite, and kaolinite are missing. Discrete smectite is present in all the samples in spite of being incompatible with the prograde evolution of the sequence. The interleaved smectite layers in chlorite and muscovite/chlorite mixed-layers show at the lattice level textural characteristics indicative of a later alteration process. After the metamorphic peak at epizonal conditions, the introduction of hot fluids through the fractures gave rise to the crystallization of Na?CK white micas and muscovite/chlorite under anchizonal conditions. In a final stage of the hydrothermal process, the cooling of the circulating fluids favored the formation of halloysite and kaolinite in the areas near to the fissures, smectites in the samples far away from the fractures, and locally, goethite. The Fe2O3 content increasing upwards indicates oxidizing conditions in the late stage of hydrothermal activity and/or eventually, an influence of a younger near-surface weathering. 相似文献
146.
Ocean Dynamics - Costa Rica has been affected by several local and distant tsunamis in the past, but the historical information is scarce and incomplete. Its Pacific coast stretches for over a... 相似文献
147.
We conducted a paleolimnological investigation of late Holocene deposits on a distal, constrained floodplain of the Cauca River, northern Colombia, i.e. the La Caimana sedimentary succession. The record starts sometime between 4,500 and 4,000 cal yr BP, when the first high-energy fluvial events inundated an ancient soil surface. From that time until about 3,260 cal yr BP, a stable and probably seasonal flooding regime was established on the floodplain. From ~3,260 to ~2,800 cal yr BP, ephemeral and shallow swamps developed on the floodplain. Their formation and duration depended on their connection with the Cauca River. From ~2,800 to ~2,400 cal yr BP, fluvial influence became more dominant, establishing a semi-permanent connection between the river and the floodplain. From ~2,400 to 1,400 cal yr BP, episodic formation of ephemeral swamps occurred. During this stage, floodplain lakes displayed high salinity and nutrient concentrations, and possibly alkaline conditions as a consequence of reduced water volume when the connection with the river was reduced or lost completely. A change in the hydrological regime occurred from ~1,400 to ~850 cal yr BP, when high-energy fluvial events were punctuated by periods of reduced flooding that enabled soil formation. Generally, connection with the Cauca River resulted in lake waters with low salinity and nutrient concentration, whereas loss of connection with the river led to lakes with greater salinity and nutrient content. Paleocurrent analyses indicate that flows came predominantly from the Cauca River, suggesting the lakes were formed by the impoundment of La Caimana Creek. The sedimentary succession of La Caimana offers a unique, high-resolution record of the evolution and dynamics of an ancient floodplain of the Cauca River and its aquatic ecosystems. 相似文献
148.
Laminated sediments in a core from Alberca de Tacámbaro, western central Mexico, provide a high-resolution record of palaeoclimatic variability for most of the Holocene. Using compositional and textural characteristics we identified 14 facies classified in biogenic, clastic and volcaniclastic groups, in which diatoms and other algal remains are the most common components. In addition to facies analysis, high-resolution geochemical data from continuous core scanning XRF and the analysis of discrete samples for organic and inorganic carbon content, provide the basis for palaeoclimatic reconstruction. The age model indicates that the record spans from 9.4 cal ka bp toad 1760. Three main phases in the sequence are identified, controlled by millennial-scale variability. During the period between 9.4 and 5.7 cal kabp , the lake is dominated by siliceous organisms. Drier conditions between 8.2 and 6.3 cal kabp are linked to decreases in summer insolation and solar irradiance. By 5.7 cal kabp , the change in sedimentation is related to the increase in El Niño Southern Oscillation frequency. Evidence of the occurrence of dry conditions during the archaeological Late Classic period (ad 600–900) and historical droughts are also documented in the Alberca de Tacámbaro record. Unprecedented changes in the landscape are recorded afterad 1520. 相似文献
149.
150.
Ana L. Santos Isabel Henriques Newton C. M. Gomes Adelaide Almeida António Correia Angela Cunha 《Aquatic Sciences - Research Across Boundaries》2011,73(1):63-77
The effects of ultraviolet-B (0.4 W m−2) radiation on the abundance, diversity and heterotrophic metabolism of bacterioneuston and bacterioplankton communities from
Ria de Aveiro (Portugal) were assessed and compared to those of freshwater communities from Lake Vela (Portugal) in microcosm
experiments. Exposure to 9 h of artificial ultraviolet radiation (UVR) led to 24–33% reduction in bacterial abundance and
up to a 70% decrease in bacterial diversity. Maximum extracellular enzyme activity and monomer incorporation rates were reduced
by 16–90% and 80–100%, respectively. Recovery of bacterial activity during post-UV dark incubations ranged from 10 to 100%
for extracellular enzyme activity and 40% for monomer incorporation rates. In general, the heterotrophic activity of bacterioneuston
was more inhibited by UVR than that of bacterioplankton. However, DGGE profiles revealed greater UVR-induced reductions in
the diversity of bacterioplankton compared to bacterioneuston. The similarity between bacterioneuston and bacterioplankton
communities in samples collected at early morning was lower than at noon (pre-exposed communities) and increased upon experimental
irradiation, possibly indicating selection for UV-resistant bacteria. The observation that UV exposure resulted in enhanced
reduction of bacterioneuston activity, but a lower reduction in bacterial diversity accompanied by enhanced dark recovery
potential compared to bacterioplankton, indicates re-directioning of bacterioneuston metabolism towards stress defence/recovery
strategies rather than the sustained heterotrophic metabolism. Our results indicate that UVR can significantly decrease the
abundance, diversity and activity of bacteria inhabiting the surface and sub-surface layers of freshwater and estuarine systems
with potentially important impacts on the biogeochemical cycles in these environments. 相似文献