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61.
Ecological quality assessment of small estuaries from the Portuguese coast based on benthic macroinvertebrate assemblages indices 总被引:1,自引:0,他引:1
Benthic macroinvertebrates communities are the most consistently emphasized biotic component of aquatic ecosystems and are one of the biological indicators required for assessment by the European Water Framework Directive. In this context, several indices based on these communities have been developed in order to assess ecological quality of estuarine systems. In the present work we used AMBI, M-AMBI, BENTIX and BAT to distinguish ecological status of five small estuarine systems of the Portuguese south and southwest coasts. Although indices outputs did not differ between systems and sampling seasons, results indicated that the metrics in which these indices are based could differentiate community structures as a result of two main gradients that force these communities: the natural variability, and the anthropogenic impact. 相似文献
62.
Geomorphic monitoring and response to two dam removals: rivers Urumea and Leitzaran (Basque Country,Spain) 下载免费PDF全文
Askoa Ibisate Alfredo Ollero Daniel Ballarín Jesús Horacio Daniel Mora Amaia Mesanza Carles Ferrer‐Boix Vanesa Acín David Granado Juan Pedro Martín‐Vide 《地球表面变化过程与地形》2016,41(15):2239-2255
Dam removal has been demonstrated to be one of the most frequent and effective fluvial restoration actions but at most dam removals, especially of small dams, there has been little geomorphological monitoring. The results of the geomorphological monitoring implemented in two dams in the rivers Urumea and Leitzaran (northern Spain) are presented. The one from the River Urumea, originally 3.5 m high and impounding 500 m of river course, was removed instantaneously whereas that in the River Leitzaran, 12.5 m high, and impounding 1500 m of river course, is in its second phase of a four‐stage removal process. Changes in channel morphology, sediment size and mobility and river bed morphologies were assessed. The monitoring included several different techniques: topographical measurements of the channel, terrestrial laser scanner measurements of river bed and bars, sediment grain size and transport; all of them repeated in four (May, August, November 2011 and May 2012) and five (July and September 2013, April and August 2014 and June 2015) fieldwork campaigns in the River Urumea and River Leitzaran, respectively. Geomorphic responses of both dam removals are presented, and compared. Morphological channel adjustments occurred mainly shortly after dam removals, but with differences among the one removed instantaneously, that was immediate, whereas that conducted by stages took longer. Degradational processes were observed upstream of both dams (up to 1.2 m and 4 m in the River Urumea and River Leitzaran, respectively), but also aggradational processes (pool filling), upstream of Inturia Dam (2.85 m at least). Less evident aggradational processes were observed downstream of the dams (up to 0.37 m and 0.50 m in the River Urumea and River Leitzaran, respectively). Flood events, especially a 100 year flood registered during the monitoring period of Mendaraz Dam removal, reactivated geomorphological processes as incision and bank erosion, whereas longitudinal profile recovery, grain‐size sorting and upstream erosion took longer. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
63.
J.?Escuder-VirueteEmail author R.?Carbonell C.?Pérez-Soba D.?Martí A.?Pérez-Estaún 《International Journal of Earth Sciences》2004,93(2):172-188
The structure of a fault zone developed in granitic rocks can be established on the basis of the spatial variability of geological, geophysical and geochemical parameters. In the North Fault of the Mina Ratones area (SW Iberian Massif, Spain), fault rocks along two studied traverses (SR-2 and SR-3 boreholes) exhibit systematic changes in mineralogy, geochemistry, fabrics and microstructures that are related to brittle deformation and alteration of granite to form cataclasite and subsequent gouge. The spatial distribution and intensity of these changes suggest a North Fault morphology that is consistent with the fault-core/damage-zone model proposed by Chester et al. (1993) to describe a fault zone architecture. North Fault damage zone thickness can be defined by the development of mechanically related mesoscopic faults and joints, that produce a Fracture Index (FI)>10. High FI values are spatially correlated with relative low seismic velocity zones (VP<5 km/s and VS<2.5 km/s in the well-logs), more probably related to a high concentration of fractures and geochemical alteration produced by meteoric water-granite interaction along fault surfaces. This correlation is the base of a geostatistical model proposed in the final part of this study to image the fault zone architecture of a granitic massif. 相似文献
64.
María Gabriela García Ondra Sracek Diego Sebastián Fernández Margarita del Valle Hidalgo 《Environmental Geology》2007,52(7):1261-1275
The concentration of arsenic measured in groundwater from three aquifers in the study area located in the Eastern Tucuman
province, Argentina, mostly depends on the lithology, but the spatial and temporal variations of concentrations seem to be
also controlled by pH changes, climatic factors, and human perturbations. The highest concentrations of As (more than 1,000 μg
L−1) were found in the shallow aquifer, made of As-rich loess, while the lowest concentrations were measured in the deep confined
aquifer, consisting of alternating layers of alluvial sands/gravels and clays. Intermediate values were measured in the semiconfined
aquifer made of the fluvial sediments deposited in the Salí River valley, that alternate in the upper part of the sedimentary
sequence with layers of loess. Because most of As in the loess is considered to be adsorbed onto Fe-oxyhydroxide coatings,
the increase of pH in the flow direction (west-east) leads to increasing arsenic concentrations towards the eastern border
of the study area. The decomposition of organic wastes poured into the Salí River or associated with local and diffuse sources
of contamination in the eastern part of the study area depletes dissolved oxygen, which leads to the reductive dissolution
of Fe and Mn oxyhydroxides, and to the subsequent release of the adsorbed and co-precipitated As. This process mainly affects
shallow groundwater and the upper part of the semiconfined aquifer. Geochemical and hydrological data also suggest that rising
water table levels at the end of the wet season may also lead to reductive dissolution of As-rich Fe oxyhydroxides in the
shallow aquifer. 相似文献
65.
Josef Bochníček Tomáš Zelinka Reviewer T. Kolbenheyer 《Studia Geophysica et Geodaetica》1981,25(4):411-412
Summary The authors prove that the solution of Laplace's equation under Neumann's boundary conditions can be transformed to an advantage into determining the field which is generated by charges, induced by the external field at surfaces of discontinuity. 相似文献
66.
C. Martín-Puertas M. P. Mata M. C. Fernández-Puga V. Díaz del Río J. T. Vázquez L. Somoza 《Geo-Marine Letters》2007,27(2-4):223-235
The Gulf of Cádiz area has been extensively surveyed in recent years and several gas-related fluid escape seafloor structures
have been identified. In this study, gravity cores, collected during the ANASTASYA/00 and ANASTASYA/01 cruises, on mud volcanoes,
hemipelagic sediments and dredged material from diapiric structures, have been studied. A comparative mineralogical analysis
by XRD and SEM of samples from different areas has been performed in order to determine whether there is a characteristic
mineralogy related to these fluid escape structures, and also to determine the origin of the mud matrix and constrain the
depth of the parent units. The mineralogical analysis reflects the different origins of the different units described in the
cores: hemipelagic material of the slope, clays that underlie the mud volcanoes and are discharged at the sea bottom surface,
and authigenic and diagenetic minerals possibly involved in the anaerobic oxidation of methane in the mud volcano sediments. 相似文献
67.
David Sanz Juan José Gómez-Alday Santiago Castaño Angel Moratalla Jorge De las Heras Pedro Emilio Martínez-Alfaro 《Hydrogeology Journal》2009,17(6):1375-1391
The Mancha Oriental System (MOS) has a surface area of 7,260 km2, making it one of the largest carbonate aquifer systems in Spain. The system sustains about 1,000 km2 of irrigated crops and supplies groundwater to 275,000 inhabitants. The economic transformation brought about by the development of extensive irrigated cropland has led to a water-balance disequilibrium of about 75 million m3/year. This input–output deficit has negative consequences in the quantity and quality of the available resources, in the river–aquifer relationship, and in the associated ecosystems as well. To understand the hydrogeological behaviour of the system, it is necessary to design a conceptual model. Further, the conceptualisation of a groundwater flow system is a requirement of the European Water Framework Directive for the characterisation of groundwater bodies. The robustness of the conceptual model depends heavily on the user capability of representing the real system. In this work, a multidisciplinary approach has been used to represent the three-dimensional geological framework and the groundwater flow conceptualisation of the MOS. Data management and three-dimensional visualisation have been carried out by means of geographical information system (GIS) tools and software for contouring and three-dimensional surface mapping. 相似文献
68.
João Magalhães Neto Heliana Teixeira Joana Patrício Alexandra Baeta Helena Veríssimo Rute Pinto João Carlos Marques 《Estuaries and Coasts》2010,33(6):1327-1339
Anthropogenic activities are a disturbance factor of coastal systems and can be widely recognized as a major threat to the
health of coastal systems. However, natural events cannot be disregarded from management issues because of their significant
influence on the communities living in these areas. Based on long-term subtidal data from the Mondego Estuary (Portugal),
the effects of natural events (e.g., floods and droughts) on macrobenthic communities were compared with the anthropogenic
events. Sampling stations were grouped into characteristic zones (mouth, north arm, south arm) so the community dynamics of
each of these estuarine areas could be followed over time. Environmental assessment was performed for stations using the Benthic
Assessment Tool (BAT), and compared with the existing pressures. Human impacts persist over a number of years and gradually
reduce ecosystem health, as discussed in the European Water Framework Directive. Paradoxically, natural events cause stronger
impacts but are of a shorter duration, which allows for a faster recovery of macrobenthic communities. The study showed that
caution should be taken when developing and implementing water policies so as not to disregard the importance of the different
events (natural and human-caused) on the ecosystem health (e.g., community degradation and water quality and ecological quality
status assessment). 相似文献
69.
70.
The coastal plain of the Río de la Plata constitutes a large wetland which develops on the right margin of the river estuary. Anthropic activities such as intensive exploitation of groundwater carried out in the vicinity of the wetland can modify the natural hydrological regime. The aim of this work is to asses the effects of intensive aquifer exploitation in coastal wetlands using hydrogeological models. Such models allow to evaluate changes in the environmental conditions of wetland at regional level. The hydrogeological model exposed in this work shows how the intensive groundwater exploitation affects the wetland area, generating important variations both in the groundwater flows and in the salinity of the groundwater. Identification of these modifications to the environment is important to generate guidelines leading to minimize these affectations. 相似文献