918 resultados para Intensive and extensive margin


Relevância:

100.00% 100.00%

Publicador:

Resumo:

Traditional water supply systems in semi-arid agrarian ecosystems, mainly irrigation canals, contribute to the diversity of the landscape and influence the composition of species. To evaluate their effect on bird communities in the breeding season, we selected a rural area in southeastern Spain, where an intricate and extensive network of irrigation canals and cultivated areas is located between two wetlands declared as Natural Parks. Birds were counted at representative points distributed throughout the canal network at which we recorded several variables related to the physical features, the vertical and horizontal structure of associated vegetation, reed development (Phragmites australis) and land use in the neighboring areas. We detected 37 bird species, most of which were also breeding in the wetlands nearby. We used Hierarchical Partitioning analyses to identify the variables most strongly related to the probability of the presence of selected species and species richness. Vegetation cover and height close to the canals, together with reed development, were the most important types of variables explaining species presence and richness. We found that current management practices for reeds in canals are not well-suited for biodiversity conservation. We therefore propose alternatives that could be implemented in the area in cooperation with stakeholders.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

The Lofoten-Vesterålen marine shelf is one of the most geologically diverse coast and offshore margin areas in Norway. This leads to huge heterogeneity in marine environments, and often high biodiversity. However, little is known yet about the benthic communities in this region. Within the ARCTOS LoVe MarineEco project the epibenthic communities of the Hola trough (Vesterålen) are analysed to give a first description of their spatial distribution. In this trough both a complex hydrodynamic system and varied topographic submarine elements occur. Trawling samples were collected for two different approaches: one in a meso-scale and another in a small-scale. For the broad scale a transect consisting in three stations was developed, while for the fine scale a small area on a sand wave field, consisting in five stations called HolaBox, was sampled. All organisms were intended to be identified to species level and colonial fauna was discarded for the analysis. Different diversity indexes were assessed (Shannon index (H’) and Pielou’s eveness (J’)). Clustering and nMDS analyses identified four statistically significant groups in terms of abundance (ind./100m2). A total amount of 211 different taxa were found within all stations. The more outer part of the transect (close to the shelf edge) presented a huge abundance of organisms and was dominated by the hemi sessile tube-builder polychaetes Nothria conchylega and Eunice dubitata and the sea urchin Gacilechinus acutus, while the more inner parts presented less abundance of individuals. Probably some upwelling produced by the Norwegian Atlantic Current (NWAC) is influencing the shelf edge increasing the primary production and, therefore, enriching the seafloor in this region. The sand wave field presented two different groups with few amount of individuals. Small-scale variability could be produced by the high heterogeneity within the different types of sand waves, while the scarce abundance of animals can be produced by the permanent changing environment that movable sand waves produce. Here more active and mobile fauna was found such as brittle stars and hermit crabs (among others). Finally, a fourth group was found in the most inner station of the transect, laying on a ridge in the central part of the trough. This station, with coarse substrate, was mainly dominated again by brittle stars and sea urchins. We can conclude that this is a really heterogeneous trough in environments and therefore in communities (even in a local scale). More detailed studies that focus in the local environmental drivers have to be carried out to get an integrated understanding of the structure of benthic communities in this system.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Trabalho Final do Curso de Mestrado Integrado em Medicina, Faculdade de Medicina, Universidade de Lisboa, 2014

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Trabalho Final do Curso de Mestrado Integrado em Medicina, Faculdade de Medicina, Universidade de Lisboa, 2014

Relevância:

100.00% 100.00%

Publicador:

Resumo:

In order to stabilise and improve their income situation, rural households are strongly encouraged to diversify their activities both within and outside the agricultural sector. Often, however, this advice is only moderately pursued. This paper addresses issues of rural household income diversification in the case of Poland. It investigates returns from rural household income strategies using propensity score matching methods and extensive datasets spanning 1998-2008. Results suggest that returns from combining farm and off-farm activities were lower than returns from concentrating on farming or on self-employment outside agriculture. This differential is stable over time although returns from diversification have relatively improved after Poland’s accession to the EU. This is also visible in the fact that since 2006 returns from combining farm and off-farm activities have evened with returns from relying solely on hired off-farm labour, thus smoothing the difference observed before the accession. Further, over the analysed period, households pursuing the diversification strategy performed better than those relying solely on unearned income. Finally, in general, the income in households combining farm and off-farm activities was higher than in those combining two off-farm income sources.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

We examined diatom preservation patterns in Pliocene age sediments of Jane Basin (ODP Site 697) and compared them with diatom distribution in more northerly sites at various sectors of the Southern Ocean. Our data from Site 697, as well as other sites from around the Southern Ocean, support the view that there was significant ice growth on Antarctica during the late Pliocene. DSDP Site 514 in the Atlantic sector shows increased relative abundance of Eucampia antarctica, an ice-related form, in the upper part of the Gauss Chron with a larger increase just above it. With one exception, all sites included in the present study show increased relative abundance of E. antarctica in the upper part of the Gauss. Our view that there was ice growth on Antarctica during the late Gauss Chron is supported by the results from ODP Site 697. While diatoms are present and percent opal is high in the early and middle Gauss Chron (suggesting more open-ocean conditions), late Gauss sediments contain low percentages of opal and few or no diatoms. This is also true for the early Matuyama Chron. If we accept spring and summer sea-ice cover as the major suppressant of diatom productivity in the Southern Ocean, then we conclude that sea-ice covered the region around Site 697 through much of the year during this interval. Further, the absence of diatoms and the low percentages of opal in middle and late Matuyama chron sediments suggests increased sea-ice cover over the Jane Basin during this time. Although warmer openocean intervals are inferred for intervals near the Olduvai and Jaramillo Subchrons, most of the Matuyama Chron was marked by extensive sea-ice cover with low seasonal contrast. Our results for the early part of the Brunhes Chron are similar, at least for the Jane Basin. During this time, sea-ice cover over the basin apparently extended well into the growing season. In contrast, the later Brunhes Chron is marked by alternating open water (during the growing season) and extensive, almost year-round, sea-ice.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Clay-mineral distributions in the Arctic Ocean and the adjacent Eurasian shelf areas are discussed to identify source areas and transport pathways of terrigenous material in the Arctic Ocean. The main clay minerals in Eurasian Arctic Ocean sediments are illite and chlorite. Smectite and kaolinite occur in minor amounts in these sediments, but show strong variations in the shelf areas. These two minerals are therefore reliable in reconstructions of source areas of sediments from the Eurasian Arctic. The Kara Sea and the western part of the Laptev Sea are enriched in smectite, with highest values of up to 70% in the deltas of the Ob and Yenisey rivers. Illite is the dominant clay mineral in all the investigated sediments except for parts of the Kara Sea. The highest concentrations with more than 70% illite occur in the East Siberian Sea and around Svalbard. Chlorite represents the clay mineral with lowest concentration changes in the Eastern Arctic, ranging between 10 and 25%. The main source areas for kaolinite in the Eurasian Arctic are Mesozoic sedimentary rocks on Franz-Josef Land islands. Based on clay-mineral data, transport of the clay fraction via sea ice is of minor importance for the modern sedimentary budget in the Arctic basins.

Relevância:

100.00% 100.00%

Publicador:

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Neogene sediments from three areas of the Northern Indian Ocean (Indus Fan, Owen Ridge, Oman Margin, ODP Leg 117) were studied in order to determine the amount, type, and preservation of organic matter as functions of the environments encountered. The work consisted of geochemical analyses on whole sediment (Total Organic Content and Rock Eval pyrolysis) and of petrographic studies on isolated organic matter by optical and scanning electron microscopy. In Indus Fan sediments, organic matter is present in low amounts, mainly as lignaceous fragments. A contrasting situation exists in Oman Margin sediments which are generally rich in amorphous autochtonous organic matter. Owen Ridge, located between Indus fan and Oman Margin areas, shows two phases of organic sedimentation as a consequence of the uplift of the ridge. The older phase (Oligocene to early or middle Miocene) is strongly influenced by detrital supply from the Indus, while the younger phase (middle Miocene to Pleistocene) is characterized by relatively high amounts of autochtonous organic matter. From a general point of view it appears that high amounts of organic matter are mainly due to good preservation of marine amorphous organic matter, such as in Oman Margin sediments and in upper pelagic levels of Indus Fan and Owen Ridge deposits. Low total organic carbon contents are correlated with low proportions of amorphous material in the total organic matter due to oxidizing conditions. This leads to a relative enrichment in components derived from resistant materials (lignin, chitin, or other resistant biopolymers) such as lignaceous fragments (Indus Fan) and/or fragments from benthic organisms and alveolate microplankton (Oman Margin).

Relevância:

100.00% 100.00%

Publicador:

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Total dissolved carbohydrates (DCHOs) were determined in interstitial waters collected at open-ocean and Peru margin sites cored during Ocean Drilling Program Leg 201. Concentrations of DCHOs ranged from 0 to ~1500 µM and showed no consistent trends between open-ocean and Peru margin sites either in the magnitude or direction of downhole interstitial water gradients. In contrast, relative DCHO concentrations (normalized to dissolved organic carbon concentrations) were higher in open-ocean vs. margin sediments. These trends are consistent with results from more shallow estuarine and nearshore continental margin sediments and may be related to changes in the overall controls on sediment organic matter remineralization with decreasing remineralization rates.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

A close look at the sedimentology of Heinrich event 4 from the northwest Labrador Sea indicates that an extended ice margin, perhaps greater than before Heinrich events 1 or 2 (H-1 and H-2), existed in the Hudson Strait region pre-Heinrich event 4 (H-4) and, that on the basis of characteristics of the sediment unit, Heinrich event-4 was different than Heinrich events 1 or 2 (i.e., larger ice sheet collapse(?), longer duration(?), "dirtier" icebergs(?)). Other data from across the southern and eastern margin of the Laurentide Ice Sheet, as well as Greenland and the North Atlantic, support this interpretation, possibly indicating a relative mid-Wisconsin glacial maximum pre-Heinrich event 4. Many of these data also indicate that Heinrich event 4 (35 ka) resulted in serious climatic and oceanographic reorganizations. We suggest that Heinrich event 4 gutted the Hudson Strait, leaving it devoid of ice for Heinrich event 3. We further hypothesize that Heinrich event 3 did not originate from axial ice transport along the Hudson Strait; thus Heinrich event 3 may be more analogous to the proposed northward advancing ice from Ungava Bay during Heinrich event 0 than to the more typical down-the-strait flow during H-1, H-2, and H-4. Consequently, the climatic and oceanographic impacts resulting from Heinrich events are highly susceptible to the type, origin, and magnitude of ice sheet collapse, something which varied per Heinrich event during the last glacial period.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

South Asia's pursuit of economic development has entailed considerable damage to and exposed the fragility of the physical environment of the region. This paper provides an analytical overview of the of the environmental problem that manifest themselves in South Asia in a comparative perspective with East and Southeast Asian countries as well as selected developed market economics. To date, South Asian development process has been environment-intensive and environment-depleting. It is argued that environmental problems are likely to set serious constraints to sustain growth in production to support a growing population. By exploring the relationship between indices of human welfare and bio-diversity conservation. the paper exposes the dichotomy of the development process. Finally, the study underscores the need for a range of policy options that rely both based and non-market based instruments in an integrated setting to enviromnentalize South Asian economic development. (C) 2004 Elsevier B.V All rights reserved.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Complete vertebrate genome sequencing has revealed a remarkable stability and uniformity in the protein-coding gene set, which at first glance might suggest that gene duplication events are relatively rare. This may be a red herring, or at least a red cichlid, as the Lake Malawi cichlid fishes show rapid and extensive duplication and diversification of their retinal cone photoreceptor opsin genes.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Electronic communications devices intended for government or military applications must be rigorously evaluated to ensure that they maintain data confidentiality. High-grade information security evaluations require a detailed analysis of the device's design, to determine how it achieves necessary security functions. In practice, such evaluations are labour-intensive and costly, so there is a strong incentive to find ways to make the process more efficient. In this paper we show how well-known concepts from graph theory can be applied to a device's design to optimise information security evaluations. In particular, we use end-to-end graph traversals to eliminate components that do not need to be evaluated at all, and minimal cutsets to identify the smallest group of components that needs to be evaluated in depth.