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31.
The mineral composition of paleosols intercalated in series of young loess was determined. The following conclusions were drawn:
- The mineralogical composition of the total soil showed correlation with the ecological conditions having prevailed during sedimentation.
- The processes of soil formation can be described well by the mineral composition of the fraction of particle size less than 0.002 mm. It displays strong similarities in the fine-dispersed fractions of soils representing identical genetic types from different loess profiles. Since paleosols of identical type are assumed to have formed under similar climatic conditions, the latter can be characterized by the mineral composition of the fine-dispersed fraction.
32.
Characterisation of productivity-diversity relationships forms an essential step towards a better understanding of biodiversity. In terrestrial systems this is a topical subject and most studies reported a hump-shaped relationship. For marine systems, however, the number of studies dedicated to this is low despite the high interest in this productivity-diversity relationship. The present study reports on meiofauna density/diversity patterns in relation to resource availability as an indicator for the productivity of the ecosystem. Standardised meiofauna samples were collected in tropical seagrass beds from three localities (Kenya, Mexico, the Philippines) in order to contrast local patterns with a more global scale. Although these sites were physically comparable, a range of resource availabilities was found. These differences between localities were mainly due to different tidal regimes and related input of organic matter. At all sites a significant positive effect of resource increase on meiofauna densities was found. This positive effect was less clear for meiofauna diversity. Highest density and diversity levels were reported for the Kenyan site and this is probably linked to a high tidal range. Pooling all localities together resulted in a significant positive linear relationship between resource availability and meiofauna density/diversity. Caution should be taken when choosing resource indicators. Chlorophyll a concentrations, for example, resulted in a positive density-productivity relationship while organic carbon content, an indicator for more refractory material, showed a negative relationship. In all cases, no hump-shaped relationship could be found suggesting that each ecosystem and each group of organisms may show a particular productivity-diversity/density relationship. 相似文献
33.
Joanna Sender Urban Danuta Różańska-Boczula Monika Garbowski Magda 《Water Resources》2020,47(2):315-324
Water Resources - The aim of the study was to show which morphometric traits of lakes influence the development of the rush zone of lakes and how buffer zone management influences analyzed features... 相似文献
34.
A study was carried out across the continental shelf and slope in the Western Indian Ocean along the Kenyan margin to unravel depth‐related species diversity patterns portrayed by different nematode families. Sediment samples were collected along four bathymetric transects at 20, 50, 200, 500, 1000 and 2000 m. Three nematode families were selected for species analysis, based on their general occurrence with relatively high numbers and diversity from shelf to slope. All three families exhibited a distinctly different shelf and slope nematode species community. However, all three families also had a significant proportion of species that displayed a eurybathic distribution. Coincidentally, Microlaimidae, the least species‐rich family had the most eurybathic species (75%) compared to Comesomatidae (39%) and Chromadoridae (32%). Total number of species per depth zone along the sampled area (gamma diversity) was three to four times the average number of species (alpha) per station. The difference was more pronounced at the slope than at the shelf. The species turnover was also higher at the slope than at the shelf stations. Each of the three families had a different diversity pattern: Comesomatidae showed a peak at mid‐depth, Chromadoridae increased with depth, and Microlaimidae showed no prominent change with depth. When the three families were combined, the shelf maintained a lower diversity compared to the slope (both local and regional). There was no consistency between genus and species diversity patterns with depth, indicating that genus diversity data may not be a proxy for species diversity. At the lowest taxonomic level (species), the slope showed a higher diversity than the shelf, whereas at higher (genus) taxonomic level the diversity was comparable between the slope and the shelf. The number of species encountered increased with the number of samples analysed and did not reach asymptote, meaning that the area was still under‐sampled. This situation points to the possibility of an even higher regional diversity. 相似文献
35.
This paper presents a comparison of persistent scatterer interferometry (PSI) monitoring results with in situ displacement measurements at the November 1990 landslide at the Bor?t uranium mill tailing deposit site after heavy rain. Although the landslide did not directly endanger people, site remediation works were undertaken due to the subsequent environmental problems. Additionally, in situ monitoring with benchmarks was established in order to detect the ground motion of the landslide body. PSI campaigning in the ?kofjelo?ko-Cerkljansko area, where the uranium mill tailing is situated, performed for the purpose of measuring displacements of natural targets near the active landslide area, also detected displacements, most probably indicating a creeping process. When comparing the pre- and post-remediation velocities at the benchmarks located on the landslide with persistent scatterers (PSs) located near the landslide, the rates could be regarded as background. The results show that the remediation works in the form of a drainage tunnel were very effective as post-remediation velocities at the landslide closer to the PSs resembled the velocities of the PSs, while the velocities of the landslide mass above the drainage tunnel slowed down, even to below the background velocities. The high correlation values between the movements of the benchmarks and the PSs also confirm that the remediation works were effective as the fluctuations in the displacement values of the landslide were very similar to those of the PSs. Nevertheless, although there are several limitations in comparing the two different datasets, the PSI technique can be complementary to conventional in situ methods. 相似文献
36.
We investigated short-term changes (two years) in nematode communities (density, diversity, biomass and community composition) in an area on the Kwintebank (Belgian Continental Shelf) that was closed for sand extraction activities and compared these patterns to nematode community characteristics from another area on the Kwintebank were sand extraction was still ongoing. Six stations were sampled in 2003 and 2004 and nematode community composition and univariate measures of diversity were compared with values obtained during the extraction period and with a "pre-impact situation" sampled in 1978. Although nematode density, diversity and biomass did not change two years after cessation of the exploitation, nematode community composition did and was more stable than in the extracted site. This is attributed to the absence of continuous disturbances associated with the extraction activities such as the creation and filling up of dredge furrows. As a consequence of the typical life history traits of nematodes, recovery seems to follow different pathways when compared to macrobenthic recovery from the same impact. 相似文献
37.
In Belgium, centralized reporting on landings of sea fisheries at the species level started in 1929. This paper summarizes the process and the results of integrating time-series, based on fragmented and disperse data sources for the period 1929–1999. The resulting database contains data by species (41), by port of landing in Belgium (4) and in ‘foreign ports,’ and by fishing area of origin (31). After quality control, total reported landings over the period 1929–2008 amounted to 3,320,518 tonnes, of which 90% was landed in the Belgian ports. After a maximum of 75,370 tonnes in 1947, annual landings declined steadily to only 26% of this peak by 2008. Currently, landings are below those achieved in 1929. The most important species in terms of landings (1929–1999) were cod (17% of all landings) and herring (16%). In terms of economic value, sole (31%) and cod (15%) were the most valuable. Close to 73% of all landings originated from 5 of the 31 fishing areas. Twenty percent of all landings (1929–1999) originated from the ‘coastal waters’, while these waters contributed nearly 60% of all landed pelagic species and 55% of all landed ‘molluscs and crustaceans’. Compared to the currently available ICES data, this local database offers advantages in temporal coverage (data from 1929 onwards), temporal scale (monthly values), and at the taxonomic level. It also provides more detailed information at the spatial scale of the southern and central North Sea, and it is the only source of historical information on landings originating from the coastal waters. Given the importance of the shallow and productive ‘Flemish banks’ as a local source of food in historical and recent times, this data is valuable for further research on the productivity of the coastal ecosystem and the local impact of fisheries. The database broadens the historical view on fisheries, underlines the decline in landings since reporting started, and serves as a basis for further (fisheries) research and policy-making in Belgium. 相似文献
38.
39.
Waldemar Magda 《Ocean Engineering》1997,24(6):551-576
A two-dimensional finite-element simulation of the wave-induced hydrodynamic uplift force acting on a submarine pipeline buried in sandy seabed sediments subject to continuous loading of sinusoidal surface waves is presented. Neglecting inertia forces, a linear-elastic stress-strain relationship for the soil and Darcy's law for the flow of pore fluid are assumed. The model takes into account the compressibility of both components (i.e., pore fluid and soil skeleton) of the two-phase medium.The results of numerical analysis are presented and discussed with respect to soil and pore fluid parameters where special attention is paid to the question of soil saturation conditions. The meaning of the results is also related to surface wave conditions. As a general conclusion, the practical, engineering recommendation is given in order to make a realistic, safe and economic estimation of the wave-induced uplift force acting on a buried submarine pipeline. 相似文献
40.
Macrobenthic community structure of soft-bottom sediments at the Belgian Continental Shelf 总被引：1，自引：0，他引：1
Within the frame of different research projects, a large number of sites at the Belgian Continental Shelf (BCS) have been sampled for the macrobenthos between 1994 and 2000. These samples cover a diverse range of habitats: from the sandy beaches to the open sea, from the gullies between the sandbanks to the tops of the sandbanks, and from clay to coarse sandy sediments. To investigate the large-scale spatial distribution of the macrobenthos of the Belgian Continental Shelf, the data of all these research projects—728 samples—were combined and analysed. By means of several multivariate techniques, 10 sample groups with similar macrobenthic assemblage structure were distinguished. Each sample group is found in a particular physico-chemical environment and has a specific species composition. Four sample groups differ drastically, both in habitat and species composition, and are considered to represent four macrobenthic communities: (1) the muddy fine sand Abra alba–Mysella bidentata community is characterized by high densities and diversity; (2) the Nephtys cirrosa community occurs in well-sorted sandy sediments and is characterized by low densities and diversity; (3) very low densities and diversity typify the Ophelia limacina–Glycera lapidum community, which is found in coarse sandy sediments and (4) the Eurydice pulchra–Scolelepis squamata community is typical for the upper intertidal zone of sandy beaches. These macrobenthic communities are not isolated from each other, but are linked through six transitional species assemblages. The transition between the A. alba–M. bidentata community and the N. cirrosa community is characterized by a reduction in the mud content and is dominated by Magelona johnstoni. The transition between the N. cirrosa and the O. limacina–G. lapidum community is distinctive by decreasing densities and coincides with a gradual transition between medium and coarse sandy sediments. From the N. cirrosa to the E. pulchra–S. squamata community, transitional species assemblages related to the transition from the subtidal to the intertidal environment were found. Each community or transitional species assemblages was found over a specific range along the onshore–offshore gradient, four types can be discerned: (1) almost restricted to the near-shore area, but possible wider distribution; (2) distributed over the full onshore–offshore gradient; (3) restricted to the near-shore area and (4) restricted to the sandy beach environment. The diversity pattern on the BCS follows this division, with species rich and poor assemblages in the near-shore area to only species poor assemblages more offshore. The distribution and diversity patterns are linked to the habitat type, distinguished by median grain size and mud content. 相似文献