Temporal changes of a macrobenthic assemblage in harsh lagoon sediments   总被引：1，自引：0，他引：1  

Serena Como  Paolo Magni   《Estuarine, Coastal and Shelf Science》2009,83(4):638-646

An opportunistic macrobenthic assemblage was studied from 2001 to 2003 in a central area of the Cabras lagoon (western Sardinia, Italy), known to be affected by environmental disturbances (i.e. organic over-enrichment of sediments, and episodic events of hypoxia/anoxia and sulphide development). We identified recurrent seasonal changes in this macrobenthic assemblage, with a general impoverishment in summer and a recovery in winter/spring. The nereids Neanthes succinea and Hediste diversicolor were found to replace the spionid Polydora ciliata as the most dominant species in the summer for 3 consecutive years. Occasional, unsynchronized appearances of small-sized deposit feeders, such as Tubificidae, Capitella cf. capitata, chironomid larvae and Hydrobia spp., were observed in winter/spring. We suggest that these changes are driven by the interplay of environmental conditions (worse in summer) with numerous biotic factors. This includes different tolerance levels of taxa to low oxygen concentrations and sulphides, variability in larval supply and post-larval transport, as well as competition for space and food between and within different functional groups, and facilitation through animal bioturbation and sediment reoxidation. A conceptual model is proposed to demonstrate how environmental conditions and biotic interactions may control the benthic assemblage in such a harsh lagoon environment.  相似文献   

Do small marinas drive habitat specific impacts? A case study from Mediterranean Sea     

Di Franco A  Graziano M  Franzitta G  Felline S  Chemello R  Milazzo M 《Marine pollution bulletin》2011,62(5):926-933

Many human activities add new structures to the marine landscape. Despite the fact that human structures cause some inevitable impacts, surprisingly little information exists on the effects of marina on natural marine assemblages. The aim of this paper is to assess habitat-specific response of benthic sessile organisms of rocky shores in relation to the presence of a small marina. Sampling was carried out at three coastal habitats (midshore, lowshore and subtidal) by means of visual censuses adopting an after-control-impact (ACI) experimental design. It appears that the marina affects the structure and composition of benthic communities of both the midshore and the lowshore. Little effect was evident on shallow subtidal assemblage structure. The results of the present study clearly show habitat-specific responses of coastal benthic assemblages to the presence of infrastructure.  相似文献   

Address databases for national SDI: Comparing the novel data grid approach to data harvesting and federated databases     

Serena Coetzee  Judith Bishop 《International journal of geographical information science》2013,27(9):1179-1209

The original purpose of addresses was to enable the correct and unambiguous delivery of postal mail. The advent of computers and more specifically geographic information systems (GIS) opened up a whole new range of possibilities for the use of addresses, such as routing and vehicle navigation, spatial demographic analysis, geo‐marketing, and service placement and delivery. Such functionality requires a database which can store and access spatial data effectively. In this paper we present address databases and justify the need for national address databases. We describe models used for national address databases, and present our evaluation framework for an address database at a national level within the context of a spatial data infrastructure (SDI). The models of data harvesting, federated databases and data grids are analyzed and evaluated according to our novel framework, and we show that the data grid model has some unique features that make it attractive for a national address database in an environment where centralized control and/or coordination is difficult or undesirable.  相似文献   

The formation of heavy hydrocarbons in molecular clouds     

Ararat G. Yeghikyan  Serena Viti  David A. Williams 《Monthly notices of the Royal Astronomical Society》2001,326(1):313-316

Laboratory data on the conversion of solid methane into large hydrocarbons by particle radiation are used to estimate the fraction of interstellar carbon converted by this process into refractory form. We find that the maximum fraction of carbon that can be converted into refractory form during the life of a dense core within an interstellar cloud is in the range of 1–5 per cent. The implication of this result is that the conversion of enough carbon into refractory form to contribute significantly to interstellar extinction requires the frequent passage of material into and out of dense cores. If so, then interstellar clouds must exist for at least 10 Myr. However, these conclusions should be regarded as preliminary until confirmed by further laboratory studies of the particle irradiation of complex ice mixtures.  相似文献   

Magnetic field seeding by galactic winds     

Serena Bertone  Corina Vogt  Torsten Enßlin 《Monthly notices of the Royal Astronomical Society》2006,370(1):319-330

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Acceptance of open source geospatial software: Assessing QGIS in South Africa with the UTAUT2 model     

Susan Henrico  Serena Coetzee  Antony Cooper  Victoria Rautenbach 《Transactions in GIS》2021,25(1):468-490

Geospatial information and technologies are widely used in South Africa, initially mostly with proprietary software but today, mature, open source alternatives such as QGIS are available. We wanted to find out if and why South African users accepted QGIS, globally the most widely used free and open source GIS. We adapted the extended unified theory of acceptance and use of technology model to test several hypotheses regarding the acceptance and use of QGIS in South Africa. 205 registered members of the Geo‐Information Society of South Africa completed a structured questionnaire. Results show that habit has the most significant influence on behavioural intention to use QGIS, followed by facilitating conditions, price value and social influence. Performance expectancy, effort expectancy, hedonic motivation and access to source code played no significant role. The findings show that adoption of QGIS in South Africa is not primarily influenced by benefits attributed to open source software, such as cost benefits, customizability, improved reliability, quality and security. The results are useful for developers of any GIS product and for choosing a GIS product for an organization, because they provide insight into the behavioural intentions of users.  相似文献   

Opposite diel patterns of nitrogen fixation associated with salt marsh plant species (Spartina foliosa and Salicornia virginica) in southern California     

Serena M. Moseman 《Marine Ecology》2007,28(2):276-287

In marine wetlands, nitrogen fixation is a potentially important nutrient source for nitrogen‐limited primary producers, but interactions between nitrogen fixers and different vascular plant species are not fully understood. Nitrogen fixation activity was compared in sediments vegetated by three plant species, Spartina foliosa, Salicornia virginica, and Salicornia bigelovii in the Kendall Frost Reserve salt marsh in Mission Bay (CA). This study addressed the effects of plant type, day and night conditions, and sediment depths on nitrogen fixation. Higher rates of nitrogen fixation were associated with S. foliosa than with either of the two Salicornia spp., which are known to compete more effectively than Spartina for exogenous nitrogen in the salt marsh environment. Rates of nitrogen fixation, determined by acetylene reduction, in sediments vegetated by S. virginica were low during the day (7.7 ± 1.2 μmol C₂H₄ m⁻² h⁻¹) but averaged 13 ± 6.6 μmol C₂H₄ m⁻² h⁻¹ at night, with particularly high rates in samples from locations with visible cyanobacterial mats. The opposite diel pattern was found for sediments containing S. foliosa plants, in which average daytime and nighttime rates of nitrogen fixation were 62 ± 23 and 21 ± 15 μmol C₂H₄ m⁻² h⁻¹, respectively. For S. foliosa, nitrogenase activity of rinsed roots and different sediment sections (0–1, or 4–5 cm depths) were measured. Although nitrogen fixation rates in vegetated sediment samples were substantial, all but one of rinsed S. foliosa root samples (n = 12) and subsurface sediments at 4–5 cm depths failed to show nitrogen fixation activity after 2 h, suggesting that the most active nitrogen fixers in these systems likely reside in surface sediments. Further, nitrogenase activity in shaded and unshaded S. foliosa samples did not differ, suggesting that nitrogen fixers may not rapidly respond to changes in plant photosynthetic activity. Average nitrogen fixation rates in S. foliosa‐vegetated samples from the Mission Bay salt marsh were on the same order as those of highly productive Atlantic coast marshes, and this microbially‐mediated nitrogen source may be similarly substantial in other Mediterranean wetlands. Sediment abiotic variables seem to exert greater control upon nitrogen fixation activity than the effects of particular plant species. Nonetheless, dominant plant species may differ substantially in their reliance on nitrogen fixation as a nutrient source, with potentially important consequences for wetland conservation and restoration.  相似文献   

Acquiring reference parameters of masonry for the structural performance analysis of historical buildings   总被引：1，自引：1，他引：0  

Meta Kržan  Samo Gostič  Serena Cattari  Vlatko Bosiljkov 《Bulletin of Earthquake Engineering》2015,13(1):203-236

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The effect of dwarf galaxy disruption in semi-analytic models     

Bruno M. Henriques  Serena Bertone  Peter A. Thomas 《Monthly notices of the Royal Astronomical Society》2008,383(4):1649-1654

We present results for a galaxy formation model that includes a simple treatment for the disruption of dwarf galaxies by gravitational forces and galaxy encounters within galaxy clusters. This is implemented a posteriori in a semi-analytic model by considering the stability of cluster dark matter subhaloes at   z = 0  . We assume that a galaxy whose dark matter substructure has been disrupted will itself disperse, while its stars become part of the population of intracluster stars responsible for the observed intracluster light. Despite the simplicity of this assumption, our results show a substantial improvement over previous models and indicate that the inclusion of galaxy disruption is indeed a necessary ingredient of galaxy formation models. We find that galaxy disruption suppresses the number density of dwarf galaxies by about a factor of 2. This makes the slope of the faint end of the galaxy luminosity function shallower, in agreement with observations. In particular, the abundance of faint, red galaxies is strongly suppressed. As a result, the luminosity function of red galaxies and the distinction between the red and the blue galaxy populations in colour–magnitude relationships are correctly predicted. Finally, we estimate a fraction of intracluster light comparable to that found in clusters of galaxies.  相似文献   

The predictability of near-coastal currents using a baroclinic unstructured grid model   总被引：1，自引：1，他引：0  

Cheryl Ann Blain  Mustafa Kemal Cambazoglu  Robert S. Linzell  Kendra M. Dresback  Randall L. Kolar 《Ocean Dynamics》2012,62(3):411-437

A limited domain, coastal ocean forecast system consisting of an unstructured grid model, a meteorological model, a regional ocean model, and a global tidal database is designed to be globally relocatable. For such a system to be viable, the predictability of coastal currents must be well understood with error sources clearly identified. To this end, the coastal forecast system is applied at the mouth of Chesapeake Bay in response to a Navy exercise. Two-day forecasts are produced for a 10-day period from 4 to 14 June 2010 and compared to real-time observations. Interplay between the temporal frequency of the regional model boundary forcing and the application of external tides to the coastal model impacts the tidal characteristics of the coastal current, even contributing a small phase error. Frequencies of at least 3 h are needed to resolve the tidal signal within the regional model; otherwise, externally applied tides from a database are needed to capture the tidal variability. Spatial resolution of the regional model (3 vs 1 km) does not impact skill of the current prediction. Tidal response of the system indicates excellent representation of the dominant M ₂ tide for water level and currents. Diurnal tides, especially K ₁, are amplified unrealistically with the application of coarse 27-km winds. Higher-resolution winds reduce current forecast error with the exception of wind originating from the SSW, SSE, and E. These winds run shore parallel and are subject to strong interaction with the shoreline that is poorly represented even by the 3-km wind fields. The vertical distribution of currents is also well predicted by the coastal model. Spatial and temporal resolution of the wind forcing including areas close to the shoreline is the most critical component for accurate current forecasts. Additionally, it is demonstrated that wind resolution plays a large role in establishing realistic thermal and density structures in upwelling prone regions.  相似文献