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51.
Joaquín Buitrago Juan Capelo Javier Gutirrez Martín Rada Ricardo Hernndez Sylvia Grune 《Estuarine, Coastal and Shelf Science》2006,66(3-4):634-642
Drowned reefs, fossil reefs or paleo-reefs, are important ecologically as areas of high biodiversity, foraging, shelter environment, and as areas supporting the spawning aggregations of economically important reef fish species. This is particularly significant when the structures are situated in a wide soft-bottom continental shelf. The presence of limestone structures, fossil reefs and pinnacles dating from circa 8 to 9 ka, to the north of the Paria Peninsula in north-eastern Venezuela, has been known to local fishermen for decades. Using echograms obtained during acoustic fisheries evaluations and the scarce previously available information, an improved location map of hard-bottom structures was made. Benthic samples to study macromolluscs were taken at depths between 54 and 93 m using an unmodified 2-m beam trawl. Four trawl samples were located over fossil reef areas while another four were situated in soft-bottom valleys between limestone structures. Fossil reefs in the area showed a highly patchy distribution. A total of 91 species from 43 Bivalvia, Gastropoda and Scaphopoda families were found, Gastropoda being the dominant class with 49 species. Paleo-reef-covered areas showed higher species richness and only 21% of the species found were common to both substrates. Gastropods Tonna maculosa and Polystira albida were the most abundant species and occurred in both substrate types. Bivalve life habits, a mixture of organism–substrate relationships, shell fixation, mobility and feeding type, differed significantly according to bottom type. Six species are recorded for the first time for eastern Venezuelan waters. Bottom heterogeneity plays an important role in marine ecosystems, providing shelter to fish populations and may be significant as breeding and nursery areas. Its presence in a region with biogeographical interest, situated in the confluence of three major provinces and with oceanographic conditions varying seasonally from upwelling dominated to Orinoco River discharges, makes this the area of interest and it should be evaluated as a possible Marine Protected Area. 相似文献
52.
H.J.B. Birks D.T. Monteith N.L. Rose Vivienne J. Jones Sylvia M. Peglar 《Journal of Paleolimnology》2004,31(4):411-431
Twenty-four lakes on Svalbard were sampled for palaeolimnological studies and are described in terms of their geographical location, catchment characteristics, water chemistry, and flora. No sediment could be retrieved from one of the lakes. There is a close correlation, as detected by redundancy analysis, between lake-water chemistry and catchment variables, particularly bedrock geology and geographical location for 23 lakes. The flora of the lake catchments is statistically related, as shown by canonical correspondence analysis, to bedrock geology, climate (geographical location), and nutrient status (bird impact). Modern pollen assemblages from eleven lakes contain 2–25% far-distance extra-regional pollen. The modern local and regional pollen depositions are dominated by Oxyria digyna, Poaceae, Saxifraga, Salix, and Brassicaceae pollen. 相似文献
53.
Patricia Roeser Nadine Dräger Dariusz Brykała Florian Ott Sylvia Pinkerneil Piotr Gierszewski Christin Lindemann Birgit Plessen Brian Brademann Michał Kaszubski Michał Fojutowski Markus J. Schwab Michał Słowiński Mirosław Błaszkiewicz Achim Brauer 《Boreas: An International Journal of Quaternary Research》2021,50(2):419-440
We revise the conceptual model of calcite varves and present, for the first time, a dual lake monitoring study in two alkaline lakes providing new insights into the seasonal sedimentation processes forming these varves. The study lakes, Tiefer See in NE Germany and Czechowskie in N Poland, have distinct morphology and bathymetry, and therefore, they are ideal to decipher local effects on seasonal deposition. The monitoring setup in both lakes is largely identical and includes instrumental observation of (i) meteorological parameters, (ii) chemical profiling of the lake water column including water sampling, and (iii) sediment trapping at both bi-weekly and monthly intervals. We then compare our monitoring data with varve micro-facies in the sediment record. One main finding is that calcite varves form complex laminae triplets rather than simple couplets as commonly thought. Sedimentation of varve sub-layers in both lakes is largely dependent on the lake mixing dynamics and results from the same seasonality, commencing with diatom blooms in spring turning into a pulse of calcite precipitation in summer and terminating with a re-suspension layer in autumn and winter, composed of calcite patches, plant fragments and benthic diatoms. Despite the common seasonal cycle, the share of each of these depositional phases in the total annual sediment yield is different between the lakes. In Lake Tiefer See calcite sedimentation has the highest yields, whereas in Lake Czechowskie, the so far underestimated re-suspension sub-layer dominates the sediment accumulation. Even in undisturbed varved sediments, re-suspended material becomes integrated in the sediment fabric and makes up an important share of calcite varves. Thus, while the biogeochemical lake cycle defines the varves’ autochthonous components and micro-facies, the physical setting plays an important role in determining the varve sub-layers’ proportion. 相似文献
54.
GeoJournal - Solid waste management practice is a matter of concern for public health and environmental protection and has become a major challenge in Syria. Improper waste management can bear... 相似文献
55.
56.
Jacqueline M. McSweeney Robert J. Chant John L. Wilkin Christopher K. Sommerfield 《Estuaries and Coasts》2017,40(4):977-993
The Delaware Estuary has a history of high anthropogenic nutrient loadings but has been classified as a high-nutrient, low-growth system due to persistent light limitation caused by turbidity. While the biogeochemical implications of light limitation in turbid estuaries have been well-studied, there has been minimal effort focused on the connectivity between hydrodynamics, sediment dynamics, and light limitation. Our understanding of sediment dynamics in the Delaware Estuary has advanced significantly in the last decade, and this study describes the impact of spatiotemporal variability of the estuarine turbidity maximum (ETM) on light-limited productivity. This analysis uses data from eight along-estuary cruises from March, June, September, and December 2010 and 2011 to evaluate the impact of the turbidity maximum on production. Whereas the movement of the ETM is controlled primarily by river discharge, the structure of the ETM is modulated by stratification, which varies with both river discharge and spring-neap conditions. We observe that the ETM’s location and structure control spatial patterns of light availability. To evaluate the relative contributions of river discharge and spring-neap variability to the location of phytoplankton blooms, we develop an idealized two-dimensional Regional Ocean Modeling System (ROMS) numerical model. We conclude that high river flows and neap tides can drive stratification that is strong enough to prevent sediment from being resuspended into the surface layer, thus providing light conditions favorable for primary production. This study sheds light on the role of stratification in controlling sediment resuspension and promoting production, highlighting the potential limitations of biogeochemical models that neglect sediment processes. 相似文献
57.
A dimensional analysis to quantify the thermal budget around lithospheric‐scale shear zones 下载免费PDF全文
The thermal evolution around shear zones is controlled by three major thermal processes: diffusion, advection and shear heating. We present a dimensional analysis to quantify, to first‐order, the relative contributions of these three processes to the thermal evolution around lithospheric‐scale shear zones. We consider 11 parameters that control the kinematics, the three‐dimensional (3‐D) geometry, the initial thermal structure and the average strength of the shear zone. Three dimensionless parameters are presented to quantify the relative contributions of the three thermal processes. We validate the dimensional analysis with 2‐D thermo‐kinematic numerical models. The applicability of the dimensional analysis to any kind of shear zone (i.e. thrust, normal‐slip and strike‐slip shear zones) makes it a useful tool that is complementary to previous numerical and analytical studies. Finally, thrust‐type shear zones are used to illustrate how the three thermal processes control the thermal evolution. 相似文献
58.
59.
Disconnected policies and actors and the missing role of spatial planning throughout the risk management cycle 总被引:2,自引:2,他引:0
Kalliopi Sapountzaki Sylvia Wanczura Gabriella Casertano Stefan Greiving Gavriil Xanthopoulos Floriana F. Ferrara 《Natural Hazards》2011,59(3):1445-1474
The present work addresses the problem of lack of coordination between policies and actors with joint competence for risk
management, i.e., civil protection, spatial planning, and sectoral planning (e.g., forest policy in the case of forest fire
risk). Spatial planning in particular is assigned a minor or no role at all though it might perfectly operate as the coordinating
policy platform; the reason is that spatially relevant analysis and policy guidance is an omnipresent component of the risk
management cycle. However, disconnected risk relevant policies turning a blind eye to spatial planning might cause several
adverse repercussions: Breaks in the response-preparedness-prevention-remediation chain (which should function as a continuum),
minimal attention to prevention, risk expansion and growth instead of mitigation, lack of synergies between involved actors
as well as duplicated or even diverging measures and funding. The authors bear witness to the above suggestions by examining
three cases of European (regional and local) risk management systems faced with failures when confronting natural hazards
(floods and forest fires). These three systems are embedded in different types of political-administrative structures, namely
those of the city of Dortmund (Germany) facing floods, Eastern Attica region (Greece), and Lazio Region (Italy) facing forest
fires. 相似文献
60.
Time-frequency analysis of magnetotelluric data 总被引:1,自引:0,他引:1