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51.
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
52.
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
53.
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
54.
In situ pore-pressure evolution during dynamic CPT measurements in soft sediments of the western Baltic Sea 总被引:1,自引:1,他引:0
Annedore?SeifertEmail author Sylvia?Stegmann Tobias?M?rz Matthias?Lange Thomas?Wever Achim?Kopf 《Geo-Marine Letters》2008,28(4):213-227
We present in situ strength and pore-pressure measurements from 57 dynamic cone penetration tests in sediments of Mecklenburg (n?=?51), Eckernförde (n?=?2) and Gelting (n?=?4) bays, western Baltic Sea, characterised by thick mud layers and partially free microbial gas resulting from the degradation of organic material. In Mecklenburg and Eckernförde bays, sediment sampling by nine gravity cores served sedimentological characterisation, analyses of geotechnical properties, and laboratory shear tests. At selected localities, high-resolution echo-sounder profiles were acquired. Our aim was to deploy a dynamic cone penetrometer (CPT) to infer sediment shear strength and cohesion of the sea bottom as a function of fluid saturation. The results show very variable changes in pore pressure and sediment strength during the CPT deployments. The majority of the CPT measurements (n?=?54) show initially negative pore-pressure values during penetration, and a delayed response towards positive pressures thereafter. This so-called type B pore-pressure signal was recorded in all three bays, and is typically found in soft muds with high water contents and undrained shear strengths of 1.6–6.4 kPa. The type B signal is further affected by displacement of sediment and fluid upon penetration of the lance, skin effects during dynamic profiling, enhanced consolidation and strength of individual horizons, the presence of free gas, and a dilatory response of the sediment. In Mecklenburg Bay, the remaining small number of CPT measurements (n?=?3) show a well-defined peak in both pore pressure and cone resistance during penetration, i.e. an initial marked increase which is followed by exponential pore-pressure decay during dissipation. This so-called type A pore-pressure signal is associated with normally consolidated mud, with indurated clay layers showing significantly higher undrained shear strength (up to 19 kPa). In Eckernförde and Gelting bays pore-pressure response type B is exclusively found, while in Mecklenburg Bay types A and B were detected. Despite the striking similarities in incremental density increase and shear strength behaviour with depth, gas occurrence and subtle variations in the coarse-grained fraction cause distinct pore-pressure curves. Gaseous muds interbedded with silty and sandy layers are most common in the three bays, and the potential effect of free gas (i.e. undersaturated pore space) on in situ strength has to be explored further. 相似文献
55.
Gerardo Aceves-Medina Ricardo Saldierna-Martínez Alejandro Hinojosa-Medina Sylvia P.A. Jimnez-Rosenberg Martín E. Hernndez-Rivas Raúl Morales-vila 《Estuarine, Coastal and Shelf Science》2008,76(4):889-901
The effect of environmental variables on the vertical structure of larval fish assemblages in a tropical coastal lagoon was analyzed. Ichthyoplankton samples were collected from the near-bottom and surface strata near the mouth of a subtropical lagoon during contrasting seasonal conditions of temperature, photoperiod, light intensity, and tidal heights. During summer, larval fish assemblages had high species richness (R) and were dominated by tropical species. During winter, assemblages had lower R values and were dominated by subtropical and temperate species. Vertical distribution patterns of the taxa were determined by the interaction of environmental variables and behavior of each species to maintain their position in a stratum in the water column, or to achieve vertical migrations induced by environmental stimuli that, in this case, were thermal gradient, column water stratification, and intensity of light. Depth position and vertical migration of fish larvae, coupled with the flood and ebb tide conditions, played an important role in their retention and displacement toward the lagoon. Fish larvae with distribution restricted to the inner part of the inlet, such as Achirus mazatlanus, Etropus sp., and several gobies, were more abundant in the near-bottom stratum during the ebb tide, allowing them to avoid exportation, whereas those that could spawn outside, but depended on the inlet as a nursery area, were more abundant near the surface during flood tide, such as Abudefduf troschelii and Stegastes rectifraenum. 相似文献
56.
Mathias Mueller Onyedika A. Igbokwe Benjamin Walter Chelsea L. Pederson Sylvia Riechelmann Detlev K. Richter Richard Albert Axel Gerdes Dieter Buhl Rolf D. Neuser Giovanni Bertotti Adrian Immenhauser 《Sedimentology》2020,67(2):849-881
Early marine diagenetic dolomite is a rather thermodynamically-stable carbonate phase and has potential to act as an archive of marine porewater properties. However, the variety of early to late diagenetic dolomite phases that can coexist within a single sample can result in extensive complexity. Here, the archive potential of early marine dolomites exposed to extreme post-depositional processes is tested using various types of analyses, including: petrography, fluid inclusion data, stable δ13C and δ18O isotopes, 87Sr/86Sr ratios, and U-Pb age dating of various dolomite phases. In this example, a Triassic carbonate platform was dissected and overprinted (diagenetic temperatures of 50 to 430°C) in a strike-slip zone in Southern Spain. Eight episodes of dolomitization, a dolostone cataclasite and late stage meteoric/vadose cementation were recognized. The following processes were found to be diagenetically relevant: (i) protolith deposition and fabric-preservation, and marine dolomitization of precursor aragonite and calcite during the Middle–Late Triassic; (ii) intermediate burial and formation of zebra saddle dolomite and precipitation of various dolomite cements in a Proto-Atlantic opening stress regime (T ca 250°C) during the Early–Middle Jurassic; (iii) dolomite cement precipitation during early Alpine tectonism, rapid burial to ca 15 km, and high-grade anchizone overprint during Alpine tectonic evolution in the Early Eocene to Early Miocene; (iv) brecciation of dolostones to cataclasite during the onset of the Carboneras Fault Zone activity during the Middle Miocene; and (v) late-stage regression and subsequent meteoric overprint. Data shown here document that, under favourable conditions, early diagenetic marine dolomites and their archive data may resist petrographic and geochemical resetting over time intervals of 108 or more years. Evidence for this preservation includes preserved Late Triassic seawater δ13CDIC values and primary fluid inclusion data. Data also indicate that oversimplified statements based on bulk data from other petrographically-complex dolomite archives must be considered with caution. 相似文献
57.
Oregon's Developmental Fisheries Program is designed to encourage the commercial exploration and development of State managed underutilized fishery resources. A key program strategy is allocating relatively secure harvest rights to pioneering entrepreneurs when a fishery successfully transitions from “developing” to “developed” status. Since the program's inception in 1993, two fisheries, sardine and bay clam, have moved from undeveloped to developed status. Case studies of these fisheries show that many challenges impact the success of the Developmental Fisheries Program including difficulties in designing and allocating asset rights, establishing operational program guidelines, selecting measurable targets that meet legislative standards for a developed fishery, and financing developmental fisheries management practices. Developmental fisheries strategies used in other regions and countries are summarized. Recommendations are made for improving Oregon's Developmental Fishery Program including establishing clear objectives and timelines for the Program and identifying appropriate renewal requirements for permits and other developmental incentives on a fishery-by-fishery basis. 相似文献
58.
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
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.
Spatial simulation of evapotranspiration of semi-arid Inner Mongolian grassland based on MODIS and eddy covariance data 总被引:4,自引:4,他引:0
Sylvia?H.?VetterEmail author David?Schaffrath Christian?Bernhofer 《Environmental Earth Sciences》2012,65(5):1567-1574
In semi-arid regions of Central Asia, water shortage results from low annual precipitation (P) with high interannual variability. Evapotranspiration (ET) dominates water balance losses entirely. Previous studies showed
large differences between individual grassland sites in the partitioning of ET into evaporation and transpiration, but only
little difference in the evaporative ratio ET/P. The hydrological model BROOK90 was applied to the Xilin river catchment in Inner Mongolia (China) in combination with data
from moderate resolution imaging spectroradiometer (MODIS) and ET measurements. The ET part of the model was parameterised
using several years of eddy covariance (EC) measurements over grasslands differing in grazing intensity and leaf area index
(LAI). Using a relatively well-established relationship of LAI and P as well as LAI and temperature derived from MODIS, the water balance components of a 16 km2 sample area in the catchment
were modelled with a 1 km2 resolution for the vegetation period of 2006. All pixels were modelled assuming a similar ET control
as at the EC sites. Spatial variation in ET as well as in the partitioning of ET between transpiration and evaporation could
be identified. The results indicate the potential of using MODIS data and BROOK90 to upscale ET of semi-arid grasslands from
site to larger grass dominated catchments. 相似文献