Bioavailability of different chemical forms of dissolved silica can affect marine diatom growth     

Samuela Capellacci  Cecilia Battocchi  Silvia Casabianca  Marco Giovine  Giorgio Bavestrello  Antonella Penna 《Marine Ecology》2013,34(1):103-111

In this study, we demonstrate that dissolved silica obtained from mineral (crystalline quartz), biogenic amorphous (diatomaceous earth) and artificial amorphous sources (Aerosil) influence the growth rate of two marine diatoms, Chaetoceros sp. and Skeletonema marinoi. Diatoms were reared in four different experimental conditions in artificial seawater containing either dissolved silica previously obtained through dissolution of the mineral crystalline quartz or two amorphous substrates, biogenic diatomaceous earth or artificial Aerosil silica. Sodium metasilicate was used as control. When the silica in the different media reached concentrations higher than 107 μm , particles were eliminated by filtration and the diatom cells were inoculated. Maximum cell density, growth and silica assimilation rates of both species in the presence of dissolved silica derived from crystalline quartz and metasilicate were higher than those obtained with the other silica sources. These results are discussed against the background of previous geochemical studies that have shown that silica–water interactions are strictly dependent on the silica polymorphs involved and on the ionic composition of the solution. Our results demonstrate that the soluble silicon compounds generated in seawater by crystalline sources are highly bioavailable compared with those generated by biogenic and amorphous materials. These findings are potentially of considerable ecological importance and may contribute to clarifying anomalous spatial and temporal distributions of siliceous organisms with respect to the presence of lithogenic or biogenic silica sources in marine environments.  相似文献   

Water quality management in Singapore: the role of institutions,laws and regulations     

Cecilia Tortajada  Yugal Kishore Joshi 《水文科学杂志》2013,58(9):1763-1774

Abstract

The paper analyses the legal and regulatory instruments for water quality management that have been set in place in Singapore for control of water pollution, and their evolution since the time of independence in 1965. The role of institutions in the strict implementation of the laws and regulations is also discussed, with special emphasis on the efficient inter-institutional coordination machinery that has made it possible. The analyses show that overall long-term planning and policy-making and a strong political will have been instrumental to give all aspects of water management high priority in the national agenda, thus directly supporting urban, industrial and commercial growth.

Editor Z.W. Kundzewicz  相似文献   

Environmental changes affecting light climate in oligotrophic mountain lakes: the deep chlorophyll maxima as a sensitive variable     

Beatriz Modenutti  Esteban Balseiro  Marcela Bastidas Navarro  Cecilia Laspoumaderes  María Sol Souza  Florencia Cuassolo 《Aquatic Sciences - Research Across Boundaries》2013,75(3):361-371

The North-Patagonian Andean lakes of Argentina are high light, low nutrient environments that exhibit development of deep chlorophyll maxima (DCM) at the metalimnetic layer during summer stratification, at approximately 1 % of surface PAR irradiance. We examined whether the position of DCM changes as a consequence of long-time (global warming: glacial clay input) and short-time (eruption: volcanic ashes) events. We performed different field studies: (1) an interlacustrine analysis of six lakes from different basins, including data of the 2011 volcanic eruption, which caused an unexpected variation in water transparency; and (2) an intralacustrine analysis in which we compared different stations along a transparency gradient in Lake Mascardi caused by glacial clay input at one end of the gradient. In these analyses, we documented changes in DCM depth and its relationship with different parameters. DCM development was not related with thermocline depth or nutrient distribution. In all cases, the only significant variables were Kd 320 nm and Kd PAR. Our study showed that suspended particles (glacial clay and volcanic ashes) can play a crucial role in transparent lakes, affecting lake features such as the phototrophic biomass distribution along the water column. Suspended solid inputs from either glacial clay or volcanic ashes produce a comparable effect, provoking a decrease in light and, consequently, an upper location of the DCM. Thus, the DCM position is highly sensitive to global changes, such as increased temperatures causing glacier recession or to regional changes caused by volcanic eruptions.  相似文献   

Our astrochemical heritage     

Paola Caselli  Cecilia Ceccarelli 《Astronomy and Astrophysics Review》2012,20(1):1-68

Our Sun and planetary system were born about 4.5 billion years ago. How did this happen, and what is the nature of our heritage from these early times? This review tries to address these questions from an astrochemical point of view. On the one hand, we have some crucial information from meteorites, comets and other small bodies of the Solar System. On the other hand, we have the results of studies on the formation process of Sun-like stars in our Galaxy. These results tell us that Sun-like stars form in dense regions of molecular clouds and that three major steps are involved before the planet-formation period. They are represented by the prestellar core, protostellar envelope and protoplanetary disk phases. Simultaneously with the evolution from one phase to the other, the chemical composition gains increasing complexity. In this review, we first present the information on the chemical composition of meteorites, comets and other small bodies of the Solar System, which is potentially linked to the first phases of the Solar System??s formation. Then we describe the observed chemical composition in the prestellar core, protostellar envelope and protoplanetary-disk phases, including the processes that lead to them. Finally, we draw together pieces from the different objects and phases to understand whether and how much we inherited chemically from the time of the Sun??s birth.  相似文献   

Electron microprobe monazite geochronology of granitic intrusions from the Montes de Toledo batholith (central Spain)     

David Orejana  Enrique Merino  Carlos Villaseca  Cecilia Prez‐Soba  Andrs Cuesta 《Geological Journal》2012,47(1):41-58

U–Th–Pb monazite dating by electron microprobe has been applied to three peraluminous granitic intrusions of the western Montes de Toledo batholith (MTB). Back scattered electron images of monazite crystals reveal a variety of internal textures: patchy zoning, overgrowths around older cores and unzoned crystals. On the basis of their zoning pattern and chemical composition, two monazite domains can be distinguished: (1) corroded cores and crystals with patchy zoning, exhibiting relatively constant Th/U ratios and broadly older ages, and (2) unzoned grains and monazite rims, with variable Th/U ratios and younger ages. The first monazite group represents inherited domains from metamorphic sources, which accounts for pre‐magmatic monazite growth events. Two average ages from Torrico and Belvís de Monroy granites (333 ± 18 and 333 ± 5 Ma, respectively) relate these cores to a Viséan extensional deformation phase. The second group represents igneous monazites which have provided the following crystallization ages for the host granite: 298 ± 11 Ma (Villar del Pedroso), 303 ± 6 Ma (Torrico) and 314 ± 3 Ma (Belvís de Monroy). Two main magmatic pulses, the first about 314 Ma and the second at the end of the Carboniferous (303–298 Ma), might be envisaged in the western MTB. While Belvís de Monroy leucogranite is likely a syn‐ to late‐tectonic intrusion, the Villar del Pedroso and Torrico plutons represent post‐tectonic magmas with emplacement ages similar to those of equivalent intrusions from nearby Variscan magmatic sectors. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Microscopic scale conductivity as explanation of magnetotelluric results from the Alps of Western Switzerland     

Gabriella Losito  Pierre-André Schnegg  Candice Lambelet  Cecilia Viti  Antonello Trova 《Geophysical Journal International》2001,147(3):602-609

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A new geodemographic classification of commuting flows for England and Wales     

Stephen Hincks  Richard Kingston  Brian Webb  Cecilia Wong 《International journal of geographical information science》2018,32(4):663-684

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Biologic and geologic characteristics of cold seeps in Monterey Bay, California     

James P. Barry  H. Gary Greene  Daniel L. Orange  Charles H. Baxter  Bruce H. Robison  Randall E. Kochevar  James W. Nybakken  Donald L. R  Cecilia M. McHugh 《Deep Sea Research Part I: Oceanographic Research Papers》1996,43(11-12)

Cold seep communities discovered at three previously unknown sites between 600 and 1000 m in Monterey Bay, California, are dominated by chemoautotrophic bacteria (Beggiatoa sp.) and vesicomyid clams (5 sp.). Other seep-associated fauna included galatheid crabs (Munidopsis sp.), vestimentiferan worms (Lamellibrachia barhami?), solemyid clams (Solemya sp.), columbellid snails (Mitrella permodesta, Amphissa sp.), and pyropeltid limpets (Pyropelta sp.). More than 50 species of regional (i.e. non-seep) benthic fauna were also observed at seeps. Ratios of stable carbon isotopes (δ¹³C) in clam tissues near 36‰ indicate sulfur-oxidizing chemosynthetic production, rather than non-seep food sources, as their principal trophic pathway. The “Mt Crushmore” cold seep site is located in a vertically faulted and fractured region of the Pliocene Purisima Formation along the walls of Monterey Canyon ( 635 m), where seepage appears to derive from sulfide-rich fluids within the Purisima Formation. The “Clam Field” cold seep site, also in Monterey Canyon ( 900 m) is located near outcrops in the hydrocarbon-bearing Monterey Formation. Chemosynthetic communities were also found at an accretionary-like prism on the continental slope near 1000 m depth (Clam Flat site). Fluid flow at the “Clam Flat” site is thought to represent dewatering of accretionary sediments by tectonic compression, or hydrocarbon formation at depth, or both. Sulfide levels in pore waters were low at Mt Crushmore (ca 0.2 mM), and high at the two deeper sites (ca 7.011.0 mM). Methane was not detected at the Mt Crushmore site, but ranged from 0.06 to 2.0 mM at the other sites.  相似文献   

Effects of high pressure,hot water shore cleaning after oil spills on shore ecosystems in the Northern Baltic proper     

Dag Broman  Björn Ganning  Cecilia Lindblad 《Marine environmental research》1983,10(3):173-187

The use of high pressure, hot water hosing techniques in oil spill clean-up operations on rocky and stony-gravelly shores drastically reduces the shore vegetation and macrofauna. The negative effects are more substantial than on oiled shores cleaned by raking and scraping. After one year the hot water cleaned shores were not restored completely.On rocky shores the high pressure, hot water technique is very efficient in terms of freeing the rocks from oil. However, due to its detrimental effects on shore organisms this type of oil spill clean-up operation can only be recommended for bird or wildlife protection areas. The cleanup method is inefficient on stony-gravelly shores due to penetration of oil into the ground and sediment and direct killing of shore organisms. The method should be avoided on these types of shores.  相似文献   

Obelia (Cnidaria, Hydrozoa, Campanulariidae): a microphagous, filter-feeding medusa     

Ferdinando Boero  Cecilia Bucci  Anna Maria Rosaria Colucci  Cinzia Gravili  & Loredana Stabili 《Marine Ecology》2007,28(S1):178-183

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