The Experts below are selected from a list of 303 Experts worldwide ranked by ideXlab platform
Frédéric Rimet - One of the best experts on this subject based on the ideXlab platform.
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Spatial heterogeneity of littoral benthic diatoms in a large lake: monitoring implications
Hydrobiologia, 2016Co-Authors: Frédéric Rimet, Agnes Bouchez, Kalman TapolczaiAbstract:Benthic diatoms inhabiting littoral zones are regarded as promising bioindicators in lakes. Some pre-standard protocols were proposed and suggested to collect a single site per lake to assess its overall quality. In large lakes, such as Lake Geneva, a spatial heterogeneity of diatom assemblages was suspected, because of differing human pressures. Thirty-five sites were sampled along the shoreline in locations showing various population densities and crossed by rivers flowing into the lake. Different assemblages were found; one corresponded to more oligotrophic areas and was mostly situated on the shoreline next to low population densities; it was mostly composed of low-profile diatoms. A second one corresponded to more eutrophic areas and was mostly situated near densely inhabited areas; it was composed of many high-profile diatoms. A third one was in close vicinity to river inlets, with high abundances of motile diatoms. This last assemblage was spatially restricted to the river plume. After testing several diatom indices, one showed better capacities to assess nutrient level (EPI-L). If we avoid areas near river inlets, the ecological quality assessed with diatom indices ranged from moderate to high ecological status depending on the vicinity situated more or less near densely populated areas.
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Sensitivity and responses of diatoms to climate warming in lakes heavily influenced by humans
Freshwater Biology, 2014Co-Authors: Vincent Berthon, Frédéric Rimet, Benjamin Alric, Marie-elodie PergaAbstract:1. Diatom communities have been shown to respond strongly to current climate warming in remote lakes, while evidence remains equivocal for lakes under strong local human pressures. 2. Temporal dynamics of planktonic diatoms in three subalpine lakes (Geneva, Annecy and Bourget) reconstructed from palaeolimnological approaches were used to assess the relative effects of phosphorus concentrations, fisheries management practices and climate warming in structuring communities over the last century. 3. Changes in total phosphorous concentration (TP), air temperature and fish predation pressure could explain the temporal dynamics of most diatom species in the sediment records. TP was found to be not only the main driver of changes in community composition but also an important factor modulating diatom sensitivity and responses to climate warming. 4. The diatom community of Lake Bourget showed the highest vulnerability and direct responses to climate warming, favouring spring species that can resist earlier stratification in mesotrophic lakes (such as Asterionella formosa, Aulacoseira islandica and Stephanodiscus parvus) and summer species that can make the best trade-off between decreasing nutrient concentrations and increased water column stability (Diatoma tenuis, A. islandica). In Lake Geneva, climate warming also contributed to shaping diatom communities but through an indirect pathway; fisheries management practices and climate warming interacted to reinforce top-down control, favouring large, colonial inedible species (Stephanodicus binderanus and A. formosa). For Lake Annecy, the most nutrient limited of the three lakes studied, no changes in diatom community structure were directly related to warmer air temperatures over the last 25 years. 5. All three lakes have been subjected to the same climate variability. Yet the magnitude and responses of their diatom communities to climate warming were dissimilar and strongly modulated by differences in lake trophic status and fish management practices.
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Changes in diatom-dominated biofilms during simulated improvements in water quality : implications for diatom-based monitoring in rivers
European Journal of Phycology, 2009Co-Authors: Frédéric Rimet, Luc Ector, Henry-michel Cauchie, Lucien HoffmannAbstract:Although benthic diatoms are used to assess river water quality, there are few data on the rate at which diatom assemblages react to changes in water quality. The aim of this study was to assess the reaction time of diatoms and to discuss the changes occurring during water quality improvement on the basis of their autecological characteristics. In order to simulate this improvement, diatom-dominated biofilms grown on artificial sandstone substrata were transferred from several polluted rivers to an unpolluted river. They were sampled three times: before transfer and 1 and 2 months after transfer. The ecology and growth-forms of the taxa explained most of the changes in species composition observed during the experiment. Adnate diatoms gradually replaced motile and stalked taxa. Gomphonema parvulum, a stalked diatom positioned vertically in the biofilm, is adapted for light and space competition in high-density algal biofilms. When transferred to an unpolluted site, this growth-form is less competitive and does not tolerate the high grazing pressure. Fistulifera saprophila is a single celled motile diatom, living in organic matrices. When the artificial substrata were transferred to the unpolluted site, this particular ecological niche disappeared quickly. On the other hand, Achnanthidium minutissimum, which is considered to be cosmopolitan and an early colonizer, increased during the first month of transfer and then decreased. It was gradually replaced by A. biasolettianum, which was the taxon best suited to this pristine stream. The changes observed differed between treatments depending on the species composition and architecture of the biofilms. In particular, biofilms dominated by stalked and motile diatoms were more quickly modified than those dominated by small motile diatoms. The diatom index reflects these changes, and its values showed that about 60 days following a water quality improvement were necessary for transferred diatom assemblages to reach diatom index values similar as those at the unpolluted river.
Jeffrey W. Krause - One of the best experts on this subject based on the ideXlab platform.
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Silicon limitation facilitates virus infection and mortality of marine diatoms
Nature Microbiology, 2019Co-Authors: Chana F. Kranzler, Michael Maniscalco, Bethanie R. Edwards, William P. Biggs, John P. Mccrow, Jeffrey W. Krause, Kay D Bidle, Mark A. Brzezinski, Benjamin A. S. Van Mooy, Andrew E AllenAbstract:Diatoms are among the most globally distributed and ecologically successful organisms in the modern ocean, contributing upwards of 40% of total marine primary productivity^ 1 , 2 . By converting dissolved silicon into biogenic silica, and photosynthetically fixing carbon dioxide into particulate organic carbon, diatoms effectively couple the silicon (Si) and carbon cycles and ballast substantial vertical flux of carbon out of the euphotic zone into the mesopelagic and deep ocean^ 3 – 5 . Viruses are key players in ocean biogeochemical cycles^ 6 , 7 , yet little is known about how viral infection specifically impacts diatom populations. Here, we show that Si limitation facilitates virus infection and mortality in diatoms in the highly productive coastal waters of the California Current Ecosystem. Using metatranscriptomic analysis of cell-associated diatom viruses and targeted quantification of extracellular viruses, we found a link between Si stress and the early, active and lytic stages of viral infection. This relationship was also observed in cultures of the bloom-forming diatom Chaetoceros tenuissimus , where Si stress accelerated virus-induced mortality. Together, these findings contextualize viruses within the ecophysiological framework of Si availability and diatom-mediated biogeochemical cycling. Using metatranscriptomics of diatom-associated viruses and quantification of extracellular viruses in coastal water samples, the authors link silicon limitation to increased virus-induced mortality of diatoms, which could have implications for marine biogeochemical cycling.
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biogenic silica production and diatom dynamics in the svalbard region during spring
Biogeosciences, 2018Co-Authors: Jeffrey W. Krause, Israel A Marquez, Mar Fernandezmendez, Ingrid Wiedmann, Philipp Assmy, Svein Kristiansen, Carlos M. Duarte, Paul Wassmann, Susana AgustíAbstract:Abstract. Diatoms are generally the dominant contributors to the Arctic Ocean spring bloom, which is a key event in regional food webs in terms of capacity for secondary production and organic matter export. Dissolved silicic acid is an obligate nutrient for diatoms and has been declining in the European Arctic since the early 1990s. The lack of regional silicon cycling information precludes understanding the consequences of such changes for diatom productivity during the Arctic spring bloom. This study communicates the results from a cruise in the European Arctic around Svalbard, which reports the first concurrent data on biogenic silica production and export, export of diatom cells, the degree of kinetic limitation by ambient silicic acid, and diatom contribution to primary production. Regional biogenic silica production rates were significantly lower than those achievable in the Southern Ocean and silicic acid concentration limited the biogenic silica production rate in 95 % of samples. Compared to diatoms in the Atlantic subtropical gyre, regional diatoms are less adapted for silicic acid uptake at low concentration, and at some stations during the present study, silicon kinetic limitation may have been intense enough to limit diatom growth. Thus, silicic acid can play a critical role in diatom spring bloom dynamics. The diatom contribution to primary production was variable, ranging from % to ∼100 % depending on the bloom stage and phytoplankton composition. While there was agreement with previous studies regarding the export rate of diatom cells, we observed significantly elevated biogenic silica export. Such a discrepancy can be resolved if a higher fraction of the diatom material exported during our study was modified by zooplankton grazers. This study provides the most direct evidence to date suggesting the important coupling of the silicon and carbon cycles during the spring bloom in the European Arctic.
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Biogenic silica production and diatom dynamics in the Svalbard region during spring
2018Co-Authors: Jeffrey W. Krause, Israel A Marquez, Ingrid Wiedmann, Mar Fernández-méndez, Philipp Assmy, Svein Kristiansen, Carlos M. Duarte, Paul Wassmann, Susana AgustíAbstract:<p><strong>Abstract.</strong> Diatoms are generally the dominant contributors to the Arctic Ocean spring bloom, which is a key event in regional food webs in terms of capacity for secondary production and organic matter export. Dissolved silicic acid is an obligate nutrient for diatoms and has been declining in the European Arctic. The lack of regional silicon cycling information precludes understanding the consequences of such changes for diatom productivity during the Arctic spring bloom. This study communicates the results from a cruise in the European Arctic around Svalbard reporting the first concurrent data on biogenic silica production and export, diatom cellular export, the degree of kinetic limitation by ambient silicic acid, and diatom contribution to primary production. Regional biogenic silica production rates were significantly lower than those achievable in the Southern Ocean and silicic acid concentration limited the biogenic silica production rate in 95&#8201;% of samples. Compared to diatoms in the Atlantic subtropical gyre, regional diatoms are less adapted for silicic acid uptake at low substrate, and at some stations during the present study, silicon limitation may have been intense enough to limit diatom growth. Thus, silicic acid can play a critical role in diatom spring bloom dynamics. Diatom contribution to primary production was variable, ranging from <&#8201;10&#8201;% to ~&#8201;100&#8201;% depending on the bloom stage and phytoplankton composition. While there was agreement with previous studies regarding the rate of diatom cellular export, we observed significantly elevated biogenic silica export. Such a discrepancy can be resolved if a higher fraction of the diatom material exported during our study was modified by zooplankton grazers or originated from melting ice. This study provides the most-direct evidence to date suggesting the important coupling of the silicon and carbon cycles during the spring bloom in the European Arctic.</p>
Susana Agustí - One of the best experts on this subject based on the ideXlab platform.
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biogenic silica production and diatom dynamics in the svalbard region during spring
Biogeosciences, 2018Co-Authors: Jeffrey W. Krause, Israel A Marquez, Mar Fernandezmendez, Ingrid Wiedmann, Philipp Assmy, Svein Kristiansen, Carlos M. Duarte, Paul Wassmann, Susana AgustíAbstract:Abstract. Diatoms are generally the dominant contributors to the Arctic Ocean spring bloom, which is a key event in regional food webs in terms of capacity for secondary production and organic matter export. Dissolved silicic acid is an obligate nutrient for diatoms and has been declining in the European Arctic since the early 1990s. The lack of regional silicon cycling information precludes understanding the consequences of such changes for diatom productivity during the Arctic spring bloom. This study communicates the results from a cruise in the European Arctic around Svalbard, which reports the first concurrent data on biogenic silica production and export, export of diatom cells, the degree of kinetic limitation by ambient silicic acid, and diatom contribution to primary production. Regional biogenic silica production rates were significantly lower than those achievable in the Southern Ocean and silicic acid concentration limited the biogenic silica production rate in 95 % of samples. Compared to diatoms in the Atlantic subtropical gyre, regional diatoms are less adapted for silicic acid uptake at low concentration, and at some stations during the present study, silicon kinetic limitation may have been intense enough to limit diatom growth. Thus, silicic acid can play a critical role in diatom spring bloom dynamics. The diatom contribution to primary production was variable, ranging from % to ∼100 % depending on the bloom stage and phytoplankton composition. While there was agreement with previous studies regarding the export rate of diatom cells, we observed significantly elevated biogenic silica export. Such a discrepancy can be resolved if a higher fraction of the diatom material exported during our study was modified by zooplankton grazers. This study provides the most direct evidence to date suggesting the important coupling of the silicon and carbon cycles during the spring bloom in the European Arctic.
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Biogenic silica production and diatom dynamics in the Svalbard region during spring
2018Co-Authors: Jeffrey W. Krause, Israel A Marquez, Ingrid Wiedmann, Mar Fernández-méndez, Philipp Assmy, Svein Kristiansen, Carlos M. Duarte, Paul Wassmann, Susana AgustíAbstract:<p><strong>Abstract.</strong> Diatoms are generally the dominant contributors to the Arctic Ocean spring bloom, which is a key event in regional food webs in terms of capacity for secondary production and organic matter export. Dissolved silicic acid is an obligate nutrient for diatoms and has been declining in the European Arctic. The lack of regional silicon cycling information precludes understanding the consequences of such changes for diatom productivity during the Arctic spring bloom. This study communicates the results from a cruise in the European Arctic around Svalbard reporting the first concurrent data on biogenic silica production and export, diatom cellular export, the degree of kinetic limitation by ambient silicic acid, and diatom contribution to primary production. Regional biogenic silica production rates were significantly lower than those achievable in the Southern Ocean and silicic acid concentration limited the biogenic silica production rate in 95&#8201;% of samples. Compared to diatoms in the Atlantic subtropical gyre, regional diatoms are less adapted for silicic acid uptake at low substrate, and at some stations during the present study, silicon limitation may have been intense enough to limit diatom growth. Thus, silicic acid can play a critical role in diatom spring bloom dynamics. Diatom contribution to primary production was variable, ranging from <&#8201;10&#8201;% to ~&#8201;100&#8201;% depending on the bloom stage and phytoplankton composition. While there was agreement with previous studies regarding the rate of diatom cellular export, we observed significantly elevated biogenic silica export. Such a discrepancy can be resolved if a higher fraction of the diatom material exported during our study was modified by zooplankton grazers or originated from melting ice. This study provides the most-direct evidence to date suggesting the important coupling of the silicon and carbon cycles during the spring bloom in the European Arctic.</p>
Carlos M. Duarte - One of the best experts on this subject based on the ideXlab platform.
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biogenic silica production and diatom dynamics in the svalbard region during spring
Biogeosciences, 2018Co-Authors: Jeffrey W. Krause, Israel A Marquez, Mar Fernandezmendez, Ingrid Wiedmann, Philipp Assmy, Svein Kristiansen, Carlos M. Duarte, Paul Wassmann, Susana AgustíAbstract:Abstract. Diatoms are generally the dominant contributors to the Arctic Ocean spring bloom, which is a key event in regional food webs in terms of capacity for secondary production and organic matter export. Dissolved silicic acid is an obligate nutrient for diatoms and has been declining in the European Arctic since the early 1990s. The lack of regional silicon cycling information precludes understanding the consequences of such changes for diatom productivity during the Arctic spring bloom. This study communicates the results from a cruise in the European Arctic around Svalbard, which reports the first concurrent data on biogenic silica production and export, export of diatom cells, the degree of kinetic limitation by ambient silicic acid, and diatom contribution to primary production. Regional biogenic silica production rates were significantly lower than those achievable in the Southern Ocean and silicic acid concentration limited the biogenic silica production rate in 95 % of samples. Compared to diatoms in the Atlantic subtropical gyre, regional diatoms are less adapted for silicic acid uptake at low concentration, and at some stations during the present study, silicon kinetic limitation may have been intense enough to limit diatom growth. Thus, silicic acid can play a critical role in diatom spring bloom dynamics. The diatom contribution to primary production was variable, ranging from % to ∼100 % depending on the bloom stage and phytoplankton composition. While there was agreement with previous studies regarding the export rate of diatom cells, we observed significantly elevated biogenic silica export. Such a discrepancy can be resolved if a higher fraction of the diatom material exported during our study was modified by zooplankton grazers. This study provides the most direct evidence to date suggesting the important coupling of the silicon and carbon cycles during the spring bloom in the European Arctic.
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Biogenic silica production and diatom dynamics in the Svalbard region during spring
2018Co-Authors: Jeffrey W. Krause, Israel A Marquez, Ingrid Wiedmann, Mar Fernández-méndez, Philipp Assmy, Svein Kristiansen, Carlos M. Duarte, Paul Wassmann, Susana AgustíAbstract:<p><strong>Abstract.</strong> Diatoms are generally the dominant contributors to the Arctic Ocean spring bloom, which is a key event in regional food webs in terms of capacity for secondary production and organic matter export. Dissolved silicic acid is an obligate nutrient for diatoms and has been declining in the European Arctic. The lack of regional silicon cycling information precludes understanding the consequences of such changes for diatom productivity during the Arctic spring bloom. This study communicates the results from a cruise in the European Arctic around Svalbard reporting the first concurrent data on biogenic silica production and export, diatom cellular export, the degree of kinetic limitation by ambient silicic acid, and diatom contribution to primary production. Regional biogenic silica production rates were significantly lower than those achievable in the Southern Ocean and silicic acid concentration limited the biogenic silica production rate in 95&#8201;% of samples. Compared to diatoms in the Atlantic subtropical gyre, regional diatoms are less adapted for silicic acid uptake at low substrate, and at some stations during the present study, silicon limitation may have been intense enough to limit diatom growth. Thus, silicic acid can play a critical role in diatom spring bloom dynamics. Diatom contribution to primary production was variable, ranging from <&#8201;10&#8201;% to ~&#8201;100&#8201;% depending on the bloom stage and phytoplankton composition. While there was agreement with previous studies regarding the rate of diatom cellular export, we observed significantly elevated biogenic silica export. Such a discrepancy can be resolved if a higher fraction of the diatom material exported during our study was modified by zooplankton grazers or originated from melting ice. This study provides the most-direct evidence to date suggesting the important coupling of the silicon and carbon cycles during the spring bloom in the European Arctic.</p>
Adnan Kasry - One of the best experts on this subject based on the ideXlab platform.
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Gambaran Diatomea pada Perairan Muara Sungai Rokan Kecamatan Bangko dan Kecamatan Batu Hampar Kabupaten Rokan Hilir sebagai Diagnosis Penunjang Identifikasi Lokasi Korban Mati Tenggelam
2014Co-Authors: Muhammad Maliki, Dedi Afandi, Adnan KasryAbstract:Diatomea investigation in the body of drowning victims is one of important investigation todetermination the drowning victims location. Diatomea is sould in the lung or another organfrom the body of victims as prove of drowning intra-vitality it means the victims are still alivewhen they are in the water and they are dead because of it. Diatomea species determining can beconcluded as a supporting diagnose to identify the location of drowning victims by comparingthe diatomea in the victims body with diatomea species in the water this research is a descriptiveresearch which is purposed for recognizing the species and the diatomea abundant in theRokan’s River Estuary of Bangko Sub-district and Batu Hampar Sub-district Rokan HilirRegency this research sample is taken from five research of stasions as purposive sampling. Thisresearch was done in April and May 2013 at Rokan’s River Estuary in Sub-district BangkoAnd Subdistrict Batu Hampar Rokan Hilir Regency. Diatomea investigation was done by usingBinocular microscope. This determining was done by using Masaharu and Yunfang atlas theabundant was searched by counted and numbered by using American Public Health Associations(APHA) formula.Diatomea was founded eight species they are: Aulocoseira sp, Diatoma sp, Nitzchia sp,Isthmia sp, Melosira sp, Navicula sp, Skeletonema sp, Bitdulphia sp. The abundant of diatomeais founded 11152,2 sel/L when the water comes up and I found 9132,6 sel/L when the water comedown with the Diatoma sp as the most dominant diatomea as a mount as 4986,4 sel/L when thewater comes up and with Diatoma sp as the most dominant Diatomea as amount as 3799,8 sel/L. Keyword : Rokan’s river estuary drowning, species and abundant diatomea
