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Barbara B. Prézelin Max M. Tilzer Oscar Schofield Clivia Haese 《Aquatic Sciences - Research Across Boundaries》1991,53(2-3):136-186
This tutorial was designed for nonbiologists requiring an introduction to the nature and general timescales of phytoplankton responses to physical forcing in aquatic environments. As such, an effort was made to highlight biological markers which might assist in identifying, measuring and/or validating physical processes controlling the variability in the distribution, abundance, composition and activity of phytoplankton communities. Given the recent advances in environmental optics and remote sensing capabilities, a special emphasis was placed on the nature and utility of phytoplankton optical properties in current bio-optical modelling efforts to predict temporal and spatial variability in phytoplankton productivity and growth. 相似文献
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Nutrient dynamics in estuaries are temporally variable in response to changing physical–chemical conditions and biogeochemical
processes involving primary producer groups such as phytoplankton, microphytobenthos, seagrass and macroalgae. In order to
reveal intra-annual changes in the biomass of primary producer groups and associated changes in estuarine nutrient dynamics,
we developed a box model, coupling water inflows and outflows and nitrogen dynamics in Wilson Inlet, a large, central-basin-dominated,
intermittently closed estuary exposed to a Mediterranean climate in Western Australia. The model is calibrated and validated
with monitoring data, aquatic plant biomass estimates and biogeochemical rate measurements. Macrophytes and their microalgal
epiphytes appear to rapidly assimilate nutrients from the first flush from the catchment in winter, but this buffer capacity
then ceases, and a phytoplankton ‘bloom’ develops in response to subsequent river runoff events in spring. Significant amounts
of bioavailable nitrogen are exported to the ocean because phytoplankton predominance occurs while the sand bar is breached.
Surface sediments play a key role for nitrogen dynamics: In late spring to autumn, high light availability at the sediment
surface stimulates high primary production by microphytobenthos, leading to reduced benthic ammonium fluxes particularly in
the deep basin. Microphytobenthos contributes about 60% of annual whole-system primary production. Despite high benthic primary
production, nitrogen release from sediments is the biggest nitrogen source to the estuary. 相似文献
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Yemen is one of the poorest countries in the world. The development of its fishery sector is increasingly being mentioned as a source of livelihood creation. The aims of this paper are to: (a) provide an overview of the institutional environment in which small-scale fishermen in Yemen operate; (b) investigate the constraints they face; and (c) discuss the potential role that co-operatives could play in such development. Small-scale fisheries in Yemen are increasingly important, yet they struggle with access to infrastructure, markets, and credit. We identify significant differences in the development of the fisheries sector in the two main fishing regions: the Gulf of Aden and the Red Sea. Overall, local capacity within co-operatives needs to be improved and private sector development should be encouraged. 相似文献
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R. R. Haese J. Schramm M. M. Rutgers van der Loeff H. D. Schulz 《International Journal of Earth Sciences》2000,88(4):619-629
Pore water and solid phase from surface sediments of the continental slope off Uruguay and from the Argentine Basin (southwestern Atlantic) were investigated geochemically to ascribe characteristic early diagenetic reactions of iron and manganese. Solid-phase iron speciation was determined by extractions as well as by Mössbauer spectroscopy. Both methods showed good agreement ( <6% deviation) for total-Fe speciation. The proportion of easy reducible iron oxyhydroxide relative to total-Fe oxides decreased from the continental slope to the deep sea which is attributed to an increase in crystallinity during transport as well as to a general decrease of iron mobilization. The product of iron reoxidation is Fe oxyhydroxide which made up less than 5% of total Fe. In addition to this fraction, a proportion of smectite bound iron was found to be redox reactive. This fraction made up to 10% of total Fe in sediments of the Argentine Basin and was quantitatively extracted by 1?N HCl. The redox reactive Fe(+II) fraction of smectite was almost completely reoxidized within 24?h under air atmosphere and may therefore considerably contribute to iron redox cycling if bioturbation occurs. In the case of the slope sediments we found concurrent iron and manganese release to pore water. It is not clear whether this is caused by dissimilatory iron and manganese reduction at the same depth or dissimilatory iron reduction alone inducing Mn(+IV) reduction by (abiotic) reaction with released Fe2+. The Argentine Basin sediment showed a significant manganese solid-phase enrichment above the denitrification depth despite the absence of a distinct pore-water gradient of Mn. This implies a recent termination of manganese mobilization and thus a non-steady-state situation with respect to sedimentation or to organic carbon burial rate. 相似文献
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Clivia?HejnyEmail author Raffaela?Sagl Daniel?M.?T?bbens Ronald?Miletich Manfred?Wildner Lutz?Nasdala Angela?Ullrich Tonci?Balic-Zunic 《Physics and Chemistry of Minerals》2012,39(5):399-412
The structure of realgar, As4S4, and its evolution with pressure have been investigated employing in situ X-ray diffraction, optical absorption and vibrational spectroscopy on single-crystal samples in diamond-anvil cells. Compression under true hydrostatic conditions up to 5.40 GPa reveals equation-of-state parameters of V 0 = 799.4(2.4) Å3 and K 0 = 10.5(0.4) GPa with \(K_0^\prime\) = 8.7. The remarkably high compressibility can be attributed to a denser packing of the As4S4 molecules with shortening of the intermolecular bonds of up to 12 %, while the As4S4 molecules remain intact showing rigid-unit behaviour. From ambient pressure to 4.5 GPa, Raman spectra exhibit a strong blue shift of the Raman bands of the lattice-phonon regime of 24 cm–1, whereas frequencies from intramolecular As-S stretching modes show negligible or no shifts at all. On pressurisation, realgar shows a continuous and reversible colour change from bright orange over deep red to black. Optical absorption spectroscopy shows a shift of the absorption edge from 2.30 to 1.81 eV up to 4.5 GPa, and DFT calculations show a corresponding reduction in the band gap. Synchrotron-based measurements on polycrystalline samples up to 45.5 GPa are indexed according to the monoclinic structure of realgar. 相似文献
6.
Niragira Sanctus D’Haese Marijke Buysse Jeroen Van Orshoven Jos Ndimubandi Jean 《GeoJournal》2021,86(2):865-884
GeoJournal - The global farming conditions have gone profound mutations that steadily increased vulnerability among smallholder farmers. As consequence, rural households have set mechanisms of... 相似文献
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