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131.
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
132.
Charles Nkoumbou Fuh Calistus Gentry Jacqueline Tchakounte Numbem Yolande Vanessa Belle Ekwe Lobé Christin Steve Nwagoum Keyamfé 《Comptes Rendus Geoscience》2017,349(4):165-174
Archaean–Paleoproterozoic foliated amphibole-gneisses and migmatites interstratified with amphibolites, pyroxeno-amphibolites and REE-rich banded-iron formations outcrop at Mafé, Ndikinimeki area. The foliation is nearly vertical due to tight folds. Flat-lying quartz-rich mica schists and quartzites, likely of Pan-African age, partly cover the formations. Among the Mafé BIFs, the oxide BIF facies shows white layers of quartz and black layers of magnetite and accessory hematite, whereas the silicate BIF facies is made up of thin discontinuous quartz layers alternating with larger garnet (almandine–spessartine) + chamosite + ilmenite ± Fe-talc layers. REE-rich oxide BIFs compositions are close to the East Pacific Rise (EPR) hydrothermal deposit; silicate BIFs plot midway between EPR and the associated amphibolite, accounting for a contamination by volcanic materials, in addition to the hydrothermal influence during their oceanic deposition. The association of an oceanic setting with alkaline and tholeiitic magmatism is typical of the Algoma-type BIF deposit. The REE-rich BIFs indices recorded at Mafé are interpreted as resulting from an Archaean–Paleoproterozoic mineralization. 相似文献
133.
Jonas V. Müller Christian Berg Jacqueline Détraz-Méroz Brigitta Erschbamer Noémie Fort Catherine Lambelet-Haueter Vera Margreiter Florian Mombrial Andrea Mondoni Konrad Pagitz Francesco Porro Graziano Rossi Patrick Schwager Elinor Breman 《山地科学学报》2017,14(4):806-810
Safeguarding plants as seeds in ex situ collections is a cost effective element in an integrated plant conservation approach. The European Alps are a regional centre of plant diversity. Six institutions have established a regional network covering the European Alps which will conserve at least 500 priority plant species and which will improve the conservation status of plant species in grassland communities in the subalpine, alpine and nival altitudinal belts. Targeted research will expand the knowledge of the ecology of target species. Public engagement activities will raise the awareness for the importance of specific conservation actions in the European Alps. 相似文献
134.
Adrian Liu Max Tegmark Judd Bowman † Jacqueline Hewitt Matias Zaldarriaga 《Monthly notices of the Royal Astronomical Society》2009,398(1):401-406
21-cm tomography is expected to be difficult in part because of serious foreground contamination. Previous studies have found that line-of-sight approaches are capable of cleaning foregrounds to an acceptable level on large spatial scales, but not on small spatial scales. In this paper, we introduce a Fourier space formalism for describing the line-of-sight methods, and use it to introduce an improved new method for 21-cm foreground cleaning. Heuristically, this method involves fitting foregrounds in Fourier space using weighted polynomial fits, with each pixel weighted according to its information content. We show that the new method reproduces the old one on large angular scales, and gives marked improvements on small scales at essentially no extra computational cost. 相似文献
135.
Bastiaan Wijnand Borsje Suzanne Jacqueline Marie Hélène Hulscher Peter Maria Jozef Herman Mindert Bareld de Vries 《Ocean Dynamics》2009,59(5):659-670
The bed of the North Sea is covered by sand waves and houses a great number of macrobenthic animals. These bio-engineers are
known to have a significant influence on the stability of the bed and thereby on the geomorphology of the seabed. This paper
proposes a parameterization of these bio-geomorphological interactions. Given the abundance of three dominant bio-engineers
on the Dutch Continental Shelf, the predicted occurrence of sand waves, in which the parameterization is included, shows significantly
better results, compared to the prediction for the default case without biology. Therefore, the inclusion of biological activity
could be important to predict the occurrence of sand waves. 相似文献
136.
Fluoride in Nebraska's Ground Water 总被引:1,自引:0,他引:1
David C. Gosselin Jacqueline Headrick F. Edwin Harvey Rod Tremblay Kimberly McFarland 《Ground Water Monitoring & Remediation》1999,19(2):87-95
Fluoride concentrations in ground water are generally low but play an important role in dental health. This study evaluates the vertical and spatial distribution of fluoride in Nebraska's ground water and examines the geological and geochemical processes that control its concentration. Data from 1794 domestic wells sampled by the Nebraska Department of Health and Human Services. Regulation, and Licensure (NDOH) had a range of fluoride concentrations from <0.1 to 2.6 mg/L. and a median concentration of 0.3 mg/L. The median fluoride concentrations for Nebraska's 13 ground water regions varied from 0.2 to 0.7 mg/L. In each of these regions, individual wells may have either insufficient or overabundant F concentrations; we recommend that individual private water systems be tested for fluoride. Based on these data, system-specific recommendations can be made regarding the necessity for fluoridation.
Geochemical data indicated that the majority of fluoride occurs as F. Dissolution of F-bearing minerals controls fluoride occurrence. Apatite plus minor amounts of fluorite along with significant ground water residence times are the primary factors controlling F in the water from the Dakota Formation in Knox County, as well as in other parts of northeastern Nebraska. In western and southwestern Nebraska, dissolution of volcanic glass is the most probable source of F Long residence times plus fluorite also may contribute to the F concentrations in the Chadron Formation. 相似文献
Geochemical data indicated that the majority of fluoride occurs as F. Dissolution of F-bearing minerals controls fluoride occurrence. Apatite plus minor amounts of fluorite along with significant ground water residence times are the primary factors controlling F in the water from the Dakota Formation in Knox County, as well as in other parts of northeastern Nebraska. In western and southwestern Nebraska, dissolution of volcanic glass is the most probable source of F Long residence times plus fluorite also may contribute to the F concentrations in the Chadron Formation. 相似文献
137.
Robert G. Hatfield Barbara A. Maher Jacqueline M. Pates Philip A. Barker 《Journal of Paleolimnology》2008,40(4):1143-1158
We examine sediment dynamics in an upland, temperate lake system, Lake Bassenthwaite (NW England), in the context of changing
climate and land use, using magnetic and physical core properties. Dating and analysis of the sedimentary records of nine
recovered cores identify spatially variable sedimentation rates across the deep lake basin. Mineral magnetic techniques, supported
by independent geochemical analyses, identify significant variations both in sediment source and flux over the last ∼2100 years.
Between ∼100 years BC and ∼1700 AD, sediment fluxes to the lake were low and dominated by material sourced from within the
River Derwent sub-catchment (providing 80% of the hydraulic load at the present day). Post-1700 AD, the lake sediments became
dominantly sourced from Newlands Beck (presently providing ∼10% of the lake’s hydraulic load). Three successive, major pulses
of erosion and increased sediment flux appear linked to specific activities within the catchment, specifically: mining activities
and associated deforestation in the mid-late nineteenth century; agricultural intensification in the mid-twentieth century
and, within the last decade, the additional possible impact of climate change. These results are important for all upland
areas as modifications in climate become progressively superimposed upon the effects of previous and/or ongoing anthropogenic
catchment disturbance. 相似文献
138.
The last decade has seen the refinement of a technique for reconstructing palaeo-ice thicknesses based on using the retained H2O and CO2 content in glassy eruptive deposits to infer quenching pressures and therefore ice thicknesses. The method is here applied to Bláhnúkur, a subglacially erupted rhyolitic edifice in Iceland. A decrease in water content from ~0.7?wt.% at the base to ~0.3?wt.% at the top of the edifice suggests that the ice was 400?m thick at the time of the eruption. As Bláhnúkur rises 350?m above the surrounding terrain, this implies that the eruption occurred entirely within ice, which corroborates evidence obtained from earlier lithofacies studies. This paper presents the largest data set (40 samples) so far obtained for the retained volatile contents of deposits from a subglacial eruption. An important consequence is that it enables subtle but significant variations in water content to become evident. In particular, there are anomalous samples which are either water-rich (up to 1?wt.%) or water-poor (~0.2?wt.%), with the former being interpreted as forming intrusively within hyaloclastite and the latter representing batches of magma that were volatile-poor prior to eruption. The large data set also provides further insights into the strengths and weaknesses of using volatiles to infer palaeo-ice thicknesses and highlights many of the uncertainties involved. By using examples from Bláhnúkur, the quantitative use of this technique is evaluated. However, the relative pressure conditions which have shed light on Bláhnúkur’s eruption mechanisms and syn-eruptive glacier response show that, despite uncertainties in absolute values, the volatile approach can provide useful insight into the mechanisms of subglacial rhyolitic eruptions, which have never been observed. 相似文献
139.
Gelatinous zooplankton species composition, distribution and abundance were investigated in the bay and the lagoon of Bizerte (North Tunisian coast) from January 2004 to December 2005. In total, 48 species were identified in the study area: 24 medusae, 11 siphonophores, four appendicularians, six chaetognaths, two pteropods and one doliolid. The hydromedusa Eutima mira was recorded for the first time in the Western Mediterranean Sea. The diversity in the Bay of Bizerte was greater than the diversity in the Bizerte lagoon. There was a loss of species diversity. Siphonophores were the most sensitive group to anthropogenic discharge. Only two species of siphonophores were recorded in the lagoon. Four species of gelatinous zooplankton, Muggiaea kochi, Lensia conoidea, Oikopleura longicauda and Podocorynoides minima were the most frequent species in the lagoon and may benefit from eutrophication. Appendicularians were numerically the most dominant group in the bay and the lagoon of Bizerte. Mesozooplankton density declined significantly in autumn and winter of 2004 and 2005 in relation to the dense aggregations of the scyphomedusae Pelagia noctiluca. Statistical analysis divided the study area into three zones: lagoon zone, bay zone and channel zone. 相似文献