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101.
Trophic Assessment in Chinese coastal systems-review of methods and application to the Changjiang (Yangtze) Estuary and Jiaozhou Bay 总被引:3,自引:0,他引:3
Yongjin Xiao João G. Ferreira Suzanne B. Bricker João P. Nunes Mingyuan Zhu Xuelei Zhang 《Estuaries and Coasts》2007,30(6):901-918
Coastal eutrophication has become one of the main threats to Chinese coastal areas during the last two decades. High nutrient
loads from human activities have modified the natural background water quality in coastal water bodies, resulting in a range
of undesirable effects. There is a need to assess the eutrophic level in coastal systems and to identify the extent of this
impact to guide development of appropriate management efforts. Traditional Chinese assessment methods are discussed and compared
with other currently-used methods, such as the Oslo-Paris Convention for the Protection of the North Sea (OSPAR) Comprehensive
Procedure and Assessment of Estuarine Trophic Status (ASSETS). The ASSETS method and two Chinese methods were tested on two
Chinese systems: the Changjiang (Yangtze) Estuary and Jiaozhou Bay. ASSETS is process based, and uses a pressure-state-response
model based on three main indices: Influencing Factors, Overall Eutrophic Condition, and Future Outlook. The traditional methods
are based on a nutrient index. ASSETS was successfully applied to both systems, classifying the Changjiang Estuary as Bad
(high eutrophication) and Jiaozhou Bay as High (low eutrophication). The traditional methods led to ambiguous results, particularly
for Jiaozhou Bay, due to the high spatial variability of data and a failure to assess the role of shellfish aquaculture in
nutrient control. An overview of the Chinese coastal zone identifies 50 estuaries and bays that should form part of a national
assessment. A comparison of methods and results suggests that ASSETS is a promising tool for evaluating the eutrophication
status of these systems. 相似文献
102.
103.
Henry P. Huntington Michelle Boyle Gwenn E. Flowers John W. Weatherly Lawrence C. Hamilton Larry Hinzman Craig Gerlach Rommel Zulueta Craig Nicolson Jonathan Overpeck 《Climatic change》2007,82(1-2):77-92
Human activities in the Arctic are often mentioned as recipients of climate-change impacts. In this paper we consider the
more complicated but more likely possibility that human activities themselves can interact with climate or environmental change
in ways that either mitigate or exacerbate the human impacts. Although human activities in the Arctic are generally assumed
to be modest, our analysis suggests that those activities may have larger influences on the arctic system than previously
thought. Moreover, human influences could increase substantially in the near future. First, we illustrate how past human activities
in the Arctic have combined with climatic variations to alter biophysical systems upon which fisheries and livestock depend.
Second, we describe how current and future human activities could precipitate or affect the timing of major transitions in
the arctic system. Past and future analyses both point to ways in which human activities in the Arctic can substantially influence
the trajectory of arctic system change. 相似文献
104.
Jonathan Reynolds 《GeoJournal》1998,45(4):245-254
The internationalising activities of retailers have tended to precede the theoretical contributions of academics. This is
particularly the case for the cultural context within which retail internationalisation takes place. Following an examination
of the growth of international retailing activity, the article reviews generic difficulties in studying inter-cultural differences
before considering the specific steps which retail practitioners have taken to understand the comparative characteristics
of retail and consumer markets through the growth of geodemographic and lifestyle analysis. Finally, we relate one of the
most significant integrative intercultural theoretical instruments to the case of retail internationalisation within Western
Europe. We find that significant insights into retailer behaviour and strategy can be gained from an understanding of the
culturally-specific characteristics of the activity.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
105.
Résumé Nous appliquons dans ce mémoire la théorie des perturbations, développée antérieuremet par l'un de nous, à la déduction des principales caractéristiques normales des perturbations compatibles avec un champ moyen donné de pression et de température. Cette deduction comprend la détermination: 1) de la configuration moyenne des perturbations dans les différentes régions étudiées; 2) des zones de creusement et de comblement et en particulier des foyers de formation et de disparition des perturbations; 3) des trajectoires, vitesses, fréquences et amplitudes moyennes des perturbations. C'est à l'ensemble de ces propriétés moyennes que nous donnons le nom de «climatologie dynamique» d'une période donnée.Après une première partie théorique, nous donnons des exemples d'application des résultats généraux à la climatologie dynamique des mois de Janvier et de Juillet pour l'Amérique du Nord, l'Atlantique Nord et l'Europe.
à ce mémoire a été assigné le Prix 1956 de la « Società Italiana di Geofisica e Meteorologia ». 相似文献
Summary In this paper we apply the theory of perturbations, previously developed by one of us, to the deduction of the main normal characteristics of the perturbations that are compatible with a given mean field of pressure and temperature. This deduction comprises the determination: 1) of the mean configuration of the perturbations for the different regions under examination; 2) of the normal deepening and filling regions of the perturbations, and particularly their formation and vanishing focuses; 3) of the mean paths, speeds, frequencies and amplitudes of the perturbations. The «dynamical climatology» we are contemplating here is concerned with all these mean properties of the perturbations for a given period.After a first theoretical part, we give some examples of the application of the general results to the dynamical climatology of January and July for North America, North Atlantic and Europe.
à ce mémoire a été assigné le Prix 1956 de la « Società Italiana di Geofisica e Meteorologia ». 相似文献
106.
Sharmishtha Dattagupta Jonathan Martin Shu-min Liao Robert S. Carney & Charles R. Fisher 《Marine Ecology》2007,28(1):193-198
Bathynerita naticoidea (Gastropoda: Neritidae) is a numerically dominant heterotrophic gastropod found at hydrocarbon seep sites on the upper Louisiana slope of the Gulf of Mexico. Snails of this species are commonly associated with beds of the methanotrophic mussel Bathymodiolus childressi (Bivalvia: Mytilidae), and their population structure mirrors that of the mussels they are found among. Previous studies have shown that these snails feed on bacteria and decomposing periostracum on the B. childressi shell. We predicted that B. naticoidea might be attracted to cues specific to its preferred habitat, such as dissolved methane, mucus from conspecific snails, or metabolites produced by B. childressi mussels. To examine this, we used a flow‐through Y‐maze system to investigate the behavior of B. naticoidea exposed to these potential cues. We found that the nerite is not attracted to methane, but is strongly attracted to seawater conditioned with B. childressi. The attractant appears to be specific to this type of mussel, and is not a soluble cue produced by conspecific snails. 相似文献
107.
Graeme T. Swindles Ivan P. Savov Charles B. Connor Jonathan Carrivick Elizabeth Watson Ian T. Lawson 《Geology Today》2013,29(6):214-217
The volcanic ash or ‘tephra’ cloud resulting from the relatively small (volume and VEI) eruption of the Icelandic volcano Eyjafjallajökull in 2010 caused major air travel disruption, at substantial global economic cost. On several occasions in the past few centuries, Icelandic eruptions have created ash and/or sulphur dioxide clouds which were detected over Europe (e.g. Hekla in 1947, Askja in 1875, and Laki in 1783). However, these historical observations do not represent a complete record of events serious enough to disrupt aviation in Europe. The only feasible evidence for this is within the geological tephra record. Ash layers are preserved in bogs and lakes where tephra deposited from the atmosphere is incorporated in the peat/mud. In this article we: 1, introduce the analysis of the Northern European sedimentary tephra record; 2, discuss our findings and modelling results; 3, highlight how these were misinterpreted by the popular media; and 4, use this experience to outline several existing problems with current tephra studies and suggest agendas for future research. 相似文献
108.
Liliane Janikian Renato Paes De Almeida Ricardo Ivan Ferreira Da Trindade Antonio Romalino Santos Fragoso‐Cesar Manoel Souza D′Agrella‐Filho Elton Luis Dantas Eric Tohver 《地学学报》2008,20(4):259-266
The Ediacaran is one of the most important periods on Earth evolution, including the first appearance of soft‐bodied macrofossils, major climatic changes and a supposed rise in free oxygen. In southernmost Brazil, this period is represented by Camaquã Supergroup, including the Bom Jardim Group and the Acampamento Velho Formation, both of which record continental palaeoenvironmental changes in a more than 5000 m thick stratigraphic succession. Age constraints are given by seven Ar‐Ar and U‐Pb determinations on volcanic rocks, which bracket these units between c. 605 and 574 Ma, revealing the best dated and most continuous documented Ediacaran continental succession to date. Depositional systems evolution supports a Phanerozoic‐type glacial context during the last Neoproterozoic glacial event and presents the Picada das Graças Formation (580 ± 3.6 Ma) as the first dated non‐glacial unit coeval to the Gaskiers Formation. 相似文献
109.
Tropical cyclones (TC) are recognized to modify the thermal structure of the upper ocean through the process of vertical mixing. Assessing the role this mixing plays in the overall stratification of the upper ocean is difficult, due to the relatively short and incomplete instrumental record. Proxy records for both TC landfalls and oceanographic stratification are preserved within the geological record and provide insight for how past changes in TC‐induced mixing have potentially affected water column structure prior to the instrumental record. Here we provide the first comparison between previously published paleo‐reconstructions of vertical ocean density and tropical cyclone activity from the western North Atlantic. A prominent lull in TC activity has been observed prior to approximately 1700 CE that extends back several centuries. This interval of low TC activity is shown to be concurrent with the timing of increased ocean stratification near Great Bahama Bank, potentially due in part to reduced TC‐induced mixing. To test whether this relationship is feasible, we present numerical results from a coarse‐resolution ocean general circulation model experiment isolating the effect of TC surface wind forcing on the upper ocean. An anomaly of roughly 0.12 kg m?3 in vertical stratification occurs above and below the mixed layer for model runs with and without TC mixing. This anomaly is roughly 25% of the entire paleo‐density signal observed just prior to 1700 CE. These results suggest that TC mixing alone cannot completely explain the density anomaly observed prior to 1700 CE, but support TC variability as an important contributor to enhancing oceanic stratification during this interval. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
110.
Timothy M. Shanahan Jonathan T. Overpeck W. E. Sharp Christopher A. Scholz Justice A. Arko 《水文研究》2007,21(13):1678-1691
Historical changes in the level of Lake Bosumtwi, Ghana, have been simulated using a catchment‐scale hydrological model in order to assess the importance of changes in climate and land use on lake water balance on a monthly basis for the period 1939–2004. Several commonly used models for computing evaporation in data‐sparse regions are compared, including the Penman, the energy budget, and the Priestley–Taylor methods. Based on a comparison with recorded lake level variations, the model with the energy‐budget evaporation model subcomponent is most effective at reproducing observed lake level variations using regional climate records. A sensitivity analysis using this model indicates that Lake Bosumtwi is highly sensitive to changes in precipitation, cloudiness and temperature. However, the model is also sensitive to changes in runoff related to vegetation, and this factor needs to be considered in simulating lake level variations. Both interannual and longer‐term changes in lake level over the last 65 years appear to have been caused primarily by changes in precipitation, though the model also suggests that the drop in lake level over the last few decades has been moderated by changes in cloudiness and temperature over that time. Based on its effectiveness at simulating the magnitude and rate of lake level response to changing climate over the historical record, this model offers a potential future opportunity to examine the palaeoclimatic factors causing past lake level fluctuations preserved in the geological record at Lake Bosumtwi. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献