Seasonal variation in di-nitrogen fluxes and associated processes (denitrification, anammox and nitrogen fixation) in sediment subject to shellfish farming influences     

Laura Minjeaud  Valerie D. Michotey  Nicole Garcia  Patricia C. Bonin 《Aquatic Sciences - Research Across Boundaries》2009,71(4):425-435

Seasonal patterns of di-nitrogen fluxes together with denitrification, anammox, and N-fixation rates were studied in sediment in an area subject to strong human pressure via waste water, tributaries and shellfish farming in the Mediterranean Sea (Carteau Cove, NW area of the Gulf of Lion). Ammonium concentration demonstrated no seasonal variation, however, a large increase in its concentration was observed over a 10 years period due to intense biodeposition of organic matter. In contrast, nitrate concentration demonstrated no seasonal or long-term (10 years) variation. The main processes affecting di-nitrogen flux magnitudes were denitrification and N-fixation. Anammox was only detected occasionally, nevertheless it represented at times up to 39% of the N₂-flux. Nitrate reducing processes were variable and denitrification showed a 20-fold increase over the past 10 years and might actually have reached its potential maximal activity. Rates of N₂ production (denitrification and anammox) were generally higher than those of N-fixation, leading to elimination of nitrogen from the ecosystem.  相似文献   

ESR dating of dental enamel from Middle Palaeolithic levels at Lazaret Cave,France     

Véronique Michel  Guanjun Shen  Patricia Valensi  Henry de Lumley 《Quaternary Geochronology》2009,4(3):233-240

ESR dating was carried out on Cervus elaphus tooth enamel samples from the depositional sequence of Lazaret Cave, Nice, France. The deposits contain Anteneandertal hominid fossils associated with abundant lithic artefacts and faunal remains. Three samples from the Mousterian occupations in complex CIII (Fouille d'entrée) yielded early uptake (EU) ages between 108 and 125 ka and linear uptake (LU) ages between 133 and 160 ka. Seven samples from the Acheulian levels in the upper part of the complex CII (Fouille d'entrée and Fouille centre) gave EU ages between 113 and 165 ka and LU ages between 147 and 210 ka, with weighted means at 131 ± 7 and 165 ± 9 ka, respectively. The results of six enamel samples from the lower Acheulian levels at Locus VIII, another place in the cave, were discarded because of their decreasing tendency with depth. The US–ESR combination method was also applied and the CSUS–ESR dates were calculated using the ESR-DATA program. Altogether, the data suggest that the Lazaret Acheulian and Mousterian occupations were rapidly formed during OIS 6.  相似文献   

Mira kinematics from Hipparcos data: a Galactic bar to beyond the Solar circle     

Michael W. Feast  Patricia A. Whitelock 《Monthly notices of the Royal Astronomical Society》2000,317(2):460-487

The space motions of Mira variables are derived from radial velocities, Hipparcos proper motions and a period–luminosity relation. The previously known dependence of Mira kinematics on the period of pulsation is confirmed and refined. In addition, it is found that Miras with periods in the range 145–200 d in the general Solar neighbourhood have a net radial outward motion from the Galactic Centre of 75±18 km s⁻¹. This, together with a lag behind the circular velocity of Galactic rotation of 98±19 km s⁻¹, is interpreted as evidence for an elongation of their orbits, with their major axes aligned at an angle of ∼17° with the Sun–Galactic Centre line, towards positive Galactic longitudes. This concentration seems to be a continuation to the Solar circle and beyond of the bar-like structure of the Galactic bulge, with the orbits of some local Miras probably penetrating into the bulge. These conclusions are not sensitive to the distance scale adopted. A further analysis is given of the short-period (SP) red group of Miras discussed in companion papers in this series. In Appendix A the mean radial velocities and other data for 842 oxygen-rich Mira-like variables are tabulated. These velocities were derived from published optical and radio observations.  相似文献   

Managing land-use effects on Northland dune lakes: lessons from the past     

Tom Stephens  Paul Augustinus  Brett Rip  Patricia Gadd  Atun Zawadski 《新西兰海洋与淡水研究杂志》2018,52(3):409-429

The Northland region of New Zealand includes numerous high-value, macrophyte-dominated dune lakes. Recent water policy reforms offer limited guidance on managing for aquatic macrophytes. In addition, dune lake histories are poorly known as regular monitoring dates to 2005 AD. Here, ca. 4000 years of lake functional behaviour is reconstructed from sedimentary archives in two Northland dune lakes (Humuhumu and Rotokawau). Results demonstrated that macrophyte dominance is sensitive to catchment erosion and hydrological drawdown. Degradation of macrophyte communities occurred in the nineteenth and twentieth centuries, earlier at Lake Humuhumu than Lake Rotokawau (post-1880 AD and post-1930 AD, respectively). In both lakes, increased erosional influx reduced macrophyte productivity, before later increases to wider trophic state (post-1970 AD). Lake-level decline is linked to increased nutrient loading at Lake Rotokawau but less so, Lake Humuhumu which is more strongly groundwater-fed. In Northland dune lakes, water-level reduction and erosional influx from land use have driven macrophyte degradation.  相似文献   

Zooplankton research off Peru: A review   总被引：2，自引：1，他引：1  

Patricia Ayn  Maria I. Criales-Hernandez  Ralf Schwamborn  Hans-Jürgen Hirche 《Progress in Oceanography》2008,79(2-4):238

A review of zooplankton studies conducted in Peruvian marine waters is given. After a short history of the development of zooplankton research off Peru, we review zooplankton methodology, taxonomy, biodiversity, spatial distribution, seasonal and interannual variability, trophodynamics, secondary production, and modelling. We review studies on several micro-, meso-, macro-, and meroplankton groups, and give a species list from both published and unpublished reports. Three regional zooplankton groups have been identified: (1) a continental shelf group dominated by Acartia tonsa and Centropages brachiatus; (2) a continental slope group characterized by siphonophores, bivalves, foraminifera and radiolaria; (3) and a species-rich oceanic group. The highest zooplankton abundances and biomasses were often found between 4–6°S and 14–16°S, where continental shelves are narrow. Species composition changes with distance from the shore. Species composition and biomass also vary strongly on short time scales due to advection, peaks of larval production, trophic interactions, and community succession. The relation of zooplankton to climatic variability (ENSO and multi-decadal) and fish stocks is discussed in the context of ecological regime shifts. An intermediate upwelling hypothesis is proposed, based on the negative effects of low upwelling intensity in summer or extremely strong and enduring winter upwelling on zooplankton abundance off Peru. According to this hypothesis, intermediate upwelling creates an optimal environmental window for zooplankton communities. Finally, we highlight important knowledge gaps that warrant attention in future.  相似文献   

Trophic modeling of the Northern Humboldt Current Ecosystem, Part II: Elucidating ecosystem dynamics from 1995 to 2004 with a focus on the impact of ENSO   总被引：1，自引：1，他引：0  

Marc H. Taylor  Jorge Tam  Vernica Blaskovic  Pepe Espinoza  R. Michael Balln  Claudia Wosnitza-Mendo  Juan Argüelles  Erich Díaz  Sara Purca  Noemi Ochoa  Patricia Ayn  Elisa Goya  Dimitri Gutirrez  Luis Quipuzcoa  Matthias Wolff 《Progress in Oceanography》2008,79(2-4):366

The Northern Humboldt Current Ecosystem is one of the most productive in the world in terms of fish production. Its location near to the equator permits strong upwelling under relatively low winds, thus creating optimal conditions for the development of plankton communities. These communities ultimately support abundant populations of grazing fish such as the Peruvian anchoveta, Engraulis ringens. The ecosystem is also subject to strong inter-annual environmental variability associated with the El Niño Southern Oscillation (ENSO), which has major effects on nutrient structure, primary production, and higher trophic levels. Here our objective is to model the contributions of several external drivers (i.e. reconstructed phytoplankton changes, fish immigration, and fishing rate) and internal control mechanisms (i.e. predator-prey) to ecosystem dynamics over an ENSO cycle. Steady-state models and time-series data from the Instituto del Mar del Perú (IMARPE) from 1995 to 2004 provide the base data for simulations conducted with the program Ecopath with Ecosim. In simulations all three external drivers contribute to ecosystem dynamics. Changes in phytoplankton quantity and composition (i.e. contribution of diatoms and dino- and silicoflagellates), as affected by upwelling intensity, were important in dynamics of the El Niño of 1997–98 and the subsequent 3 years. The expansion and immigration of mesopelagic fish populations during El Niño was important for dynamics in following years. Fishing rate changes were the most important of the three external drivers tested, helping to explain observed dynamics throughout the modeled period, and particularly during the post-El Niño period. Internal control settings show a mix of predator–prey control settings; however a “wasp-waist” control of the ecosystem by small pelagic fish is not supported.  相似文献   

Decline of brown trout (Salmotrutta) in Switzerland - how to assess potential causes in a multi-factorial cause-effect relationship.     

Patricia Burkhardt-Holm 《Marine environmental research》2008,66(1):181-182

A considerable decline in fish catch in Switzerland triggered a 5-year project (Fischnetz) to investigate potential causes. The results of many field and laboratory studies, together with literature and historical data, indicated a need for a concise synthesis of the results. Therefore, Bayesian probability network (BPN) and weight-of-evidence (WOE) approaches were applied. Here, these both approaches are compared and evaluated. In addition, the potential reasons for the (mis)match in the two approaches were evaluated. In both studies, proliferative kidney disease (PKD), caused by a parasite, and the clinical outbreak supported by various factors, was a very probable single parameter. WOE assessed habitat and streambed quality as likely for contributing to impaired health, recruitment and abundance at single sites only, but this parameter was assessed to be the most important and ubiquitous stressor in the BPN. Mismatches suggested that these factors were either not considered or not equally assessed by the different models, which is due to different endpoints, incomplete data sets and different handling of these various data sets by the applied synthesis approaches.  相似文献   

Experimental study of the dependence of embryonic development of Trachurus trachurus eggs on temperature     

Cunha  M. Emilia; Vendrell  Catarina; Goncalves  Patricia 《ICES Journal of Marine Science》2008,65(1):17-24

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Welcome mats? The role of seagrass meadow structure in controlling post-settlement survival in a keystone sea-urchin species     

Patricia Prado  Javier Romero  Teresa Alcoverro 《Estuarine, Coastal and Shelf Science》2009

Processes acting on the early-life histories of marine organisms can have important consequences for the structuring of benthic communities. In particular, the degree of coupling between larval supply and adult abundances can wield considerable influence on the strength of trophic interactions in the ecosystem. These processes have been relatively well described in rocky systems and soft-sediment communities, and it is clear that they are governed by very different bottlenecks. Seagrass meadows make interesting study systems because they bear structural affinities to both soft sediments as well as rocky substrates. We examined the early-life history of Paracentrotus lividus, one of the dominant herbivores in Mediterranean seagrass meadows, to identify the drivers of population dynamics in this species. We measured spatial and temporal variability in sea urchin post-settlement in 10 Posidonia oceanica meadows in the North-Western Mediterranean over a period of two years, and compared the numbers with the one-year old cohort a year later (i.e. the new population recruitment) as well as between successive size–age groups. Urchin post-settlers differed substantially between meadows but were present in both years in all meadows surveyed, suggesting that larval supply was not limiting for any of the studied sites. However, in six of the studied meadows, the one-year cohort of urchins was absent in both years, indicating that post-settlement processes strongly affected urchins in these meadows. In contrast, in four of the studied meadows, there was a strong coupling between post-settlers and one-year cohort individuals. These meadows were structurally different from the others in that they were characterised by an exposed matrix of rhizomes forming a dense seagrass mat. This mat apparently strongly mediates post-settlement mortality, and its presence or absence dictates the successful establishment of urchin populations in seagrass meadows. As the population aged, the relationship between size–age groups decreased evidencing the action of other processes. Yet, these results indicate that differences in physical structure are a vital bottleneck for sea urchin populations in seagrass meadows. Exploring the interaction between ecosystem structure and early-life history may provide a broader and more unified framework to understand the dynamics of a range of benthic habitats, including rocky substrates, soft sediments and seagrass meadows.  相似文献   

Economics, ethics, and climate policy: framing the debate     

Richard B. Howarth  Patricia A. Monahan 《Global and Planetary Change》1996,11(4):187-199

This paper examines the economic and ethical dimensions of climate policy in light of existing knowledge of the impacts of global warming and the costs of greenhouse gas emissions abatement. We find that the criterion of economic efficiency, operationalized through cost-benefit analysis, is ill-equipped to cope with the pervasive uncertainties and issues of intergenerational fairness that characterize climate change. In contrast, the concept of sustainable development—that today's policies should ensure that future generations enjoy life opportunities undiminished relative to the present—is a normative criterion that explicitly addresses the uncertainties and distributional aspects of global environmental change. If one interprets the sustainability criterion to imply that it is morally wrong to impose catastrophic risks on unborn generations when reducing those risks would not noticeably diminish the quality of life of existing persons, a case can be made for significant steps to reduce greenhouse gas emissions.  相似文献