The short term (hourly scale) variability of heterotrophic prokaryote (HP) vertical distribution and respiratory activity, was investigated in the north-western (NW) Mediterranean Sea. HP vertical distribution was determined on board by flow cytometry analysis of seawater samples collected by series of CTD casts. Cell counts and viability were determined for all samples. HP respiratory rates were determined later in the laboratory from filtered seawater samples (23 dm3) from 300–1 150-m depth. The average cell viability was 94.8%±2.2% (n=240). There was no accumulation of dead cells, due to quick decay of damaged cells. In the epipelagic layer, three HP groups were distinguished, two (HNA1, HNA2) whose cells exhibited a high nucleic acid content and one (LNA) with low nucleic acid content cells. HNA2 was most populated at 50 m but not detected at 90 m and below, presumably aerobic anoxygenic photoheterotrophic bacteria (AAPs). The variability in HP abundance was mainly confined in the upper 80 m. A few secondary peaks of HP abundance were observed (80–150 m) in connection with abundance troughs in the surface layer. HP cells were continuously present in a wide layer around 500 m (mean 191×103 cells/cm3). Below this layer, HP abundance randomly exhibited peaks, coupled to respiratory rate peaks. The HP abundance and variability in the water column was suppressed during a strong wind event. The observed sporadic variability was tentatively interpreted through a pulsed carbon-export mechanism induced by the microorganism production of dissolved polysaccharides, followed by flocculation and rapid sinking. This mechanism would thus contribute to (i) preventing organic matter accumulation in the epipelagic layer, (ii) seeding the water column with live HP cells, and (iii) supplying the aphotic water column with fresh and labile organic matter. This important vertical flux mechanism needs further observations and modelling.
Forecasting the state of large marine ecosystems is important for many economic and public health applications. However, advanced three-dimensional (3D) ecosystem models, such as the European Regional Seas Ecosystem Model (ERSEM), are computationally expensive, especially when implemented within an ensemble data assimilation system requiring several parallel integrations. As an alternative to 3D ecological forecasting systems, we propose to implement a set of regional one-dimensional (1D) water-column ecological models that run at a fraction of the computational cost. The 1D model domains are determined using a Gaussian mixture model (GMM)-based clustering method and satellite chlorophyll-a (Chl-a) data. Regionally averaged Chl-a data is assimilated into the 1D models using the singular evolutive interpolated Kalman (SEIK) filter. To laterally exchange information between subregions and improve the forecasting skills, we introduce a new correction step to the assimilation scheme, in which we assimilate a statistical forecast of future Chl-a observations based on information from neighbouring regions. We apply this approach to the Red Sea and show that the assimilative 1D ecological models can forecast surface Chl-a concentration with high accuracy. The statistical assimilation step further improves the forecasting skill by as much as 50%. This general approach of clustering large marine areas and running several interacting 1D ecological models is very flexible. It allows many combinations of clustering, filtering and regression technics to be used and can be applied to build efficient forecasting systems in other large marine ecosystems. 相似文献
Although pesticides are primarily degraded in the topsoil, significant attenuation can be expected in groundwater systems where the transit time of pesticides usually are orders of magnitude longer than in the soil. Because degradation and transport processes in the subsurface take place at time scales of months to years or even decades, direct measurements of natural attenuation are hampered by practical and logistical limitations (for instance the limited duration of sampling or a correct estimation of the pesticide flux into groundwater). Indirect methods such as measuring the changes in the ratio of degradation product to parent compound as a function of transit time in the aquifer, along a flow line provide a possible alternative. This paper presents a simple mathematical formulation of the relationship between transit time in the subsurface and changes in that ratio, and allows estimating the transformation rate of both parent compound and degradation product. The applicability of the method is illustrated in a case study investigating atrazine attenuation in a fractured sandstone aquifer. 相似文献
The in situ measurement of Sr isotopes in carbonates by MC‐ICP‐MS is limited by the availability of suitable microanalytical reference materials (RMs), which match the samples of interest. Whereas several well‐characterised carbonate reference materials for Sr mass fractions > 1000 µg g?1 are available, there is a lack of well‐characterised carbonate microanalytical RMs with lower Sr mass fractions. Here, we present a new synthetic carbonate nanopowder RM with a Sr mass fraction of ca. 500 µg g?1 suitable for microanalytical Sr isotope research (‘NanoSr’). NanoSr was analysed by both solution‐based and in situ techniques. Element mass fractions were determined using EPMA (Ca mass fraction), as well as laser ablation and solution ICP‐MS in different laboratories. The 87Sr/86Sr ratio was determined by well‐established bulk methods for Sr isotope measurements and is 0.70756 ± 0.00003 (2s). The Sr isotope microhomogeneity of the material was determined by LA‐MC‐ICP‐MS, which resulted in 87Sr/86Sr ratios of 0.70753 ± 0.00007 (2s) and 0.70757 ± 0.00006 (2s), respectively, in agreement with the solution data within uncertainties. Thus, this new reference material is well suited to monitor and correct microanalytical Sr isotope measurements of low‐Sr, low‐REE carbonate samples. NanoSr is available from the corresponding author. 相似文献
Biogeochemical processes in sediments under the influence of the Rhône River plume were studied using both in situ microelectrodes and ex situ sediment core incubations. Organic carbon (OC) and total nitrogen (TN) content as well as stable carbon isotopic composition of OC (δ13COC) were analysed in 19 surface sediments to determine the distribution and sources of organic matter in the Rhône delta system. Large spatial variations were observed in both the total O2 uptake (5.2 to 29.3 mmol m−2 d−1) and NH4+ release (−0.1 to −3.5 mmol m−2 d−1) rates at the sediment–water interface. The highest fluxes were measured near the Rhône River mouth where sedimentary OC and TN contents reached 1.81% and 0.23% respectively. Values of δ13COC ranged from −26.83‰ to −23.88‰ with a significant seawards enrichment tracing the dispersal of terrestrial organic matter on the continental shelf. The amount of terrestrial-derived OC reaches 85% in sediments close to the Rhône mouth decreasing down to 25% in continental shelf sediments. On the prodelta, high terrestrial OC accumulation rates support high oxygen uptake rates and thus indicating that a significant fraction of terrestrial OC is remineralized. A particulate organic carbon (POC) mass balance indicates that only 3% of the deposited POC is remineralized in prodelta sediments while 96% is recycled on the continental shelf. It was calculated that a large proportion of the Rhône POC input is either buried (52%) or remineralized (8%), mostly on the prodelta area. The remaining fraction (40%) is either mineralized in the water or exported outside the Rhône delta system in dissolved or particulate forms. 相似文献
Biological diversity, or biodiversity, is high on the international agenda for nature conservation. Marine and coastal ecosystems account for an important share of the biological diversity on Earth. As a consequence many international conventions, European legislation and national laws refer to marine biodiversity. The protection of marine biodiversity is a complex legal issue as it requires consideration of geographic (between land and sea), political (between conservation and exploitation), and economic (between fisheries, tourism, intellectual property and many other sectors) factors. Like Matryoshka dolls, marine biodiversity is a heterogeneous notion difficult to address as one discrete area in the development of policy agendas or juridical frameworks. In the past decade, the EU has been very active in Promoting Integrated Coastal Zone Management and in developing a framework for an Integrated Maritime Policy. This article reviews the status of marine biodiversity in the policy and legal initiatives of the European Union, a challenging issue to both the objectives of conservation and to the concept of integration. 相似文献
We present a comparison between several methods used to reconstruct fluxes and vertical profiles of wind, temperature and
humidity from measurements at two levels in the atmospheric surface layer for different practical applications. An analytical
method and an iterative method are tested by evaluating the quality of estimations of surface fluxes from detailed field measurements
obtained during a campaign on the site of Lannemezan in the south-west of France. The iterative method yields better results,
but the analytical one can give results of the same level of accuracy provided that specific constants in its formulation
are modified. Then these techniques are applied to wind and temperature reconstruction for an experiment dedicated to wind
power estimates over flat terrain. If turbulent fluxes are not needed, a simple power law appears to be sufficient, as the
method based on Monin–Obukhov theory does not improve the accuracy of the vertical profile reconstruction. 相似文献
Raw wastewaters were massively spread on sandy luvisols near Paris from 1899 to 2002, leading to high trace metals (TM) pollution of soils. Mass balance calculations were performed on a soil profile to assess vertical migration of TM. The contamination was estimated by subtracting the natural pedo-geochemical background of the horizons. TM inputs were estimated using Cr as an invariant. It is shown that Pb and Cr remained in the surface horizon, while Ni, Cd, Cu and Zn migrated downward, being more or less trapped depending on the physicochemical properties of the horizons. To cite this article: C. Dère et al., C. R. Geoscience 338 (2006).相似文献
Recent Russian legislative and policy documentation concerning national progress towards sustainable development has suggested that the attainment of such a state would represent the first stage in the development of the noosphere as outlined by the Russian scientist Vladimir Ivanovich Vernadsky (1863-1945). This paper explores Vernadsky’s model of evolutionary change through a focus on his work on the biosphere and noosphere in an attempt to further understanding of the way in which Russia is approaching the concept of sustainable development in the contemporary period. It is argued that the official Russian interpretation of the noosphere idea tends to obscure the evolutionary and materialist foundations of Vernadsky’s biosphere-noosphere conceptualisation. At the same time, the concluding section of the paper suggests that the scope of Vernadsky’s work can be used to stimulate the search for a more coherent approach to work in areas of sustainable development and sustainability across the span of the social and physical sciences. 相似文献