(Table 2, page 50) Toolik lake sediment chemistry (0-1 cm interval)

The sediments within Toolik Lake in arctic Alaska are characterized by extremely low rates of organic matter sedimentation and unusually high concentrations of iron and manganese. Pore water and solid phase measurements of iron, manganese, trace metals, carbon, nitrogen, phosphorus, and sulfur are consistent with the hypothesis that the reduction of organic matter by iron and manganese is the most important biogeochemical reaction within the sediment. Very low rates of dissolved oxygen consumption by the sediments result in an oxidizing environment at the sediment-water interface. This results in high retention of upwardly-diffusing iron and manganese and the formation of metal-enriched sediment. Phosphate in sediment pore waters is strongly adsorbed by the metal-enriched phases. Consequently, fluxes of phosphorus from the sediments to overlying waters are very small and contribute to the oligotrophic nature of the Toolik Lake aquatic system. Toolik Lake contains an unusual type of lacustrine sediment, and in many ways the sediments are similar to those found in oligotrophic oceanic environments.

Organic carbon flux and remineralization in surface sediments

Organic carbon fluxes through the sediment/water interface in the high-latitude North Atlantic were calculated from oxygen microprofiles. A wire-operated in situ oxygen bottom profiler was deployed, and oxygen profiles were also measured onboard (ex situ). Diffusive oxygen fluxes, obtained by fitting exponential functions to the oxygen profiles, were translated into organic carbon fluxes and organic carbon degradation rates. The mean Corg input to the abyssal plain sediments of the Norwegian and Greenland Seas was found to be 1.9 mg C/m**2/d. Typical values at the seasonally ice-covered East Greenland continental margin are between 1.3 and 10.9 mg C/m**2/d (mean 3.7 mg C/m**2/d), whereas fluxes on the East Greenland shelf are considerably higher, 9.1-22.5 mg C/m**2/d. On the Norwegian continental slope Corg fluxes of 3.3-13.9 mg C/m**2/d (mean 6.5 mg C/m**2/d) were found. Fluxes are considerably higher here compared to stations on the East Greenland slope at similar water depths. By repeated occupation of three sites off southern Norway in 1997 the temporal variability of diffusive O2 fluxes was found to be quite low. The seasonal signal of primary and export production from the upper water column appears to be strongly damped at the seafloor. Degradation rates of 0.004-1.1 mg C/cm**3/a at the sediment surface were calculated from the oxygen profiles. First-order degradation constants, obtained from Corg degradation rates and sediment organic carbon content, are in the range 0.03-0.6/a. Thus, the corresponding mean lifetime of organic carbon lies between 1.7 and 33.2 years, which also suggests that seasonal variations in Corg flux are small. The data presented here characterize the Norwegian and Greenland Seas as oligotrophic and relatively low organic carbon deep-sea environments.

Particle positions of numerical experiments 1 to 4

In mixed sediment beds, erosion resistance can change relative to that of beds composed of a uniform sediment because of varying textural and/or other grain-size parameters, with effects on pore water flow that are difficult to quantify by means of analogue techniques. To overcome this difficulty, a three-dimensional numerical model was developed using a finite difference method (FDM) flow model coupled with a distinct element method (DEM) particle model. The main aim was to investigate, at a high spatial resolution, the physical processes occurring during the initiation of motion of single grains at the sediment-water interface and in the shallow subsurface of simplified sediment beds under different flow velocities. Increasing proportions of very fine sand (D50=0.08 mm) were mixed into a coarse sand matrix (D50=0.6 mm) to simulate mixed sediment beds, starting with a pure coarse sand bed in experiment 1 (0 wt% fines), and proceeding through experiment 2 (6.5 wt% fines), experiment 3 (10.5 wt% fines), and experiment 4 (28.7 wt% fines). All mixed beds were tested for their erosion behavior at predefined flow velocities varying in the range of U 1-5=10-30 cm/s. The experiments show that, with increasing fine content, the smaller particles increasingly fill the spaces between the larger particles. As a consequence, pore water inflow into the sediment is increasingly blocked, i.e., there is a decrease in pore water flow velocity and, hence, in the flow momentum available to entrain particles. These findings are portrayed in a new conceptual model of enhanced sediment bed stabilization.

Stable carbon and oxygen isotope record of foraminifera from DSDP Hole 30-289

Sediments accumulate on the sea floor far from land with rates of a few millimetres to a few centimetres per thousand years. Sediments have been accumulating under broadly similar conditions, subject to similar controls, for the past 10 8 years and more. In principle we should be able to study the distribution of climatic variance with frequencies over the range 10**-3 to 10**-7 cycles per year with comparative ease. In fact, nearly all our data are heavily weighted towards the youngest part of the geological record. We study frequencies higher than 10**-4 cycles per year in the special case of a Pleistocene interglacial (the present one), and frequencies in the range 10**-4 to 10**-5 cycles per year in the special case of an ice-age. Although these may be of more direct interest to mankind than earlier periods, it may well be that we will understand the causes of climatic variability better if we can examine their operation over a longer time scale and under different boundary conditions. Rather than review the available data, I have collected some new data to show the feasibility of gathering a data base for examining climatic variability without this usual bias toward the recent. The most widely applicable tool for extracting climatic information from deep-sea sediments is oxygen isotope analysis of calcium carbonate microfossils. It is generally possible to select from the sediment both specimens of benthonic Foraminifera (that is, those that lived in ocean deep water at the sediment-water interface) and specimens of planktonic Foraminifera (that is, those that lived and formed their shells near the ocean surface, and fell to the sediment after death). Thus one is able to monitor conditions at the surface and at depth at simultaneous moments in the geological past. The necessity to analyse calcareous microfossils restricts investigation to calcareous sediments, but even with this restriction in sediment type there are many factors governing the rate of sediment accumulation. On a global scale, sediment accumulates so as to balance the input to the oceans from continental erosion. Even when averaged globally, long-term accumulation rates have varied by almost a factor of ten (Davies et al., 1977, doi:10.1126/science.197.4298.53). At the regional scale, surface productivity and deep-water physical and chemical conditions also affect the sediment accumulation rate. Since all these are susceptible to variation and may well vary in response to climatic change as well as other factors, it is extremely hazardous to attempt to express any climatic variable as a function of time on the basis of measurements originally made as a function of depth in sediment. Although time has been used as a basis for plotting Figs. i-8, these should be regarded as freehand sketches of climatic history rather than as time-series plots.

Understanding arsenic mobility and speciation in lake sediments impacted by ore roasting near Giant mine, NWT

The roasting of gold-bearing arsenopyrite at Giant mine (Northwest Territories) between 1949 and 1999 released approximately 20,000 tonnes of toxic arsenic-bearing aerosols in the local aerial environment. Detailed examination of lake sediments, sediment porewaters, surface waters and lake hydrology sampled from three lakes of differing limnological characteristics was conducted in summer and winter conditions. Samples were analyzed for solid and dissolved elemental concentrations, speciation and mineralogy. The three lakes are located less than 5km from the mine roaster, and downwind, based on predominant wind direction. The objective of the study was to assess the controls on the mobility and fate of arsenic in these roaster-impacted subarctic lacustrine environments. Results show that the occurrence of arsenic trioxide in lake sediments coincides with the regional onset of industrial activities. The bulk of arsenic in sediments is contained in the form of secondary sulphide precipitates, with iron oxides hosting a minimal amount of arsenic near the surface-water interface. The presence of geogenic arsenic is likely contained as dilute impurities in common rock-forming minerals, and is not believed to be a significant source of arsenic to sediments, porewaters or lake waters. Furthermore, the well correlated depth-profiles of arsenic, antimony and gold in sediments may help reveal roaster impact. The soluble arsenic trioxide particles contained in sediments act as the primary source of arsenic into porewaters. Dissolved arsenic in reducing porewaters both precipitate as secondary sulphides in situ, and diffuse upwards into the overlying lake waters. Arsenic diffusion out of porewaters, combined with watercourse-driven residence time, are estimated to be the predominant mechanisms controlling arsenic concentrations in overlying lake waters. The sequestration of arsenic from porewaters as sulphide precipitates, in the study lakes, is not an effective process in keeping lake-water arsenic concentrations below guidelines for the protection of the freshwater environment and drinking water. Seasonal impacts on lake geochemistry derive from ice covering lake waters, cutting them off from of atmospheric oxygen, along with the exclusion of solutes from the ice. Such effects are limited in deep lakes but are can be an important factor controlling arsenic precipitation and mobility in ponds.

Laboratory Investigation of Diluted Bitumen Trapping and Dissolution in Gravel

The Canadian economy is largely dependent on the distribution of large volumes of oil to domestic and international markets by a long network of pipelines. Unfortunately, accidents occur, and oil can leak or spill from these pipelines before it reaches its destination. Of particular concern are the long-term consequences of oil spills in freshwater, which include sinking of oil in water and the contamination of sensitive areas, such as where fish (e.g., salmon) deposit their eggs in gravel-dominated river sediments. There is a knowledge gap regarding the fate and behaviour of oil in river sediment. To this end, this study aimed at finding the potential for diluted bitumen (dilbit) oil to become trapped in gravel and to transfer hydrocarbons into water by dissolution, which are harmful to aquatic life. Two sets of laboratory experiments were conducted to simulate conditions of an oil spill on an exposed bank or in shallow water. In the first set, by conducting capillary pressure-saturation (Pc-Sw) experiments it was found that dilbit can enter gravel pores without much resistance and approximately 14% of the pore volume can be occupied by discontinuous single or multipore blobs of dilbit following imbibition of water. Air-water Pc-Sw experiments done in laboratory 1-D columns required gravity correction and could be successfully scaled to predict dilbit-water Pc-Sw curves, except for the trapped amount of dilbit. Trapped dilbit constituents can be dissolved into the water flowing through gravel pores (hyporheic flow) at different velocities. In the second set, dissolution experiments suggested that for the duration of the test, hydrocarbons that cause acute toxicity dissolve rapidly, likely resulting in a decrease in their effective solubility. However, dilbit saturation changed only <2% within that time. Chronically toxic PAH compounds were also detected in the effluent water. The total concentration of all detected PAHs and alkylPAHs exceeded the threshold literature value to protect early-life stage fish. Observations of decreased concentrations with increased aqueous velocities as well as less than equilibrium concentrations indicated that the mass transfer was rate-limited. A correlation was developed for the mass transfer rate coefficient to understand the mass transfer behaviour beyond the conditions used in the experiments, which had a Reynolds number exponent similar to the studies of NAPL dissolution in groundwater.

Obligation des États de coopérer en droit international des cours d’eau transfrontaliers : état du droit et étude du cas Chinois

Le principe de coopération est considéré depuis longtemps comme l’une des pierres angulaires du droit international, toutefois, l’existence d’une obligation de coopérer en droit international reste encore controversée. Les ressources en eau, à cause de leur fluidité et de leurs multiples usages, démontrent toujours l’interdépendance humaine. En matière de cours d’eau transfrontaliers, la Convention de New York inclut explicitement dans son texte l’obligation générale de coopérer comme l’un de ses trois principes fondamentaux. Il nous incombe alors de voir quelle obligation de coopérer les États souverains s’imposent dans leurs pratiques ? Pour répondre à cette question, nous procédons tout d’abord à une étude positiviste du contenu normatif de l’obligation de coopérer. Nous constatons que l’incorporation de la notion de l’obligation de coopérer dans le principe de la souveraineté est une tendance manifeste du droit international qui a évolué du droit de coexistence composé principalement des règles d’abstention, au droit de coopération qui comporte essentiellement des obligations positives de facere, dont la plus représentative est l’obligation de coopérer. Néanmoins, il n’existe pas de modèle unique d’application pour tous les États, chaque bassin disposant de son propre régime coopératif. Pour mesurer l’ampleur des régimes coopératifs, nous étudions cinq paramètres : le champ d’application, les règles substantielles, les règles procédurales, les arrangements institutionnels et le règlement des différends. Quatres modèles de coopération ressortent : le mécanisme consultatif (l’Indus), le mécanisme communicateur (le Mékong), le mécanisme de coordination (le Rhin) et le mécanisme d’action conjointe (le fleuve Sénégal). Pour ce qui est de la Chine, il s’agit de l’État d’amont en voie de développement le plus important dans le monde qui a longtemps été critiqué pour son approche unilatérale dans le développement des eaux transfrontières. Nous ne pouvons pas cependant passer sous silence les pratiques de coopération qu’elle a développées avec ses voisins. Quelle est son interprétation de cette obligation générale de coopérer ? Notre étude des pratiques de la Chine nous aide, en prenant du recul, à mieux comprendre tous les aspects de cette obligation de coopérer en droit international. Afin d’expliquer les raisons qui se cachent derrière son choix de mode de coopération, nous introduisons une analyse constructiviste qui est plus explicative que descriptive. Nous soutenons que ce sont les identités de la Chine qui ont déterminé son choix de coopération en matière de cours d’eau transfrontaliers. Notre étude en vient à la conclusion que même s’il y a des règles généralement reconnues, l’obligation de coopérer reste une règle émergente en droit international coutumier. Ses modes d’application sont en réalité une construction sociale qui évolue et qui peut varier énormément selon les facteurs culturels, historiques ou économiques des États riverains, en d’autres mots, selon les identités de ces États. La Chine est un État d’amont en voie de développement qui continue à insister sur le principe de la souveraineté. Par conséquent, elle opte pour son propre mécanisme consultatif de coopération pour l’utilisation des ressources en eau transfrontalières. Néanmoins, avec l’évolution de ses identités en tant que superpuissance émergente, nous pouvons probablement espérer qu’au lieu de rechercher un pouvoir hégémonique et d’appliquer une stratégie unilatérale sur l’utilisation des ressources en eau transfrontalières, la Chine adoptera une stratégie plus coopérative et plus participative dans l’avenir.

Nutrient fluxes on an intertidal mudflat in Marennes-Oleron Bay, and influence of the emersion period

Fluxes of nutrients (NH sub(4) super(+), NO sub(3) super(-), PO sub(4) super(3-) and Si(OH) sub(4)) were studied on an intertidal mudflat in Marennes-Oleron Bay, France, at two different seasons and at different times of the emersion period. Fluxes through the sediment-water interface were both calculated from vertical profiles of nutrient concentration in pore-water (diffusive fluxes, JD) and measured in light and dark benthic mini-chambers (measured fluxes, J sub(0)). Results indicate that ammonia was mainly released in summer while nitrate was mainly taken up in late winter. This uptake from the overlying water was probably due to the coupling of nitrification-denitrification within the sediment. The J sub(0) /J sub(D) ratio further indicates that bioturbation likely enhanced ammonia release in summer. Concerning phosphate, the comparison of diffusive and measured fluxes suggests that PO sub(4) super(3-) could be assimilated by the biofilm in winter while it was released in summer at a high rate due to both bioturbation and desorption because of the relative summer anoxic conditions. Silica was always released by the sediment, but at a higher rate in summer. Statistically significant differences in measured fluxes were detected in dark chambers at different times of low tide, thus suggesting a short-term variability of fluxes. Microphytobenthos preferred ammonia to nitrate, but assimilated nitrate when ammonia was not available. It also turned out that benthic cells could be limited in nitrogen during low tide in late winter. In summer, ammonia was not limiting and microphytobenthic activity significantly decreased the measured flux of NH sub(4) super(+) in the middle of low tide when its photosynthetic capacity was highest.

Artificial Skin - Culturing of Different Skin Cell Lines for Generating an Artificial Skin Substitute on Cross-Weaved Spider Silk Fibres

Background: In the field of Plastic Reconstructive Surgery the development of new innovative matrices for skin repair is in urgent need. The ideal biomaterial should promote attachment, proliferation and growth of cells. Additionally, it should degrade in an appropriate time period without releasing harmful substances, but not exert a pathological immune response. Spider dragline silk from Nephila spp meets these demands to a large extent. Methodology/Principal Findings: Native spider dragline silk, harvested directly out of Nephila spp spiders, was woven on steel frames. Constructs were sterilized and seeded with fibroblasts. After two weeks of cultivating single fibroblasts, keratinocytes were added to generate a bilayered skin model, consisting of dermis and epidermis equivalents. For the next three weeks, constructs in co-culture were lifted on an originally designed setup for air/liquid interface cultivation. After the culturing period, constructs were embedded in paraffin with an especially developed program for spidersilk to avoid supercontraction. Paraffin cross-sections were stained in Haematoxylin & Eosin (H&E) for microscopic analyses. Conclusion/Significance: Native spider dragline silk woven on steel frames provides a suitable matrix for 3 dimensional skin cell culturing. Both fibroblasts and keratinocytes cell lines adhere to the spider silk fibres and proliferate. Guided by the spider silk fibres, they sprout into the meshes and reach confluence in at most one week. A well-balanced, bilayered cocultivation in two continuously separated strata can be achieved by serum reduction, changing the medium conditions and the cultivation period at the air/liquid interphase. Therefore spider silk appears to be a promising biomaterial for the enhancement of skin regeneration.