Jens Kristian Gundersen

Pathways of organic carbon oxidation in three continental margin sediments

We have combined several different methodologies to quantify rates of organic carbon mineralization by the various electron acceptors in sediments from the coast of Denmark and Norway. Rates of NH4+ and Sigma CO2 liberation sediment incubations were used with O2 penetration depths to conclude that O2 respiration accounted for only between 3.6-17.4% of the total organic carbon oxidation. Dentrification was limited to a narrow zone just below the depth of O2 penetration, and was not a major carbon oxidation pathway. The processes of Fe reduction, Mn reduction and sulfate reduction dominated organic carbon mineralization, but their relative significance varied depending on the sediment. Where high concentrations of Mn-oxide were found (3-4 wt% Mn), only Mn reduction occurred. With lower Mn oxide concentrations more typical of coastal sediments, Fe reduction and sulfate reduction were most important and of a similar magnitude. Overall, most of the measured O2 flux into the sediment was used to oxidized reduced inorganic species and not organic carbon. We suspect that the importance of O2 respiration in many coastal sediments has been overestimated, whereas metal oxide reduction (both Fe and Mn reduction) has probably been well underestimated.

Diffusive and total oxygen uptake of deep-sea sediments in the eastern South Atlantic Ocean:in situ and laboratory measurements

Abstract Total O 2 uptake rates were measured by the benthic flux chamber lander ELINOR, and O 2 microprofiles were measured by the profiling lander PROFILUR in the eastern South Atlantic. Diffusive O 2 fluxes through the diffusive boundary layer and the depth distribution of O 2 consumption rates within the sediment were calculated from the obtained microprofiles. The depth integrated O 2 consumption rate agreed closely with the diffusive O 2 uptake at all stations. Total O 2 uptake was 1.2–4.2 times the diffusive O 2 uptake, and the difference correlated with the abundance of macrofauna in the sediment. Diffusive O 2 uptake and O 2 -penetration depths correlated with the organic content of the sediments and exhibited an inverse correlation with water depth. Total and diffusive rates of in situ O 2 uptake were higher than previously published data for shelf and abyssal sediments in the Atlantic, but were comparable to rates from upwelling areas in the eastern Pacific. Laboratory measurements on recovered sediment cores showed lower O 2 penetration depths and higher diffusive uptake rates than in situ measurements. The differences increased with increasing water depth. We primarily ascribe this compression of O 2 profiles to a transiently increased temperature during recovery and enhanced microbial activity in decompressed sediment cores. Total O 2 uptake rates measured in the laboratory on macrofauna-rich stations were, in contrast, lower than those measured in situ because of underrepresentation and disturbance of the macrofauna.

Improved nitrogen removal by application of new nitrogen-cycle bacteria

In order to meet increasingly stringentEuropean discharge standards, new applicationsand control strategies for the sustainableremoval of ammonia from wastewater have to beimplemented. In this paper we discuss anitrogen removal system based on the processesof partial nitrification and anoxic ammoniaoxidation (anammox). The anammox process offersgreat opportunities to remove ammonia in fullyautotrophic systems with biomass retention. Noorganic carbon is needed in such nitrogenremoval system, since ammonia is used aselectron donor for nitrite reduction. Thenitrite can be produced from ammonia inoxygen-limited biofilm systems or in continuousprocesses without biomass retention. Forsuccessful implementation of the combinedprocesses, accurate biosensors for measuringammonia and nitrite concentrations, insight inthe complex microbial communities involved, andnew control strategies have to be developed andevaluated.

In situ microsensor studies of a shallow water hydrothermal vent at Milos, Greece

Abstract The microenvironment and microcirculation of a shallow water hydrothermal vent system was studied together with the benthic primary production at Milos, Greece. In situ microprofiles of O 2 , pH, H 2 S and temperature were obtained using a miniaturised version of a profiling instrument. The sediment temperature increased toward the centre of the vent system, reaching a surface maximum of 100°C in the central yellow coloured sulfidic area. The oxygen penetration depth decreased from the unaffected sediment surrounding the vent system towards the vent centre; however, at the inner vent area the O 2 penetration increased again. Similar results were obtained during laboratory measurements. H 2 S concentrations increased rapidly beneath the oxygenated zone in the different vent areas and reached values of approximately 900 μM at sediment depths of 7–17 mm in the central vent areas. The microprofiles resolved a microcirculative pattern where local pressure differences caused by outflowing seep fluids induced a downward transport of oxygenated water, creating small convective cells which efficiently reoxidised H 2 S of the seep fluid. Patches of benthic diatoms covered the sediment surface in the areas surrounding the vent system. The net photosynthesis of this community increased from 25 to 41.8 mmol O 2 m −2 d −1 from early morning to midday. The amount of carbon fixed daily, as calculated from the in situ oxygen microprofiles, accounted for 0.67 mmol C m −2 d −1 . Laboratory incubations indicated that photosynthesis was not carbon limited and consequently the excess dissolved inorganic carbon contained in the vent fluids presumably had no effect on benthic primary production.

Calibration and performance of the stirred flux chamber from the benthic lander Elinor

Abstract Flow velocities and O2 microgradients were measured by use of minithermistors and O2 microelectrodes inside a laboratory model of the chamber from the benthic lander, Elinor. The sensors were introduced from below through small holes in the chamber bottom and penetrated up through the sediment. Flow velocities and the diffusive boundary layer (DBL) could thereby be studied with a minimum of disturbance. In the central part of the chamber covering 9% of the area, the DBL was thicker and the flow rates significantly lower than in the rest of the hydrodynamically uniform chamber. Average flow velocities of 2.4–4.6 cm s−1 and average DBL thicknesses of 220–625 em were measured at stirring rates of 8–15 rpm and water column heights of 10–15 cm. In homogeneous impermeable sediments, the average diffusive O2 uptake calculated from O2, microprofiles was equal to the total O2 uptake within ±3%. Radial pressure gradients in the stirred chamber were 1–3 Pa. Such pressure gradients may induce advective pore water transport in permeable sediments and increase the flushing of animal burrows in bioturbated sediments.

The Early Diagenetic Formation of Organic Sulfur in the Sediments of Mangrove Lake, Bermuda

Due to a low mineral content, the sapropelic sediments depositing in Mangrove Lake, Bermuda, provide an excellent opportunity to explore for possible additions of sulfur to organic matter during the early stages of diagenesis. We evaluated early diagenetic organic sulfur transformations by monitoring the concentrations and stable isotopic compositions of a number of inorganic and organic sulfur pools, thereby accounting for all of the sulfur in the sediments. We have identified and quantified the following sulfur pools: porewater sulfate, porewater sulfide, elemental sulfur, pyrite sulfur, hydrolyzable organic sulfur (HYOS), chromium-reducible organic sulfur (CROS), and nonchromium-reducible organic sulfur (Non-CROS). Of the organic sulfur pools, the Non-CROS pool is by far the largest, followed by CROS, and finally HYOS. By 60 cm depth these pools contribute, respectively, to 85, 7.9, and 3.6% of the total solid phase sulfur. The HYOS pool is probably of biological origin and shows no interaction with the sulfur compounds produced during diagenesis. By contrast, CROS is produced, most likely, from the diagenetic addition of polysulfides to functionalized lipids in the upper, H2S-poor, elemental sulfur-rich, region of the sediment. A portion of this sulfur pool is unstable and decomposes on contact with the H2S-rich porewaters. The portion of CROS that remains in the sulfidic waters appears to readily exchange sulfur isotopes with H2S. While some of the Non-CROS pool is of biological origin, some is also formed by the diagenetic addition of sulfur to organic compounds in the upper H2S-poor region of the sediment. By contrast with CROS, Non-CROS is not diagenetically active in the H2S-rich porewaters. Overall, somewhere between 27 and 53 % of the organic sulfur buried in Mangrove Lake sediments is of diagenetic origin, with the remaining organic sulfur derived from biosynthesis. We extrapolate our Mangrove Lake results and calculate that in typical coastal marine sediments between 11 and 29 μmol g−1 of organic sulfur will form during early diagenesis, of which 2–5 μmol g−1 will be chromium reducible.

Human oocyte respiration-rate measurement – potential to improve oocyte and embryo selection?

Oocyte and embryo selection are not highly successful, with fewer than 10% of oocytes in assisted reproduction resulting in a delivery. Techniques for oocyte and embryo selection rely on highly subjective morphology assessment, with few true quantitative techniques available. One aspect of oocyte health that could be considered is the ability to produce ATP through respiration. Using a non-invasive technology, the respiration rates of individual human oocytes were recorded in an attempt to correlate respiration and oocyte health with probable subsequent development. Oocytes used were either immature or mature, non-fertilized oocytes from a clinical assisted reproduction programme. Differences in respiration rates between oocytes within a cohort and between cohorts of oocytes were recorded. The differences between cohorts reflected many of the currently known differences in oocyte health, related to age and FSH concentrations. However, within a cohort, differences between oocytes were observed, with some having high rates and others low. Oocytes with respiration rates of between 0.48 and 0.55 nl O(2)/h were viable, with lower rates consistent with lack of continued in-vitro maturation or atresia. This technology may have a future in the clinical laboratory as a predictor of oocyte health and ability to develop into an embryo with greater potential of delivery.

Adaptation, test and in situ measurements with O2 microopt(r)odes on benthic landers

Oxygen microopt(r)odes have recently been introduced as an alternative to microelectrodes in the field of aquatic biology. We here describe adaptation, test results and first in situ measurements made with O2 microopt(r)odes on deep-sea benthic landers. This includes a detailed description of the sensors, the mechanical mounting, and the necessary measuring system. Hydrostatic pressure effects on the sensors and the optical penetrators are evaluated and discussed. Further, in situ micoopt(r)ode data obtained by a profiling lander (Profilur) and a benthic chamber lander (Elinor) are presented, discussed and compared to measurements obtained simultaneously by Clark type O2 microelectrodes. The obtained data demonstrated that opt(r)odes are a realistic and good alternative to electrodes for landers and other measuring platforms during deep-sea deployments.

Simulation of early diagenetic processes in continental slope sediments off southwest Africa: the computer model CoTAM tested

Abstract Pore water of marine sediments recovered from two stations of the continental slope off southwest Africa were investigated. We present computer simulations of in situ and laboratory concentration profiles of oxygen as well as laboratory concentration profiles of nitrate, calcium, pH and alkalinity. The simulations were carried out with help of a numerical model (CoTAM) to describe the transport and the reaction of dissolved species in sediments. CoTAM is based on an operator-splitting approach comprising the independent calculation of transport and chemical reaction. The consumption rates of oxygen and nitrate were determined by optimal fits to the measured pore water profiles of these species. It could be shown that measured concentrations of nitrate in pore water correspond to a decomposition of organic matter with C N ratios between 3 and 3.7. However, artificially increased subsurface nitrate concentrations due to core recovery cannot be excluded, but our results show much greater deviations from expected concentrations (assuming Redfield stoichiometry) than previously reported from comparative studies (i.e. [Martin and Sayles, 1996]). Oxygen consumption in situ was shown to be distinctively lower than measured in multicorer cores after recovery. Simulations with varying denitrification rates indicate reduced diffusive nitrate release into the bottom water by up to 50% compared to shipboard results. Effects of nitrification and denitrification on pore water pH, carbonate alkalinity and calcium concentrations were simulated by recalculating concentrations of these species with regard to calcite equilibrium. For these calculations we used the standard software PHREEQE as a subroutine of CoTAM. Calcium and carbonate alkalinity increase due to solid phase calcite dissolution. ΔpH was calculated to be an order of magnitude lower within the zone of oxygen depletion than indicated by shipboard results. This difference is mainly related to non-equilibrium conditions during pH measurements.