Mario Laima

NH4+ turnover in intertidal sediments of Marennes-Oléron Bay (France): effect of sediment temperature

NH4+ turnover plays an important role in benthic compartment as source of nutrient for primary production. The intertidal mudflats of the Marennes-Oleron Bay are characterized by high fluctuations of sediment temperature that generally ranges from 10 to 30 degreesC during emersion periods. Influence of sediment temperature on NH4+ processes was investigated. Grass ammonification and NH4+ incorporation kinetics were studied using the N-15 isotope dilution method. The method was first adapted to these very fine sediments and applied to 2 upper sediment layers (0-2 and 2-4 cm) at different incubation times of up to 120 h. The effect of sediment temperature on gross ammonification and NH4+ incorporation rates was investigated at 10, 20 and 30 degreesC. There was a strong increase of both rates as a function of temperature, gross ammonification rates ranged from 0 to 17 mug NH4+-N.g(-1) dw.d(-1) and NH4+ incorporation rates from 2 to 13 mug N.g(-1) dw.d(-1) between 10 and 30 degreesC. This study showed that short-term temperature variations during the emersion period should be taken into account in quantifying NH4+ turnover in intertidal sediments and that benthic regeneration of NH4+ significantly supports benthic and planktonic primary production in Marennes-Oleron Bay. It suggests also that there is no N-limitation for benthic primary production in this bay and that there is up to 44 % of NH4+ produced in surface sediments, which can diffuse to the water column and become available to phytoplankton.

A new experimental setup for studying the formation of phosphate binding iron oxides in marine sediments. Preliminary results

AbstractA new laboratory method is introduced to study theformation of phosphate binding iron(III) oxides at theredox boundary in marine sediments. A sediment core isgiven a very well-defined oxic-anoxic interface byplacing a 0.45 µm filter between the sediment andthe overlying water. After a period of 1

Effects of benthic diatoms, fluff layer, and sediment conditions on critical shear stress in a non-tidal coastal environment

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Modelling of Suspended Matter Transport from the Oder River

months thefilter is covered with a layer of fresh iron oxides,formed by the oxidation of upward diffusing Fe2+from the sediment pore water. The formed iron oxidesare investigated by electron probe X-ray microanalysis(EXPMA). With a sediment core from the brackish BalticSea the average molar composition of 788 formedparticles is Fe1.00±0.13P0.55±0.06Ca0.37±0.04 plus unknown amounts of O, H andC. The results show that the particles have a uniformcomposition, and that calcium plays an important rolein the phosphate binding. The laboratory method is auseful supplement to in situ sampling forstudies of iron oxides.

Recovery of 15NH4+ in labelling experiments on coastal marine sediments

Abstract Geografisk Tidsskrift, Danish Journal of Geography 99: 1–7, 1999 A new portable instrument, the Laberex chamber—LAB oratory ERosional EXperiments—for studies of the “fluff layer” and sediment critical shear stress is described. The chamber consists of a cylindric plexiglass tube with an inner diameter of 84 mm. A four-bladed impeller connected to a motor is placed in the centre of the chamber. Rotation of the impeller induces resuspension. Light attenuation is measured across the centre line in the chamber at a wave length of 633 nm (red light). A PC automatically controls both the stirring voltage that is increased at predetermined time-intervals and collects data from the light attenuation meter every second. Velocity distributions in the chamber and the relation between stirring voltages and critical shear stress are known from laser doppler measurements in the chamber.

A New Video Controlled, Hydraulically Damped Corer for Sediment/Water Interaction Studies

Sixteen sediment samples were collected from a square grid (4x4) with a horizontal distance of about 150 m between positions in Arhus Bay in the south-west Kattegat (14 to 15 m water depth). Critical shear stress (τ c ) was measured in all samples and related to sediment parameters: grain-sizes, organic matter, water content, porosity, and chlorophyll-a (chl-a) content, in upper layers. Samples were divided into a low (A) τ c . group and a high (B) τ c group in relation to an erosion rate. A significant (P<0.001) difference in median τ c was found between groups A (0.0284 N m -2 ) and B (0.0380 N m -2 ). Average chl-a concentrations in groups A (1.4 μg g -1 ) and B (1.8 μg g -1 ) were not significantly different (P=0.47) but there was a significant and positive correlation (r 2 : 0.7, P<0.0001) between τ c and diatom film abundance. Sediment organic matter and water content were significantly higher in group B compared with A, which contradicts that watery and organic rich sediments generally exhibit low τ c . This was explained by the presence of a diatom film cover on the fluff layer that inhibits the action of erosive forces. A fluff layer is characterized by a high water and organic content. The fluff layer was present in the majority of the samples but the highest average chl-a content and a significant (P=0.020) higher abundance of diatom film was observed in group B (high τ c ). Benthic diatoms were dominated by Haslea crucigeroides, Pleurosigma strigosum, and Bacillaris paxillifer. Spatial variability of sediment parameters was high and variability of a stabilit/erodibility parameter even exceeded those recorded for highly heterogeneous tidal flats. The occurrence of benthic diatoms at 14-15 m of water depth in the eutrophic Arhus Bay was supposedly related to a measured increase in Secci depth in the bay and thereby increased light penetration depth.

Fluff deposition on intertidal sediments: effects on benthic biota, ammonium fluxes and nitrification rates

Abstract It has been found that the measurement of NH4+ in extracts of marine sediments was influenced by factors which inhibit the indophenol colour development, and through gel chromatography, diffusion, dilution and internal standard assays, it was possible to determine the extent of this interference. The measurement of NH4+ in KCl extracts and porewater, using internal standards, indicated that colour development was inhibited 13% and 51%, respectively. Dilution of samples alleviated this inhibition, but more than five-fold dilution was necessary for some extracts. Diffusion of NH3, collection and measurement generally gave concentrations comparable with those derived from the use of internal standards. These data suggest that the indophenol reagents should be added to sufficient diluted sediment extracts or to diffusates from extracts, to prevent interference to the colour development of NH4+.

Nutrient Dynamics in Southwestern Kattegat, Scandinavia: Modelling Transport, Budget and Consequences of Reduced Terrestrial Loads,

In order to quantify the riverine sediment flux to the Arkona Basin, the transport pathways and fate of fine-grained suspended matter discharged from the Oder River from October 1996 to October 1997 were simulated using the MIKE3 modelling system, including a cohesive sediment transport module. Results indicate that about 550,000 regular tons of sediment are transported to the Arkona Basin annually. There is some indication that transport is episodic and mainly governed by wind events. There is a general tendency for the sediment transported from the Oder to be diverged into a pathway either to the north towards the Arkona Basin (2/3) or to the east towards the Bornholm Basin (1/3) over time-scales of several months. Primary sedimentation along a vertical transsect from the mouth of the Oder River to the Arkona Basin generally takes place in the form of easily resuspended fluffy material. Critical shear stress for the resuspension of this fluff is 0.02 N/m 2 . Generally, such thresholds are exceeded 5-6 times per month in shallow water (D 10 m) during wind events normally only lasting a few hours. Vertical sedimentation fluxes measured in shallow water are less than 10 g/m 2 /day during short periods with calm weather. A comparison with average rates of 80-115 g/m 2 /day measured during 3-month observation periods indicates that the resuspension rate in shallow water is about 8-10 times higher than the primary sedimentation rate. The shallow water areas above the 20 m isobath are non-depositional areas acting as temporal deposits for sediment transported from the Oder River through Pomeranian Bay to the Arkona Basin or the Bornholm Basin.