Exchange of nutrients and oxygen across the sediment-water interface below a Sparus aurata marine fish farm in the north-western Mediterranean Sea

Purpose: This study analyzes the effects of aquaculture activities in open seawater in the north-western coastal waters of the Mediterranean Sea. It is the first of its kind to be based on benthic flux data gathered in situ below fish farms for this particular area. Materials and methods: Samples were collected on four sampling campaigns over a 1-year cycle under a Sparus aurata fish farm facility where benthic fluxes were measured in situ using light and dark benthic chambers. Bottom water and sediment samples were also collected. Data were compared to those for a nearby control station. Results and discussion: Significant differences were found (ANOVA, p < 0. 05) between concentrations of organic matter (OM), total phosphorus and redox potentials in sediments located under the cages and those of the control station. The consumption of dissolved oxygen (DO) by sediment and positive ammonium (NH4 +) fluxes was stimulated by OM content, with correlations of r = -0. 60 (p < 0. 01) and r = 0. 70 (p < 0. 01), respectively. The OM content of sediments was found to be consistently higher under the cages than at the control station, with the highest value (1. 8 ± 0. 7 %) under the cages observed during the early summer; values of DO and NH4 + fluxes were -64 ± 17 and 12. 7 ± 1. 0 mmol m-2 day-1, respectively. PO4 3- fluxes were consistently higher in the fish farm sediments (between 0. 58 and 0. 98 mmol m-2 day-1) than those observed at the control station. Nitrate (NO3 -) fluxes were found to be consistently negative due to denitrification occurring in the sediments and were related to the concentration of NO3 - in bottom waters (r = 0. 92, p < 0. 01). Si fluxes were shown to be associated with water temperature (r = 0. 59, p < 0. 05). Conclusions: The results imply that sediments located below cages accumulate organic matter originating from aquaculture activities, especially during summer months when this activity increases. Sediments undergo biogeochemical changes that mainly affect fluxes of DO, NH4 + and soluble reactive phosphorus, although these do not seem to have a significant impact on the quality of the water column due to the hydrodynamic characteristics of the area. © 2012 Springer-Verlag.We would like to thank the Caja del Mediterraneo for a predoctoral fellowship fund for this research and Antonio Asuncion Acuigroup Maremar manager for the facilities and support in conducting the study. The translation of this paper was funded by the Universidad Politecnica de Valencia, Spain. We are grateful for the valuable comments of the anonymous reviewers on previous versions of the manuscript.Morata Higón, T.; Sospedra, J.; Falco Giaccaglia, SL.; Rodilla Alama, M. (2012). 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Geochemistry in an area recently uncovered from the Filchner ice shelf

Sediments were studied in the southern Weddell Sea (Antarctica)that had been both covered by the ice shelf prior to 1986 (ICS) and outside the ice shelf (IFS). The composition of particulate matter in these sediments shows that the sedimentation under the ice shelf is quantitatively similar to that outside the ice shelf, except that the former has a negligible content of easily degradable organic matter, indicating a very low biochemical activity. The (210)pb profile, from the ICS station, gave a sedimentation rate of 0.02 cm y(-1). This accumulation rate, combined with a particulate carbon content of approximately 1%, yields an annual net accumulation of 1.7 g C m(-2). The profiles of nutrients in the interstitial water (under the ice shelf) indicate a very small flux to the overlaying water. Outside the ice shelf the flux is significantly higher, though still small. Copyright (C) 1996 Elsevier Science Ltd

Oxygen distribution and bioirrigation in Arctic fjord sediments (Svalbard, Barents Sea)

The penetration of oxygen into silty fjord sediments from northern Norway and SW Svalbard was studied at 6 sites during a research cruise to the northern Barents Sea. Profiles of oxygen were measured by microelectrodes on retrieved sediment cores in a thermostated flow aquarium and used to develop composite, 2-dimensional images of the oxygen distribution. Oxygen penetrations ranged from 3 to 11 mm with a mean depth of 6 to 8 mm. The mean diffusive oxygen uptake rates across the sediment-water interface ranged from 2.8 to 13.4 mmol O2 m–2 d–1. The diffusive flux accounted for 60 to 95% of the total oxygen uptake of the sediments as measured in situ by a flux chamber lander. The sediments were densely populated by fauna such as tube-dwelling polychaetes. Inhabited and relict tubes of 1 to 2.5 mm diameter reached densities of up to 1 cm–2, and about 15% of all oxygen microprofiles showed evidence of advective oxygen flow through the tubes. Based on oxygen microprofiles and data on burrow geometry and density, burrows extending down into the anoxic sediment extended the oxic sediment volume by 2 to 10% and thereby enhanced the oxygen flux. Anoxic microenvironments were not detected, but during inactivity of polychaetes their tubes became depleted in oxygen relative to the surrounding sediment

Benthic in situ respiration in the upwelling area off central Chile

Benthic O-2 uptake rates and O-2 microprofiles were measured in the upwelling area off central Chile. Measurements were performed both in situ and in the laboratory on recovered sediment cores. Comparison between the 2 data sets confirmed retrieval and handling artifacts inferred from previous studies. Onboard measurements indicated that the effects were mainly associated with core warming during recovery. Fauna mediated O-2 uptake was significant even at abyssal depths and generally in situ O-2 uptake rates were higher and showed stronger attenuation with water depth than previous measurements performed in the NE Pacific. However, O-2 uptake rates and O-2 penetration depths were very similar to measurements performed in the SE: Atlantic, and the compiled data sets were approximated by simple exponential equations relating the measurements to water depth. By comparing our total O-2 in situ uptake rates to simultaneous measurements of primary production (PP) and new production (NP) of the overlying water column, it was calculated that the benthic mineralization accounted for 13 to 66% of the PP and for 28 to 92% of the NP at water depths shallower than 1000 m. At water depths from 1000 to 4000 m, the benthic mineralization equaled 2 to 11% of the PP and 22 to 38% of the NP. The benthic mineralization thereby accounted for a significant turnover of organic material even at the abyssal stations. The presented data add to the limited number of in situ deep sea mineralization measurements from the southern hemisphere

A benthic lander for tracer studies in the sea bed: In situ measurements of sulfate reduction

A new benhic lander for in situ tracer studies to a water depth of 6000 m is presented. This instrument allows in situ injections of radiolabeled sulfate into six enclosed sediment cores to determine sulfate reduction rates to 60 cm sediment depth. In order to correct for possible artifacts caused by decompression and rise in ambient water temperature during ascent and recovery of the instrument, one set of three cores was incubated in situ for 20 h, whereas another set was injected shortly before the ascent. The turnover of sulfate in the latter was subtracted from the first set to calculate the true in situ rates. This approach was tested in the laboratory on sediment cores from a coastal marine sediment. The results of a deployment at 155 m in the Gotland Basin, Baltic Sea, are presented. Sulfate reduction rates were measured to a sediment depth of 40 cm both in situ by the lander and in parallel onboard the ship. Results of in situ and laboratory incubations match well, showing slightly higher rates in the laboratory cores, especially in the deeper sediment strata. (C) 1998 Elsevier science Ltd. All rights reserved

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

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 O2, pH, H2S 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 O2 penetration increased again. Similar results were obtained during laboratory measurements. H2S 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 H2S 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 O2 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

High-resolution metal gradients measured by in situ DGT/DET deployment in Black sea sediments using an autonomous benthic lander

DET (Diffusive equilibration in thin films) and DGT (diffusive gradients in thin films) have been deployed in situ using an autonomous benthic lander to measure concentrations and induced fluxes of Fe and Mn (DET/DGT) and trace metals (DGT) in pore waters at millimeter spatial resolutions. The newly developed deployment system is described, and based on these first results, its strengths and weaknesses are discussed. Deployments were made in the Western Black Sea in shelf sediments overlain by well‐oxygenated water at a water depth of 77 m. Maxima of the redox‐sensitive metals at 4 and 8 cm deep within the sediment indicated that two zones of reduction dominated the geochemistry. Sharp, but systematic, features were superimposed on this general picture and were well replicated in the profiles of Mn, Co, and Cd, but the sharp features in the Fe profile were offset from those of the others elements by several millimeters. Detection of this functional discrimination between Fe and Mn as regulators of trace metals would not have been possible using more conventional sampling procedures