Benthic Chamber Experiments Research Articles

Insights on geochemical cycling of U, Re and Mo from seasonal sampling in Boston Harbor, Massachusetts, USA

This study examined the removal of U, Mo, and Re from seawater by sedimentary processes at a shallow-water site with near-saturation bottom water O 2 levels (240–380 μmol O 2/L), very high organic matter oxidation rates (annually averaged rate is 880 μmol C/cm 2/y), and shallow oxygen penetration depths (4 mm or less throughout the year). Under these conditions, U, Mo, and Re were removed rapidly to asymptotic pore water concentrations of 2.2–3.3 nmol/kg (U), 7–13 nmol/kg (Mo), and 11–14 pmol/kg (Re). The depth order in which the three metals were removed, determined by fitting a diffusion-reaction model to measured profiles, was Re < U < Mo. Model fits also suggest that the Mo profiles clearly showed the presence of a near-interface layer in which Mo was added to pore waters by remineralization of a solid phase. The importance of this solid phase source of pore water Mo increased from January to October as the organic matter oxidation rate increased, bottom water O 2 decreased, and the O 2 penetration depth decreased. Experiments with in situ benthic flux chambers generally showed fluxes of U and Mo into the sediments. However, when the overlying water O 2 concentration in the chambers was allowed to drop to very low levels, Mn and Fe were released to the overlying water along with the simultaneous release of Mo and U. These experiments suggest that remineralization of Mn and/or Fe oxides may be a source of Mo and perhaps U to pore waters, and may complicate the accumulation of U and Mo in bioturbated sediments with high organic matter oxidation rates and shallow O 2 penetration depths. Benthic chamber experiments including the nonreactive solute tracer, Br −, indicated that sediment irrigation was very important to solute exchange at the study site. The enhancement of sediment–seawater exchange due to irrigation was determined for the nonreactive tracer (Br −), TCO 2, NH 4 + , U and Mo. The comparisons between these solutes showed that reactions within and around the burrows were very important for modulating the Mo flux, but less important for U. The effect of these reactions on Mo exchange was highly variable, enhancing Mo (and, to a lesser extent, U) uptake at times of relatively modest irrigation, but inhibiting exchange when irrigation rates were faster. These results reinforce the observation that Mo can be released to and removed from pore waters via sedimentary reactions. The removal rate of U and Mo from seawater by sedimentary reactions was found to agree with the rate of accumulation of authigenic U and Mo in the solid phase. The fluxes of U and Mo determined by in situ benthic flux chamber measurements were the largest that have been measured to date. These results confirm that removal of redox-sensitive metals from continental margin sediments underlying oxic bottom water is important, and suggest that continental margin sediments play a key role in the marine budgets of these metals.

Benthic nutrient fluxes along an estuarine gradient: influence of the pinnid bivalve Atrina zelandica in summer

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 288:151-164 (2005) - doi:10.3354/meps288151 Benthic nutrient fluxes along an estuarinegradient: influence of the pinnid bivalve Atrina zelandica in summer M. Gibbs1,*, G. Funnell1, S. Pickmere1, A. Norkko2, J. Hewitt1 1National Institute of Water and Atmospheric Research Ltd., PO Box 11-115, Hamilton, New Zealand2Department of Marine Ecology, Göteborg University, Kristineberg Marine Research Station, 45034 Fiskebäckskil, Sweden *Email: m.gibbs@niwa.co.nz ABSTRACT: Benthic nutrient fluxes (BNF) can supply 30 to 100% of the nutrient requirements of benthic and pelagic algae in an estuary, and can, thus, potentially sustain benthic and pelagic primary production within the estuarine food web. While BNF can be influenced by microbial processes, epibenthic suspension-feeding bivalves have the potential to alter fluxes by their influence on the community composition of surrounding macrofauna and benthic boundary conditions, and their feeding activities. In Mahurangi Harbour, New Zealand, the large suspension feeding pinnid Atrina zelandica (hereafter referred to as Atrina) occupies large areas of the harbour floor. Consequently, Atrina have the potential to substantially influence the BNF and, thus, primary production, and the food supply to the filter feeding community within the harbour, including the rack-farmed Pacific oyster aquaculture industry. Mahurangi Harbour is almost always isohaline, but exhibits a strong gradient in suspended sediment concentration, which declines from head to mouth. As Atrina increase their rate of pseudofaeces production with increases in suspended sediment concentration, we conducted in situ light and dark paired benthic chamber experiments with and without Atrina at 4 stations along this turbidity gradient, to determine their effect on BNF. Our results showed substantially greater BNF from Atrina beds than bare sediments. We also found greater net BNF (difference between Atrina beds and bare sediment) in the less turbid water under dark conditions, but enhanced water column nutrient supply in the more turbid water in light, due to Atrina excretion of ammoniacal nitrogen (NH4-N). On an areal basis, we estimate that BNF from Atrina beds may account for up to 80% of the nutrient supply for pelagic primary production and, thus, they are of major importance to the sustainability of aquaculture in this harbour. KEY WORDS: Benthic nutrient flux · Benthic chambers · Estuarine turbidity gradient · Atrina zelandica · Microphytobenthos Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 288. Online publication date: March 10, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

Trace element determination in seawater by ICP-SFMS coupled with a microflow nebulization/desolvation system.

Direct and simultaneous determination of Al, Ag, As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Pb, Sb, U, V and Zn in diluted (1:10 v:v) seawater from the Antarctic Ocean and the Venice Lagoon at the ng mL(-1) and pg mL(-1) level has been performed by using an inductively coupled plasma sector field mass spectrometer (ICP-SFMS). Samples were analysed by using a PFA microflow nebulizer coupled with a desolvation system or a PFA microflow nebulizer coupled with a Teflon spray chamber, respectively. Measurements were carried out at low (LR, m/Delta m=300), medium (MR, m/Delta m=3,000) and high (HR, m/Delta m=7,500) resolutions depending on the studied isotope. To avoid contamination, sample pre-treatment was carried out in a clean laboratory equipped with a Class 100 vertical laminar flow hood. Concentration ranges (minimum-maximum in ng mL(-1)) found in the Antarctic seawater samples (in depth profiles) were: Ag 0.0004-0.0018, As 0.69-1.32, Cd 0.031-0.096, Co 0.018-0.065, Cr 0.18-0.46, Cu 0.04-1.58, Fe 0.13-1.63, Mn 0.02-0.12, Mo 5.97-12.46, Pb 0.007-0.074, Sb 0.033-0.088, U 0.5-1.9, V 0.6-2.5 and Zn 0.16-0.80. Concentration ranges (min-max in ng mL(-1)) found in the Venice Lagoon water samples (temporal profile from a benthic chamber experiment) were: Al 0.24-0.61, Ag 0.007-0.031, As 1.42-2.27, Cd 0.050-0.182, Co 0.440-1.461, Cr 0.15-0.34, Cu 0.81-2.46, Fe 0.25-1.66, Mn 11.6-31.7, Mo 6.50-10.6, Pb 0.047-0.225, Sb 0.240-0.492, U 1.7-3.3, V 1.3-2.8 and Zn 5.20-21.5. The detection limits range between 0.06 pg mL(-1) for Ag and U to 15 pg mL(-1) for Fe. In order to check the accuracy of the analytical procedure, measurements of the trace elements in a certified reference material (coastal Atlantic seawater, CASS-4-NRCC) were compared with the certified values. In addition, the results from the Antarctic and Venice Lagoon samples were compared with those obtained by using different analytical techniques.

Benthic Respiration and Inorganic Nutrient Fluxes in the Estuarine Region of Patos Lagoon (Brazil)

In situ benthic flux chamber experiments were performed during late austral spring and early summer of 1996 at eleven nearshore locations in the southern Patos Lagoon, Brazil. The Patos Lagoon is the largest lagoonal system in South America and is a very important nursery ground for local fin fish and shell fish fisheries. These are the first benthic flux measurements made in Patos Lagoon and they suggest that remineralizationwithin the sediments may dominate the recycling of organic matter and nutrients in thelagoon. Measured oxygen benthic fluxes (45–160 mmol m-2 d-1) are sufficientto remineralize reported mean water column carbon fixation while phosphate and fixednitrogen benthic fluxes (-0.4–2 and -1.1–4.2 mmol m-2 d-1, respectively)are sufficient to supply 100% and 25% of the required water column nutrient demand,respectively. Although of limited areal and temporal coverage, these initial studiesdemonstrate that sediments play a major role in the metabolism and nutrient cyclingwithin the Patos Lagoon Estuary and that future studies of lagoonal biogeochemistrymust consider exchange with the bottom.

Nitrogen Dynamics in Sandy Freshwater Sediments (Saginaw Bay, Lake Huron)

Sediment-water nitrogen fluxes and transformations were examined at two sites in Saginaw Bay, Lake Huron, as a model for sandy freshwater sediments. Substantial ammonium release rates (74 to 350 μmole NH 4 +/m 2/h 1) were observed in flow-through cores and in situ benthic chamber experiments. Sediment-water ammonium fluxes were similar at the inner and outer bay stations even though inner bay waters are enriched with nutrients from the Saginaw River. The high net flux of remineralized ammonium into the overlying water from these sandy sediments resembles typical data for marine systems (11 to 470 μmole NH 4 +/m 2/h 1) but were higher than those reported for depositional freshwater sediments (0 to 15 μmole NH 4 +/m 2/h 1; Seitzinger 1988). Addition of montmorillonite clay (ca. 1 kg dry weight/m 2) to the top of the sandy cores reduced ammonium flux. Mean “steady-state” ammonium flux following clay addition was 46 ± 2 (SE) % of the initial rates as compared to 81 ± 8% of the initial rates without clay addition. Zebra mussel excretion dominanted ammonium regeneration in the inner bay where the bivalve was abundant, but addition of zebra mussel feces/psuedofeces (3.0 g dw/m 2) to sediments did not increase ammonium or nitrate flux. Partial nitrification of ammonium at the sediment-water interface was suggested by removal of added 15NH 4 + from lake water passing over dark sediment cores. Sediment-water fluxes of nitrogen obtained from flow-through sediment cores resembled those from in situ benthic chambers. However, extended static incubations in gas-tight denitrification chambers caused more of the regenerated nitrogen to be nitrified and denitrified than occurred with the other two measurement systems.

Benthic fluxes of cadmium, lead, copper and nitrogen species in the northern Adriatic Sea in front of the River Po outflow, Italy

Trace heavy metal (Cd, Pb and Cu) and nitrogen species (N-NO 3, N-NO 2 and N-NH 4) fluxes between sediment and water were examined for approximately 4 days, in a coastal marine station located in the northern Adriatic Sea in front of the River Po outflow. An in situ benthic chamber, equipped with electronic devices for monitoring and adjustment of oxygen and pH and with a temperature detector, was used. The benthic chamber experiment enabled study of the temporal trend of metals and nutrients when oxygen concentration varied in a controlled environment. Although particular care was devoted to chamber deposition and parameter control, sediment resuspension occurred at the beginning of the experiment and O 2 fluctuations were observed during the course of the experiment. Pb concentration was affected by both resuspension and oxic conditions in bottom water, which prevented determination of any reasonable Pb flux value. Cd and Cu, not influenced by oxygen fluctuations, reached an equilibrium phase in a short period with initial positive fluxes from sediment of 0.68 (S.D.=0.07) and 6.9 (S.D.=5.6) pmol cm −2 h −1, respectively. With regard to nitrogen species, the highest positive flux was that of N-NH 4 (10.5, S.D.=2.4, nmol cm −2 h −1) whose concentration increased in the chamber, while nitrate concentration (initial flux of −5.7, S.D.=1.5, nmol cm −2 h −1) immediately decreased after the beginning of the experiment. Nitrite concentration was almost constant throughout the experiment and its flux was generally low (initial flux 0.1, S.D.=0.9, nmol cm −2 h −1).

Benthic Fluxes and Pore Water Profiles in the Tigullio Gulf

Diffusive fluxes of elements (NO− 2, NO− 3, NH+ 4, SiO2, PO3- 4, Cl−, SO2- 4, Fe, Mn) have been measured by applying the Fick's first law in two stations of the Tigullio Gulf: the first one characterized by sandy sediments rich in vegetal detritus and the second one, located to within the tourist harbour, characterized by a silty-clay sediments. Benthic fluxes were measured only in the second station by means of benthic chamber experiments. Although the significant presence of dissolved oxygen in the surface sediments, and the evidence of processes usually occurring in oxidised sediments such as nitrification, both stations also presented characteristics of anoxic sediments such as high oxygen consumption rate and high pore water concentrations of ion, manganese and N-ammonia and reactive orthophosphate. In both stations, sediments seemed to represent a potential source for most of the chemical species studied, although fluxes were not confirmed for ion, manganese and reactive orthophosphate in benthic chamber experiments. Diffusive fluxes presented a general agreement for both stations, with higher fluxes of N-nitrate and N-nitrite at the first station were oxidative processes of N-ammonia in the upper layer of the sediments seemed to be more active. the comparison between diffusive and benthic fluxes showed a possible contribution of bioturbation.

Research On Zooplankton in the Gulf of Rapallo

Zooplankton samples, collected in autumn 1996 from two stations in the Gulf of Rapallo, Ligurian Sea (Rapallo Harbour and Prelo Bay, which is a more open site with lower human impacts) were analysed. at both stations, the community was dominated by copepods (mainly juveniles and adults of different species of Acartia and Oithona) and meroplankton (mainly polychaete larvae). Total zooplankton abundance in the harbour waters was significantly higher than in the nearby bay. the occurrence of Acartia grani in Rapallo Harbour and Pteriacartia josephinae in Prelo Bay is noteworthy, as they are reported for the first time in the Ligurian Sea, and A. grani has not previously been recorded to the Italian coastline. A three-day benthic chamber experiment aimed to quantify nutrient fluxes between the sediment and water column was performed in the Rapallo Harbour: the profound effects of confinement on the composition and abundance of zooplankton within the incubation chamber are discussed.

Porewater nutrient fluxes in a shallow fetch-limited estuary

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 183:39-47 (1999) - doi:10.3354/meps183039 Porewater nutrient fluxes in a shallow fetch-limited estuary C. E. Oldham1,*, P. S. Lavery2 1Centre for Water Research, The University of Western Australia, Nedlands, Western Australia 6907, Australia 2Centre for Ecosystem Management and School of Natural Sciences, Edith Cowan University, Joondalup, Western Australia 6027, Australia *E-mail: oldham@cwr.uwa.edu.au ABSTRACT: The Swan River Estuary is a shallow meso-eutrophic system in SW Australia. The dominant summer wind pattern in the region includes a strong SW sea breeze each afternoon. We hypothesised that such a regular and significant wind event may be important in causing the release of sediment porewater with subsequent effects on water quality and nutrient dynamics. To test this, we conducted a multidisciplinary field experiment in 1996 during which we measured temperature microstructure profiles (to yield turbulence parameters), velocity profiles, light profiles and nutrient profiles. Bottom shear stresses were estimated via the viscous-dissipation method, which can be used in stratified and unstratified water bodies or during convective cooling, all of which are likely to affect sediment-water dynamics in shallow systems. We observed that, after the sea breeze began, there was a dramatic breakdown of temperature stratification, an increase in mean velocities and an increase in turbulence levels at the sediment-water interface. This coincided with a doubling of water column ammonium concentrations. However, this pulse of nutrients was shown to occur prior to conditions necessary for sediment resuspension. We therefore attribute the increased porewater fluxes to interactions between increasingly energetic hydrodynamics and the benthic environment. The technique used here to measure porewater fluxes as a function of hydrodynamic forcing is an excellent alternative to benthic chamber experiments, which isolate the sediments from the overlying hydrodynamics. KEY WORDS: Porewater fluxes · Resuspension · Subtidal pumping · Ammonium Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 183. Publication date: July 06, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Influence of radial pressure gradients on solute exchange in stirred benthic chambers

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 141:303-311 (1996) - doi:10.3354/meps141303 Influence of radial pressure gradients on solute exchange in stirred benthic chambers Glud RN, Forster S, Huettel M Bromide was used as a conservative tracer for evaluating the effect of stirring-induced radial pressure gradients in 2 typical benthic chamber designs. One chamber was square, with side lengths of 30 cm (volume 9.0 l), and the other was cylindrical, with a diameter of 19 cm (volume 2.5 l). It was demonstrated that radial pressure gradients associated with chamber water rotation could induce advective porewater transport in both chambers. The intensity of the advective porewater transport was a function of sediment permeability and stirring rate. Stirred at 12 rpm, solute transport changed from diffusive to advective at a sediment permeability >2 x 10-12 in the square chamber and >5 x 10-12 m-2 in the cylindrical chamber. The sediment permeability at which solute exchange was still controlled by diffusion could be increased by almost 1 order of magnitude in the square chamber by decreasing the stirring rate to 7 rpm. The sediment permeability values can be used as a guide to when benthic chamber experiments can be performed without introducing a serious stirring-induced artefact. Lander · Benthic exchange · Flux chambers · Convection · Pressure gradients · Bromide Full text in pdf format PreviousExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 141. Publication date: October 03, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.

Mathematical models for estimating fluxes at the sediment-water interface in benthic chamber experiments

Experimental data collected by means of benthic chambers have been used to develop simple mathematical models in order to predict heavy metal and non-metal fluxes at the sediment-water interface. In particular, two mathematical models have been applied to Ba, Co, Fe, Pb, Mn and Cu.

Nitrogen cycling across the sediment-water interface in an eutrophic, artificially oxygenated lake

Processes controlling the nitrogen (N) exchange between water and sediment in eutrophic Lake Sempach were studied using three different independent methods: benthic flux chambers, interstitial water data and hypolimnetic mass balances. The sediments released NH 4 + (1.1–16.1 mmoles m−2 d−1), NO 2 - (0.1–0.4 mmoles m−2 d−1) and dissolved organic N (<0.25 mmoles m−2 d−1). A net NO 3 - consumption (2.4–11.1 mmoles m−2 d−1) related to the NO 3 - concentrations in the overlying water was observed in all benthic chamber experiments. The flux of the reactive species NO 3 - and NH 4 + was found to depend on hydrodynamic conditions in the water overlying the sediment. For this reason, benthic chambers overestimated the fluxes of inorganic N compared to the other methods. Thus, in short-term flux chamber experiments the sediment may either become a sink or a source for inorganic N depending on the O2 concentration in the water overlying the sediment and the stirring rate. As demonstrated with a15NO 3 - experiment, nitrate-ammonification accounted for less than 12% of the total NO 3 - consumption. After six years of artificial oxygenation in Lake Sempach, a decrease in hypolimnetic total inorganic nitrogen (TIN) was observed in the last two years. The occurrence of dense mats of H2S-oxidizingBeggiatoa sp. indicated micro-aerobic conditions at the sediment surface. Under these conditions, a shorter distance between the ecological niches of nitrifying and denitrifying bacteria, and therefore a faster NO 3 - -transport, can possibly explain the lowering of TIN by enhanced net denitrification.

A free-vehicle benthic chamber instrument for sea floor studies

A new free-vehicle instrument has been developed that is capable of performing controlled benthic chamber experiments on the sea floor at water depths up to 6 km. The instrument emplaces a single 30 × 30 cm titanium chamber in the sediments with little sediment disturbance. At pre-set equally spaced time intervals, a total of 18 individual samples or chemical tracers may be withdrawn from or injected into the chamber waters. The volume of water removed or added in each operation is balanced by bottom water which enters or leaves the chamber through a long, open tube. At the termination of the experiment a hydraulic system closes a scoop beneath the chamber capturing the sediments in the chamber for further study. The instrument is simple to deploy, has been extremely reliable in the field, and has yielded geochemically consistent results.

Organic carbon oxidation and benthic nitrogen and silica dynamics in San Clemente Basin, a continental borderland site

Organic carbon oxidation rates in San Clemente Basin were determined by benthic chamber experiments using the Bottom Lander, along with studies of pore water chemistry. Non-steady-state diagenetic models are developed for interpreting concentration-time data from the benthic chamber experiments. O 2, NO 3 −, and SO 4 2− are all important oxidants for organic carbon at our study site. Regenerated fixed nitrogen was consumed by NO 3 − reduction. There is a flux of NO 3 − into the sediments, and the benthic flux of NH 4 + is undetectable. The total rate at which fixed nitrogen is removed from the oceans at this site is about twice the flux of PON to the sea floor. SiO 2 fluxes calculated from interfacial pore water gradients are in satisfactory agreement with those determined using the Lander. Most silica dissolution must therefore occur within the sediments, although interstitial profiles show that little dissolution occurs below 1 cm depth.