Subtidal Sediments Research Articles

Retention and fate of groundwater-borne nitrogen in a coastal bay (Kinvara Bay, Western Ireland) during summer

The magnitude of submarine groundwater discharge (SGD) and its contribution to nitrogen biogeochemistry in a small embayment in the Western Coast of Ireland subject to occasional hypoxia were investigated during summer. Time series (24 h) of 222Rn, NO3−, NO2−, NH4+, dissolved reactive silicate (DRSi) and salinity (June 2010, July and September 2011 and July 2013), total dissolved phosphorus (TDP) (September 2011 and July 2013) and dissolved organic nitrogen (DON) (July 2013) were measured at the mouth of the bay and coupled with relevant sediment–water fluxes and input loadings to derive nutrient budgets. In-situ activity ratios of the naturally occurring radium isotopes 224Ra and 223Ra were employed in parallel to the freshwater fraction method to determine the timescale of freshwater retention in the system. Based on 222Rn mass balances (n = 4), the mean groundwater (±SE) discharge into Kinvara Bay was 10.4 ± 6.3×104 m3 days−1, delivering average loads of 376 ± 67 kg Si day−1 (as DRSi), 1.6 ± 0.2 kg P day−1 (as TDP) and ~280 kg N day−1 of dissolved nitrogen (272 ± 49 DIN, essentially as NO3−, and 8.2 ± 1.6 DON), which correspond to ~98.8, 49.1 and ~93.5 % of total allochthonous nutrient inputs respectively. Expressed on an areal basis and annual scale the exogenous N summer loading of Kinvara is equivalent to 25.9 g N m−2 year−1. Our biogeochemical budgets indicate that tight benthic-pelagic coupling contributes to the very high retention levels of N within the bay with subtidal sediments acting as a link in the internal N cycle via DNRA, while ~18 % of the exogenous N load is removed by benthic denitrification. Rapid cycling of DON into bioavailable forms of N within the timescale of freshwater retention in the system (~7 days) contributes ~50 % to local biological N fixation. Nutrient availability ratios are N:P ~173 and Si:P ~503, indicating that primary production is P-limited while the carbon yield (~3.01 × 105 mol C day−1, or ~0.313 kg C m−2 year−1) suggests the bay is eutrophic during the summer. SGD-borne Nitrogen loading is therefore the major driver of eutrophication in Kinvara Bay. Our biogeochemical characterization is consistent with the observed phytoplankton community composition and species succession and justifies the local observation of HAB’s. In addition, the relative magnitude of DNRA-promoted N retention compared to N removal by denitrification, coupled with seasonal hypoxia, suggests that the system is advanced in the chronological sequence of eutrophication effects on shallow coastal systems.

A Synthesis of Depositional Trends In Intertidal and Upper Subtidal Sediments Across the Tidal–Fluvial Transition In the Fraser River, Canada

Abstract Sedimentological, neoichnological, palynological, and geochemical trends from upper subtidal and intertidal positions on channel bars in the lower Fraser River, Canada are synthesized into a single, coherent framework. From these data we define criteria for determining depositional position in shallow water depths in tide-influenced rivers. Three sedimentological trends are observed from the river mouth, through the locus of mud deposition (within the turbidity maximum zone (TMZ)), and into the freshwater-tidal zone. (1) The recurrence (per meter) and thickness of mud beds increase towards the TMZ and tapers in both the landward and seaward directions. (2) Muddy current ripples and graded current ripples are most abundant in the TMZ; they are less common with decreasing brackish-water influence and are absent in the freshwater river reach. (3) Heterolithic bedding (i.e., flaser, wavy, and lenticular) is common in the TMZ, less common seaward, and absent from the freshwater realm. In addition to the sedimentological trends, four ichnological trends parallel decreasing water salinity. With decreasing salinity, there is: (1) a decrease in bioturbation intensity from BI 2–3 to BI 0–1; (2) a decrease in the abundance of bioturbated beds; (3) a marked decrease in the diversity of traces from 5–6 forms to 1–2 forms; and, (4) a decrease in the diameter and length of traces. Traces are rare to absent in the tidal freshwater zone. Palynological and geochemical trends generally follow ichnological trends but are less obvious. Neither dinocyst abundance nor geochemical signature can be used to determine relative position in a tide-influenced river channel, although dinocyst abundances greater than 1% indicate significant marine influence, and 0–1% marine dinocysts indicate tidal influence. Although it is not feasible to determine exact depositional position within the tidal–fluvial transition, our results suggest that it is possible to determine where sediments were deposited relative to the TMZ. In turn, predicting relative depositional position can assist in unraveling stratigraphy and in recognizing nested channels in architecturally complex sedimentary successions.

Longshore variability of beach states and bar types in a microtidal, storm-influenced, low-energy environment

Beach classification models are widely used in the literature to describe beach states in response to environmental conditions. These models were essentially developed for sandy barred to barless beaches in micro- to meso-tidal environments subject to moderate to high wave energy conditions and have been based on field studies over limited stretches of coast. Here, we further interrogate the performance of the Australian beach classification scheme by analysing beach states and corresponding bar types on a regional scale in a storm-influenced, low wave-energy, microtidal environment, using a large and unique spatial and temporal dataset of supra- and subtidal beach morphology and sedimentology. The 200km-long coast of the Gulf of Lions in the Mediterranean consists of quasi-continuous sandy beaches with a well-developed double sandbar system. All the reported classical beach states were observed on this coast, from reflective to dissipative, along with two more unusual states: the rock platform-constrained beach state which is associated with bedrock outcrops, and the non-barred dissipative beach state which is more commonly found in large tidal-range settings. LiDAR bathymetry shows that the transitions between beach state zones are marked mainly headlands but transitions also occur progressively along stretches of continuous sandy beach. The longshore distribution of beach states and associated bar types on a regional scale can be related to the variability of hydrodynamic conditions (wave incidence and energy) and sediment characteristics (particle size). However, the influence of these parameters on beach state seems to be largely controlled by the geological context such as the presence of a river mouth, headland or rock platform. Finally, we assessed the ability of the parameter Ω, commonly used to characterise beach states, which combines wave characteristics and sediment fall velocity, to predict the observed beach states and bar types using a very large set of hydrodynamic and sedimentary data. Our results, based on high frequency spatial sampling, show that the fall velocity of the subtidal sediment coupled with wave statistics one month prior the observed beach state strongly improved the predictive power of the parameter Ω.

Using oyster tissue toxicity as an indicator of disturbed environments

Crassostrea virginica (the Eastern or American oyster) bioaccumulates pollutants from the water column, and therefore, its tissues can be used as bioindicators of past and present estuarine health. In this pilot project, we decided to investigate whether its tissues would be a suitable medium for toxicity testing using tissues from a variety of southern Texas locations of known and suspected anthropogenically impacted and unimpacted areas. We also conducted toxicity tests on sediments adjacent to oyster reefs using standard protocols for sediment toxicity. We tested the toxicity of tissues and sediments on the luminescent bacteria Vibrio fischeri, whose bioassays are commonly referred to by the trade name Microtox®. Microtox tests are quick, relatively inexpensive and sensitive to a range of contaminants. Evidence from this preliminary study suggests that conducting toxicity tests on oyster tissues may predict localized contamination better than when conducting toxicity tests on subtidal sediment. The refinement of these methods to use oyster tissues to detect contamination may be especially useful for environmental impact studies and/or studies where rapid and inexpensive information is needed.

Effects of live and post-mortem shell structures of invasive Pacific oysters and native blue mussels on macrofauna and fish

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 518:123-138 (2015) - DOI: https://doi.org/10.3354/meps11044 Effects of live and post-mortem shell structures of invasive Pacific oysters and native blue mussels on macrofauna and fish P. Norling1,3,*, M. Lindegarth2, S. Lindegarth2, Å. Strand2 1Norwegian Institute for Water Research, Gaustadalléen 21, 0349 Oslo, Norway 2Department of Biology and Environmental Sciences - Tjärnö, University of Gothenburg, 452 96 Strömstad, Sweden 3Present address: Swedish Agency for Marine and Water Management, Box 11 930, 404 39 Gothenburg, Sweden *Corresponding author: pia.c.norling@gmail.com ABSTRACT: Blue mussels Mytilus edulis and the invasive Pacific oyster Crassostrea gigas are both ecosystem engineering species which modify the environment, thus having large effects on associated species. With the introduction of the Pacific oyster, a new biogenic structure has been added to subtidal sediment habitats in Scandinavia. By conducting a field experiment, the effects of live and post-mortem shell structures of C. gigas and M. edulis on associated infauna, epibenthic fauna and fish on the Swedish west coast were evaluated. Plots with 5 different treatments (live Pacific oysters, oyster shells, live blue mussels, mussel shells and sand control) were constructed on bare sandy sediment at 2 subtidal localities. Epibenthic macrofauna and fish were sampled with a drop trap, and sediment and infauna samples were collected with sediment cores. Live bivalve treatments had significant effects on organic content of the sediment; however, no treatment effects on infauna were found. In contrast, abundance and biomass of epibenthic fauna increased 4 to 8 times and species richness increased in the presence of the bivalves or their shells, compared to the sand control. Epibenthic fauna abundance and biomass was higher in the oyster shell treatment compared to the live bivalve treatments, which in turn had higher abundance and biomass than the mussel shell treatment. In general, the mussel shell treatment favoured small crustaceans, while the oyster shell and live bivalve treatments favoured fish and larger invertebrate species. Based on these results, we conclude that further establishment of the Pacific oyster in Swedish waters will cause large changes to community structure of benthic macrofauna and fish. KEY WORDS: Non-indigenous species · Ecosystem engineering · Habitat modification · Macroinvertebrates · Infauna · Epibenthic fauna · Sediment community · Crassostrea gigas · Mytilus edulis Full text in pdf format Supplementary material PreviousNextCite this article as: Norling P, Lindegarth M, Lindegarth S, Strand Å (2015) Effects of live and post-mortem shell structures of invasive Pacific oysters and native blue mussels on macrofauna and fish. Mar Ecol Prog Ser 518:123-138. https://doi.org/10.3354/meps11044 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 518. Online publication date: January 07, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Temporal Trend in the Transfer of Sellafield-Derived 14C into Different Size Fractions of the Carbonate Component of NE Irish Sea Sediment

From 1994 onwards, radiocarbon discharges from the Sellafield nuclear fuel reprocessing plant have been made largely to the northeast Irish Sea. They represent the largest contributor to UK and European populations of the collective dose commitment derived from the entire nuclear industry discharges. Consequently, it is important to understand the long-term fate of 14C in the marine environment. Research undertaken in 2000 suggested that the carbonate component of northeast Irish Sea sediments would increase in 14C activity as mollusk shells, which have become enriched in Sellafield-derived 14C, are broken down by physical processes including wave action and incorporated into intertidal and subtidal sediments. The current study, undertaken in 2011, tested this hypothesis. The results demonstrate significant increases in 14C enrichments found in whole mussel shells compared to those measured in 2000. Additionally, in 2000, there was an enrichment above ambient background within only the largest size fraction (>500 μm) of the intertidal inorganic sediment at Nethertown and Flimby (north of Sellafield). In comparison, the present study has demonstrated 14C enrichments above ambient background in most size fractions at sites up to 40 km north of Sellafield, confirming the hypothesis set out more than a decade ago.

Biogeochemical dynamics of exogenous methane in an estuary associated to a mangrove biosphere; The Sundarbans, NE coast of India

The distribution, sources and fate of dissolved CH4 were monitored in a mangrove associated estuary of the Sundarbans from January 2011 to December 2012. This tropical estuary was polyhaline (salinity range between 19.06±4.33 and 27.09±0.59), well mixed and net heterotrophic. Average dissolved CH4 concentrations in estuarine surface and bottom waters were 69.90 and 56.17nM, respectively, showing a very high degree of super-saturation (≈2869±571%). Dissolved CH4 was significantly correlated with salinity but not with other physicochemical and biological properties of the estuarine water, indicating its exogenous origin. Average dissolved CH4 concentration in sediment pore water was 53.4 times higher than estuarine water, suggesting significant CH4 influx from the sediment to the estuary via advective and diffusive transports. Average advective and diffusive CH4 fluxes from intertidal and sub-tidal sediments were 159.52 and 8.45μmolm−2d−1, respectively. The average dissolved CH4 oxidation rate in the estuarine water column was 20.59nmolL−1d−1. Being highly supersaturated with respect to atmospheric equilibrium the estuary acts as a source of 0.093Gg CH4 annually to the atmosphere with an average flux of 8.88μmolm−2d−1. In the estuarine CH4 cycle the advective flux and CH4 oxidation were recorded as the predominant input and output processes, respectively. Finally, a box model representing the CH4 biogeochemical cycle in this estuarine mangrove habitat derived a CH4 export flux from the estuary to the adjacent continental shelf of 0.485Ggyr−1.

Cable bacteria associated with long-distance electron transport in New England salt marsh sediment.

Filamentous Desulfobulbaceae have been proposed as 'cable bacteria', which electrically couple sulfide oxidation and oxygen reduction in marine sediment and thereby create a centimetre-deep suboxic zone. We incubated New England salt marsh sediment and found long-distance electron transport across 6 mm and 16S rRNA genes identical to those of previously observed cable bacteria in Aarhus Bay sediment incubations. Cable bacteria density in sediment cores was quantified by fluorescence in situ hybridization. In contrast to the coastal, subtidal sediments with short-termed blooms of cable bacteria based on rapidly depleted iron sulfide pools, the salt marsh cable community was based on ongoing sulfate reduction and therefore probably more persistent. Previously observed seasonal correlation between Desulfobulbaceae dominance and extensive reduced sulfur oxidation in salt marshes suggest that cable bacteria at times may have an important role in situ.

Functional response of an adapted subtidal macrobenthic community to an oil spill: macrobenthic structure and bioturbation activity over time throughout an 18-month field experiment

An experimental oil spill was carried out in order to assess in situ responses of a macrobenthic community of shallow subtidal sediments historically exposed to petroleum contamination. Both structural and functional (bioturbation activity) parameters of the community, subjected or not to a pulse acute contamination (25,000 ppm), were studied for 18 months. No difference in the community structure was detected between contaminated and control sediments, from 6 to 18 months of experimentation. Vertical distributions of organisms, however, were affected by the presence of oil contamination leading to a deeper burial of some polychaete species. In the same time, changes in sediment-reworking activity and more especially a deeper particle burying in sediments subjected to acute oil contamination were shown. These results highlight the need to complete the analysis of community structure by assessing functional aspects, such as bioturbation activity, a process integrating various aspects of benthic behaviour (e.g. feeding, locomotion, burrow building) in order to estimate real (structural and functional) and long-term effects of oil contamination on benthic communities.

Two new nematodes, Pseudelzalia longiseta gen. nov., sp. nov. and Paramonohystera sinica sp. nov. (Monhysterida: Xyalidae), from sediment in the East China Sea

Pseudelzalia longiseta gen. nov, sp. nov. and Paramonohystera sinica sp. nov. from subtidal sediment in the East China Sea are described. Pseudelzalia is characterized by 6 labial papillae and 10 cephalic setae, cylindrical buccal cavity, elongate (>2 anal body diameter) spicules, and conico-cylindrical tail devoid of terminal setae. It differs from Elzalia by the absence of terminal setae. Pseudelzalia longiseta sp. nov. is 647–853 μm long, has 7–8 μm long cervical setae, 11–14 μm long caudal setae, 25–41 μm long spicules about 2.1–2.7 anal diameter, and pointed tail-tip. Paramonohystera sinica possesses 12 cephalic setae, a character found in four congeners: Paramonohystera buetschlii (Bresslau and Schuurmans Stekhoven in Schuurmans Stekhoven, 1935, Paramonohystera pilosa Boucher, 1971, Paramonohystera concinna Lorenzen, 1977 and Paramonohystera halerba Fadeeva and Belogurov, 1987. It differs from P. buetschlii by shorter body (933–1023 μm versus 2000–2200 μm); from P. pilosa by the much shorter spicules (79–88 μm versus 167 μm) and narrower head (13–16 µm versus 32 µm); from P.concinna by smooth cephalic setae (versus segmented); and from P. halerba by the absence of two rows of setae on the ventral side of the tail (versus present). Based on the evaluation of nominal species, we recognize 14 valid species and provide an emended diagnosis and a tabular key for Paramonohystera.http://www.zoobank.org/urn:lsid:zoobank.org:pub:474B8F17-AED7-4078-8176-DFC499B78526

Overview of Research into the Coastal Effects of the Macondo Blowout from the Coastal Waters Consortium: A GoMRI Consortium

ABSTRACT The Coastal Waters Consortium (CWC) led by Louisiana Universities Marine Consortium is one of eight Gulf of Mexico Research Initiative research consortia. The CWC focuses on: oil transport and fate, chemical evolution and biological degradation, and environmental effects.The following is an overview of a portion of the research conducted within the consortium. The consortium works in a system that was impacted by the Deepwater Horizon oil disaster and additionally impacted by freshwater diversions resulting in changes in salinity, tropical storms, and hurricanes. First, we conducted model simulations assessing oil transport into the Barataria Bay estuary, which indicate that easterly winds and feeding of the anticyclonic gyre in the Louisiana Bight pushed the oil into Barataria Bay. In subtidal sediments adjacent to oiled marshes, marsh detritus from eroding marsh edges eventually became entrained in the sediment column. Biotic impacts vary. The above-ground plant biomass appears healthy at the individual sampling sites; overall the most seaward (i.e., likely oil-impacted) areas of Terrebonne and Barataria Bay have shown, via satellite data, a distinct decline in marsh vegetation coverage since 2010. Oysters appear to be affected by predation and salinity variation. Microbial diversity from marsh-edge sediments is distinct from before and after the spill, and between unoiled and oiled marshes, with lower diversity in oiled marshes; but the greatest community composition shifts are in marshes affected by the freshwater diversions. Changes in microbial diversity in the water column at the stream-side edge of oiled marshes are extensive and are related to marsh edge erosion. In contrast, oiling of marshes had no impact on ammonia oxidizer or denitrifier abundances and on soil biogeochemical process rates 2+ years post-spill. Analysis of long-term offshore phytoplankton community and hypoxia data indicate some signal of the Macondo oil, but these components of the ecosystem remain mostly influenced by the fresh water and nutrients delivered by the Mississippi River. The consortium continues to work to tease apart oil impacts, effects of salinity, natural variation, and disturbance from tropical storms and hurricanes to determine the trajectory for health of shelf waters and Louisiana's marshes.

Levels of Cd, Cu, Pb and V in marine sediments in the vicinity of the Single Buoy Moorings (SBM3) at Mina Al Fahal in the Sultanate of Oman

Recently in the Sultanate of Oman, there has been a rapid surge of coastal developments. These developments cause metal contamination, which may affect the habitats and communities at and near the coastal region. As a result, a study was conducted to assess the level of metal contamination and its impact on the marine sediments in the vicinity of the Single Buoy Moorings 3 (SBM3) at Mina Al Fahal in the Sultanate of Oman. Marine subtidal sediment samples were collected from six different stations of the SBM3 for the period ranging from June 2009 to April 2010. These samples were then analyzed for their level and distribution of the heavy metals of cadmium (Cd), copper (Cu), lead (Pb) and vanadium (V). Overall, low concentrations of all four heavy metals were measured from the marine sediments, indicating that the marine at SBM3 is of good quality.

Geographical distribution and abundance of Ctenocheilocaris galvarini (Crustacea: Mystacocarida) along the coast of Chile

The mystacocarid Ctenocheilocaris galvarini is a member of the intertidal meiofauna in exposed sandy beaches along the coast of Chile. Originally described by Dahl (1952) from sub-tidal sediment off Isla Guafo, the only other published record is from semi-fine intertidal sand in Las Cruces. This paper presents a variety of new records of C. galvarini based on both quantitative and qualitative sampling of the coast of Chile between 18°S and 54°S. Ctenocheilocaris galvarini is found primarily in southern Chile, south of 32°, in the intertidal zone of intermediate beaches, in fine sand (Wentworth scale) most likely distributed between the level of the water-table and the surface, but avoiding dry sand.

Recent surface marine sediments of Cocos Island in Costa Rica

Subtidal sediments of Isla del Coco (Cocos Island), Costa Rica were described in their grain size, sorting, organic matter, and carbonates from 27 dredge samples (3–75 m), collected in April 2010. The organic matter range between 1.37–3.31% and carbonates presented a mean of 74±17%. The sorting was moderately or poorly. The grain size ranged between 0.1–1.1mm. The pattern is that sediment change from inner to mouth of bays. Carbonates and gravel fractions increased offshore and organic matter have high values inner the bays. Input of vegetal debris and mud was from the rivers of this island covered with rain and cloud forest.

N2 fluxes in sediments of the Elbe Estuary and adjacent coastal zones

ABSTRACT: The conversion of reactive nitrogen species to N 2 during denitrification in sedimentsmay be one of the most valuable ecosystem services provided by estuarine and intertidal environ-ments near river discharge areas. To quantify the rates and limiting factors of denitrification in theestuary of the Elbe River and adjacent Wadden Sea (SE North Sea), we measured sediment N 2 fluxes across subtidal and intertidal sediments, and along gradients in nitrate and organic matterconcentrations. We conducted 2 sampling campaigns, in March and September 2009, duringwhich N 2 fluxes were quantified by N 2 /Ar measurements in sediment core incubations, and com-pared to isotope pairing results in September 2009. At ambient nitrate concentrations, sediments inthe inner Elbe Estuary produced N 2 fluxes of up to 156 µmol N m −2 h −1 . In September, nitrate con-centration in bottom water and organic matter content in sediments limited N 2 production; suchlimitations were not observed in March. We extrapolated the estuarine sediment nitrogen removalof March and September to the present-day area of intertidal and subtidal sediments in the ElbeEstuary between the port of Hamburg and the transition to the North Sea. Our estimate suggeststhat 3.3 ± 1.2 kt nitrate-N are removed in sediments in this region in spring and summer. This im-plies that reactive nitrogen removal in the inner Elbe Estuary reduces the spring/summer load ofthe Elbe River (47 kt N) by around 7%, a reduction that is much lower than commonly assumed forestuaries, and significantly lower than nitrate removal in the Elbe was in historical times.KEY WORDS: Denitrification · Nitrogen cycle · Eutrophication · Elbe Estuary

Biotic and Abiotic Processes In the Formation and Diagenesis of Permian Dolomitic Stromatolites (Zechstein Group, NE England)

Abstract The Crinkly Bed of the Upper Permian Zechstein Group succession (Roker Formation = Hauptdolomit, Z2C) in northeast England is a distinctive 1.4-meter-thick unit that has been interpreted as a stromatolite of microbial origin, or, alternatively, as the result of purely abiotic precipitation. Close examination of this stratigraphically significant unit shows that it is the result of both physical and microbial processes, and was deposited in hypersaline shallow water immediately following lowstand evaporite deposition within the Zechstein basin. The internal structure of the Crinkly Bed consists of fine, millimeter scale laminae of alternating clotted peloidal or aphanitic micritic layers and granular laminae composed of silt-size peloids, with rare hollow spheroids. The lamination is extremely regular in thickness and laterally persistent for up to 4 meters. A microbial community composed of coccoid and filamentous microorganisms, inferred from fossil evidence, colonized the original sediment surface. It is suggested that this biofilm was responsible for the precipitation of both the micrite laminae and most of the peloids of the granular laminae; the peloids are consequently interpreted as autochthonous. This interpretation of a microbial origin is consistent with the microstructure and geochemical signatures of the micritic dolomite, which constitutes both the continuous micritic laminae and the peloids themselves. Primary dolomite precipitation is hypothesized to have taken place from marine to slightly hypersaline waters, mediated by bacterial metabolism, similar to the process that operates in modern intertidal microbial mats. The Crinkly Bed shows macro-structures that vary along a continuum from symmetrical to asymmetrical, centimeter scale, ripple-like structures, some showing interference patterns, through to domical and conical structures, more typical of stromatolites. The more ripple-like structures have a lamination of microbial origin identical to that within the domal–conical stromatolites; there is no internal cross lamination. Their origin is equivocal: they could be the result of physical (current- or wave-induced) deformation of a surficial biofilm, or their form could be inherited from true mechanically deposited ripples (not observed) that provided a template for biofilm growth. Changes in the nature and strength of the wave and/or current regime, and possibly in the community structure of the microbial mat, produced this array of microbially induced macrostructures (MISS). The latter, plus the absence of desiccation features indicative of intertidal to supratidal deposition, suggest subtidal sedimentation at a depth of several meters. Intergranular gypsum cement precipitated during early diagenesis, and ferroan sparry dolomite precipitated during burial. Tertiary uplift and the consequent exposure to meteoric waters resulted in the precipitation of calcite cements that replaced gypsum and pre-existing dolomite, probably via the biological mediation of heterotrophic bacteria. The interpretation of this distinctive stratigraphic unit illustrates the difficulty in distinguishing between biotic and abiotic processes in the sedimentary record.

Influence of Sediment Type on Antipredator Response of the Softshell Clam,Mya arenaria

Mya arenaria (Softshell Clam) inhabit a wide range of intertidal and subtidal sediment types in the western North Atlantic. They avoid predation by burrowing deeply in the sediment. We investigated the effect of sediment type on the antipredator responses of Softshell Clams to Carcinus maenas (Green Crab) as well as the relative costs and benefits of living in different sediment types. Clam burrowing depth, growth, and Green Crab predation rate were observed in experimental plots of mud, sand, and gravel. Clams exposed to crabs burrowed deeper than did control clams in all sediment types, but clams burrowed deepest in finer sediment types. Clams in coarser sediments also had thicker shells and suffered lower rates of predation than did those in mud. These results suggest distinctive costs and benefits associated with inhabiting different sediment types. For Softshell Clams, coarse sediments are most costly metabolically, but have lower predation risk compared to finer sediments.

Background level and composition of polybrominated diphenyl ethers (PBDEs) in creek and subtidal sediments in a rural area of Korea

To study background levels of polybrominated diphenyl ethers (PBDEs) in Korea, concentrations of PBDEs were measured for creek and subtidal sediments around Goseong Bay. Total concentrations of PBDEs (Σ19PBDE) in creek sediments ranged from 0.18 to 13.95ng/g dry weight and were about twice those in subtidal sediments. PBDE concentrations were about two orders of magnitude lower than those reported in industrially active regions of Korea and other countries. BDE 209 was a major congener, accounting for 79.0% and 78.5% of total PBDEs in creek and subtidal sediments, respectively. This is consistent with the high consumption of deca-BDE in Korea and the very high octanol–water partition coefficient of deca-BDE. The relative compositions of PBDEs in creek and subtidal sediments were similar. BDE 209 and Σ19PBDE had statistically significant correlations with total organic carbon, the lower brominated congeners had a poor correlation with total organic carbon.

The effects of wastewater effluent and river discharge on benthic heterotrophic production, organic biomass and respiration in marine coastal sediments

We examine effects of high river particulate flux and municipal wastewater effluent on heterotrophic organic carbon cycling in coastal subtidal sediments. Heterotrophic production was a predictable (r2=0.95) proportion (56%) of oxidized OC flux and strongly correlated with organic/inorganic flux. Consistent growth efficiencies (36%) occurred at all stations. Organic biomass was correlated with total, OC and buried OC fluxes, but not oxidized OC flux. Near the river, production was modest and biomass high, resulting in low P/B. Outfall deposition resulted in depleted biomass and high bacterial production, resulting in the highest P/B. These patterns explain why this region is production “saturated”. The δ15N in outfall effluent, sediments and dominant taxa provided insight into where, and which types of organisms feed directly on fresh outfall particulates, on older, refractory material buried in sediments, or utilize chemosynthetic symbiotic bacteria. Results are discussed in the context of declining bottom oxygen conditions along the coast.

An estimate of the inventory of technetium-99 in the sub-tidal sediments of the Irish Sea

Published results from earlier studies have provided indications that measurable quantities of technetium-99 (99Tc) have accumulated in the sub-tidal sediments of the Irish Sea. This is due to the enhanced discharges from the Sellafield nuclear reprocessing plant in Cumbria, UK (between 1994 and 2004). Depth distributions of 99Tc concentrations in sub-tidal sediments have been determined from a limited number of Irish Sea sites, following the collection of deep sediment cores (up to 2 m in depth), sampled in two research cruise surveys in 2005 and 2006. Vertical concentration profiles of 99Tc from a range of substrates in the Irish Sea are presented here and these have been used to produce an estimate of the total inventory of 99Tc residing in the sub-tidal sediments of the Irish Sea. Significant variation was observed between 99Tc concentrations in the sediment samples, as well as in the shape of individual depth profiles. As anticipated, concentrations tended to be greater on fine-grained (muddy) substrates and showed a general decrease with distance from Sellafield. Vertical concentration profiles of 137Cs, and 137Cs data from published work, have also been considered to evaluate the use of the relatively few 99Tc core data (upon which to determine the 99Tc inventory).The inventories of 99Tc and 137Cs are estimated to have been of the order of 30 and 455 terabecquerels (TBq), respectively, or ∼2% of the total cumulative Sellafield discharge for each of the two radionuclides. The residence half-time of 137Cs in the sub-tidal sediments of the Irish Sea is estimated to be in the order of ∼16 years. Therefore, as the Kd values for 99Tc and 137Cs are similar, this also provides an indicative value to predict future losses of 99Tc from the sediment reservoir.