Sediment Particulate Organic Matter Research Articles

Blue carbon in sediment from Sanggou Bay: composition, burial flux and its response to human activities

Marine primary production and terrestrial input are the main sources of buried carbon in sediments of marginal seas. Only marine-source carbon buried in sediments, fixed and stored by marine ecosystems, belongs to “blue carbon” and reflects marine ecosystems’ carbon sink function. The pattern of buried blue carbon in sediments, its flux, and its relationship with environmental changes remain unclear. The study aimed to investigate the composition of blue carbon in the sediments of Sanggou Bay, a special type of marginal sea. The analysis of sediment carbon sources was conducted through the C/N ratio and microscopic examination. The study also examined the long-term changes in the blue carbon burial fluxes. Results showed Blue carbon, which is sea-sourced carbon, accounted for about 23% of the total carbon content and its concentration ranged from 0.17% to 0.51%, with an average of about 0.25% ± 0.10%. The content of organic blue carbon in this sea area ranges from 0.09% to 0.26%, with an average of around 0.18% ± 0.04%. It constitutes approximately 72% of the buried blue carbon in the sediment, making it the primary component of buried blue carbon. Meanwhile, the content of inorganic blue carbon ranges from 0.01% to 0.32%. Over the past 70 years, the burial fluxes of sedimentary blue carbon, organic blue carbon and inorganic blue carbon in the Sanggou Bay are about 0.54 ± 0.22 mmol/(cm2a), 0.38 ± 0.07 mmol/(cm2a) and 0.17 ± 0.22 mmol/(cm2a), respectively; their long-term changes have been significantly affected by human aquaculture activities. Large-scale raft-rack aquaculture activities have caused a reduction in water flow velocity and an increase in the deposition of particulate organic matter, which in turn has led to the burial of organic blue carbon in the sediment. Additionally, the competition between aquaculture products and small calcareous organisms, such as mussels, foraminifera, may have inhibited the growth of small calcareous organisms. We suggest this has resulted in reduced burial fluxes of inorganic blue carbon and a decrease in its proportion among total blue carbon in the sea area. Our findings imply that aquaculture activities in Sanggou Bay had a negative impact on the burial of blue carbon in the sediments.

Impacts of autochthonous particulate organic matter on redox-conditions and elimination of trace organic chemicals in managed aquifer recharge

Autochthonous carbon fixation by algae and subsequent deposition of particulate organic matter can have significant effects on redox conditions and elimination of trace organic chemicals (TOrCs) in managed aquifer recharge (MAR). This study investigated the impacts of different algae loadings (0–160 g/m2) and infiltration rates (0.06–0.37 m/d) on overall oxygen consumption and elimination of selected TOrCs (diclofenac, formylaminoantipyrine, gabapentin, and sulfamethoxazole) in adapted laboratory sand columns. An infiltration rate of 0.37 m/d in conjunction with an algae load of 80 g/m2 (dry weight) sustained oxic conditions in the sand bed and did not affect the degradation of TOrCs. Thus, the availability of easily degradable organic carbon from algae did not influence the removal of TOrCs at an influent concentration of 1 µg/L. In contrast, a lower infiltration rate of 0.20 m/d in combination with a higher algae loading of 160 g/m2 caused anoxic conditions for 30 days and significantly impeded the degradation of formylaminoantipyrine, gabapentin, sulfamethoxazole, and diclofenac. Especially the elimination of gabapentin did not fully recover within 130 days after pulsed algae deposition. Hence, measures like micro-sieving or nutrient control are required at bank filtration or soil aquifer treatment sites with low infiltration rates.

Effects of spatial scale on assessments of suspension bivalve aquaculture for productivity and environmental impacts

Proper evaluations of productivity and environmental impacts of bivalve aquaculture are necessary to achieve sustainable operations in coastal marine systems. Estimation of organic matter budgets using completely mixed one-box models provides an easy approach to help stakeholders of environmental management and aquaculture fisheries obtain an overview of the interactions between aquaculture and the environment. However, estimations and interpretations are highly dependent on the spatial scale of assessments because the distributions of aquaculture facilities and ecosystem structures are spatially heterogeneous. The objective of the present study was to examine how the spatial scale of assessments for the budgets of particulate organic matter (POM) affects the interpretation of the site-specific food supply for suspension oyster aquaculture and impacts of oyster biodeposition on local bottom environments. Based on the actual distribution of oyster farms in a temperate bay on the northeast coast of Japan, we estimated [food supply]/[food demand] (S/D) for oysters as well as the relative contribution of oyster biodeposition to the total deposition of POM (Brel) in the bay along a gradient of spatial scales l from 0.5 m to 4000 m. Although food limitation for aquaculture oysters has been reported in the study bay, S/D was greater than 1 (ranging from 16 to 154) over the spatial scale gradient. S/D tended to be relatively high and overestimated for l < 200 m and l > 1400 m due to the nature of completely mixed one-box models, but relatively lower at intermediate scales. Brel was higher in assessments at farms or smaller scales (e.g., l < 100 m) and was relatively lower at larger scales (e.g., <0.2 at the scale of >500 m). Based on our model-based calculations, the patterns of variation in S/D along the spatial scale gradient are considered to be universal; however, the scale at which S/D values are relatively low varies depending on site-specific conditions, including primary productivity and current velocity. Our findings suggest that estimated budgets of POM need to be carefully interpreted, accounting for model assumptions as well as the influence of the spatial scale of assessments.

Benthic O2 uptake by coral gardens at the Condor seamount (Azores)

Using the non-invasive aquatic eddy covariance technique, we provide the first oxygen (O2) uptake rates from within coral gardens at the Condor seamount (Azores). To explore some of the key drivers of the benthic O2 demand, we obtained benthic images, quantified local hydrodynamics, and estimated phototrophic biomass and deposition dynamics with a long-term moored sediment trap. The coral gardens were dominated by the octocorals Viminella flagellum and Dentomuricea aff. meteor. Daily rates of O2 uptake within 3 targeted coral garden sites (203 to 206 m depth) ranged from 10.0 ± 0.88 to 18.8 ± 2.0 mmol m-2 d-1 (mean ± SE) and were up to 10 times higher than 2 local sandy reference sites within the seamount summit area. The overall mean O2 uptake rate for the garden (13.4 mmol m-2 d-1) was twice the global mean for sedimentary habitats at comparable depths. Combined with parallel ex situ incubations, the results suggest that the octocorals might contribute just ~5% of the observed O2 uptake rates. Deposition of particulate organic matter (POM) assessed by the sediment trap accounted for less than 10% of the O2 demand of the coral garden, implying a substantial POM supply circumventing the deployed traps. Our results expand the database for carbon turnover rates in cold-water coral habitats by including the first estimates from these largely understudied coral gardens.

Nickel Binding Affinity with Size-Fractioned Sediment Dissolved and Particulate Organic Matter and Correlation with Optical Indicators

In rivers, the distribution and reactivity of heavy metals (HMs) are affected by their binding affinity with sediment dissolved organic matter (DOM) and particulate organic matter (POM). The HM-OM binding affinity affected by the interaction between DOM and POM is not well studied. This study investigated the Ni binding affinity to size-fractioned overlaying water DOM and alkaline extracted sediment POM solution (AEOM). The DOM/AEOM filtrates (&lt;0.45 μm) were sequentially separated into five nominal molecular weight (MW) solutions. The AEOM optical indicators had lower autochthonous, higher terrestrial sources, and lower aromaticity than the DOM. The Ni mass (72.3 ± 6.4%) was primarily distributed in the low molecular weight DOM (&lt;1 kDa), whereas the Ni (93.5 ± 0.4%) and organic carbon (OC) mass (85.3 ± 1.0%) were predominantly distributed in the high molecular weight AEOM. The Ni and DOM binding affinity, ([Ni]/[DOC])DOM ratio ranging from 0.76 to 27.32 μmol/g-C, was significantly higher than the ([Ni]/[DOC])AEOM ratios, which ranged from 0.64 to 2.64 μmol/g-C. The ([Ni]/[DOC])AEOM ratio correlated significantly with the selected optical indicators (r = 0.87–0.92, p &lt; 0.001), but the ([Ni]/[DOC])DOM ratio correlated weakly with the optical indicators (r = 0.13–0.40, p &gt; 0.05). In the present study, the Ni binding affinity with size-fractioned DOM/AEOM agrees with the hypothesis of the DOM and POM exchange conceptual model in sediment. The POM underwent a hydrolysis/oxidation process; hence, AEOM had a high molecular weight and stable chemical composition and structure. The Ni mainly attached to the high molecular weight AEOM and the ([Ni]/[DOC])AEOM ratios had a strong correlation with the AEOM optical indicators. In contrast, DOM had a high ([Ni]/[DOC])DOM ratio in low molecular weight DOM.

Bottom-water deoxygenation at the Peruvian margin during the last deglaciation recorded by benthic foraminifera

Abstract. Deciphering the dynamics of dissolved oxygen in the mid-depth ocean during the last deglaciation is essential to understand the influence of climate change on modern oxygen minimum zones (OMZs). Many paleo-proxy records from the eastern Pacific Ocean indicate an extension of oxygen-depleted conditions during the deglaciation, but the degree of deoxygenation has not been quantified to date. The Peruvian OMZ, one of the largest OMZs in the world, is a key area to monitor such changes in near-bottom-water oxygenation in relation to changing climatic conditions. Here, we analysed the potential to use the composition of foraminiferal assemblages from the Peruvian OMZ as a quantitative redox proxy. A multiple regression analysis was applied to a joint dataset of living (rose-bengal-stained, fossilizable calcareous species) benthic foraminiferal distributions from the Peruvian continental margin. Bottom-water oxygen concentrations ([O2]BW) during sampling were used as the dependant variable. The correlation was significant (R2=0.82; p&lt;0.05), indicating that the foraminiferal assemblages are rather governed by oxygen availability than by the deposition of particulate organic matter (R2=0.53; p=0.31). We applied the regression formula to three sediment cores from the northern part of the Peruvian OMZ between 3 and 8∘ S and 997 and 1250 m water depth, thereby recording oxygenation changes at the lower boundary of the Peruvian OMZ. Each core displayed a similar trend of decreasing oxygen levels since the Last Glacial Maximum (LGM). The overall [O2]BW change from the LGM and the Holocene was constrained to 30 µmol kg−1 at the lower boundary of the OMZ.

Source identification of polycyclic aromatic hydrocarbons in soil sediments: Application of different methods

Polycyclic aromatic hydrocarbons (PAHs) are organic compounds that tend to rapidly associate to particulate organic matter in sediments due to their hydrophobic characteristics, inducing toxic, carcinogens and mutagens effects to many living organisms. The monitoring and identification of the sources of PAHs in sediments is relevant especially because they are the main reservoir and secondary source of contamination of aquatic systems. To identify the sources there are different methods for data treatment that complement each other: evaluation of profiles distribution, source-specific diagnostic ratios of PAHs and principal component analysis (PCA). To demonstrate the applicability of these different methods, concentrations of PAHs from sediments of four Portuguese estuarine systems were used: Ria de Aveiro, Tagus River, Sado River and Ria Formosa, in order to identify the sources.

Impacts of flocculation on the distribution and diagenesis of iron in boreal estuarine sediments

Abstract. Iron (Fe) plays a key role in sedimentary diagenetic processes in coastal systems, participating in various redox reactions and influencing the burial of organic carbon. Large amounts of Fe enter the marine environment from boreal river catchments associated with dissolved organic matter (DOM) and as colloidal Fe oxyhydroxides, principally ferrihydrite. However, the fate of this Fe pool in estuarine sediments has not been extensively studied. Here we show that flocculation processes along a salinity gradient in an estuary of the northern Baltic Sea efficiently transfer Fe and OM from the dissolved phase into particulate material that accumulates in the sediments. Flocculation of Fe and OM is partially decoupled. This is likely due to the presence of discrete colloidal ferrihydrite in the freshwater Fe pool, which responds differently from DOM to estuarine mixing. Further decoupling of Fe from OM occurs during sedimentation. While we observe a clear decline with distance offshore in the proportion of terrestrial material in the sedimentary particulate organic matter (POM) pool, the distribution of flocculated Fe in sediments is modulated by focusing effects. Labile Fe phases are most abundant at a deep site in the inner basin of the estuary, consistent with input from flocculation and subsequent focusing. The majority of the labile Fe pool is present as Fe (II), including both acid-volatile sulfur (AVS)-bound Fe and unsulfidized phases. The ubiquitous presence of unsulfidized Fe (II) throughout the sediment column suggests Fe (II)-OM complexes derived from reduction of flocculated Fe (III)-OM, while other Fe (II) phases are likely derived from the reduction of flocculated ferrihydrite. Depth-integrated rates of Fe (II) accumulation (AVS-Fe + unsulfidized Fe (II) + pyrite) for the period 1970–2015 are greater in the inner basin of the estuary with respect to a site further offshore, confirming higher rates of Fe reduction in near-shore areas. Mössbauer 57Fe spectroscopy shows that refractory Fe is composed largely of superparamagnetic Fe (III), high-spin Fe (II) in silicates, and, at one station, also oxide minerals derived from past industrial activities. Our results highlight that the cycling of Fe in boreal estuarine environments is complex, and that the partial decoupling of Fe from OM during flocculation and sedimentation is key to understanding the role of Fe in sedimentary diagenetic processes in coastal areas.

A mesocosm study of oxygen and trace metal dynamics in sediment microniches of reactive organic material

Deposition of particulate organic matter (POM) induces diagenetic hot spots at the sediment-water interface (SWI). Here we explore the effects of intensive POM degradation for metal mobilization at the SWI. By using a combined planar optode-DGT (diffusive gradient in thin-films) sensor we obtained simultaneous measurements of dissolved O2 and trace metal dynamics around an aggregate of reactive organic matter placed on the SWI of a sediment mesocosm. The aggregate induced a rapid, highly localized, decrease in O2 concentration, resulting in an anoxic feature at the SWI. Co-located with this feature, we observed intense Fe and Mn mobilization, removal of Co, Ni and Zn and found evidence for the concurrent release and precipitation of Pb within a small confined volume. We also identified two small microniches in the anoxic sediment below the SWI, defined by elevated trace metal mobilization. Differences between the metal release rates in these two microniches indicate that they were formed by the mineralisation of different types of organic matter buried in the sediment. Our results provide direct empirical evidence for the potential importance of POM-induced reactive microniches when considering the fluxes of metals from and within aquatic sediments, and suggest that other elements’ cycles may also be affected.

Origin of remineralized organic matter in sediments from the Rhone River prodelta (NW Mediterranean) traced by Δ14C and δ13C signatures of pore water DIC

Rivers are important links between continents and oceans by transporting terrestrial particulate organic matter (POM) to continental shelf regions through estuaries or deltas and the Mediterranean basin is a good example of this strong linkage. In the vicinity of river mouths, an important fraction of the terrestrial POM settles on the seafloor, sometimes mixed with marine POM, where both can be recycled or buried. In the Rhone River prodelta, previous studies have investigated the origin of the POM in the sediments. They pointed at the large fraction of terrestrial POM in the sediments and the transition to older POM fractions in offshore direction. These studies suggested that terrestrial POM could be an important food source for benthic heterotrophic organisms in this area. In this study, the δ13C and Δ14C signatures of dissolved inorganic carbon (DIC) and DIC:NH4+ ratio in sediment pore water have been measured along a nearshore-offshore transect. The data were compared with available datasets concerning isotopic signature and C:N of the POM in bottom waters and suspended particles from the Rhone River and sediments from its delta, in order to determine which fraction of the POM is actually mineralized. Our results show that a fraction of terrestrial POM corresponding to riverine plankton is preferentially mineralized. Indeed, 13C-depleted riverine POM (δ13C=−25 to −27‰) which is enriched with 14C (Δ14C=+400 to +500‰) and shows a C:N<8 gets mostly mineralized. This isotopic signature differs from that of sediment POM which highlights the selective mineralization already observed in other river deltas. In the Mediterranean context with large human influence in river watersheds such as dam building, our results highlight the importance of riverine primary production versus eroded organic matter in coastal carbon budgets.

Identification of Burrowing Shrimp Food Sources Along an Estuarine Gradient Using Fatty Acid Analysis and Stable Isotope Ratios

Two species of burrowing shrimp occur in high densities in US West Coast estuaries, the ghost shrimp, Neotrypaea californiensis, and the blue mud shrimp, Upogebia pugettensis. Both species of shrimp are considered ecosystem engineers as they bioturbate and irrigate extensive galleries within the sediment. While their burrows comprise a dominant habitat type in west coast estuaries, little is known about these shrimps’ diet and their role in estuarine food webs. The primary goals of this study were to identify major components of burrowing shrimp diets and detect variation in these diets along an estuarine gradient using combined fatty acid (FA) and stable isotope (SI) analyses. Shrimp and potential food sources including eelgrass blades, epiphytes, Ulva, sedimentary particulate organic matter (SPOM), burrow walls, and particulate organic material (POM) were sampled at different locations within Yaquina Bay, Oregon in August 2012. Both SI and FA analyses indicated differences in food resources assimilated by shrimp along the estuarine gradient. SI values showed that diets for U. pugettensis consisted of carbon sources derived primarily from POM and SPOM, while POM and epiphytes were primary carbon sources for N. californiensis. Shrimp from lower estuarine sites had high levels of 16:1ω7 and 20:5ω3 FAs suggesting their diet is enriched with marine diatoms. Shrimp from upriver showed greater proportion of FA associated with dinoflagellates and terrestrial sources as indicated by a high percentage of C18 polyunsaturated FAs (PUFAs). This is the first study to evaluate diets of these two shrimp species using complimentary FA and SI approaches.

The deep-sea neogastropod Buccinum scalariforme: Reproduction, development and growth

Specimens of the neogastropod Buccinum scalariforme (60–70mm shell height) collected between 700 and 1450m depth along the continental slope of eastern Canada were kept for 4 years in mesocosm settings. Their mating, spawning and development were assessed, thereby generating the first complete life cycle account of a deep-sea gastropod. Egg laying occurred in March and September, with a total of 9 egg masses laid in 2013 and 2015, coinciding with periods of maximum deposition of particulate organic matter (phytodetritus). Oviposition lasted 2–3 days and the female protected the egg mass for ~3 more days until it had hardened. Typically, egg masses contained 50–75 egg capsules, each measuring 5–8mm in diameter. A capsule contained between 100 and 150 spherical eggs (300–500µm) of which ≤50 developed into embryos. Potential fecundity calculated from the entire egg mass at spawning was between 1500 and 2250 propagules; it drastically decreased over ~4–5 months of development to an effective fecundity of 30–50 juveniles emerging from the mass (0–2 juveniles per capsule). Development went through early embryonic stages in ~15 days and reached the trocophore in 15–21 days, followed by intracapsular veliger larva (480µm) and intracapsular pediveliger (~1000µm) after ~90 days. Completion of development relied on oophagy and adelphophagy. The juveniles hatched at a shell height of 1–2mm and consumed the capsule membrane. Over 2.5 years, they reached a maximum size of ~8–10mm shell height at an average of 9.8µmday−1. Estimations indicate that B. scalariforme could require between 20 and 50 years to reach maximum adult size. Large gastropods like B. scalariforme are among the most abundant motile benthic invertebrates of the bathyal zone of eastern Canada. Knowledge of their reproductive biology constitutes a first step in assessing their vulnerability and resilience to ever growing anthropogenic pressures, including fisheries, and oil/gas exploration and exploitation.

Palynological evidence for sustained deep-marine conditions during the Eocene–Miocene in the southern Gulf of Mexico distal continental margin

The present study represents the first attempt to provide palynological data about the southern Gulf of Mexico distal continental margin during the Eocene−Miocene time interval. In addition to documenting the types of fossil palynomorphs preserved in these economically critical rock sequences, this study also provides important information about the accumulation and preservation of total sedimentary particulate organic matter along with their paleoenvironmental and paleoceanographic implications. This was accomplished through the analysis of cored sediments from the Deep Sea Drilling Project Site 94 north of the Yucatan Peninsula and Site 540 south of the Western Florida Escarpment. The present findings from the deep waters of southern Gulf of Mexico are expected to greatly assist hydrocarbon geoscientists in their exploration and development efforts, reducing investment risk and drilling uncertainty. Two palynofacies assemblages were recognized based on particulate organic matter analysis: marine-dominated palynofacies A and terrestrially influenced palynofacies B. The organic compositions of these two palynofacies along with the recovered dinoflagellate cyst community suggest that while sustained oceanic depositional conditions were prevalent, occasional influxes of terrestrial organic material of variable magnitudes occurred. These short-term influxes were especially pronounced during the late Eocene and earliest Oligocene and appear to have happened in response to the cooling and slight global sea-level drop that occurred at ca. 38−33.5 Ma. The preserved terrestrial palynomorphs in the samples indicate coastal plain and estuarine vegetation sources in general, except during the Eocene-Oligocene transition, when anemophilous pollen specimens mostly derived from farther inland and montane sources were recovered.

Sources of sediment carbon sequestered in restored seagrass meadows

Seagrass meadows accumulate carbon in sediments as a result of in situ production and sedimentation of particulate organic matter (OM). We quantified the contribution of OM sources to the sediment carbon pool in restored seagrass meadows of different ages (unvegetated and 4 and 10 yr since restoration) in the Virginia coastal bays. Using carbon (C) and nitrogen (N) stable isotopes, we estimated the contribution of seagrass (Zostera marina), benthic diatoms and sestonic particles (BD/S), and macroalgae (MA) to the sediment OM pool influenced by restoration (top 10 cm) with a Bayesian mixing model. Marsh grass was not a likely source based on C:N ratios of the sediment OM. The 4 and 10 yr seagrass meadows had similar OM source contributions to the top 10 cm of sediment, which were distinct from those of unvegetated sites. Seagrass, BD/S, and MA contributed 41, 56, and 3%, respectively, in the 10 yr age treatments and 50, 46, and 4%, respectively, in the 4 yr age treatments. Diagenesis of OM sources had little impact on the source contribution estimates. In combination with carbon accumulation rates at these sites (37 g C m −2 yr −1 ), these results indicate that 10 yr after seeding, restored seagrass meadows accumulated sea- grass carbon at a rate of 14.3 g C m −2 yr −1 and non-seagrass carbon (BD/S and MA) at a rate of 22.4 g C m −2 yr −1 . This study demonstrates how seagrass restoration contributes to the sequestra- tion of 'blue carbon' and quantifies the impact restored seagrass meadow age has on stored sedi- ment carbon.

Assessing benthic oxygen fluxes in oligotrophic deep sea sediments (HAUSGARTEN observatory)

Benthic oxygen fluxes, an established proxy for total organic carbon mineralization, were investigated in oligotrophic deep sea sediments. We used three different in situ technologies to estimate the benthic oxygen fluxes at an Arctic deep sea site (2500m depth, HAUSGARTEN observatory) with limiting conditions of low oxygen gradients and fluxes, low turbulence and low particle content in the benthic boundary layer. The resolved eddy covariance turbulent oxygen flux (−0.9±0.2 (SD)mmol O2m−2d−1) compared well with simultaneous dissolved oxygen flux measurements carried out with a microprofiler (−1.02±0.3 (SD)mmol O2m−2d−1) and total oxygen uptake obtained by benthic chamber incubations (−1.1±0.1 (SD)mmol O2m−2d−1). The agreement between these different techniques revealed that microbial-mediated oxygen consumption was dominant at this site. The average benthic flux equals a carbon mineralization rate of 4.3g Cm−2yr−1, which exceeds the annual sedimentation of particulate organic matter measured by sediment traps.The present study represents a detailed comparison of different in situ technologies for benthic flux measurements at different spatial scales in oligotrophic deep sea sediments. The use of eddy covariance, so far rarely used for deep sea investigations, is presented in detail.

Sources contribution for benthic invertebrates: an inter-lake comparison in a flood plain system

To explore temporal variation in trophic relationships of benthic invertebrates in the Middle Parana River floodplain, we performed stable isotopes analysis (SIA) in two lakes with contrasting morphologies during both dry and flooding periods. Lake 1 is permanently connected, large and deep with a narrow aquatic–terrestrial transition zone (ATTZ), and Lake 2 is temporarily connected, small and shallow with a wide ATTZ. The source contribution analysis showed that macrophytes and sediment particulate organic matter are important basal resources. We found sharp temporal variations with regard to gatherer–collectors in Lake 2, being sediment particulate organic matter the most important source during dry period. However, during flooding, macrophytes and epiphyton increased their importance. Our results reveal temporal variations in trophic interactions, suggesting that hydrologic and morphologic characteristics of water bodies can be important factors determining food web structure. Besides, we provide evidence from floodplain lakes of the Middle Parana River, which contradicts the general idea that algae is the main carbon source in floodplain rivers.

Modeling the impact of floating oyster (Crassostrea virginica) aquaculture on sediment-water nutrient and oxygen fluxes

Bivalve aquaculture relies on naturally occurring phytoplankton, zooplankton, and detritus as food sources, thereby avoiding external nutrient inputs that are commonly associated with finfish aquaculture. High filtration rates and concentrated bivalve biomass within aquacul- ture operations, however, result in intense biodeposition of particulate organic matter (POM) on surrounding sediments, with potential adverse environmental impacts. Estimating the net deposi- tional flux is difficult in shallow waters due to methodological constraints and dynamic processes such as resuspension and advection. In this study, we combined sediment trap deployments with simulations from a mechanistic sediment flux model to estimate seasonal POM deposition, resus- pension, and processing within sediments in the vicinity of an eastern oyster Crassostrea virginica farm in the Choptank River, Maryland, USA. The model is the stand-alone version of a 2-layer sediment flux model currently implemented within larger models for understanding ecosystem responses to nutrient management. Modeled sedimentwater fluxes were compared to observed denitrification rates and nitrite + nitrate (NO2 � +NO3 � ), phosphate (PO4 3� ) and dissolved O2 fluxes. Model-derived estimates of POM deposition, which represent POM incorporated and processed within the sediment, comprised a small fraction of the material collected in sediment traps. These results highlight the roles of biodeposit resuspension and transport in effectively removing oyster biodeposits away from this particular farm, resulting in a highly diminished local environmental impact. This study highlights the value of sediment models as a practical tool for computing inte- grated measures of nitrogen cycling as a function of seasonal dynamics in the vicinity of aqua - culture operations.

Regional benthic food web structure on the Alaska Beaufort Sea shelf

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 531:15-32 (2015) - DOI: https://doi.org/10.3354/meps11340 Regional benthic food web structure on the Alaska Beaufort Sea shelf Lauren M. Divine1,*, Katrin Iken1, Bodil A. Bluhm1,2 1School of Fisheries and Ocean Sciences, University of Alaska Fairbanks, PO Box 757220, Fairbanks, Alaska 99775-7220, USA 2Department of Arctic and Marine Biology, UiT-The Arctic University of Norway, 9037 Tromsø, Norway *Corresponding author: lmdivine@alaska.edu ABSTRACT: Trophic structure and resilience of regional benthic food webs were studied on the Alaska Beaufort Sea shelf across 3 geographic regions (east, central, and west) and 2 depth ranges (14 to 90 m [shallow] and 100 to 220 m [deep]). Carbon (δ13C) and nitrogen (δ15N) isotope ratios were measured from water column and sediment particulate organic matter (POM) as markers of primary food sources and from common benthic invertebrate taxa. Isotopic niche space (δ13C-δ15N) occupied by benthic taxa provided measures of community-wide trophic redundancy and separation. δ13C values of the water column and sediment POM were patchy but generally indicative of terrestrial input across the shelf, especially near the mouth of the Colville River (< -25.5‰). Food web structures in the shallow and deep western Beaufort regions, however, reflected marine carbon inputs, with most consumers occupying intermediate trophic levels (TLs) and food webs of intermediate trophic redundancy and separation relative to the other regions. In the central shallow and east regions, the terrestrial carbon found in sediments was mirrored in consumer tissues. The central deep region contained the highest proportions of higher TL taxa, particularly within the predator feeding guild, possibly reflecting resource partitioning of a limited prey spectrum. The comparatively large isotopic niche space in the central deep region, with high trophic niche separation but low trophic redundancy, suggests that this region may be most vulnerable to perturbations. This study provides a valuable new understanding of benthic food web dynamics in the understudied Alaska Beaufort Sea region and represents a baseline for future comparison. KEY WORDS: Benthos · Carbon · Feeding guild · Nitrogen · Stable isotope · Trophic structure Full text in pdf format PreviousNextCite this article as: Divine LM, Iken K, Bluhm BA (2015) Regional benthic food web structure on the Alaska Beaufort Sea shelf. Mar Ecol Prog Ser 531:15-32. https://doi.org/10.3354/meps11340 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 531. Online publication date: July 02, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Temporal variation of the gammaridean fauna (Crustacea, Amphipoda) associated with the sponge Mycale angulosa (Porifera, Demospongiae) in southeastern Brazil

Marine sponges are advantageous microhabitats because of their complex architecture. The system of internal canals provides circulation of water and deposition of particulate organic matter, ensuring availability of food and shelter. Diminutive amphipods have little difficulty penetrating the spaces of sponges and remain in their aquiferous systems as one of the most abundant taxa in this association. This study evaluated the temporal variation of the gammaridean amphipod species associated with the sponge Mycale angulosa. Sponge samples were collected every three months over one year at Pontal da Cruz Beach, Sao Sebastiao Channel, southeastern Brazil. The amphipod assembly varied over time, while the amphipod density and sponge biomass remained approximately constant. Six species contributed to the temporal variation infaunal composition, highlighting the importance of the natural history of each species.

Dissolved amino acids in oceanic basaltic basement fluids

The oceanic basaltic basement contains the largest aquifer on Earth and potentially plays an important role in the global carbon cycle as a net sink for dissolved organic carbon (DOC). However, few details of the organic matter cycling in the subsurface are known because great water depths and thick sediments typically hinder direct access to this environment. In an effort to examine the role of water–rock–microorganism interaction on organic matter cycling in the oceanic basaltic crust, basement fluid samples collected from three borehole observatories installed on the eastern flank of the Juan de Fuca Ridge were analyzed for dissolved amino acids. Our data show that dissolved free amino acids (1–13nM) and dissolved hydrolyzable amino acids (43–89nM) are present in the basement. The amino acid concentrations in the ridge-flank basement fluids are at the low end of all submarine hydrothermal fluids reported in the literature and are similar to those in deep seawater. Amino acids in recharging deep seawater, in situ amino acid production, and diffusional input from overlying sediments are potential sources of amino acids in the basement fluids. Thermodynamic modeling shows that amino acid synthesis in the basement can be sustained by energy supplied from inorganic substrates via chemolithotrophic metabolisms. Furthermore, an analysis of amino acid concentrations and compositions in basement fluids support the notion that heterotrophic activity is ongoing. Similarly, the enrichment of acidic amino acids and depletion of hydrophobic ones relative to sedimentary particulate organic matter suggests that surface sorption and desorption also alters amino acids in the basaltic basement. In summary, although the oceanic basement aquifer is a net sink for deep seawater DOC, similar amino acid concentrations in basement aquifer and deep seawater suggest that DOC is preferentially removed in the basement over dissolved amino acids. Our data also suggest that organic carbon cycling occurs in the oceanic basaltic basement, where an active subsurface biosphere is likely responsible for amino acid synthesis and degradation.