Organic Matter In Surface Sediments Research Articles

Particulate organic matter in surface sediments of the Laptev Sea (Arctic Ocean): application of maceral analysis as organic-carbon-source indicator

Surface sediments from the Laptev Sea and adjacent continental slope were studied for their composition of particulate organic matter (OM) by means of maceral analysis. The composition of macerals in sediments gives information about the environment, terrigenous supply from the hinterland, and marine OM. With reference to their biological sources, we distinguish between terrigenous and marine macerals. We found that the particulate OM in the surface sediments of the Laptev Sea is predominantly of terrigenous origin (Ø: 78%). However, distinct variations exist when looking in detail. In the shelf area, sediments may contain up to 99% terrigenous OM. Freshwater algae occur directly north of the river mouths, reflecting the strong fluvial influence. Relatively high amounts of marine OM (20–40%) are restricted to the upper continental slope, the Vilkitsky Strait and west of the New Siberian Islands, explained by increased surface-water productivity due to increased fluvial nutrient supply, open-water conditions, and phytoplankton blooms at the ice-edge.

Nature of organic matter in surface sediments from the Pakistan continental margin and the deep Arabian Sea: amino acids

The role of organic carbon input, sedimentation rate and bottom water oxygenation (BWO) for organic matter (OM) degradation was investigated using surface sediments collected from above, within and below the oxygen minimum zone (OMZ) within varying sedimentary regimes along the Pakistan continental margin. For this, samples from 47 box cores and multi cores were analyzed for their bulk component (organic carbon, total nitrogen, carbonate, opal) and amino acid concentrations. The results are compared to plankton net samples from the Arabian Sea, sinking particles collected at the Pakistan continental margin, cultured sedimentary deep-sea bacteria, and data from the deep Arabian Sea basins. High organic carbon and amino acid concentrations were found in the laminated sediments of the OMZ, in bioturbated sediments immediately below the OMZ, and below regions of high productivity in the western Arabian Sea. The contribution of amino acids to organic carbon and total nitrogen as well as the molar contribution of certain non-protein amino acids do not mirror these differences in OC contents. No clear trend in relation to sediment structure or water depth is observed. In contrast to these established indicators of OM degradation, the molar contribution of the aromatic amino acid tyrosine (Tyr) exhibits a distinct pattern. Its contribution is relatively high in sediments at depths above the OMZ and further increases towards the center of the OMZ. Below the OMZ, it decreases continuously with increasing water depth. In addition, for samples from similar depths and bottom water oxygen contents Tyr shows systematic differences between varying sedimentary regimes. The lack of a distinct trend for the established indicators does not support the idea of a predominant control of BWO on quantitative OM preservation. Nevertheless, the variability of Tyr in relation to water depth or the sedimentary regime suggests that (i) the productivity-related OC input, (ii) the bulk accumulation rate, and (iii) BWO influence the alteration of the sedimentary OM by controlling its oxygen exposure time.

Ecological Effects of Macroalgal Harvesting on Beaches in the Peel-Harvey Estuary, Western Australia

Macrophyte harvesting is used to manage macroalgal accumulations in eutrophic estuaries throughout the world. Despite the widespread use of harvesting as a management tool, little research has addressed the effects on beach ecosystems. This paper reports on experimental investigations into the short- and long-term effects of macroalgal harvesting on beaches in the Peel-Harvey estuarine system, Western Australia. The short-term effects were examined of a single harvesting event on macrophyte biomass, sediment organic content and the density, species richness and composition of macroinvertebrates and fish of intertidal habitats of a regularly harvested beach. Long-term effects of harvesting were assessed by comparing this area with nearby beaches that have never been harvested. Harvesting caused an immediate decrease in the biomass of macrophyte detritus and densities of epifauna and fish. All of these variables recovered to values similar to non-harvested areas within two months. There was no effect on surface sediment organic matter or densities or richness of benthic infauna. The beach that had been harvested for several years had similar macroinvertebrate assemblages to those on a non-harvested beach at which macroalgae did not accumulate. In contrast, both beaches had different faunal assemblages to a beach that had never been harvested and on which algal accumulations occur. It was concluded that at regularly harvested sites the disturbance caused by harvesting is temporary (in the order of days to weeks). In the long-term, harvesting may mimic the natural flushing of beaches, preventing the detrimental effects of algal accumulation and producing faunal assemblages not unlike those found at beaches without accumulations. In highly eutrophic systems, such as the Peel-Harvey estuarine system, harvesting may be an effective beach management tool.

Organic carbon accumulation and preservation in surface sediments on the Peru margin

Concentrations and characteristics of organic matter in surface sediments deposited under an intense oxygen-minimum zone on the Peru margin were studied in samples from deck-deployed box cores and push cores acquired by submersible on two transects spanning depths of 75 to 1000 m at 12° and 13.5°S. The source of organic matter to the seafloor in these areas is almost entirely marine material as confirmed by the narrow range of δ 13 C of organic carbon obtained in the present study (−20.3 to −21.6‰; PDB) and the lack of any relationship between pyrolysis hydrogen index and carbon isotope composition. Organic carbon contents are highest (up to 16%) on the slope at depths between 75 and 350 m in sediments deposited under intermediate water masses with low dissolved oxygen concentrations (<5 μmol/kg). Even at these low concentrations of dissolved oxygen, however, the surface sediments that were recovered from these depths are dominantly unlaminated. Strong currents (up to 30 cm/s) associated with the poleward-flowing Peru Undercurrent were measured at depths between 160 and 300 m on both transects. The seafloor in this range of water depths is characterized by bedforms stabilized by bacterial mats, extensive authigenic mineral crusts, and (or) thick organic flocs. Constant advection of dissolved oxygen, although in low concentrations, active resuspension of surficial organic matter, activity of organisms, and transport of fine-grained sediment to and from more oxygenated zones all contribute to greater degradation and poorer initial preservation of organic matter than might be expected under oxygen-deficient conditions. Dissolved-oxygen concentrations ultimately may be the dominant affect on organic matter characteristics, but reworking of fine-grained sediment and organic matter by strong bottom currents and redeposition on the seafloor in areas of lower energy also exert important controls on organic carbon concentration and degree of oxidation in this region.

A reassessment of the sources and importance of land-derived organic matter in surface sediments from the Gulf of Mexico

Organic matter in surface sediments from two onshore-offshore transects in the northwestern Gulf of Mexico was characterized by a variety of techniques, including elemental, stable carbon, radiocarbon, and molecular-level analyses. In spite of the importance of the Mississippi River as a sediment source, there is little evidence for a significant terrigenous input based on the low carbon:nitrogen ratios (8–5) and the enriched δ 13C values of bulk sedimentary organic carbon (−19.7‰ to −21.7‰). Radiocarbon analyses, on the other hand, yield depleted Δ 14C values (−277‰ to −572‰) which indicate that a significant fraction of the sedimentary organic carbon (OC) in all these surface sediments must be relatively old and most likely of allochthonous origin. CuO oxidations yield relatively low quantities of lignin products (0.4–1.4 mg/100 mg OC) along with compounds derived from proteins, polysaccharides, and lipids. Syringyl:vanillyl and cinnamyl:vanillyl ratios (averaging 1.6 and 0.5, respectively) and acid:aldehyde ratios for both vanillyl and syringyl phenols (averaging 0.8 and 1.2, respectively) indicate that the lignin present in sediments originates from nonwoody angiosperm sources and is highly degraded. The δ 13C values of lignin phenols in shelf sediments are relatively depleted in 13C (averaging −26.3‰) but are increasingly enriched in 13C at the slope sites (averaging −17.5‰ for the two deepest stations). We interpret these molecular and isotopic compositions to indicate that a significant fraction (≥50%) of the lignin and, by inference, the land-derived organic carbon in northwestern Gulf of Mexico sediments ultimately originated from C 4 plants. The source of this material is likely to be soil organic matter eroded from the extensive grasslands of the Mississippi River drainage basin. Notably, the mixed C 4 and C 3 source and the highly degraded state of this material hampers its recognition and quantification in shelf and slope sediments. Our data are consistent with higher than previously estimated inputs of land-derived organic carbon to regions of the ocean, such as the Gulf of Mexico, with significant sources of terrigenous C 4-derived organic matter.

Biological mixing intensity and rates of organic carbon accumulation in North Carolina slope sediments

Sediment accumulation rates and biological mixing intensities were determined at three sites on the North Carolina slope based on profiles of naturally occurring14C,210Pb and234Th. The three sites all were at a water depth of 850 m with a spacing of 150–180 km between sites. Sediment accumulation rates increase from south to north from values of 7 cm ky−1 at Site I, to 160 cm ky−1 at Site II, to 1100 cm ky−1 at Site III. The organic carbon burial rate at these sites also increases in the northward direction from 0.65 (Site I) to 20 (Site II) to ⪕150 g Corg m−2 year−1 (Site III). These data indicate that continental margin environment can exhibit highly variable carbon fluxes over relatively small distances on the seafloor. The rate of organic carbon accumulation at Site III is one of the highest values reported for the marine environment. Based on these accumulation rates and dissolved inorganic carbon flux estimates from each site, the seabed organic carbon preservation efficiency (i.e. the ratio of Corg accumulation rate to Corg deposition rate times 100) was estimated to vary from 6.0% to 54% to 88% at Sites I, II and III, respectively. The14C age of organic matter in surface sediments was older at Site III (1800 years BP) than at Sites I and II (800 years BP), indicating that Site III receives a greater proportion of old sediment from either up-slope areas or from terrigenous sources. Inventories of excess234Th (half-life of 24 days) were used as a tracer for particle flux covering the 100 days prior to the October 1989, July–August 1990 and August 1991 cruises. The mean234Th inventories at the three sites were 4.7 ± 1.9, 8.4 ± 6.3and23.1 ± 7.3dpm cm−2 for Sites I, II and III, respectively. Profiles of excess234Th activity reveal that the biological mixing intensity is greater at Site III (meanDb = 19 ± 11cm2year−1, n = 5) than at either Site I (meanDb = 6.0 ± 6.2cm2year−1, n = 6) or Site II (meanDb = 4.6 ± 5.2cm2year−1, n = 9). In addition to the trend in mixing coefficients, the depth of particle mixing on a 100-day time scale generally is greater at Site III than at the other two sites. These observations of particle mixing intensity are consistent with the northward increase in the mean abundance of macrofauna (300microns) from mean values of 9400 m−2 at Site I, to 21,400 m−2 at Site II, to 55,500 m−2 at Site III. For the three study sites off North Carolina, a strong correlation (R2 = 0.99, p = 0.06) exists between macrofaunal abundance and the organic carbon deposition rate. An equally strong correlation (R2 = 0.99, P = 0.04) occurs between macrofaunal abundance and the234Th inventories (index of 100-day particle flux). Fine-sand size glass tracer beads were dispersed at these three sites by submersible and then the field plots were sampled ≈1 year later. The vertical distributions of beads at the three sites are consistent with a higher mixing intensity at Site III than at the other two sites, but the estimated mixing coefficients generally are lower than those determined from the profiles of234Th. The slower mixing of the glass beads may be the result of their low food value and/or their relatively large size (compared to the surrounding fine-grained sediments).

A Simulation Model of a Deep Meiobenthic Compartment: A Preliminary Approach

Abstract. On the basis of data obtained during the ECOMARGE programme and during an annual survey of a deep station (910 m), a first attempt at modelling the carbon flux through a simplified benthic system is presented. Three compartments are simulated: organic matter, bacteria, nematodes. Several hypotheses are proposed by the present simulation: constant or seasonal input of organic matter, intra‐compartmental control or lack thereof. The pulses related to the seasonal input of organic matter and to the internal kinetics of the system are described. Nine to 11 mg C · m‐2· d‐1 are necessary to equilibrate the carbon budget of this simplified deep‐sea benthic system.SummaryA simulation model is used to estimate the importance of energy transfers which could equilibrate the needs of a deep nematode community in the course of time.The observed values for the compartments are obtained from the annual survey of a deep station (910m) of the ECOMARGE programme. Surface sediment organic matter concentrations ranged from 0.50 % to 0.56 % sediment dry weight (or 67,000 mg C · m‐2 to 75,000 mg C · m‐2, respectively), for a mean near‐bottom flux input of 33g C · m‐2· a‐1 (90mg · m‐2· d‐1). The mean organismal biomass approximated to 30 mg C · m‐2 for the bacteria and 37 mg C · m‐2 for the meiofauna.In the simulations, when 9–11% of the input flux are used by the system (9–10 mg C · m‐2· d‐1), the meiofauna compartment is maintained close to the osberved level, while bacterial biomass (9 mg C · m‐2) is lower than the observed value. At lower rates (&lt;8%), the meiobenthic compartment disappears, at higher rates (&gt; 12%) the simulated biomasses show unrealistic values. With a seasonal input flux, the periods of the meiofauna biomass pulses correspond well with the observed data. The mean time lag between the maximum values of the organic matter input and the simulated maximum biomass is 60 days, slightly smaller than the observed value.

Seasonal and annual variations in the organic matter contributed by the St Lawrence River to the Gulf of St. Lawrence

The St. Lawrence River discharges a substantial volume of water (405 km 3/a) containing suspended (SPM; 3.42 × 10 6t) and dissolved (68.0 × 10 6t) materials to the Gulf of St. Lawrence. The total load contains organic carbon in paniculate (POC; 3–14% of SPM), and dissolved (DOC; 3.76 ± 0.63 mg/l) form. The concentration of POC (and particulate organic nitrogen) is positively correlated with discharge (increased during the spring flood and the fall enhancement of flow), but concentration of DOC is not so simply related to discharge. In consequence, the total organic carbon (POC + DOC) load is relatively invariant, and increased annually by only 2–3% despite a progressive increase of 8% in discharge over the years of this study. Seasonal differences in the composition of the particulate organic matter (POM) are interpreted as reflecting dominant contributions from within-river production in summer and from terrestrial sources in spring and fall. In years when the annual discharge was greater than average, a higher proportion of the POM was terrigenous. The organic matter in surface sediments of the estuary to which the river discharges is predominantly of terrestrial provenance.

Coastal upwelling and a history of organic-rich mudstone deposition off Peru

Summary The present-day upwelling circulation off Peru, the regional pattern of organic matter in surface sediments and the stable carbon isotope characteristics of Neogene and Quaternary carbonate lithologies suggest a unique feedback mechanism in continental margin deposition and subsequent alteration after burial. In such a scenario, the high bioproductivity, the position of a poleward flowing undercurrent and the rate of subsidence of margin basins appear to be the principal variables controlling this mechanism. Transfer of organic matter from the sea surface to the sea floor is particularly efficient in the upwelling ecosystem off Peru. Preservation and burial are enhanced by high bulk sedimentation rates along the upper continental slope (between 11°–15°S) at depths where the subsurface current velocities decrease below those normally associated with the poleward flow. Burial and preservation are diminished, however, where shallow water depths promote continuous reworking of the bottom sediments by onshore flows and alongshore water movement (between 6°–10°S). The resulting sedimentary facies are distinctly different from each other in that the former process yields an organic-rich (&gt; 5 wt % C org ) and the latter process yields a calcareous (&gt; 15 wt % CaCo 3 ) mud facies. The bulk sediment accumulation and individual component fluxes are estimated for both portions of the margin situated between 6° and 15°S latitude and lying in &lt; 500 m of water depth. Furthermore, the chemical environment of organic-matter decomposition in the rapidly accumulating carbonate-poor facies is dominated by microbial fermentation and methanogenesis, whereas, the muds containing lesser amounts of organic matter are dominated by microbial sulphate reduction. These differences in facies composition persist throughout the subsequent stages of compaction and diagenesis. Most prominent among these is the formation of ‘organic’ dolomites with distinctly different isotopic signatures and mineral assemblages. The original upwelling facies (i.e., organic-rich muds or calcareous muds), the extent of reworking by subsurface currents, and the subsidence history of the margin basins may be inferred from these sedimentary signatures.

Organic matter in surface sediments of Lake Constance

Organic matter in surface sediments of Lake Constance

Regulation of sedimentary cation exchange capacity by organic matter

The bulk cation exchange capacity (CEC) of surface sediments from Long Island Sound results primarily from the organic carbon content of the sediments. The exchange capacity of the organic matter in surface sediments is calculated to be 6.4 meq/g organic carbon (2.1 meq/g organic matter). The total sedimentary CEC is highly correlated to acid-leachable Mg, several transition metals, and organic carbon. However, Mg and Fe concentrations are 7–10 times higher than can be accounted for by cation exchange reactions. Thus, mechanisms other than cation exchange on the organic matter must influence transition-metal distributions in Long Island Sound.

Relationships between microbial distributions and the anaerobic decomposition of organic matter in surface sediments of Long Island Sound, USA : Aller, R. C. and J. Y. Yingst, 1980. Mar. Biol., 56(1): 29–42

Relationships between microbial distributions and the anaerobic decomposition of organic matter in surface sediments of Long Island Sound, USA : Aller, R. C. and J. Y. Yingst, 1980. Mar. Biol., 56(1): 29–42

Relationships between microbial distributions and the anaerobic decomposition of organic matter in surface sediments of long Island Sound, USA

Relative rates of the anaerobic decomposition of organic matter in the upper 10 cm of sediment from two stations in central Long Island Sound, USA, were compared. Sediment samples from discrete depth intervas were incubated anoxically and changes in SO 4 = , NH 4 + , bacterial numbers, extractable adenosine triphosphate (ATP), organic matter, and organic carbon were measured as a function of time and temperature. At both stations (∼15 and ∼34 m water-depths, respectively), the calculated rates of SO 4 = reduction and NH 4 + production decreased exponentially (approximately) with depth below the sediment-water interface. Over the same depth interval, ATP concentrations dropped by a factor of ∼6 to 7 and bacterial numbers were lower by a factor of 2 to 3. These decreases in SO 4 = reduction, NH 4 + production, bacterial numbers, and ATP, reflect a change in the physiological state of microbial populations with depth in the sediment and are consistent with the conclusions that the quantity of easily utilizable organic matter changes rapidly below the sediment surface and that food limitation controls the basic depth distribution of microbial activity. The average rates of SO 4 = reduction, ∼29 to 39 mM year-1 (22°C), in the top 10 cm are similar at both stations studied here, as well as at an additional station from a previous study. In contrast, average NH 4 + production differs by a factor of ∼2 at the two stations, reflecting differences in the C:N ratio of the organic matter supplied to the sediment surface and differences in particle reworking by macrofauna at each site. The apparent activation energy of SO 4 = reduction was 19±1 kcal mole-1 and that of NH 4 + production, 18±3 kcal mole-1. The overall quantity of carbon required to support the calculated average SO 4 = reduction rate in the top 10 cm is 23 g C m-2 year-1 and represents ∼36% of all the carbon available to the benthos annually and ∼11% of the net primary production in the water column. Directly measured fluxes of NH 4 + from sediments to overlying water at both stations agree well with those predicted from production rates obtained by the incubation techniques.

Land-derived organic matter in surface sediments from the Gulf of Mexico

Lignin oxidation products and 13C/ 12C ratios were compared as indicators of land-derived organic matter in surface sediments from the western Gulf of Mexico. Whole sediments were reacted with cupric oxide to yield phenolic oxidation products that indicated the types and relative amounts of the lignins that were present. Measurements of lignin concentration and carbon isotope abundances both indicated a sharp offshore decrease of land-derived organic matter in most areas of the western Gulf. This decrease results primarily from mixing of terrestrial and marine organic matter. The terrestrially derived material in these sediments has a lignin content similar to that of grasses and tree leaves. Flowering plants contribute most of the sedimented lignin compounds. These lignins apparently occur in the form of well-mixed plant fragments that are transported to sea by rivers and deposited primarily on the inner continental shelf.

Terrigenous Organic Matter in Surface Sediments from the Gulf of St. Lawrence

Marine sediments containing land-derived organic matter can be identified by a combination of high organic carbon concentration, high C and H relative to N, and the presence of lignin. Sediments with this combination of characteristics have been found in certain environments within the Gulf of St. Lawrence, in particular, in close proximity to pulp and paper mills.