Sediment Organic Carbon Content Research Articles

Activity and community structures of sulfate-reducing microorganisms in polar, temperate and tropical marine sediments.

Temperature has a fundamental impact on the metabolic rates of microorganisms and strongly influences microbial ecology and biogeochemical cycling in the environment. In this study, we examined the catabolic temperature response of natural communities of sulfate-reducing microorganisms (SRM) in polar, temperate and tropical marine sediments. In short-term sediment incubation experiments with (35)S-sulfate, we demonstrated how the cardinal temperatures for sulfate reduction correlate with mean annual sediment temperatures, indicating specific thermal adaptations of the dominant SRM in each of the investigated ecosystems. The community structure of putative SRM in the sediments, as revealed by pyrosequencing of bacterial 16S rRNA gene amplicons and phylogenetic assignment to known SRM taxa, consistently correlated with in situ temperatures, but not with sediment organic carbon concentrations or C:N ratios of organic matter. Additionally, several species-level SRM phylotypes of the class Deltaproteobacteria tended to co-occur at sites with similar mean annual temperatures, regardless of geographic distance. The observed temperature adaptations of SRM imply that environmental temperature is a major controlling variable for physiological selection and ecological and evolutionary differentiation of microbial communities.

Sedimentation of particulate organic carbon on the Amundsen Shelf, Antarctica

We examined the recent history of sedimentary organic carbon (SOC) accumulation on the western Amundsen Shelf, to help characterize the biological carbon pump in the Amundsen Sea, Antarctica. Vertical sedimentary profiles (in the upper 21-cm) of SOC content, radio- and stable-carbon isotopes were obtained at four locations in the western Amundsen Sea: near the shelf break, inside the polynya near the Dotson Ice Shelf, and at both the periphery and the center of the Amundsen Sea polynya. Profiles were representative not only of various distances from the coast, but also of various summertime sea ice conditions and bottom depths. The SOC content (up to 1.1%) and the radiocarbon content were distinctly higher at the periphery and at the center of the polynya than at the other sites. The SOC and 14C contents were generally consistent with the spatial distribution of primary productivity in the surface water. A linear SOC accumulation rate of about 1.0gCm−2yr−1 was determined from the conventional 14C ages of bulk SOC below the surface mixed layer at the periphery and at the center of the polynya, for the time period of 3.1–4.7kyr before present (BP). This linear SOC accumulation rate was about 20 times greater than the rates determined at the two other sites for the period of 4.6–15.7kyr BP. Note that all values are for uncorrected 14C ages. At the center of the polynya, a sudden change in SOC accumulation rate was observed at about 16cm depth, corresponding to 4.7kyr BP, implying that changes (during this time period) in physical environments greatly affected primary production, SOC burial and/or supply of allochthonous particles to this site. The vertical distribution of 14C content in the sediments implies that aged organic matter, likely associated with resuspended sediments, was also being deposited inside the polynya, in addition to autochthonous biogenic particles. If our estimation of SOC accumulation is extrapolated to the western Amundsen Shelf between 110°W and 120°W, approximately 3×1010gCyr−1 is buried on the shelf, with ~90% of SOC accumulation occurring in the Amundsen Sea polynya.

Spatial patterns of benthic bacterial communities in a large lake

To gain insights into the spatial pattern of microbial communities in Poyang Lake, we collected a total of 42 sediment samples from each of the four major parts of the lake in October 2010. We analyzed the spatial patterns of microbial biomass and microbial community composition using the phospholipid fatty acids (PLFA) method. The mean total microbial biomass was 2.28 mg PLFA/kg dry weight (wt) ranging from 0.25 to 6.56 mg PLFA/kg dry wt, indicating a high‐spatial variation. The coefficients of variations (CVs) of the bacterial and fungal biomasses were 73 and 80%, respectively. In addition, the CVs of biomasses for the seven bacterial groups ranged from 62 to 92%, which included anaerobic bacteria, Gram‐positive bacteria (G+), Gram‐negative bacteria (G−), aerobic bacteria (AE), actinomycetes (A), sulfate‐reducing bacteria (S), and methane‐oxidizing bacteria. In our study, the ammonium concentrations both in the water and in the sediment were closely correlated to the total microbial biomass and the biomasses of bacterial groups, while the ratios of fungal to bacterial biomass (F/B) and G−/G+ were correlated with ammonium concentration only in the water. In addition, F/B in the lake sediment was significantly correlated with the nitrogen content and the ratio of organic carbon to total nitrogen contents in the sediment (C/N). Moreover, the ammonium concentrations in the water and in the sediment, water dissolved organic carbon (DOC), sediment nitrogen content, and sediment organic carbon content were strongly linked to the spatial variation of bacterial community composition. Our results show that the C and N availability in the water and in the sediment are key predictors for microbial biomass and microbial community composition in Poyang Lake.

Multidecadal Field Data Support Intimate Links between Phytoplankton Dynamics and PCB Concentrations in Marine Sediments and Biota.

We analyzed three decades of field observations in the North Sea with additive models to infer spatiotemporal trends of chlorophyll a concentration, sediment organic carbon content, and polychlorinated biphenyls (PCBs) concentrations in mussels and sediments. By doing so, we separated long-term changes in PCB concentrations from seasonal variability. Using the inferred seasonal variability, we demonstrated that phytoplankton blooms in spring and autumn correspond to the annual maxima of the organic carbon content (r = 0.56; p = 0.004) and the PCB concentrations in sediments (r = 0.57; p = 0.004). Furthermore, we found a negative correlation between the PCB concentrations in sediments and in blue mussels (Mytilus edulis; r = -0.33, p = 0.012), which is probably related to the cleansing of the dissolved PCB phase driven by sinking organic matter during phytoplankton blooms and the filter-feeding behavior of the blue mussel. The present research demonstrates the role of seasonal phytoplankton dynamics in the environmental fate of PCBs at large spatiotemporal scales.

Organic Carbon Burial in Lakes and Reservoirs of the Conterminous United States.

Organic carbon (OC) burial in lacustrine sediments represents an important sink in the global carbon cycle; however, large-scale OC burial rates are poorly constrained, primarily because of the sparseness of available data sets. Here we present an analysis of OC burial rates in water bodies of the conterminous U.S. (CONUS) that takes advantage of recently developed national-scale data sets on reservoir sedimentation rates, sediment OC concentrations, lake OC burial rates, and water body distributions. We relate these data to basin characteristics and land use in a geostatistical analysis to develop an empirical model of OC burial in water bodies of the CONUS. Our results indicate that CONUS water bodies sequester 20.8 (95% CI: 9.4-65.8) Tg C yr(-1), and spatial patterns in OC burial are strongly influenced by water body type, size, and abundance; land use; and soil and vegetation characteristics in surrounding areas. Carbon burial is greatest in the central and southeastern regions of the CONUS, where cultivation and an abundance of small water bodies enhance accumulation of sediment and OC in aquatic environments.

Occurrence of Polychlorodibenzothiophenes in Nanjing Section of the Yangtze River, China.

Sediment and water samples collected from 8 sites of the Yangtze River in Nanjing section were characterized with 31 congeners of polychlorodibenzothiophenes (PCDTs). Concentrations and percentage compositions of these PCDTs in water and sediments were analyzed by gas chromatography-mass spectrometry. Results showed that ∑PCDT concentrations in sediments were higher (0.86-1.75μg/kg) than those in water (0.56-1.30μg/L). A linear relationship existed between ∑PCDT concentrations and total organic carbon content in sediments, whereas there was a poor linearity between ∑PCDTs concentrations and dissolved organic carbon content in water phase. Moreover, percentage compositions showed that penta-chlorinated DTs were the predominant congeners both in sediments and water. Differences existed in the percentage compositions between water and sediments. Highly chlorinated DTs accounted for a larger proportion in sediments than those in water. In conclusion, the present study showed the prevalent contamination by PCDTs in sediments and water from the Nanjing section of the Yangtze River.

Sediment flow paths and associated organic carbon dynamics across a Mediterranean catchment

Abstract. Terrestrial sedimentation buries large amounts of organic carbon (OC) annually, contributing to the terrestrial carbon sink. The temporal significance of this sink will strongly depend on the attributes of the depositional environment, but also on the characteristics of the OC reaching these sites and its stability upon deposition. The goal of this study was to characterise the OC during transport and stored in the depositional settings of a medium-sized catchment (111 km2) in SE Spain, to better understand how soil erosion and sediment transport processes determine catchment-scale OC redistribution. Total organic carbon (TOC), mineral-associated organic carbon (MOC), particulate organic carbon (POC), total nitrogen (N) and particle size distributions were determined for soils (i), suspended sediments (ii) and sediments stored in a variety of sinks such as sediment wedges behind check dams (iii), channel bars (iv), a small delta in the conjunction of the channel and a reservoir downstream (v), and the reservoir at the outlet of the catchment (vi). The data show that the OC content of sediments was approximately half of that in soils (9.42 ± 9.01 g kg−1 versus 20.45 ± 7.71 g kg−1, respectively) with important variation between sediment deposits. Selectivity of mineral and organic material during transport and deposition increased in a downstream direction. The mineralisation, burial or in situ incorporation of OC in deposited sediments depended on their transport processes and on their post-sedimentary conditions. Upstream sediments (alluvial wedges) showed low OC contents because they were partially mobilised by non-selective erosion processes affecting deeper soil layers and with low selectivity of grain sizes (e.g. gully and bank erosion). We hypothesise that the relatively short transport distances, the effective preservation of OC in microaggregates and the burial of sediments in the alluvial wedges gave rise to low OC mineralisation, as is arguably indicated by C : N ratios similar to those in soils. Deposits in middle stream areas (fluvial bars) were enriched in sand, selected upon deposition and had low OC concentrations. Downstream, sediment transported over longer distances was more selected, poorly microaggregated, and with a prevalence of silt and clay fractions and MOC pool. Overall, the study shows that OC redistribution in the studied catchment is highly complex, and that the results obtained at finer scales cannot be extrapolated at catchment scale. Selectivity of particles during detachment and transport, and protection of OC during transport and deposition are key for the concentration and quality of OC found at different depositional settings. Hence, eco-geomorphological processes during the different phases of the erosion cycle have important consequences for the temporal stability and preservation of the buried OC and in turn for the OC budget.

Weak Correlation Between Methane Production and Abundance of Methanogens Across Three Brackish Marsh Zones in the Min River Estuary, China

Methane production is influenced by the abundance of methanogens and the availability of substrates. Sulfate-reducing bacteria (SRB) also play an important role in the anaerobic decomposition of organic matter. However, the relationships between methane production and abundance of methanogen and pore water substrates in estuarine brackish marshes are poorly characterized, and even to our knowledge, no published research has explored the relationship between methane production rate and pore water dimethyl sulfide (DMS) concentration. We investigated methane production rate, abundances of methanogens and SRB, sediment organic carbon contents, and concentrations of pore water substrates (acetate and DMS) and terminal electron acceptors (SO4 2−, NO3 −, and Fe3+) at a brackish marsh landscape dominated by Phragmites australis marsh, Cyperus malaccensis marsh, and Spartina alterniflora marsh in the Min River estuary, southeast China. The average rates of methane production over the entire 30 cm of the sediment profile (5 cm sampling interval) in the three marshes were 0.142, 0.058, and 0.067 μg g−1 day−1, respectively. The abundance of both methanogens and SRB in the sediment of the P. australis marsh with the highest sediment organic carbon content was higher than in the C. malaccensis and S. alterniflora marshes. Mean pore water DMS concentrations over the entire 30 cm of the sediment profile under the S. alterniflora marsh were higher than those in the C. malaccensis marsh and P. australis marsh. Methane production rate correlated weakly with the abundance of methanogens across the three marsh zones together, but did not correlate with the concentrations of pore water acetate and DMS. Our results suggest that the abundance of methanogens is controlled by sediment organic carbon supply, and further, methane production is affected by the abundance of methanogens in the subtropical estuarine brackish marshes.

Sources of organic matter in the sediments of Baoxiang river reservoir, Dianchi watershed

Baoxiang river reservoir, a semi-natural water body, is characteristised by eutrophication, which is significantly harmful to regional human health and sustainable development. The sediments are sources and sinks of nutrients. In addition to providing important habitats for aquatic organisms, sediments play a significant role in determining the overall environmental quality of a watershed. Organic carbon in sediments plays an important role in release and transformation of aquatic pollutants, which is one of the main causes of eutrophication. In this study,profiles of TOC, C/N ratio, δ13C and grain sizes in the sediments of Baoxiang river reservoir, Dianchi watershed were used to demonstrate the sources and change of sedimentary organic matter and explore reservoir eutrophication sensitivity to human activities.Considering the characteristics of topography and human activities of the study area, with the help of GPS(Global Positioning System), two reservoir bottom sediments(A and B) profiles were collected during dry period. Our results showed that the sources of sedimentary organic matter were different in the different sampling locations. C/N ratios in the sediment A varied from 2.93 to 11.73, with bulk δ13C(‰) values ranging from-23.66‰ to-21.78‰. This indicated that organic matters mainly from aquatic organisms and terrestrial input contributed little to the sedimentary organic matters. The concentrations of organic matters were influenced significantly by the grain sizes. The concentrations of sedimentary organic matters and total nitrogen in the sediment B varied from 14.62 to 24.93 g ·kg-1, and 2.11 to 3.3 g·kg1, respectively,higher than that of the sediment A, and with bulk δ13C(‰) values of-28.36‰ to-26.36‰.The grain sizes were mainly composed of clay and silt. This demonstrated that organic matters in the sediment B came mainly from terrestrial input, which is an indication of the main effect of human activities, not the sediment grain size.Based on the volume percentage of sediment in each size fraction, we found that grain size in the sediment A is classified as thick, indicating poor sorting and strong water movement. The sediment B is characteristized with fine particles, with clay and fine sand as the main components and low water flow. Correlation analysis between sediment grain size and organic carbon contents showed that they were highly correlated in the sediment A. Synchronous change was found in mean sediment grain size and precipitation.

Anthropogenic impacts on meiobenthic Ostracoda (Crustacea) in the moderately polluted Kasado Bay, Seto Inland Sea, Japan, over the past 70 years

Two sediment cores were obtained from Kasado Bay, a moderate-polluted enclosed bay in Japan, to examine anthropogenic impacts on Ostracoda over the past ca. 70years. We analyzed ostracode abundance and diversity, grain size, and CHN, and used 210Pb and 137Cs as the dating method. The present study showed that cross-plot comparisons of ostracode abundance and each environmental factor, based on sediment core data, could be used to identify ostracode species as indicators for anthropogenic influences. Ostracode abundance reflected mainly the changes that had occurred in total organic carbon content in sediments related to eutrophication, but heavy metal concentration did not directly influence several ostracode abundance in the bay. Environmental deterioration because of eutrophication started in the 1960s. The regulations regarding the chemical oxygen demand in waters introduced in the 1980s probably influence ostracode abundance for certain species in this period. Currently, Kasado Bay is not experiencing severe degradation.

Urban biogeochemistry of trace elements: What can the sediments of stormwater ponds tell us?

Humans are greatly modifying biogeochemical cycles, in part, by increasing the abundance of many trace elements in heavily developed environments. As a means to study the biogeochemical cycling of trace elements in the urban landscape, we examined their accumulation in the sediments of ponds located in residential developments. To do so, we measured the content of trace elements (Ti, V, Cr, Co, Ni, Cu, Zn, Mo, Ag, Cd, Ba, Tl, Pb) and minerals (Na, Mg, Al, K, Ca, Mn, Fe) in the sediments of stormwater management ponds located in residential catchments of southern Ontario, Canada. Trace elements and associated mineral composition of the sediments primarily clustered in three groups. In one group, several trace elements (e.g., Co and V) were correlated to soil-related minerals (Al and Fe), which indicate a predominant role of soil erosion in their movement across the urban landscape. Elements in the second group (Cd, Pb, Cu, Zn, and Mo) were positively correlated with sediment organic carbon content suggesting an importance of internal pond processing such as adsorption to organic matter. In the third group, Ca and Ag negatively correlated with most other elements likely because, at least for Ca, importation of carbonates in coarse particulate material (i.e., sand) dilutes the concentration of other trace elements. Variability in trace elements among ponds and between municipalities suggests that these elements are deposited and move differently among catchments in a relatively homogenous urban landscape. Our results demonstrate a trace element biogeochemistry in urban environments that is connected to human sources, physical disturbance of the landscape, biological processing, and underlying geological composition of the catchment.

A cross-section analysis of sedimentary organic matter in a mangrove ecosystem under dry climate conditions: The Somone estuary, Senegal

Mangrove sediments are an important organic matter (OM) reservoir and play a major role in the carbon cycle. Since the 1990s, these ecosystems were subjected to numerous studies, in order to quantify the sedimentary sink for organic carbon (OC) and to characterize the organic matter sources, but remain poorly studied in Western Africa. The aim of our study is to quantify the organic carbon content and to identify the OM origin stored in the Somone mangrove sediments. Studied area is characterized by a (i) dry climate conditions with a higher rate of evaporation, (ii) lack of freshwater input by river, and (iii) tide dominated system. Here, we focus on physico-chemical properties of sediments (temperature, pH and redox), sediment grain size, water content, particulate organic carbon and dissolved organic carbon from a series of 40cm-deep cores in four tidal contexts: mudflat, Rhizophora, and Avicennia mangroves and barren area. Results show that total organic carbon (TOC) contents range between 0.34 and 3.92wt.% and are higher in sediments from mudflat and Rhizophora mangrove than in sediments from Avicennia mangrove and barren area. Indeed, sediments stored under Avicennia is subjected to suboxic conditions initiated by roots system and crabs bioturbation; while under Rhizophora and mudflat, local anoxic conditions are prevalent as suggest the negative Eh values and the occurrence of framboidal pyrites. Mangrove sediments of the Somone estuary contain an autochthonous lignocellulosic-derived organic matter. The youngest and stunted form of the Somone mangrove explains the low organic carbon content of sediments; where dry climate conditions limit the organic matter production by the mangrove forest.The shallow depth at which the organic matter of the former mudflat was found confirms that the Somone mangrove is subjected to a low sedimentation rate. This suggests that organic carbon burial depends on others processes than sedimentation. Then, in the Somone mangrove ecosystem, both of pneumatophores and burrowing crab activities are the main factors that control OM degradation (Avicennia station) while anaerobic conditions (mudflat and Rhizophora) promote OM preservation.

Sources and distribution of organic matter in thirty five tropical estuaries along the west coast of India-a preliminary assessment

Studies characterizing the sources of organic matter (OM) to the west coast of India (WCI) and its continental shelf are limited. This study examined sedimentary OM in 35 estuaries along the WCI using molecular biomarkers (lignin phenol), elemental ratio (C/N), and stable carbon isotope (δ13C) values. Multivariate statistical techniques, such as cluster analysis, identified similar sedimentary chemical properties among the estuaries and their distribution patterns highlight the strong control of geographical provenance on sedimentary OM composition from south to north along the WCI. Results of an end-member mixing model reveal that terrigenous sources (C3 plants, C4 plants, and soil) contribute ∼80% of estuarine OM, with the remaining 20% derived from marine sources (marine plankton and estuarine macrophytes). In the estuaries of large rivers, such as the Narmada and Sabarmati rivers, C4 plants and soil OM were found to be the dominant contributors of OM, which is likely the result of an abundance of C4 vegetation and agriculture in their catchment areas.High OC (organic carbon content) of sediments (0.5–5%) from the WCI estuaries indicates that large amounts of OM are present in the sediments. The sources of OM (plant and soil) shift substantially throughout the study area, corresponding to changes in land use patterns along the Western Ghats. Sediments with low nitrogen contents (C/N > 15−20) and degraded lignin ((Ad/Al)V = 0.4–0.6 and DHBA/V = 0.16–0.34) were observed in all estuaries, indicating humification and/or degradation of OM originating from terrestrial plants (bio-degradation) and soil (de-mineralization). The collective results of this study illustrate the benefits of using biomarkers (lignin phenols) along with C/N and δ13C values for evaluating land use changes and the impacts of land use changes on aquatic ecosystems.

Environmental drivers of the Canadian Arctic megabenthic communities.

Environmental gradients and their influence on benthic community structure vary over different spatial scales; yet, few studies in the Arctic have attempted to study the influence of environmental gradients of differing spatial scales on megabenthic communities across continental-scales. The current project studied for the first time how megabenthic community structure is related to several environmental factors over 2000 km of the Canadian Arctic, from the Beaufort Sea to northern Baffin Bay. Faunal trawl samples were collected between 2007 and 2011 at 78 stations from 30 to 1000 m depth and patterns in biomass, density, richness, diversity, and taxonomic composition were examined in relation to indirect/spatial gradients (e.g., depth), direct gradients (e.g., bottom oceanographic variables), and resource gradients (e.g., food supply proxies). Six benthic community types were defined based on their biomass-based taxonomic composition. Their distribution was significantly, but moderately, associated with large-scale (100–1000 km) environmental gradients defined by depth, physical water properties (e.g., bottom salinity), and meso-scale (10–100 km) environmental gradients defined by substrate type (hard vs. soft) and sediment organic carbon content. We did not observe a strong decline of bulk biomass, density and richness with depth or a strong increase of those community characteristics with food supply proxies, contrary to our hypothesis. We discuss how local- to meso-scale environmental conditions, such as bottom current regimes and polynyas, sustain biomass-rich communities at specific locations in oligotrophic and in deep regions of the Canadian Arctic. This study demonstrates the value of considering the scales of variability of environmental gradients when interpreting their relevance in structuring of communities.

Recovery of organic-enriched sediments through microbial degradation: implications for eutrophic estuaries

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 503:41-58 (2014) - DOI: https://doi.org/10.3354/meps10747 Recovery of organic-enriched sediments through microbial degradation: implications for eutrophic estuaries Thomas Valdemarsen1,*, Cintia O. Quintana1,2, Erik Kristensen1, Mogens R. Flindt1 1Institute of Biology, University of Southern Denmark, 5230 Odense M, Denmark 2Institute of Oceanography, University of São Paulo, São Paulo 05508-070, Brazil *Corresponding author: valdemarsen@biology.sdu.dk ABSTRACT: Sediments in eutrophic estuarine ecosystems may become heavily enriched with organic carbon (OC). This OC is primarily of low reactivity and, therefore, has moderate effects on sediment biogeochemical cycling. Nonetheless, OC levels of >1% reduce sediment stability and cause frequent resuspensions and high water turbidity, which affect the recovery of ecosystem functioning. Significant reduction of sediment OC content to <1% is, therefore, needed before ecosystems can fully recover. It was investigated whether organic-rich sediments with 2.5 to 4.4% OC (180–310 mol m–2) from the eutrophic Odense Fjord (Denmark) can recover by microbial degradation. Defaunated sediment cores from various habitats were subjected to long-term (~2 yr) degradation experiments. Total OC content was measured initially and OC degradation was measured regularly from CO2 effluxes and closed anoxic sediment incubations. OC degradation was high initially, but faded exponentially at all stations before stabilizing at 6 to 15 mmol OC m-2 d-1 after 100 to 150 d. Hence, over the 2 yr experiment OC degradation corresponded to only 3 to 5% reduction of initial OC. Temporal degradation patterns analyzed by exponential decay models suggested that sedimentary OC consisted of 2 pools with different reactivity plus a non-reactive pool. OC with the highest turnover (k = 0.5 × 10-2 to 5.5 × 10-2 d-1) was quantitatively the least important (0.3-4.3% of total OC), while OC with lower reactivity (k = 0.1 × 10-3 to 2.0 × 10-3 d-1) constituted a higher proportion (4-58% of total OC in organic-rich sediments). Furthermore, 43 to 95% of sediment OC was non-degradable. Our results suggest that partial recovery (5-57% reduction of initial OC) may occur within 23 to 50 yr. However, complete recovery of organic-rich sediments to <1% OC seems unlikely due to large pools of non-reactive OC. Eutrophication, therefore, leads to irreversible OC accumulation in sediments, which prolongs the recovery time for estuarine ecosystems after reductions in nutrient loading. KEY WORDS: Organic matter · Degradation · Mineralization · Oligotrophication · Recovery time · Exponential decay · G-model Full text in pdf format PreviousNextCite this article as: Valdemarsen T, Quintana CO, Kristensen E, Flindt MR (2014) Recovery of organic-enriched sediments through microbial degradation: implications for eutrophic estuaries. Mar Ecol Prog Ser 503:41-58. https://doi.org/10.3354/meps10747 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 503. Online publication date: April 29, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.

Difference in organic carbon contents and distributions in particle-size fractions between soil and sediment on the Southern Loess Plateau, China

The purpose of this study was to assess the effect of long-term cultivation and water erosion on the soil organic carbon (OC) in particle-size fractions. The study site is located at Nihegou Watershed in the Southern Loess Plateau, China. The soil at this site is loess with loose and silty structure, and contains macropores. The results showed that the OC concentrations in sediments and in the particle-size fractions of sediments were higher than those in soils and in the particle-size fractions of soils. The OC concentration was highest in the clay particles and was lowest in the sand particles. Clay particles possessed higher OC enrichment ability than silt and sand particles. The proportions of OC in the silt fractions of soil and sediment were the highest (mean value of 53.87% and 58.48%, respectively), and the total proportion of OC in the clay and silt fractions accounted for 96% and 98% of the total OC in the soil and sediment, respectively. The loss of OC was highest in silt particles, with an average value of 0.16 Mg ha−1 y−1, and was lowest in the sand (0.003 Mg ha−1 y−1). This result suggests that the fine particle-size fraction in the removed sediment may be an important indicator to assess soil OC losses.

Variations in sediment organic carbon among different types of small natural ponds along Druridge Bay, Northumberland, UK

Small natural ponds from Druridge Bay, Northumberland (UK), were sampled to investigate the variations in sediment organic carbon (OC) content among pond types. Sediment OC was highest in uncompacted sediments from permanent ponds with extensive natural vegetation (means ranged between 7.68 and 12.86% OC) but lower in compacted sediments (mean 3.72% OC) or from ponds in arable or pasture fields (mean 3.44% OC) and from adjacent soil controls (means of 3.13–3.38% OC). The extent of 4 distinct pond types (permanent naturally vegetated, arable field, grass pasture field, and dune slack) varied across years. This study highlights ecological variations among pond types that can result in large variations in sediment OC content and, combined with annual variations to the extent of ponds, poses significant implications for upscaling carbon burial rates based solely on combined surface area.

Sediment deposits and organic carbon sequestration along mangrove coasts of the Leizhou Peninsula, southern China

Mangroves are an important affecter of atmospheric CO2 level via sequestrating carbon and trapping sediments. However, their sequestrating effectiveness varies with vegetation development and sedimentation processes under site-specific hydrogeomorphic settings. In order to detect the determinants of organic carbon sequestration, this study investigated four mangrove fringing locations along the coast of the Leizhou Peninsula. Surface and core sediment samples were collected from these sites and analyzed for grain-size distribution, sedimentary organic carbon content (SOCC) and stable isotope signature (δ13Corg). It is found that a significantly higher concentration and density of organic carbon were preserved in the interior surface sediments regardless of location or surface grain size distribution. The sedimentary environments, as indicated by core sediment analysis, are controlled under low-to moderately low-energy conditions. Fluvial action on these sedimentary environments decreases from the river dominated site to the tide dominated site. The more stable energy condition favored both sediment and organic carbon accumulation in the mudflat subzone. However, as revealed by δ13C signature, sedimentary organic carbon of the core samples from the four sites was dominantly derived from suspended particulate matter except the tide-dominated offshore core. Whereby, we conclude that vegetation provided control on the surface sedimentary organic carbon distribution via its influence onmangrove debris input and fluid energy condition over the intertidal surface, while hydrogeomorphology determined the long-term organic carbon burial via its impact on the local sedimentation accretion rate and the proportion of autogenous organic carbon sequestration.

Occurrence, sources and transport pathways of natural and anthropogenic hydrocarbons in deep-sea sediments of the eastern Mediterranean Sea

Abstract. Surface sediments collected from deep basins (1018–4087 m depth) of the eastern Mediterranean Sea (Ionian Sea, southern Aegean Sea and northwestern Levantine Sea) were analyzed for aliphatic and polycyclic aromatic hydrocarbons as tracers of natural and anthropogenic inputs. Concentrations of total aliphatic hydrocarbons, n-alkanes and the unresolved complex mixture (UCM) of aliphatic hydrocarbons varied significantly, ranging from 1.34 to 49.2 μg g−1, 145 to 4810 ng g−1 and 0.73 to 36.7 μg g−1, respectively, while concentrations of total polycyclic aromatic hydrocarbons (PAHs) ranged between 11.6 and 223 ng g−1. Molecular profiles of determined hydrocarbons reflect a mixed contribution from both natural and anthropogenic sources in deep-sea sediments of the eastern Mediterranean Sea, i.e., terrestrial plant waxes, degraded petroleum products, unburned fossil fuels and combustion of grass, wood and coal. Hydrocarbon mixtures display significant variability amongst sub-regions, reflecting differences in the relative importance of inputs from various sources and phase associations/transport pathways of individual hydrocarbons that impact on their overall distribution and fate. Hydrocarbon concentrations correlated significantly with the organic carbon content of sediments, indicating that the latter exerts an important control on their transport and ultimate accumulation in deep basins. Additionally, water masses' circulation characteristics also seem to influence the regional features and distribution patterns of hydrocarbons. Our findings highlight the role of deep basins/canyons as repositories of both natural and anthropogenic chemical species.

Study on the sorption behaviour of estrone on marine sediments

The sorption behaviour of estrone (E1) on marine sediments treated by different methods was systematically investigated. About 22h was required for sorption equilibrium of E1. Sorption isotherms of E1 were well fitted with Freundlich model. The sorption behaviour of E1 on HCl-treatment and H2O-treatment sediments related significantly with the sediment organic carbon contents. Additionally, clay minerals and surface areas of sediments played dominant roles in the sorption of E1 on H2O2-treatment sediments. Some external factors which could affect sorption behaviour of E1 were also investigated. Our results showed that the sorption capacity of E1 on the sediments increased with the increasing concentrations of cationic surfactant cetyltrimethylammonium bromide (CTAB), nonionic surfactant polyoxyethylene (80) sorbitan esters (Tween 80) and salinity of seawater. In contrast, the sorption capacity of E1 decreased with the increasing concentration of anionic surfactant sodium dodecylbenzene sulfonate (SDBS), pH value and temperature of seawater.