A biogeochemical study of sediments from the eutrophic Lake Lugano and the oligotrophic Lake Brienz,Switzerland

The biomarker composition and stable isotope (C, O) ratio values of organic matter (OM) and carbonate from sediment cores from the oligotrophic Lake Brienz and the eutrophic Lake Lugano (both in Switzerland) are compared, in order to obtain information about OM sources and transformation processes. Eutrophic conditions at Lake Lugano are reflected in elevated total organic carbon (TOC) content and hydrogen index (HI) values, as well as higher lipid concentrations. Parallel down core trends in δ¹³C values of TOC and calcite in the Lake Lugano sediments reflect bioproductivity cycles. Variations in δ¹⁸O values of calcite are consistent with changes in mean summer temperature over the time interval covered by the core. In contrast, such a correlation does not exist for Lake Brienz and there the stable isotope composition of calcite reflects its allochthonous origin. In the sediments of both lakes, fatty acid (FA) distributions and the composition of n-alkanols and n-alkanes indicate highly variable proportions of autochthonous OM sources (algae, zooplankton, bacteria) and OM from land plants. Enhanced in situ microbial synthesis during sediment deposition in Lake Lugano is suggested by the higher TOC-normalised concentrations of branched chain FAs (C₁₅–C₁₇), hopanoic acids and triterpenoid alcohols (i.e. tetrahymanol, diplopterol). Variations in the concentrations of cholesterol are related to contributions from zooplankton and/or green algae, while sitosterol concentrations reflect the input of vascular plants. Periods of increased input of OM from diatoms are evidenced by high 24-methylcholesta-5,22-dien-3β-ol (either epibrassicasterol or brassicasterol) and/or highly branched isoprenoid (HBI) alkenes concentrations. High relative concentrations of diplopterol in Lake Lugano sediments are consistent with the predominance of cyanobacteria commonly observed in eutrophic lakes. The presence of archeol and hydroxyarcheol in very low concentrations in the Lugano sediments argues for the activity of methanogens and/or anaerobic methanotrophs.Differences in OM degradation processes are reflected in higher chlorin index values in the Brienz sediments but higher saturated vs. unsaturated n-FAs in the core from Lugano. Higher concentrations of branched chain FAs and 16:1ω7 n-FA, as well as enhanced 18:1ω7/18:1ω9 n-FA, are consistent with enhanced bacterial biomass in the Lugano water column or sediments. The preservation of phytol seems to be enhanced in sediments with a high relative contribution of land plant OM. Major factors affecting OM accumulation in the lakes are differences in OM sources (i.e. terrestrial OM vs. autochthonous production), extent of bacterial activity and most likely oxygen availability in the water column.     

Amino acid and amino sugar transformation during sedimentation in lacustrine systems

We compared the degradation behaviour of amino sugars (ASs) and amino acids (AAs) during sedimentation in two lakes. Concentrations of individual ASs and AAs were measured in plankton, sediment trap and sediment samples from Lake Zug (LZ; eutrophic, stratified, permanently anoxic below 170 m) and Lake Brienz (LB; oligotrophic, oxic throughout the water column). In the plankton samples AAs comprised 37–50% of the organic carbon (C_org) and 41–65% of the N. With increasing water depth the fraction of C_org and N as AAs almost halved in both lakes. At the sediment surface the contribution of AAs to the C_org pool was slightly greater, but in the sediments the proportion further decreased downwards to values of 1% of the C_org pool in LB and 8% in LZ, and 3% and 17% of the N pool, respectively. ASs contributed to a smaller extent to the planktonic organic matter (OM). Within the water column, the contribution decreased in both lakes. In contrast, in the sediments the contribution of ASs to the C_org and N pools increased slightly with depth, indicating AS accumulation. We applied degradation indices based on ASs, AAs and chlorins, which all revealed transformation with OM sedimentation. However, some indices were more sensitive to early degradation (e.g. reactivity index) and others to an intermediate level of degradation (e.g. chlorin index and non-protein AAs). Despite the different trophic status and redox conditions, the general pattern of degradation was similar in both lakes, but was more pronounced in the sediments of the eutrophic LZ.     

Organic fades in Recent sediments of carbonate platforms: Southwestern Puerto Rico and Northern Belize

Our organic facies model of a platform environment is based on the analysis of (1) total organic carbon, (2) visual protokerogen types and hydrogen indices of the sediments, (3) sediment mineralogy and grain size, and (4) reef patterns, water circulation, and relief of the adjacent land.TOC values are lowest on reefs and outer platforms (0.2%); intermediate in sediments fringing carbonate islands (0.5–2.0%), on sea-grass meadows (0.5–0.7%), and in forereef lagoons (0.1–0.7%); highest in inner platform lagoons (0.5–5.0%) and mangrove swamps (2.7–3.5%). Paniculate organic matter comprises structured terrestrial, marine, and amorphous types. On average, terrestrial material accounts for 28% of OM in Puerto Rico and 12% in Belize. The mean hydrogen index of the sediment is 355 (mg hydrocarbons/g TOC) in Puerto Rico and 719 in Belize.This study indicates that TOC values are mainly related to platform subenvironment, while OM types are controlled by distance from the shoreline. Organic facies dominated by structural terrestrial OM occur closer to the shore, whereas toward the shelf margin marine and amorphous OM contents increase.     

Organic matter and lipids in sediments of Lake Bled (NW Slovenia): Source and effect of anoxic and oxic depositional regimes

Sources of organic matter (OM) and lipids were assessed and factors affecting OM degradation were studied for two sediment cores representing distinct depositional regimes (i.e., the oscillating oxic to suboxic/anoxic western basin and oxic Zaka Bay) for eutrophic Lake Bled, NW Slovenia. Lower surface organic carbon (OC) concentration was determined in the western basin than for Zaka Bay sediments (5.1 vs. 5.4 wt% dry sediment, respectively), but one order of magnitude greater total lipid concentration was observed in the former. Also, there was a higher proportion of autochthonous OM in the western basin (77% vs. 66%) on the basis of atomic C/N ratios. Lipid-based origin assessment suggested a similar contribution of autochthonous OM in the western basin (64–77%), but a lower one in Zaka Bay (<50%). It seems that redox potential is the main factor governing OM degradation in the western basin. In contrast, a contribution from more refractory terrestrial OM, via the surface inflow in Zaka Bay, and higher sedimentation rates may surpass redox effects in Zaka Bay. Overall, oxygen may play a more important role in degradation of the more labile pool (i.e., lipids) than bulk OM. Higher apparent degradation rate constants (k′) for lipids also suggested a greater lability than for OC, while respective k′ values were higher in the oxic than anoxic environment.     

太湖沉积物中微生物多样性垂向分布特征

运用化学分析方法和PCR-DGGE技术,从沉积物化学及分子生物学角度对太湖沉积物理化性质(pH、Eh)、营养盐及微生物多样性的垂向分布及相关性进行研究。结果表明:沉积物-上覆水接触界面处于轻度还原状态,在表层8.0cm左右以下,Eh随沉积深度的增加迅速下降,还原性逐渐增强,到15.0～22.5cm深度区间内,Eh值基本稳定,还原性最强,之后随深度的进一步增加,Eh呈"之"型缓慢升高。沉积物pH随深度的增加先降低后缓慢升高,pH在整个剖面上变化幅度不大,在7.2～7.6变动。沉积物中含有丰富的营养盐,总氮(TN)、总磷(TP)最高含量分数和有机质(OM)的最高百分比分别为2.436mg/g、0.731mg/g和3.817%,其剖面特征表明,沉积物表层TN和OM远高于底层,其含量随深度增加而降低。TP随着沉积深度的增加呈"之"型缓慢减少。不同深度沉积物的微生物群落呈现出明显的空间分布多样性差异,不同深度沉积物的微生物群落结构之间的相似性和动态性存在差异。多元相关分析结果显示,TN与OM显著相关,理化指标、营养盐中任一指标含量与微生物群落多样性指标之间存在相关性,但不显著,微生物多样性是营养盐及环境物理、化学和生物等多方面共同作用的结果。     

Assessing the factors controlling high sedimentation rates from the latest Barremian–earliest Aptian in the hemipelagic setting of the restricted Organyà Basin,NE Spain

The Organyà Basin, south–central Spanish Pyrenees, developed as a marginal depocenter during a rapid extensional phase of anticlockwise rotation of the Iberian plate. As a result of increased subsidence, an important change in sedimentation occurred from the late Barremian to the Aptian leading to unusually high sediment accumulation rates. Approximately 1000 m of hemipelagic marls and limestones accumulated during this time interval.Here we studied the basal 85 m of the hemipelagic facies of the El Pui section, Organyà Basin, that are characterized by alternating 15 cm – ∼3 m thick beds of limestone and marls. Geochemical analyses indicate high total inorganic carbon (TIC) values (average 70%) suggesting enhanced CaCO₃ production and deposition. SEM analyses of the samples indicate high abundance of calcareous nannofossils, which together with the absence of shallow water taxa characteristic of the Urgonian Carbonate platform of Organyà, and the lack of sedimentary facies attributable to carbonate platform components point to nannofossils as the main source for the elevated TIC. Organic-rich levels (total organic carbon (TOC) up to 1.74%) concurrent with positive excursions up to 2‰ in δ¹³C_org, imply enhanced preservation of organic matter (OM) in the basin. In addition, pronounced peaks of δ¹³C_org higher than the global average suggest superimposed local factors related to intensified ¹²C removal due to primary productivity. Biomarker analyses and the δ¹³C_org profile suggest an autochthonous origin of the OM from phytoplankton and possible additional contributions from microbial communities.X-ray diffraction (XRD) results attest for sustained terrestrial fluxes as the source of nutrients to the basin because of a 30% average non-carbonate bulk mineral content in the sediment. The non-carbonate fraction is dominated by quartz (average, 14%) whereas the clay mineral assemblages are characterized by high illite content (>73 relative%) with minor concentrations of kaolinite (<5%), illite /smectite mixed layers (<17%) and chlorite (<15%), consistent with a provenance from the Paleozoic metamorphic terranes adjacent to the Organyà Basin.The integrated results suggest a high sediment accumulation rate (5 cm/ky–7.5 cm/ky) and enhanced carbon burial during the latest Barremian–earliest Aptian in the hemipelagic setting of the El Pui section.     

Ammonium release characteristics of the sediments from the shallow lakes in the middle and lower reaches of Yangtze River region,China

Ammonium release from sediments has significant effects on the water quality in eutrophic lakes. In this study, the ammonium release kinetics and adsorption–desorption processes were investigated in 13 sediments of 6 shallow lakes from the middle and lower reaches of Yangtze River region, China. The results show that First Order Model best described the ammonium release process, the maximal release capacity had a strong correlation with organic matter (OM), cationic exchange capacity (CEC), total nitrogen (TN) and total phosphorus (TP). But it only had a weak correlation with Fe, Ca and Al. The ammonium release capacity in more polluted sediments was higher than that in less polluted sediments. The average release rate within 0–5 min was the highest among the experimental period, the amount released within 0–5 min accounted for approximately 50–70% of the total release capacity. The ammonium release rate had a significant and positive correlation with OM. But it did not have a strong correlation with TN, TP, Fe, Ca and Al. The ammonium potential release capacity (obtained when the water/sediment ratio was about 2,500) had strong and positive relation with OM and maximal release capacity, and it may provide useful information for the sediment release risk assessment. Henry Model best described the ammonium sorption isotherms, and ammonium adsorption–desorption equilibrium concentration can be considered as the ammonium release threshold to assess the release risk in the sediments.     

Geochemical Characteristics of Amino Acids in Sediments of Lake Taihu, A Large, Shallow, Eutrophic Freshwater Lake of China

To examine the biogeochemistry of amino acids (AAs) in the sediment of Lake Taihu, surface sediments (0–3 cm) and deeper sediments (18–21 cm) were collected at 21 sites from different ecotype zones of the lake. AAs were extracted from the sediments, and the total hydrolyzable amino acids (THAA) were determined by high-performance liquid chromatography instrument. The THAA contents in Taihu sediment were much lower than that in marine sediments, ranging from 6.84 to 38.24 μmol g⁻¹ in surface sediments and from 2.91 to 18.75 μmol g⁻¹ in deeper sediments in Taihu, respectively. AAs were a major fraction of the organic matter (OM) and organic nitrogen in Taihu sediments. The AAs on average contributed 8.2% of organic carbon (OC) and 25.0% of total nitrogen (TN) from surface sediments, and 5.9% of OC and 20.5% of TN in deeper sediments, respectively. AA composition provided very useful information about the degradation of OM. Glycine (Gly) and lysine (Lys) were the predominant forms of AAs in the sediments, irrespective of lake regions, followed by alanine, glutamic acid, serine (Ser), and aspartic acid (Asp). The high concentrations of Gly, Lys, and Ser suggested that these forms of AAs were relatively refractory during OM degradation in sediments. The relationship between the Asp/Gly ratio and Ser + Thr [mol%] indicated that OM in surface sediment was relatively fresher than that in deeper sediments. The AAs-based degradation index (DI) gave a similar conclusion. The composition and DI of AAs in surface sediments are markedly different across different zones in Taihu. The percentages of AAs to organic carbon (AA-C%) and total nitrogen (AA-N%) were higher in phytoplankton-dominated zones than those in macrophyte-dominated zones. These results suggest that DI could provide useful information about the degradation of OM in shallow lakes such as Taihu.     

Transformation of the group composition of organic matter from the channel deposits of a small river affected by anthropogenic activity

The group composition of organic matter (OM) was studied in the channel sediments of the Pakhra River under natural condition and in the zone affected by the town of Podol’sk, Moscow oblast. It was found that the natural alluvium is poor in OM (C_org = 0.65%), the composition of which is dominated by humus acids (81.8% of C_org) at minor fractions of residual OM (16.7%) and lipids (1.5%). Anthropogenic muds formed in the river channel in the zone affected by urban pollution are conspicuous in high OM content (C_org = 1.26–2.60%), the composition of which is enriched in lipids (up to 10–20%) and residual OM (up to 27.3–48.6%), whereas the fraction of humus acids decreases to 29.6–57.1%. The muds are most significantly enriched in lipids (their specific concentration increases by factors of 6–59 compared with the natural alluvium) and residual OM (by factors of 3–11). The amount and character of the group composition of OM from anthropogenic muds are controlled by the specific features of the sources of sedimentary material in the river and the character of the environment of alluvium sedimentation in the zone affected by an industrial town.     

Distribution of <Emphasis Type="Italic">n</Emphasis>-alkanes in the ferromanganese nodule–sediment–pore water system (Clarion–Clipperton Fracture Zone)

The paper presents the first results of a comparative study of the composition and distribution of organic matter (OM) (C_org, n-alkanes, Pr, Phy) in samples of the ferromanganese nodule–sediment–pore water system taken at a single site in the Clarion–Clipperton Fracture Zone, Pacific Ocean. Samples were taken during Cruise 120 of R/V James Cook in 2015. The results of the comparison of organogeochemical parameters in the lipid fraction of OM in ferromanganese nodules of different size and morphology with the underlying sediment (0–1 cm) and pore water revealed both principle genetic affinity of OM therein and significant discrepancies between the processes of diagenesis during the formation and growth of each individual ore sample.     

The Chemical Nature of Phosphorus in Subtropical Lake Sediments

The phosphorus (P) composition of sediment profiles in three subtropical lakes of contrasting trophic state in Florida, USA, was determined by sequential fractionation and solution ³¹P NMR spectroscopy. Sediment from Lake Annie, an oligo-mesotrophic sinkhole with moderately acidic sediment (pH 5.4; loss on ignition 58 %), contained higher total P concentrations than sediment from eutrophic Lake Okeechobee (pH 7.7, loss on ignition 36 %) and hyper-eutrophic Lake Apopka (pH 7.5, loss on ignition 69 %). The chemical nature of sediment P varied markedly among the three lakes, suggesting the predominance of different diagenetic processes. Lake Okeechobee sediment was dominated by inorganic P, indicating the dominance of abiotic reactions; Lake Annie sediment contained abundant organic P throughout the sediment profile, indicating the importance of organic P stabilization at acidic pH; Lake Apopka contained almost half of its sediment P in microbial biomass, indicating the importance of biotic processes in regulating P dynamics. Solution ³¹P NMR spectroscopy of NaOH–EDTA extracts revealed that organic P occurred mainly as phosphomonoesters in all lakes. However, sediment from Lake Apopka also contained abundant phosphodiesters and was the only lake to contain detectable concentrations of polyphosphate, perhaps due to a combination of alternating redox conditions and high concentrations of inorganic phosphate and organic carbon. Organic P concentrations determined by sequential fractionation and solution ³¹P NMR spectroscopy were similar for all lakes when microbial P was included in values for sequential fractionation. We conclude that the chemical nature of sediment P varies markedly depending on trophic state and can provide important information on the dominant processes controlling P cycling in subtropical lakes.     

Sources and distribution of terrigenous organic matter delivered by the Atchafalaya River to sediments in the northern Gulf of Mexico

Suspended sediments (SS) from the Atchafalaya River (AR) and the Mississippi River and surficial sediment samples from seven shallow cross-shelf transects west of the AR in the northern Gulf of Mexico were examined using elemental (%OC, C/N), isotopic (δ¹³C, Δ¹⁴C), and terrigenous biomarker analyses. The organic matter (OM) delivered by the AR is isotopically enriched (∼−24.5‰) and relatively degraded, suggesting that soil-derived OM with a C4 signature is the predominant OM source for these SS. The shelf sediments display OC values that generally decrease seaward within each transect and westward, parallel to the coastline. A strong terrigenous C/N (29) signal is observed in sediments deposited close to the mouth of the river, but values along the remainder of the shelf fall within a narrow range (8-13), with no apparent offshore trends. Depleted stable carbon isotope (δ¹³C) values typical of C3 plant debris (−27‰) are found near the river mouth and become more enriched (−22 to −21‰) offshore. The spatial distribution of lignin in shelf sediments mirrors that of OC, with high lignin yields found inshore relative to that found offshore (water depth > 10 m).The isotopic and biomarker data indicate that at least two types of terrigenous OM are deposited within the study area. Relatively undegraded, C3 plant debris is deposited close to the mouth of the AR, whereas more degraded, isotopically enriched, soil-derived OM appears to be deposited along the remainder of the shelf. An important input from marine carbon is found at the stations offshore from the 10-m isobath. Quantification of the terrigenous component of sedimentary OM is complicated by the heterogeneous composition of the terrigenous end-member. A three-end-member mixing model is therefore required to more accurately evaluate the sources of OM deposited in the study area. The results of the mixing calculation indicate that terrigenous OM (soil-derived OM and vascular plant debris) accounts for ∼79% of the OM deposited as inshore sediments and 66% of OM deposited as offshore sediments. Importantly, the abundance of terrigenous OM is 40% higher in inshore sediments and nearly 85% higher in offshore sediments than indicated by a two-end-member mixing model. Such a result highlights the need to reevaluate the inputs and cycling of soil-derived OM in the coastal ocean.     

Natural and Post-Urbanization Signatures of Hypoxia in Two Basins of Puget Sound: Historical Reconstruction of Redox Sensitive Metals and Organic Matter Inputs

Hypoxia has been observed in Hood Canal, Puget Sound, WA, USA since the 1970s. Four long sediment cores were collected in 2005 and age-dated to resolve natural and post-urbanization signatures of hypoxia and organic matter (OM) sources in two contrasting basins of Puget Sound: Main Basin and Hood Canal. Paleoecological indicators used for sediment reconstructions included pollen, stable carbon and nitrogen isotopes (??¹³C and ??¹⁵N), biomarkers of terrestrial OM (TOM), biogenic silica (BSi), and redox-sensitive metals (RSM). The sedimentary reconstructions illustrated a gradient in RSM enrichment factors as Hood Canal > Main Basin, southern > northern cores, and pre-1900s > 1900?C2005. The urbanization of Puget Sound watersheds during the 1900s was reflected as shifts in all the paleoecological signatures. Pollen distributions shifted from predominantly old growth conifer to successional alder, dominant OM signatures recorded a decrease in the proportion of marine OM (MOM) concomitant with an increase in the proportion of TOM, and the weight % of BSi decreased. However, these shifts were not coincidental with an overall increase in the enrichment of RSM or ??¹⁵N signatures indicative of cultural eutrophication. The increased percentage of TOM was independently verified by both the elemental ratios and lignin yields. In addition, isotopic signatures, BSi, and RSMs all suggest that OM shifts may be due to a reduction in primary productivity rather than an increase in OM regeneration in the water column or at the sediment/water interface. Therefore, the reconstructions suggested the Hood Canal has been under a more oxygenated ??stance?? during the twentieth century compared to prior periods. However, these 2005 cores and their resolutions do not encompass the period of high resolution water column measurements that showed short-lived hypoxia events and fish kills in Hood Canal during the early twenty-first century. The decoupling between the increased watershed-scale anthropogenic alterations recorded in the OM signatures and the relatively depleted RSM during the twentieth century suggests that physical processes, such as deep-water ventilation, may be responsible for the historical variation in oxygen levels. Specifically, climate oscillations may influence the ventilation and/or productivity of deep water in Puget Sound and particularly their least mixed regions.     

Variability of tetraether lipids in Yellow River-dominated continental margin during the past eight decades: Implications for organic matter sources and river channel shifts

Glycerol dialkyl glycerol tetraethers (GDGTs) and bulk organic geochemical parameters were examined for a short core from the Bohai Sea, a Yellow River-dominated continental margin. A three end member mixing model using branched/isoprenoid tetraethers (BIT) index, δ¹³C and C/N shows that the average fractions of soil, marine and plant organic matter (OM) during the period of 1933–2011 are 67.7% (38–92%), 26.1% (0–58%) and 6.2% (0–23%), respectively. Abrupt changes of sedimentary OM compositions around 1953, 1976 and 1996 are synchronous with the Yellow River mouth relocations. The BIT index values (0.33–0.80) present a stronger correlation with crenarchaeol abundance (R² = 0.88) than branched GDGTs abundance (R² = 0.27), suggesting that variations of marine Thaumarchaeota abundance rather than soil OM inputs is the first order factor controlling the BIT index values, although this proxy has been widely used for soil OM. The comparison between the BIT index, nutrient status and historical Yellow River sediment load indicates that the high sensitivity of the BIT index to the Yellow River channel shifts cannot be explained by a nutrient stimulation mechanism, but instead is likely caused by the restriction of Thaumarchaeota growth in highly turbid water due to the enormous sediment inputs from Yellow River. Our study demonstrates that local conditions should be considered when applying the BIT index as an environmental proxy.     

Origin and composition of organic matter in tidal flat sediments from the German Wadden Sea

Two sediment cores of up to 550 cm length from an intertidal flat of the German Wadden Sea near the island of Spiekeroog were investigated for the quantity and composition of fossil organic matter (OM). The lowermost parts of the cores are dominated by grey mud of a salt marsh facies containing mainly terrestrial OM estimated to account for 60–75% of the total OM, based on δ¹³C values and the ratio of short to long chain n-alkanols. The terrigenous origin of the dominant fraction is indicated, among others, by high proportions of C₂₉ sterols and long chain n-alkanes typical of plant waxes. Coarse shell beds overlying the grey mud at 2–2.5 m depth represent a flooding and erosion event possibly related to heavy storm floods in the Middle Ages. Within the intertidal sand-dominated sediments in the upper parts of the cores total organic carbon (TOC) contents are generally low, ranging from 0.1% to 0.5%, and correlate well with the amount of mud fraction (r² 0.90). At the surface, marine OM has not undergone intense diagenetic alteration and so is the dominant fraction. Eroded peat particles are common throughout most of the sequence and values of the Phragmites peat indicator (PPI) > 5 indicate an origin from reed peat due to a high relative abundance of the n-C₂₄ alkane. Changes in the composition of microbial communities over the depth interval investigated are documented by varying compositions of unsaturated fatty acids with 16 and 18 carbons. Eicosapentaenoic acid (EPA) was detected along the entire cores and indicates the presence of EPA-producing bacterial strains.     

Tectonic and climate control of oil shale deposition in the Upper Cretaceous Qingshankou Formation (Songliao Basin, NE China)

Oil shales were deposited in the Songliao Basin (NE China) during the Upper Cretaceous period, representing excellent hydrocarbon source rocks. High organic matter (OM) contents, a predominance of type-I kerogen, and a low maturity of OM in the oil shales are indicated by bulk geochemical parameters and biomarker data. A major contribution of aquatic organisms and minor inputs from terrigenous land plants to OM input are indicated by n-alkane distribution patterns, composition of steroids, and organic macerals. Strongly reducing bottom water conditions during the deposition of the oil shale sequences are indicated by low pristane/phytane ratios, high C₁₄-aryl-isoprenoid contents, homohopane distribution patterns, and high V/Ni ratios. Enhanced salinity stratification with mesosaline and alkaline bottom waters during deposition of the oil shales are indicated by high gammacerane index values, low MTTC ratios, high β-carotene contents, low TOC/S ratios, and high Sr/Ba ratios. The stratified water column with anoxic conditions in the bottom water enhanced preservation of OM. Moderate input of detrital minerals during the deposition of the oil shale sequences is reflected by titanium concentrations. In this study, environmental conditions in the paleo-lake leading to OM accumulation in the sediments are related to sequence stratigraphy governed by climate and tectonics. The first Member of the Qingshankou Formation (K₂qn₁) in the Songliao Basin, containing the oil shale sequence, encompasses a third-order sequence that can be divided into three system tracts (transgressive system tract—TST, highstand system tract—HST, and regressive system tract—RST). Enrichment of OM changed from low values during TST-I to high-moderate values during TST-II/III and HST-I/II. Low OM enrichment occurs during RST-I and RST-II. Therefore, the highest enrichment of OM in the sediments is related to stages of mid-late TST and early HST.     

Diagenesis of Organic Matter in the Top Layer of the Sediments of the Peter the Great Bay in Hypoxia Locations

During Cruise 62nd of the R/V “Professor Gagarinsky” in September, 2014, the carbonate system of sediments and contents of nutrients and organic carbon in pore water were studied in two geochemical stations located in hypoxia areas in the Peter the Great Bay. It was established that the concentrations of silica, phosphorus, and ammonium increase by 5, 10, and 20 times, respectively, with sediment depth to 70–80 cm. The alkalinity, dissolved inorganic carbon, and the partial pressure of carbon dioxide significantly increase with depth, while рН value and organic matter (ОM) decrease. Changes in the chemical composition of pore water with sediment depth (0–80 cm) are caused by anaerobic microbial degradation of OM, concentration of which in the top sediment layer is 2–3%. The degradation products of OM in the bottom waters of bay and pore waters of bottom sediments indicate that its main sources are diatoms. During hypoxia, the oxygen demand rate by sediment surface near Furugelm Island is estimated to be 5 mmol/(m² day). A combination of such factors as downwelling circulation, the absence of photosynthetically active radiation, and the high oxygen demand rate at the water/sediment interface provides hypoxia formation in the depressions of the Peter the Great Bay bottom topography.     

Evolution of organic matter in lignite-containing sediments revealed by analytical pyrolysis (Py–GC–MS)

Newly vegetated sites provide opportunities to enlighten organic matter (OM) transformation mechanisms in soils and sediments at very early stages of development which, in turn, is relevant to better understand general ecosystem functioning. Mine acid soils and sediments in the Lusatian open cast lignite mining district (Germany) contains a high concentration of fossil carbon (lignite) in ad mixture with recent OM from the local vegetation, both contributing to the humified OM pool. In this study, analytical pyrolysis (Py–GC–MS) was used to monitor the different C sources (lignite or plant derived) in developing mine tailing soils and sediments and their degree of degradation in contrasting environments. Representative vegetation and the organic carbon (OC) rich soil/sediment fraction (humus fraction) were sampled at two depths (0–5 and 5–10 cm) in three plots along a transect covering an upland forest soil, a partially submerged sediment at the land–water interface and a constantly submerged sediment. The analysis of plant (lipds, isoprenoids, methoxyphenols and carbohydrates) and possible lignite (alkyl napththalenes, alkyl benzenes and PAHs) biomarkers released after pyrolysis supports previous findings in the area using other proxies. It was possible to discern OM sources in soil/sediment humus fractions, both from the substrate (lignite) as well as from the prevailing vegetation of the area. Environmental conditions in the submerged sediment seem to favour OM protection and the accumulation of decomposing plant material, whereas more intense OM degradation seems to prevail in the land–water interface areas characterized by fluctuating water level. In addition, a well resolved series of organic sulfur compounds (OSCS) found in the submerged sediments of rehabilitated acid lakes, indicates the possible occurrence of particular mechanisms of C preservation in this extreme anoxic S rich environment, i.e. via sulphur “quenching” with plant derived lipids during early diagenesis.     

Diagenetic cycling of arsenic in the sediments of eutrophic Baldeggersee,Switzerland

Sedimentation and benthic release of As was determined in Baldeggersee, a eutrophic lake in central Switzerland. Sediment traps recorded As sedimentation during 1994, including a flood event in spring. Diagenetic processes were studied using porewater profiles at the sediment–water interface and in deeper sediment strata deposited in the mesotrophic lake (before 1885). Sediment cores were used to calculate the accumulation and to construct the balance of sedimentation and remobilisation. The results showed that the lake sediment acts as an efficient sink for As. Only 22% of the particulate As flux reaching the sediment surface was remobilised at the sediment–water interface. The As accumulation in the recent varved section of the eutrophic lake was 40 mg As m⁻² a⁻¹. Iron reduction in older sediment caused a remobilisation of 1.2 mg As m⁻² a⁻¹. This upward flux from the deeper sediment was quantitatively immobilised in the recent sulfidic sediments. The flood event in spring contributed about 34% of the yearly sediment load and led to distinct peak profiles of dissolved As in the porewater. This evidence for rapid remobilisation disappeared within months.     

长江口表层沉积物孢粉相特征及其在碳循环中的意义

选自长江口F2-F5站住的4个表层沉积物及其粒度分级（1～8Ф）样品,经过孢粉相和热解检测,探讨有机质特征及其在碳循环中的命运。未分级样品的孢粉相主要由木质组织、丝炭和黑团块组成,显示陆地输入有机质的贡献巨大。样品分级后,孢粉相面貌发生显著变化。细粒的8函中无定形为主,其他粒级（2～7Ф）中主要由结构有机质组成。细粒的...