Terrestrial Organic Matter Input Research Articles

Quality of Sediment Organic Matter Determines the Intertidal N2O Response to Global Warming

AbstractEstuaries and coasts are areas of intense biogeochemical cycling and are sensitive to global climate change. However, the effect of temperature increase on the emissions of the powerful greenhouse gas nitrous oxide (N2O) in different estuarine and coastal areas is still uncertain. In this study, we used laboratory incubation experiments to investigate increasing temperatures (12, 25, and 35°C) and tidal effects on N2O fluxes in intertidal sediments from the East China coast (ECC). Overall, the ECC acts as a net source of atmospheric N2O and exhibited considerable spatial variability over three orders of magnitude (from −0.17 to 8.4 μmol m−2 h−1). The warming promoted N2O emissions in most intertidal areas, while reducing N2O emissions at some sampling sites. In addition, the overall effect of flooding on N2O emissions changed from a positive to a negative effect with increasing temperature. By combining the sediment properties of all the sampling sites, we found that large differences in N2O emissions at the same amended floodwater nitrogen concentration were due to the quality and quantity of sediment organic matter. Sediment derived mainly from marine sources emitted more N2O than sediment derived from terrestrial sources. This suggests that the mangroves, salt marshes, and intertidal zones of estuaries have a mitigating effect on N2O emissions due to their elevated terrestrial organic matter inputs. This research improves our understanding of the impact of future global climatic changes on intertidal N2O fluxes, which can inform future studies and models and can be used to constrain intertidal N2O emissions.

Source of organic matter and paleoenvironment of deposition of crude oils from the Niger Delta Basin

The study employed thirteen (13) crude oil samples from thirteen (13) producing wells, with the aim of examining the source of organic matter and the paleoenvironment of deposition. The crude oils were deasphaltened and the maltene fraction fractionated to obtain the saturates. The saturates were subjected to gas chromatography mass spectrometer (GCMS) analysis for the steranes, Isoprenoids and n-alkanes, and triterpanes and hopanes biomarker chromatograms. The biomarker composition of the studied oils indicates weakly oxic and reducing environmental conditions for the studied samples, consistent with marine deltaic environment of deposition. The study shows that the oils are associated with a mix of terrestrial and marine organic matter with a comparatively higher terrestrial and lower marine algae organic matter input. The oleanane index of 1.8 and the presence of oleanane in the studied samples denote higher terrigenous plant input into the source rock the generated the crude oils.

Geochemical evidence of lake environments favorable for the formation of excellent source rocks: A case study from the third member of the Eocene Shahejie Formation in the Qikou Sag, Bohai Bay Basin, eastern China

Lacustrine hydrocarbon source rocks with high quantity and quality of organic matter (OM) are developed within the third member of the Eocene Shahejie formation (Es3) in the Qikou Sag of the Huanghua Depression, Bohai Bay Basin, Eastern China. However, the paleolake environments associated with deposition of these rocks remain relatively undescribed, restricting our understanding of the biogeochemical processes which contributed to the development of excellent source rocks and inhibiting efforts for exploration of lacustrine hydrocarbon deposits. In this study, 18 core samples from the Es3 interval of Well Gangshen 4 in Qikou Sag were subject to a detailed analysis of bulk OM, biomarkers, molecular carbon isotopes, trace elements, and phosphorus (P) to investigate the environment and ecosystem of the ancient lake in which the rocks were deposited. High values of gammacerane index (av. 0.35) recorded in the samples reveals the oxic-anoxic stratification in the water column that persisted for the majority of the year due to the hot climate and great depth of the lake during this period. Meanwhile 13C-depleted hopanes (lower than −63.2‰) indicate an input of OM from chemoautotrophic and methanotrophic bacteria, supported by the production of CO2 and CH4 due to the anaerobic respiration of OM in the hypolimnion or sediments. The abundances of total organic carbon (TOC) relative to total P (TOC/P, mole ratio, av. 289.9) indicates the preferential release of P from sediments in an anoxic environment. However, the low (<2.0) Ni/Co and V/Cr ratios and moderate (av. 1.48) pristane/phytane (Pr/Ph) ratios suggest periodic oxidation of the hypolimnion, which may be a result of replenishment of oxygen during the short-term mixing of the water column driven by seasonal cooling and wind disturbance. Excess P was introduced into the epilimnion via mixing, which initiated high algal productivity after further stratification of the water column. Algal OM produced in this early stratification phase was crucial for the formation of excellent source rocks. The large variation of δ13C in TOC, n-alkanes, and isoprenoids reflects changes in CO2 concentrations or carbon isotopes in the photic zone, which may be attributable to increased inputs of terrestrial OM in response to a changing climate.

Biomarker Characterization of Oil Seepages in Tomori Basin, Central Sulawesi, Indonesia

Tomori Basin is located close to the Banggai Basin which has several productive oil fields. Further investigation of the hydrocarbon potential in Tomori Basin is an important issue as potential hydrocarbon resources are indicated by the discovery of several oil seepages in the area. This study identified Tomori Basin oil seepage characteristics using a biomarker analysis approach. The Wosu and Kolo Areas were the main objectives of this study. Oil seepage characteristics were determined using Gas Chromatography (GC) and Gas Chromatography-Mass Spectrometry (GC-MS) methods to generate biomarker data which could be analysed to identify organic matter origin, oxic and anoxic conditions, source facies, or depositional environment. Based on the GC analysis of is oprenoids, the Pristane C19/Phytane C20 ratio (Pr/Ph) of Wosu Oil was 0.75, indicating anoxic conditions typical of a hypersaline environment. Kolo Oil had a Pr/Ph ratio of 3.37 indicative of terrestrial organic input under oxic conditions. A cross plot between Pristane/nC17 and Pr/Ph ratios indicates that Wosu Oil derives from a highly anoxic environment with algae/bacterial organic matter input whereas Kolo Oil derives from a suboxic-oxic environment dominated by terrestrial organic matter input. Trycyclic terpene analysis from C19 to C25 shows Wosu Oil seepages tend to originate from an environment of mixed terrestrial and marine organic matter (transitional environment). Overall, biomarker characteristics indicate that Wosu Oil originated from organic matter in a hypersaline and anoxic environment, whereas Kolo Oil originated from terrestrial matter in a suboxic – oxic environment.

Anthropogenic Inputs of Terrestrial Organic Matter Influence Carbon Loading and Methanogenesis in Coastal Baltic Sea Sediments

Coastal regions globally have experienced widespread anthropogenic eutrophication in recent decades. Loading of autochthonous carbon to coastal sediments enhances the demand for electron acceptors for microbial remineralization, often leading to rearrangement of the sediment diagenetic zonation and potentially enhancing fluxes of methane and hydrogen sulfide from the seafloor. However, the role of anthropogenic inputs of terrestrial organic matter (OMterr.) in modulating diagenesis in coastal sediments is often overlooked, despite being of potential importance in regions of land-use and industrial change. Here we present a dated 4-m sediment and porewater geochemistry record from a eutrophic coastal location in the northern Baltic Sea, to investigate sources of recent carbon loading and their impact on modern diagenetic processes. Based on an end-member mixing model of sediment N/C ratios, we observe that a significant fraction of the late-20th century carbon loading at this location was contributed by OMterr.. Furthermore, analysis of lignin in this material shows depleted ratios of syringyl/vanillyl (S/V) and cinnamyl/vanillyl (C/V) phenols, indicative of enhanced inputs of woody gymnosperm tissue likely from forest industries. The rapid loading of organic matter from combined terrestrial and autochthonous sources during the late 20th century has stimulated methanogenesis in the sediment column, and shoaled the sulfate-methane transition zone (SMTZ) to a depth of 5–20 cm. Optical parameters of colored dissolved organic matter confirm that OMterr. is actively degrading in the methanogenic layer, implying a role for this material in diagenetic processes. Porewater CH4, SO42− δ13C-DIC, and ∑S2− data suggest that the modern SMTZ is a broad zone in which organoclastic sulfate reduction, methanogenesis and anaerobic oxidation of methane (AOM) co-occur. However, fluxes of CH4 and SO42− show that rates of these processes are similar to other marine locations with a comparably shallow SMTZ. We suggest that the shallow depth of the modern SMTZ is the principal reason for high observed diffusive and ebullitive methane fluxes from sediments in this area. Our results highlight that anthropogenic activities lead to multiple pathways of carbon loading to coastal sediments, and that forest industry impacts on sedimentation in the northern Baltic Sea may be more widespread than previously acknowledged.

Upper Jurassic to Lower Cretaceous source rocks in the Norwegian Barents Sea, part I: Organic geochemical, petrographic, and paleogeographic investigations

This study provides a subregional to regional characterization of organofacies changes within the two members of the Upper Jurassic to Lower Cretaceous Hekkingen Formation (i.e. Alge and Krill) by integrating geochemical and petrographic analysis with paleogeographic models.The gross kerogen composition of the Hekkingen Formation is dominated by terrestrial macerals. This preponderance of land-derived particles is more pronounced in the Krill Member than in the underlying Alge Member. There is a greater proportion of marine macerals within distal areas of the Hammerfest Basin and well 7218/1-S in the southern Bjørnøyrenna Fault Complex. This shift in the relative proportion of marine and terrestrial macerals is ascribed to changes in the location of the depositional sites with respect to the sources of the terrestrial materials.The Alge Member features the highest levels of total organic carbon (TOC ≥7 wt %), but the more discrete and organically poorer beds of the Krill Member still remain sufficiently rich to be considered petroleum source rocks (TOC ≥2 wt %). Hydrogen indices (HI) between 50 and 400 mg HC/g TOC recorded throughout the entire formation indicate that the kerogen within both members has similar oil and gas generation capabilities. These low to moderate HI values are indicative of immature Type III to II-III kerogens and are generally consistent with the high proportions of terrestrial macerals. Prior to thermal maturation, marine type II kerogens (i.e. ≤ 400 mgHC/gTOC) probably existed in the marine liptinite-rich rocks in the distal Hammerfest Basin and Bjørnøyrenna Fault Complex. At least three factors controlled the detected variability in geochemical parameters: dilution rates of organic matter, varying inputs of terrestrial versus marine organic matter, and the degree of preservation. The documented variability in organic-rich facies assists in reducing source rock risk in the study area, but also helps explorationists understand source rock distribution across other shelfal areas.

Famennian inertinite-bearing marine shale facies as indicator of wildfire event in north of Gondwana

ABSTRACT The Late Devonian witnessed landscape evolution, increased atmospheric O2 level, intense organic and volcanic activities and initial expansion of earliest wildfires. This paper is focused on petrographic and geochemical studies of Famennian inertinite-bearing marine shale facies in northern Kerman (central Iran), a Late Devonian key area in north of Gondwana.Our studies point to a wildfire activity. During the Famennian, the wildfire activity occurred in lowland vegetation (covered by lycopods) under warm and humid conditions. The moderately hot burning temperature (446.7°C to 487.9°C) of the fire and the type of the land vegetation suggest prevalence of a surface wildfire. Following the burning of the land plants, the ground became exposed to weathering that could result in erosion of the soil. Inputs of terrestrial organic matter, nutrients (particularly phosphate) and detrital materials into a nearshore marine environment were mainly controlled by proximity of the depositional environment to the terrestrial source, intense continental weathering of rocks and the soil in the land, wildfire and continental runoff during rainfall. Generally, preservation and enrichment of organic matter and formation of macerals were controlled by wildfire activity, transportation, oxidation, bacterial/fungal degradation and detrital input.

A sediment record of terrestrial organic matter inputs to Dongting Lake and its environmental significance from 1855 to 2019

The extensive anthropogenic activities and their potential impacts on lakes during the Anthropocene could be recorded in the sediments. In this study, the composition of biomarkers (i.e., n-alkanes and n-fatty acids), total organic carbon (TOC), and particle size in 210Pb-dated sediment cores from West Dongting Lake were investigated to trace the historical trend of anthropogenic inputs and their environmental significance. The TOC content was in the range of 3.15–27.32 mg g−1. The n-alkanes and n-fatty acids were distributed from C11–C33 and C12:0–C34:0, respectively. The short- and long-chain biomarkers accounted for a significant proportion of the total. Aquatic plants and algae living in West Dongting Lake were the main source (short-chain) followed by leaf waxes derived from terrestrial C3 plants (long-chain), as demonstrated by their concentrations. The variations of the key indicators i.e., the carbon preference index (CPI), aquatic plant n-alkane proxy (Paq), vascular plant n-alkane proxy (Pwax), and the ratio of unit short- to long-chain n-alkanes (L/H) also indicated that the aliphatic hydrocarbon fractions were mainly composed of short- and long-chain biomarkers. The sedimentary biomarkers had a significant temporal heterogeneity, which was controlled by different factors and sedimentary processes. Fine particles (<16 µm) were the dominant particle size (66.91%–78.52%) in the sediment. Both values of the dry/wet climate proxy (Kd) and average particle size were consistent over time. The dominance of terrestrial C3 plant-derived long-chain molecules gradually changed, with algae-derived short-chain molecules then becoming dominant. The hot and drought climate conditions and enhanced agricultural inputs from 1855 to 2019 in the watershed resulted in a decrease of terrestrial C3 plants and rapid growth of algae in the lake water.

Chromophoric dissolved organic matter (CDOM) in a subtropical estuary (Galveston Bay, USA) and the impact of Hurricane Harvey.

The landfall of Hurricane Harvey in August 2017 provided the opportunity to study the impact of extreme freshwater discharge on chromophoric dissolved organic matter (CDOM) properties in a subtropical estuary (Galveston Bay, Texas). Both fluorescence spectroscopy (excitation-emission matrices) and a three-component parallel factor analysis (PARAFAC) model identified changes in CDOM properties. Comparing to Coble's peaks, component 1 was similar to peak C, component 2 to peak M, and component 3 to peak B. Results clearly show three periods with distinct CDOM properties: a dry season, a wet season, and Hurricane Harvey. The dry season was characterized by higher values of the spectral slope and fluorescence and biological indices. The wet season was characterized by high values of PARAFAC components 1 and 2 (humic-like) and the absorption coefficient at 350 nm. Some CDOM components were highly correlated with salinity, indicating conservative mixing. Component 3 (protein-like) had a low correlation to salinity, suggesting degradation or production processes in the bay. Silicates and NO3- + NO2- had negative relationships with salinity and a positive one with PARAFAC components 1 and 2. PARAFAC component 3 was correlated with dissolved oxygen and chlorophyll a, suggesting a relationship between CDOM fluorescent components and phytoplankton activity. High values of the humification index were observed immediately after Hurricane Harvey, indicating increased input of terrestrial organic matter into the bay. Hurricane Harvey increased CDOM levels and humification, and the variability and changes seem to be mostly due to freshwater discharge from the San Jacinto River and not the Trinity River. The influx of freshwater was sufficient to eliminate the salinity gradient in Galveston Bay and significantly change CDOM properties. Galveston Bay recovered quickly from the hurricane and associated flux of freshwater, returning to pre-hurricane CDOM characteristics in less than 2 months.

Geochemical characteristics and mechanism of organic matter accumulation of marine-continental transitional shale of the lower permian Shanxi Formation, southeastern Ordos Basin, north China

The marine-continental transitional shale is widely distributed in the Lower Permian Shanxi Formation of the southeast Ordos Basin. The primary factors controlling organic matter accumulation of the Shanxi shale are still obscure. In this study, we used mineralogy and organic geochemistry, coupled with major and trace element geochemistry to analyze the paleoenvironment and their effects on organic matter enrichment, and established the accumulation model of organic matter in the Shanxi transitional shale. Results show that the mineralogical composition of the Shanxi shale is dominated by clay and quartz (averaging of 62.8 and 33.3%, respectively). The Shanxi shale has relatively high TOC contents and thermal maturity (Ro) (averaging of 1.25% and 2.66%, respectively), and predominantly contains type III kerogen. The significantly low paleoproductivity indicates that this factor plays not the primary role of organic matter accumulation. Ti and Al concentrations indicate a strong terrestrial input, simultaneously bringing abundant terrestrial organic matter, which is favourable for its enrichment. The warm and humid climate condition enhanced higher plant growth and provenance weathering. The δU, U/Th, V/Cr and Ni/Co values show dysoxic-oxic environments, suggesting relatively poor preservation conditions for organic matter. Comprehensive analysis shows that the terrestrial organic matter input, paleoclimate and redox conditions are the primary factors controlling the organic matter accumulation of the Shanxi shale. • The paleoproductivity is significantly low during the Shanxi shale deposition. • The terrestrial detrital input is strong, carrying abundant terrestrial organic matter. • The paleoclimate and redox conditions triggered organic matter accumulation to some extent. • An accumulation model of organic matter in the Shanxi Formation was established.

Terrestrial Organic Matter Inputs to Nearshore Marine Sediment Under Prolonged Drought Followed by Significant Rainfall as Indicated by Lignin

Terrestrial organic matter (TOM) exported to nearshore marine regions may be altered by drought or large amounts of precipitation. We examined how significant precipitation in southern California during the winter seasons of 2015 and 2016, following a prolonged drought from 2011 to 2015, impacted the quantity and quality of TOM transported to nearshore kelp forests of the Santa Barbara Channel. Based on organic matter content, lignin oxidation by-products, and carbon isotopic signatures, biomarkers of TOM were detected in stream, estuarine, and marine sediments. Quantitative measures of lignin differentiated between the three environments. Qualitative lignin signatures revealed temporal patterns that appeared in stream, estuarine, and marine sediment. These patterns indicated that TOM delivered into nearshore coastal regions from mountain watersheds was less degraded over time and its source material changed through time. Our findings suggest lignin oxidation compounds can be used as biomarkers of TOM transported during storm events from coastal watersheds into nearshore marine sediment.

Dibenzothiophenes, phenyldibenzothiophenes, and benzo[b]naphthothiophenes in crude oils and source rock extracts from the Niger Delta Basin, Nigeria, and their applications as source facies, depositional environments, and thermal maturity indicators

The distribution of dibenzothiophenes, phenyldibenzothiophenes, and benzo[b]naphthothiophenes and their geochemical significance in the crude oils and source rocks from Niger Delta Basin have been investigated by gas chromatography-mass spectrometry. The dimethyldibenzothiophenes, 4-phenyldibenzothiophene, and benzo[b]naphtho[2,1-d]thiophene were the most abundant among the dibenzothiophene and its derivatives in the crude oils and rock samples. The phenyldibenzothiophene ratio-1 and phenyldibenzothiophene ratio-2 values in the rock samples were in the ranges of 0.08 to 0.67 and 0.20 to 2.53, respectively, while the 4-/1-methyldibenzothiophene, 4,6-/(1,4 + 1,6)-dimethyldibenzothiophene, 2,4,6-/(2,4,7 + 2,4,8)-trimethyldibenzothiophene, phenyldibenzothiophene ratio-1, and phenyldibenzothiophene ratio-2 values in the crude oils ranged from 1.52 to 5.82, 0.76 to 1.98, 0.77 to 1.22, 0.11 to 0.42, and 0.30 to 0.75, respectively. These values indicate source rocks and crude oils with mixed input of terrestrial and marine organic matter and deposited in lacustrine-fluvial/deltaic environments within immature to early mature stages. Four isomers of MDBT were also present in appreciable amounts in all the samples studied. The distribution patterns of MDBTs were generally observed in the order 4-MDBT > 2+3-MDBT > 1-MDBT in the crude oils and rock samples. The (1 + 4)-/(2+3)-methyldibenzothiophene ratio in the oils and rock samples ranged from 0.03 to 0.13 and 1.31 to 2.54, respectively. These values suggested source rocks with shale lithologies. A cross plot of (1+4)-/(2+3)-methyldibenzothiophene versus pristane/phytane measured on rock samples and crude oils from Niger Delta was used to study the influence of depositional environment and lithology on the distribution of the MDBT isomers. This cross plot clearly showed that the source rocks and crude oils studied have shale lithologies and were distinguished into lacustrine and fluvial/deltaic/freshwater environments and thus proposed in this study as a potential lithology and paleoenvironment indicator. This study showed that dibenzothiophenes, phenyldibenzothiophenes, and benzo[b]naphthothiophenes were effective in determining the origin, depositional environments, and thermal maturity status of crude oils and source rocks in the Niger Delta Basin, Nigeria.

Occurrence and geochemical significance of fluorene and alkylfluorenes in crude oils and source rock extracts from Niger Delta basin, Nigeria

The crude oils and their source rocks from Niger Delta basin, Nigeria were investigated by optical microscopy for the maceral compositions and by gas chromatography - mass spectrometry (GC-MS) for the composition, distribution and abundances of saturated and aromatic biomarkers. The data obtained showed that the rock samples and crude oils were formed from the mixed input of terrestrial and marine organic matter, and deposited under oxic to sub-oxic conditions in a lacustrine-fluvial/deltaic environment. The aliphatic maturity parameters calculated for the source rocks and oil samples showed that they have immature to early mature; and early oil window maturity respectively, whereas aromatic maturity ratios indicated that they were within immature to peak of oil generation and beyond; and peak to late oil generative window, respectively. The crude oils and source rocks were characterized by the dominance of C2-fluorenes over other alkylated homologues. The predominance of C2 fluorenes over other alkylated homologues might have been influenced by source facies and depositional environments. The relative percentages of fluorenes (FLs %), dibenzofurans (DBFs %) and dibenzothiophenes (DBTs %) values for the rock samples range from 9.36 to 38.04 %, 35.82–71.60 % and 10.02–42.52 %, respectively, while the crude oils have ranges of values from 18.91 to 56.38 %, 24.90–72.34 % and 5.99–19.02 %, respectively. These values showed that the crude oils and source rocks originated from the mixture of organic matter (terrestrial and marine) with higher contribution from terrestrial organic matter and deposited in a marine/brackish-saline lacustrine/swampy environments. The abundance and distribution of fluorenes and its derivatives were found to be effective in determining the origin and depositional environments of crude oils and source rocks in the Niger Delta Basin, Nigeria.

Spatial heterogeneity in fatty acid abundance and composition across surface sediments of Lake Taihu, Eastern China: Implications for the use of lipids in evaluating carbon cycling and burial in lake systems

Fatty acids (FAs) present in the surface sediments of Lake Taihu were analyzed for spatial heterogeneity in abundance and composition in order to test the suitability of these lipids to indicate variation in sources and preservation status of organic matter (OM) in sediments. The results indicate that terrestrial plant-derived FAs were relatively enriched in Meiliang and Zhushan Bays, the most eutrophic regions of Lake Taihu, while FAs of phytoplankton origin were relatively low. This unexpected result might reflect a preferential degradation of phytoplankton OM and phytoplankton-derived FAs. Furthermore, massive inputs of refractory terrestrial OM could significantly dilute concentrations of phytoplankton FAs. In sediments from East Bay, phytoplankton-derived FAs were more abundant than in Zhushan Bay, although this region had the lowest levels of nutrients and the lowest phytoplankton productivity. This result was attributed to a greatly enhanced preservation of labile FAs, probably caused by reduced sediment resuspension in this region with dense growth of submerged macrophytes. Phytoplankton productivity and terrestrial OM inputs were moderate in Central Region, but abundances of all FAs and ratios of C16:1/n-C16, C18:1/n-C18 and C18:1ω7/C18:1ω9 both reached their lowest in sediments from this region, possibly as a result of significant degradation of FAs driven by strong sediment resuspension. Sediments from Gonghu Bay and Southern Region were relatively enriched in phytoplankton FAs, and this was ascribed to low inputs of terrestrial OM, which limited the dilution effect. In contrast to FAs, short-chain n-alkane abundances provided an accurate indication of variation in phytoplankton input.

Preservation of organic matter in shale linked to bacterial sulfate reduction (BSR) and volcanic activity under marine and lacustrine depositional environments

Black organic-rich shale is a sedimentary product of strongly reducing environmental water bodies, and is the main source of shale oil and gas. During its formation, the presence of sulfate promotes bacterial sulfate reduction (BSR), but little attention has been paid to how BSR affects the preservation of organic matter (OM) in different sedimentary environments. In this study, the Wufeng-Longmaxi Formations from the Sichuan Basin, the Chang-7 Member (the seventh member of the Triassic Yanchang Formation) from the Ordos Basin, the Qingshankou and Nenjiang Formations in the Songliao Basin, as well as the New Albany shale from the Appalachian Basin are selected for investigation. Results show that there is a positive correlation between total sulfur (TS) and total organic carbon (TOC) contents, and the sulfate reduction index (SRI) and TOC show two-stage exponential changes. When the SRI is higher than 1.375, the overall TOC content is low, indicating that a large amount of organic matter is consumed through intense BSR. When the SRI is lower than 1.375, the TOC content is significantly higher, indicating that weak BSR has relatively little effect on organic matter degradation.In the normal marine sedimentary environment for the New Albany shale in North America, the high concentration of sulfate was conducive to BSR, but the increased input of terrestrial OM compensated for the marine OM consumption by BSR, resulting in a high TOC value in the shale. Volcanic activity provides additional sulfates into the water column and triggers BSR occurrence, but the high concentration of nutrients brought by volcanic activity in the shales of the Wufeng-Longmaxi Formations and the Chang-7 Member promoted paleoproductivity, offset the effect of OM consumption by BSR, and resulted in the high TOC values seen in these shales. When a large amount of sulfate was input into terrestrial lakes through volcanic activity or marine transgression, there were significantly different effects on the preservation of organic matter in lacustrine shales. Nutrients from the volcanic activity increased the paleoproductivity of lakes during the Chang-7 period, while decreasing the impact of BSR on OM, resulting in a high TOC value in the Chang-7 Member shale. However, when the lacustrine basin was subjected to marine transgression, paleoproductivity weakly increased and BSR consumed a larger proportion of the OM, reducing the TOC values and forming the relatively low TOC shale of the Qingshankou and Nenjiang Formations in the Songliao Basin.

Impacts of long-term land use on terrestrial organic matter input to lakes based on lignin phenols in sediment records from a Swedish forest lake

Organic carbon burial in lake sediments plays an important role in the global carbon cycle, and is heavily affected by the terrestrial organic matter input. However, few studies have focused on long-term changes in terrestrial organic matter input to lakes in response to land-use changes. The aim of this study was to assess variations in sedimentary terrestrial organic matter over the last 1000 years based on lignin biomarker records from two sediment cores from Lake Skottenesjön, southwestern Sweden. In combination with pollen-based quantitative land cover reconstruction, we investigated the impacts of centennial-scale land-use changes on terrestrial organic matter input to lake sediments. The results show that human activities in the catchment had significant impacts on terrestrial organic export by modifying the vegetation cover. Intensified use of the forest in the 18th and 19th centuries led to enhanced soil erosion, and increased terrestrial organic matter input to the lake. Although farmland expanded between the 12th and the middle of 14th century, no significant change in terrestrial organic matter input was observed at that time. Much higher export of terrestrial organic and minerogenic matter to the lake was observed during the period of modern forestry in the 20th century as compared to previous periods of minor forest disturbance, such as 11th century. The changes in the vegetation cover in the catchment considerably modified the composition of terrestrial organic matter deposited in the lake sediments, which is reflected by the composition of lignin phenols. This study demonstrates that the combination of lignin phenols analysis and pollen-based quantitative land cover reconstruction is a useful approach for investigating long-term changes in terrestrial organic matter delivery to lake ecosystems.

The Occurrence and Distribution of Oleanane Biomarkers in Crude Oils as an Index

Oleanane biomarkers are age diagnostic indicators and source of organic matter input in fossil fuels which can unravels the stage of development of a petroleum system in the petroleum generating rock. Representative samples of crude oil obtained from two separate fields in the southern Nigeria province were evaluated geochemically using Gas Chromatography–Mass Spectrometry. The data obtained from the analysis of the crude oil samples revealed the presence of the 18α (H)-oleanane biomarker. The occurrence of 18α (H)-oleanane biomarker in the Niger Delta oils provides diagnostic evidence on age and organic matter source in all samples. The results of the Oleanane indices for all samples ranged from 0.32 to 1.03 (> 0.30), which suggests that the oils are from Tertiary age source rocks with resilient terrestrial organic matter input. Only crude oil sample KD03 had an Oleanane index of 0.03 (< 0.30), which shows crude oils derived from a late cretaceous or younger age with some marine input. The presence of 18α (H)-Oleanane in Niger Delta crude oils is a confirmation of an earlier postulation that most crude oils from the region had a greater terrestrial organic matter input.

Future changes in the Dominant Source Layer of riparian lateral water fluxes in a subhumid Mediterranean catchment

The ‘Dominant Source Layer’ (DSL) is defined as the riparian zone (RZ) depth stratum that contributes the most to water and solute fluxes to streams. The concept can be used to explain timing and amount of matter transferred from RZs to streams in forest headwaters. Here, we investigated the potential impact of future climate changes on the long-term position of the DSL in a subhumid Mediterranean headwater catchment. We used the rainfall-runoff model PERSiST to simulate reference (1981–2000) and future (2081–2100) stream runoff. The latter were simulated using synthetic temperature, precipitation, and inter-event length scenarios in order to simulate possible effects of changes in temperature, rainfall amount, and rainfall event frequency and intensity. Simulated stream runoff was then used to estimate RZ groundwater tables and the proportion of lateral water flux at every depth in the riparian profile; and hence the DSL. Our simulations indicated that future changes in temperature and precipitation will have a similar impact on the long-term DSL position. Nearly all scenarios projected that, together with reductions in stream runoff and water exports, the DSL will move down in the future, by as much as ca. 30 cm. Shallow organic-rich layers in the RZ will only be hydrologically activated during sporadic, large rainfall episodes predicted for the most extreme inter-event length scenarios. Consequently, terrestrial organic matter inputs to streams will decrease, likely reducing catchment organic matter exports and stream dissolved organic carbon concentrations. This study highlights the importance of identifying vertical, hydrologically active layers in the RZ for a better understanding of the potential impact of future climate on lateral water transfer and their relationship with surface water quality and carbon cycling.

Anthropogenic impact on the organic carbon sources, transport and distribution in a subtropical semi-enclosed bay

Suspended particulate organic carbon (POC) and sedimentary total organic carbon (TOC) in coastal areas play critical roles in the global carbon cycle, yet sources and dynamics of coastal POC and TOC have been affected by various anthropogenic activities such as aquaculture, sewage discharge, dam construction and land reclamation. To better understand the anthropogenic impacts on coastal organic carbon, this study was carried out in a representative semi-enclosed bay, Dongshan Bay, Southeast China. Through analyses of stable isotopic compositions of both POC (δ13CPOC and δ15NPN) and TOC (δ13CTOC and δ15NTN), the ratio of total organic carbon vs. total nitrogen (C/N), grain size, Chl-a concentrations and hydrological parameters, our study led to the following main findings: 1) During flood season, the distribution of δ13CPOC, δ13CTOC, δ15NPN and δ15NTN values within the bay did not follow the conventional land-sea transition pattern. This distribution pattern indicated more terrestrial organic matter input seaward, which contrasts with the conventional organic matter distribution along the estuarine gradient. 2) Using the organic δ13C, δ15N and C/N signatures of different endmembers, we found that the sources of organic matter deposited in the bay were strongly related to anthropogenic activities, including municipal wastewater discharge, aquaculture, land reclamation and sluice-dyke construction. Furthermore, 3) by applying the Grain Size Trend Analysis Model and the previously-estimated residual current directions, we suggested that human activities have not only altered the sources of organic matter to the semi-enclosed bays, but also significantly modified their transportation and deposition patterns, and might influence the ultimate fate of organic matter into and out of Dongshan Bay. The conclusions of this study should be applicable to similar coastal bays around the world.

North Sea salt-marsh archives trace past storminess and climate variability

Intertidal coastal wetlands are regularly exposed to storm surges and associated flooding, resulting in the recurrent accretion of reworked sediments on the salt-marsh surfaces. In this context, well-stratified salt-marsh sediment sequences provide an exceptional archive to evaluate the response of coastal wetlands to past storm-climate variability. Hence, this study focusses on the investigation of two sedimentary salt-marsh sequences from the south-eastern German North Sea coast (Bay of Tümlau and Friedrichskoog) to understand how and to which extent changes in the storm-surge climate are transferred into the sediment archive. This objective is particularly challenging as German mainland salt marshes have been greatly altered by human activities over the last century. To overcome this problem, this study combines different sedimentological and geochemical proxy data, using mean grain sizes together with ln(Br/Cl), Br/Corg, and ln(Zr/Rb) ratios, to allow for the identification of storm-surge layers. Local changes in the sedimentary organic matter supply are reflected by the ln(Br/Cl) ratio. There, abrupt drops in the ln(Br/Cl) data coincide with relatively coarser textured sand layers, indicating impacts by regional storm surges during winter, while intervals of comparable higher ln(Br/Cl) values may represent deposition during spring to fall. The Br/Corg record reflects the marine versus terrestrial organic matter input and reveals a long-term increase starting during the first half of the 20th century towards recent times, resembling the observed amplification in North Sea storminess. A similar trend is reflected by the ln(Zr/Rb) ratio (since 1950 CE), which can be used as a proxy for the grain-size distribution. Periodic fluctuations in the ln(Zr/Rb) ratio at inter-decadal timescales (10–19 years) suggest a close linkage between local sediment accretion and large-scale atmosphere-ocean climate oscillations over the North Atlantic and Europe, and thus related storm-surge frequency and intensity. Periodic variability on decadal scales was also identified in the ln(Br/Cl) record at the less human-modified and more naturally developed salt marsh at the Bay of Tümlau (12–22 years), likewise indicating a relation between North Sea storminess and associated shifts in the seasonal signal of the primary production and sediment texture to oscillations in the atmosphere-ocean system. On the contrary, similar periodicities are lacking for the intense modified salt marsh at Friedrichskoog. Apparently, the salt-marsh depositional system in the Bay of Tümlau reacts more sensitively to super-regional climatic changes, respectively, the natural depositional processes in the salt marsh at Friedrichskoog are superimposed by the more intense local human activities.