Contribution Of Organic Matter Research Articles

Eocene-Oligocene paleoenvironmental changes in the South Orkney Microcontinent (Antarctica) linked to the opening of Powell Basin

The scarcity of paleo-records from the Antarctic Peninsular region of the Southern Ocean hinders our understanding of the timing of the opening of Drake Passage, specifically in the region of the South Orkney Microcontinent (SOM) and Powell Basin, between the Scotia and Antarctic plates. At Ocean Drilling Program (ODP) Hole 696B, SOM sediments recovered from the upper Eocene-lower Oligocene (~37.6–32.2 Ma) enable us to gain insight into paleoceanographic and paleoclimatic changes during gateway opening across the major Cenozoic climate shift —the Eocene-Oligocene transition— when the Antarctic ice sheet first reached sea-level. We propose the following sequence of events, based on a multi-proxy analysis of sediment facies, mineralogy, and organic matter geochemistry (TOC, TN, C/N ratio, δ 13 C, δ 15 N, and n -alkanes). During the late Eocene (~37.6–35.5 Ma) the SOM was attached to the Antarctic Peninsula, and terrigenous sediments of likely local origin were deposited in shallow waters under conditions of reduced‑oxygen/low-salinity, and temperate climate. In the latest Eocene (~35.5–34.1 Ma), terrigenous input was reduced due to the separation of the SOM from the Antarctic Peninsula by proto-Powell Basin opening. Decreased sediment supply during continuous deepening of the SOM led to deposition of a condensed section with significant glauconitization, recurrent winnowing by bottom currents, and suboxic conditions near the sediment-water interface. At the time of the Eocene-Oligocene transition (EOT; ~34.1–33.6 Ma) two upward-coarsening sediment sections were deposited within an overall upward-fining section, which we interpret as records of regressive phases due to ice sheet expansion. During the early Oligocene (~33.6–33.2 Ma) the SOM deepened further because of continued opening of Powell Basin, and organic-rich sediments were deposited as a result of enhanced biological production, partially driven by enhanced upwelling. Major cooling caused a change from forests indicating relatively humid temperate conditions in the late Eocene, to forests indicative of dry and cool conditions in the Oligocene, as shown by biomarker records, which also indicate weakening contributions of terrestrial organic matter to the marine sedimentary record. We thus conclude that a shallow gateway, the proto-Powell Basin, formed at ~35.5 Ma, as seen in the decreased delivery of proximal, coarse terrigenous sediments to the SOM margin; this was followed by a long-term deepening trend, interrupted by EOT regression due to continent-wide ice sheet build-up. Opening of the proto-Powell Basin could have provided a shallow-water pathway for water flowing from the Drake Passage-Scotia Sea towards the northern Weddell Sea, enhancing upwelling at the southern SOM shelf margin. Hence, increased marine productivity across the EOT might have resulted from the combined effects of the opening of Powell Basin and climate cooling. • Eocene-Oligocene sediments at Site 696 evidences a sustained relative sea-level rise in the SOM. • Our results point to the formation of the proto-Powell Basin at ~35.5 Ma. • Opening of Powell Basin provided a shallow-water pathway for water flowing towards the Weddell Sea. • We describe enhancing upwelling at the southern margin of the SOM shelf. • A shift from relatively humid temperate to dry and cool forests occurs between the Eocene and Oligocene.

Isotopic constraints on sources of organic matter and environmental change in Lake Yangzong, Southwest China

Anthropogenic disturbances have been widely documented to affect organic matter (OM) sources in lakes; however, most studies have revealed the unreliability of estimating ecological changes from a single or a few sediment cores within a single lake. Here, we combined multi-core analyses, including total organic carbon and total nitrogen contents and their stable carbon and nitrogen isotope ratios (δ13Corg and δ15N, respectively) with a Bayesian isotope mixing model to track the origins of OM and characterize the environmental changes in Lake Yangzong, a plateau lake located in the Yunnan Plateau, Southwest China. The results showed that allochthonous OM (C3 plants: 31.2–78.3%; soil OM: 4.4–26.6%) was the dominant sediment OM source, and the contributions of plankton, soil OM, and sewage decreased from the south to the north. The temporal increase in δ15N might have indicated an increase in nitrogen discharge caused by human activities, whereas the variation of δ13Corg was mainly controlled by allochthonous sources. Further analysis showed that there were significant differences in the lake environment evolution at different sites from the 1950s in response to anthropogenic disturbances. For example, there was a significant shift in the lake environment at the southern site (S1) from the 1990s, whereas a rapid environmental change was documented at the middle site (S2) over the past half-century. Rapid environmental fluctuation occurred at the northern site (S3) owing to soot air pollution occurring on the north shore of the lake from 1970 to 1990. These findings reveal the spatiotemporal characteristics of ecological changes and highlight the sensitivity of the deep-water area of deep lakes to anthropogenic disturbances.

Geochemical Characterization of the Eocene Coal-Bearing Source Rocks, Xihu Sag, East China Sea Shelf Basin, China: Implications for Origin and Depositional Environment of Organic Matter and Hydrocarbon Potential

Eocene coal-bearing source rocks of the Pinghu Formation from the W-3 well in the western margin of the Xihu Sag, East China Sea Shelf Basin were analyzed using Rock-Eval pyrolysis and gas chromatography–mass spectrometry to investigate the samples’ source of organic matter, depositional environment, thermal maturity, and hydrocarbon generative potential. The distribution patterns of n-alkanes, isoprenoids and steranes, high Pr/Ph ratios, abundant diterpanes, and the presence of non-hopanoid triterpanes indicate predominant source input from higher land plants. The contribution of aquatic organic matter was occasionally slightly elevated probably due to a raised water table. High hopane/sterane ratios and the occurrence of bicyclic sesquiterpanes and A-ring degraded triterpanes suggest microbial activity and the input of microbial organisms. Overwhelming predominance of gymnosperm-derived diterpanes over angiosperm-derived triterpanes suggest a domination of gymnosperms over angiosperms in local palaeovegetation during the period of deposition. The high Pr/Ph ratios, the plot of Pr/n-C17 versus Ph/n-C18, the almost complete absence of gammacerane, and the distribution pattern of hopanes suggest that the samples were deposited in a relatively oxic environment. Generally, fluctuation of redox potential is coupled with source input, i.e., less oxic conditions were associated with more aquatic organic matter, suggesting an occasionally raised water table. Comprehensive maturity evaluation based on Ro, Tmax, and biomarker parameters shows that the samples constitute a natural maturation profile ranging from marginally mature to a near peak oil window. Hydrogen index and atomic H/C and O/C ratios of kerogens suggest that the samples mainly contain type II/III organic matter and could generate mixed oil and gas.

Contributions of aerosol chemical composition and sources to light extinction during haze and non-haze days in Taiyuan, China

To better understand the causes of visibility degradation in Taiyuan, the concentrations of PM1.5 and main chemical compositions were analyzed during the period from July 28, 2014 to April 26, 2015. The average concentration of PM1.5 during the sampling period was 107.6 ± 51.0 μg/m3. The concentrations of secondary inorganic water-soluble ions (SIA, the sum of SO42−, NO3− and NH4+), OC and EC were 31.0 μg/m3, 14.6 μg/m3 and 6.0 μg/m3, accounting for 28.8%, 13.5% and 5.6% of PM1.5, respectively. Light extinction coefficients (bext) were estimated by the revised US Interagency Monitoring of Protected Visual Environments (IMPROVE) equation. (NH4)2SO4 (48.7%) was the largest contributor to bext in summer, while the contribution of organic matter (OM) to bext was the highest in spring (25.0%) and winter (42.0%). Compared with non-haze days in summer and winter, the contributions of (NH4)2SO4 and NH4NO3 to bext during haze days increased, while the contributions of OM, EC, fine soil and coarse matter (PM1.5-10) decreased. Air masses from the southern areas had the largest bext and contribution of (NH4)2SO4 in summer and winter. The results of source apportionment by positive matrix factorization model found that secondary sulfate, secondary nitrate, coal combustion, vehicle emission, fugitive dust, biomass burning were the main sources to bext in Taiyuan. Secondary sulfate (81.7%) and coal combustion (43.1%) were the largest contributors to the bext in summer and winter during haze days, respectively. The results of our study could improve the understanding of the major sources that affect visibility degradation in Taiyuan.

Contributions of Organic and Mineral Matter to Vertical Accretion in Tidal Wetlands across a Chesapeake Bay Subestuary

Persistence of tidal wetlands under conditions of sea level rise depends on vertical accretion of organic and inorganic matter, which vary in their relative abundance across estuarine gradients. We examined the relative contribution of organic and inorganic matter to vertical soil accretion using lead-210 (210Pb) dating of soil cores collected in tidal wetlands spanning a tidal freshwater to brackish gradient across a Chesapeake Bay subestuary. Only 8 out of the 15 subsites had accretion rates higher than relative sea level rise for the area, with the lowest rates of accretion found in oligohaline marshes in the middle of the subestuary. The mass accumulation of organic and inorganic matter was similar and related (R2 = 0.37). However, owing to its lower density, organic matter contributed 1.5–3 times more toward vertical accretion than inorganic matter. Furthermore, water/porespace associated with organic matter accounted for 82%–94% of the total vertical accretion. These findings demonstrate the key role of organic matter in the persistence of coastal wetlands with low mineral sediment supply, particularly mid-estuary oligohaline marshes.

Bacteriohopanepolyols signature in sediments of the East China Sea and its indications for hypoxia and organic matter sources

The bacterial biomarker group of bacteriohopanepolyols (BHPs) has shown a significant potential to track terrestrial inputs and to respond to environmental changes. A total of 12 BHPs were detected in surface sediments of the East China Sea (ECS), with the contents of 3.79–361 μg/g TOC. The spatial distribution patterns and correlation analyses of bacteriohopanetetrol (BHT) and soil marker BHPs in sediments of the ECS indicate that they were mainly derived from marine autochthonous and terrestrial sources, respectively. The Rsoil index presented an “offshore decrease” trend, with the contribution of terrestrial organic matter (OM) decreasing from 63% in the coastal waters to 0.81% in the outer seas. This suggests that sedimentary OM in the coastal waters is mainly from terrestrial sources while that in the outer seas is dominantly from marine sources. The spatial distribution patterns and correlation analyses suggest mainly marine sources for the BHT-isomer in the ECS. Thus, although the co-eluted BHT-x and BHT-34R cannot be distinguished, the BHT-isomer in the ECS may be mainly BHT-x derived from marine bacteria rather than BHT-34R derived from terrestrial bacteria. Zones with high value of BHT-isomer ratios in sediments were consistent with the seasonal hypoxic zones in the ECS; furthermore, these ratios were negatively correlated with dissolved oxygen concentrations in the bottom waters. These results indicate that hypoxic environments are beneficial to BHT-isomer production, further confirming that the BHT-isomer can be a biomarker for marine hypoxia. Aminotetrol and aminopentol were closely related to the aerobic methane-oxidation gene pmoA and dissolved CH4, suggesting their potential as markers for aerobic methane oxidation.

Enhanced terrestrial runoff during Oceanic Anoxic Event 2 on the North Carolina Coastal Plain, USA

Abstract. A global increase in the strength of the hydrologic cycle drove an increase in the flux of terrigenous sediments into the ocean during the Cenomanian–Turonian Oceanic Anoxic Event 2 (OAE2) and was an important mechanism driving nutrient enrichment and thus organic carbon burial. This global change is primarily known from isotopic records, but global average data do not tell us anything about changes at any particular location. Reconstructions of local terrigenous flux can help us understand the role of regional shifts in precipitation in driving these global trends. The proto-North Atlantic basin was one of the epicenters of enhanced organic carbon burial during OAE2, so constraining terrigenous flux is particularly important in this region; however, few local records exist. Here, we present two new OAE2 records from the Atlantic Coastal Plain of North Carolina, USA, recognized with calcareous nannoplankton biostratigraphy and organic carbon isotopes. We use carbon / nitrogen ratios to constrain the relative contribution of marine and terrestrial organic matter; in both cores we find an elevated contribution from vascular plants beginning just before OAE2 and continuing through the event, indicating a locally strengthened hydrologic cycle. Terrigenous flux decreased during the brief change in carbon isotope values known as the Plenus carbon isotope excursion; it then increased and remained elevated through the latter part of OAE2. Total organic carbon (TOC) values reveal relatively low organic carbon burial in the inner shelf, in contrast to black shales known from the open ocean. Organic carbon content on the shelf appears to increase in the offshore direction, highlighting the need for cores from the middle and outer shelf.

Pore structure and sorption capacity investigations of Ediacaran and Lower Silurian gas shales from the Upper Yangtze platform, China

The shale gas potential of Ediacaran and Lower Silurian shales from the Upper Yangtze platform is assessed in this study with a focus on the contributions of clay minerals and organic matter to sorption capacity. For this purpose, a multidisciplinary assessment was carried out using petrophysical, mineralogical, petrographic and geochemical methods. In terms of TOC contents (4.2%), brittle mineral contents (68.6%) and maximum gas storage capacities (0.054–0.251 mmol/g) Ediacaran shales from this study show comparable properties to other producing shale gas systems although the thermal maturity is extremely high (VRr = 3.6%). When compared to lower Silurian shales from the same region, it is evident that (1) deeper maximum burial and (2) a lack of silica-associated preservation of the pores resulted in a relatively lower mesopore volume, higher micropore volume fraction and lower overall porosity (Ediacaran shales: 1.4–4.6%; Silurian shales: 6.2–7.4%). Gas production is therefore retarded by poor interconnectivity of the pore system, which was qualitatively demonstrated by comparing experimental gas uptake kinetics. TOC content exhibits a prominent control on sorption capacity and micropore volume for both shales. However, different contributions of clay minerals to sorption capacity were identified. This can partly be attributed to different clay types but is likely also related to burial-induced recrystallisation and different origins of illite. Additionally, it was shown that variations in sorption capacity due to incorrect estimates of clay mineral contribution are in the same range as variations due to differences in thermal maturity.Article highlightsPore structure and gas storage characteristics are evaluated for the first time for Ediacaran Shales from the Upper Yangtze platformDue to a lower free gas storage capacity and diffusivity, the Ediacaran shale can be regarded as a less favorable shale gas prospect when compared to the Silurian shaleClay mineral contribution to sorption capacity is evaluated taking clay mineralogy into considerationMaturity-related changes of organic matter sorption capacity have been discussed on the basis of a compiled data set

Adaptive monitoring approach to assess dissolved organic matter dynamics during rainfall events.

Rainfall events induce water quality transformation in river systems influenced by the watershed land use and hydrology dynamics. In this context, an adaptive monitoring approach (AMA) is used to assess non-point sources (NPS) of pollution events, through dissolved organic matter (DOM) contribution. The case study is a monitoring site in a semi-urban watershed characterized by NPS contribution. An integrated quali-quantitative method for DOM based on dissolved organic carbon (DOC) content, spectroscopic techniques of excitation-emission fluorescence (EEF), and UV-visible absorbance is proposed. The results indicate a mix of allochthonous and autochthonous DOM characteristics from NPS sources associated to vegetation area influence (A285/DOC of 15.43 L (g cm)-1 and SUVA254 of 2.11 L (mg m)-1). The EEF signals showed more humic-like than protein-like characteristics with peaks A and C (approximately 5.72 r.u.) more intense than peaks B, T1, and T2 (approximately 4.33 r.u.), indicating NPS from the soil leachate. The absorbance ratio values indicate a mix of organic compounds with greater proportion of refractory characteristics with high aromaticity and molecular weight (approximately A300/A400 of 4.15 and A250/A365 of 4.48), associated with the surface wash-off of accumulated residual and subsurface soil erosion, which contribute to complex organic matter structures. The fluorescence indexes, overall, indicated allochthonous sources with intermediate humic characteristics (FI ≈ 1.43, BIX ≈ 0.65, and HIX ≈ 7.98). The proposed integrated optical property strategy represents an opportunity for better understanding of DOM dynamic assessment for identifying potential mitigation techniques for organic pollution control and improving water quality conditions.

Unraveling sedimentary precursors and metal enrichment of high-grade metamorphosed manganese-rich rocks from the Borborema Province, northeastern Brazil

The Paleoproterozoic Lagoa do Riacho manganese deposit in the Borborema Province is central to unravelling the genesis of Paleoproterozoic manganese deposits, Paleoproterozoic redox evolution and genetic relationship to the West African Craton. With manganese contents averaging 35 wt%, the Lagoa do Riacho manganese unit is lithologically subdivided into oxidized and silicate manganese ores and a garnetite (garnet-rich rocks) subgroup. The oxidized manganese ore consists mainly of pyrolusite, manganese-oxyhydroxide and spessartine. The silicate manganese ore has rhodonite, tephroite and spessartine. Garnetite contains spessartine and minor quartz and rhodonite. The main host rocks include garnet quartzite and graphite-bearing pelitic gneiss. The composition of carbonate inclusions in spessartine-rhodonite and Ca-Mn fractionation between garnet core and rim suggests all these manganese-rich rocks probably formed from protoliths of marl composition. Biogenic, syn-sedimentary graphite in the manganese-rich rocks and their host rocks indicates organic matter was deposited along with the marl protolith. Within this general context and through chemical-petrological relations, we outline an initial environment involving anoxic sediments' deposition (eg., organic matter-rich manganese marl and black shales, and wackes) on the seafloor. The presence of spessartine, rhodonite, and tephroite suggests peak metamorphic conditions reached amphibolite facies conditions (6–7 kbars and 550–700 °C). Amphiboles indicate later retrograde stages and carbonate veins suggest a possible hydrothermal stage after manganese deposition. The metamorphosed manganese-rich rocks were upgraded to medium-grade manganese ores during exposure to surface water. Our results indicated that the manganese-rich rocks and their host rocks were generated in a sedimentary context, possibly in a marine setting with carbonate and organic matter contribution.

Effect of decomposition products produced in the presence or absence of epigeic earthworms and minerals on soil carbon stabilization

Microbial use efficiency is thought to greatly influence organic carbon storage in soils through the formation of decomposition products and their stabilization as organo-mineral complexes. Earthworm activity may play a significant role in these processes. Of the three ecological earthworm groups only two (endogeic and anecic species) are thought to be involved in soil organic carbon (SOC) stabilization as they are living in mineral soil. The aim of this study was to investigate the role of decomposition products produced, with and without minerals, by epigeic earthworms living at the litter-soil interphase for carbon stabilization. We investigated the impact of eight different types of decomposition products on CO2 emissions, microbial biomass, watersoluble C, mineral N and SOC pool allocation of an arenic cambisol during 79 days under laboratory conditions.Our results indicated that the nature of decomposition products affected their impact on SOC mineralization and soil physico-chemical parameters. In general, the presence of epigeic earthworms during OM decomposition decreased CO2 emissions after soil addition of decomposition products and increased microbial carbon use efficiency when compared to those produced without earthworms. Mineral-containing decomposition products increased CO2 emissions after their addition to soil when compared to their mineral free counterparts. They also changed carbon allocation to physico-chemically protected pools, decreasing the contribution of particulate organic matter when compared to mineral free decomposition products. Extrapolation of the data showed that these short-term effects were not necessarily long-term in nature, but they also indicated that microbial products produced in the presence of epigeic earthworms and minerals may increase SOC sequestration in the amended soil. We therefore conclude that the nature of decomposition products is crucial for their fate in soil and that in contrast to the general paradigm, epigeic earthworms could have an important role to play in SOC sequestration through the formation of material susceptible to be protected, when incorporated into mineral soil.

Spatial–temporal variations in riverine carbon strongly influenced by local hydrological events in an alpine catchment

Abstract. Headwater streams drain >70 % of global land areas but are poorly monitored compared with large rivers. The small size and low water buffering capacity of headwater streams may result in a high sensitivity to local hydrological alterations and different carbon transport patterns from large rivers. Furthermore, alpine headwater streams on the “Asian water tower”, i.e., Qinghai–Tibetan Plateau, are heavily affected by thawing of frozen soils in spring as well as monsoonal precipitation in summer, which may present contrasting spatial–temporal variations in carbon transport compared to tropical and temperate streams and strongly influence the export of carbon locked in seasonally frozen soils. To illustrate the unique hydro-biogeochemistry of riverine carbon in Qinghai–Tibetan headwater streams, here we carry out a benchmark investigation on the riverine carbon transport in the Shaliu River (a small alpine river integrating headwater streams) based on annual flux monitoring, sampling at a high spatial resolution in two different seasons and hydrological event monitoring. We show that riverine carbon fluxes in the Shaliu River were dominated by dissolved inorganic carbon, peaking in the summer due to high discharge brought by the monsoon. Combining seasonal sampling along the river and monitoring of soil–river carbon transfer during spring thaw, we also show that both dissolved and particulate forms of riverine carbon increased downstream in the pre-monsoon season due to increasing contribution of organic matter derived from thawed soils along the river. By comparison, riverine carbon fluctuated in the summer, likely associated with sporadic inputs of organic matter supplied by local precipitation events during the monsoon season. Furthermore, using lignin phenol analysis for both riverine organic matter and soils in the basin, we show that the higher acid-to-aldehyde (Ad/Al) ratios of riverine lignin in the monsoon season reflect a larger contribution of topsoil likely via increased surface runoff compared with the pre-monsoon season when soil leachate lignin Ad/Al ratios were closer to those in the subsoil than topsoil solutions. Overall, these findings highlight the unique patterns and strong links of carbon transport in alpine headwater catchments with local hydrological events. Given the projected climate warming on the Qinghai–Tibetan Plateau, thawing of frozen soils and alterations of precipitation regimes may significantly influence the alpine headwater carbon transport, with critical effects on the biogeochemical cycles of the downstream rivers. The alpine headwater catchments may also be utilized as sentinels for climate-induced changes in the hydrological pathways and/or biogeochemistry of the small basin.

Contrasting lipid biomarkers in mountain rivers in the Nepal Himalayas: Organic matter characteristics and contribution to the fluvial carbon pool

The Nepal Himalayas is the source of many glacial and spring-fed river systems crisscrossing the mountainous terrain. There is an increasing recognition of small mountain rivers (SMRs) to have a significant combined export of dissolved and particulate organic carbon to the global carbon flux. We analyzed fluvial sediments from two SMRs and compared the results with two large mountain rivers (LMRs) in Nepal. We investigated the organic matter (OM), its compositional variability, and seasonal export using a suite of lipid biomarkers, namely n-alkanes, n-alkanoic acids, n-alkanols, and sterols. The SMRs indicated a similarity in lipid distribution and were affected by a strong seasonal variability. The LMRs showed a distinct contrast in the distribution of lipids in suspended sediments. Bedload sediments in SMRs were derived from diverse sources with weak terrigenous dominance all-year-round compared to the suspended load. Functional lipids (n-alkanoic acids and n-alkanols) were the major constituents in SMR sediments, indicating better preservation. In contrast, n-alkane concentration dominated over other fractions in suspended sediments retrieved from LMRs. The biomarker trends differentiate SMRs from LMRs with lower transformed/degraded OM in SMRs. A common observation was the strong presence of even carbon compounds in short-chain n-alkanes in SMR bedload sediments and their predominance in suspended sediments in LMRs. Such an unusual trend is attributed to specific biomarker sources from the catchment and ongoing processes in fluvial systems. Topsoil colonized by fungal species under moist acidic conditions and autochthonous bacteria contributes to the organic matter pool in shallow SMRs. In LMRs, the contribution from thermally mature sedimentary hydrocarbons and the diagenetic reduction of n-alkanoic acids to n-alkanes are additional contributors to the allochthonous carbon pool. The differences in lipid concentrations, their distribution, seasonality, and the size of rivers suggest differential preservation/degradation of the organic matter pool and their importance in contributing to the carbon budget.

Arctic lagoon and nearshore food webs: Relative contributions of terrestrial organic matter, phytoplankton, and phytobenthos vary with consumer foraging dynamics

Characterizing energy flow and trophic linkages is fundamental to understanding the functioning and resilience of Arctic ecosystems under increasing pressure from climate change and anthropogenic exploitation. We used carbon and nitrogen stable isotopes to examine trophic dynamics and the relative contribution of terrestrial organic matter, water column phytoplankton, and phytobenthos (benthic micro- and macro-autotrophs as well as sea ice algae) to the food webs supporting 45 macroconsumers in three Arctic coastal lagoon ecosystems (Krusenstern, Sisualik, Akulaaq) and the adjacent Kotzebue Sound with varying degrees of connectivity in Cape Krusenstern National Monument, Alaska. A two-source (water column particulate organic matter and benthic sediment organic matter), two-isotope trophic dynamics model informed by a Bayesian isotope mixing model revealed that the Lagoon-Kotzebue Sound coastal ecosystem supported consumers along a trophic position continuum from primary consumers, including amphipods, copepods, and clams to trophic level five predators, such as seastars, piscivorous fishes, seals, and seabirds. The relative contribution of the three primary producer end members, terrestrial organic matter (41 ± 21%), phytoplankton (25 ± 21%), and phytobenthos (34 ± 23%) varied as a function of: 1) consumer foraging ecology and 2) consumer location. Suspension feeders received most of their carbon from food webs based on phytoplankton (49 ± 11%) and terrestrial organic matter (23 ± 5%), whereas herbivores and detritivores received the majority of their carbon from phytobenthos-based food webs, 58 ± 10% and 60 ± 8%, respectively. Omnivores and predators showed more even distributions of resource reliance and greater overall variance among species. Within the invertebrates, the importance of terrestrial organic matter decreased and phytobenthos increased with increasing trophic position. The importance of terrestrial organic matter contribution increased with lagoon proximity to major rivers inputs and isolation from Kotzebue Sound. Several taxa with cultural and subsistence food importance to local communities showed significant reliance (30–90% of baseline carbon) on food chains linked to fresh terrestrial organic matter. Our study indicates that terrestrial-marine linkages are important to the function of Arctic coastal lagoon ecosystems and artisanal fisheries. These linkages are likely to strengthen in the future with regional changes in erosion and runoff associated with climate change and anthropogenic disturbance.

Biomarker and Carbon Isotopic Evidence of Marine Incursions in the Himalayan Foreland Basin During Its Overfilled Stage

AbstractThe final stages of evolution of the Himalayan foreland basin (HFB) are preserved in the Siwalik Group of rocks deposited by meandering and/or braided rivers in the western and central regions of HFB. However, the time‐equivalent deposits in the eastern part of the foreland provide contradictory evidence of both terrestrial and marine environments. To address the ambiguity, molecular level characterization and stable isotopic composition of organic matter (OM) have been employed in the late Miocene‐Pliocene sequence of the eastern HFB. The n‐alkane distribution, carbon isotopic (δ13C) signature of n‐alkanes and distribution of hopane and sterane isomers suggest OM contributions from both marine and terrestrial sources during the late Miocene period. Increase in short‐chain n‐alkane abundance and gammacerane index, low pristane/phytane ratio, higher δ13C values, higher regular sterane/17α‐hopane, C31R/C30‐hopane and C27/C29 steranes ratios and presence of C30 sterane provides substantial evidence of stratified anoxic conditions and marine influences at specific stratigraphic intervals. During the late Miocene period, mixing of marine OM sources with terrestrial sources argue for marginal marine depositional conditions amid fluvial‐dominating environments. The entry of marine waters in the eastern HFB through the pre‐existing cratonic troughs possibly resulted from eustatic or relative sea‐level rise. No further evidence of marine incursions is observed in the younger Pliocene sediments. The higher detrital influx from the rising Himalayas, the onset of Northern Hemisphere Glaciation and evolution of physical barriers such as Shillong Massifs and Barind Tracts altogether led to the cessation of marine incursions into the HFB.

Carbon and nitrogen isotopic compositions of particulate organic matter in the upwelling zone off the east coast of Hainan Island, China

The isotopic compositions (δ13C and δ15N) and C/N ratios of suspended particulate organic matter (POM) were investigated off the east coast of Hainan Island in the South China Sea during summer. Coastal upwelling influenced the nearshore stations of transects S2 and S3, and higher δ13C and δ15N values suggested that coastal upwelling played a significant role in determining the POM sources. The POM at the nearshore area of transect S1 was controlled by the coastal current and freshwater discharge. Additionally, organic matter may be transported to the offshore area via tidal movements in transects S1 and S3. Based on the stable isotope analysis in an R model, the marine organic matter contribution in the upwelling area (19%) was higher than that in the other areas (transect S1 and the offshore area) (7%). The δ13C and δ15N values and C/N ratios reflect the carbon and nitrogen sources and their cycling in the upwelling zone off the east coast of Hainan Island.

Enhanced terrestrial organic matter burial in the marine shales of Yangtze platform during the early Carboniferous interglacial interval

The supply and preservation of terrestrial organic matter (TOM) during early Carboniferous glacial-interglacial intervals in South China were investigated with respect to their roles in paleo-environmental variation and organic matter (OM) accumulation in black shales. The marine redox proxies such as V/Cr, Corg/P ratios, and Mo–U covariation indicate a fully oxic water condition during the earliest Visean, while dominant oxic with occasional suboxic water conditions prevailed during the early to middle Visean. High sedimentary δ15N values (1.9–6.3‰) suggest the existence of enhanced water-column denitrification in the expanded oxygen minimum zones (OMZs) during the earliest Visean, whereas lower δ15N values (avg. 2.6‰) during the early to middle Visean indicate a decreasing water column denitrification in the reduced OMZs. Both the organic matter compositions and the relationship between Corg/N ratios and δ13Corg values indicate a significant contribution of terrestrial OM in the marine sediments, and the low abundance of marine OM is mainly attributed to the low paleoproductivity as evidenced by low P/Ti and Ba/Al ratios. One reason for such a high contribution of TOM is that a large amount of plant debris and wildfire-derived OM was preserved during Tournaisian glacier time and then released and buried rapidly in the marine sediments during the interglacial interval of Visean due to the temperature-driven glacial melting. The rapid transportation of large quantity of TOM from land to ocean may have resulted in remarkable drawdown of atmospheric pCO2 and subsequent cool climate, as evidenced by the decoupled relationship between δ13Corg and δ13Ccarb values. In summary, the sinking of TOM flux during the sea level lowstand and highstand may be the controlling factor for the paleo-environmental variation as well as OM accumulation in the Visean black shales.

Contribution of Particulate and Mineral-Associated Organic Matter to Potential Denitrification of Agricultural Soils

Water-extractable organic carbon (WEOC) is considered as the most important carbon (C) source for denitrifying organisms, but the contribution of individual organic matter (OM) fractions (i.e., particulate (POM) and mineral-associated (MOM)) to its release and, thus, to denitrification remains unresolved. Here we tested short-time effects of POM and MOM on potential denitrification and estimated the contribution of POM- and MOM-derived WEOC to denitrification and CO2 production of three agricultural topsoils. Suspensions of bulk soils with and without addition of soil-derived POM or MOM were incubated for 24 h under anoxic conditions. Acetylene inhibition was used to determine the potential denitrification and respective product ratio at constant nitrate supply. Normalized to added OC, effects of POM on CO2 production, total denitrification, and its product ratios were much stronger than those of MOM. While the addition of OM generally increased the (N2O + N2)-N/CO2-C ratio, the N2O/(N2O + N2) ratio changed differently depending on the soil. Gas emissions and the respective shares of initial WEOC were then used to estimate the contribution of POM and MOM-derived WEOC to total CO2, N2O, and N2O + N2 production. Water-extractable OC derived from POM accounted for 53–85% of total denitrification and WEOC released from MOM accounted for 15–47%. Total gas emissions from bulk soils were partly over- or underestimated, mainly due to nonproportional responses of denitrification to the addition of individual OM fractions. Our findings show that MOM plays a role in providing organic substrates during denitrification but is generally less dominant than POM. We conclude that the denitrification potential of soils is not predictable based on the C distribution over POM and MOM alone. Instead, the source strength of POM and MOM for WEOC plus the WEOC’s quality turned out as the most decisive determinants of potential denitrification.

Salud ambiental de playas rocosas en distintos partidos de la Provincia de Buenos Aires

Seas and oceans are impacted by multiple human activities such as urban spills, maritime transport and tourism, among others. These human-generated pressures are directly impacting marine ecosystems, generating pollution, loss of habitat or introduction of exotic species. The objective of this work was to evaluate the environmental health of different beaches belonging to four coastal districts of the Province of Buenos Aires: Necochea, General Alvarado, General Pueyrredón and Mar Chiquita. The study was approached from the variability in the community structure (richness, evenness and diversity), as well as characterizing this structure from the analysis of functional traits and functional diversity indexes (functional features and indexes of functional diversity: functional richness, functional evenness, functional divergence, functional dispersion, functional specialization and quadratic entropy) and environmental quality indexes (AMBI and M-AMBI) in response to different pollution scenarios due to anthropogenic impact (sewage effluent, streams, submarine outfall and beaches for recreational use with no contribution from other sources). Results showed that both the structure and composition of the species assemblage varied significantly between sites. The AMBI and M-AMBI index reflected good environmental health at all beaches, categorizing all sites as ‘good’ (or slightly disturbed), except Quequén site which was categorized as ‘poor’ (or heavily disturbed). This site also presented a composition of the assembly of functional features characteristic of areas that present contamination by organic matter (low relative mobility, deposit feeders, tubular and/or gallery inhabitants and 1st order opportunistic species). The traditional approach reflected the differences in the community structure of the different beaches and the functional approach complemented this result by showing that the functional traits covered by the different species of the benthic communities are mainly related to the contribution of organic matter that each beach receives (streams, rainwater, effluents or submarine emissaries).

Distribution of Steranes and Triterpanes Biomarkersas Indication of Depositional Environment and Maturity of Sargelu and Kurrachine Formations in Different Wells Northern Iraq

Eight cuttings samples were obtained from Sargelu and Kurrachine formations in different wells at different depths to detect steranes and triterpanes biomarkers as an indicator of the depositional environments and thermal maturity of organic matter. This was accomplished using GC-MS technology. The diasterane/sterane ratio showed low ratios in analyzed samples (BJS2, JKS3, BJK1, JKK4, JKK7) as in most marine carbonate sources, while algal-bacterial organic matter contribution for the samples analyzed based on the predominance of C23 tricyclic relative to the C19 tricyclic terpene and the C23 tricyclic greater than C24 tricyclic terpane. The Gammacerane index indicated that normal salinity conditions during depositions. The biomarkers related to maturation such as diasterane/sterane, Ts/(Ts+Tm), and C29Ts/C29 hopane show that the organic matter in Ain Zalah well (Sargelu Formation) is within early mature (oil window).