Composition Of Sedimentary Organic Matter Research Articles

Late-Holocene paleoreconstruction of the Southwestern Atlantic Ocean: A multiproxy understanding of the paleoclimatic, paleoproductivity and paleotemperature variability

A multiproxy evaluation focusing on sedimentological, molecular, and isotopic proxies was used to reconstruct the environmental changes on the SW Atlantic Ocean margin enabling an integrated assessment of this basin’s Late-Holocene oceanographic and climatic dynamics. Variations in paleoproductivity, climate, and sea surface temperature (SST) indicate three phases throughout the core. The first phase (2800–1600 cal yr BP) showed a generally low marine and terrigenous organic matter input, marked by terrigenous material input pulses transported by the Brazil Current (BC) from small rivers of the South Brazil Bight (SBB) and/or Paraiba do Sul River. The second interval (1600–1300 cal yr BP) registered the lowest levels of fine sediments, total organic carbon content, and concentrations of all analyzed lipid biomarkers, indicating the occurrence of a semi-stationary meander of the BC that hindered the sedimentation of fine sediments. This phase may indicate a varied timing and duration due to the sparsed radiocarbon data. The third interval (1300 cal yr BP to modern years) presented the highest levels of marine and terrigenous proxies and were influenced by the strengthening of the South America Monson System (SAMS), the El Niño Southern Oscillation (ENSO) events, and the NE winds, which caused higher precipitation in the La Plata River drainage basin. A northward displacement of the Brazil Coastal Current (BCC) and the transport of the Plata Plume Water (PPW) to the central regions of the SBB, as well as the occurrence of more regular upwelling events may also influence the sedimentary organic matter composition. SST showed a variation up to ~3.2°C through the core and was related to the influence of the BC current associated with the Tropical Water (TW) and the South Atlantic Central Water (SACW), and the PPW influence on the shelf.

Characterization of sediment organic matter in the outer Yangtze River Estuary using stable isotopes, optical techniques, and FT-ICR-MS: Implications for the carbon burial mechanism

The burial of sediment organic matter (SOM) in the estuary and shelf plays an important role in the global carbon cycle. However, it is challenging to determine the source, composition, and burial of SOM in the coastal sea, especially at the molecular level. This was explored in the coastal area outside the largest Yangtze River of China with multiple techniques including elemental and stable isotopic analysis, absorption spectroscopy, fluorescence excitation-emission matrices coupled with parallel factor analysis (EEMs-PARAFAC), and ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). The end-member mixing analysis based on δ13C and δ15N showed a dominance of marine contribution (up to 70%) at most stations while the terrestrial contribution increased to >55% nearshore in summer at a high fluvial sediment flux. This was consistent with the offshore decreasing humic-like C1 and C2, humification index (HIX), %lignin-like compounds, and %CHO but increasing tryptophan-like C3, biological index (BIX), %protein-like compounds, and %CHOS from EEMs-PARAFAC and FT-ICR-MS analysis. The %clay correlated positively with SOM content, HIX, %lignin-like compounds, O/C, and modified aromaticity index (AImod) but correlated negatively with %C3, H/C, and the relative abundance of labile formulas (MLBL), while %silt showed contrasting correlations. These results indicated the fine clay sediments adsorbed more humified, aromatic, oxygenated, and terrestrial compounds that were probably more resistant to biodegradation and thus had a higher burial efficiency than those on the silty sediments. Principal component analysis based on SOM indices further revealed different characteristics of SOM in the nearshore, northern offshore, and southern offshore regions, which were probably dependent on the delivery by local current systems. Overall, these findings contributed to unraveling the source and molecular composition of SOM associated with different grain size sediments and local current delivery, which are fundamental for understanding the factors underlying carbon burial in the complex coastal environment.

The increasing influence of oyster farming on sedimentary organic matter in a semi-closed subtropical bay

Oyster farming activities play a pivotal role in the biogeochemical cycles of coastal marine ecosystems, particularly in terms of sedimentary carbon cycling. To gain deep insights into the influence of expanding oyster culture on the sedimentary carbon cycle, surface sediments were collected from the Maowei Sea, which is the largest oyster farming bay in south China, based on six filed surveys between July 2010 and December 2022. The sediment samples were analyzed for total organic carbon (TOC), total nitrogen (TN), stable carbon and nitrogen isotopes (δ13C and δ15N) to evaluate the inter-annual variations in the source contribution to sedimentary organic matter (SOM). The results revealed that the average contents of sedimentary TOC and TN were 0.67 ± 0.41 % and 0.06 ± 0.03 %, respectively. Fluctuations in the C/N molar ratios ranged from 5.8 to 23.6, with an average of 12.6 ± 2.9, indicating a significant terrestrial input contribution to SOM in the study area. Furthermore, the integration of stable isotope analysis and Bayesian mixing model demonstrated a gradual increase in the mean proportion of shellfish biodeposition to SOM, from 12.0 ± 5.6 % in July 2010 to 21.1 ± 7.3 % in December 2022, consistent with the progressive expansion of oyster aquaculture along this coastal area, thereby emphasizing the substantial influence of oyster farming on SOM composition. With the anticipated expansion of oyster farming scale and production in the future, shellfish biodeposition is expected to assume a more important role in shaping SOM dynamics and sedimentary organic carbon cycling in coastal waters. Overall, this study provided an important perspective for better assessing the impact of expanding mariculture scale on coastal biogeochemical cycles, thereby making valuable contributions to future policy formulation concerning mariculture and ecological conservation.

Fatty acids and stable isotopes distribution in the mangrove dominated Parnaíba River Delta

Characterizing the origin and quality of the organic matter (OM) present in estuaries, as well as its export toward the ocean, is a key issue to better understanding the carbon cycle and its impact on global change. In this study, fatty acid markers and δ13C and δ15N values were used to characterize the particulate and sedimentary organic matter composition in the large mangrove-dominated Parnaíba Delta, known as a large reservoir of blue carbon. The presence of some long-chain fatty acids and other mangrove OM markers, such as the 18:2ω6 and 18:3ω3, indicated that the material produced in mangroves contributed largely to the particulate organic matter of water and sediments of the delta. Their presence in further oceanic stations also reveals the mangrove material is exported to the adjacent coastal ocean. In the main river channel, the higher contribution of 18:2ω6 in the sediments than in the mangrove regions, indicated an additional source related to anthropogenic activities, probably agriculture. The branched fatty acids found in the samples point to the presence of bacteria and indicated the intense modifications of the organic matter in the region, reflecting the heterotrophic nature of the delta. In addition, the predominance of saturated fatty acids in the delta suggests that the organic matter exported to the coastal ocean is dominated by detrital material.

Characterization of biotic and abiotic signatures of modern lake sediments of western India, and its palaeo-environmental implications

A multi-proxy study of biotic and abiotic components was conducted on surface sediment samples from six lakes/wetlands located along the western transitional boundary of the contemporary Indian Summer Monsoon (ISM) in the Indian Subcontinent. The primary goal is to assess the suitability of various proxies as representatives of modern vegetation, environmental and climatic conditions. The collected data indicate significant variations in the composition and density of pollen in response to climate-induced and anthropogenic ecological changes throughout the northwest India transect. The palynological studies from eastern Rajasthan shows high forest elements in comparison to western Haryana and western Uttar Pradesh. In addition, the palynological data was juxtaposed with other biotic proxies such as diatom and isotopic studies, along with geochemical proxies and paleomagnetic data of the surface lake sediments. The presence of marker pollen taxa including Cerealia type Poaceae, Chenopodiaceae, and Brassicaceae, allows for distinct recognition of anthropogenic activities throughout the whole transect. The diversity and distribution of diatoms also support the palynological data in response to climate-induced and anthropogenic ecological changes. Furthermore, grain size, geochemistry (TOC/TN ratio with stable carbon isotope), and magnetic susceptibility data offer crucial insights about the sediment's depositional settings and general mineralogical composition. Stable carbon isotope data shows C3 dominance in relatively humid areas and C4 dominance in semi-arid areas, suggesting climate-driven control over sediment organic matter composition. Canonical correspondence analysis (CCA) indicates that biotic variables (pollen, diatom, stable isotopic composition) are significantly controlled by modern precipitation and temperature. Redundancy analysis reveals a significant influence of current average temperature and precipitation on major element oxide variations in surface lake sediments. Therefore, we propose using palynological, stable carbon isotope, diatom data, along with grain size, environmental magnetism, and geochemistry, to establish a multiproxy modern analogue for quantitative palaeoclimatic reconstructions. As a result, this study provides the first modern analogues from a climate-sensitive region that separates the area under ISM influence from an area with meager precipitation in western India.

Sedimentary organic matter applied to paleoenvironmental reconstruction of the Devonian of the Paraná Basin, SW Gondwana

The study of sedimentary organic matter (SOM) is essential for understanding paleoenvironmental conditions and depositional settings of geological formations. This paper explores the Devonian strata of the Paraná Basin, utilizing SOM analysis to reconstruct paleoenvironments and identify global events. The Devonian period is notable for significant geological and biological changes, including mass extinctions and extensive organic-rich sediment deposition. By examining the composition, distribution, and diagenesis of SOM in this region, we aim to elucidate the paleoenvironmental dynamics and depositional history. The Devonian outcrops in the state of Mato Grosso do Sul, Brazil rocks reveal distinct depositional characteristics, when compared to those found on the eastern border of the basin. The palynofacies analysis was conducted on 59 samples from four outcrops (MS-26, MS-29, MS-30 and MS-70), which age spans from Pragian to Givetian. The main groups and subgroups of the SOM were identified: amorphous organic matter (AOM) (“amorphous organic matter” and pseudoamorphous), phytoclasts (opaques, non-opaque-non biostructured, cuticles, membranes and Spongiophyton) and palynomorphs (spores, freshwater algae, scolecodonts, chitinozoan and acritarchs). The SOM was grouped into three palynofacies associations: opaques, land-derived and marine+AOM. In the Pragian—Emsian interval (MS-26, MS-29 and MS-30), a prevalent occurrence of phytoclasts and marine microphytoplankton is noted, with their distribution exhibiting distinct alternations in each section suggesting a deposition in the marine environment ranging from onshore to offshore. In the Givetian (MS-70 outcrop), we detected a progressive increase and diversification of marine elements (e.g., acritarchs), indicating a transgressive phase probably related with the Kačák event.

Long-term dynamics of organic matter inputs in sediments of Lake Balkhash, arid Central Asia: Coupled climate and anthropogenic influences

Lake sediments as reservoirs of organic matter (OM) play crucial roles in the carbon burial and carbon cycle on the regional and global scales. However, the long-term history and patterns of sedimentary organic matter (SOM) inputs from various sources and its response to multiple drivers are not well constrained. Here, we demonstrated variations in the source and composition of SOM and the potential regulating factors using the multi-biomarker (n-alkanes, fatty acids, and alcohols) signatures in a core span the last ∼ 250 years from Lake Balkhash. The highest Paq (proportions of aquatic macrophytes) and relatively low short-chain lipid contents in sediments before 1860 CE indicate the dominant OM inputs from aquatic macrophytes and minor inputs from microalgae. This can be attributed to the humid conditions during the late Little Ice Age (LIA). The decreased Paq and the highest CPIH (carbon preference index for high molecular weight) in sediments deposited in 1860 ∼ 1930 CE revealed considerably elevated OM inputs from emergent plants coeval with declined aquatic macrophytes contributions. This pattern of OM inputs was likely caused by large variables of water levels during the climate transition period, promoting the growth of emergent plants and inhibited aquatic macrophytes. In sediments from 1930 ∼ 2016 CE, much higher terrestrial OM inputs and prevailing microalgal OM inputs were reflected by the highest principal components of each source, whereas the lowest Paq indicates minimal OM inputs from aquatic macrophytes. These changes were probably caused by intensification of anthropogenic perturbations, e.g., land reclamation, promoting more terrestrial OM and nutrients transported into the lake. These findings suggested that SOM inputs are highly linked to lake environmental changes and can be profoundly influenced by climate variability and anthropogenic activities, which provides insights into patterns of carbon burial and carbon cycle in lake-catchment systems in arid regions.

Impacts of temperature and fluid seepage on organic matter composition in sediments of an active hydrothermal basin

Marine sediments are one of the largest organic carbon (OC) sinks on Earth. Yet, major knowledge gaps remain in our understanding of sedimentary OC cycling, particularly regarding temperature-induced alteration processes of OC from different sources. Here, we investigate OC-rich sediments of Guaymas Basin (Gulf of California) across two hydrothermal areas, one with only conductive geothermal heating and the other additionally experiencing seepage of hydrocarbon-rich fluids from deeper layers. We use Pyrolysis-Gas Chromatography/Mass Spectrometry (Py-GC/MS) to investigate diagenetic OC changes and show that cold control sites in both hydrothermal areas are dominated by similar contributions of lipid-derived compounds, nitrogenous (likely protein-derived) compounds, carbohydrates, and polyaromatic hydrocarbons (PAHs). These OC compound groups are largely derived from phytoplankton detritus from overlying water. Conductively heated sediments, which reach in situ temperatures of ∼ 80 °C, have similar general OC compositions and contents to these cold sites, but show evidence of diagenetic modifications of individual carbohydrate groups in deeper layers. By contrast, strong decreases in carbohydrate and nitrogenous compound abundances at the seep sites indicate that these compound groups are not only modified but also selectively degraded at the higher temperatures (>80 °C) of these sites. Increases in pyrolysis products of PAHs, prist-1-ene, and alkanes with depth, moreover, show that import of OC by deep hydrothermal fluids contributes significantly to sedimentary OC pools mainly in deeper layers of these sites. Our study provides the first comprehensive analysis of major OC compound groups in Guaymas Basin sediment and indicates that the supply of OC by hydrothermal fluid flow only has minor impacts on particulate organic matter compositions at the seafloor, even at active seep sites. We furthermore show that temperatures up to ∼ 80 °C already result in thermochemical modifications of organic matter (OM) that are potentially linked to the onset of kerogen formation. The sequence and time scales of chemical modifications and activations in relation to temperature are an important subject for future investigations.

Organic matter composition in sediments recording sea surface phytoplankton community structure in Prydz Bay of Antarctica

The coastal zones in Antarctica play an important role in the polar carbon cycle through the efficiency of the biological pump. In this study, Prydz Bay in East Antarctica was selected to investigate factors controlling organic matter composition in sediments using source-dependent biomarkers. The results show that fatty acids are the most abundant biomarkers in sediments, followed by sterols, fatty alcohols, and alkanes. Although microalgae are well known to be the main source of sedimentary organic matter in Prydz Bay, the distribution of low molecular weight branched alkanes and alkenes with an even–odd predominance suggest the importance of bacteria during organic matter transformation, and its contribution to sedimentary organic matter. High concentrations of highly branched isoprenoid alkenes (HBIs) with a distinctive enriched 13C signature indicate substantial inputs of ice algae to sediments. Principal component analysis of source-dependent biomarkers reveals that the spatial heterogeneity of organic composition in sediments of Prydz Bay is mainly controlled by the distribution of sea surface phytoplankton community in different geographical zones. Redundancy analysis demonstrates that seasonal sea-ice cover is the main driver for blooms of distinctive algae in each geographical zone as a result of spatial succession of the phytoplankton community. The result clearly exhibits that, at least in Prydz Bay, spatial succession of the sea surface phytoplankton community in austral summer can be recorded in sediments, suggesting that a high-resolution sediment record of source-dependent biomarkers can be used to reconstruct the evolution of sea surface phytoplankton community structure during geological history in Antarctic coastal zones.

Composition and distribution of sedimentary organic matter in nearshore Berriasian strata (‘German Wealden’) of the eastern Lower Saxony Basin, NW Germany

Abstract In the Lower Saxony Basin of Northern Germany, the Earliest Cretaceous (Berriasian, ‘German Wealden’) is represented by organic-rich shales assigned to the Isterberg Formation, which have been deposited under brackish-lacustrine conditions in a partially restricted basin. Towards the southern basin margin, these shales interfinger with nearshore sandstones sourced from the Deister-Hils delta. In order to better understand the environmental conditions and depositional dynamics of the Isterberg Fm, the sedimentary organic matter has been studied with a combined approach including bulk rock organic geochemistry and palynofacies analysis. The lower part (W 1 to W 3) is interpreted to reflect very shallow-water conditions and episodic emergence, indicated by multiple occurrences of palaeosol horizons, rhizoliths and intercalated coal beds formed within a mud-dominated and protected domain of the delta plain. The overlying sand-rich interval represents a nearshore deltaic setting. A distinct change is observed in the upper part (W 4), indicating more distal conditions characterized by clay-dominated sedimentation, abundant lumachelle interbeds and a predominance of aquatic-derived organic matter. The newly acquired data fill a gap in the record between the proximal and distal strata of the Berriasian Lower Saxony Basin and provide new insights into the accumulation and preservation of organic matter within this exceptional depositional setting.

Holocene organic matter composition in relation to relative sea level stands and associated morphometric changes of a lagoonal system

Garzón Lagoon is a temperate shallow coastal lagoon influenced by sea level variation. A study on the isotopic composition of Holocene sedimentary organic matter was performed. Although the system was subject to significant changes in sea level, leading to important changes in the lagoon morphometry during the Holocene, the composition of the organic matter was rather surprisingly constant, being dominated by particulate organic matter of marine origin, and to a lesser extent of terrestrial origin. By ∼5000 yr BP, the sea level was +5 m amsl, and the lagoon displayed the largest morphometric dimensions. Once the sea level decreased towards 3000 yr BP and present times, the lagoon area progressively decreased. Even though we inferred significant changes in morphometry, the composition of the organic matter remained relatively constant, as the lagoon was always connected to the ocean, a condition that remains today, at least intermittently during storms or heavy rains. Only after the 1960s, a slight change in the organic matter composition was detected, consisting of a decrease in particulate organic matter of terrestrial origin.

The Effects of Blanket Bog Erosion on Aquatic Macrophytes in an Irish Soft Water Lake

abstract: The Irish Roundstone bog area is characterised by its many oligotrophic soft water lakes surrounded by blanket bogs. These lakes are mainly dominated by isoetid vegetation, adapted to limited nutrient and carbon availability. Peat erosion from surrounding bogs may lead to organic matter accumulation in these lakes, which could increase nutrient availability and pose a threat to isoetid vegetation. Here, we determined whether three distinct vegetation groups (dominated by Lobelia dortmanna, Eriocaulon aquaticum or Juncus bulbosus ) in the Irish soft water lake Kankoge differed in sediment and (pore)water chemistry. Elemental composition of in-lake accumulated organic matter was compared with organic matter from blanket bogs to link peat erosion to differences in vegetation. Our results show that parts of the lake with accumulated organic matter had higher inorganic carbon and ammonium concentrations in the sediment pore water. These sites were mainly dominated by J. bulbosu s, amounting to plant biomass more than 20 times higher than sites with no or low organic matter accumulation and isoetid dominated vegetation. Eriocaulon aquaticum was present at all sites, even those with high sediment organic matter. By comparing elemental composition of sediment organic matter to the surrounding blanket bog, we show that in-lake organic matter accumulation likely resulted from peat erosion.

Changes in surface sediment carbon compositions in response to tropical seagrass meadow restoration

Seagrass meadows are declining at a global scale, threatening their capacity as blue carbon sinks. Restoration of seagrasses (via seagrass seeds or plant transplantation) may recover their carbon sequestration capacity. Previous studies have predominantly focused on sediment organic carbon (SOC), while variations in sediment carbon compositions remain poorly understood, limiting our comprehension of the influence of seagrass restoration on sediment carbon stability. Here, we researched the differences in surface (0–3 cm) sediment carbon compositions in response to tropical seagrass transplantation among species (Thalassia hemprichii and Enhalus acoroides); specifically, differences in labile, recalcitrant and refractory SOC, as well as sediment inorganic carbon (SIC) compositions variations under transplanted T. hemprichii and E. acoroides communities. It was found that seagrass transplantation enhanced suspended particle organic matter, and epiphyte and macroalgae input to surface sediment, which recovered the surface SOC concentration and stock rapidly to natural levels (increased ∼1.6-fold) within two years following transplantation. The elevated contribution of epiphyte and macroalgae significantly increased the surface labile sediment organic matter (SOM), but not the recalcitrant and refractory SOM composition after short-term transplantation. Meanwhile, surface SIC was significantly elevated, which might be mainly ascribed to allochthonous carbonate particle trapped under transplanted area with implications for carbon sequestration. The higher canopy and longer leaf seagrass species, E. acoroides, had elevated SOC, SIC and was more labile composition, compared to T. hemprichii transplant. Overall, this research suggests that tropical seagrass transplantation can increase the surface SOC, SIC concentration by increasing the labile organic matter and allochthonous carbonate particle input, respectively, with varying significantly among seagrass species.

High-resolution record of temporal change in organic matter burial over the past ∼8,600 years on the northwestern continental slope of the South China Sea

Sedimentary organic matter (SOM) on continental slopes in marine regions can sensitively record climatic and environmental changes. In this study, total organic carbon content (TOC), total nitrogen content (TN), and their stable isotope compositions (δ13C and δ15N) for sediments of core G02 were investigated (at ∼24.2-year resolution) to reveal the temporal variations in organic matter sources and the main controls on the sources and distribution of buried organic matter on the northwestern continental slope of the South China Sea over the last ∼8600 years. Results of a δ13C binary mixing model reveal that ∼82.3 ± 3% of SOM is derived from marine autochthonous sources. We suggest that the carbon and nitrogen contents and compositions of SOM are governed by distinct factors. The more positive δ15N values before the Pulleniatina Minimum Event occurrence are ascribed to stronger subsurface water intrusion by the Kuroshio Current, which led to enhanced subsurface denitrification and in turn counteracted the effect of mixing with surface water caused by the East Asian winter monsoon. Sedimentary δ13C values show a fluctuant decrease during ca. 8.6–3.0 cal kyr BP and a conspicuous increase during ca. 3.0–1.4 cal kyr BP. These changes are attributed to the decrease of marine productivity induced by the continuous weakening East Asian monsoon effect and the decrease of terrigenous organic carbon input induced by the weakened Indian summer monsoon precipitation, respectively. Since ca. 1.4 cal kyr BP, human activities have become the dominant factor in controlling the production and distribution of organic carbon. The results provide an important basis for understanding of source-sink processes of organic matter and the factors influencing these processes on continental slopes in low-latitude marginal seas.

Anthropogenically driven changes to organic matter input in sediments of Lake Chaohu, Eastern China, over the past 166 years

Characterizing how and to what extent human activities have influenced organic matter (OM) input in lake sediments is essential for a thorough study of the carbon cycle and carbon burial in lake systems, but this issue has not yet been addressed. Here, the source and composition of OM in sediments of Lake Chaohu, Eastern China, over the past 166 years, were determined by analyzing stratigraphic variations in aliphatic hydrocarbons and OM pyrolysis parameters in a dated sediment core. These data, coupled with documental records, were further used to elucidate the pattern and controlling factors of OM input in the sediments. The lowest hydrogen index (HI), lowest long-chain n-alkane concentrations, and highest Paq (proxy of aquatic macrophyte input) in sediments prior to ca. 1956 indicate a minimal input of OM from phytoplankton and terrestrial plants and a larger input from submerged macrophytes. This may represent the features of OM input in primitive conditions given the mild human activities around the lake before the 1950s. In sediments from ca. 1962 to 1985, elevated HI and C17/C16n-alkane ratios indicate a greater input from phytoplankton, while the high abundances of long-chain n-alkanes and αβ-hopanes reflect an anomalously high input from terrestrial plant and fossil OM. These variations might have been caused by the rapid development of agriculture during this period, which accelerated catchment erosion and petroleum contamination and promoted the transport of allochthonous OM and nutrients to the lake. The lowest Paq in sediments during this period indicates reduced input from submerged macrophytes, probably resulting from a dam installation that modified the water to an unfavorable plant depth. In sediments after ca. 1989, the highest values of HI, short-chain n-alkane abundances, and C17/C16n-alkane ratios indicate a further increase in OM input from phytoplankton, a response to domestic and industrial discharge and subsequent lake eutrophication.

A stable isotopic approach for quantifying aquaculture-derived organic matter deposition dynamics in the sediment of a coastal fish farm

The stable carbon and nitrogen isotopic compositions (δ13C and δ15N) of sedimentary organic matter (OM) in fish farms (FFs) were investigated to quantify the aquaculture-derived OM deposition dynamics in the sediment. The dual isotopic compositions of mixed OMs in surface sediments at FFs differed significantly (p < 0.05) from those at reference sites, indicating an increased deposition of fish feces or uneaten feed in the sediments. Furthermore, OM source apportionments revealed that the quantitative contribution of fish feces (23.3 mg g−1 dw) during farming activities was significantly higher than that of other natural OM sources (C3 plants and phytoplankton). After the disassembly of fish cages, the deposited fish feces may be preferentially degraded through processes that require a large amount of oxygen consumption (<0.1 kg C m−2 yr−1). Our isotopic approach may be helpful for assessing the impact of FF wastes and for taking measures to minimize environmental deterioration.

Composition of sedimentary organic matter in Thrissur Kole wetland, southwest India

Composition of sedimentary organic matter in Thrissur Kole wetland, southwest India

Earthquake, floods and changing land use history: A 200-year overview of environmental changes in Selenga River basin as indicated by n-alkanes and related proxies in sediments from shallow lakes

The Selenga River basin, located in southern Siberia, is an important component of the Lake Baikal ecosystem, and comprises approximately 80 % of the Baikal watershed. Within the Selenga River basin, two localized study regions were chosen. The first, the Selenga Delta, is one of the largest inland freshwater floodplains in the world and plays an important role in the ecosystem functioning of Baikal. It purifies the river waters before they enter the lake and acts as a refuge for many of Baikal's endemic species. The second location, the Gusinoozersk region, is southwest of Lake Baikal and the Selenga Delta, and was chosen as a more heavily industrialized region within the Selenga River basin. Anthropogenic activities, including industry, urban settlements, aquaculture and agriculture, have historically increased ecological damage within this area. We assessed possible drivers of changes in sedimentary organic matter (OM) composition within two shallow lakes (SLNG04 and Black Lake), located in the Selenga Delta and the Selenga watershed, respectively. We focused on individual n-alkanes, one of the most abundant and common lipids used to provide information on past vegetation and used multivariate statistics to disentangle changes in the sources of sedimentary OM over time. The depositional OM history of SLNG04B core can be divided in four zones: (i) major influence of non-emergent vascular plants, typically found in transitional environments (ca. 1835 to ca. 1875); (ii) increased influence of grasses/herbs (ca. 1880 to ca. 1910); (iii) transition from non-emergent vascular plants and grasses/herbs to submerged and floating macrophytes and phytoplankton (ca. 1915 to ca. 1945); (iv) maintenance of autochthonous OM from submerged and floating macrophytes and phytoplankton (ca. 1945 to ca. 2014). The depositional OM history of the Black Lake core can be divided in two main zones: (i) major influence of non-emergent vascular plants and submerged and floating macrophytes (ca. 1915 to ca. 1980); (ii) increased influence of grasses/herbs and phytoplankton (ca. 1980 to ca. 2010). Natural events (e.g., an earthquake in 1862 caused flooding and subsidence of much of the land surrounding SLNG04 lake and a further catastrophic flood event in 1897) and anthropogenic activities (e.g., nutrient pollution from expansion of agricultural and livestock population) changed the composition of sedimentary OM resulting in ecological shifts across trophic levels in the Selenga River basin.

Outcomes of feeding activity of the sea cucumber Holothuria tubulosa on quantity, biochemical composition, and nutritional quality of sedimentary organic matter

IntroductionHolothuria tubulosa is one of the most common sea cucumbers in the Mediterranean Sea, generally associated with organically enriched coastal sediments and seagrass beds. As a deposit-feeder, it is responsible for strong bioturbation processes and plays a putative key role in sedimentary carbon cycling and benthic trophodynamics. With the aim of exploring the potential use of holothuroids as a tool for remediating eutrophicated sediments, we investigated the effects of H. tubulosa on sedimentary organic matter quantity, biochemical composition, and nutritional quality.MethodsHolothuroids and associated samples of ambient sediments were collected in two sites located in the Central-Western Mediterranean Sea (Sardinia, Italy) and characterized by different trophic status backgrounds: the site of Oristano characterized by sandy-muddy sediments and the presence of mariculture plants (ranked as meso-eutrophic) and the site of Teulada characterized by sandy sediments and Posidonia oceanica meadows (ranked as oligo-mesotrophic). We compared the biochemical composition (proteins, carbohydrates, lipids) of ambient sediment vs sea cucumbers feces and the sedimentary protein content vs protein content in the sediments retrieved in different gut sections (esophagus, mid gut, end gut) of the holothuroid.ResultsOur results reveal that holothuroids feeding on meso-eutrophic sediments can increase protein (1.5 times) and lipid (1.3 times) content through their defecation, thus making these substrates a more labile food source for other benthic organisms. We report here that H. tubulosa feeding on meso-eutrophic sediment is most likely able to actively select particles rich in labile organic matter with buccal tentacles, as revealed by the protein content in the esophagus that is up to 2-folds higher than that in the source sediment. According to the inverse relationship between assimilation rates and availability of organic substrates and the optimal foraging theory, H. tubulosa feeding on oligo-mesotrophic sediments showed potential assimilation of proteins ca. 25% higher than that of specimens feeding on meso-eutrophic sediments.DiscussionOur results reveal that H. tubulosa feeding on meso-eutrophic sediments can profoundly influence the benthic trophic status, specifically modifying the biochemical composition and nutritional quality of organic matter, thus paving the way to its possible use in bioremediation actions of eutrophicated sediments and in Integrated Multi-Trophic Aquaculture systems.

Exploration of changes in the chemical composition of sedimentary organic matter and the underlying processes during biodegradation through advanced analytical techniques

Environmental context Organic matter (OM) biodegradation plays a key role as it is one of the main processes causing changes in the amount, composition and properties of OM in sediment. However, a complete understanding of its processes and mechanisms is still not reached. In this study, we aim to explore the chemical composition changes during biodegradation and identify underlying processes. Rationale Although the scientific community has widely investigated organic matter biodegradation processes, only a limited number of studies have explored the molecular changes of this material, whereas its structure, composition and origin play a key role in these processes. Methodology We decided to examine the effects of biodegradation on the chemical composition of sedimentary organic matter and to explore the underlying mechanisms. We conceived a laboratory-based degradation experiment utilising organic-rich sediments artificially composed of two contrasting organic matter end-members (i.e. soil and algae) under two oxygen conditions. The sediment samples before and after incubation were then analysed by laser desorption ionisation–Fourier-transform–ion cyclotron resonance–mass spectrometry for molecular characterisation and by thermally assisted hydrolysis and methylation gas chromatography–mass spectrometry in order to offer insights into the mechanisms driving the biodegradation processes. Results Our results from molecular characterisation unveiled distinct pathways of biodegradation contingent upon the source material. Moreover, they hinted at a predilection for altering high molecular weight compounds like lignin &amp; carboxylic-rich alicyclic molecules (CRAM) and condensed aromatic structures (CAS), manifesting as a conversion into lower molecular weight counterparts. Furthermore, the complementary findings from biomarker analyses underscored the influence of environmental factors – specifically oxygen conditions and microbial communities – on organic matter decomposition. Discussion Although this study is a controlled laboratory experiment and more studies are needed, it demonstrates the intricate interplay among chemical, biological and environmental factors that profoundly shape the reactivity of organic matter. This study underscores the critical need for persistent inquiry, aimed at unravelling the factors and conditions governing the diverse pathways of biodegradation.