Total Organic Carbon Ratio Research Articles

Efficiency-enhancing methods for predicting nitrogen mineralization characteristics in paddy soils using soil properties and rapid soil extraction

Soil mineralized nitrogen (N) is a vital component of soil N supply capacity and an important N source for rice growth. Unveiling N mineralization (Nm) process characteristics and developing a simple and effective approach to evaluate soil Nm are imperative to guide N fertilizer application and enhance its efficiency in various paddy soils with different physicochemical properties. Soil properties are important driving factors contributing to soil Nm differences and must be considered to achieve effective N management. Nevertheless, discrepancies in Nm capacity and other key influencing factors remain uncertain. To address this knowledge gap, this study collected 52 paddy soil samples from Taihu Lake Basin, south China, which possesses vastly different physicochemical properties. The samples were subjected to a submerged anaerobic incubation experiment at a constant temperature to obtain the soil Nm characteristics. In addition to other analyses, reaction kinetics models were employed to compare characteristic differences between Nm potential (Nmp) and short-term accumulated mineralized N (Amn) processes in relation to soil physicochemical properties. Based on these relationships, simplified Nmp prediction methods for paddy soils were established. The results revealed that the Nmp values in pH < 6.50, pH range from 6.50 to 7.50, and pH > 7.50 were 145.18 mg kg-1, 88.64 mg kg-1 and 21.03 mg kg-1, respectively. Significantly, after comparing different incubation days, short-term Amn at 14 days showed a good correlation (P < 0.01) with Nmp (R2 = 0.94), indicating that the prevailing short-term incubation experiment is an acceptable marker for Nmp. Moreover, Nmp correlated well with the ultraviolet absorbance obtained at 260 nm using NaHCO3 extraction (Na260), streamlining the Nmp estimation method further. The incorporating easily obtainable soil properties, including pH, total nitrogen (TN), and the ratio of total organic carbon to TN (C/N) alongside Na260 for Nmp evaluation allowed the multiple regression model, Nmp = 58.62 × TN - 23.18 × pH + 13.08 × C/N +86.96 × Na260, to achieve high predictive accuracy (R2 = 0.95). The reliability of this prediction was further validated with published data in paddy soil from the same region and the other rice regions, demonstrating the regional applicability and prospects of this model. This study underscored the roles of soil properties in Nm characteristics and mechanisms and established a site-specific prediction model based on rapid extraction and edaphic properties from the paddy soil, paving the way for developing rapid, precise Nm prediction models.

Wildfire-vegetation-climate-human interactions in the central Taiwan region during 17.3–2.0 cal kyr BP, inferred from sediments of Toushe Basin

In this study, a long-term relationship amongst wildfire, vegetation, climate, and human in the central Taiwan region, spanning from 17.3 to 2.0 cal kyr BP, is explored. To investigate this relationship, multiple proxy approaches were employed, including charcoal (CHAR and fire frequency), pollen data (Liew et al., 2006), magnetic susceptibility, and the carbon isotopic composition of organic carbon, along with the elemental ratio of total organic carbon to total nitrogen in the core sediments of the Toushe Basin, central Taiwan. From 17.3 to 14.5 cal kyr BP, the Toushe Basin experienced drier climate conditions, leading to high-intensity fires and reduced area of wetland. Between 14.5 and 11.5 cal kyr BP, a wetter climate corresponded with low-intensity fires and an increase in tree prevalence. From 11.5 to 5.0 cal kyr BP, the climate remained relatively stable with peaks of extreme wet phases, with frequent low-intensity fires promoting herbaceous plant growth. During the period from 5.0 to 2.0 cal kyr BP, wetter conditions persisted, but increased human activities likely intensified high-intensity fires, resulting in reduced tree and herbaceous plant populations and an expansion of wetlands, leading to complex impacts on the region's ecological dynamics. The pollen diversity index (PDI) and pollen richness index (PRI) showed that ecological diversity in the Toushe Basin decreased with high-intensity fires and increased with low-intensity fires, highlighting the complex interactions between natural and human factors during 17.3–2.0 cal kyr BP. In addition, this study showed a strong link between El-Niño events and increased wildfire activity in the Toushe Basin. El-Niño conditions, with reduced rainfall and increased dryness, likely heightened wildfire frequencies and intensity by lowering moisture levels and ignition thresholds. Increased lightning during these periods further exacerbated wildfires. This connection highlights El-Niño ‘s role in driving high-intensity fires, impacting the region's vegetation and ecological dynamics.

Continuous deposition of pre-aged organic carbon in the southern Mariana Trench since the last deglaciation

One of the key challenges in understanding the role of hadal trenches in the marine organic carbon (OC) cycle is the need to distinguish OC sources, assess accumulation rates, and identify controlling processes. To address this, sediment core samples from the southern Mariana Trench were analyzed for their contents and carbon isotopes (13C and 14C) of both total OC (TOC) and saturated long-chain fatty acid (n-LCFA). Our findings indicate that sedimentary OC in the southern Mariana Trench is primarily derived from marine sources, as indicated by TOC-δ13C values ranging from −19.9‰ to −17.0‰ and the ratios of TOC to total nitrogen (TOC/TN) of 5.5–8.4. The 14C ages of TOC and n-LCFA ranged from 7159 to 22,662 yr and 8713 to 22,819 yr, respectively, with both showing gradual down-core increasing trends. This allows for a conservative estimation of sedimentation rate of 17.5–18.7 cm kyr−1 in the southern Mariana Trench, leading to a sedimentary OC accumulation rate of 529–942 g C m−2 kyr−1, which is 1–2 orders of magnitude higher than that observed in the abyssal plain. We propose that the continuous lateral downslope transport played a significant role in focusing pre-aged OC into the southern Mariana Trench. Therefore, hadal trenches are likely to accumulate substantial amounts of sedimentary OC in the deep ocean.

High levels of soil calcium and clay facilitate the recovery and stability of organic carbon: Insights from different land uses in the karst of China.

Soil organic carbon (SOC) is a crucial medium of the global carbon cycle and is profoundly affected by multiple factors, such as climate and management practices. However, interactions between different SOC fractions and land-use change have remained largely unexplored in karst ecosystems with widespread rock outcrops. Owing to the inherent heterogeneity and divergent response of SOC to land-use change, soil samples with close depth were collected from four typical land-use types (cropland, grassland, shrubland, and forestland) in the karst rocky desertification area of China. The aim of this study was to explore the responses of SOC dynamics to land-use types and underlying mechanism. The results showed that land-use type significantly affected SOC contents and its fractions. Compared with cropland, the other three land uses increased the total organic carbon (TOC), microbial biomass carbon (MBC), and non-labile organic carbon (NLOC) contents by 6.11-129.44%, 32.58-173.73%, and 90.98-347.00%, respectively; this demonstrated that a decrease in both labile and recalcitrant carbon resulted in SOC depletion under agricultural land use. Readily oxidized organic carbon (ROC) ranged from 42 to 69%, accounting for almost half of the TOC in the 0-40-cm soil layer. Cropland soil showed significantly higher ROC:TOC ratios than other land-use types. These results indicated that long-term vegetation restoration decreased SOC activity and improved SOC stability. Greater levels of soil exchangeable calcium (ECa) and clay contents were likely responsible for higher stabilization and then accumulation of SOC after vegetation restoration. The carbon pool index (CPI) rather than the carbon pool management index (CPMI) exhibited consistent variation trend with soil TOC contents among land-use types. Thus, further study is needed to validate the CPMI in evaluating land use effects on soil quality in karst ecosystems. Our findings suggest that land-use patterns characterized by grass or forest could be an effective approach for SOC-sequestration potential and ensure the sustainable use of soil resources in the karst area.

Geochemical and mineralogical features as indicators of sulfate-methane transition zones in shallow gas-bearing offshore sediments from Zhoushan

Subsurface shallow gas, primarily composed of biogenic methane (>95%), is highly-enriched in global offshore sediments. The redox conditions of methane-rich pore fluid play a crucial role in shaping the geochemical signatures associated with the anaerobic oxidation of methane (AOM) and vertical displacement of sulfate-methane transition zones (SMTZs) within deep sedimentary records. However, long-period, and continuous records of AOM and SMTZs in shallow gas-bearing offshore sediments are sparse. Here, we employed a comprehensive analyses of iron sulfide, elemental, and stable isotopies on a 63-m drilled sediment core (JC-1) from offshore Zhoushan. Four different layers U1–U4 were identified in 11.5–24 mbsf, 24−42 mbsf, 42−51 mbsf, and 51−63 mbsf, respectively, as revealed by the lithofacies and sedimentary structures. By comparing the pyrite contents, total sulfur to total organic carbon ratios, and δ34S-chromium-reducible sulfur values, the commonly seen organoclastic sulfate reduction occurred in U1 and U2, whereas significant AOM activities were found in U1 and U4. Further, the peaks of total sulfur to total organic carbon ratios, sulfur contents, and multiple positive δ34S-chromium-reducible sulfur values indicated the presence of AOM in SMTZs at 18.3, 52, and 59 mbsf. These intervals were featured by a sub-oxic or anoxic condition with strong methane seepages, evident from the scarcity of metals and the enrichment of Mo/Al and U/Al ratios. The presence of multiple SMTZs was consistent with the pore-water data of the adjacent YS4 and YS7 cores. In light of these findings, it is prudent to exercise caution when utilizing geochemical indicators, such as trace element proxies and the δ34S values of sulfide minerals, to comprehend the progression of fluctuating depositional settings in reaction to sea-level fluctuations and shallow gas reservoirs. This study provides a new perspective to better understand the evolution of unsteady depositional environments in response to sea-level changes and shallow gas reservoirs.

Late Quaternary marine transgressions off the Shandong Peninsula inferred from paleosalinity indicators: Implications for Holocene mud wedge formation

Mud depocenters play an important role in the sediment source–sink system of marginal seas; however, the factors controlling the formation of mud deposits are not well understood. This study focused on Core LHSD-1, which is located on the southern margin of the Shandong Peninsula mud wedge in the northwestern part of the South Yellow Sea. Elemental ratios, such as the C/S ratio (the mass ratio of total organic carbon and total sulfur) and Sr/Ba ratio, were used to track the changes in paleosalinity during the late Quaternary and to investigate the mechanisms that influenced the formation of the mud wedge off the Shandong Peninsula. Our results indicate that Core LHSD-1 likely recorded two transgression events, corresponding to MIS3 and MIS1. Following sea-level rise after the Last Glacial Maximum (LGM), transgressive deposition began in the study area at approximately 11.5 kyr BP. During the early Holocene, fluctuating water salinity was recorded by Sr/Ba ratios, which became stable at approximately 6.8 kyr BP when the sea level reached its highstand. At the same time, the modern current system was established, and a significant amount of terrestrial material, such as refractory organic carbon and iron, has been transported to the study area by enhanced coastal currents, which was documented by elevated C/S ratios (C/S > 2.8) in mud sediments. Our findings indicate that marine transgressions controlled the initial development of the mud depocenter and that the establishment of the modern ocean current system promoted the rapid deposition of mud sediments, which corresponded to the growth of global mud depocenters.

Role of Hazelnut Husk Compost and Phosphate Solubilizing Bacteria in Improving Productivity and Quality Parameters of Wheat (Triticum aestivum L.) and Their Effects on Some Soil Biological Properties

ABSTRACT Implementing compost can assist in improving soil structure and enable nutrient mobilization to plants that initiate an appropriate soil balance. In a greenhouse experiment, the influence of hazelnut husk compost (HHC), both in single and in combination with the phosphate solubilizing bacteria (PSB) on the wheat yield, yield parameters, and soil biological properties were investigated. A significant increase in yield and its quality parameters was recorded when the soil was treated with different doses of compost and bacteria. It was observed copious improvements in the soil biological properties with these applications. The microbial biomass carbon and total organic carbon ratios (Cmic:Corg) ranged from 1.51 to 2.09, were also remarkable in the organic amended soils. However, in all the treatments, the co-inoculation of bacteria with compost enhanced all the parameters significantly more than their individual applications. The highest yield increase over control (22.12%) was recorded from the integrated application of organic source and bio-fertilizer. This reflects a synergistic relationship between the compost and bacteria that eventually enhanced wheat production. It is therefore concluded that using HHC and PSB in soil can unfold promising possibilities for better soil health, which in the long run can contribute to sustainable food production.

Response of mangrove development to paleoclimate variation over the past 3,550 years in Phang Nga Province, Thailand

High-resolution reconstruction of the development of mangrove forests in the late Holocene is the basis for scientifically predicting the fate of mangroves. In this paper, we analyze the contribution of mangrove-derived organic matter (CMOM) from sediment core G in Phang Nga Province, Thailand by using a ternary end-member mixing model based on stable organic carbon isotope (δ13C) and the molar ratio of total organic carbon to total nitrogen (C/N (molar)). The variations of the CMOM in Phang Nga Province over the past ∼3,550 cal yr BP indicate that mangrove forests underwent three periods of flourishing: ∼3,550–2,720 cal yr BP, ∼1,960–1,240 cal yr BP and ∼500–0 cal yr BP, and two periods of degradation: ∼2,720–1,960 cal yr BP and ∼1,240–500 cal yr BP. Of the potential factors that affect mangrove development, relative sea level (RSL) changes and regional hydrological conditions did not have notable effects on mangrove flourishing/degradation. However, paleoclimate variations, especially the air temperature and rainfall controlled by the Indian Summer Monsoon (ISM) were the primary factors. The mangrove development reconstructed by the CMOM in Phang Nga Province, Thailand was extremely synchronized with that in the Yingluo Bay and Qinzhou Bay of Southwest China and on the west coast of India Peninsula. This study provides evidence that mangrove development controlled by the Asian monsoon in tropical Asia has regional synchronism.

Decreased Westerly moisture transport leads to abrupt vegetation change in northern Central Asia during late MIS3: Evidence from Zeketai Loess, Ili Basin

Moisture transportation to (semi-)arid Central Asia is influenced by the interplay of multiple atmospheric circulation patterns. The mechanism underlying the hydroclimate evolution in CA has recently received increasing attention. In northeastern CA, most of the precipitation falls in summer, counter to other westerly-dominated regions of CA where precipitation maximizes in boreal winter. The marine isotope stage (MIS) 3 offers a unique opportunity to examine the mechanisms driving hydroclimate variations during warm periods of the ice age in the CA. However, due in part to reliable proxies for reconstruction, the hydroclimate and vegetation change during MIS3 in northeastern CA have not been well studied. Here, we use grain size and magnetic susceptibility data from the Zeketai loess profile to reconstruct historical shifts in precipitation patterns during MIS3 in the Ili Basin from arid Central Asia (ACA). Notably, abrupt changes around 35 ka are evident in the grain size and magnetic susceptibility records, reflecting a transition to reduced wind intensity and increased aridity. Subsequent analysis of plant leaf waxes (n-alkanes), hydrogen isotopic composition of n-alkanes (δDn-alkane), and stable carbon isotope ratios of total organic carbon (δ13Corg) within the loess profile indicates a concurrent shift towards more shrubs, aligning with reduced moisture availability. The δ13Corg record further elucidates that during MIS3, the Ili Basin predominantly harbored C3 vegetation. However, the alteration in δ13Corg and δDn-alkane to more positive values at approximately 35 ka substantiates the transition to more drought-resistant vegetation. Furthermore, we link the paleo-hydroclimate variations to the decrease in solar radiation and the strengthening of the Atlantic Meridional Overturning Circulation (AMOC) and Siberian High during late MIS3. This joint influence weakens the Westerly winds and subsequently diminishes the conveyance of moisture to CA.

Diatom records in sediments for eutrophication process of Lake Xian'nv, China since the mid-20th century

&lt;p&gt;To well understand the eutrophication process for inland lakes where more lands had been used for agriculture and industry without adequate environmental protections, 9 surface sediments and 1 core sediment in Lake Xian’nv which was located in the middle of Jiangxi Province were chosen. Combined with 210Pb and 137Cs geochronology, nutrient index including total nitrogen (TN), total phosphorus (TP), total organic carbon (TOC), Carbon nitrogen ratio (C/N), diatoms assembles and TDI index of eutrophic diatoms were compared quantitatively and conducted to elucidate the eutrophication process using statistical methods. The results showed a total of 155 years from 1863 to 2018 were recorded from the entire sediment core. The nutrient level in 23 centimeters below the surface of the sediment core where was synchronized with reservoir construction indicated TN, TP, TOC, and Carbon nitrogen ratio had been gradually increased since the construction of Dam. In surface sediments, the three diatoms with higher average relative abundance were Achnanthidium minutissimum, Navicula Bory, and Aulacoseira granulata with a value of 54.2 %, 29.4 %, and 15.3 % respectively. Significant changes of the diatom communities from 1955 to 2009 had been recorded, where diatom communities could be classified into four distinct periods. In the first few years after the reservoir was built, the dominant diatoms were epiphytic and benthic diatom communities represented by Navicula cincta、Fragilaria ulna, and Cocconeis placentula in zone I on the bottom floor covered from 1955 to 1961. However, planktonic diatom communities were dominant after 1983 which were mainly constituted by Aulacoseira alpigena、Cyclostephanos dubius、Cyclotella meneghiniana, and Cyclotella radiosa . Both TDI index of eutrophic diatoms and Principal Component Analysis (PCA) revealed the succession from benthic diatoms to planktonic diatoms and changes in nutrient levels.&lt;/p&gt;&#x0D;

Holocene millennial-scale variability of coastal environments on the southern coast of Korea and its controlling factors

AbstractCoastal evolution is influenced by past sea-level changes and resultant shifts from fluvial- to marine-dominant environments and the accompanying significant geochemical and isotopic changes in the water mass and sediments. We investigated the elemental and isotopic features of coastal sedimentary cores (27 m in length) from a small paleo-bay located on the southern coast of Korea to determine such geochemical variability and specify past changes in the bay environment and anoxic conditions and possible links to past climate changes. We analyzed total organic carbon (TOC), total sulfur (TS), their isotopes (δ13CTOC and δ34STS), and pyrite. The δ13CTOC values ranging from −25 to −19‰ (a proxy for terrestrial influence) were lower than average (−22.5‰) before 8300 cal yr BP and since 500 cal yr BP, while the intervening Early to Late Holocene showed higher δ13CTOC values, indicating a shallow coastal environment. The δ34STS values fluctuating between −35 and +5‰ resembled sedimentation rate change. Based on the changes in the ratios of TOC to TS (C/S ratios), sedimentation rate, and δ34STS, we found five possible periods with higher salinity and intensified anoxic conditions at millennial timescales: 8900–8200, 7950–6500, 5200–4300, 3500–2600, and 2000–1100 cal yr BP. These intensified anoxic conditions seem to have been influenced by increased air temperature and sea-surface temperature conditions, which could have intensified the intensity of thermal stratification (less ventilation and mixing) between surface and bottom waters and resultant anoxic conditions.

Impacts of snow-farming on alpine soil and vegetation: A case study from the Swiss Alps

Snow-farming is one of the adaptive strategies used to face the snow deficit in ski resorts. We studied the impact of a shifting snow-farming technique on a pasture slope in Adelboden, Switzerland. Specifically, we compared plots covered by a compressed snow pile for 1.5, 2.5 or 3.5 years, which then recovered from the snow cover for three, two or one vegetation seasons, respectively, with control plots situated around the snow pile.In plots with >1.5 years of compressed snow pile, plant mortality was high, recovery of vegetation was very slow, and few plant species recolonized the bare surface. Soil biological activity decreased persistently under prolonged snow cover, as indicated by reduced soil respiration. The prolonged absence of fresh plant litter and root exudates led to carbon (C) limitation for soil microbial respiration, which resulted in a significant decrease in the ratio of total organic carbon to total nitrogen (TOC/TN) under the snow pile.Microbial C, nitrogen (N) and phosphorus (P) immobilization decreased, while dissolved N concentration increased with compressed snow cover. Longer snow cover and a subsequent shorter recovery period led to higher microbial C/P and N/P but lower microbial C/N. Nitrate and ammonium were released massively once the biological activity resumed after snow clearance and soil aeration.The soil microbial community composition persistently shifted towards oxygen-limited microbes with prolonged compressed snow cover. This shift reflected declines in the abundance of sensitive microorganisms, such as plant-associated symbionts, due to plant mortality or root die-off. In parallel, resistant taxa that benefit from environmental changes increased, including facultative anaerobic bacteria (Bacteroidota, Chloroflexota), obligate anaerobes (Euryarchaeota), and saprophytic plant degraders.We recommend keeping snow piles in the same spot year after year to minimize the area of the impacted soil surface and plan from the beginning soil and ecosystem restoration measures.

Activation of peroxymonosulfate by Co2P via interfacial radical pathway for the degradation and mineralization of carbamazepine

Peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) have raised wide attention due to the efficient degradation of pollutants. However, the low efficiency in PMS activation is still a challenge for practical application. Herein, an economic Co2P catalyst with surface-active center was constructed for PMS activation to induce fast degradation of carbamazepine (CBZ). Particularly, the removal ratio of CBZ in the Co2P/PMS system could achieve at 98% in 10 min, accompanied with the removal ratio of total organic carbon (TOC) reached 60% in 60 min. Characterizations indicated that interfacial transformation of Coδ+ to Co2+ promoted electron-rich Co center formation, which supplied electrons for PMS to produce SO4•–and •OH that were responsible for the efficient degradation of CBZ. Furthermore, potential interferences from the real water matrix, dosage of the catalyst and PMS, and variation of initial pH were carefully studied for practical applications. Besides, three possible degradation pathways of CBZ were proposed and the toxicity of the products was predicted. However, the generation of more toxic intermediates was found in the system for the radical (SO4•–and •OH) oxidation is a non-selective oxidation process. Particularly, we expect that this work can provide new insights into the regulation of reaction mechanisms, degradation routes and safe transformation in PMS-AOPs for wastewater treatment.

Rapid environmental changes in the Lake Qinghai basin during the late Holocene

The Lake Qinghai Basin is sensitive to global and regional climate change because of its unique geographical location. It is the hotspot for paleoclimate research in East Asia. In this study, we reconstructed the environmental evolution of the Lake Qinghai since ∼9 ka by using a high-resolution peat and fluvial-lacustrine record (Laoyinggou profile) obtained at the foot of Nanshan Mountain. Based on 8 AMS14C dates and lithology, loss on ignition (LOI), total organic matter (TOC), X-ray fluorescence (XRF) core-scanning measurements, ratio of total organic carbon to nitrogen (TOC/TN), and sediment particle sorting coefficients, we show that during the Middle Holocene (∼9–4.4 ka BP) this region was primarily dominated by the Asian summer monsoon, with a consistent, warm, and humid environment. By contrast, during the late Holocene (4.4 ka to present), the climatic context in this area fluctuated dramatically at the millennial scales. The low TOC content, lower TOC/TN ration and strong hydroclimatic indicate six rapid climate change events, which occurred at ∼4.0 ka, ∼3.6 ka, ∼3.2 ka, ∼2.8 ka, ∼2.1 ka, and ∼1.4 ka, all of which coincided to cold episodes in the North Atlantic Ocean.

Evaluation of Different Reverse Osmosis Membranes for Textile Dyeing and Finishing Wastewater Reuse

Different commercial reverse osmosis (RO) membranes from Vontron and DuPont Filmtec were evaluated for textile dyeing and finishing wastewater (TDFW) reuse in China. All six tested RO membranes produced qualified permeate meeting TDFW reuse standards at a water recovery ratio (WRR) of 70% in single batch tests. The rapid decline of apparent specific flux at WRR over 50% was mainly ascribed to feed osmotic pressure increase caused by concentrating effects. Multiple batch tests using Vontron HOR and DuPont Filmtec BW RO membranes with comparable permeability and selectivity demonstrated the reproducibility and showed low fouling development. The occurrence of carbonate scaling on both RO membranes was identified by scanning electron microscopy and energy disperse spectroscopy. No obvious organic fouling was detected on both RO membranes by attenuated total reflectance Fourier transform infrared spectrometry. From the orthogonal tests, with an integrated RO membrane performance index (i.e., 25% rejection ratio of total organic carbon + 25% rejection ratio of conductivity + 50% flux ratio of final to initial) as a target, the optimal parameters were determined as WRR of 60%, cross-flow velocity (CFV) of 1.0 m/s, temperature (T) of 20 °C for both RO membranes, while trans-membrane pressures (TMP) of 2 and 4 MPa were optimal for Vontron HOR RO membrane and DuPont Filmtec BW RO membrane, respectively. Both RO membranes with the optimal parameters produced good permeate quality for TDFW reuse and kept a high flux ratio of final to initial, demonstrating the effectiveness of the orthogonal tests.

Late Quaternary marine transgressions inferred from the pyrite sulfur content and isotopes within core sediments from the southeast coast of China

Paleoenvironmental reconstructions of coastal areas during geological history are critical for understanding past responses to marine transgression. Identifying transgressive layers in sedimentary strata is therefore of great importance. To this end, we examined the content and isotopic composition of pyrite sulfur, in combination with classical organic geochemical indicators (e.g., C/N ratio and the δ13C of organic carbon), to trace the marine transgressions along the southeast coast of China since Marine Isotope Stage (MIS) 5. Our results suggest that the mass ratio of total organic carbon and pyrite sulfur (C/S ratio) is sensitive to seawater intrusion. Three transgressive layers were identified by low C/S ratios in core NDGK2, which correspond to sea level rise during MIS5, MIS3, and MIS1. Sediments deposited during MIS1 are represented by low C/S ratios with an average of 2.31, while those deposited during MIS5 and MIS3 have slightly higher C/S ratios, indicating a less extensive influence of seawater. Pyrite production in sediments deposited during MIS5 and MIS3 may have been limited by sulfate supply, as reflected by more positive values of δ34Spyr, whereas pyrites deposited during MIS1 were likely formed without sulfate limitation, as reflected by more negative values of δ34Spyr. The isotopic signals of pyrite sulfur thus further confirm the inference based on the C/S ratio. The magnitude of the transgression increased from MIS5 to MIS1, which is in agreement with the findings from classical organic geochemical indicators examined in this study, as well as geochemical and micropaleontological salinity indicators from previous studies. Our findings provide a promising method for identifying marine transgressions and their magnitude from the depositional record, especially when sedimentary strata lack diagnostic micropaleontological and sedimentological characteristics.

Organic C Fractions in Topsoil under Different Management Systems in Northeastern Brazil

The conversion from native forest to other land-use systems can decline the soil organic carbon (SOC) in tropical soils. However, conservationist management could mitigate SOC losses, promoting the functioning and stability of agricultural soils. This study aimed to address the influence of conversion from native forest to different land-use systems on SOC fractions in Northeastern Brazil. Topsoil soil samples were collected in areas under pasture (PAS), no-tillage (NT1 and NT2), eucalyptus (EUC), and native forests of Cerrado in Northeastern, Brazil. Total organic C, microbial biomass (MBC), particulate (POC), and mineral-occluded organic C (MOC), as well as fulvic acids (C-FA), humic acids (C-HA), and humin (C-HUM) fractions were accessed. The results showed that land conversion maintained similar levels of humic fractions and total organic carbon (TOC) stocks in the PAS, NT1, NT2, and EUC as compared to native Cerrado. Soils with the input of permanent and diverse fresh organic material, such as NT2, PAS, and EUC, presented high levels of MBC and POC, and the lowest C-FA:TOC and C-HA:TOC ratios. The land conversion to agricultural systems that include cropping rotations associated with pasture species such as Mombasa grass and eucalyptus prevents topsoil losses of active C compartments in the Cerrado of the Brazilian Northeast. It suggests that sustainable and conservationist management should be emphasized to maintain and improve the status of soil organic C.

Changes in the carbon source and storage in a cultivation area of macro-algae in Southeast China

Macro-algae culture has recently attracted attention in China because of its capability to sequester carbon. Here, radionuclides, total organic carbon (TOC), and nitrogen (TN) were examined in a cultivation area of macro-algae in Southeast China. At the reference site, the ratio of TOC to TN (C/N, 8.1 ± 0.2, mean ± SD) did not exhibit discernible variation over the past 70 years. In contrast, in the cultivation area, C/N descended from 9.0 ± 0.2 around 1960 to 8.3 ± 0.2 between 1960 and 1990 and 7.6 ± 0.2 after 1990, coincident with the recorded kelp production in this area, indicating an influence of macro-algae culture-associated activities on carbon origin. Using a model, algal culture-associated activities contributed 23 ± 7 % between 1963 and 1990 and 53 ± 8 % between 1990 and 2022 to TOC. The burial of culture-associated TOC varied from 0.15 to 1.23 mg-C cm−2 yr−1, implying the unneglectable influence on carbon storage.

Isotopic characteristics and sources of suspended particulate organic matter in a reservoir of Chinese desert grassland areas: the influence of dry and wet seasons and the role of atmospheric deposition.

It is essential to study the sources of suspended particulate organic matter (SPOM) for a comprehensive understanding of the carbon and nitrogen cycles in reservoir located in desert grassland areas. Atmospheric deposition is an important pathway for human and natural nutrients to enter water ecosystems. Previous studies have focused on hotspot areas, but neglected the impact of atmospheric deposition on reservoirs in desert grassland regions with little rainfall, long freezing periods, and a dusty climate. In this study, we measured the contents of organic carbon, total nitrogen, the isotopic composition (δ13C and δ15N), and the ratio of total organic carbon to total nitrogen (C/N ratios) for SPOM in the reservoir and its watershed across both dry and wet seasons using carbon and nitrogen isotope techniques. We also analyzed the sources of SPOM in the reservoir using the end-member mixing model. The results showed that the variation range in SPOM for δ13C was - 28.3 to - 21.8‰; for δ15N, it was 2.3 to 8.7‰; and the C/N ratios were 8.12 to 19.12. The variation range of δ13C for atmospheric particulate matter was - 20.0 to - 25.0‰; for δ15N, it was 2.3 to 11.9‰; and the C/N ratios ranged from 7.22 to 17.81. The main sources of carbon in the SPOM were atmospheric deposition and terrestrial C3 plants. The origins were significantly different between the wet and dry periods. Atmospheric nitrogen deposition and soil erosion were the primary sources of particulate nitrogen in the reservoir.

Evolution of organic matter quantity and quality in a warm, hypersaline, alkaline lake: The example of the Miocene Nördlinger Ries impact crater, Germany

The Nördlinger Ries (NR) impact crater in southern Germany contains Miocene lacustrine fine-grained post-impact sediments, which were deposited under saline, alkaline, and hydrologically closed aquatic conditions. To obtain information on the organic matter quantity, quality and environmental evolution, samples from one central (NR 1973) and one more marginal (Enkingen SUBO-18) well were analyzed by pyrolytic, organic geochemical and micro-petrographic techniques. Deposits of the marginal drilling can be linked to the thicker stratigraphic units of the well from the lake center based on total organic carbon (TOC), hydrogen index (HI) and lithology. Central deposits contain mainly hydrogen-rich type I kerogen with a mean HI of 447 mg HC/g TOC, whereas the marginal sequence contains type II-III kerogen with an average HI of 206 mg HC/g TOC. In the center, high total sulfur (TS) over TOC ratios of 1.5 on average, and δ13C values of biomarkers in combination with low α-/total MTTC (α-/total methyl-trimethyltridecyl chromans ∼ &amp;lt;0.6) and Pr/Ph ratios &amp;lt;0.2 suggest the prevalence of hypersaline water. Salinity only decreased during deposition of the uppermost Miocene units, when the then shallow alkaline lake turned, at least temporarily, into acidic-neutral conditions during the time of peat deposition. A similar trend, but at overall lower salinities is recorded for the marginal site. Water stratification in the center is stronger than in the marginal domain based on salinity variation. Anoxic bottom water prevailed in the whole lake, as recorded by exceptionally low Pr/Ph ratios (∼&amp;lt;0.2), the occurrence of des-A-lupane and small pyrite framboids (&amp;lt;5 µm) except for the youngest layers of the Miocene lake. Autochthonous, halophilic red algae/plankton prevailed as reflected by abundant C27steranes, while terrestrial material and aerobic bacteria significantly contributed to the OM only in the latest stages of lake as evident from abundant vitrinite/inertinite particles, high values of diterpenes/C27sterane (up to 255) as well as low values of C27-29regular steranes/C29-32hopanes (&amp;lt;0.5). The same trend, but less well resolved, can be seen at the margin of the paleo-lake.