Validation of Soil Enzyme Activity Assay for a Biogeochemical Cycling Index in Biochar Amended Soils

Biochar offers several benefits as a soil amendment, including increased soil fertility, carbon sequestration, and water-holding capacity in nutrient-poor soils. Here, we performed a series of enzyme assays on pine biochar-amended soils, comparing multiple enzyme activities (EAs) simultaneously determined in the same soil sample vs. the sum of individual EAs involved in the C, N, S, and P cycles to provide information of the impacts of biochar on biogeochemical cycling. The combination of these four EAs has been considered an indicator of soil health due to their role in the reactions that release bioavailable nutrients in the cycling of C (β-glucosidase), N and C (β-glucosaminidase), P (acid phosphomonoesterase), and S (aryl-sulfatase) in soils. Comparisons of the theoretical EAs and the CNPS activity assay approaches in the biochar-modified soil revealed similar activity trends with the different concentrations of added biochar. Two years after adding biochar, study results showed the amended soils did not retain more pNP substrate than the un-amended control soils in three different pH buffers (5.5, 5.8, and 6.5) commonly used in EA reactions. Finally, we performed a third experiment to determine if the biochar previously added to the EAs interfered with the reactions’ enzyme or substrate. The results indicated that greater activity was measured using the combined assay, which suggests the CNPS activity method was less affected by biochar than the individual EAs. Our findings indicate that the potential soil biochemical-health index, CNPS activity (combination of four enzymes) assay is more robust than the individual EAs and can be used as an alternative tool to monitor soil functioning.

Migration and role of zinc in biogeochemical cycles in the Antarctic Ice Sheet and the Southern Ocean

Zinc(Zn),a widespread metal in the Earth’s crust,serves as a crucial nutrient in the Southern Ocean’s primary production.Studies on Zn in Antarctic snow and ice offer insights into the origins of this metal and its transport routes,as well as its impact on the biogeochemical processes within the Antarctic atmosphere–land–ocean system.This review examines research on the spatial and temporal distribution of Zn in Antarctic snow and ice,as well as in Southern Ocean waters.It includes an overview of advanced methods for sampling and analyzing Zn,along with explanations for the observed variations.The review also discusses various sources of Zn as a nutrient to the Southern Ocean.Finally,it addresses prospective issues related to the use of Zn isotopes in identifying atmospheric sources and their biogeochemical effects on the development of the Southern Ocean ecosystem.

Nanozyme-mediated elemental biogeochemical cycling and environmental effects

In Earth systems,thousands of terragrams(Tg)(1 Tg=10^(12) g)of mineral nanoparticles move around annually.Some mineral nanoparticles have exhibited unexpected intrinsic enzyme-like characteristics(so called“mineral nanozymes”),and are ubiquitously distributed in natural ecosystems such as the atmosphere,oceans,waters,and soils.Compared with natural enzymes,these mineral nanozymes have several advantages such as tunable catalytic efficiency and robustness to harsh conditions,e.g.,heat,acid,and alkaline conditions.As mineral nanozymes are new products of multidisciplinary cross-cutting,they have been widely applied in various fields.This review,for the first time,systematically introduces the species and properties of mineral nanozymes in Earth systems,discusses the critical roles played by nanozymes in environmental biogeochemical cycles,compiles the interfacial processes and mechanisms of mineral nanozymes,and provides an overview of the future prospects of mineral nanozymes.

ENSO impacts on litter stocks and water holding capacity in secondary forests in eastern Amazonia

Among the impacts of climate change,there is the intensification of phenomena such as the El Niño South-ern Oscillation(ENSO)responsible for El Niño and La Niña.However,understanding their effects on the functional pro-cesses of forests is limited.Therefore,this study evaluated the effects of ENSO on litter stock and water holding capac-ity(WHC)in a successional forest in eastern Amazonia.Evaluations occurred in periods with the most rainfall in El Niño(2019)and least in La Niña(2021)years.Twelve permanent plots were used to sample litter.ENSO effects were evident for WHC,higher during El Niño.However,this influence was not clear for litter,as only in the rainy season effects were found.There was a positive correlation of WHC with precipitation and humidity,while litter stocks were negatively correlated with temperature and wind speed.Although the subject of this study requires long-term assessments,preliminary results suggests that,depending on the intensity of ENSO,forest functional processes can be strongly impacted and altered.The conclusion reinforces warnings by the scientific community about the impacts of climate change on the maintenance of litter stocks,decomposition and,consequently,the biogeochemical cycle and essential ecosystem services for the maintenance of Amazonia biodiversity.The need to develop long-term research to understand the effects of climatic change on litter stocks and water holding capacity is highlighted,especially in Amazonia.

Biogeochemical cycles of selenium in Antarctic water

Both vertical and horizontal profiles of total dissolved selenium,dissolved organic and inorganic selenium,including Se(IV)and Se(VI),as well as particulate selenium in seawater were obtained on a basis of newly developed separation technique form Antarctic Ocean,where the prodiction of deep waters occurs.The results exhibited that the concentrations of Se(IV) and Se(VI) were elevated and the total concentration in the surface of the high latitude waters (1. 31 nmol/L) was above those at lower latitudes (1.09 nmol/L) and also that previously reported from the Southern Ocean(1.18 nmol/L,Suzuki,1987).Preliminary investigation using specifically designed microlayer-sampler,that was first employed to identify the main biogeochemical proeesses,revealed Antarctic Ocean being functioning as a potential source as selenium in sea-air exchange. The mean life time of the selenium,detected as Se(IV) in deep water, was also estimated rather shorter than the residence time of the water mass, based on the samples collected from the cruise of China's Sixth Scientific Expedition.

Effects of river damming on biogenic silica turnover:implications for biogeochemical carbon and nutrient cycles

Rivers link terrestrial ecosystems and marine ecosystems, and they transport large amounts of substances into oceans each year, including several forms of silicon(Si), carbon(C), and other nutrients. However, river damming affects the water flow and biogeochemical cycles of Si, C, and other nutrients through biogeochemical interacting processes. In this review, we first summarize the current understanding of the effects of river damming on the processes of biogeochemical Si cycle, especially the source, composition, and recycling process of biogenic silica(BSi). Then, we introduce dam impacts on the cycles of C and some other nutrients. Dissolved silicon in rivers is mainly released from phytolith dissolution and silicate weathering. BSi in suspended matter or sediments in most rivers mainly consists of phytoliths and mainly originates from soil erosion. However, diatom growth and deposition in many reservoirs formed by river interception may significantly increase the contribution of diatom Si to total BSi, and thus significantly influence the biogeochemical Si,C, and nutrient cycles. Yet the turnover of phytoliths and diatoms in different rivers formed by river damming is still poorly quantified. Thus, they should be further investigated to enhance our understanding about the effects of river damming on global biogeochemical Si, C and nutrient cycles.

Contribution of phytoliths to total biogenic silica volumes in the tropical rivers of Malaysia and associated implications for the marine biogeochemical cycle

The contribution of phytoliths to total biogenic silica(BSi) volumes in rivers worldwide,and the associated implications for the biogeochemical cycle,require in-depth study.Based on samples from rivers in Peninsular Malaysia,this project investigated the source and characteristics of B Si found in Asian tropical rivers,as well as the process of reverse weathering taking place in these fluvial systems.Results indicated that BSi samples collected in sediments consisted of phytolith,diatom and sponge spicules.Phytoliths,predominantly of the elongate form,comprised 92.8%-98.3% of BSi in the Pahang River.Diatom BSi in this river consisted mainly of pennatae diatoms,but represented a relatively small proportion of the total BSi volume.However,diatom BSi(predominantly of the Centricae form) was more prevalent in the Pontian and Endau Rivers with shares of 68.8% and 79.3% of the total BSi volumes,respectively,than Pahang River.Carbon contents of the BSi particulates ranged from 1.85% to 10.8% with an average of 4.79%.These values are higher than those recorded in other studies to date,and indicate that BSi plays a major role in controlling permanent carbon burial.This study suggests that phytoliths from terrestrial plants are the primary constituents of BSi in the rivers of Peninsular Malaysia,and therefore represent a significant proportion of the coastal silica budget.

Impacts of silicon on biogeochemical cycles of carbon and nutrients in croplands

Crop harvesting and residue removal from croplands often result in imbalanced biogeochemical cycles of carbon and nutrients in croplands, putting forward an austere challenge to sustainable agricultural production. As a beneficial element, silicon（Si） has multiple eco-physiological functions, which could help crops to acclimatize their unfavorable habitats. Although many studies have reported that the application of Si can alleviate multiple abiotic and biotic stresses and increase biomass accumulation, the effects of Si on carbon immobilization and nutrients uptake into plants in croplands have not yet been explored. This review focused on Si-associated regulation of plant carbon accumulation, lignin biosynthesis, and nutrients uptake, which are important for biogeochemical cycles of carbon and nutrients in croplands. The tradeoff analysis indicates that the supply of bioavailable Si can enhance plant net photosynthetic rate and biomass carbon production（especially root biomass input to soil organic carbon pool）, but reduce shoot lignin biosynthesis. Besides, the application of Si could improve uptake of most nutrients under deficient conditions, but restricts excess uptake when they are supplied in surplus amounts. Nevertheless, Si application to crops may enhance the uptake of nitrogen and iron when they are supplied in deficient to luxurious amounts, while potassium uptake enhanced by Si application is often involved in alleviating salt stress and inhibiting excess sodium uptake in plants. More importantly, the amount of Si accumulated in plant positively correlates with nutrients release during the decay of crop biomass, but negatively correlates with straw decomposability due to the reduced lignin synthesis. The Si-mediated plant growth and litter decomposition collectively suggest that Si cycling in croplands plays important roles in biogeochemical cycles of carbon and nutrients. Hence, scientific Si management in croplands will be helpful for maintaining sustainable development of agriculture.

Biogeochemical Dynamics of Molybdenum in a Crater Lake:Seasonal Impact and Long-Term Removal

Despite a large variety of processes that can control Mo and its potential to become an environmental tracer of euxinic environment, this element is not often studied in lakes. The aim of this paper is to identify main seasonal biogeochemical processes that involve Mo in a well constrained freshwater system (Lake Pavin water-column) in order to evaluate their respective importance. In Lake Pavin, 4 main processes have been identified: 1) the transitional process represented by Mo assimilation of by phytoplankton in the epilimnion (nitrogen biological fixation and nitrate assimilation);2) transient process represented by dissolved Mo adsorption onto Fe and Mn metal oxides at oxic/anoxic interface (depth 50 - 60 m);3) Mo precipitation where apparent sulfide production rate is maximum, and from 80 m depths;4) release of dissolved Mo due to Mo benthic flux or input from a deep source.

Nitrous oxide emissions following seasonal freeze-thaw events from arable soils in Northeast China

Seasonal soil freeze-thaw events may enhance soil nitrogen transformation and thus stimulate nitrous oxide （N2O） emissions in cold regions. However, the mechanisms of soil N2O emission during the freeze-thaw cycling in the field remain unclear. We evaluated N2O emissions and soil biotic and abiotic factors in maize and paddy fields over 20 months in Northeast China, and the structural equation model （SEM） was used to determine which factors affected N2O production during non-growing season. Our results verified that the seasonal freeze-thaw cycles mitigated the available soil nitrogen and carbon limitation during spring thawing period, but simultaneously increased the gaseous N2O-N losses at the annual time scale under field condition. The N2O-N cumulative losses during the non-growing season amounted to 0.71 and 0.55 kg N ha 1 for the paddy and maize fields, respectively, and contributed to 66 and 18% of the annual total. The highest emission rates （199.2- 257.4 μg m-2 h-1） were observed during soil thawing for both fields, but we did not observe an emission peak during soil freezing in early winter. Although the pulses of N2O emission in spring were short-lived （18 d）, it resulted in approximately 80% of the non-growing season N2O-N loss. The N2O burst during the spring thawing was triggered by the combined impact of high soil moisture, flush available nitrogen and carbon, and rapid recovery of microbial biomass. SEM analysis indicated that the soil moisture, available substrates including NH4＋ and dissolved organic carbon （DOC）, and microbial biomass nitrogen （MBN） explained 32, 36, 16 and 51% of the N2O flux variation, respectively, during the non-growing season. Our results suggested that N2O emission during the spring thawing make a vital contribution of the annual nitrogen budget, and the vast seasonally frozen and snow-covered croplands will have high potential to exert a positive feedback on climate change considering the sensitive response of nitrogen biogeochemical cycling to the freeze-thaw disturbance.

Effect of long-term continuous cropping of strawberry on soil bacterial community structure and diversity

Long-term monoculture leads to continuous cropping （CC） problems, which complicate agricultural production, both locally and abroad. This study contrasted the different bacterial community compositions, physicochemical properties and enzyme activities of strawberry soil subjected to CC, CC rhizosphere （CCR）, non-CC （NCC） and non-CC rhizosphere （NCCR） treatments. The soil physicochemical properties and enzyme activities were significantly reduced after long-term CC. In addition, five variation trends were observed for the 11 major bacterial genera in the soil. Sphingomonas was the only stable group among all treatments. The proportions of Novosphingobium, Rhodoplanes, Povalibacter, Cellvibrio and Stenotrophobacterdecreased after CC. The relative abundances of Pelagibius, Thioprofundum and AIIokutzneria increased only in the CC treatment. Nitrospira were more abundant in rhizosphere soil than in non-rhizosphere soil. The relative abundance of Bacillus increased after CC. Redundancy analysis revealed that Bacillus, Pelagibius and AIIokutzneria had significant negative correlations with the soil physicochemical properties and enzyme activities. Therefore, these genera may be the key bacteria influenced by the physicochemical properties and enzyme activities altered by replanting. These results indicate that long-term CC of strawberry leads to less favourable rhizosphere soil conditions, which can be understood as a stress-induced response of the bacterial community diversity. Further research is needed to determine how the quality of soil is reduced by the shift in the diversity of the soil bacterial community.

Isolation and characterization of ferrous-and sulfur-oxidizing bacteria from Tengchong solfataric region,China

Microbial oxidation and reduction of iron and sulfur are important parts of biogeochemical cycles in acidic environments such as geothermal solfataric regions. Species of Acidithiobacillus and Leptospirillum are the common ferrous-iron and sulfur oxidizers from such environments. This study focused on the Tengchong sofataric region, located in Yunnan Province, Southwest China. Based on cultivation, 9 strains that grow on ferrous-iron and sulfuric compounds were obtained. Analysis of 16S rRNA genes of the 9 strains indicated that they were affiliated to AcidithiobaciUus, Alicyclobacillus, Sulfobacillus, Leptospirillum and Acidiphilium. Physiological and phylogenetic studies indicated that two strains （TC-34 and TC-71） might represent two novel members of Alicyclobacillus. Strain TC-34 and TC-71 showed 94.8%-97.1% 16S rRNA gene identities to other species of Alicyclobacillus. Different from the previously described Alicyclobacillus species, strains TC-34 and TC-71 were mesophilic and their cellular fatty acids do not contain w-cyclic fatty acids. Strain TC-71 was obligately dependent on ferrous-iron for growth. It was concluded that the ferrous-iron oxidizers were diversified and Alicyclobacillus species were proposed to take part in biochemical geocycling of iron in the Tengchong solfataric region.

Variations of nutrient elements and its effect on ecological environment off the Changjiang estuarine waters

On the basis of the date obtained in two cruises during October 1997 and May 1998, the concentration distribution and the variation of present species of nutrient elements in the water masses are described. The transform mechanism of present species of nutrients and the of differrnt water masses, frontal area and thermohaline transition layer on convergence or divergence and the biogeochemical cycle of nutrient elements off the Changjiang Estuary are studied. Meanwhile, the environmental capaci- ty of nutrients is primarily estimated: they are 1.803 x 104t DIN and 6.18 x 102t PO43- -P in autumn, and 4.20x 102t PO43- -P in spring.

Release the iron: does the infection of magnetotactic bacteria by phages play a role in making iron available in aquatic environments?

Magnetotactic bacteria(MTB)are ubiquitous prokaryotes that orient along magnetic field lines due to magnetosomes’biomineralization within the cell.These structures are ferrimagnetic organelles that impart a magnetic moment to the cell.To succeed in producing magnetosomes,MTB accumulate iron in(i)cytoplasm;(ⅱ)magnetosomes;and(ⅲ)nearby the organelle.It has already been estimated that a single MTB has an iron content of 10 to 100-fold higher than Escherichia coli.Phages are the most abundant entity in oceans and are known for controlling nutrient flow such as carbon and nitrogen by viral shunt and pump.The current work addresses the putative role of phages that infect MTB on the iron biogeochemical cycle.Can phage infection in MTB hosts cause a biogenic iron fertilization-like event in localized microenvironments?Are phages critical players in driving magnetosome biomineralization genes(BGs)horizontal transfer?Further investigation of those events,including frequency of occurrence,is necessary to fully comprehend MTB’s effect on iron cycling in aqueous environments.

Present status of aerosol research in China

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Background Concentration of Copper and Cadmium in Water from a High Industrialized and Urban Coastal System (Baixada Santista, Brazil)—Contribution to a Monitoring Program

The Baixada Santista coastal region is well known in the context of the high atmospheric, soil and aquatic pollution levels derived from port, industrial, domestic and urban activities existent there, mainly in function of the Cubatão industrial pole and port of Santos. The contamination by trace metals in this region is rarely measured in water column when compared with metal determinations in sediment studies. This study aims to evidence the levels of dissolved copper and total cadmium concentrations in estuarine and seawater waters using electrochemical analysis as a chronopotentiometric stripping polarography, which could improve the environmental monitoring program. The study was performed in the Bay of Santos reaching two estuarine channels (Santos and São Vicente Channels) in two tide periods in summer 2001. This region is influenced by terrestrial and anthropogenic inputs of trace metals to seawater. The results showed that dissolved copper and total cadmium in water presented the maxima concentrations of 45.4 nM and 2.6 nM respectively. They not reached the limits proposed by Brazilian Environmental Law (CONAMA), that indicate, as reference, a maximum of 123 nM and 350 nM for dissolved copper and total cadmium, respectively and, considering seawater coastal system (salinity > 30, class 2) and also brackish water (class 2). Although the values were under the maximum recommended for each metal, the concentrations were not negligible in relation to the other polluted areas in the world. The values distribution along the system showed a progressive increase in direction to the inner part of the system that naturally compromises the local biota whose is more exposed to the bioaccumulation processes, and this data corresponds to an important reference preterit value to the monitoring program. The trace metal bioaccumulation by mangrove vegetation and by the biota in the internal part of the estuarine channels increase the risk of the poorly population that living in the internal part of the estuary, used to the seafood consumption. The contribution of this study is important to guide the protective policies destined to recuperate the natural conditions of this system, mainly considering that in the decade 1980, there was a case of toxic contamination, causing hydrocephaly in newborns. It proves the existence of risks to the human health and to the balance of the ecosystem, even with the decrease of pollution after that, the environmental evaluation needs to know the background values to guide environmental protection.

水电梯级开发真的破坏下游河段营养盐情势吗?

River damming is believed to largely intercept nutrients,particularly retain more phosphorus(P)than nitrogen(N),and thus harm primary productivity,fishery catches,and food security downstream,which seriously constrain global hydropower development and poverty relief in undeveloped regions and can drive geo-political disputes between nations along trans-boundary rivers.In this study,we investigated whether reservoirs can instead improve nutrient regimes downstream.We measured different species of N and P as well as microbial functions in water and sediment of cascade reservoirs in the upper Mekong River over 5 years and modelled the influx and outflux of N and P species in each reservoir.Despite partially retaining total N and total P,reservoirs increased the downstream flux of ammonium and soluble reactive phosphorus(SRP).The increase in ammonium and SRP between outflux and influx showed positive linear relationships with the hydraulic residence time of the cascade reservoirs;and the ratio of SRP to dissolved inorganic nitrogen increased along the reservoir cascade.The lentic environment of reservoirs stimulated algae-mediated conversion of nitrate into ammonium in surface water;the hypoxic condition and the priming effect of algae-induced organic matter enhanced release of ammonium from sediment;the synergy of microbial phosphorylation,reductive condition and sediment geochemical properties increased release of SRP.This study is the first to provide solid evidence that hydropower reservoirs improve downstream nutrient bioavailability and N-P balance through a process of retention-transformation-transport,which may benefit primary productivity.These findings could advance our understanding of the eco-environmental impacts of river damming.

Sulfur mediated heavy metal biogeochemical cycles in coastal wetlands:From sediments,rhizosphere to vegetation

The interactions and mechanisms between sulfur and heavy metals are a growing focus of biogeochemical studies in coastal wetlands.These issues underline the fate of heavy metals bound in sediments or released into the system through sediments.Despite the fact that numerous published studies have suggested sulfur has a significant impact on the bioavailability of heavy metals accumulated in coastal wetlands,to date,no review article has systematically summarized those studies,particularly from the perspective of the three major components of wetland ecosystems(sediments,rhizosphere,and vegetation).The present review summarizes the studies published in the past four decades and highlights the major achievements in this field.Research and studies available thus far indicate that under anaerobic conditions,most of the potentially bioavailable heavy metals in coastal wetland sediments are fixed as precipitates,such as metal sulfides.However,fluctuations in physicochemical conditions may affect sulfur cycling,and hence,directly or indirectly lead to the conversion and migration of heavy metals.In the rhizosphere,root activities and microbes together affect the speciation and transformation of sulfur which in turn mediate the migration of heavy metals.As for plant tissues,tolerance to heavy metals is enhanced by sulfur-containing compounds via promoting a series of chelation and detoxification processes.Finally,to further understand the interactions between sulfur and heavy metals in coastal wetlands,some major future research directions are proposed.

Partial organic fertilizer substitution promotes soil multifunctionality by increasing microbial community diversity and complexity

Partial substitution of synthetic nitrogen(N)with organic fertilizers(PSOF)is of great significance in improving soil ecosystem functions in systems that have deteriorated due to the excessive application of chemical N fertilizer.However,existing studies typically focus on individual soil functions,neglecting the fact that multiple functions occur simultaneously.It remains unclear how PSOF influences multiple soil functions and whether these impacts are related to soil microbial communities.Here,we examined the impacts of partial substitutions(25%–50%)of chemical N fertilizer with organic form(pig manure or municipal sludge)in a vegetable field on soil multifunctionality,by measuring a range of soil functions involving primary production(vegetable yield and quality),nutrient cycling(soil enzyme activities,ammonia volatilization,N leaching,and N runoff),and climate regulation(soil organic carbon sequestration and nitrous oxide emission).We observed that PSOF improved soil multifunctionality,with a 50%substitution of chemical N fertilizer with pig manure being the best management practice;the result was strongly related to the diversities and network complexities of bacteria and fungi.Random forest analysis further revealed that soil multifunctionality was best explained by the bacterial-fungal network complexity,followed by available phosphorus level and bacterial diversity.The PSOF also shifted the composition of bacterial and fungal communities,with increased relative abundances of dominant bacteria phyla,such as Bacteroidetes,Gemmatimonadetes,and Myxococcota,and fungal phyla,such as Basidiomycota and Olpidiomycota.The observed increases in soil multifunctionality were consistent with significant increases in the relative abundances of keystone taxa such as Blastocladiomycota,Chaetomiaceae,and Nocardiopsaceae.Together,these findings indicate that PSOF can enhance interactions within and among microbial communities and that such practices have the potential to improve soil ecosystem multifunctionality and contribute to the development of sustainable agriculture.

Influencing factors and significance of organic and inorganic nitrogen isotopic compositions in lacustrine sedimentary rocks

Comprehensive nitrogen biogeochemical cycle has been reconstructed for representative lacustrine organic-rich sedimentary rock in China,namely the Triassic Yanchang Formation(YF,199–230 Ma)in Ordos and the Cretaceous Qingshankou Formation(QF,86–92 Ma)in Songliao basins,by evaluating the organic and inorganic nitrogen isotopic compositions rather than only organic or bulk nitrogen isotopic compositions.The results indicate that the nitrogen isotope values of bulk rock(δ^(15)N_(bulk))in the non-metamorphic stage are significantly different from that of kerogen,which challenge the conceptual framework of sedimentary nitrogen isotope interpretation.Theδ^(15)N_(bulk)from the YF and QF were lower than their respective the nitrogen isotope values of kerogen(δ^(15)N_(ker)),with offsets up to5.1‰,which have the inverse relationship for the metamorphosed rock.Thermal evolution did not significantly modify the d15N of bulk rock and kerogen.The d15N of sediments from the YF(δ^(15)N_(bulk),1.6‰–5.6‰)were lower than that of rock from the QF(δ^(15)N_(bulk),10.2‰–15.3‰).The nitrogen isotope values of silicate incorporated nitrogen(δ^(15)N_(sil))were slightly lower than those of the d15Nker in the YF and obviously lower for the QF.The fact that different nitrogen cycles occur in the YF and QF due to the different depositional redox conditions leads to different isotopic results.The YF water environment dominated by oxic conditions is not conducive to the occurrence of denitrification and anammox,and no abundant N2 loss leads to the relatively lightδ^(15)N_(bulk).In the stratified water for the QF,redox transition zone promotes denitrification and anammox,resulting in the heavyδ^(15)N_(bulk)of rock and promotes the DNRA,resulting in heavyδ^(15)N_(ker)and lowδ^(15)N_(sil).