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Metal stable isotopes in marine carbonates have been widely used as novel proxies for metal cycling through the geological past. Amongst these metals, copper (Cu) and zinc (Zn) have received great attention owing to their vital roles in metabolic processes. However, whether modern marine biogenic carbonates record the seawater isotope signatures of Cu (δ65Cu) and Zn (δ66Zn) and mechanisms and factors controlling isotope fractionation of these metals remain unclear, hindering applications of both isotope systems in paleoceanography. Here we present annually-resolved records of δ65Cu and δ66Zn in seven coral (Porites) cores sampled from different marine settings in the South China Sea and the Luzon Strait, western Pacific. We find that the aragonitic skeletons of corals are enriched in light Cu but heavy Zn isotopes relative to surface seawaters, with δ65Cu and δ66Zn in the range of −0.16 ± 0.06‰ to 0.40 ± 0.05‰ and 0.06 ± 0.04‰ to 0.46 ± 0.08‰ (2SD), respectively. The coral δ65Cu exhibits significant inter- and intra-colony variations, which are most likely controlled by Rayleigh-type fractionation in the calcifying fluids of corals rather than by changes in environmental factors or seawater δ65Cu. We thus suggest that δ65Cu in ancient carbonates may not be a direct record of Cu isotope compositions in coeval seawaters. In contrast, coral δ66Zn shows insignificant temporal variation, and the Zn isotope fractionation between individual corals and seawaters are relatively small and constant (0.10 ± 0.05‰, n = 33, 2SD). This limited Zn isotope fractionation is much lower than that determined during inorganic precipitation of calcite, which is likely due to pH up-regulation by the coral that changes aqueous Zn speciation, and preferential organic complexation of the heavy Zn isotopes in the calcifying fluids. Therefore, Porites corals are promising archives for tracking historical changes of surface seawater δ66Zn. Our new datasets of reef carbonates, particularly the coral δ65Cu values which are measured for the first time, could provide a better constrain on marine Cu and Zn geochemistry and their modern oceanic mass and isotope budgets.

Phosphorus (P) availability in soils controls critical functions and properties of terrestrial ecosystems. Vertical distribution patterns of P concentration and speciation in soil profiles provide historical records of how pedogenic processes redistribute and transform P and thus change its availability in soils, which, however, remain poorly understood. We determined the patterns in three forest soil profiles of contrasting climate, using fine sampling intervals, P K-edge X-ray absorption near edge (XANES) spectroscopy and chemical extractions. The major features of the patterns persist under the contrasting climate. The total P concentration decreases from A to B horizons, reaches a minimum in the B horizons, and then increases towards the upper C horizons, but with little variations with depth in the lower C horizons. Both calcium-bound inorganic P (Ca–Pi) and organic P (Po) decrease and Fe- and Al-bound Pi [(Fe + Al)–Pi] increases in proportion downward in the A horizons because dust inputs and accumulation of organic matter both decline with increasing depth. Ca–Pi is negligible and (Fe + Al)–Pi is dominant in the B horizons due to strong weathering. There is a strong downward increase in Ca–Pi proportion and decrease in (Fe + Al)–Pi proportion from the lower B to the upper C horizons. New Ca–Pi seems to form in the upper C horizons where downward leaching Ca2+ and phosphate accumulate due to the low water permeability of the soils. In the lower C horizons, Ca–Pi increases and (Fe + Al)–Pi decreases with increasing depth due to decreasing chemical weathering. Regarding P bioavailability, the proportion of occluded P (Pocc) shows an increasing and decreasing trend with increasing depth, being the highest in the B horizons; however, there are no consistent trends for non-occluded P (Pn-occ). While the P vertical patterns can be understood by considering the relative importance of different pedogenic processes, climate affects the intensities of these processes and thus the details of the patterns. When depth-integrated, warmer/wetter climate results in decreases in the proportions of both Ca–Pi and Pn-occ but increases in the P loss and the proportions of Po, (Fe + Al)–Pi, and Pocc. Regardless of soil depth and climate, the Pi speciation, i.e., the relative proportions of Ca–Pi and (Fe + Al)–Pi over total Pi, correlates well with soil pH and weathering degree (Chemical Index of Alteration, CIA), and the Po concentration correlates with pedogenic Fe and Al and organic carbon concentration. The correlations suggest that the Pi speciation is primarily controlled by soil geochemistry/mineralogy, and the Po concentration by both soil geochemistry/mineralogy and biological activities. Pocc correlates with CIA, and thus is mainly controlled by soil mineralogy; but Pn-occ correlates weakly with soil properties, probably due to its susceptibility to combined influences of dust inputs, leaching, biological activities, and adsorption on minerals. The above quantitative relationships may help predict P speciation and availability in diverse soils. We further show that soil profiles, and climate and CIA gradients are useful tools for studying P transformations, particularly for the Pi pool, during pedogenesis. This study provides an integration and synthesis of controls of climatic and edaphic variables on P dynamics in forest soils.

A large number of gases are releasing from the medium-high temperature geothermal fields distributed along the large-scale strike-slip fault zones in the southeastern margin of the Tibetan Plateau. In this study, 11 hot spring water and the associated bubbling gas samples were collected along the Xianshuihe-Anninghe fault zones (XSH-ANHFZ) and analyzed for chemical and isotopic compositions. The $${\delta ^{18}}{{\rm{O}}_{{{\rm{H}}_2}{\rm{O}}}}$$ and $$\delta {{\rm{D}}_{{{\rm{H}}_2}{\rm{O}}}}$$ values indicate that hot spring waters are predominantly meteoric origin recharged from different altitudes. Most water samples are significantly enriched in Na+ and HCO3− due to the dissolution of regional evaporites, carbonates and Na-silicates. 3He/4He ratios of the gas samples are 0.025–2.73 times the atmospheric value. The 3He/4He ratios are high in the Kangding region where the dense faults are distributed, and gradually decrease with increasing distance from Kangding towards both sides along the Xianshuihe fault zones (XSHFZ). Hydrothermal fluids have dissolved inorganic carbon (DIC) concentrations from 2 to 42 mmol L−1, δ13CDIC from −6.9‰ to 1.3‰, $${\delta ^{13}}{{\rm{C}}_{{\rm{C}}{{\rm{O}}_2}}}$$ from −7.2‰ to −3.6‰ and Δ14C from −997‰ to −909‰. Combining regional geochemical and geological information, the CO2 sources can be attributed to deep-sourced CO2 from mantle and metamorphism of marine carbonate, and shallow-sourced CO2 from the dissolution of marine carbonate and biogenic CO2. The mass balance model shows that 11±6% of the DIC is sourced from the dissolution of shallow carbonate minerals, 9±8% formed by pyrolysis of sedimentary organic matter, 80±9% derived from deep metamorphic origin and mantle-derived CO2. Among them, the deep-sourced CO2 in Anninghe fault zones (ANHFZ) is merely metamorphic carbon, whereas ca. 12% and ca. 88% of the deep-sourced CO2 in the XSHFZ are derived from the mantle and metamorphic carbon, respectively. The average deep-sourced CO2 flux in the Kangding geothermal field is estimated to be 160 t a−1. If all the hot springs in various fault zones in the southeastern margin of the Tibetan Plateau are taken into account, the regional deep-sourced CO2 flux would reach ca. 105 t a−1. These results show that the deep-sourced CO2 released from non-volcanic areas might account for a considerable proportion of the total amount of global deep-sourced carbon degassing, which should be paid more attention to.

Little is known about the formation processes of nitrooxy organosulfates (OSs) by nighttime chemistry. Here we characterize nitrooxy OSs at a molecular level in firework-related aerosols in urban Beijing during Chinese New Year. High-molecular-weight nitrooxy OSs with relatively low H / C and O / C ratios and high unsaturation are potentially aromatic-like nitrooxy OSs. They considerably increased during New Year's Eve, affected by the firework emissions. We find that large quantities of carboxylic-rich alicyclic molecules possibly formed by nighttime reactions. The sufficient abundance of aliphatic-like and aromatic-like nitrooxy OSs in firework-related aerosols demonstrates that anthropogenic volatile organic compounds are important precursors of urban secondary organic aerosols (SOAs). In addition, more than 98 % of those nitrooxy OSs are extremely low-volatility organic compounds that can easily partition into and consist in the particle phase and affect the volatility, hygroscopicity, and even toxicity of urban aerosols. Our study provides new insights into the formation of nitrooxy organosulfates from anthropogenic emissions through nighttime chemistry in the urban atmosphere.

Snow serves as a vital scavenging mechanism to gas-phase and particle-phase organic nitrogen substances in the atmosphere, providing a significant link between land-atmosphere flux of nitrogen in the surface-earth system. Here, we used optical instruments (UV-vis and excitation-emission matrix fluorescence) and a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) to elucidate the molecular composition and potential precursors of snow samples collected simultaneously at four megacities in North China. The elemental O/N ratio (≥3), together with the preference in the negative ionization mode, indicates that the one and two nitrogen atom-containing organics (CHON1 and CHON2) in snow were largely in the oxidized form (as organic nitrates, -ONO2). This study assumed that scavenging of particle-phase and gas-phase organic nitrates might be significant sources of CHON in precipitation. A gas-phase oxidation process and a particle-phase hydrolysis process, at a molecular level, were used to trace the potential precursors of CHON. Results show that more than half of the snow CHON molecules may be related to the oxidized and hydrolyzed processes of atmospheric organics. Potential formation processes of atmospheric organics on a molecular level provide a new concept to better understand the sources and scavenging mechanisms of organic nitrogen species in the atmosphere.

This study investigated the effects of different elevated CO2 concentrations [ambient CO2 concentration (CK), CK plus 40 μmol mol-1 (T1), CK plus 200 μmol mol-1 (T2)] on photosynthetic characteristics and growth of rice (Oryza sativa L.) and winter wheat (Triticum aestivum L.). The results showed that T2 treatment decreased the net photosynthetic rate and leaf nitrogen content (LNC) but increased the light-saturated net photosynthetic rate of rice. Additionally, T2 treatment increased biomass accumulation and yield in both rice and winter wheat to some extent. T1 treatment, however, had little effect on photosynthetic parameters, LNC, biomass, and yield during the rice and winter wheat growing seasons. The above results suggest that the photosynthesis and growth responses of rice and winter wheat to different CO2 concentrations differed, in general, the increase of CO2 concentrations influenced more photosynthetic performance and growth of C3 plants than lower CO2 concentrations.

Tectonically active high relief areas are proposed to have a substantial impact on climate regulation throughout the Cenozoic. Here, we present lithium (Li) isotope data of the dissolved load and suspended particulate material from the basins of the Yalong River and the Jinsha River, which drain the high-relief borders of the eastern Tibetan Plateau and constitute the headwaters of the Yangtze River. Dissolved δ7Li values are relatively low and constant in the Jinsha River mainstream (+6.8‰ to +9.7‰) compared to the higher and downstream increasing values in the Yalong River mainstream (+10.8‰ to +17.5‰). Furthermore, dissolved δ7Li values in the major tributaries of the Jinsha and Yalong River are highly variable and increase downstream from +11.4‰ to +29.4‰ and from +9.0‰ to +23.6‰, respectively. Robust correlations between Li, Na, and Cl concentrations identify that evaporite dissolution in the uppermost headwaters of the Jinsha River basin controls the Li budget and riverine δ7Li values of the mainstream and has a significant impact on dissolved Li in the Yangtze River. In contrast to the Jinsha River mainstream, dissolved Li in the Yalong River mainstream and the Jinsha and Yalong River tributaries are dominantly derived from the dissolution of silicates. δ7Li variations in the Yalong River basin and the Jinsha tributaries reflect little Li uptake by clays in the upper reaches and more Li uptake by clays in the lower reaches of the river basins. SWR/D ratios (where SWR is the chemical silicate weathering rate, and D is the total denudation rate) highlight an intermediate silicate weathering intensity under a kinetically limited weathering regime for the study area. However, positive correlations between dissolved δ7Li value and silicate weathering intensity proxies (such as Si/(Nasil + K) and K/(Nasil + K)) indicate an increasing weathering intensity downstream. A positive correlation between dissolved δ7Li values and the annual precipitation and a negative one between δ7Li values and elevation indicates that larger annual precipitation under a flattening relief results in a stronger silicate weathering intensity, thus, more Li uptake in clays and higher riverine δ7Li values in the lower reaches. Compared to the lower reaches of Yangtze River basin (∼+20‰), lower dissolved δ7Li values in its headwater of this study suggest that the increase in δ7Li of seawater over the Cenozoic is influenced by weathering in floodplains that developed due to erosion of high mountains, rather than weathering of mountain belts itself. Combined with silicate weathering rates of the eastern border of the Tibetan Plateau, the highest riverine δ7Li values in its catchments come along with the highest silicate weathering rates and high CO2 consumption, suggesting that a more elevated topography may have an important role in the drawdown of CO2 during the Cenozoic.

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To characterize secondary organic aerosols (SOA) over the Tianjin region, we studied the SOA tracers derived from isoprene, α/β-pinene, β-caryophyllene, and aromatics in PM2.5 collected at an urban...

Molecular compositions and stable carbon isotope ratios (δ13C) of n-alkanes and fatty acids (FA) were investigated in urban aerosols from Beijing, China. Seasonal trends for n-alkanes showed a high...

This study investigates the concentrations and δ15N values of NH4+ in PM2.5 at three heights (8, 120, and 260 m) on a 325 m tower in urban Beijing. NH4+ concentrations were lower during the Parade ...

Nitrate (NO3−) is a key component of secondary inorganic aerosols and PM2.5. However, the contributions of nitrogen oxides (NOx) emission sources to NO3− in PM2.5 remain poorly constrained. This study measured nitrogen (N) isotopes of NO3− (hereafter as δ15N-NO3-) in PM2.5 collected at Beijing in 2014. We observed that δ15N-NO3- values in PM2.5 (−2.3‰ − 19.7‰; 7.3 ± 5.4‰ annually) were significantly higher in winter (11.9 ± 4.4‰) than in summer (2.2 ± 2.5‰). The δ15N differences between source NOx and NO3− in PM2.5 (hereafter as Δ values) were estimated by a computation module as 7.8 ± 2.2‰ − 10.4 ± 1.6‰ (8.8 ± 2.4‰). Using the Δ values and δ15N values of NOx from major fossil (coal combustion, vehicle exhausts) and non-fossil sources (biomass burning, microbial N cycle), contributions of major NOx sources to NO3− in PM2.5 were further estimated by the SIAR model. We found that seasonal variations of δ15N-NO3- values in PM2.5 of Beijing were mainly caused by those of NOx contributions from coal combustion (38 ± 10% in winter, 20 ± 9% in summer). Annually, NOx from coal combustion, vehicle exhausts, biomass burning, and microbial N cycle contributed 28 ± 12%, 29 ± 17%, 27 ± 15%, and 16 ± 7% to NO3− in PM2.5, respectively, showing actually comparable contributions between non-fossil NOx (43 ± 16%) and fossil NOx (57 ± 21%). These results are useful for planning the reduction of NOx emissions in city environments and for elucidating relationships between regional NOx emissions and atmospheric NO3− pollution or deposition.

Accurately quantifying the budget of carbon sources and sinks in hydropower reservoirs is important for evaluating the cleanliness of hydroelectricity. However, current research on carbon emissions from reservoirs has rarely taken into account the organic carbon (OC) buried in sediment. Only greenhouse gas emissions from the water-air interface at reservoirs have been examined, which would result in an overestimation of the greenhouse effect of reservoirs. In November 2017, this study investigated the distribution of sediment in the Hongfeng Reservoir (HFR) in southwest China, a typical large hydropower reservoir, by using an underwater seismology monitoring system. We estimated the flux of OC into sediment using the results of a sediment survey and a dataset compiled from references. Our results show that, the HFR retained 200,715 t of OC in the sediment since its impounding after dam construction to the sampling year of 2017, when the average burial flux was 3,521 t-C a−1 (106 g C a−1) and the modern burial flux was 5,449 t-C a−1. After excluding the exogenous OC, the modern valid carbon sink of the sediment was 4,632 t per year. Under the current state of the reservoir, taking the modern valid carbon sink value, the carbon emissions from the reservoirs surface, and the discharge water from the dam into consideration, the net carbon sink of the HFR is found to be 1,098.9 t-C a−1. If the hydroelectricity generated by the reservoir is converted to a carbon sink, then the total net carbon sink becomes 12,972.9 t-C a−1. This work argues that both reservoir sediment and hydroelectricity are important carbon sinks and both should be included in assessments of the greenhouse effects of reservoirs.

Accurate determination of lithium (Li)isotopic composition in natural geological samples is the basis for Li isotope geochemical studies. In this study, a method contained preparation of geological materials (water and rock) and accurate determination of Li isotopic composition was set up. The separation of Li from water and rock samples was implemented by a single column containing 1.5 mL of Bio-Rad AG 50W-X12 (200–400 mesh) resin, with 0.40 M HCl and 1.0 M HCl as eluents. Only 8.5 and 14 mL of eluents were used to separate Li from water and rock samples with this method, respectively. Blank signal of the operation procedure was (2.4 ± 0.1) mV, which was almost same as the 2.3 mV of the 2% HNO3 signal used in this study. Experimental results showed that Li isotopic fractionation during leaching process was significant and deviation of δ7Li values in these samples with incompletely recovered Li reached up to 50‰. Lithium isotopic ratios were determined by multi-collector ICP-MS (Nu Plasma II) using the sample standard bracketing (SSB) method. L-SVEC standard with similar Li concentration to samples (about 80 ng mL−1) was used in this study. The external precision (2σ) of this technique, determined by repeated measurement of pure Li standard solutions and seawater was

2,5-substituted-6-(4-nitrophenyl)-5H-thiazolo[3,2-a]pyrimidin-7-amines. This method, optimized under microwave conditions, was highly efficient and environmentally benign and delivered the desired products in good yields (89–96%) in short reaction time (

Total carbon content of the atmospheric suspended particulate matters consisted of as high as 89-93% organic carbon (OC) in Ulaanbaatar aerosol without showing seasonal variation. However, limited aerosol measurements have been conducted on these OC rich aerosols particularly for high molecular weight constituents. In order to address the gap above, abundance of high molecular weight humic-like substances (HULIS) in total suspended particulates (TSP) from Ulaanbaatar atmospheric aerosol were determined for the first time. HULIS molecular structure was characterised for different seasons using carbon content and UV absorbance measurements coupled with solid phase extraction methods. Although, HULIS contributions to water soluble organic fraction of the winter and summer aerosols were similar HULIS carbon concentration was higher in winter samples (9-37 mg·L-1) than in summer (2-6 mg·L-1). Consequently quantity of aromatic moieties and degree of aromaticity varied between seasons.

Organic aerosols (OA) that make up a large fraction (up to 90%) of the fine aerosol (PM2.5) mass have severe impact on the Earth’s climate system and can cause adverse risk to human health. Diacids and related compounds are ubiquitous in PM2.5 in different environments and accounts for a substantial fraction in OA. Because of their high water-solubility, they can influence the hygroscopic properties and capacity of cloud condensation nuclei formation activity of aerosols and thus affect the indirect radiative forcing in the atmosphere. However, their origins, secondary formation and transformations and seasonality are not fully understood yet. To better understand the seasonal characteristics, origins and photochemical processing of OA in the Tianjin region, North China, we studied the molecular distributions and seasonal variations of water-soluble diacids, oxoacids and α-dicarbonyls in PM2.5 collected at an urban and a suburban sites in Tianjin, an ideal location to study the aerosols, over a one-year period from July 2018 to June 2019. We found significant changes in concentrations and composition of diacids and related compounds from season to season at both the sites. Here, based on the results obtained together with the meteorology, oxidants (O3 and NO2) and SO2, loading and the backward air mass trajectories, we discuss the possible origins and possible secondary formation pathways of diacids and related compounds in the Tianjin region.

Little is known about the formation processes of nitrooxy-organosulfates (nitrooxy-OSs) by nighttime chemistry. Here we characterize nitrooxy-OSs at a molecular level in firework-related aerosols in urban Beijing during Chinese New Year. High-molecular-weight nitrooxy-OSs with relatively low H / C and O / C ratios and high unsaturation, which are potentially aromatic-like nitrooxy-OSs, considerably increased during the New Year’s Eve. We find that large quantities of carboxylic-rich alicyclic molecules possibly formed by nighttime reactions. The sufficient abundance of aliphatic-like and aromatic-like nitrooxy-OSs demonstrates that both anthropogenic and biogenic volatile organic compounds are essential precursors of urban secondary organic aerosols (SOA). Besides, more than 98 % of nitrooxy-OSs were extremely low-volatile organic compounds that could easily partition into and consist in the particle phase, and affected the volatility, hygroscopicity, and even toxicity of urban aerosols. Our study provides new insights into the formation of nitrooxy-organosulfates from anthropogenic emissions through nighttime chemistry in the urban atmosphere.

Since the industrial revolution, it has been assumed that fossil-fuel combustions dominate increasing nitrogen oxide (NOx) emissions. However, it remains uncertain to the actual contribution of the non-fossil fuel NOx to total NOx emissions. Natural N isotopes of NO3− in precipitation (δ15Nw-NO3−) have been widely employed for tracing atmospheric NOx sources. Here, we compiled global δ15Nw-NO3− observations to evaluate the relative importance of fossil and non-fossil fuel NOx emissions. We found that regional differences in human activities directly influenced spatial-temporal patterns of δ15Nw-NO3− variations. Further, isotope mass-balance and bottom-up calculations suggest that the non-fossil fuel NOx accounts for 55 ± 7% of total NOx emissions, reaching up to 21.6 ± 16.6Mt yr−1 in East Asia, 7.4 ± 5.5Mt yr−1 in Europe, and 21.8 ± 18.5Mt yr−1 in North America, respectively. These results reveal the importance of non-fossil fuel NOx emissions and provide direct evidence for making strategies on mitigating atmospheric NOx pollution., This study investigates in the importance of non-fossil fuel NOx emissions in the surface-earth-nitrogen cycle. The study shows how changes of regional human activities directly influence δ15N signatures of deposited NOx to terrestrial environments and that emissions have largely been underestimated.

The production of fluorescent dissolved organic matter (FDOM) by phytoplankton and its subsequent degradation, both of which occur constantly under diurnal-day time sunlight and by night time dark-microbial respiration processes in the upper layer of surface waters, influence markedly several biogeochemical processes and functions in aquatic environments and can be feasibly related to global warming (GW). In this work sunlight-mediated high-temperature was shown to accelerate the production of FDOM, but also its complete disappearance over a 24-h diurnal period in July at the highest air and water temperatures (respectively, 41.1 and 33.5 °C), differently from lower temperature months. Extracellular polymeric substances (EPS), an early-state DOM, were produced by phytoplankton in July in the early morning (6:00–9:00), then they were degraded into four FDOM components over midday (10:00–15:00), which was followed by simultaneous production and almost complete degradation of FDOM with reformation of EPS during the night (2:00–6:00). Such transformations occurred simultaneously with the fluctuating production of nutrients, dissolved organic carbon (DOC), dissolved organic nitrogen (DON) and the two isotopes (δ15N and δ18O) of NO3−. It was estimated that complete degradation of FDOM in July was associated with mineralization of approximately 15% of the initial DOC, which showed a nighttime minimum (00:00) in comparison to a maximum at 13:00. FDOM identified by excitation-emission matrix spectroscopy combined with parallel factor analysis consisted of EPS, autochthonous humic-like substances (AHLS) of C- and M-types, a combined form of C- and M-types of AHLS, protein-like substances (PLS), newly-released PLS, tryptophan-like substances, tyrosine-like substances (TYLS), a combined form of TYLS and phenylalanine-like substances (PALS), and their degradation products. Finally, stepwise degradation and production processes are synthesized in a pathway for FDOM components production and their subsequent transformation under different diurnal temperature conditions, which provided a broader paradigm for future impacts on GW-mediated DOM dynamics in lake water.

The production of fluorescent dissolved organic matter (FDOM) produced from phytoplankton and its subsequent degradation both of which occur constantly under diurnal-day time sunlight and by night time dark-microbial processes, influence markedly several biogeochemical processes and functions in aquatic environments and can be feasibly related to global warming (GW). In this work sunlight-mediated high-temperature was shown to accelerate the production of FDOM, but also its complete disappearance over a 24-h diurnal period in July, but not in lower temperature months. In July, extracellular polymeric substances (EPS), an early-state DOM, were produced from phytoplankton in early morning (06:00–09:00), then were degraded into four FDOM components over midday (10:00–15:00), which was followed by simultaneous production and almost complete degradation of FDOM with reformation of EPS during night time (02:00–06:00). Such transformations occurred simultaneously with the fluctuating production of nutrients (NH4+, NO3−, NO2−, PO43− and dissolved Si), dissolved organic carbon (DOC), dissolved organic nitrogen (DON) and the two isotopes (δ15N and δ18O) of NO3−. The FDOM components identified by fluorescence excitation-emission matrix (EEM) spectroscopy combined with parallel factor (PARAFAC) analysis consisted of EPS, autochthonous humic-like substances (AHLS) of C and M types distinctly, a combined form of C and M types of AHLS, protein-like substances (PLS), newly-released PLS, tryptophan-like substances (TLS), tyrosine-like substances (TYLS), a combined form of TYLS and phenylalanine-like substances (PALS), as well as their degradation products. Finally, stepwise degradation and production processes are synthesized in a pathway for FDOM components production and their subsequent transformation under different diurnal temperature conditions, which provided a broader paradigm for future impacts on GW-mediated DOM dynamics in lake water.

Summary Microbe-mineral interactions have shaped the surface of the Earth and impacted the evolution of plants and animals. Although more than two-thirds of known mineral species have biological imprints, how the biotransformation of minerals may have benefited microbial development, beyond nutritional and energetic use, remains enigmatic. In this research, we have shown that biogenic ferrihydrite nanoparticles are extensively formed at the interface between an actively growing fungus and an iron-containing mineral, hematite. These biogenic nanoparticles formed through the fungus-hematite interactions can behave as mimetic catalysts, similar to nanozymes that imitate peroxidase, which scavenges hydrogen peroxide for the mitigation of potential cytotoxicity. Evidence from various X-ray spectroscopic analyses indicated that non-lattice oxygen in the nanomaterials was chiefly responsible for this catalytic activity, rather than through the conventional mechanisms of iron redox chemistry. Cryo-scanning electron microscopy, high-resolution (∼30 nm) 3D volume rendering, and biomass analyses further confirmed that the organism was active and capable of mediating the catalytic reactions. We therefore hypothesize that this confers an advantage to the organism in terms of protection from oxidative stress and ensuring the acquisition of essential iron. This work raises new questions about the roles of biogenic nanomaterials in the coevolution of the lithosphere and biosphere and provides a step toward understanding the feedback pathways controlling the evolution of biogenic mineral formation.

Secondary organic aerosols (SOA) that account for a substantial and often a dominant fraction of total OA mass are formed by photooxidation of various precursors derived from anthropogenic and biogenic sources in the atmosphere. They have serious impacts on the Earth’s climate system directly by scattering and absorbing solar radiation and indirectly by acting as cloud condensation nuclei, and adverse effects on human health. In recent times, considerable attention has been paid on laboratory studies, preferably in gas-phase, in order to understand the chemistry of SOA formation. However, the studies on SOA formation in aqueous phase are limited, which are mainly focused on high abundant volatile organic compounds (e.g., isoprene) and/or their oxidation products, but not on fatty acids (except oleic acid). To better understand the air-water interface photochemistry of fatty acids and their transformations to lower homologous monoacids and more oxygenated species such as diacids and related compounds in atmospheric waters (fog, cloud and aqueous aerosol), we conducted batch UV irradiation experiments on a saturated (stearic acid, C18H36O2) and an unsaturated (linoleic acid, C18H32O2) fatty acids for different time periods (age, 0-120 h) in aqueous-phase. All the irradiated samples were analyzed for measurements of mono- and di-acids, oxoacids and α-dicarbonyls. We found high abundances of monoacids followed by diacids, pyruvic acid and α-dicarbonyls in less aged samples, whereas C3 and C4 diacids were abundant in the more aged samples. Our results imply that the photochemical oxidation of fatty acids and subsequent transformations of the product species in atmospheric waters are significant and their contribution to more oxygenated SOA is increased with aging in the atmosphere.

Superoxide, produced photochemically as well as microbially, is an important reactant present in seawater and a major source of hydrogen peroxide. Superoxide decay may occur through catalyzed or uncatalyzed dismutation forming H2O2 and O2, through oxidation to O2, or through reduction into H2O2. Under definite circumstances, the redox processes that are different from dismutation could produce or consume H+, thereby altering the pH of seawater. In order to alter the pH, these processes have to involve, together with O2•, redox couples that exchange e and H+ in a ratio other than 1:1. This potential pH modification is dependent on several factors, including the extent of H+ imbalance, the rate of formation/transformation of superoxide (which reaches a steady-state concentration in seawater), and the alkalinity of seawater (which varies globally from 2.10 to 2.45 mmol L1 and buffers the pH variations). In the present study, an estimate of the possible pH changes associated with photochemically-produced superoxide in the global ocean has been provided. Among the important approximations that were required to perform the calculations, one was that it was not possible to include the microbially generated O2•, as a geographic distribution of microbial processes is not available. Unfortunately, the microbial production of O2• is comparable to or at certain times even higher than its photochemical production. Despite the above-stated and certain other limitations, it may be inferred that the tropical and equatorial oceans, because of the high O2• photoproduction rates, would be having the highest potential of undergoing pH variations (up to 0.005 pH units in ten years). Along the tropical/equatorial latitude belt, at comparable sunlight irradiance, such variations are expected to be the largest (0.005 pH units) in the Indian Ocean due to a relatively low alkalinity, in the range of 2.2–2.3 mmol L1. The lowest variations (0.003–0.004 pH units) are expected in the Atlantic Ocean, because of a relatively high alkalinity in the range of 2.3–2.4 mmol L1. The main requirement for the O2• chemistry to impact the pH of seawater significantly is that the H+-imbalance reactions should be maintained for a sufficiently long period of time. The pH effect is most probably to be operational in the river-impacted coastal areas (potential candidates are the areas affected by the following rivers: Ganges, Mekong, Irrawaddy, Zambezi, Amazon River, Orinoco, Mississippi, and Rio Grande), which are characterized by a continuous flow of redox-active organic compounds into the seawater.

Firework (FW) emission has strong impacts on air quality and public health. However, little is known about the molecular composition of FW-related airborne particulate matter (PM) especially the organic fraction. Here we describe the detailed molecular composition of Beijing PM collected before, during, and after a FW event in New Year's Eve evening in 2012. Subgroups of CHO, CHNO, and CHOS were characterized using ultrahigh resolution Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometry. These subgroups comprise substantial fraction of aromatic-like compounds with low O/C ratio and high degrees of unsaturation, some of which plausibly contributed to the formation of brown carbon in Beijing PM. Moreover, we found that the number concentration of sulfur-containing compounds especially the organosulfates was increased dramatically by the FW event, whereas the number concentration of CHO and CHON doubled after the event. The co-variation of CHO, CHON, and CHOS subgroups was suggested to be associated with multiple atmospheric aging processes of aerosols including the multiphase redox chemistry driven by NOx, O3, and •OH. These findings highlight that FW emissions can lead to a sharp increase of high molecular weight compounds particularly aromatic-like substances in urban PM, which may affect the light absorption properties and adverse health effects of atmospheric aerosols.

In order to better understand the molecular composition and sources of organic aerosols in Tianjin, a coastal megacity in North China, ambient fine aerosol (PM2.5) samples were collected on a day/night basis from November to December 2016 and from May to June 2017. The organic molecular composition of PM2.5 components, including aliphatic lipids (n-alkanes, fatty acids, and fatty alcohols), sugar compounds, and photooxidation products from isoprene, monoterpene, β-caryophyllene, naphthalene, and toluene, was analysed using gas chromatography–mass spectrometry. Fatty acids, fatty alcohols, and saccharides were identified as the most abundant organic compound classes among all of the tracers detected in this study during both seasons. High concentrations of most organics at night in winter may be attributed to intensive residential activities such as house heating as well as the low nocturnal boundary layer height. Based on tracer methods, the contributions of the sum of primary and secondary organic carbon (POC and SOC respectively) to aerosol organic carbon (OC) were 24.8 % (daytime) and 27.6 % (night-time) in winter and 38.9 % (daytime) and 32.5 % (night-time) in summer. In detail, POC derived from fungal spores, plant debris, and biomass burning accounted for 2.78 %–31.6 % (12.4 %; please note that values displayed in parentheses in the following are average values) of OC during the daytime and 4.72 %–45.9 % (16.3 %) at night in winter, and 1.28 %–9.89 % (5.24 %) during the daytime and 2.08 %–47.2 % (10.6 %) at night in summer. Biomass-burning-derived OC was the predominant source of POC in this study, especially at night (16.0±6.88 % in winter and 9.62±8.73 % in summer). Biogenic SOC from isoprene, α-∕β-pinene, and β-caryophyllene exhibited obvious seasonal and diurnal patterns, contributing 2.23±1.27 % (2.30±1.35 % during the daytime and 2.18±1.19 % at night) and 8.60±4.02 % (8.98±3.67 % and 8.21±4.39 %) to OC in winter and summer respectively. Isoprene and α-∕β-pinene SOC were obviously elevated in summer, especially during the daytime, mainly due to strong photooxidation. Anthropogenic SOC from toluene and naphthalene oxidation showed higher contributions to OC in summer (21.0±18.5 %) than in winter (9.58±3.68 %). In summer, toluene SOC was the dominant contributor to aerosol OC, and biomass burning OC also accounted for a high contribution to OC, especially at night-time; this indicates that land/sea breezes also play an important role in the aerosol chemistry of the coastal city of Tianjin in North China.

This study aims to clarify the relationship between chemical weathering of rocks and the carbon budget of rivers and better understand the weathering mechanisms of plateau watersheds. We chose to study the Jinsha River, which originates from the Tibetan Plateau and also is in the upper reaches of the Changjiang River. Analysis of hydrochemistry, radiogenic strontium isotope and stable calcium isotopes were conducted of the Jinsha River water samples, which were collected along its mainstream and main tributaries in the summer. The results show that the water chemistry of the mainstream waters is dominated by evaporite weathering, which have low 87Sr/86Sr values (0.7098–0.7108) and wide range of Sr contents (2.70–9.35 μmol/L). In contrast, tributaries of the Jinsha River have higher 87Sr/86Sr (0.7090–0.7157) and lower Sr contents (∼1 μmol/L). Moreover, the Ca isotopic compositions in the mainstream (0.87–1.11‰) are heavier than the tributaries (0.68–0.88‰) and could not be fully explained by the conventional mixing of different sources. We suggest that secondary carbonate precipitation fractionates Ca isotopes in the Jinsha River, and fractionation factors are between 0.99935 and 0.99963. At least 66% of Ca was removed in the mainstream of the Jinsha River through secondary mineral precipitation, and the average value is ∼35% in the tributaries. The results highlight that evaporite weathering results in more carbonate precipitation influencing Ca transportation and cycling in the riverine system constrained by stable Ca isotopic compositions and water chemistry.

The terrestrial biogeochemical silicon (Si) cycle may significantly influence the stabilization of soil organic carbon (SOC), and thus plays an important role in regulating the global carbon (C) balance and climate change. Processes involved in Si-enhanced SOC stability at a decadal or centennial scale include protection of SOC through amorphous Si and interactions of Si-iron and Si-aluminum. Strategic manipulation of the Si cycle in terrestrial ecosystems offers a new opportunity to enhance soil C sequestration. Rock powder amendment, establishment of Si-rich plant buffer strips and innovative management practices that return Si-rich biomass materials to soil can be implemented as strategies to enhance soil C sequestration through regulating the terrestrial Si cycle. However, quantifying (i) the contribution of different processes to the enhancement of soil dissolved Si and secondary Si minerals, (ii) the relative importance of different SOC stabilization mechanisms, and (iii) the potential and cost of different measures has not been attempted.

The late Carboniferous-early Permian coal seams of the Qinshui Basin in Shanxi Province are the most prolific producer of coalbed methane (CBM) in China. Methane formed in the late Triassic during deep burial and reheating in late Jurassic-early Cretaceous driven by magmatic underplating. Basin inversion brought the coal seams to 400-700 m from the surface in the mid-late Cenozoic. Here we present results of a study aimed at understanding the origin of the methane, and how it was affected by Cenozoic exhumation of the basin. Methane from a 12 km traverse perpendicular to the basin margin in the southeast part of the basin have stable isotope compositions (δ13C = -30.2 to -35.2‰, and δD = -155 to -194‰) indicating a thermogenic origin with limited biogenic input. They are, however, lighter than expected based on coal maturity, and C1/(C2+C3) (>1000) are significantly higher than typical thermogenic methane (

The feedbacks of climate variability on CO2 consumption fluxes and carbon dynamics are thought to play an important role in moderating the global carbon cycle. High-frequency sampling campaigns and analyses were conducted in this study to investigate temporal variations of river water chemistry and the impacts of climate variability on CO2 consumption fluxes and carbon dynamics for the Xijiang River, Southwest China. Physical processes modify biogeochemical processes, so major ions display different responses to changing discharge. The annual CO2 consumption rate is (6.8 +/- 0.2) x 10(6) ton/year by carbonate weathering and (2.4 +/- 0.3) x 10(6) ton/year by silicate weathering. The annual CO2 consumption flux is much higher than most world rivers, and strong CO2 consumption capacities are observed in catchments in Southwest China. Lower negative delta C-13(DIC) values are found in the high-flow season which corresponds with high temperatures compared to those in the low-flow season. High discharge will accelerate material transport, and high temperatures will increase primary production in the catchment, both of which can be responsible for the shift of delta C-13(DIC) values in the high-flow season. Increased mineral weathering and biological carbon influx in the catchment are the main factors controlling carbon dynamics. Overall, these findings highlight the sensitivity of CO2 consumption fluxes and carbon dynamics in response to climate variability in the riverine systems. Plain Language Summary There are feedbacks between climate variability and CO2 consumption fluxes by chemical weathering and carbon dynamics. Significant temporal variations of major ions and delta C-13(DIC) are observed in the Xijiang River. Multiple biogeochemical processes occur under various hydrological conditions, shifting major ions concentrations, and delta C-13(DIC). The annual CO2 consumption rate is (6.8 +/- 0.2) x 10(6) ton/year by carbonate weathering and (2.4 +/- 0.3) x 10(6) ton/year by silicate weathering. The annual CO2 consumption rates in the Xijiang River only account for a small fraction in the global CO2 consumption rates; the CO2 consumption capacity is much higher than the global average, while much lower than its source tributaries (Beipan and Nanpan Rivers). Slow subsurface flow paths with longer transit times switch to rapid near-surface flow paths with shorter transit times, as discharge increases. High temperatures increase reaction rates, and high discharge rates remove transport limitation, both of which would accelerate the chemical weathering rates. In the high-flow season, high discharge accompanying with high temperatures, large amounts of delta C-13-depleted biological carbon, flushes into the river, affecting the carbon dynamics.

1. Exotic plant invasion has been changing the vegetation composition and function of terrestrial ecosystems. Nitrogen (N) and phosphorus (P) are often the limiting nutrients for terrestrial plants. However, under invasive pressure, in situ plant N and P usage mechanisms remain poorly understood but are pivotal for a better understanding of plant invasion and coexistence in invaded ecosystems. 2. Nitrogen and P concentrations, natural N-15 abundance (delta N-15 values) were investigated in leaves and soils under different invasive pressures (here expressed as the biomass percentages of invasive plants in each plot) for two invasive species (Chromolaena odorata and Ageratina adenophora) in Xishuangbanna in tropical China. 3. Soil N and P concentrations revealed the relatively N-rich but P-poor status of our study site. Under invasion, soil inorganic N (dominated by ammonium) and available P did not increase significantly. The leaf N and P of invasive plants increased, while leaf N increased but P decreased for native species. Natural delta N-15 mass balance between leaves and soil inorganic N sources revealed that ammonium dominated N utilization in both natives and invaders. Invasive plants showed ammonium utilization with increasing leaf N levels, while native plants under no invasion showed nitrate utilization with increasing leaf N levels. 4. Synthesis. Increased soil ammonium availability contributed to preferential ammonium utilization by invasive plants and elevated ammonium utilization in natives, but the P competition of natives decreased in invaded ecosystems. These novel insights into nutrient dynamics in invaded ecosystems enhance our understanding of plant invasion and coexistence mechanisms.

High arsenic groundwater generally coexists with elevated Fe2+ concentrations (mg L−1 levels) under reducing conditions, but an explanation for the extremely high arsenic (up to ∼2690) concentrations at very low Fe2+ (i.e., μg L−1 levels) in groundwater of Datong Basin remains elusive. Field groundwater investigation and laboratory microcosm experiments were implemented in this study. The field groundwater was characterized by weakly alkaline (pH 7.69 to 8.34) and reducing conditions (Eh −221.7 to −31.9 mV) and arsenic concentration averages at 697 μg L−1. Acinetobacter (5.9–51.3%), Desulfosporosinus (4.6–30.2%), Brevundimonas (3.9–19%) and Pseudomonas (3.2–14.6%) were identified as the dominant genera in the bacterial communities. Bacterially mediated arsenate reduction, Fe(III) reduction, and sulfate reduction are processes occurring (or having previously occurred) in the groundwater. Results from incubation experiment (27 d) revealed that nitrate, arsenate, and Fe(III)/sulfate reduced sequentially with time under anoxic conditions, while Fe(III) and sulfate reduction processes had no obvious differences, occurring almost simultaneously. Moreover, low Fe2+ concentrations were attributed to initially high pH conditions, which relatively retarded Fe(III) reduction. In addition, arsenic behavior in relation to groundwater redox conditions, matrices, and solution chemistry were elaborated. Bacterial arsenate reduction process proceeded before Fe(III) and sulfate reduction in the incubation experiment, and the total arsenic concentration (dominated by arsenite) gradually increased from ∼7 to 115 μg L−1 as arsenate was reduced. Accordingly, bacterially mediated reductive desorption of arsenate is identified as the main process controlling arsenic mobility, while Fe(III) reduction coupled with sulfate reduction are secondary processes that have also contributed to arsenic enrichment in the study site. Overall, this study provide important insights into the mechanism controlling arsenic mobility under weakly alkaline and reducing conditions, and furnishes that arsenate reduction by bacteria play a major role leading to high accumulation of desorbed arsenite in groundwater.

The δ15N of nitrate (NO3−) and particulate organic nitrogen (PON) was used to study the sources and fate of nitrogen in the impounded Maotiao River, southwest China. During months when the reservoi...

Estimates of biogeochemical processes and the proportion of N2O production in the aquatic system of impoundments are important to quantify nitrogen cycling, particularly during stratification perio...

Plant nitrogen (N) use is a key component of the N cycle in terrestrial ecosystems. The supply of N to plants affects community species composition and ecosystem processes such as photosynthesis and carbon (C) accumulation. However, the availabilities and relative importance of different N forms to plants are not well understood. While nitrate (NO3−) is a major N form used by plants worldwide, it is discounted as a N source for Arctic tundra plants because of extremely low NO3− concentrations in Arctic tundra soils, undetectable soil nitrification, and plant-tissue NO3− that is typically below detection limits. Here we reexamine NO3− use by tundra plants using a sensitive denitrifier method to analyze plant-tissue NO3−. Soil-derived NO3− was detected in tundra plant tissues, and tundra plants took up soil NO3− at comparable rates to plants from relatively NO3−-rich ecosystems in other biomes. Nitrate assimilation determined by 15N enrichments of leaf NO3− relative to soil NO3− accounted for 4 to 52% (as estimated by a Bayesian isotope-mixing model) of species-specific total leaf N of Alaskan tundra plants. Our finding that in situ soil NO3− availability for tundra plants is high has important implications for Arctic ecosystems, not only in determining species compositions, but also in determining the loss of N from soils via leaching and denitrification. Plant N uptake and soil N losses can strongly influence C uptake and accumulation in tundra soils. Accordingly, this evidence of NO3− availability in tundra soils is crucial for predicting C storage in tundra., ツンドラの生態系でも硝酸イオンは大切な窒素源だった --最先端の測定技術で「見えない」硝酸イオンの重要性を検証--. 京都大学プレスリリース. 2018-03-14.

Currently, there is a lack of systematic knowledge concerning carbon (C) biogeochemical cycles in impounded rivers. In this study, we investigated different C species and related environmental factors from July 2007 to June 2008 and from May 2011 to May 2012 in the impounded Wujiang River, SW China to understand the influence of dam construction on the riverine C cycle. The results showed that average concentrations of dissolved CO2, dissolved inorganic C (DIC), dissolved organic C, and particulate organic C (POC) were 81.73 μmol/L, 2283.55 μmol/L, 158.11 μmol/L, and 37.54 μmol/L, respectively. Meanwhile, δ13CDIC ranged from − 10.07‰ to − 4.92‰ with an average of − 8.33‰, while δ13CPOC ranged from − 35.30‰ to − 22.28‰ with an average of − 29.20‰. Thermal and chemical stratifications developed seasonally and exerted a significant influence on the C cycle of the released water. The C species and related δ13C showed remarkable heterogeneity in time and space. Evidence from δ13C demonstrated that the C system in this river was primarily influenced by carbonate weathering, whereas in the reservoir, it was primarily controlled by algal activity. The coefficients of variance for different C species in the reservoir and released water were higher than those in the river. Our study indicated that biological activity became a key controlling factor for the C biogeochemical cycle and accelerated it after damming, especially in the warm seasons. The results of this study have important implications for understanding the C cycle in elongated and deep reservoirs.

To understand the origins, secondary formation and seasonality of carbonaceous aerosols in North China, we collected PM2.5 samples on day- and night-time bases in summer and winter 2016 from a typical metropolis, Tianjin, and studied their carbonaceous components and stable carbon isotope ratios of total carbon (δ13CTC). PM2.5 ranged from 21.2 μg m−3 to 74.8 μg m−3 in summer and 25.3–816 μg m−3 in winter. On average, organic carbon (OC) elemental carbon (EC) and water-soluble OC were found to be higher (3–5 times) in winter than that in summer. Secondary organic carbon that estimated by EC-tracer method was enhanced by a factor of 7 in winter compared to that in summer. δ13CTC showed a small enrichment of 13C (average −25.41 ± 0.34‰) in summer compared to that (−24.42 ± 0.44‰) in winter. Linear relations and mass ratios of selected carbonaceous components and δ13CTC imply that the carbonaceous aerosols in Tianjin were mainly derived from biomass burning emissions and photochemical processing in summer. In winter, coal combustion emissions and in situ secondary formation of organics, including water-insoluble OC (WIOC), were dominant. This study warrants a need to understand the formation mechanisms of WIOC in the urban atmosphere and thus to reconcile the atmospheric models.

Understanding of the binding characteristics of wetland dissolved organic matter (DOM) and different metals is important for the quantitative assessment of the environmental behavior of metals in wetlands. In this study, different types of spectroscopy including ultraviolet-visible absorption, Fourier transform infrared, and fluorescence spectroscopy was used to investigate the binding characteristics of Fe3+, Cu2+, Cr3+, Cd2+, and Zn2+ with DOM from wetland water. Differential absorption spectra identified binding sites for these five metals in this wetland DOM at 210 nm, 280 nm, 335 nm, and > 400 nm regions. The low binding capacity of DOM in this wetland with Cd and Zn indicated that the toxicity and environmental effects of these metals in this wetland warrant further study. The calculated △EEM combined with fluorescence regional integration (FRI) analysis clearly revealed that Fe and Cu preferred to bind with humic-like DOM while Cd and Zn preferred to bind with protein-like DOM in this wetland. △EEM successfully demonstrated the characteristics of DOM complexing with different metals and could be a compelling tool in evaluating metal-DOM interactions. In addition, 2D-FTIR-COS identified the binding sites and the dynamic processes of binding at the functional group level. Metals preferentially bind with the C O, C O functional group, and then binds to the O H functional group. This study revealed that different DOM components will facilitate the migration of different metals in the environment and provided new slights into an improved understanding of migration and transformation of metals in aquatic environments.

Microbial mat extracellular polymeric substances (EPS) and their fate and transformation in natural waters are unidentified under diurnal condition. EPS from highly saline arid origins were characterised and exposed to natural sunlight conditions to identify its physico-chemical changes over 72 h. Fourier Transform Infrared Spectroscopy (FTIR) and potentiometric titration analyses confirmed the presence of −COOH and –OH functional groups in raw EPS. In addition, size exclusion chromatography (SEC) confirmed the presence of two proteins-sized molecules in the original EPS which were found to degrade upon sunlight exposure. The excitation-emission matrix (EEM) and parallel factor (EEM-PARAFAC) identified two fluorescent components: A combined humic-like and protein-like component, and an individual tyrosine-like component. FTIR in irradiated samples confirmed degradation of EPS by showing presence of the −CH 3 group at 1377 cm −1 . Two proteins-sized molecules identified in SEC were degraded, thereby causing to significant changes in the pH and redox potential (Eh). Correspondingly, three fluorescent components were identified in irradiated samples using EEM-PARAFAC modelling and found to change in their fluorescence intensities upon sunlight exposure. It is therefore suggested that photochemical processes are important for sequential transformation of EPS into various organic substances in surface waters.

Terrestrial lipid biomarkers are one of the key tracers in the studies of atmospheric aerosols. Here, we investigated such organic compounds in marine aerosols collected at Chichijima Island, the western North Pacific for two 4-year periods: 1990–1993 and 2006–2009. A homologous series of lipid biomarkers including C18–C37 n-alkanes, C9–C34 fatty acids, and C14–C35 fatty alcohols were determined by gas chromatography/mass spectrometry (GC/MS). The atmospheric levels of these tracers increased from 1990–1993 to 2006–2009. Their seasonal trends were clearly characterized by winter–spring maxima and summer–fall minima. The relative abundance of the high-molecular-weight (HMW) n-alkanes (C25–C37) and n-alcohols (C20–C35) in total HMW lipids peaked in winter and winter/fall, respectively, whereas those of HMW fatty acids (C20–C34) peaked in summer. Air-mass backward trajectory analyses suggest that the Asian continent, Southeast Asia including tropical regions, and the Central Pacific are the main source regions. The seasonal shift and distribution of the carbon preference index and average chain length for the HMW lipids were controlled by the changes in climatic factors and source regions. The higher abundance of terrestrial lipids during 2006–2009 than 1990–1993 indicates a higher emission from terrestrial plantation in the 2000s than in the early 1990s in upwind regions of East Asia. Furthermore, HMW lipid compounds exhibited much stronger positive correlations with levoglucosan, a biomass-burning tracer, during 2006–2009 than 1990–1993, suggesting that biomass-burning emissions contributed more significantly in this century.

The release of biospheric organic matter (OM) stored in the humus-rich black soils of Northeast China is highly susceptible to permafrost thaw and agriculturally induced erosion processes, and plays a disproportionate role in the global carbon cycle. However, the perturbations of global change and anthropogenic activities on riverine export of particulate organic carbon (POC) in the high-latitude agricultural areas remain poorly constrained. In the present study, this knowledge gap was filled by identifying the provenances of particulate organic matter (POM) and the erosional flux of POC from the rivers draining Northeast China. The elemental (POC%, PON% and C/N ratio) and isotopic (δ13C and δ15N) compositions of POM in suspended particulate matter (SPM) from the rivers in Northeast China (the Songhua River (SRB) and Liao River basins (LRB)) were analyzed. The results showed that during the wet season, the δ13C and δ15N values of POM in SPM were −25.8 ± 1.2‰ and 6.6 ± 2.2‰ respectively. Elemental and isotopic characteristics of the SPM samples and potential sources indicated that the sources of POM differed significantly among different sampling periods and sites. During the wet season, Soil OM was the primary POM contributor. Compared to the SRB, autochthonous OM made relatively larger contributions to POM in the LRB. During the dry season, for the SPM samples mainly from the LRB, the δ13C and δ15N values of POM were −22.7 ± 4.3‰ and 3.1 ± 2.4% respectively, suggesting that effluent detritus was the predominant source. The flux and yield of SPM revealed the seasonal and spatial variations of physical erosion rate that controls POC export. Seasonally, up to 61% of the annual SPM load and 58% of the annual POC flux of the SRB occurred in May and August due to thawing processes and increasing precipitation. Spatially, the lower reaches of the SRB had the highest SPM yield and contributed more than half of the annual SPM load of the SRB, likely attributable to the high intensity of agricultural activities. Globally, the POC% in SPM and POC yield of the SRB were larger than a series of the world's largest rivers under a given SPM condition, suggesting the high sensitivity of terrestrial OM export to erosion. These findings highlight the perturbation and mobilization of terrestrial OM in Northeast China under intensive agricultural activities and ongoing global climate change.

Particulate inorganic carbon (PIC) is one of the most important components of carbon cycle in hydropower reservoirs. However, the processes of production, migration, and transformation of PIC in hydropower reservoirs are still unclear. As such, we investigated the concentration and carbon isotope composition of PIC and dissolved inorganic carbon and related environmental parameters of hydropower reservoirs on the Wujiang River, Southwest China, to understand these processes. The observed δ13C datasets demonstrated that the river PIC is derived from exogenous carbonate weathering and endogenous carbonate precipitation, whereas the reservoir PIC is dominated by authigenic PIC driven by phytoplankton. The reservoir PIC concentration and δ13CPIC showed seasonal stratification in the water profile, the extent of which depends on surface photosynthesis and bottom respiration. The influence of phytoplankton on the production and transformation of PIC was different among the reservoirs with different ages and trophic levels, and the δ13C technique can reveal these processes very well. This study improves the comprehensive understanding of carbon cycling in hydropower reservoirs and environmental effects of river damming.

Rivers play an important role in global water and carbon cycling, but there are still large uncertainties concerning evaporation and aquatic photosynthesis. Here we combined measurements of water chemistry, isotopic compositions (i.e., δ D w , δ 18 O w , δ 13 C DIC and ▵ 14 C DIC ) and geographic characteristics (i.e., river width) to elucidate in-stream hydrological and biogeochemical processes across rivers in Hainan Island, China. The results showed that dissolved inorganic carbon (DIC) in river waters was largely of modern origin, with about 95% from contemporary biogenic sources based on an isotopic mass balance of ▵ 14 C DIC . Significant evaporation and aquatic primary production co-occurred in these tropical rivers with large amounts of water and DIC being rapidly turned over in the water column, altering the water cycle and the carbon balance. High rates of evaporation and aquatic primary production were observed in the headwater segments, with narrow river width but broad available reactive surface area at the air-water interface. The asymmetric aquatic photosynthesis at different river segments caused the spatial heterogeneities of dissolved solutes. The results suggest that the available reactive area at the water-air interface is responsible for synchronous water loss and dissolved carbon evolution in flat tropical rivers. This study provides evidence that intense evaporation and aquatic photosynthesis mainly occurred in headwater segments, which has implications for understanding global carbon cycling.

To constrain sources of anthropogenic nitrogen (N) deposition is critical for effective reduction of reactive N emissions and better evaluation of N deposition effects. This study measured δ15N signatures of nitrate (NO3−), ammonium (NH4+) and total dissolved N (TDN) in precipitation at Guiyang, southwestern China and estimated contributions of dominant N sources using a Bayesian isotope mixing model. For NO3−, the contribution of non-fossil N oxides (NOx, mainly from biomass burning (24 ± 12%) and microbial N cycle (26 ± 5%)) equals that of fossil NOx, to which vehicle exhausts (31 ± 19%) contributed more than coal combustion (19 ± 9%). For NH4+, ammonia (NH3) from volatilization sources (mainly animal wastes (22 ± 12%) and fertilizers (22 ± 10%)) contributed less than NH3 from combustion sources (mainly biomass burning (17 ± 8%), vehicle exhausts (19 ± 11%) and coal combustions (19 ± 12%)). Dissolved organic N (DON) accounted for 41% in precipitation TDN deposition during the study period. Precipitation DON had higher δ15N values in cooler months (13.1‰) than in warmer months (−7.0‰), indicating the dominance of primary and secondary ON sources, respectively. These results newly underscored the importance of non-fossil NOx, fossil NH3 and organic N in precipitation N inputs of urban environments.