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Hydropower plays an important role in the supply of renewable energy, but it also exerts a great influence on the river continuum. Understanding nutrient cycling and microbial community succession in hydropower reservoirs is key to weighing hydroelectric pros and cons. However, the underlying control mechanisms are still not well known, especially with respect to the impacts of hydrological conditions. Based on a comprehensive survey of hydropower reservoirs along the Wujiang River in SW China and an integration of published data, we found that reservoir physicochemical and biological stratifications and planktonic microbial community assembly were synergistically evolving, and reservoir hydraulic load (i.e., mean water depth per unit retention time) was a key factor controlling the strength of stratifications, CO

To better understand the origins and photochemical processing (aging) of organic aerosols (OA), we studied fine aerosols (PM

Calcium is a critical element in the global carbon cycle due to its role in carbon sequestration via silicate weathering and carbonate formation. Here we apply calcium (δ

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.

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 Fe

Sulfur (S) dynamics in soils formed from granite remain poorly understood despite its importance as an essential plant macronutrient and component of soil organic matter. We used stable S isotope ratios to trace the sources and biogeochemical processes of S in four forest soil profiles developed on granite under contrasting climate conditions. The soil S is derived mainly from decomposing litter; no significant geogenic contribution to its content is noted as a result of the low S concentration of the granite (~ 5 μg/g). Colder/drier climate results in high organic S retention at the surface due to weak mineralization of organic S. Although warmer/wetter climate increases the S mineralization and leaching loss, SO42− adsorption is an important S retention process in the subsurface. The vertical distribution of S isotope compositions in the soil profiles across the four sites indicates (i) a downward increase in δ34S values in the upper profiles due to continuous mineralization of organic S with an occasional decrease in δ34S values in the subsurface due to dissimilatory sulfate reduction (DSR), (ii) constantly high δ34S values in the middle profiles due to the low water permeability, and (iii) a downward decrease in δ34S values in the low profiles due to increased contribution of bedrock with depth. Regardless of the variation in soil depth and climate, the total S concentration is proportional to the pedogenic Fe/Al minerals, suggesting the important role of secondary Fe/Al minerals in retaining S in soils. This study provides an integration and synthesis of controls of climatic and edaphic variables on S dynamics in forest soil profiles developed on granite.

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.

Soil water stable isotope compositions (SWSI; i.e., δD and δ18O) and soil moisture content (SMC) are widely used to illuminate water exchange processes across the atmosphere-land interface. Thus, the knowledge of spatiotemporal dynamics of these two variables is critical to help our understanding of relevant ecohydrological processes. However, in comparison to the efforts for elucidating the spatiotemporal variability in SMC, much less attention was paid to understand the spatiotemporal variability in SWSI, which also raises the question as to whether SWSI and SMC share similar spatiotemporal features. To this end, the spatiotemporal dynamics of SWSI and SMC were jointly investigated on a karst hillslope with eight sampling campaigns among two years. The method of temporal stability analysis (TSA) was adopted to evaluate the spatiotemporal patterns of SWSI and SMC in this study. Generally, both δD and δ18O exhibited considerable temporal and spatial variations; meanwhile, the variations in δD and δ18O values were relatively smaller than that of SMC. In addition, in comparison with the spatial pattern of SMC, there were no clear relationships between the standard deviation (SD) and the spatial mean of δD or δ18O. However, the SD of line-conditioned excess (lc-excess) and its mean values displayed a strong negative correlation, indicating that the spatial variations in lc-excess increased with soil evaporation. Moreover, SWSI displayed weaker temporal stability than SMC and no clear controlling factors were identified, suggesting that the spatiotemporal dynamics of SWSI might be more complex than that of SMC. This study provided comprehensive field evidence that there existed profound spatiotemporal variability in SWSI and its spatiotemporal features were different from SMC, highlighting that the spatiotemporal variability in SWSI needs to be considered in isotope-based estimations and it should be investigated separately from the spatiotemporal characteristics of SMC in future studies.

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.

Carbon (C) cycling and phytoplankton community succession are very important for hydropower reservoir ecosystems; however, whether the former controls the latter or the reverse is still debated. To understand this process, we investigated phytoplankton species compositions, stable C isotope compositions of dissolved inorganic C and particulate organic C (δ13C-DIC and δ13C-POC), and related environmental factors in seven hydropower reservoirs on the Wujiang River, Southwest China. A total of 36 algal genera from seven phyla were identified, and phytoplankton community exhibited obvious temporal and spatial difference. The δ13C-DIC (from -9.96 to -3.73‰) and δ13C-POC (from -33.44 to -21.17‰) co-varied with the algal species succession and increased markedly during the shift of dominant species from Bacillariophyta to Pyrrophyta or Cyanophyta. In addition, the strong C fixation in the euphotic layer resulted in great δ13C-DIC and CO2 stratification in the reservoir profile. Statistical analyses and C isotope evidence demonstrate that an increase in water temperature triggers phytoplankton community succession, and that CO2 availability is a key to drive the succession direction, and in turn, C cycling is enhanced when phytoplankton are dominated by Pyrrophyta or Cyanophyta in hydropower reservoirs. This study confirms that C cycling and phytoplankton community succession interact with each other and evolve synchronously, and will be helpful to systematically evaluate the environmental consequences of river damming.Keywords: Carbon biogeochemical cycling; Phytoplankton community succession; Stable carbon isotope; Reservoir effect; Wujiang River.

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.

The present study seeks to evaluate the application of the 238U-234U-230Th radioactive disequilibrium methodology for the determination of the regolith production rates in thick weathering profiles marked by long histories, encountered under various climate regimes, but still very little studied by these techniques. For this purpose, 238U-234U-230Th disequilibria have been analyzed in a ≈ 11 m-deep profile developed on a granitic bedrock in south China (Longnan, Jiangxi Province) under a subtropical climate. The results demonstrate that in such deep weathering profiles the determination of weathering rates from the analysis of U-series nuclides in bulk rock samples cannot be recovered by applying in one step to the entire alteration profile the modeling approach classically used to interpret the U-series nuclides, i.e. the “gain and loss” model. The modeling has to be made on subsections of relatively small size (10Be data from the same profile, when assuming non steady-state erosion of the upper part of the profile. Slow denudation rates similar to the U-series derived production rates of 2 m/Ma can thus be obtained with a minimum exposure time of 40 ky, and an inherited component of 20-25*104 at/g originating from the exhumed deeper part of the profile. Altogether the data demonstrate that the combined analysis of U-series and cosmogenic nuclides, which has the potential to become a relevant approach to constrain the dynamics of continental surfaces, requires (a) dense and deep sampling for both nuclides studies, and (b) also to consider more systematically the polyphased and variable history of erosion of the continental surface during the Quaternary. These results have implications for the interpretation of long-term accumulation of 10Be at depth and 10Be data variations in granitic alteration profiles.

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 (

Marine aerosol samples collected from the South China Sea (SCS) to East Indian Ocean (EIO) during a cruise from March 10 to April 26, 2015 were studied for diacids and related compounds. In view of the air mass backward trajectories and source regions of geographical features, the cruise area is segregated into the South China Sea (SCS), the East Indian Ocean off the coast of western Indonesia (EIO-WI), the EIO off the coast of Sri Lanka (EIO-SL), Malacca and Sri Lanka docking point (SLDP). Total concentrations of diacids, oxoacids and α-dicarbonyls were much higher at SLDP followed by the SCS, Malacca, and the lowest at the EIO-WI. In this study, oxalic acid (C2) is the dominant diacid during the cruise, followed by malonic acid (C3) in the SCS, EIO-WI, EIO-SL and Malacca, whereas succinic acid (C4) diacid was relatively more abundant than C3 diacid in SLDP. Except for SLDP, C3/C4 mass ratios were always greater than 1, and no significant difference was observed among the cruise. The C2/C4 and C2/total diacids ratios also showed the similar trends. Average mass ratios of adipic acid (C6) to azelaic acid (C9) were less than unity except for at EIO-WI; the mass ratios of phthalic acid (Ph) to azelaic acid (C9) were less than 2 except for at SCS. The concentrations of diacids were higher when the air masses originated from the terrestrial regions than those from the remote oceanic regions. Based on the molecular distributions of organic acids, the mass ratios and linear correlations of selected compounds in each area, we found that the oxidation of biogenic volatile organic compounds (BVOCs) released from the ocean surface and subsequent photochemical oxidations were the main contributors to diacids, oxocarboxylic acids and α-dicarbonyls over the SCS to EIO. In addition, the continental outflow that enriched with the anthropogenic VOCs and their aging influenced the organic aerosol loading, particularly over the SCS. The emissions from local terrestrial vegetations as well as fossil fuel combustion and subsequent in-situ photochemical oxidation also played a prominent role in controlling the organic aerosols loading and molecular distributions of diacids and related compounds at SLDP.

Exploring the relationship between weathering and erosion is essential for understanding the evolution of landscapes and formation of soil under the influence of climate, tectonics, and topography. We measured the bulk chemistry of regoliths and calculated their weathering rates and intensity in three locations in China: Inner Mongolia in the mid-temperate semi-humid zone; Jiangxi Province, in the mid-subtropical humid zone; and Hainan Province, in the tropical humid zone. These profiles exhibited increased weathering with increasing temperature and precipitation. The low-gradient profile exhibited stronger weathering of saprolite than of soil, whereas the high-gradient profile showed a more constant weathering pattern. The regolith in the cold climate was the product of easily weatherable minerals, whereas weathering of K-feldspar and even secondary minerals occurred in hot and humid climates. The weathering of subtropical profiles was both supply- and kinetic-limited, controlled by weathering and erosion. The tropical profile experienced supply-limited weathering, indicating slow erosion and an intense weathering profile; the mid-temperate profile was not classifiable due to weak erosion and weathering. Long-term weathering fluxes of these profiles show that Si, Na, and K (or Mg) represent the bulk of the mass lost through weathering. This study underscores that weathering of granitic regolith is controlled by both climatic conditions and landscape.

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.

Soil heterotrophic respiration (HR) is an important source of soil-to-atmosphere CO2 flux, but its response to changes in soil water content (θ) is poorly understood. Earth system models commonly use empirical moisture functions to describe the HR–θ relationship, introducing significant uncertainty in predicting CO2 flux from soils. Generalized, mechanistic models that address this uncertainty are thus urgently needed. Here we derive, test, and calibrate a novel moisture function, fm, that encapsulates primary physicochemical and biological processes controlling soil HR. We validated fm using simulation results and published experimental data, and established the quantitative relationships between parameters of fm and measurable soil properties, which enables fm to predict the HR–θ relationships for different soils across spatial scales. The fm function predicted comparable HR–θ relationships with laboratory and field measurements, and may reduce the uncertainty in predicting the response of soil organic carbon stocks to climate change compared with the empirical moisture functions currently used in Earth system models., Empirical moisture functions that describe the relationship between soil heterotrophic respiration and moisture introduce considerable uncertainty in soil CO2 flux predictions. Here, the authors derive a process-based moisture function by incorporating mechanisms that control soil heterotrophic respiration.

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.