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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.

Mantle degassing transect across different tectonic units within a plate convergent setting has been well documented for oceanic convergent margins by systematic changes in geochemistry (e.g., 3He/4He, δ13C, and CO2/3He) of hydrothermal gases. However, little is known about spatial variations in volatile geochemistry across a continental convergent margin. In this study, we identify a mantle degassing transect in the southeastern Tibetan Plateau using He-CO2 systematics of hydrothermal gases, which extends from India-Asia continental convergent margin to intra-continent extensional region. δ13C-CO2 (−11.8‰ to −3.1‰) and CO2/3He (1.7 × 108 to 7.1 × 1011) values of hydrothermal gases show large variations that are consistent with modification by secondary physico-chemical processes, such as multi-component mixing, hydrothermal degassing, and calcite precipitation. Three levels of He degassing can be recognized based on 3He/4He dataset (0.01–5.87 RA) of the hydrothermal gas samples and their distances to volcanic centers. A magmatic level He degassing (35–74% mantle He) is found near active and/or Quaternary volcanoes fed by mantle-derived magmas. With increasing distance to volcanic centers, the outgassed magmatic volatiles are gradually diluted by crustal components (e.g., radiogenic 4He), defining a transitional level He degassing (13–33% mantle He). The 3He/4He values (8.16–8.48 RA) of olivine phenocrysts indicate a MORB (mid-ocean ridge basalts)-type mantle source for the magmatic and transitional levels of He degassing that are localized in Quaternary volcanic fields. In contrast, a background level He degassing (

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.

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.

Based on Terrestrial Cosmogenic Nuclide (TCN) constraints from depth profiles of one granitic regolith from Wumingshan and five fluvial terraces from Xianshuihe and Zagunao rivers, we discuss the timing of the last deglaciation, the landscape-scale denudation and fluvial incision rates across the eastern Tibetan Plateau, in relation to previous work. We present a three-dimensional-graph visualization approach and corresponding constraints to better assess the feasibility and applicability of cosmogenic nuclides depth-profile dating. The exposure age (older than 19.4 ka) of the Wumingshan regolith corresponds to the retreat of the palaeo-Daocheng ice cap, which covered the Yidun terrane during the Last Glacial Maximum (LGM). Most basin-wide denudation rate data in the eastern Tibetan Plateau are lower than 130 mm/ka (47%, n = 90), which is consistent with the Wumingshan regolith denudation rate (lower than 52.8 mm/ka), and thus indicate that the landscape-scale denudation has been stabilized after the last deglaciation. Considering the reduction of integrated bulk density due to the accumulation of lower-density loess, we estimate mean exposure ages of Xianshuihe and Zagunao river terraces of 4.0 ± 0.7 ka, 5.9 ± 0.3 ka, 13.4 ± 2.0 ka, and 16.6 ± 1.4 ka. The observed increase in incision rate from 0.39 mm/yr over long timescale (∼600 ka) to 5.88 mm/yr over the last 15 ka at the Xianshuihe river site is probably due to the transition from glacial to interglacial climatic conditions. The fewer abandoned terraces along the Zagunao river after the Heinrich event 1 (H1) indicates that the climate change during the latest glacial-interglacial transition impacted less the landscape evolution in a relatively lower elevation area. Comparison with previously reported fluvial incision rates elsewhere across the eastern margin of the Tibetan Plateau indicates that incision rates are mainly influenced by abrupt climate change or intensified summer monsoon since the early Holocene, but probably controlled by regional tectonic uplift or fluvial headward retreat as the timescale increases. Overall, we propose a synthetic pattern of landscape evolution mainly dominated by long-term tectonic uplift together with fluvial headward erosion, episodically influenced by climatic change throughout the late Quaternary.

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

The evolution of atmospheric CO2 and the pH of the ocean can be reconstructed by the boron isotopic composition (δ11B) of marine carbonates, which is influenced by the δ11B of the seawater. Boron (B) in the ocean is primarily affected by continental weathering through rivers. Thus, it is essential to understand the behavior of B and B isotopes in rivers and the factors affecting riverine B, which require a better understanding of sources and processes of B in river systems. This review evaluates the inventories of B reservoirs contributing to rivers and investigates the processes regulating the B isotope geochemistry of rivers. B is widespread at the Earth’s surface and shows a wide range of concentrations between reservoirs. Different reservoirs also exhibit significant variations in B isotopic compositions. Mixing and Rayleigh effects are mainly responsible for the variations in the δ11B values of meteoric precipitation, which result in marine (δ11B = +37 ± 7‰), anthropogenic (δ11B = +9 ± 10‰), and mixing types (δ11B = +17 ± 13‰) of meteoric precipitation. The contribution of B to rivers from carbonate dissolution is negligible. Marine and non-marine evaporites have distinct δ11B values (marine δ11B: + 27 ± 9.4‰ and non-marine δ11B: −2 ± 8.6‰) that primarily reflect their different depositional environments. S-type granites that are tourmaline-free have an estimated δ11B value of −14.2 ± 4.9‰ and a Na/B value of 140 ± 34. Non-S-type granites have a δ11B value of −8.9 ± 6.7‰ and a Na/B value of 1190 ± 170. Intraplate basalts exhibit a δ11B value of −5.2 ± 4.4‰ and a Na/B value of 3300 ± 770. Subduction-related basalts have a δ11B value of + 0.3 ± 7.3‰ and a Na/B value of 1060 ± 830. Shale has high B contents of siliciclastic sedimentary rocks (104 ± 92 ppm). The inferred δ11B values of marine and continental shales are −8‰ and −16‰, respectively. The effects of metamorphism can vary widely depending on the geologic setting and type of protolith. The δ11B values of wastewater are investigated based on their industrial, agricultural, and urban sources. This inventory of B reservoirs can be useful for studies on rivers on a continental scale. In regolith and groundwater, B isotopic fractionation mainly occurs due to water-rock interactions and the biological cycle of B, whereas adsorption on sediments leads to minor B isotopic fractionation in rivers. In groundwater, the reactive transport model reveals that the δ11B value of river water is sensitive to hydrological conditions. In regolith, the steady-state mass balance model is used to predict the B isotope behavior of soil solution in different weathering regimes. In the supply-limited regime (where chemical weathering is limited by tectonic forcing), the precipitation of secondary minerals controls the variations in the δ11B values of soil solution, leading to an increase in the difference in the δ11B values between soil solution and parent rock (δ11Bdiss−δ11Brock) with lower denudation rates, whereas secondary mineral dissolution produces the opposite change in δ11B. In the kinetically limited regime (where chemical weathering is limited by climate), the biological cycle controls the variations in the δ11B values of soil solution, and the δ11B values of soil solution generally become closer to those of parent rock with higher denudation rates. The relationship between the denudation rates and δ11Bdiss−δ11Brock is thus not monotonous, indicating that additional constraints are required to distinguish between the two regimes. Understanding of B isotope geochemistry of rivers can be improved by better constraints on B end-member estimates, investigation of the B isotopic fractionation caused by weathering and biological cycling in regolith, and assessment of atmospheric and biological sub-cycle.

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

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.

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.

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.

Land use and land cover (LULC) products derived from remote sensing data are fundamental to the earth's surface ecological environment studies. Various LULC products have different data sources with large uncertainties and varying spatio-temporal resolutions. In this study, our objectives are to understand the accuracy of the current LULC products at the coastal area of Tianjin city. We conducted accuracy verification and comparative analysis of the LULC datasets available from different sources, MCD12Q1, CGLS-LC100, FROM_GLC, GLC_FCS30 and GlobeLand30 for the years of 2010, 2015, 2017 and 2020, at varying spatial resolutions 500–100–30–10 m. Using land cover dataset for these years, we conducted time-series analysis of land cover changes and driving factors. Results showed that GLC_FCS30-2020 has the highest classification accuracy (72.57%), followed by GlobeLand30-2020 (72.23%) and GlobeLand30-2010 (70.10%). The classification accuracy is related to the spatial resolution of original data source and the classification system. The verification accuracies of all products are found to be lower than their official announcements. Additionally, the accuracy comparison among different land types indicated that the classification accuracy of agricultural land, impervious surface, and water bodies is high, while that of forest, grassland, and shrubs is low. According to the spatio-temporal pattern analysis of land cover changes in Tianjin during 2010–2020, the area of agricultural land is slowly decreasing, and construction land is increasing, and the increase results mainly from the conversion of agricultural land and grassland. The rapid population growth, economic development and policy guidance are the main driving factors.

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.

Extensional rift systems provide important pathways for the release of large amounts of deeply-sourced CO2 into the atmosphere. Continental rifting zones (e.g., East African rift) are thus invoked to be important for understanding the links between CO2 outgassing and global climate change associated with continental breakup. However, deeply-sourced CO2 emissions from extensional rift systems in continental collision zones remain poorly understood. Here, we focus on hydrothermal CO2 emissions from the southern segment of the Yadong-Gulu rift (YGR), the largest extensional rift in southern Tibetan Plateau, aiming at delineating rift-related CO2 emissions from the India-Asia continental collision zone. In-situ measurements of diffuse soil CO2 emissions indicate that average soil CO2 fluxes from the Kangbu, Mengzha, and Chaduo hydrothermal fields are 40, 700, and 255 g m−2 d−1, respectively. Combined with average soil CO2 fluxes (20–437 g m−2 d−1) from central and northern YGR, we speculate a relatively steady-state CO2 degassing pattern for the entire rift. The magnitude of soil CO2 fluxes of the YGR is higher than that of representative areas of the East African rift system. Evidence from 3He/4He reveals a pure crustal origin for CO2-bearing fluids in southern YGR, while the involvement of mantle CO2 is recognized in the central and northern rift segments. We suggest that metamorphic decarbonation of crustal rocks at variable depths is the primary cause for CO2 origin in southern YGR, which differs from the magma‑carbonate interaction model of central and northern YGR. Ternary mixing calculation based on He-CO2 systematics of hydrothermal gases indicates dominant contributions from carbonate rocks to total carbon inventory, with mantle CO2 contributions absent in southern YGR but discernible in northern YGR. The characteristic high proportions of crustal CO2 (>90%) distinguish the YGR from extensional rifts fed primarily by mantle CO2 in continental rifting zones. Our results reveal a crustal-scale carbon cycle in accretionary wedge of the India-Asia continental collision zone, together with magmatic front setting of the central and northern YGR, outlining a transect of the rift-related CO2 emissions across continental collision zones. This would contribute to better understanding the role of continental assembly in deeply-sourced CO2 emissions and global carbon budget.

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.

Silicon (Si) is beneficial for rice health and production by alleviating various biotic and abiotic stresses. However, the continual export of grain off-farm may result in Si deficiency for rice plants. The current levels of plant available Si (PASi) in rice paddies in China remain unclear, as do the factors that control PASi content in these soils. We conducted a nationwide sampling campaign across the paddy fields of China between 2016 and 2019, and used calcium chloride extractable Si (Si-CaCl2) and buffered acetate extractable Si (Si-NaAc, pH = 4) to quantify PASi. We show that Si-CaCl2 pool was mainly influenced by mean annual temperature (MAT), soil salinity, soil organic carbon (SOC), mean annual precipitation (MAP), and soil pH, suggesting both pedological and biological control mechanisms. However, the Si-NaAc pool was influenced most by soil pH, MAT and MAP, implying pedological control. Compared to data from the 1990s, the Si-NaAc content decreased by 14.1% on a national scale with an annual decline rate of 0.54%. Based on our investigation, at least 65% of China’s paddy fields are deficient in PASi, which is an increase in area of ~15% over the last 20 years. The principal regions where PASi deficiency was recorded are mainly located in southern China, with the levels of Si deficiency lowering as the paddy fields are located further north. The continual off-site removal of PASi from rice grain and straw will need to be addressed through the use of Si-fertilizers, including organic amendments, to maintain a productive and sustainable rice industry in China.

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.

In order to assess the impact of the monsoonal climate on denudation, physical erosion, and chemical weathering processes, we measured cosmogenic nuclides 10Be, 26Al and immobile element Zr in five granitic regolith profiles across Northeast to South China. The 10Be and 26Al concentrations are 2.98 × 104–25.20 × 104 atoms g−1 and 2.18 × 105–16.62 × 105 atoms g−1, respectively. Compiling previous depth profile data from Leymon and Beacon Heights, we find that the 26Al/10Be ratios systematically increase or decrease with the depth. Our numerical model shows that muons contributions can produce higher 26Al/10Be ratios (greater than 6.75) in both steady-state and non-steady state scenarios, which can result in underestimated burial age (initial 26Al/10Be ratio) and exaggerated denudation rates (due to non-negligible production from muons) for the application of dual-nuclide in Earth Science. The denudation rates, chemical weathering rates and physical erosion rates derived from cosmogenic nuclides and Zr are 28–45, 9–31 and 6–22 m Ma−1, respectively. Chemical weathering rates, excluding the JLN profile, comprise a large proportion of the denudation rates (greater than 50%). Despite the wide range of mean annual precipitation (MAP) and mean annual temperature (MAT), the denudation rates vary without an apparent gradient from northeast to south. However, the physical erosion and chemical weathering results show good relationships with climate, suggesting the limitation type changed from kinetic-limited in the north, to supply-limited in the south. Chemical weathering indices (chemical index of alteration, CIA and weathering intensity factor, WIF) also indicate that the extent of chemical weathering strengthens from northeast to south and increases with chemical weathering rates, but decreases with physical erosion rates.

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.

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 the top 11 m of a lateritic profile developed on a granitic bedrock in south China (Longnan, Jiangxi Province) under a subtropical climate. The results demonstrate that in such a weathering profile 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 (

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.

Metal contaminations from smelting have been widely reported, however, the study on metal mobility or transfer characteristics in soil profiles after a sudden wastewater overflow is far limited. This study was undertaken to investigate distribution and potential mobility of heavy metals in soils flooded by smelting wastewater in Hechi, China. Total heavy metal/metalloid levels were measured in topsoil, profile and profile pore-water taken in-situ. Enrichment factor (EF) and nemero synthesis index (P N ) were used to detect the contribution of anthropogenic emissions to trace element fluxes and pollution levels, respectively. Soil-water partition coefficient (K d ) was used to reflect the fate and the mobility of elements. Results showed topsoil were seriously contaminated with Sb (289–3100 mg kg − 1 ), Pb (444–6388 mg kg − 1 ), Zn (294–923 mg kg − 1 ), Cu (59–192 mg kg − 1 ), Cd (12–34 mg kg − 1 ), and As (32–405 kg − 1 ), and P N values indicated this area was in severe or strongly pollution level. Higher EF values of Sb, Zn, Cd and As were found in the flooded soils, and P N in flooded area was 5 times of that in the unflooded sites, indicating wastewater flooding aggregated pollution in the low-lying area. The Sb, Pb, and Cd concentrations declined drastically with profile but dropped to constant levels below a depth of about 20 cm. In contrast, Zn and Cu in flooding soils declined first and then increased to another extreme value even at depth of 50 cm. Pore-water profiles exhibited the similar declining trends of vertical metal/metalloid distribution pattern. The K d values ranged from 10 2 –10 6 L kg − 1 , and the mobility and bioavailability of the six elements in the profiles declined in the following order: Sb > Zn > Cu > Cd > As > Pb. The relatively low K d values for some depth intervals may reflect adsorption decrease or migration increase of metal/metalloid. However, it is worth to further study and assess their potential risk to environment in longer period.

This study focuses on the chemical and Sr isotopic compositions of the dissolved load of the rivers in the Liao River basin, which is one of the principal river systems in northeast China. Water samples were collected from both the tributaries and the main channel of the Liao River, Daling River and Hun-Tai River. Chemical and isotopic analyses indicated that four major reservoirs (carbonates (+gypsum), silicates, evaporites and anthropogenic inputs) contribute to the total dissolved solutes. Other than carbonate (+gypsum) weathering, anthropogenic inputs provide the majority of the solutes in the river water. The estimated chemical weathering rates (as TDS) of silicate, carbonate (+gypsum) and evaporites are 0.28, 3.12 and 0.75 t/km2/yr for the main stream of the Liao River and 7.01, 25.0 and 2.80 t/km2/yr for the Daliao River, respectively. The associated CO2 consumption rates by silicate weathering and carbonate (+gypsum) weathering are 10.1 and 9.94 × 103 mol/km2/yr in the main stream of the Liao River and 69.0 and 80.4 × 103 mol/km2/yr in the Hun-Tai River, respectively. The Daling River basin has the highest silicate weathering rate (TDSsil, 3.84 t/km2/yr), and the Hun-Tai River has the highest carbonate weathering rate (TDScarb, 25.0 t/km2/yr). The Raoyang River, with an anthropogenic cation input fraction of up to 49%, has the lowest chemical weathering rates, which indicates that human impact is not a negligible parameter when studying the chemical weathering of these rivers. Both short-term and long-term study of riverine dissolved loads are needed to a better understanding of the chemical weathering and controlling factors.