Sediment Flux Research Articles

Imbalance of sediment transport in a meso-tidal bay: effect of tidal pumping and residual circulation

In-situ mooring systems with acoustic Doppler current profilers were installed in the western (TM01) and eastern (TM02) parts of Yeosu Bay from September 3 to October 2, 2021, to understand the controlling mechanisms of suspended sediment transport. In the bay, freshwater from the Seomjin River freely exchanges with seawater from the open sea. Over the mooring period, current flows were mainly dominated by ebb tides. Power spectral density analysis of the suspended sediment concentration (SSC) exhibited a quarter-diurnal (6.21 h) frequency at TM01 and a semi-diurnal (12.42 h) frequency at TM02. The results suggested that SSC variations in the western part were driven primarily by local sediment resuspension, while they were influenced predominantly by horizontal advection in the eastern part. Differences in SSC variation at the two stations could be due to the physical properties of the bed sediments (TM01: sandy mud containing shell fragments, TM02: mud). Such current flows and SSC variations over the tidal cycles caused an imbalance of sediment transport. At TM01, the sediment fluxes were dominantly seaward due to tidal pumping (88% of the total) and the discharge of suspended sediments in the surface layer by residual circulation. At TM02, landward sediment fluxes were driven primarily by the residual current (73% of the total). Although the suspended sediment fluxes tended to be compensated and balanced mutually by circulation over the entire period, the suspended sediment fluxes at TM02 were approximately twice higher than those at TM01. This was caused by the difference in SSC asymmetry between flood and ebb at the two stations. The mechanisms controlling the transport of suspended sediment could vary spatially, and the relative contribution of tidal pumping and residual circulation could result in an imbalance of sediment transport.

Kinetically controlled metal-elastomer nanophases for environmentally resilient stretchable electronics

Nanophase mixtures, leveraging the complementary strengths of each component, are vital for composites to overcome limitations posed by single elemental materials. Among these, metal-elastomer nanophases are particularly important, holding various practical applications for stretchable electronics. However, the methodology and understanding of nanophase mixing metals and elastomers are limited due to difficulties in blending caused by thermodynamic incompatibility. Here, we present a controlled method using kinetics to mix metal atoms with elastomeric chains on the nanoscale. We find that the chain migration flux and metal deposition rate are key factors, allowing the formation of reticular nanophases when kinetically in-phase. Moreover, we observe spontaneous structural evolution, resulting in gyrified structures akin to the human brain. The hybridized gyrified reticular nanophases exhibit strain-invariant metallic electrical conductivity up to 156% areal strain, unparalleled durability in organic solvents and aqueous environments with pH 2–13, and high mechanical robustness, a prerequisite for environmentally resilient devices.

Effect of Seismicity and Tectonic‐Glacial Interactions on Submarine Megaslides

AbstractEnhanced sedimentation at glacial margins can produce submarine megaslides (>10,000 km3). We report a single megaslide in the Surveyor Fan, Gulf of Alaska. Minimum extant size is ∼16,124 km2 in area and ∼9,080 km3 in volume. Slope failure occurred ∼1.2 Ma at the onset of the mid‐Pleistocene transition (MPT). With accretion along the Aleutian‐Alaska Trench, the original volume is conservatively ∼16,280 km3, with only a 140 km run‐out due to its blocky, high shear strength nature. We suggest the megaslide was triggered by a major sediment influx at the onset of the MPT, when glacial‐interglacial cycles shifted from 41 to 100 Kyr. The absence of repeat megaslides may reflect a changing balance between seismic strengthening and sediment flux, where later sedimentation driven by cross‐shelf ice streams results in thin, fluidized, non‐cohesive slides. Continued accretion of the Surveyor Fan and megaslide also reduces critical wedge taper, further inhibiting major failure.

Does a braided river aggrade or degrade in response to changes in water and sediment fluxes?

Braided rivers undergo continuous morphological evolution in response to variations in water and sediment fluxes associated with a plethora of natural and anthropogenic disturbances, which has to date remained poorly understood. Here, a one-dimensional hydro-sediment-morphodynamic model is proposed for braided rivers. It is built upon an extended synthetic channel geometric model which encodes the essential, three-dimensional morphological information into a one-dimensional synthetic channel. It is first applied to the Rees River (New Zealand) to investigate overall morphological evolution (aggradation/degradation) during a single flood event. It is shown that the channel tends to degrade with increasing peak discharge and decreasing sediment supply, while the effect of baseflow discharge on aggradation/degradation is negligible unless the baseflow discharge exceeds a critical value. Then the proposed model is applied to resolve long-term morphological evolution in the Tuotuo River (China) reach (up to the year 2050), the source region of the Yangtze River, in response to projected water and sediment fluxes. Sustained degradation in the river reach is observed. The present study yields a viable physics-based method to predict overall aggradation or degradation of braided rivers under unsteady water and sediment fluxes over both short and long time scales.

Quantity and quality characteristics of DOM loss in sloping cropland under natural rainfall in Southwestern China

Rainfall events lead to dissolved organic matter (DOM) loss in sloping cropland, resulting in a high risk of soil carbon emissions and water pollution. However, limited studies have concentrated on the quality of DOM during different loss pathways in sloping cropland. In this study, the characteristics of DOM loss were explored during different loss pathways (surface runoff, interflow (0–20 cm), interflow (20–40 cm), and sediment) under different slope gradients (10° and 15°), based on natural rainfall. The results showed that surface runoff was the primary carrier of DOM in the sloping cropland, occupying 33 %-43 % of the total loss flux. The slope gradient significantly increased the DOM loss flux of surface runoff and sediment (p < 0.05). Parallel factor analysis (PARAFAC) analyses indicated that four fluorescent components of DOM were detected in both the runoff and sediment. The humic-like components (C1 and C2) accounted for higher than 70 % of the DOM in surface runoff. The protein-like components (C3 and C4) tended to dominate the DOM in the sediment and accounted for 63.02 %-66.93 %. An increased slope gradient exacerbated hydrophobic carbon loss in runoff. The hydrophobicity and aromaticity of DOM in sediment were higher than those in surface runoff. The molecular weight and bioavailability of DOM in sediment were lower than those in surface runoff. The range of humification index (HIX) was 0.63–0.70, indicating a low degree of DOM humification in sloping cropland. Our study clarified the differences between DOM quantity and quality during different loss pathways, which can provide a theoretical foundation for the effective prevention and control of DOM loss and the sustainable agricultural development of sloping cropland.

Smartphone-Based Color Evaluation of Passive Samplers for Gases: A Review

The application of smartphone-based color evaluation of passive sampling devices for gases has only been sparsely reported. The present review aims to compile available publications with respect to the configuration of the passive samplers, conditions of smartphone photographing, analytical procedures for color detection and quantification (including calibration processes), and their application to different target gases. The performance of the methods—whenever available—is presented regarding the analytical specifications selectivity, sensitivity, and limit of detection in comparison with other color evaluation methods of passive samplers. Practical aspects like requirements of instrumentation and ease of use will be outlined in view of the potential employment in education and citizen science projects. In one section of the review, the inconsistent terminology of passive and diffusive sampling is discussed in order to clarify the distinction of information obtained from the uptake of the passive samplers between gas-phase concentration and the accumulated deposition flux of gaseous analytes. Colorimetric gas sensors are included in the review when applied in passive sampling configurations and evaluation is performed with smartphone-based color evaluation. Differences in the analytical procedures employed after the passive sampling step and prior to the detection of the colored compounds are also presented.

An examination of point-particle Lagrangian simulations for assessing time-resolved hydroacoustic particle flux measurements in sediment-laden flows.

Accurate modelling and prediction of sediment transport in aquatic environments is essential for sustainable coastal and riverine management. Current capabilities rely on physical process-based numerical models and fine-scale sediment flux measurements. High-resolution hydroacoustic instrumentation has emerged as a promising tool for such measurements. However, challenges arise due to the inherent complexity of ultrasound scattering processes. This study introduces a numerical modelling using a point-particle approach to simulate the echoes backscattered by such instrumentation in sediment-laden flow conditions. The model considers geometric, statistical, particle cloud, and flow-induced effects on sediment velocity, concentration, and flux estimates using an acoustic concentration and velocity profiler as a reference. The model performance is assessed here under unidirectional constant flow conditions in terms of velocity, concentration, and time-resolved sediment flux estimates for a large range of the particles' advection speed and sampled volume sizes. Application to the estimation of the measurement accuracy of sediment flux in these flows is also considered, with a final error on the flux seen to be partially controlled by the residence time of particles within the sampled volumes. The proposed model provides insights into scattering processes and offers a tool for investigating robust sediment flux estimation techniques in various flow conditions.

Effects of Seasonal Variations in Seagrass Density and Storms on Sediment Retention and Connectivity Between Subtidal Flats and Intertidal Marsh

AbstractBoth submerged aquatic vegetation and salt marsh are important coastal ecosystems known for their effectiveness in sediment trapping and carbon burial. However, their proximity can lead to competition for limited sediment resources, potentially compromising their capacity to facilitate sufficient sediment deposition to withstand sea‐level rise. Here we applied the Delft3D flow and sediment transport model in a shallow coastal bay to assess how seasonal variations in seagrass density and storms modulate sediment retention and connectivity between subtidal flats and intertidal marsh. Results show that submerged seagrass meadows acted as temporary storage for fine sediment and altered the timing of sediment transport to an adjacent marsh through seasonal growth cycles. When seagrass occupied subtidal flats, sediment flux to the marsh was controlled by seasonal seagrass density variations, with peak fluxes during winter senescence. In contrast, wave‐induced sediment resuspension on the flats was the major contributor for marsh sediment input in the simulation with no seagrass, with peak storm‐driven fluxes in summer/autumn. Overall, seagrass meadows significantly increased annual sediment accumulation on the vegetated subtidal flats by tenfold, while reducing annual marsh sediment flux and edge erosion by 20%. Seagrass meadows and marsh were both able to maintain a sediment deposition rate comparable to the rapid sea‐level rise at the study site despite the absence of terrestrial sediment sources. Our findings highlight the strong seasonal control subtidal aquatic vegetation has in the vertical and horizontal dynamics of tidal flat‐marsh systems and provide insights that can inform wetland restoration and management strategies in similar systems.

Topography‐Based Particle Image Velocimetry of Braided Channel Initiation

AbstractRiver channels shape landscapes through gradual migration and abrupt avulsion. Measuring the motion of braided rivers, which have multiple channel threads, is particularly challenging, limiting predictions for landscape evolution and fluvial architecture. To address this challenge, we extended the capabilities of image‐based particle image velocimetry (PIV)—a technique for tracking channel threads in images of the surface—by adapting it to analyze topographic change. We applied this method in a laboratory experiment where a straight channel set in non‐cohesive sediment evolved into a braided channel under constant water and sediment fluxes. Topography‐based PIV successfully tracked the motion of channel threads if displacements between observations were less than the channel‐thread width, consistent with earlier results from image‐based PIV. We filtered spurious migration vectors with magnitudes less than the elevation grid spacing, or with high uncertainties in magnitude and/or direction. During braided channel initiation, migration rates varied with the channel planform development, showing an increase as incipient meanders developed, a decrease during the transitional braiding phase, and consistently low values during the established braiding phase. In this experimental setup, migration rates varied quasi‐periodically along stream at the half scale of initial meander bends. Lateral migration with respect to the mean flow direction was much more pronounced than streamwise migration, accounting for approximately 80% of all detected motion. Results demonstrate that topography‐based PIV has the potential to advance predictions for bank erosion and landscape evolution in natural braided rivers as well as bar preservation and stratigraphic architecture in geological records.

Modeling the Cross‐Sectional Dynamics of Tidal Sandbanks in Sediment‐Scarce Conditions

AbstractTidal sandbanks are large‐scale dynamic bedforms that consist of sandy sediment. They have been observed in shallow seas with varying sediment supply, including sediment‐scarce environments like the Flemish Banks, Zeeland Banks, and Norfolk Banks. However, we do not yet understand how scarcity affects sandbank evolution. Therefore, we have developed an idealized nonlinear process‐based model with the aim of studying cross‐sectional shape and migration under sediment‐scarce conditions. Scarcity is included through a non‐erodible layer from which no sediment can be entrained. Our results show that bank height and width decrease when the sediment budget decreases. The bank height is more sensitive to scarcity than bank width. Furthermore, sand scarcity decreases (and may even reverse) bank asymmetry and increases migration rate when a residual current is present. The migration rate attains a maximum for a specific sediment budget, which is controlled by the ratio of the cross‐sectional area of the sandbank and the tide‐averaged sediment flux. Our findings show that sandbank dynamics are strongly affected by scarcity, which is critical for seas with receding sediment stocks (e.g., through extraction).

Impact of dam construction on sediment transport capacity: A case study of the Three Gorges Reservoir

AbstractReservoir sedimentation affects lifespan, hydropower generation, water resource use, and ecosystem sustainability. In this study, using measured data from the world‐renowned Three Gorges Reservoir (TGR), sediment transport capacity was analysed from 2002 to 2020 at four TGR gauging stations (Cuntan, Qingxichang, Wanxian, and Miaohe). The result indicated that: (1) a significant decrease in sediment transport capacity occurred in the TGR before and after dam construction, with an overall reduction of 82% in the perennial backwater zone. Notably, Qingxichang, Wanxian, and Miaohe experienced reductions of 40%, 91%, and 59%, respectively. Since the initial operation phase, their maximum monthly sediment transport capacity has consistently occurred in July. (2) Changes in the water level in front of the dam, the incoming flow, and sediment influxes were the primary factors driving the annual variations in sediment transport capacity. Among the factors affecting the variation of sediment transport capacity along the TGR, the influence of the cross‐sectional morphology was more pronounced than that of the distance from the dam. Sediment transport capacities in the wide and shallow sections were considerably lower than those in the narrow and deep sections. (3) A sediment transport amplitude index () was proposed to assess the sediment dynamics within the TGR, which effectively characterized the sedimentation conditions based on the relative importance of these influencing factors. These findings provide a theoretical basis for operational strategies in the TGR and offer insights into the patterns of sediment transport capacity changes in reservoir areas before and after dam construction in other river‐type reservoirs.

Seasonal dynamics of water and sediment in the permafrost basin of the Qinghai‐Tibet plateau and its driving factors

AbstractClimate change has regulated cryosphere‐fed rivers and altered interannual and seasonal sediment dynamics, with significant implications for terrestrial material cycles and downstream aquatic ecosystems. However, there has been a notable scarcity of research focusing on the patterns of water–sediment transport within these permafrost zones. Integrating 6 years (2017–2022) of in‐situ observational data from FengHuoShan basin with the partial least squares‐structural equation modelling (PLS‐SEM) method, we analyse the driving factors, characteristics and seasonal patterns of the water–sediment transport process. We observed a gradual increase in both suspended sediment flux (SSF, Mt/yr) and runoff (Q, km3/yr) within the basin, with annual growth rates of 1.34%/yr and 0.75%/yr, respectively. It is worth noting that these growth rates exhibit seasonal variations, with the highest values observed in spring (SSF: 1.76%/yr, Q: 1.71%/yr). This indicates that the response to climate change is more pronounced in spring compared with summer and autumn. Through mathematical statistics and the PLS‐SEM model, we found that temperature plays a predominant role in the dynamics of water–sediment in both spring and autumn, whereas rainfall exerts a more significant impact during the summer. Most suspended sediment concentration (SSC, kg/m3) peak events throughout the year are primarily driven by rainfall. Affected by the freeze–thaw cycle of permafrost, SSC and discharge (Q, m3/s) exhibit distinct seasonality. SSC and Q demonstrate a clockwise trend; both Q and SSC begin to increase from May and peak in August before declining. The insights gleaned from this study hold significant implications for water resource management and soil conservation strategies in the region, particularly in the face of ongoing climatic changes characterized by warming and increased humidity.

The Incomplete Record of Autogenic Processes Sets Limits on Signal Detectability

AbstractSpectral analysis is a central tool regularly used by the scientific community to identify the presence of periodic processes within a time series of information, as spectral peaks at an imposed periodicity can be differentiated from internal (autogenic) variance. In scientific disciplines, such as seismology, the time series of information is of high temporal resolution. Hence, although temporal gaps are present, they do not impact the overall noise structure, meaning that the full spectrum of autogenic variance can be reconstructed. However, power spectra generated from stratigraphic information are affected by temporal incompleteness due to varying episodes of erosion and geomorphic stasis, which generate gaps over a range of scales. This removes information related to the natural and autogenic variability present within sediment‐transport systems, which makes it challenging to accurately reconstruct the structure and strength of paleo‐surface processes, which defines the detectability of past environmental signals. We explore how incompleteness impacts the temporal structure of autogenic noise within power spectra, and how this influences the detectability of spectral spikes related to environmental signals. We utilize a sediment flux time series from a physical rice pile and progressively degrade these data to mimic varying degrees of stratigraphic incompleteness. We find that incompleteness strongly influences the timescales and spectral structure of autogenic noise evident, and can render signals over all periodicities undetectable within a highly incomplete time series. This offers the ability to confidently justify the interpretation of subtle environmental signals from field measurements and understand the records that may best preserve paleoenvironmental variability.

Size Distributions and Health Risks of Particulate Polycyclic Aromatic Hydrocarbons in the Atmosphere at Coastal Areas in Ningbo, China.

Most current research focusing on the health risk assessments of particulate polycyclic aromatic hydrocarbons (PAHs) have not analyzed the size distributions and human respiratory deposition rates. In the present study, size-separated particulate matter (PM) was collected in the coastal area of Ningbo using an Anderson eight-stage air sampler over a 1-year period (2014-2015). The 16 US Environmental Protection Agency priority PAHs associated with PM were pretreated with rapid solvent extraction and analyzed by gas chromatography-mass spectrometry. The respiratory exposure assessment was determined using the multiple-path particle dosimetry (MPPD) model. The results show that all PAHs exhibited bimodal distribution with one mode peak in accumulation mode (0.43-0.65 µm) and another mode peak in coarse mode (4.7-5.8 µm). In addition, a low coefficient of divergence of PAHs between PM2.1 and PM2.1-10 indicated a high spatial heterogeneity in source factor contribution and formation mechanism. The deposition fluxes (tracheobronchial + pulmonary) of PM were highest for children in the size range of 3.3 µm < particle diameter (Dp) < 9 µm, while for males and females the highest fluxes occurred in the size range of 1.1 µm < Dp < 2.1 µm. The depositions of coarse PM in children were significantly higher than those in adults. The benzo[a]pyrene equivalent (BaPeq) depositions of dibenz[a,h]anthracene ranged from 1.4e-04 to 0.015 ng h-1, which were highest among the PAHs. The PAHs on particles with Dp >4.7 µm contributed approximately three times more to children than to males and females. Therefore, the toxicity of coarse PM to children needed attention. The incremental lifetime cancer risks (ILCR) for children, males, and females were estimated to be 2.92 × 10-7, 1.82 × 10-7, and 2.38 × 10-7, respectively, which were below the cancer risk guideline value (10-6). These ILCR values were much lower than the risks calculated without considering particle size distributions and respiratory depositions. The combination of the size-segregated sampling technique and the MPPD model can effectively avoid the overestimation of human respiratory exposure. Environ Toxicol Chem 2024;43:1364-1377. © 2024 SETAC.

Considering the Size Distribution of Elements in Particle Matter and Oxidation Potential: Association before and after Respiratory Exposure

Oxidation potential (OP), reflecting the redox activities of particle matter (PM), is considered an optimal measure to explain the biological effects of PM exposure. However, the size resolution of the relationship between OP and chemical composition in PM, especially how the relationship changes after respiratory exposure, has not been well investigated. In this study, size-resolved indoor PM10 samples were collected from a waste recycling plant from November to December 2021 using an Anderson eight-stage cascade impactor. OP, measured by a dithiothreitol (DTT) assay (defined as OPDTT), and elements, determined by inductively coupled plasma–mass spectrometry (ICP-MS) in size-resolved PM, were determined to check their relationships and the related human exposure risk. The results indicated that compared with PM0.4 and PM0.4–2.1, PM2.1–10 contributed the most to total OPDTT and its bound elements contributed the most to potential health risks, both before and after respiratory exposure. The association between OPDTT and the elements varied with PM size. Pearson correlation analysis showed that the PM0.4- and PM0.4–2.1-bound elements were moderate-to-strongly positively correlated with OPvDTT (r: 0.60–0.90). No significant correlation or dose–response relationship was found in PM2.1–10. After respiratory exposure, several PM0.4- and PM0.4–2.1-bound elements had a moderate-to-strongly positive correlation with deposition fluxes of OP (defined as OPFlux) (0.69–0.90). A generalized linear model analysis showed that the interquartile range (IQR) increase in the PM-bound elements (ng h−1) was associated with a 41.7–58.1% increase in OPFlux. Our study is a special case that enriches the knowledge of the association between OPDTT and the chemical composition of PM of different sizes, especially after respiratory exposure, but the generalizability of the findings to other settings or types of PM may be limited. The associations among OPDTT, other chemical compositions of PM, and human exposure risk merit further research.

Ca isotopic gradients in epeiric marine carbonates: Diagenetic origins of and significance for Ca cycle reconstructions

Marine carbonates record geochemical information on the state of Earth’s surface environment in the geological past, but recrystallization during burial can make the records difficult to interpret. Here, we report shore to basin gradients in δ44Ca values in matrix limestone and burrow dolomite across a sequence of Late Ordovician (Katian Stage) burrow-mottled carbonates in the Williston Basin, an intracratonic epeiric marine basin in North America. Both gradients are interpreted to have diagenetic origins. The gradient in limestone δ44Ca values developed in a bathymetrically controlled sediment- to fluid-buffered diagenetic system operating between the center and the edges of the basin. Two dolomitizing events formed the gradient in dolomite δ44Ca values. The sediment-buffered end of the limestone gradient preserves the δ44Ca value of the original carbonate mud (∼–1.28 ± 0.10 ‰). The fluid-buffered end of the gradient conserves the δ44Ca value of contemporaneous seawater (–0.47 ± 0.10 ‰), because: (1) pore water exchange drivers operated with greater variety and intensity in shallow water settings, (2) shallow nearshore deposits exchanged more Ca with seawater during recrystallization to diagenetic calcite than deeper offshore deposits, and (3) diagenetic calcite formed with negligible fractionation under equilibrium conditions. The gradient conserves the local value of Δsed (–0.81 ± 0.20 ‰) despite its diagenetic origin, and the magnitude of Δsed is consistent with primary calcite precipitation in a ‘calcite sea’. Field assessment of the equilibrium Ca isotope fractionation factor between calcite and dolomite of –0.41 ± 0.17 ‰ at ambient temperature is applied to correct basin-centered dolomite for fractionation, yielding –1.62 ± 0.27 ‰, which is very different from the –0.25 ± 0.07 ‰ value of Ca in evaporatively concentrated seawater from which the dolomite originally formed. Applying the same fractionation factor to correct literature data on early diagenetic dolomite in the Great Basin, North America, yields –0.69 ± 0.22 ‰ for the δ44Ca value of seawater, which is ∼0.2 ‰ lower than ‘normal marine’ waters in stratigraphically equivalent deposits in the Willison Basin, and 0.44 ‰ lower than evaporatively concentrated seawater during a brief period of basin restriction and anhydrite deposition. The nearly 0.5 ‰ variation in the δ44Ca value of Katian seawater falls within the range of scatter in the brachiopod reconstruction of seawater Ca isotopes. Here, we propose that the true ocean record of secular change lies towards the bottom of the range of scatter, and that the higher values in the record reflect local Ca cycling and circulation restriction in epeiric seas. Epeiric seas cultivate the fluid-buffered diagenetic conditions required to promote Ca isotope exchange between reactive carbonate sediments and seawater through carbonate mineral dissolution/recrystallization, crystal coarsening by way of Ostwald ripening, and replacive dolomitization. It is not the apportioning of kinetically fractionated aragonite and calcite in the carbonate deposition flux that drove secular changes in global value of Δsed between ‘calcite’ and ‘aragonite’ seas, but rather the replacement of kinetic fractionations with equilibrium fractionations during fluid-buffered diagenesis with seawater.

Production of oxygenated volatile organic compounds from the ozonolysis of coastal seawater

Abstract. Dry deposition of ozone (O3) to the ocean surface and the ozonolysis of organics in the sea surface microlayer (SSML) are potential sources of volatile organic compounds (VOCs) to the marine atmosphere. We use a gas chromatography system coupled to a Vocus proton-transfer-reaction time-of-flight mass spectrometer to determine the chemical composition and product yield of select VOCs formed from ozonolysis of coastal seawater collected from Scripps Pier in La Jolla, California. Laboratory-derived results are interpreted in the context of direct VOC vertical flux measurements made at Scripps Pier. The dominant products of laboratory ozonolysis experiments and the largest non-sulfur emission fluxes measured in the field correspond to Vocus CxHy+ and CxHyOz+ ions. Gas chromatography (GC) analysis suggests that C5–C11 oxygenated VOCs, primarily aldehydes, are the largest contributors to these ion signals. In the laboratory, using a flow reactor experiment, we determine a VOC yield of 0.43–0.62. In the field at Scripps Pier, we determine a maximum VOC yield of 0.04–0.06. Scaling the field and lab VOC yields for an average O3 deposition flux and an average VOC structure results in an emission source of 10.7 to 167 Tg C yr−1, competitive with the DMS source of approximately 20.3 Tg C yr−1. This study reveals that O3 reactivity to dissolved organic carbon can be a significant carbon source to the marine atmosphere and warrants further investigation into the speciated VOC composition from different seawater samples and the reactivities and secondary organic aerosol (SOA) yields of these molecules in marine-relevant, low NOx conditions.

Temporal-spatial characteristics and sources of heavy metals in bulk deposition across China

With the rapid development of industries, agriculture, and urbanization (including transportation and population growth), there has been a significant alteration in the emission and atmospheric deposition of heavy metal pollutants. This has consequently given rise to a range of ecological and environmental health issues. In this study, we conducted a comprehensive two-year investigation on the temporal and spatial distribution characteristics of heavy metals in atmospheric deposition across China based on the Nationwide Nitrogen Deposition Monitoring Network (NNDMN). The atmospheric bulk deposition of Lead (Pb), Arsenic (As), Nickel (Ni), Selenium (Se), Chromium (Cr) and Cadmium (Cd) were 6.32 ± 1.59, 4.49 ± 0.57, 1.31 ± 0.21, 1.05 ± 0.16, 0.60 ± 0.06 and 0.21 ± 0.03 mg m−2 yr−1, respectively, with a large variation among the different regions of China. The order for atmospheric deposition flux was Southwest China > Southeast China > North China > Northeast China > Qinghai-Tibet Plateau and rural area > urban area > background area. The concentrations of heavy metals in bulk deposition exhibit seasonal variation with higher levels observed during winter compared to summer and spring, which are closely associated with anthropogenic activities. The Positive Matrix Factorization (PMF) results indicated that combustion, industrial emissions and traffic are the primary contributors to atmospheric deposition of heavy metals. The single factor pollution index (Pi) of heavy metals is consistently below 1, and the composite pollution index (Ni) is 0.16 across China, indicating that atmospheric heavy metal deposition is at a pollution-free level. The comprehensive potential ecological risk index of heavy metals is 11.8, with Cd exhibiting the highest single factor potential ecological risk index at 7.09, suggesting that more attention should be paid to Cd deposition in China. The present study reveals the spatial-temporal distribution pattern of atmospheric heavy metals deposition in China, identifying regional source characteristics and providing a theoretical foundation and strategies for reducing emissions of atmospheric pollutants.

Observation of ozone deposition flux and its contribution to stomatal uptake over a winter wheat field in eastern China

Ground-level ozone (O3) poses a significant threat to food security in China. Therefore, it is imperative to conduct a comprehensive scientific evaluation of the potential hazards posed by O3 to agricultural crops. This study continuously observed variation in meteorological factors, O3 concentration, O3 deposition rate and flux, and quantified the distribution characteristics of O3 deposition flux in stomatal and non-stomatal pathways. Results suggested that the O3 dry deposition rate and flux in winter wheat fields exhibited relatively stable variations at night but pronounced fluctuations during the day. Their mean values were 0.31 cm s−1 and -0.0044 μmol m−2·s−1, respectively, with peak values occurring at 08:30 and 14:00. The cumulative O3 total flux during the main growth season of winter wheat was 26.1 mmol m−2, with stomatal and non-stomatal fluxes accounting for 7.7 mmol m−2 and 18.4 mmol m−2, respectively. The proportions of total O3 flux in stomatal and non-stomatal channels were 29.5% and 70.5%, respectively, with daytime proportions being 39.7% and 60.3%, respectively. These findings provide crucial insights for future accurate assessments of crop yield loss due to O3 at the earth's surface.

Emissions and Atmospheric Dry and Wet Deposition of Trace Metals from Natural and Anthropogenic Sources in Mainland China

Trace metals from natural and anthropogenic sources impact the atmospheric environment and enter the soil through dry and wet atmospheric deposition, ultimately affecting human health. In this study, we established an emission inventory of Pb, As, Cr, and Cd in East Asia (80° E–140° E, 15° N–50° N) for the year 2017, including dust and anthropogenic sources from both land and marine. We modified the Community Multiscale Air Quality (CMAQ) model to provide gridded data on concentrations, as well as dry and wet atmospheric deposition fluxes of metals, with a focus on mainland China. The emissions of Pb, As, Cr, and Cd in East Asia were 19,253, 3415, 3332, and 9379 tons, respectively, in 2017, with 55%, 69%, 25%, and 58% distributed in the fine mode. The spatial distribution of atmospheric concentrations and dry deposition of trace metals was similar to that of emissions, while the spatial distribution of precipitation-related wet deposition was further east and greater in the south than in the north. In mainland China, the average bulk-deposition fluxes of Pb, As, Cr, and Cd were 1036.5, 170.3, 465.9, and 185.0 μg·m−2·year−1, respectively. Our study provides gridded data on trace metals in mainland China, which can be used for assessing air quality, human exposure risks, and metal inputs to soils.