Atmospheric Inputs Research Articles

Unraveling the sources of major, trace and rare earth elements in the waters of a high latitude proglacial environment: Weathering vs. atmospheric signature in Northern Patagonia

Glaciers are important water reservoirs and are extremely sensitive to the effects of climate change. The Manso River basin, in Northwest Patagonia, Argentina, is a typical hydrological system with actively retreating glaciers. In this article, the proglacial environment was examined to assess the sources and the geochemical processes responsible for the chemical signatures of the following water subsystems: 1) clean glacial meltwaters (supraglacial influence, fed by “clean ice” glaciers); 2) dirty glacial meltwaters (subglacial influence, fed by “dirty ice” debris-covered glacier); and 3) proglacial runoff (river). Results indicated that clean glacial meltwaters present high dissolved immobile and nonmobile trace elements, derived from atmospheric input with an anthropogenic component in Pb, Cu, V, and Ni. Dissolved concentrations of Sr, Mn, Rb, and major ions are the result of carbonation and hydrolysis processes. The dirty glacial meltwater presents the highest dissolved load due to the highest water-rock interaction. The proglacial runoff presents intermediate physicochemical characteristics. At the site where the clean and dirty glacial meltwaters mix, the cation denudation rate is 2075 meq+ m−2 y−1. Downstream, geochemical inverse modeling indicates that the Manso Superior River system produces, by weathering reactions, a rate of dissolved load of 2.67 108 mol year−1, along with a CO2 sequestration of 2.05 108 mol year−1, denoting that proglacial environments are an important scenario in the CO2 cycle. The results of this work provide a baseline for future studies in proglacial environments and highlight the importance of assessing metal concentrations and mobilization within the Andean cryosphere.

Contrasting potential for biological N2 fixation at three polluted central European Sphagnum peat bogs: combining the 15N2-tracer and natural-abundance isotope approaches

Abstract. Availability of reactive nitrogen (Nr) is a key control on carbon (C) sequestration in wetlands. To complement the metabolic demands of Sphagnum in pristine rain-fed bogs, diazotrophs supply additional Nr via biological nitrogen fixation (BNF). As breaking the triple bond of atmospheric N2 is energy-intensive, it is reasonable to assume that increasing inputs of pollutant Nr will lead to BNF downregulation. However, recent studies have also documented measurable BNF rates in Sphagnum-dominated bogs in polluted regions, indicating the adaptation of N2 fixers to changing N deposition. Our aim was to quantify BNF in high-elevation peatlands located in industrialized central Europe. A 15N2-tracer experiment was combined with a natural-abundance N-isotope study at three Sphagnum-dominated peat bogs in the northern Czech Republic in an attempt to assess the roles of individual BNF drivers. High short-term BNF rates (8.2 ± 4.6 g N m2 d−1) were observed at Malé mechové jezírko, which receives ∼ 17 kg Nr ha−1 yr−1. The remaining two peat bogs, whose recent atmospheric Nr inputs differed from Malé mechové jezírko by only 1–2 kg ha−1 yr−1 (Uhlír̆ská and Brumiště), showed zero BNF. The following parameters were investigated to elucidate the BNF difference: the NH4+-N / NO3--N ratio, temperature, wetness, Sphagnum species, organic-N availability, possible P limitation, possible molybdenum (Mo) limitation, SO42- deposition, and pH. At Malé mechové jezírko and Uhlír̆ská, the same moss species (S. girgensohnii) was used for the 15N2 experiment; therefore, the host identity could not explain the difference in BNF at these sites. Temperature and moisture were also identical in all incubations and could not explain the between-site differences in BNF. The N : P stoichiometry in peat and bog water indicated that Brumiště may have lacked BNF due to P limitation, whereas non-detectable BNF at Uhlír̆ská may have been related to the 70-fold higher SO42- concentration in bog water. Across the sites, the mean natural-abundance δ15N values increased in the following order: atmospheric deposition (−5.3 ± 0.3 ‰) < Sphagnum (−4.3 ± 0.1 ‰) < bog water (−3.9 ± 0.4 ‰) < atmospheric N2 (0.0 ‰). Only at Brumiště was N in Sphagnum significantly isotopically heavier than in atmospheric deposition, possibly indicating a longer-term BNF effect. Collectively, our data highlight spatial heterogeneity in BNF rates under high Nr inputs as well as the importance of environmental parameters other than atmospheric Nr pollution in regulating BNF.

Distribution, Transfer, and Health Risk of Organochlorine Pesticides in Soil and Water of the Huangshui River Basin.

The potential negative impacts of organochlorine pesticides on the environment and human health continue to receive attention. In order to study the spatial distribution characteristics of organochlorine pesticides in the inland alpine region, researchers collected soil and water samples in the Huangshui River Basin of the Qinghai-Tibetan Plateau and tested them for organochlorine pesticide residues represented by dichlorodiphenyltrichloroethane (DDT) and hexachlorohexane (HCH). The study identified the sources of OCPs by component analysis. We also constructed the LEVEL III model, applicable to the Huangshui River Basin, and used it to study the migration patterns of OCPs in various environmental media. OCPs were detected at low levels in the study area environment. The results of the OCPs source analysis show that there are both historical residuals and new sources in the region. Residual DDTs may originate from the mixture of technical DDTs and dicofol, and HCHs may originate from lindane or technical HCH. DDTs are mainly stored in soil, the input and output pathways are mainly atmospheric advection input and output, and its transport behavior in the environment is mainly air-soil exchange. Carcinogens in the study area pose little threat to people exposed to contaminated soil and contaminated water, but the cancer risk to children is greater than to adults. This study is helpful to managers of regional pesticide management and control.

Accumulation, ecological health risks, and source identification of potentially toxic elements in river sediments of the Qinghai-Tibet Plateau, China

The Qarhan Salt Lake is the largest brine lake on the Qinghai-Tibet Plateau (QTP), which contains some potentially toxic elements (PTEs) due to the increase of human activities. This study endeavor encompassed the collection of 62 sediment samples from eight rivers that recharge the Qarhan Salt Lake, and the measurement of seven PTEs' concentrations (As, Hg, Pb, Cd, Cu, Ni, and Zn). Results indicated that the concentrations of most PTEs were lower than their local soil background values, except for Hg and Cd, which surpassed the background contents by 6.8 and 1.1 times, respectively. The Igeo and PLI outcomes demonstrated a relatively low level of Hg contamination. Hg was the most hazardous elements with the mean ecological risk factor of 273.88. The Hazard Index (HI) values for PTEs were computed at 0.20 and 0.46 for adults and children, respectively, indicating that neither group was at a non-carcinogenic risk. Through the utilization of source identification methods, this study identified three predominant sources responsible for PTEs in the area: natural geogenic sources, anthropogenic sources and atmospheric deposition inputs. The findings of this study provide a robust scientific foundation for the management of the ecological environment security of rivers in the QTP.

Trace Metal Fluxes of Cd, Cu, Pb and Zn From the Congo River Into the South Atlantic Ocean Are Supplemented by Atmospheric Inputs

AbstractThe Congo River supplies vast quantities of trace metals (TMs) to the South Atlantic Ocean, but TM budgets for the Congo plume derived using radium isotopes for GEOTRACES cruise GA08 suggest additional input other than the river outflow. Considering the tight correlations between most dissolved TMs and salinity in the plume and the high rainfall during the wet season over the Congo shelf, we hypothesized that wet atmospheric deposition is a TM source to the Congo plume. Observed TM concentrations in rainwaters across the Congo shelf were mostly comparable to values from previous work in the North Atlantic and Mediterranean Sea. Wet deposition contributed the equivalent of 43% dCd, 21% dCu, 20% dPb and 68% dZn of the Congo River fluxes. Our findings show an important role of wet deposition in supplying TMs to the South Atlantic overlapping with the region that receives substantial TM fluxes from the Congo River.

Trace elements in the water column of high-altitude Pyrenean lakes: Impact of local weathering and long-range atmospheric input

High altitude (alpine) lakes are efficient sentinels of environmental processes, including local pollution and long-range atmospheric transfer, because these lakes are highly vulnerable to ongoing climate changes and increasing anthropogenic pressure. Towards improving the knowledge of trace element geochemistry in the water column of alpine lakes, we assessed 64 physico-chemical parameters, including macro- and micronutrients, major and trace element concentrations in the water column of 18 lakes in the Pyrenees, located along the border between France and Spain.Lake depth, morphology, retention time and watershed rock lithology did not exhibit sizable impact on major and trace element concentrations in the water column. However, acidic (pH = 4.7 ± 0.2) lakes were distinctly different from circumneutral lakes (pH = 6.8 ± 0.5) as they exhibited >10 times higher concentrations of SO42− and trace metals (Fe, Mn, Zn, Cd, Pb, Co, Ni, Be, Al, Ga and REEs). While some of these elements clearly mark the presence of sulphide-rich minerals within the watershed (Fe, Zn, Cd and Pb), the increased mobility of lithogenic elements (Be, Al, Ga and REEs) in acidic lakes may reflect the leaching of these elements from silicate dust derived from atmospheric deposits or surrounding granites. At the same time, compared to circumneutral lakes, acidic lake water displayed lower concentrations of dissolved oxyanions (As, Mo, V, B and W) and elevated SO42− concentrations. The latter could lead to efficient Ba removal from the water column. The exploitation of metal ores within the watershed of three lakes clearly impacted high Zn and Cd concentrations observed in their water column, despite two of these lakes not being acidic. We conclude that local impacts have a greater effect on the water column than long-range atmospheric inputs and that dissolved trace element concentration measurements can be used for revealing sulphide-rich minerals or acid mine drainage within the lakes’ watershed.

Atmospheric dependence of the direct, diffuse, and global clear-sky conversion ratios between solar photosynthetic active irradiance and photon flux

The ratio of the global solar photosynthetic active radiation (PAR) photon flux (in μmol/m2s) to global solar PAR irradiance (in W/m2) is of interest to convert one into another. This ratio is usually considered as a constant value close to its extraterrestrial value, 4.55μmol/J. However, this ratio depends on the spectral composition of solar radiation at ground level and it is different for the diffuse and beam components of solar irradiance. Under clear-sky conditions, the three PAR ratios (global, beam and diffuse) are determined by the local atmospheric composition and the relative air mass. In this work, the SMARTS spectral irradiance model with MERRA-2 atmospheric inputs is used to evaluate the dependence of these ratios under clear-sky conditions with air mass, aerosol optical depth (AOD), precipitable water vapor and ozone column. The accuracy of the SMARTS beam spectral irradiance is previously assessed using local spectroradiometer measurements. The clear-sky ratios for the diffuse and direct components increase with increasing air mass, while the global ratio shows only a weak air mass dependence. The clear-sky ratios can be modeled with simple bi-variate linear models in air mass and AOD. These results can be used in similar climatic regions to convert PAR flux to PAR irradiance and vice versa with increased accuracy for the global, direct, and diffuse radiation under cloud-free conditions.

MATHEMATICAL MODELS OF METHANE CONSUMPTION BY SOILS: A REVIEW

MATHEMATICAL MODELS OF METHANE CONSUMPTION BY SOILS: A REVIEW

The Chemical Weathering of Rocks and Its Carbon Sink Effect in the Naqu River Basin of the Nujiang River Source Area, Southwest China

Carbon plays an important role in global climate change. The mechanisms of carbon sources and carbon sinks have also received wide attention from society, and the physical and chemical characteristics of riverine ions can reflect the chemical weathering of rocks and carbon sink capacity of river basins. Based on the data on river, rainwater, and rock samples from 2019, this study used various methods, such as ion ratio diagrams and ternary diagrams, to analyze the chemical characteristics of water; the chemical weathering and carbon sink effects of rocks were also calculated while assuming three scenarios based on the main sources of ions in the Naqu River. The results showed that for the whole catchment, the main ion sources in the river were: carbonate rock chemical weathering > silicate rock chemical weathering > evaporite dissolution > atmospheric precipitation input. According to the calculations, in the three scenarios, the carbonate weathering rates were 16.84, 11.32, and 14.08 t/km2/yr, and the carbon sink capacities were 66.47, 121.13, and 93.80 mol/km2/yr, respectively; the evaporite weathering rates were 2.20, 9.63, and 5.92 t/km2/yr, respectively. The silicate chemical weathering rate and carbon sink capacity did not change significantly in either scenario, with 6.82 t/km2/yr and 248.6 mol/km2/yr, respectively. This study quantified the ion sources in the Naqu River basin and accurately analyzed their chemical genesis, which helps in understanding the role of the rivers of the Qinghai–Tibet Plateau in the global carbon cycle and global climate change, in addition to providing a reference for the scientific development of the Nujing River.

Factors influencing the difference in dissolved ion inputs to the forest floor between deciduous and coniferous stands: comparison under high and low atmospheric deposition conditions

It is necessary to clear the relationship between physical and vegetation factors on the processes governing dissolved ion inputs to the forest floor to estimate correctly the values of atmospheric input to the forest. This study identified the factors influencing the differences in dissolved ion inputs to the forest floor between coniferous evergreen and broad-leaved deciduous species by analyzing the phenological variations of dry deposition and canopy exchange calculated by the canopy budget model under a high-deposition site near the city of Tokyo and a low-deposition site 84 km further away. At low-deposition site, vegetation factors such as capture efficiency did not explain the differences in Na+ or Cl− dry deposition. Leaf physiological characteristics influenced the differences in the Mg2+ and Ca2+ canopy leaching values, and phenology, leaf wettability, and diffusion processes from water film into leaves influenced the differences in NH4+ and NO3− input processes between tree types. At the high-deposition site, differences in the dry deposition of Na+, SO42−, Cl−, Mg2+, Ca2+, NH4+, and NO3− between tree types were influenced by differences in capture efficiency between coniferous and broad-leaved canopies in the leafed period and by the absence of leaves in deciduous species after leaf fall. These results indicated that atmospheric deposition affected the capture efficiency of coniferous trees for dry deposition and enhanced the difference of dissolved ion inputs to the forest floor between coniferous and deciduous species.

Effects of Urbanization and Forest Fragmentation on Atmospheric Nitrogen Inputs and Ambient Nitrogen Oxide and Ozone Concentrations in Mixed Temperate Forests

AbstractUrban ecosystems around the globe experience greater atmospheric nitrogen (N) deposition compared to rural areas and are particularly vulnerable to fragmentation due to land use change. However, while the influences of urbanization and forest fragmentation on atmospheric inputs to temperate forests have been determined separately, the combined effects of the two changes on temperate forest ecosystems have yet to be assessed. To investigate these combined effects, we deployed throughfall collectors to measure atmospheric N inputs and passive samplers to measure nitrogen oxides (NOx) and ozone (O3) throughout the 2018 and 2019 growing seasons in seven temperate forest sites along an urbanization gradient from Boston to central Massachusetts. We found a positive relationship between the amount of impervious surface area (% ISA) surrounding each site and throughfall nitrate () inputs at the forest edge, with urban edge inputs nearly double the rate at rural edge sites. There were higher rates of inputs in the rural forest interior than edge sites, while urban sites experienced significantly higher concentrations of NOx and O3 both in the interior and at the edge compared to rural sites. Atmospheric N inputs were significantly elevated in the early (May–July) compared to the late (August–November) growing season and concentrations of NOx and O3 were also elevated in the midgrowing season (June–September). Our results demonstrate that together, urbanization and forest fragmentation lead to greater rates of atmospheric N inputs and ambient pollutant concentrations of NOx and O3 in temperate forests of the northeastern U.S.

Lake Kivu River Tributaries Physicochemical Characteristics and Status of Waters, Democratic Republic of Congo Side

Rivers often play a vital role in the transport of major natural chemicals entering through a variety of pathways, including atmospheric inputs, chemical weathering of minerals, mechanical erosion of rocks and soil particles, and soil leaching. Increased anthropogenic activities on the shoreline of Lake Kivu combined with existing land use practices may increase changes in river water quality and composition. Knowing the physico-chemical and biological contribution of each tributary of the lake is vital for the management of its biodiversity. This study aimed at determining the physico-chemical characteristics, water quality indices and identifying the polluted tributary rivers that feed Lake Kivu on the Congo side. The physicochemical characteristics were determined for each water sample following water quantity protocol for each analysis at the Malacology Laboratory of the Biology Department of Lwiro Research Center. Two pollution level indices were used to determine the level of organic pollution in watercourses. The physico-chemical characteristics of rivers vary from one river to another depending on the anthropogenic activities around the different sub-basins of these rivers. The state of the rivers presented here reveals that the majority of them are moderately polluted and others slightly polluted. No rivers were very heavily polluted or good in the Lake Kivu basin on the DR Congo side. There is a strong or moderate correlation between certain parameters and the water quality indices used in this study (LISEC and OPI). Due to increase in anthropogenic activities near watercourses, further research is needed and the combination of several complex analytical methods should be used in the future to better characterize these waters.

Isotope Constraints on Nitrate Exchanges Between Precipitation and Forest Canopy

AbstractAtmospheric nitrogen (N) deposition is a key process influencing plant‐soil N processes and associated functions of forest ecosystems. However, the N deposition into soils based on open‐field precipitation observations remains inaccurate due to the unconstrained precipitation‐canopy N exchanges, which prevents a better evaluation of N deposition effects on forest N cycles and functions. Nitrate () is a major form of reactive N. Based on a data synthesis of fluxes and isotopes (15N, 17O, 18O) of atmospheric inputs in forests, here we constructed a new method to quantify fractions and fluxes of throughfall () contributors (nitrification () and particulates () in canopies, the original precipitation ()) and then constrain precipitation‐canopy exchanges (i.e., gains from canopy and losses due to canopy retention). Generally, was higher in fluxes but lower in N and O isotopes than , suggesting higher gains than losses and canopy nitrification as a gain contributor. 10%−18% and 40%−47% of were gained from canopy and , respectively, while 43% ± 25% and 20% ± 74% of the original were lost after passing through canopies of broadleaved and coniferous forests, respectively. Importantly, both gain and loss fluxes were found increasing with the fluxes. This work unlocked fractions and fluxes of major precipitation‐canopy exchange processes and revealed a stimulating mechanism of atmospheric pollution on precipitation‐canopy exchanges.

Accumulation of microplastics in soil after long-term application of biosolids and atmospheric deposition

Land-applied biosolids can be a considerable source of microplastics in soils. Previous studies reported microplastics accumulation in soils from biosolid application, however, little is known about the contribution of atmospherically deposited microplastics to agricultural soils. In this study, we quantified and characterized microplastics in soils that have been amended with biosolids over the past 23 years. We also collected atmospheric deposition samples to determine the amount and type of plastics added to soils through atmospheric input over a period of about 2 years. Soil samples were taken from a replicated field trial where biosolids have been applied at rates of 0, 4.8, 6.9, and 9.0 t/ha every second crop. The biosolids were anaerobically digested and dewatered, and were applied by spreading onto the soil surface. Soil and atmospheric samples were extracted for microplastics by Fenton's reaction to remove organic matter followed by flotation in a zinc chloride solution to separate plastic from soil particles. Samples were analyzed for microplastics by optical microscopy and Laser Direct Infrared Imaging Analysis (LDIR). The mean number of microplastics identified from biosolids samples was 12,000 particles/kg dry biosolids. The long-term applications of biosolids to the soil led to mean plastics concentrations of 383, 500, and 361 particles/kg dry soil in the 0–10 cm depth for low, medium, and high biosolids application rates, respectively. These plastic concentrations were not significantly different from each other, but significantly higher than those found in non biosolids-amended soil (117 particles/kg dry soil). The dominant plastic types by number found in biosolids were polyurethane, followed by polyethylene, and polyamide. The most abundant plastics in soil samples were polyurethane, polyethylene terephthalate, polyamide, and polyethylene. Atmospheric deposition contributed to 15 particles/kg dry soil per year and was mainly composed of polyamide fibers. This study shows that long-term application of biosolids led to an accumulation of microplastics in soil, but that atmospheric deposition also contributes a considerable input of microplastics.

Responses of a common tropical epiphyte, Asplenium nidus, to changes in water and nutrient availability.

Epiphytes are highly dependent on atmospheric inputs of water and nutrients. Reductions in water availability associated with warming and climate change and continual atmospheric nitrogen (N) deposition can affect plant growth but few studies have evaluated the effects of changes in both water and nutrient availabilities on epiphytes. We experimentally tested whether epiphyte growth is more water- or nutrient-limited, if nutrient limitation was stronger for nitrogen or phosphorus, and whether nutrient limitation interacts with water availability. We applied watering (high and low) and nutrient addition (control, +N, +P, +N+P) treatments to greenhouse-grown Asplenium nidus, a common epiphytic fern found in many tropical and subtropical wet forests. We measured leaf area production and leaf elemental concentrations to assess how A. nidus growth and physiology respond to changes in water and nutrient availabilities. We found that leaf growth of A. nidus was more affected by water availability than nutrient addition and the effect of adding nutrients was not fully realized under low-water availability. Among the different nutrient treatments, +N+P had the greatest effects on A. nidus growth and physiology in both watering treatments. Watering treatment changed leaf elemental concentrations but not their ratios (i.e. C:N and N:P). Nutrient addition altered C:N and N:P ratios and increased the concentration of the added elements in leaves, with more pronounced increases in the high-watering treatment. We conclude that the growth of A. nidus is more water- than nutrient-limited. When nutrient limitation occurs (i.e. under high-water availability), nutrient co-limitation is stronger than limitation by N or P alone. This result taken together with studies of other epiphytes suggests greater water than nutrient limitation is likely widespread among epiphytic plants. The limited effects of nutrient addition in the low-water treatment suggest that the effect of atmospheric N deposition on epiphyte growth will be limited when water availability is low.

Terrigenic helium in brackish groundwaters of Kuwait, probable influences from hydrocarbon resources

The presence of helium in groundwater can shed light on its age, migration patterns, and potential recharge locations. The 4He, 3He/4He, 20Ne, and major ions concentrations in groundwater samples were analysed. He concentration in groundwaters of the Kuwait group aquifers ranged from 3.82 × 10−8 to 1.33x−6 cm3STP/g and that of Dammam formation ranged from 9.97 × 10−8 to 1.62 × 10−6 cm3STP/g. The distribution of He was inferred to be influenced by geological structures and it was found that He decreased with Cl concentration and δ18O with few exceptions. The δ18O signatures reflect mixing between aquifers. The higher He fluxes were recorded during the Last Glacial Maximum, but they rose steadily over time. Most of the north Kuwait samples, dating from 1650 to 348 yBP, had a tritiogenic component similar to the present atmosphere, as indicated by RA (Air normalized He ratios) values, which was inferred to be due to the decay of tritium derived from meteoric impact. Magnitude 2–4 earthquake epicenters occurred more frequently in areas with lower RA values. Lateral flow was predominant with insitu (He derived from rock matrix along the flow) and exogenous sources (vertical upward cross formational flow, atmospheric input and from hydrocarbon reservoirs). Groundwater samples near oil fields were found to contain more terrigenic He, suggesting its migration to shallow waters through fault planes. The presence of more He in brackish groundwater at a shallow depth may be indicative of an abundant source beneath. He excess (Heex) and air corrected He excess (ΔHe%) are indicators of non-neuclogenic and radiogenic He sources, such as the exsolution from adjoining hydrocarbon fields through structurally weaker planes.

Comparative C, N, and S cycling along a Californian grassland chronosequence

Carbon (C), nitrogen (N), and sulfur (S) are elements strongly influenced by biological cycling and redox reactions in soils, but few comparative analyses have investigated the behaviors of these elements with time. Thus, we examined changes in content and isotope composition of soil profiles along a chronosequence (58–212 kyr) of marine terraces on the central California coast, in an area with significant background geochemical research. Unlike in other chronosequences in more humid locations, the total C, N, and S in these soils did not vary strongly with age, possibly due to the retention of phosphorus (P). The total pools of soil N and S cannot be explained by wet deposition of NO3 and SO4 alone, suggesting other sources of atmospheric inputs such as NH4+ and dimethyl sulfide. Total C and N declined in a characteristic logarithmic pattern with depth, while S did not. The ratio of extractable soil nitrate (NO3) to total N declined with depth, suggesting strong biological demand via various avenues. In contrast, the ratio of extractable sulfate (SO4) to total S increased with depth, suggesting that S was in biological excess. We used a simple reactive transport model to integrate the depth profiles of total C and N and their isotope values. The depth trends of total concentrations suggested one-pool residence times of approximately 500 to 1000 y, consistent with turnover times calculated by mass balance. Depth trends of stable isotope values indicated that N is isotopically fractionated at a magnitude twice that of C, consistent with observed 15N-depleted nitrous oxide (N2O) emissions during the dry summer months. The isotope composition of S (total and SO4) suggests some isotope enrichment during biogeochemical cycling, but far less than observed for N. Thus, despite significant chemical weathering and elemental loss over time, the biogeochemical cycles of C, N, and S remain relatively unaffected by soil age in this climatic setting.

Seasonal variations of metals and metalloids in atmospheric particulate matter (PM2.5) in the urban megacity Hanoi

Fine particulate matter (PM2.5) in the atmosphere is of particular concern due to its adverse effects on human health and its impact on global warming. Southeast Asia is a hot spot for fossil fuel combustion with recurrent release of large plumes spreading over the ocean and neighbouring countries. Due to the complex mixture of PM2.5, the atmospheric sources contribution related to local and regional emissions in Hanoi (northern Vietnam) is still ill-constrained. Here, we present a year-round study (November 2019 to December 2020) with measurements of 18 metals and metalloids (MM) and lead isotopes in the PM2.5 fraction to quantify weather-related atmospheric inputs and to assess risk to human health. Anthropogenic inputs from fossil fuel combustion accounted for about 80% in PM2.5. We found high PM2.5-bound MM concentrations often exceeding national and global standards with a low risk of chronic inhalation and carcinogenicity, mainly attributable to Cr. During winter monsoon (northeastern winds), stable weather conditions led to the enrichment of long-range air mass transport of local particulate emissions. During the summer monsoon (southeastern winds), warm and moist winds reduced coal contribution in PM2.5. Our study highlights the need for a strict implementation of policies to control hazardous MM emissions by reducing fossil fuel combustion. On the one hand, reducing coal-related activities could reduce Cr emissions and therefore improve the risks to human health. On the other hand, public policies should encourage conversion to green transport in order to reduce petrol combustion and thus limit global warming.

Hg isotope evidence for oceanic oxygenation during the Cambrian Explosion

The Cambrian explosion is a critical evolutionary milestone in life history, but the mechanistic relationship between the Cambrian explosion, rising atmospheric and oceanic oxygen levels, and the primary productivity remains controversial. Here, we present new mercury (Hg) isotope data from Cambrian marine sediments of the ∼521–514 Ma Yu’anshan and Shuijingtuo Formations (Nanhua Basin, South China), which preserve the famous ∼518 Ma Chengjiang and Qingjiang Cambrian Biotas, respectively. We find evidence that, prior to Cambrian animal diversification, local terrestrial and/or atmospheric inputs are important drivers of Hg enrichment in the shallow shelf Yu’anshan and Shuijintuo Formations. Elevated Hg and total organic carbon (TOC) concentrations of coeval deeper shelf and slope sections of the Niutitang Formation are mainly attributed to upwelling of Hg associated with dissolved organic carbon (Hg-DOC) from pelagic seawater, unrelated to locally high primary productivity. During the deposition of fossiliferous strata, negative shifts of Δ199Hg and δ202Hg values in the shallow water shelf shales from the Shuijingtuo Formation, combined with similar Hg isotope characteristics in the deeper shelf and slope shales, demonstrate a significant shallow and deep-water oxygenation event took place in the Nanhua Basin. A comparable negative shift of Δ199Hg values occurs in coeval Indian Craton sediments, suggesting this oxygenation event could be regional, or possibly even global, in scale. Our newly-collected Hg isotope data provide strong evidence that rising molecular oxygen levels in both surface and deep seawater are associated with enhanced marine primary productivity and could be a critical driver of the Cambrian explosion. Finally, we also argue that Hg isotopes are an emerging and promising redox proxy for studies of Precambrian seawater, but the chemical response of Hg to atmospheric and ocean oxygenation requires further calibration.

Distribution and trends of mercury in aquatic and terrestrial biota of New York, USA: a synthesis of 50 years of research and monitoring.

Mercury (Hg) inputs have particularly impacted the northeastern United States due to its proximity to anthropogenic emissions sources and abundant habitats that efficiently convert inorganic Hg into methylmercury. Intensive research and monitoring efforts over the past 50 years in New York State, USA, have informed the assessment of the extent and impacts of Hg exposure on fishes and wildlife. By synthesizing Hg data statewide, this study quantified temporal trends of Hg exposure, spatiotemporal patterns of risk, the role that habitat and Hg deposition play in producing spatial patterns of Hg exposure in fish and other wildlife, and the effectiveness of current monitoring approaches in describing Hg trends. Most temporal trends were stable, but we found significant declines in Hg exposure over time in some long-sampled fish. The Adirondack Mountains and Long Island showed the greatest number of aquatic and terrestrial species with elevated Hg concentrations, reflecting an unequal distribution of exposure risk to fauna across the state. Persistent hotspots were detected for aquatic species in central New York and the Adirondack Mountains. Elevated Hg concentrations were associated with open water, forests, and rural, developed habitats for aquatic species, and open water and forested habitats for terrestrial species. Areas of consistently elevated Hg were found in areas driven by atmospheric and local Hg inputs, and habitat played a significant role in translating those inputs into biotic exposure. Continued long-term monitoring will be important in evaluating how these patterns continue to change in the face of changing land cover, climate, and Hg emissions.