Atmospheric Inputs Research Articles

Impacts of Extreme Weather on Mercury Uptake and Storage in Subtropical Forest Ecosystems

AbstractAs climate change accelerates, extreme weather events become more severe and frequent. We analyzed the datasets of decade‐long observation (2005–2020) of mercury (Hg) stored in two subtropical evergreen forests to understand the impacts of extreme weather on the sequestration of atmospheric Hg in forest ecosystems. Results show a weak correlation between litterfall Hg and atmospheric Hg0 concentration. Droughts and snowstorms significantly disturb Hg accumulation in litterfall and soils. Litterfall Hg concentration and deposition both display an increasing trend during the period of extended droughts in 2011–2014, but a decreasing trend after droughts. This is caused by the water stress that influences the change of tree physiology and processes of foliage Hg0 uptake. Snowstorm damages large areas of canopy, which leads to substantial canopy epiphyte cover mixed into the forest floor, thus considerably increasing soil Hg concentrations. Over a decadal timescale, soil Hg variabilities are shaped by the combined effects of atmospheric Hg inputs and processes of organic soil mineralization mediated climatic factors. Our study highlights that the accelerated climate change increases the unpredictability of Hg accumulation in terrestrial ecosystems. Future studies are needed for better understanding the response of Hg biogeochemical cycling to climate change among different terrestrial biomes.

Heavy Metals in Marine Surface Sediments of Daya Bay, Southern China: Spatial Distribution, Sources Apportionment, and Ecological Risk Assessment

Daya Bay, especially in the northwestern region, which is a nature reserve with larval economic fish and shrimp populations, is no longer an unpolluted marine environment due to the recent increases in anthropogenic activities. This study collected seasonal surface sediment samples from 20 sites in northwestern Daya Bay to evaluate pollution and ecological risks and to identify possible sources and transport pathways of heavy metals (Cd, Pb, Cr, Cu, Zn, Hg, As). The results showed that all the heavy metal concentrations were below the established primary standard criteria, except for concentrations of Cr in spring, as well as Cu and Zn in autumn at several sampling stations, which had excess rates of 35, 4.76, and 4.76%, respectively. The geoaccumulation index (Igeo) values of heavy metals indicated that all sites had unpolluted to moderate pollution levels. In comparison to the samples collected in autumn, those in spring experienced a higher degree of pollution, particularly Cr and As. The ecological risk indices of heavy metals in sediments ranged from 225.86 to 734.20 in spring and from 196.69 to 567.52 in autumn, suggesting that most sites had a moderate ecological risk or a considerable ecological risk, and very few a had high ecological risk. Moreover, ArcGIS10.2 software was used to visualize their spatial distribution, and the results were similar in both spring and autumn. The results of the Pearson correlation analysis and principal component analysis showed that Cu, Hg, and Pb might be affected by anthropogenic activities, and As might be derived from natural sources such as atmospheric inputs. A cluster analysis showed that heavy metals were mainly affected by the negative impacts of human beings on the environment.

Mass-Balance Modeling of Metal Loading Rates in the Great Lakes

Major elements and nutrients are key water quality monitoring targets in the Great Lakes, but large-scale and long-term data for (trace) metals remains comparatively scarce. Consequently, the sources and processes controlling metal loading rates and potential accumulation in the lakes are not as well constrained. Here, we present a comprehensive assessment of select metal loads in the Great Lakes basin, aggregating tributary and connecting channel loads as well as estimates for atmospheric input and sedimentation. In total, 26,845 hydrometric and water quality datapoints from major environmental surveillance programs were compiled into mass-balance calculations and dynamic simulations for 1980–2020. Conservative element (Na, Cl) loads were used to calibrate the black-box approach, and mass-balance for these elements could be achieved at ≥90% and long-term trends accurately reproduced. In contrast, biogeochemically reactive (trace) metals Cu, Ni, Zn and Pb displayed highly variable source-sink behavior across the Great Lakes. Our results show that i) atmospheric inputs, tributary loads, and sedimentation all affect the concentrations and temporal trends of the studied metals but differently in the upper versus lower lakes, ii) smaller tributaries can be disproportionately important to lake-wide metal budgets, and iii) current loading rates may yield increasing lake-wide average Cl concentrations (e.g., up to 2.3 mg/L in Lake Superior) but decreasing metal concentrations (e.g., down to <0.25 μg/L Cu in Lake Ontario) by 2100. This work provides important quantitative baselines for metal loads in the Great Lakes and may help optimize surveillance and management strategies for the preservation of Great Lakes water quality.

Geochemical evolution of soils on Reunion Island

Chemical weathering of basaltic rocks plays a major role in the regulation of the global carbon cycle at geological timescales, in particular tropical, basaltic islands although representing a small area of exposed land. Although soils from Hawai’i have been extensively studied, other tropical islands have received much less attention. In this study, we investigate the mineralogical and geochemical composition of three weathering profiles developed on stable landforms (planèzes) of Reunion Island, Indian Ocean. Pyroxenes and feldspars are progressively replaced by gibbsite and halloysite, and differences in weathering extent could be accounted for by the variable composition of the parent material. Only where soil has been developing for up to two million years we observe a complete loss of primary minerals and soluble elements throughout the entire profile. Elsewhere, complete loss is only achieved in the top meter. Chemical erosion and CO2 consumption fluxes estimated using soil geochemistry at the study sites, correspond to a small fraction of the overall fluxes for Reunion Island. These observations suggest that stable landforms play a limited role on chemical weathering on tropical, basaltic island, where hydrothermal alteration and weathering of rapidly eroding regions dominate. These results also show that, despite extreme weather events, stable landforms of Reunion Island, preserve a large fraction of their soluble element budget (including nutrients) for 100,000′s of years (possibly replenished by atmospheric inputs).Moreover, modelling of uranium-series isotope compositions shows that, in the topsoil, weathering ages (time elapsed since onset of chemical weathering) are similar to the age of the parent material for each profile, providing an independent validation of the use of uranium-series isotopes in weathering profiles to derive weathering ages and soil production rates. All profiles show a decrease in production rates with decreasing depth and a negative relationship between production rates and weathering ages, illustrating the depletion of soluble material with time. While production rates exceed 100 mm/kyr in the early stages of basalt weathering, they slow down to only a few mm/kyr after a million years.

A versatile method for computing optimized snow albedo from spectrally fixed radiative variables: VALHALLA v1.0

Abstract. In climate models, the snow albedo scheme generally calculates only a narrowband or broadband albedo, which leads to significant uncertainties. Here, we present the Versatile ALbedo calculation metHod based on spectrALLy fixed radiative vAriables (VALHALLA version 1.0) to optimize spectral snow albedo calculation. For this optimization, the energy absorbed by the snowpack is calculated by the spectral albedo model Two-streAm Radiative TransfEr in Snow (TARTES) and the spectral irradiance model Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART). This calculation takes into account the spectral characteristics of the incident radiation and the optical properties of the snow based on an analytical approximation of the radiative transfer of snow. For this method, 30 wavelengths, called tie points (TPs), and 16 reference irradiance profiles are calculated to incorporate the absorbed energy and the reference irradiance. The absorbed energy is then interpolated for each wavelength between two TPs with adequate kernel functions derived from radiative transfer theory for snow and the atmosphere. We show that the accuracy of the absorbed energy calculation primarily depends on the adaptation of the irradiance of the reference profile to that of the simulation (absolute difference &lt;1 W m−2 for broadband absorbed energy and absolute difference &lt;0.005 for broadband albedo). In addition to the performance in terms of accuracy and calculation time, the method is adaptable to any atmospheric input (broadband, narrowband) and is easily adaptable for integration into a radiative scheme of a global or regional climate model.

Coprecipitation of Mercury from Natural Iodine-Containing Seawater for Accurate Isotope Measurement.

Oceans play a key role in the global mercury (Hg) cycle, but studies on Hg isotopes in seawater are rare due to the extremely low Hg concentration and the lack of a good preconcentration method. Here, we introduce a new coprecipitation method for separating and preconcentrating Hg from seawater for accurate isotope measurement. The coprecipitation was achieved by sequential addition of 0.5 mL of 0.5 M CuSO4, 1 mL of 0.5 M Na2S, and 1 mL of 0.5 M CuSO4 reagents, which allowed for quantitatively precipitating Hg from up to 10 L of seawater. The protocol was validated by testing synthetic solutions with varying Hg and iodide (I-) concentrations and by comparing the reaction times of various reagents added. The method resulted in a quantitative recovery of 98 ± 12% (n = 32, two standard deviations, 2 SD) and a relatively low procedure blank (103 pg of Hg, n = 8). The precipitates were filtrated and analyzed for Hg isotopes. Repeated measurements of synthetic seawaters spiked with certificated standard materials (NIST 3133 and 3177) using the entire method gave identical Hg isotope ratios with near-quantitative Hg recovery, indicating no isotope fractionation during preconcentration. A total of six nearshore seawater samples from the Yellow Sea and the Bohai Sea (China) were analyzed using the coprecipitation method. The data showed a large fractionation of Hg isotopes and revealed the possible impact of both atmospheric and anthropogenic inputs to the coastal seawater Hg budget, implying the potential application of this method in studying marine Hg systematics and global Hg cycling.

An Implementation of Open Source-Based Software as a Service (SaaS) to Produce TOA and TOC Reflectance of High-Resolution KOMPSAT-3/3A Satellite Image

The majority of cloud applications are created or delivered to provide users with access to system resources or prebuilt processing algorithms for efficient data storage, management, and production. The number of cases linking cloud computing to the use of global observation satellite data continues to rise, owing to the benefits of cloud computing. This study aims to develop a cloud software as a service (SaaS) that yields reflectance products in high-resolution Korea Multi-Purpose Satellite (KOMPSAT)-3/3A satellite images. The SaaS model was designed as three subsystems: a Calibration Processing System (CPS), a Request System for CPS supporting RESTful application programming interface (API), and a Web Interface Application System. Open-source components, libraries, and frameworks were used in this study’s SaaS, including an OpenStack for infrastructure as a service. An absolute atmospheric correction scheme based on a Second Simulation of a Satellite Signal in the Solar Spectrum (6S) radiative transfer code with atmospheric variable inputs was used to generate the top-of-atmosphere (TOA) and top-of-canopy (TOC) reflectance products. The SaaS implemented in this study provides users with the absolute atmospheric calibration functionality to apply their KOMPSAT-3/3A satellite image set through a web browser and obtain output directly from this service. According to experiments to check the total performance time for images, bundled with four bands of red, green, blue, and near-infrared, it took approximately 4.88 min on average for the execution time to obtain all reflectance results since satellite images were registered into the SaaS. The SaaS model proposed and implemented in this study can be used as a reference model for the production system to generate reflectance products from other optical sensor images. In the future, SaaS, which offers professional analysis functions based on open source, is expected to grow and expand into new application fields for public users and communities.

Phosphorus cycling in the upper waters of the Mediterranean Sea (PEACETIME cruise): relative contribution of external and internal sources

Abstract. The study of phosphorus cycling in phosphate-depleted oceanic regions, such as the Mediterranean Sea, has long suffered from methodological limitations, leading to a simplistic view of a homogeneous surface phosphate pool with concentrations below the detection limit of measurement above the phosphacline. During the PEACETIME (Process studies at the air-sea interface after dust deposition in the Mediterranean Sea) cruise, carried out from 10 May to 11 June 2017, we conducted co-located measurements of phosphate pools at the nanomolar level, alkaline phosphatase activities and atmospheric deposition of phosphorus, across a longitudinal gradient from the west to the central Mediterranean Sea. In the phosphate-depleted layer (PDL), between the surface and the phosphacline, nanomolar phosphate was low and showed little variability across the transect spanning from 6 ± 1 nmol L−1 in the Ionian basin to 15 ± 4 nmol L−1 in the westernmost station. The low variability in phosphate concentration contrasted with that of alkaline phosphatase activity, which varied over 1 order of magnitude across the transect. Nanomolar phosphate data revealed gradients of phosphate concentration over density inside the PDL ranging between 10.6 ± 2.2 µmol kg−1 in the westernmost station to values close to zero towards the east. Using the density gradients, we estimated diapycnal fluxes of phosphate to the PDL and compared them to atmospheric deposition, another external source of phosphate to the PDL. Phosphate supply to the PDL from dry deposition and diapycnal fluxes was comparable in the western part of the transect. This result contrasts with the longtime idea that, under stratification conditions, the upper waters of the Mediterranean Sea receive new P almost exclusively from the atmosphere. The contribution of atmospheric deposition to external P supply increased under the occurrence of rain and Saharan dust. Although this finding must be taken cautiously given the uncertainties in the estimation of diapycnal fluxes, it opens exciting questions on the biogeochemical response of the Mediterranean Sea, and more generally of marine oligotrophic regions, to expected changes in atmospheric inputs and stratification regimes. Taken together, external sources of phosphate to the PDL contributed little to total phosphate requirements which were mainly sustained by in situ hydrolysis of dissolved organic phosphorus. The results obtained in this study show a highly dynamic phosphorus pool in the upper layer of the euphotic zone, above the phosphacline, and highlight the convenience of combining highly sensitive measurements and high-resolution sampling to precisely depict the shape of phosphate profiles in the euphotic zone with still unexplored consequences on P fluxes supplying this crucial layer for biogeochemical cycles.

EVALUATION OF RISK ASSESSMENT FACTORS AMONG SELECTED METALS IN ROADSIDE GROWN CEREALS OF THE SUDAN SAVANNA ECOLOGY OF NIGERIA

Phytoaccumulation of metals (Cd, Cr, Cu, Pb, Zn) in roadside grown wheat and maize varieties ( Pavon-76, Siettecerros, Zea mays L. and Zea mays everta L.) and the toxicity and phytoremediation capability of the plants was investigated. Four sampling sites, roadside (SU 1, SU 3) and distant sites (SU 2 and SU 4) were selected by principle to represent the level of pollution near major traffic routes and were the reference sampling points. Whole plant metal levels of the four crops were determined using the multi-elemental technique- Energy Dispersive X-ray Fluorescent (EDXRF) and double beam AAS at A.B.U Zaria. Plant uptake factor (PUF), soil-plant transfer coefficient (TC) and translocation factor (TF) was computed for each metal. Pearson correlation analyses between the risk assessment factors of the metals were evaluated. Results revealed a positive significant (P&lt;0.05) relationship between PUF/TC and PUT/TF for Cr and Zn in Pavon-76, PUF/TC for Cr and Zn in the two species of Zea mays L. and Cu in Siettecerros indicates atmospheric inputs and special ability or strong selective ability of each of the crops to accumulate certain metals. The inverse correlation between PUF/TC, PUF/TF and TC/TF among the metals indicates the proximity of SU 1 to the major highway, influence of traffic density, atmospheric inputs and geological material and a combination of other factors. This study reveals the potentialities of these varieties of Wheat and Maize which are terrestrial higher plants as accumulators of metallic elements and phytoremediators of roadside soil pollution

Increase of litterfall mercury input and sequestration during decomposition with a montane elevation in Southwest China

Litterfall mercury (Hg) input has been regarded as the dominant Hg source in montane forest floor. To depict combining effects of vegetation, climate and topography on accumulation of Hg in montane forests, we comprehensively quantified litterfall Hg deposition and decomposition in a serial of subtropical forests along an elevation gradient on both leeward and windward slopes of Mt. Ailao, Southwest China. Results showed that the average litterfall Hg deposition increased from 12.0 ± 4.2 μg m−2 yr−1 in dry-hot valley shrub at 850–1000 m, 14.9 ± 6.8 μg m−2 yr−1 in mixed conifer-broadleaf forest at 1250–2400 m, to 23.1 ± 8.3 μg m−2 yr−1 in evergreen broadleaf forest at 2500–2650 m. Additionally, the windward slope forests had a significantly higher litterfall Hg depositions at the same altitude because the larger precipitation promoted the greater litterfall biomass production. The one-year litter Hg decomposition showed that the Hg mass of litter in dry-hot valley shrub decreased by 29%, while in mixed conifer-broadleaf and evergreen broadleaf forests increased by 22–48%. The dynamics of Hg in decomposing litter was controlled by the temperature mediated litter decomposition rate and the additional adsorption of environmental Hg during decomposition. Overall, our study highlights the litterfall mediated atmospheric mercury inputs and sequestration increase with the montane elevation, thus driving a Hg enhanced accumulation in the high montane forest.

Characteristics of Atmospheric Inorganic Nitrogen Wet Deposition in Coastal Urban Areas of Xiamen, China

To evaluate the impact of increasing atmospheric nitrogen deposition input to the coastal ecosystem, measurements were conducted to analyze the inorganic nitrogen wet deposition to Xiamen Island during April to August in 2014. Using ion chromatography and shown to contain main nine water-soluble ions—including Na+, NH4+, K+, Mg2+, Ca2+, Cl−, NO−, NO3−, and SO42−—we analyzed the composition of the wet deposition sample and verified the contribution of different ions to the different sources. The results showed that the mean NO3−-N and NH4+-N concentration in rainfall for five months was 4.55 ± 5.15 mg·L−1 (n = 31) and 1.20 ± 1.16 mg·L−1 (n = 33), respectively. Highest NO3−-N (74.65 mg·N·L−1) and NH4+-N (16.06 mg N·L−1) values were both observed in May. Maximum NO3−-N deposition (507.5 mg·N·m−2) was also in May, while the highest NH4+-N deposition (99.8 mg·N·m−2) was in June. The total inorganic wet nitrogen flux during sampling period was 11.1 kg·N·ha−1. The HYSPLIT backward air masses trajectory and USEPA PMF model was used, as the composition of the air masses passing over the sample area were impacted from three sources: fertilizers and biomass combustion, formation of secondary aerosol, and Marine aerosols. The concentration ratio of SO42− and NO3− in ranged between 0.5 and 3 in rainfall samples with an average of 1.34, suggesting that the contribution from vehicle exhaust to air pollution in the sample area is increasing. Long-term continuous monitoring of wet deposition in this region needs to be expanded to fully understand the impacts of human activity on air quality and to quantify N deposition to local marine ecosystems.

Tracing the Atmospheric Input of Seawater-Dissolvable Pb Based on the Budget of 210Pb in the East Sea (Japan Sea)

In order to determine the atmospheric input of 210Pb and seawater-dissolvable Pb in the East Sea (Japan Sea), we measured the concentrations of total 210Pb and dissolved Pb (&amp;lt;0.2 μm) in seawater and 210Pb and 226Ra in sinking particles. The East Sea is deep (∼3700 m) and enclosed by surrounding continents except for the shallow sills (&amp;lt;150 m). Since the East Sea is located off the East Asian continent under the westerlies, the concentrations of 210Pb and dissolved Pb in this sea are significantly affected by terrestrial sources through the atmosphere. The vertical profiles of total 210Pb and dissolved Pb generally showed a surface maximum and then decreased with depth. The concentrations of dissolved Pb in the surface water were 2 and 3 times higher than those in the North Pacific and North Atlantic Oceans, respectively. Using an independent box model (upper 1000 m or 2000 m), we estimate the atmospheric input of 210Pb to be 1.46 ± 0.25 dpm cm−2 y −1, which is within the range of published results from the land-based sites (0.44–4.40 dpm cm−2 y −1) in South Korea, China, and Japan. Based on this flux, the residence time of total 210Pb in the East Sea is calculated to be approximately 7.1 ± 1.6 years, which is twice lower than the previous estimation. Combining the residence time of 210Pb and the inventory of dissolved Pb, the atmospheric input of seawater-dissolvable Pb is estimated to be 0.98 ± 0.28 nmol cm−2 y −1. This flux is approximately 25% of the Pb flux through the wet deposition (acid-leachable fraction). Thus, our results suggest that the flux and fate of atmospheric Pb in the ocean can be successfully determined using an accurate mass balance model of naturally occurring 210Pb.

Influence of atmospheric deposition on biogeochemical cycles in an oligotrophic ocean system

Abstract. The surface mixed layer (ML) in the Mediterranean Sea is a well-stratified domain characterized by low macronutrients and low chlorophyll content for almost 6 months of the year. In this study we characterize the biogeochemical cycling of nitrogen (N) in the ML by analyzing simultaneous in situ measurements of atmospheric deposition, nutrients in seawater, hydrological conditions, primary production, heterotrophic prokaryotic production, N2 fixation and leucine aminopeptidase activity. Dry deposition was continuously measured across the central and western open Mediterranean Sea, and two wet deposition events were sampled, one in the Ionian Sea and one in the Algerian Basin. Along the transect, N budgets were computed to compare the sources and sinks of N in the mixed layer. In situ leucine aminopeptidase activity made up 14 % to 66 % of the heterotrophic prokaryotic N demand, and the N2 fixation rate represented 1 % to 4.5 % of the phytoplankton N demand. Dry atmospheric deposition of inorganic nitrogen, estimated from dry deposition of nitrate and ammonium in aerosols, was higher than the N2 fixation rates in the ML (on average 4.8-fold). The dry atmospheric input of inorganic N represented a highly variable proportion of biological N demand in the ML among the stations, 10 %–82 % for heterotrophic prokaryotes and 1 %–30 % for phytoplankton. As some sites were visited on several days, the evolution of biogeochemical properties in the ML and within the nutrient-depleted layers could be followed. At the Algerian Basin site, the biogeochemical consequences of a wet dust deposition event were monitored through high-frequency sampling. Notably, just after the rain, nitrate was higher in the ML than in the nutrient-depleted layer below. Estimates of nutrient transfer from the ML into the nutrient-depleted layer could explain up to a third of the nitrate loss from the ML. Phytoplankton did not benefit directly from the atmospheric inputs into the ML, probably due to high competition with heterotrophic prokaryotes, also limited by N and phosphorus (P) availability at the time of this study. Primary producers decreased their production after the rain but recovered their initial state of activity after a 2 d lag in the vicinity of the deep chlorophyll maximum layer.

Canadian Arctic Archipelago Shelf‐Ocean Interactions: A Major Iron Source to Pacific Derived Waters Transiting to the Atlantic

AbstractContinental shelves are important sources of iron (Fe) in the land‐dominated Arctic Ocean. To understand the export of Fe from the Arctic to Baffin Bay (BB) and the North Atlantic, we studied the alteration of the Fe signature in waters transiting the Canadian Arctic Archipelago (CAA). During its transit through the CAA, inflowing Arctic Waters from the Canada Basin become enriched in Fe as result of strong sediment resuspension and enhanced sediment‐water interactions (non‐reductive dissolution). These high Fe waters are exported to BB, where approximately 10.7 kt of Fe are delivered yearly from Lancaster Sound. Furthermore, if the two remaining main CAA pathways (Jones Sound and Nares Strait) are included, this shelf environment would be a dominant source term of Fe (dFe + pFe: 26–90 kt y−1) to Baffin Bay. The conservative Fe flux estimate (26 kt y−1) is 1.7–38 times greater than atmospheric inputs, and may be crucial in supporting primary production and nitrogen fixation in BB and beyond.

Steps towards the development of a Peat Fire Danger Rating System in Indonesia

Fire danger rating systems (FDRS) are a critical tool, used around the world to help predict and prevent wildfires. Forest and land fires are a severe problem in Indonesia, with smoke and haze production exacerbated by the country’s extensive tropical peatlands, many of which are drained and burn almost annually. The Indonesian FDRS was established in 1999 under the Meteorological, Climatological, and Geophysical Agency, in partnership with other government agencies, and is largely based on atmospheric data. Indonesia’s FDRS differentiates land types, including peatlands, but only predicts surface fire risk, rather than the risk of peatland surface fires becoming below-ground peat fire – which emit greater amounts of haze-producing smoke. This study proposes how Indonesia’s FDRS might be further developed to include below-ground peat fire risk. This was achieved based on consultation with government agencies which manage and provide data to Indonesia’s FDRS, and the establishment of a Peat FDRS Stakeholder Engagement Network. We describe which biophysical, social-economic or atmospheric input variables are needed in such a model to quantify the peat fire risk. We present what field data is currently available (e.g. weather) and which factors require additional data collection, including some aspects of land and social data, and, notably, bio-physical ground data on fuel loads and fuel moisture content. Data is presented by type, historical availability, scale and reliability, presented in a visually clear colour-coded table. This information can support the development of a specific peat fire risk section within Indonesia’s current FDRS.

The peat bog at Zinnwald-Georgenfeld revisited after 25 years: Geochemical investigation of water, Sphagnum moss and peat cores

From 1992 to 1994, trace metal concentrations of bog water, Sphagnum mosses and peat cores of the bog “Georgenfelder Hochmoor” at Zinnwald-Georgenfeld in the Eastern Ore Mountains (Germany) were investigated. A sampling campaign in September 2019 allows the comparison of the older measurements with today's trace metal concentrations. No changes were found in the bog waters, while the trace metal concentrations of the Sphagnum mosses have decreased significantly. Due to the low growth rate of the peat and despite certain heterogeneity between the peat cores, the investigated elemental data for the peat sampled in the 1990s and in 2019 are in the same concentration range. The maximum concentrations are measured in the upper samples of all peat cores for the analysed elements (except sulphur). Compared to upper crustal data, a different behaviour of the elements is observed: Cr, Sc, Ti, and V, rare earth elements show crustal ratios, while Al and Si are also influenced by crust-air fractionation. Cd, Cu, Ni, Pb, and Zn are additionally enriched by anthropogenic atmospheric inputs from industry and transport. These results confirm the assumption that peat cores record past atmospheric deposition.

The geochemistry of Irish rivers

Study regionIreland Study focusMultiple studies have established that catchment geology and weathering regime strongly influence surface water chemistry, and that geochemical cycling can vary due to seasonal climatic conditions. However, fewer studies have focused on the influence these controls in a holistic manner. We relate the water chemistry of a country-wide Irish river survey to atmospheric input, underlying geology, and the influence of bogs. Climatic conditions were defined by an atypically wet winter and an unusually dry summer, providing the opportunity to investigate river chemistry variation across hydrologic conditions. Sampling included 21 of Ireland’s 22 largest rivers ranked by discharge, first-order and second-order streams draining bog lands, a second-order stream draining a limestone catchment, and downstream transects along the River Shannon. All samples were analyzed for major elements, selected trace elements, and nutrients, and a subset was analyzed for δ34SSO4. New hydrological insightsMost catchments were dominated by carbonate weathering with little contribution from the weathering of aluminosilicates. River water composition also varied geographically along the prevailing wind direction due to inputs from marine aerosols, with additional weathering components important in some systems. Seasonal influences could be seen in the chemistry of the headwaters of the River Shannon, while the lower reaches of the river exhibited less variable behavior throughout seasonal changes, likely due to the influence of lakes in the River Shannon system.

Microplastics in a Remote Lake Basin of the Tibetan Plateau: Impacts of Atmospheric Transport and Glacial Melting.

Plastic pollution is fast becoming one of the most pressing global issues that we currently face. Remote areas, such as the polar regions and the Tibetan Plateau, are now also exposed to microplastic contamination. However, with the impact of global warming, the transport of microplastics within the glacier-lake basins in such regions remains unclear. In this work, the Nam Co Basin in the Tibetan Plateau was selected to study the characteristics of microplastics in the rain fallout, lake water, glacial runoff, and non-glacial runoff. Fiber and films were the most common microplastic morphologies in all water samples; a higher proportion (37%) of light-weighing polypropylene and small-size (50-300 μm, ∼30%) microplastics were found in the glacial runoff. Air mass trajectory analysis showed that microplastics could be transported through the atmosphere over a distance of up to 800 km. For microplastic loading in lakes, the atmospheric fallout was estimated to be 3.3 tons during the monsoon season, whereas the contributions of glacial runoff (∼41 kg) and non-glacial runoff (∼522 kg) were relatively low. For the microplastic loading in glaciers, the atmospheric deposition was ∼500 kg/yr, and the output caused by glacial melting only accounted 8% of the total atmospheric input. All these results suggested that the dominant pathway through which microplastics enter remote mountainous lake basins is atmospheric deposition, and once deposited on glaciers, microplastics will be stored for a long time. This work provides quantitative evidence elucidating the fate of microplastics in alpine lake environments.

Dissolved Black Carbon and Semivolatile Aromatic Hydrocarbons in the Ocean: Two Entangled Biogeochemical Cycles?

Dissolved black carbon (DBC) plays a role in the oceanic carbon cycle. DBC originates from the heating and incomplete combustion of organic matter, including fossil fuels, a shared origin with polycyclic aromatic hydrocarbons (PAH). DBC is quantified using the benzene polycarboxylic acids produced by oxidation of the organic extract, a fraction of which derive from PAHs and other semivolatile aromatic-like compounds (SALCs). However, the current view of the DBC cycle does not take into account the inputs and sinks known for PAHs, such as diffusive air–water exchange and degradation. A meta-analysis of oceanic PAHs, SALCs, and DBC concentrations shows that SALCs account for 16% of DBC (ranging from 5% to 31%). Such a large contribution of semivolatile aromatic hydrocarbons to DBC is consistent with the large atmospheric input of SALCs (estimated as 400 Tg C y–1). Furthermore, photodegradation at the surface ocean and microbial degradation in the water column of semivolatile DBC can be important sinks, consistent with the ubiquitous occurrence of the degradation genes of the metabolic routes for aromatic hydrocarbons. Future work should focus on the characterization of semivolatile DBC and its degradation in order to constrain its contribution to refractory organic matter and the anthropogenic perturbation of the carbon cycle.

Hydrochemical characteristics and groundwater quality in the thick loess deposits of China.

Water quality and quantity should be paid more attention in regions with arid climate and thick vadose zones since the limited groundwater cannot be replenished rapidly once polluted. This study focused on the Loess Plateau of China to investigate the geochemical mechanism affecting groundwater chemistry and to calculate contribution rates of multiple sources to groundwater solutes. We employed multiple methods (diagrams, bivariate analyses, hierarchical cluster analysis (HCA), sodium adsorption ratio (SAR), water quality index (WQI), correlation analysis, and forward model) for the above purposes. We collected 64 groundwater samples in the thick loess deposits in June 2018 (flood season) and April 2019 (dry season). The average concentrations of cation were in the order of Ca2+ > Na+ > Mg2+ > K+ in the flood season, and Na+ > Ca2+ > Mg2+ > K+ in the dry season. The order of anions contents in the flood season and the dry season were HCO3- > SO42- > Cl- > NO3-. The major hydrochemical facies were Ca-HCO3 and Ca·Mg-HCO3 in the flood season and Na·Ca-HCO3·SO4 and Na-HCO3 in the dry season, respectively. Most of the groundwater (95% in the flood season and 96% in the dry season) was suitable for drinking, and the overall water quality was acceptable for irrigation. Mineral dissolution and cation exchange were important natural processes affecting groundwater chemistry. The forward model showed that the contribution of atmospheric input, anthropogenic input, evaporite dissolution, silicate weathering, and carbonate weathering to solutes in groundwater was 2.3±1.5%, 5.0±7.1%, 19.3±21.4%, 42.8±27.3%, and 30.6±27.1% in the flood season, and 9.1±6.4%, 3.4±5.2%, 20.3±15.9, 56.6±23.2%, and 10.7±15.4% in the dry season, respectively. Obviously, silicate and carbonate weathering contribute the most to groundwater chemistry in the flood season, while silicate weathering and evaporite dissolution contribute the most in the dry season. Although the overall contribution of anthropogenic inputs was insignificant, it was the dominant source of solutes for local groundwater. This study provides fundamental information for water management in arid areas.