Atmospheric Dust Deposition Research Articles

Biogeochemical cycling of dissolved manganese in the Arabian Sea

The study of marine biogeochemical cycling of Mn, a bio-essential trace metal, is crucial to decipher its relative role in controlling the production and diversity of marine phytoplankton. Furthermore, Mn oxides and oxyhydroxides act as sinks for other trace elements in the water column, and Mn redox cycling may exert a major control on the vertical distribution of these elements. Dissolved Mn (dMn) concentrations are measured along two GEOTRACES-India (GI) transects, GI05 and GI10, for a basin-wide investigation of biogeochemical controls on the dMn distribution in the Arabian Sea (AS). Surface dMn distribution shows a strong spatial gradient, with relatively dMn-rich levels in the eastern AS (3.4–5.7 nmol kg−1) compared to the central and western AS (1.2–2.3 nmol kg−1). This correlates with the higher model estimates of soluble Mn input from the atmospheric dust deposition in the eastern AS (∼1.5–2.0 times of input in the western and central AS), and probable additional Mn input from riverine discharge and shallow shelf region of the eastern AS. In the south-eastern AS, a correlated increase in surface dMn with a decrease in salinity indicates the Mn input by the advection of dMn-rich, low-salinity Bay of Bengal (BoB) surface waters to the AS under the influence of the Northeast Monsoon Current. Our mass balance estimates for dMn in the euphotic waters (upper 100 m) suggest important contributions from atmospheric Mn deposition (14–99% of the total estimated input flux), and dMn input/dilution (13–74% of the total estimated input or removal flux) due to lateral/vertical advective-eddy diffusive mixing. Mn-oxidation and passive scavenging are determined to be the dominant processes for the dMn removal (61–99%) from the euphotic zone (upper 100 m), while export via Mn bio-assimilation is comparatively negligible.In the AS denitrification zone, the observed dMn maxima in the upper thermocline depths (∼200–400 m) result from the in situ reductive dissolution of Mn oxides and oxyhydroxides, and lateral advective-eddy diffusive Mn flux from the reducing sediments of the western Indian margin. Outside the denitrification zone, in the northern and western AS, a shift of dMn maxima to the lower thermocline waters (∼500 m) indicates the change in the source region and dMn input from the reducing margins of the north (Pakistan Margin) and north-western AS (Oman Margin), intersecting the core of the oxygen minima at the depth range of 400–600 m.Deep water (>1500 m) dMn concentrations are low (<0.3 nmol kg−1) in most of the AS regions. Anomalous dMn enrichment in the deep waters is observed in the southern and western AS, presumably indicating the influence of hydrothermal plumes emanating from the active hydrothermal vents over the Carlsberg Ridge and spreading ridges in the Gulf of Aden. A correlated and localized increase in dMn and dAl levels close to the Murray Ridge hints at dMn input from the sediment resuspension over the ridge and subsequent Mn dissolution in low-oxygen waters (DO < 20 µM) and/or diffusive flux from the Mn-rich pore waters.

Effect of parent material and atmospheric deposition on the potential pollution of urban soils close to mining areas

The aim of this study is to analyse the concentration and determine the sources of potentially toxic elements (PTEs) in urban soils under the influence of mining activities. To this end, topsoil samples were collected in the public parks and green areas in Minas de Riotinto (a town next to one of the largest open pit mines in the world) and Aracena (a nearby town outside the area of influence of the mine). After determining the concentrations of elements of interest Cr, Co, Ni, Cu, Zn, As, and Pb— the values were compared in terms of the soil location and origin (in-situ or ex-situ), and with the background and regulatory levels for the region. The elemental concentrations in the fine fraction of the soils (particles <50 μm) were also measured. The concentrations of some PTEs (Cu, As and Pb), also found in the dust from nearby mines, were higher in the in-situ soils of Minas de Riotinto than in those of Aracena. The concentrations of PTEs in ex-situ soils of both towns were much lower than in in-situ soils, and similar between the two locations, revealing the influence of the parent material as a primary source of PTEs. However, the concentrations of As and Cu in the ex-situ soils of Minas de Riotinto were significantly higher than in those of Aracena, while a significant increase of these elements in the fine fraction was seen for both in-situ and ex-situ soils. These two elements are directly related to mining activity, implying that atmospheric deposition of dust from the mines contributes to the greater concentration of PTEs in the soils of Minas de Riotinto. Because these sources lead to soils with potentially dangerous concentrations of pollutants, they should be further studied in relation to their long-term influence on human health.

Atmospheric dust addition under elevated CO2 restructured phytoplankton community from the Arabian Sea: A microcosm approach

Atmospheric dust deposition in the North Indian Ocean, particularly in the Arabian Sea significantly impacts phytoplankton productivity. Importantly, the steady increase in Sea Surface Temperature (SST) of the Arabian Sea may intensify oligotrophy and the significance of atmospheric dust input for phytoplankton growth may escalate in the future. Furthermore, the globally increasing atmospheric CO2 is simultaneously impacting the surface ocean by decreasing its pH called Ocean Acidification (OA). We present here the first experimental study showing the impacts of atmospheric dust input under the simulated OA scenario on the natural phytoplankton communities from the Arabian Sea (winter monsoon). Phytoplankton cell density and chlorophyll (Chla) contents were enhanced in response to dust addition. The external input of inorganic nitrogen and iron (from dust) were the key growth-promoting factors that increased the relative contribution of micro and nanophytoplankton irrespective of the CO2 levels, whereas picophytoplankton decreased. The predominance of pennate diatoms and non-diatoms was mostly due to low dissolved silicate (DSi) availability. The cell density of the pennate diatoms Pseudo-nitzschia sp., Nitzschia sp., and Cylindrotheca closterium increased by several orders of magnitude in response to dust addition under OA. The dinoflagellates, Alexandrium sp., and Gymnodinium sp. showed higher tolerance to OA and proliferated in response to dust input. The present experimental conditions can be compared to the future ocean scenario (low DSi, OA, and dust input) where the proliferation of non-palatable/ toxigenic phytoplankton taxa may be expected which has the potential to impact ecological processes like trophic transfer, carbon cycling, and fisheries.

Modern Deposition of Atmospheric Dust in the Northeast Indian Ocean

Modern Deposition of Atmospheric Dust in the Northeast Indian Ocean

Distribution and cycling of dissolved aluminium in the Arabian Sea and the Western Equatorial Indian Ocean

Dissolved aluminium (dAl) distribution has been studied over the full vertical water column profiles along the GEOTRACES-India (GI) transect, GI-05, in the Arabian Sea (AS) and the Western Equatorial Indian Ocean (W-Eq.IO) during the fall inter-monsoon period. Surface dAl distribution in the AS demonstrates an east-west gradient, i.e., elevated dAl (6.5–21.6 nM) close to the Indian coastal region and low dAl (1.5–3.6 nM) along the western boundary of the AS. Rapid surface dAl removal due to relatively high biological productivity and a decrease in atmospheric dust deposition during the fall inter-monsoon result in low surface dAl levels in the western AS. Mass balance for surface dAl variation in the AS reveals very short scavenging removal timescales (0.01–0.47 yr) between the mid-summer and fall inter-monsoon period. Further, dAl input/dilution due to surface water advection is found to play an important role in controlling the surface dAl variation, varying between 190 and 300% of the dust-supported dAl input in different regions of the AS. These results have important implications for the use of surface dAl as a proxy of dust deposition in the AS. In the W-Eq.IO, a relative increase observed in the surface dAl concentrations, compared to the western AS and the central equatorial region, suggests a local dAl input, presumably, due to the dust influx from the Somali coast. Probable mechanism for this could be dust input from Somalia to the coastal western equatorial region and subsequent advection of the dAl enriched coastal waters to the offshore sampling sites, facilitated by mesoscale eddies.The intrusions of the high salinity water masses (the Arabian Sea High Salinity Water and the Persian Gulf Water) in the thermocline depths (~75–300 m) are observed to carry the dAl-rich signal of their formation regions to the open AS. This dAl enrichment in thermocline waters is, however, mostly restricted to the northern and north-western AS during the study period. Correlated dissolved Al and Fe maxima observed in the deep water over the Murray Ridge in the northern AS suggest Al and Fe release from reactive clay minerals (e.g., illite), found abundantly in the sediments deposited over the ridge. Further, elevated dAl levels were also seen near the Laxmi-Panikkar-Palitana ridge system (~10.0 nM) and the Carlsberg Ridge (~4.5 nM) in the AS and the W-Eq.IO, respectively.

Reliability assessment and paleo-oceanographic signals of geochemical and isotopic indicators in the North Pacific Subtropical Gyre

As the largest marine ecosystem on our planet, the North Pacific Subtropical Gyre (NPSG) plays an important role in global environmental and climate change. However, little is known about its environmental changes in an orbital scale. In this study, a constant flux model with excess 230Th was used to establish a time frame for our sediment core. Several geochemical and isotopic indicators were evaluated for their reliability in reconstructing paleoenvironment, including grain size distribution (GSD), Ti, Cu, Zn, Ba, total organic carbon (TOC), total nitrogen (TN), TOC/TN ratio, organic carbon and nitrogen isotopic composition (δ13C, δ15N). In addition, appropriate indicators were used to reveal changes in atmospheric dust deposition and biological productivity during the glacial and interglacial periods in the NPSG. Our results show that in such a low sedimentary environment, TOC, TN, TOC/TN ratio, δ13C, δ15N, Cu and Zn has been altered with the degradation of organic matter in the early diagenesis process. In contrast, GSD and Ti-derived eolian dust flux (Feolian) are suitable indicators for atmospheric dust deposition, and the mass accumulation rate of biogenic silica (MARBSi) and the deposition flux of excess Ba after correction for diffusion (Fexess Ba) are suitable for the reconstruction of biological productivity. The productivity during the glacial periods of Marine Isotope Stage (MIS) 2–4 and 6 is higher than the interglacial periods of MIS 1, 5, which corresponds well to the coarser dust particles and higher eolian dust supply. Therefore, we propose that different with former works in the subtropical Pacific, the fluctuations in productivity in the NPSG is mainly controlled by atmospheric dust deposition on a millennial scale.

Impact of dust addition on the microbial food web under present and future conditions of pH and temperature

Abstract. In the oligotrophic waters of the Mediterranean Sea, during the stratification period, the microbial loop relies on pulsed inputs of nutrients through the atmospheric deposition of aerosols from both natural (e.g., Saharan dust), anthropogenic, or mixed origins. While the influence of dust deposition on microbial processes and community composition is still not fully constrained, the extent to which future environmental conditions will affect dust inputs and the microbial response is not known. The impact of atmospheric wet dust deposition was studied both under present and future environmental conditions (+3 ∘C warming and acidification of −0.3 pH units), through experiments in 300 L climate reactors. In total, three Saharan dust addition experiments were performed with surface seawater collected from the Tyrrhenian Sea, Ionian Sea, and Algerian basin in the western Mediterranean Sea during the PEACETIME (ProcEss studies at the Air–sEa Interface after dust deposition in the MEditerranean sea) cruise in May–June 2017. Top-down controls on bacteria, viral processes, and community, as well as microbial community structure (16S and 18S rDNA amplicon sequencing), were followed over the 3–4 d experiments. Different microbial and viral responses to dust were observed rapidly after addition and were, most of the time, more pronounced when combined with future environmental conditions. The dust input of nutrients and trace metals changed the microbial ecosystem from a bottom-up limited to a top-down controlled bacterial community, likely from grazing and induced lysogeny. The relative abundance of mixotrophic microeukaryotes and phototrophic prokaryotes also increased. Overall, these results suggest that the effect of dust deposition on the microbial loop is dependent on the initial microbial assemblage and metabolic state of the tested water and that predicted warming and acidification will intensify these responses, affecting food web processes and biogeochemical cycles.

Monitoring, Source Identification and Environmental Risk of Potentially Toxic Elements of Dust in Isfahan Province, Central Iran.

The aim of this study was to identify potentially toxic elements (PTEs) associated with airborne particulate matters (PMs) and their source identification and environmental risk in Isfahan Province, central Iran. Dust samples were collected from various locations included three urban and four rural locations. Results revealed the eastern part of the region as the main source of dust and showed that the highest monthly atmospheric dust deposition was in July (5.53g m-2). The mean concentrations of Zn, Pb, Cu and Cd were respectively 279, 63, 49 and 0.5mg kg-1 in dust samples, whereas Cd showed the highest ecological risk index. Dust samples of urban areas showed considerable and very high levels of pollution indices for Pb and Zn, respectively. Among the metals, Zn showed the highest enrichment factor (>5), mainly due to anthropogenic sources. The comprehensive ecological risk index of PTEs revealed the moderate and considerable risk of Isfahan and Najafabad cities, respectively.

Biological carbon pump efficiency enhanced by atmospheric dust deposition in the North Pacific Subtropical Gyre

We examine the flux and composition of sinking particles collected at 4500 m depth in the southeastern part of the North Pacific Subtropical Gyre (NPSG) from August 2011 to June 2012. Satellite-derived net primary production was higher in January–May 2012 compared with the rest of the study period. Both the biogenic and lithogenic particle fluxes were significantly higher in spring (March–May 2012) than at other times. The export efficiency via the transfer of produced organic carbon to the deep ocean interior (i.e., carbon sequestration) doubled during this time. Two prominent particle flux peaks were observed in March and May 2012, coinciding with the atmospheric dust-deposition peaks within the temporal resolution of the data. Coincident increases in the biogenic and lithogenic particle fluxes suggest that dust deposition in the NPSG enhances the biological carbon-pump efficiency. Strong coupling between the particulate organic carbon and biogenic opal fluxes implies that nutrient supply via atmospheric dust deposition stimulated diatom growth in this area. Dust deposition during the productive season therefore plays an important role in carbon sequestration.

Potentially toxic elements in weathered waste-rocks of Fushun western opencast mine: distribution, source identification, and contamination assessment.

To understand the current status of the contamination of potentially toxic elements (PTEs) after closing the Fushun Western Opencast Mine, this study has focused on the concentration, contamination assessment, and source identification of eight PTEs in weathered waste-rocks in four distinct areas of the mine. The mean concentrations of Ni, Cr, Zn, Cu, Pb, Hg, Cd, and As were 79.4, 86.3, 126, 64.8, 16.9, 1.04, 1.94, and 6.27mgkg-1, respectively. The results demonstrated that Ni, Cr, Zn, Cu, Pb, Hg, Cd, and As were contaminated to different extents in different weathered waste-rocks and waste-rocks, among which there was considerable Cd contamination. Coal gangue area (CGA) exhibited the most polluted weathered waste-rocks, which can be attributed to severe pollution and moderate ecological hazards. Self-combustion gangue (SCG) contamination of waste-rocks was considerably serious and caused severe pollution and considerable ecological harm. Health risk assessments demonstrated that Hg had the highest non-carcinogenic risk. Ingestion of PTEs was found to be a primary route of exposure, while dermal and inhalation exposure was negligible. Principal component analysis (PCA) demonstrated that there were roughly three sources of PTEs in the weathered waste-rocks of the mine, natural sources related to the weathering of parent rocks, and human sources, including industrial emissions, mining activities, and atmospheric dust deposition and resuspension. This study advances our knowledge of PTEs in mines and provides policymakers with a reference for designing strategies to protect mine-based ecosystems.

Characteristics of sediment resuspension on a deep abyssal plain in the Eastern Tropical Pacific Ocean

We examined the biogenic and lithogenic particle composition and radiocarbon content of sinking particulate organic carbon to investigate sediment resuspension and its contribution to sinking particles on the deep abyssal plain of the Eastern Tropical Pacific Ocean. Samples were collected using sediment traps from August 2011 to July 2012 at depths of 4500 and 4950 m (50 m above the seafloor); above and within the benthic nepheloid layer (BNL), respectively. Biogenic particles derived from export production were the major source of sinking particles and their flux showed a unimodal temporal distribution, with larger values between February and April. At a depth of 4500 m, the lithogenic material flux was slightly greater than, or similar to, the flux of atmospheric dust deposition. In comparison, lithogenic material and excess Mn consistently showed a greater contribution to resuspended particles at 4950 m. The lithogenic material flux was proportional to the biogenic flux. These observations imply that resuspended particles exist at a background concentration in the BNL throughout the year, and are scavenged by sinking biogenic particles, especially during the high flux period.

Simultaneous quantitative speciation of selected toxic elements in water using high performance liquid chromatography coupled to inductively coupled plasma-mass spectrometry (HPLC-ICP-MS)

The aim of this study was to conduct multi-elemental speciation of As(III), dimethylarsinic acid (DMA), monomethylarsenic acid (MMA), As(V) and Cr(VI) in water samples using high performance liquid chromatography coupled to inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) in a single analytical run. Chromatographic parameters, spectral interference identification, and elimination and the performance characteristics of the method were successfully optimized for quantification of As(III), DMA, MMA, As(V), Cr(VI) and Cr(III) in water samples. The percentage errors of 6.93–43.2% for identified potential interferences were eliminated by applying the inter-element mathematical correction method. The limit of detection (LOD) and limit of quantification (LOQ) of As species and Cr(VI) were varied from 0.040-0.298 μg L−1 and 0.133–2.98 μg L−1, respectively. The LOD and LOQ of total As, Cr and Pb determined using ICP-MS were ranged from 0.013-0.203 μg L−1 and 0.045–0.675 μg L−1, respectively. The accuracy of the method was confirmed by achieving the percentage recovery of 83.4% for As species, 90.2% for Cr(VI) and 110–118% for total concentrations of As, Cr and Pb using standard reference material for trace elements in water (SRM 1643f). Furthermore, the accuracy of the speciation analysis method was checked using the spiking and recovery studies and yielded percentage recoveries in the range of 78.3–95.4% for the analyte species. The quantities of species determined in water samples were in the range of 0.314–0.402 μg L−1 for As(III), 0.168–0.533 μg L−1 for DMA, 0.226–0.312 μg L−1 for MMA, 0.191–0.459 μg L−1 for As(V), 0.500–3.28 μg L−1 for Cr(VI) and 0.390–12.6 μg L−1 for Cr(III) in high-flow seasonal state of the river. In the low-flow seasonal state, concentrations varied from 0.314-0.391 μg L−1 for As(III), <0.094 μg L−1 for DMA, 0.315–26.7 μg L−1 for MMA, 0.290–0.744 μg L−1 for As(V), 0.426–5.42 μg L−1 for Cr(VI) and 0.424–96.8 μg L−1 Cr(III). Total concentrations of As, Cr and Pb in water samples of high-flow seasonal state ranged from 0.949-1.88 μg L−1, 1.08–14.9 μg L−1 and 0.190–33.8 μg L−1, respectively. In low-flow seasonal state, the total concentrations of As, Cr and Pb in water samples varied from 1.13-26.5 μg L−1, 3.28–97.5 μg L−1 and 0.455–0.610 μg L−1, respectively. The variations between analytes species and total As, Cr and Pb in seasonal states of the river were statistically insignificant (p > 0.05) at a 95% confidence level except for DMA. The nonpoint sources pollution such as atmospheric deposition of dust released from coal mining, power stations, sewage effluents discharge and agricultural activities are presumably the sources of potentially toxic elements in the Mokolo River.

Long‐term ecosystem and biogeochemical research in Loch Vale watershed, Rocky Mountain National Park, Colorado

AbstractLoch Vale watershed was instrumented in 1983 with initial support from the National Acid Precipitation Assessment Program to ask whether ecosystems of Rocky Mountain National Park (RMNP) were affected by acidic atmospheric deposition. Research and monitoring activities were expanded in 1991 by the U.S. Geological Survey Water, Energy, and Biogeochemical Budgets program to understand the processes, and their interactions, controlling water, energy, and biogeochemical fluxes. With help from many collaborators we have characterized trends and patterns in atmospheric deposition, climate, and hydrology, including glaciers and other ice features. Instead of acidic deposition, we documented high atmospheric inputs of reactive nitrogen (Nr), and have studied the ecological consequences in soils, surface water, and vegetation. Using paleolimnology, we documented the onset of human‐caused change to lake primary producers ca. 1950 in response to increased Nr deposition and warming. Our results provided the basis for the Colorado Nitrogen Deposition Reduction Plan, a state policy that aims to reduce Nr emissions to protect resources in RMNP by 2032. Carbon cycle research revealed mountain wetlands now release more carbon than they store, and respiration and methane flux occurs even during winter through deep snow packs. Trend analyses found export of Nr to be closely tied to atmospheric inputs, but can lag in response to drought. Current research explores consequences of the combination of warming, changes in precipitation dynamics, and atmospheric deposition of Nr and dust on stream and lake CO2 dynamics, lake biology and trophic state, and soil carbon composition. Dramatic increases in park visitors have prompted studies on the effects of recreational use on water quality. New tools such as remote sensing and high frequency instream water quality sensors are being applied to lake and stream studies. Monitoring, combined with experiments, models, and spatial comparisons is an essential foundation for science‐based resource management.

Evaluating the Rate of Atmospheric Dust Deposition in Isfahan Province

The present study investigates seasonal and spatial variations in atmospheric dust deposition rate (DDR) and the concentration of dust-borne heavy metals in the eastern part of Isfahan as well as Segzi plain located in the central part of Iran. Dust samples were collected from nine different sites on a monthly basis from December 2016 to September 2017. The total concentrations of Pb and Zn were measured. The lowest value of DDR was observed in the winter due to low amount of precipitation, and the highest value was recorded in the summer. Seasonal distribution of the concentration of dust-borne heavy metals revealed that almost all the metals follow the pattern: fall ˃ spring ˃ summer. Spatial distribution of dust-borne Pb and Zn followed almost the same trend and the highest concentrations were observed in the western parts of the study area. It seems that fossil fuel, vehicle traffic, and industrial activities are the most important anthropogenic factors contributing to dust-borne heavy metals in the study area.

Dust-borne microbes affect Ulva ohnoi's growth and physiological state.

The marine macroalgae Ulva sp. is considered an ecosystem engineer in rocky shores of temperate waters worldwide. Ulva sp. harbors a rich diversity of associated microbial epibionts, which are known to affect the algae's typical morphological development and 'health'. We examined the interaction between airborne microbes derived from atmospheric aerosols and Ulva ohnoi growth and physiological state. Specifically, we measured U. ohnoi growth rates and photosynthetic efficiency (Fv/Fm), alongside its microbial epibionts abundance, activity and diversity following dust (containing nutrients and airborne microorganisms) or UV-treated dust (only nutrients) amendments to filtered seawater. Parallel incubations with epibionts-free U. ohnoi (treated with antibiotics that removed the algae epibionts) were also tested to specifically examine if dust-borne microbes can replenish the epibiont community of U. ohnoi. We show that viable airborne microbes can restore U. ohnoi natural microbial epibionts communities, thereby keeping the seaweed alive and 'healthy'. These results suggest that microbes delivered through atmospheric aerosols can affect epiphyte biodiversity in marine flora, especially in areas subjected to high annual atmospheric dust deposition such as the Mediterranean Sea.

Multivariate linear regression models for predicting metal content and sources in leafy vegetables and human health risk assessment in metal mining areas of Southern Jharkhand, India.

The present study was intended to investigate the metal concentrations in the leafy vegetables, irrigation water, soil, and atmospheric dust deposition in the iron and copper mining areas of Southern Jharkhand, India. The study aimed to develop a multivariate linear regression (MVLR) model to predict the concentration of metals in leafy vegetables from the metals in associated environmental factors and assessment of the risk to the local population through the consumption of leafy vegetables and other allied pathways. The developed species-specific MVLR models were well fitted to predict the concentration of metals in the leafy vegetables. The coefficient of determination values (R2) was greater than 0.8 for all the species-specific models. Risk assessment was carried out considering multiple pathways of ingestion, inhalation, and dermal contact of vegetables, soil, water, and free-fall dust. Consumption of leafy vegetables was the major route of metal exposure to the local population in both the metal mining areas. The average hazard index (HI) value considering all the metals and pathways was calculated to be 5.13 and 12.1, respectively for iron and copper mining areas suggesting considerable risk to the local residents. Fe, As, and Cu were the major contributors to non-carcinogenic risk in the Iron mining areas while in the case of copper mining areas, the main contributors were Co, As, and Cu.

The elemental enrichments at Dajiuhu Peatland in the Middle Yangtze Valley in response to changes in East Asian monsoon and human activity since 20,000 cal yr BP

Here we present multiproxy inorganic geochemical records from a peat core (ZK5) from the Dajiuhu Basin in central China to investigate peatland deposition processes and atmospheric metal pollution and to explore their relationships with East Asian monsoon change and human activities in the Middle Yangtze Valley since 20,000 cal yr BP. The peat physicochemical data including total organic carbon (TOC), trace elements, and grain-size show that the site has changed from a lake during the cold-wet Last Glacial Maximum (LGM; 20,000–18,000 cal yr BP), to a marshy wetland during the mild last deglaciation (18,000–11,500 cal yr BP) and a peatland during the mostly warm and dry Holocene (11,500 cal yr BP–present). This general sequence corresponds with changes in East Asian monsoon indicated by stalagmites δ18O records and boreal summer insolation. Marked decreases in trace element concentrations correspond to two periods of peatland expansion during the abrupt hydroclimatic transitions from the LGM to the last deglaciation and from the last deglaciation to the early Holocene. Warm-dry mid-Holocene might induce high organic matter decomposition in peat sediments. Increasing natural element concentrations since the late Holocene are correlated with the weakening of the summer monsoon and elevated atmospheric dust deposition. Increasing Cu and Pb concentrations in peat record indicate large-scale Cu smelting during the Bronze Age and excessive coal burning during the 10th century or so. The anthropogenic heavy metals were transported by prevailing East Asian summer monsoon and deposited in the Dajiuhu Basin during periods of heightened human activities. Our compilation of heavy metals records across China confirmed the noticeable impacts of the historical human activity on deposition environments during the late Holocene. Consequently, trace elements from the Dajiuhu Basin are reliable proxies for capturing monsoon climate-induced peatland deposition response and present important evidence for a historical atmospheric heavy metal pollution in the Middle Yangtze Valley. Our results offer useful references for peatland evolution and protection under the background of global change.

Meteorological patterns, technical validation, and chemical comparison of atmospheric dust depositions and bulk sand in the Arabian Gulf region.

This study reports seasonal variations of meteorological parameters, atmospheric dust and dust-borne heavy metals concentrations measured, over a period of two years, next to two major airports (Dubai International Airport and Abu Dhabi International Airport) in the Gulf Cooperation Council (GCC) region. On-line monitoring stations were installed at each location next to dust samplers used to frequently collect PM2.5 and PM10 on Teflon filters for metal analysis. Clear seasonal variation in meteorological parameters were identified. The particulate matter concentrations depicted from the two locations were continuously monitored. The PM2.5 concentration ranged from 50 to 100μg/m3 on normal days but reached 350-400μg/m3 per day during mild storms. The PM10 levels ranged between 100 and 250μg/m3 during normal days and spiked to 750μg/m3 during mild storms. Energy Dispersive X-Ray Analysis (EDS) revealed the presence of significant amounts of alkali and alkaline earth metals, which pose potential harm to aircraft engines. ICP analysis showed the presence of heavy and toxic metals in concentrations that may pose harm to human health. Bulk sand samples from Abu Dhabi sites showed chemical similarities to the atmospheric dust samples. The concentrations of heavy metals, PM2.5, and PM10 are at levels that require further monitoring due to their impact on human health. The two years meteorological monitoring, with the seasonal variations, provided additional regional data in the Arabian Gulf. Furthermore, the study concluded that Sand and Dust storms (SDS) occur more frequently at the northern Arabian Gulf compared to its southern region. The chemical correlation between atmospheric dust and regional desert sand suggests the localized origin of the smaller dust particles that may form by breaking apart of the ground sand grains. As a result of the ongoing urbanization in the region, it is essential to collect additional data from various locations for a longer period of time.

Sediment carbon storage increases in tropical, oligotrophic, high mountain lakes

• El Sol and La Luna are valuable sentinels of global change by displaying detectable signs of anthropic disturbances from 1950 onwards. • The higher mass accumulation rates and organic carbon burial rates from 1950 onwards are result of human activities and atmospheric dust deposition. • Sharing the same climatic conditions, climate change unlikely caused the recent higher organic carbon burial observed in both lakes. High mountain lakes are valuable sentinels of global change because they are sensitive to environmental stress and integrate changes in the atmosphere and their catchment areas. This study tested the hypothesis that local and regional anthropogenic stressors have affected productivity, sedimentation, and organic carbon burial in two tropical high mountain lakes in central Mexico. We studied changes in the water column (Secchi disc depth, total suspended solids (TSS), and chlorophyll- a concentrations) and surface sediments (chlorophyll- a and organic carbon concentrations) in El Sol Lake and La Luna Lake during the period 2000–2018, and organic carbon burial rates in sediment cores (∼1884–2014) dated with lead-210 ( 210 Pb). We observed increasing water turbidity, TSS, and organic carbon in surface sediments in El Sol Lake. Different responses of the two lakes were caused by lower pH in La Luna Lake and a threefold residence time of TSS in El Sol Lake compared to La Luna Lake, mostly attributable to their different surface/volume ratios. Organic carbon burial rates were slightly higher at La Luna Lake until 2000, when they became higher at El Sol Lake due to increasing sediment accumulation and organic carbon concentrations. In both lakes, results show significantly higher organic carbon burial rates since the 1950s, likely resulting from the deposition of human-induced wind-blown particles derived from activities at the volcano slopes and long-distance transport from highly urbanized areas. Anthropogenic impacts rather than climate change, therefore, caused the recent higher organic carbon burial rates observed in both lakes. Methods and findings from this study provide a valuable basis for comparing changes in other high mountain lakes worldwide.

Multiple interacting environmental drivers reduce the impact of solar UVR on primary productivity in Mediterranean lakes

Increases in rainfall, continental runoff, and atmospheric dust deposition are reducing water transparency in lakes worldwide (i.e. higher attenuation Kd). Also, ongoing alterations in multiple environmental drivers due to global change are unpredictably impacting phytoplankton responses and lakes functioning. Although both issues demand urgent research, it remains untested how the interplay between Kd and multiple interacting drivers affect primary productivity (Pc). We manipulated four environmental drivers in an in situ experiment—quality of solar ultraviolet radiation (UVR), nutrient concentration (Nut), CO2 partial pressure (CO2), and light regime (Mix)—to determine how the Pc of nine freshwater phytoplankton communities, found along a Kd gradient in Mediterranean ecosystems, changed as the number of interacting drivers increased. Our findings indicated that UVR was the dominant driver, its effect being between 3–60 times stronger, on average, than that of any other driver tested. Also, UVR had the largest difference in driver magnitude of all the treatments tested. A future UVR × CO2 × Mix × Nut scenario exerted a more inhibitory effect on Pc as the water column became darker. However, the magnitude of this synergistic effect was 40–60% lower than that exerted by double and triple interactions and by UVR acting independently. These results illustrate that although future global-change conditions could reduce Pc in Mediterranean lakes, multiple interacting drivers can temper the impact of a severely detrimental driver (i.e. UVR), particularly as the water column darkens.