Accumulation In Sediments Research Articles

Organochlorine pesticide accumulation in fish and catchment sediments of Lake St Lucia: Risks for Africa’s largest estuary

Although use of organochlorine pesticides (OCPs) has been banned or severely limited on a global basis, concerning concentrations continue to be reported in many tropical and subtropical regions of the world. These habitats often support high levels of unique biodiversity and vulnerable communities that depend on the environment for their survival. We investigated threats associated with OCP contamination at Lake St Lucia, a global hotspot for biodiversity and a UNESCO World Heritage Site in South Africa. Lake St Lucia is sustained largely by surface runoff from catchment areas where significant quantities of OCPs have historically been used in agriculture and where DDT continues to be used for disease control. Sediments (n = 40) collected from the two largest fluvial inputs to Lake St Lucia showed that these rivers represent important sources of contaminants, with ∑OCP concentrations ranging between 74 and 510 ng g−1. Measured HCH, dieldrin, ∑DDT and ∑chlor concentrations exceeded NOAA sediment toxicity guidelines in the majority of samples analysed. Bioaccumulation was assessed by examining residue concentrations in muscle tissues from two abundant fish species from Lake St Lucia. OCPs were detected in all samples analysed, with total concentrations ranging 860–5000 ng g−1 lw and 390–3200 ng g−1 lw for Oreochromis mossambicus (n = 17) and Clarias gariepinus (n = 41), respectively. A health risk assessment indicated potential dietary risk associated with exposure to aldrin, dieldrin and heptachlor, although the cumulative effect of OCPs on human health, ecosystem biodiversity and long-term ecotourism sustainability remains unknown.

ANME-1 archaea may drive methane accumulation and removal in estuarine sediments.

ANME-1 archaea subsist on the very low energy of anaerobic oxidation of methane (AOM). Most marine sediments shift from net AOM in the sulfate methane transition zone (SMTZ) to methanogenesis in the methane zone (MZ) below it. In White Oak River estuarine sediments, ANME-1 comprised 99.5% of 16S rRNA genes from amplicons and 100% of 16S rRNA genes from metagenomes of the Methanomicrobia in the SMTZ and 99.9% and 98.3%, respectively, in the MZ. Each of the 16 ANME-1 OTUs (97% similarity) had peaks in the SMTZ that coincided with peaks of putative sulfate-reducing bacteria Desulfatiglans sp. and SEEP-SRB1. In the MZ, ANME-1, but none of the putative sulfate-reducing bacteria or cultured methanogens, increased with depth. Our meta-analysis of public data showed only ANME-1 expressed methanogenic genes during both net AOM and net methanogenesis in an enrichment culture. We conclude that ANME-1 perform AOM in the SMTZ and methanogenesis in the MZ of White Oak River sediments. This metabolic flexibility may expand habitable zones in extraterrestrial environments, since it enables greater energy yields in a fluctuating energetic landscape.

Mercury accumulation in sediments of Lhù’ààn Mânʼ (Kluane Lake, YT): Response to past hydrological change

ABSTRACT Northern lakes provide many ecosystem services, including the provision of traditional foods and clean water. These systems are vulnerable to climate-driven changes in hydrology and contaminant accumulation, but the direction and magnitude of projected changes are poorly constrained. One contaminant of concern is mercury; currently, we cannot accurately predict how mercury accumulation in lakes will respond to climate-induced changes, especially in lakes with glacial inflows and complex hydrology. Sediment cores collected from two regions of a glacially fed lake (Lhù’ààn Mân’; Kluane Lake, Yukon, Canada) were analyzed to investigate controls on sediment mercury accumulation in the context of previously described hydrological changes. Differences in catchment contributions drove differences in sediment mercury accumulation between lake regions during the Duke River hydrological period (ca. 750–1650). During the more recent Slims River hydrological period (ca. 1650–2015), mercury accumulation did not differ between regions, and mercury was delivered to the lake primarily via catchment organic matter and carbonate-rich sediments from the largest, glacially derived inflow (Slims River). Recent climate-induced geomorphic change caused loss of the main lake inflow (Slims River) in 2016, making Kluane Lake an ideal system for future investigations of how loss of glacial inflow will affect mercury accumulation in northern lakes.

Evaluation of heavy metals in sediment, water and Macrophyte (Eicchornea crassipes) of Yamuna River at Delhi

To examine the degree of contamination in Yamuna River at Delhi, eight heavy metal (Pb, Cd, Hg, Cu, Cr and Zn) were assessed in soil, water and macrophyte (Eicchornea Crassipes). Heavy metals are one among the toxic chemicals and accumulation in sediments and plants has been posing serious health impacts. The occurrence heavy metals in water were found in the order: Cr> Zn> Pb> Cu> Cd> Hg. In sediment order was: Cr ˃ Zn ˃ Pb ˃ Cu ˃ Cd ˃ Hg and in macrophyte (Eicchornea Crassipes) in order: Zn ˃ Pb ˃ Cr ˃ Cu ˃ Cd ˃ Hg. The analyses of macrophytes and sediment samples help in evaluating pollution status in aquatic environment. Heavy metals in water was found above the recommended level set by WHO for drinking.

Ecological risk assessment of toxic metal contamination in a significant mining basin in Turkey

Emet River Basin is a worldwide significant mining area and contains the most important boron and chromium deposits of Turkey. In this study, water and sediment quality of Emet River Basin was evaluated using some toxic element risk assessment indices. Samples were collected seasonally from 8 locations and nickel (Ni), chromium (Cr), arsenic (As), zinc (Zn), lead (Pb), copper (Cu) and cadmium (Cd) accumulations in water and sediment were analysed using an ICP-OES. Water Quality Index (WQI), Heavy Metal Pollution Index (HPI), Heavy Metal Evaluation Index (HEI) and Degree of Contamination Index (Cdeg) were applied to the data for assessing the water quality and Biological Risk Index (BRI), Potential Ecological Risk Index (PERI), Geo-Accumulation Index (Igeo), Contamination Factor (CF) and Pollution Load Index (PLI) were applied to the data for assessing the sediment quality. According to the results of WQI, HPI, HEI and Cdeg, As and Cr were recorded as the most dangerous toxicants; according to the results of BRI, Igeo, CF and PLI, Cd, As and Pb were recorded as the most dangerous toxicants; and according to the results of PERI, Ni and Cr were recorded as the most dangerous toxicants among the investigated elements. The seasonal average values of applied ecological indices for the water of the basin ranged 71.41–888.29 for WQI, 85.97–915.76 for HPI, 4.04–49.80 for HEI and − 2.95–42.80 for Cdeg. The seasonal average values of applied ecological indices for the sediment of the basin ranged 33.72–130.56 for PERI, 0.14–0.93 for BRI, − 3.92–5.99 for Igeo and 0.45–1.20 for PLI. In addition to the intensive agricultural applications around the region, the geological structure of the watershed was considered as the main cause of the high heavy metal accumulations in basin waters and sediments.

Relevance and magnitude of 'Blue Carbon' storage in mangrove sediments: Carbon accumulation rates vs. stocks, sources vs. sinks

Mangrove ecosystems store large amounts of 'Blue Carbon', in particular in the sediment. Research in the past decade has emphasized the quantitative significance of carbon storage in mangrove forests in climate change mitigation, mainly by determining carbon stocks and calculating potential CO2 emissions caused by mangrove degradation. However, while this approach focuses on the total amount of carbon that can be lost to degradation, it fails to capture the amount that is sequestered annually. Therefore, carbon accumulation in mangrove sediments also needs to be taken into account. This study (i) explains the differences between carbon stocks and carbon accumulation rates (CAR), (ii) it addresses the geographical variation of carbon storage and underlying factors and (iii) it assesses the global relevance of 'Blue Carbon' sequestration in mangrove sediments. Results indicate that reducing uncertainties in carbon storage estimates of individual systems requires a representative set of data that covers within-system variability. An example from Indonesia illustrates that a mangrove ecosystem with a high C stock can have a low CAR and vice versa. It is therefore conceivable that coastal environmental settings with high allochthonous supply of mineral sediment, organic matter and nutrients mostly have low carbon stocks, but high CARs. As these settings represent >80% of the global mangrove area they are most important in terms of long-term carbon storage. While a C stock is a measure of the "vulnerability potential" in the case of ecosystem degradation or total loss, a CAR is rather a measure of the "mitigation potential" of carbon storage in mangrove ecosystems. The global carbon storage in mangrove sediments of 32 Tg yr−1 estimated from CARs in this study is at the upper end of the range of global budgets (14.6–31.1 Tg yr−1, mean 22.9 Tg yr−1). It highlights that the mangrove carbon sink may be larger than previously thought, but the high variation in the global average CAR of 233 ± 280 g C m−2 yr−1 also indicates the need for further data.

The value of carbon sequestration and storage in coastal habitats areas in North West of Morocco

Morocco, like the rest of the world, is experiencing a climate change that threatens a number of wetlands. Marine ecosystems contribute to the regulation of the Earth’s climate, but their degradation releases large quantities of greenhouse gases (GHGs) such as carbon dioxide (CO2) into the atmosphere. This paper aimed to map and model changes in carbon storage and sequestration for coastal habitats using the INVEST model, using the Sidi Moussa-Oualidia lagoon complex as a case study. To achieve this objective, several data were used, namely, land use and land cover maps between 2003 and 2020, as well as data on the amount of carbon stored in the three basins; biomass, sediment carbon (soil) and dead carbon (litter), and the annual rate of carbon accumulation in biomass and sediment. The results obtained in this work allowed us to compare the two former and current carbon stock and net sequestration scenarios and to evaluate the social cost of carbon in the study area. This study can facilitate the development of a coastal rehabilitation strategy to take advantage of the benefits of these wetlands and, at the same time, to conserve the ecosystem services provided by these environments, including the CBCS.

Ecological and Human Health Risk Assessment of Sediments near to Industrialized Areas along Langat River, Selangor, Malaysia

ABSTRACT Rapid industrialization at Kuala Langat, Selangor have raised environmental and health concerns among the public. Surface sediments from a total of 10 stations, covering the upstream and downstream sites near to plastic recycling factories along Langat River were collected and analyzed for its physicochemical properties, bioavailable heavy metals concentration and pollution degree. Ecological risk assessment of heavy metals was carried out using several pollution indices such as geoaccumulation index (), contamination factor (CF), contamination degree (CD), enrichment factor (EF), pollution load index (PLI) and potential ecological risk index (PERI). For human health risk assessment, non-carcinogenic risk of heavy metals (Cd, Cr, Cu, Pb and Zn) was assessed using hazard quotient (HQ) and hazard index (HI) whereas carcinogenic risk of heavy metals (Cd, Cr and Pb) was assessed using carcinogenic risk index (RI) and total risk (TR). The heavy metal accumulation in sediments in terms of concentration was in the order of Pb > Zn > Cu > Cr > Cd and the mean concentration of the heavy metals were lower than the background value except Pb. The PLI result indicated that the sediment at Langat River was unpolluted but posed low ecological risk by Cr, Cu and Zn, low to moderate ecological risk by Cd, and low to considerable ecological risk by Pb as shown by PERI result. However, non-dietary ingestion of sediment from Langat River showed possible risk of non-carcinogenic effects at certain sites whereas tolerable carcinogenic risk at almost all sites. Organic matter, silt, clay, pH and base saturation showed significant relationship with the heavy metals concentration, indicating the transformation and accumulation factor of heavy metals in river sediment. This study is important to increase the awareness of sediment pollution at Langat River and provide information to the stakeholders in Kuala Langat for future planning and policies to protect the local ecosystem and residents.

Factors influencing the occurrence and distribution of microplastics in coastal sediments: From source to sink

Microplastic (MP) pollution is attracting growing global attention, but little is known about the factors influencing MP occurrence and distributions in marine sediments. Here, MPs were sampled from the sediments of two semi-enclosed bays (Jinghai Bay and Laizhou Bay) and two coastal open zones (Lancelet Reserve and Solen grandis Reserve) in China. The order of MP abundance was Jinghai Bay > Laizhou Bay > Lancelet Reserve > Solen grandis Reserve. Average MP diversity indices for Laizhou Bay (1.84 ± 0.18), Lancelet Reserve (1.59 ± 0.43), S. grandis Reserve (1.58 ± 0.89), and Jinghai Bay (1.43 ± 0.14) revealed Laizhou Bay had the most complicated MP sources. A significant negative correlation between MP abundance and sediment grain size occurred in the semi-enclosed coastal zones (p = 0.004, r = −0.618) rather than in the open coastal zones (p = 0.051, r = −0.480), indicating small sediment particles can strongly enhance MP accumulation in semi-enclosed costal sediments. Although anthropogenic activities influence the MP distribution at source, the composition of regional and local sediments might impact MP occurrence in semi-enclosed coastal zones from the sink. These results help to improve our understanding of the fate and inventory of MPs in coastal sediments.

Why productive lakes are larger mercury sedimentary sinks than oligotrophic brown water lakes

AbstractMercury accumulation in lake sediments is a widespread environmental problem due to the biomagnification of Hg in the aquatic food chain. Soil Hg concentrations, catchment vegetation, erosion, and lake productivity are major factors controlling the accumulation of Hg in lakes. However, their influence on the Hg mass balance in lakes with different catchment characteristics and trophic state is poorly understood. In this multilake study, we decipher the effects of catchment vegetation (coniferous vs. deciduous forest), soil Hg content, and trophic state on Hg sedimentation at six lakes in Germany. We investigated Hg concentrations in leaves, soils, and the lake's water phase. Soils under coniferous stands show slightly higher Hg concentrations than under deciduous forest. Hg concentrations in the water phase were higher in the oligotrophic brown water lakes (8.1 ± 5.6 ng L−1 vs. 3.0 ± 1.9 ng L−1). Lower Hg concentrations in sediment trap material indicate dilution by algae organic matter in the mesotrophic lakes (0.12–0.17 μg g−1 vs. 0.57–0.89 μg g−1). However, Hg accumulation rates in sediment traps were up to 14‐fold higher in the mesotrophic lakes (113–443 μg m−2 yr−1) than in the brown water lakes (32–144 μg m−2 yr−1), which could not be explained by higher Hg fluxes to the productive lakes. Hg mass balance calculation reveals that water phase Hg scavenging by algae is the major reason for the intense Hg export to the sediments of productive lakes which makes them significantly larger sedimentary sinks than oligotrophic brown water lakes.

Human impact on C/N/P accumulation in lake sediments from northeast China during the last 150 years.

Lakes and lake sediments are significant components of the global carbon (C) cycle, and may store very large amounts of organic matter. Carbon sequestration in lakes is subject to substantial temporal and spatial variation and may be strongly affected by human activities. Here, we report accumulation rates (AR) of organic C (OC), total nitrogen (TN) and total phosphorous (TP), and investigate their responses to anthropogenic impact over the past 150 years by analyzing 62 sediment cores from 11 shallow lakes in the Songnen Plain, northeast China. From the center of each of the lakes, we selected one master core for age determination by 210Pb and 137Cs radioisotopes. The contents of OC, TN, TP, dry bulk density and mass specific magnetic susceptibility were then determined for all cores. The regional OCAR, TNAR and TPAR up-scaling from the multiple cores yielded mean values of 51.63±15.13, 2.50±0.98, and 0.90±0.21gm-2 yr-1, respectively. Nutrient AR in the studied lakes increased by a factor of approximately 2×from the middle 19th century to the 1950s, and approximately 5×after the 1950s. Elemental ratios show that the increase in OCAR is mainly the result of C autogenesis from the growth of aquatic plants stimulated by agricultural intensification, including increased chemical fertilizer application and farmland expansion. Significantly enhanced nutrient burial by these lakes after the 1950s resulted from increased anthropogenic impacts in northeast China. More sustainable agricultural practises, including a decrease in P fertilizer use, would result in a lowering of OCAR, TNAR and TPAR in the future.

Phosphate mineral accumulation in lake sediment to form a secondary phosphate source: A case study in lake sediment around Eppawala Phosphate Deposit (EPD) in Sri Lanka

Global phosphorus scarcity will result in significant consequences for future food security with the depletion of current phosphate reserves. Therefore, exploration of new phosphorus sources is essential to address future phosphorus scarcity. The current study investigated the geochemical potential of lake sediment around the Eppawala Phosphate Deposit (EPD) in Sri Lanka to be used as a low-grade phosphorus source for agricultural purposes. Jaya-Ganga is a man-made water canal that drains through the EPD feeding three lakes, namely, upstream Ihalahalmilla Lake and Koon Lake, and downstream Kiralogama Lake with respect to the EPD. Three cores (cores A, B, and C) were collected from the above three lakes and major oxides and minerals distributions along the cores were analyzed. Notable high enrichment of phosphorus pentoxide (P2O5) content and high P2O5 solubility values were measured in the top 60 cm sediment layer in Core B and throughout the Core C compared to the Core A. This high enrichment of P2O5 content in the same sediment columns were confirmed by the comparison with the Upper Continental Crust (UCC) values and literature survey. According to the X-ray Diffraction (XRD) results, phosphate minerals, such as fluorapatite, crandallite, and millisite were abundantly found in the same sediment columns. Therefore, these phosphate minerals can be considered as pathfinding minerals for soluble phosphates in sediment cores. Thus, sediment with high P2O5 content and high solubility in downstream Kiralogama Lake showed the potential for application of these sediments as a direct phosphate source in agricultural purposes. Furthermore, the current study has introduced a new area of interest, i.e., soil and sediments around major phosphate deposits, for the exploration of new phosphate sources to meet future phosphorus demand.

СОДЕРЖАНИЕ ПИГМЕНТОВ В ФИТОПЛАНКТОНЕ, ЭПИФИТОНЕ И ДОННЫХ ОТЛОЖЕНИЯХ ОЗЕРА НЕРО

This article presents new data of spectrophotometric determination of pigment concentrations in phytoplankton, epiphyton and bottom sediments of the shallow highly productive Lake Nero based on survey materials in summer 2017. The average concentrations of chlorophyll a were 73.5±6.1 μg/L in phytoplankton and 40.7±21.4 mg/m2 of substrate in epiphyton, the sum of chlorophyll a with pheopigments in bottom sediments was 313±20.6 μg/g dry sediment. These values are comparable to those in the previous observation years. The parameters of pigment degradation were characterized by low values in the functioning communities of phytoplankton and epiphyton and reached the highest values in bottom sediments. The spatial distribution of algal pigments depended on the presence of macrophyte thickets. Overgrowing of the territory with macrophytes affected the content of pigments in phytoplankton negatively but the pigment accumulation in bottom sediments positively. The trophic state of the lake remains hypertrophic, as in previous years of observation.

Assessment the Seasonal Variability and Enrichment of Toxic Trace Metals Pollution in Sediments of Damietta Branch, Nile River, Egypt

This work appraises the extent of toxic trace metals and seasonal pollution degree in Damietta branch sediments of the River Nile of Egypt. The toxic trace metals Fe, Mn, Cd, Co, Cu, Ni, Pb, and Zn were analysed in sediments from six sites during the summer and winter seasons. The metal concentrations and organic matter were determined using inductively-coupled-plasma mass spectrometry and loss-on-ignition, respectively. Multivariate statistical methods were used in order to allocate the possible metals sources and their relationships in sediments. The seasonal mean sequence of toxic trace metals was: Fe > Mn > Zn > Pb > Cu > Ni > Co > Cd. The mean Cd, Pb, and Zn values exceeded the sediment quality guidelines and average shale and they represent severe potential toxicity for aquatic organisms. Cu and Co were enriched during winter. The geo-accumulation index stipulated that metal pollution degree in the sequence of: Pb > Zn > Cd > Co > Cu > Mn > Ni > Fe. The highest metal pollution index reported in winter in sites S4/S5 and during summer in sites S4–S6. Different agricultural, wastewater discharge, fisheries, and industrial activities, as well as the effect of dilution/concentration during summer/winter seasons, are the main factors that contributed to metal accumulations in Damietta branch sediments. Continuous monitoring and evaluation of toxic trace metal concentrations of the Damietta sediments and similar localities worldwide can help to protect the ecosystem from harmful metal contaminations.

Heavy Metal Accumulation and Release Risks in Sediments from Groundwater–River Water Interaction Zones in a Contaminated River under Restoration

This study investigated the accumulation and release risks of heavy metals As, Cd, Co, Cr, Cu, Ni, Pb, and Zn in representative contaminated river-bed and river-side sediments from a groundwater–ri...

Restoration of Lake Okeechobee, Florida: mission impossible?

Canfield DE Jr, Bachmann RW, Hoyer MV. 2020. Restoration of Lake Okeechobee, Florida: mission impossible? Lake Reserv Manage. XX:XXX–XXX. Legally mandated eutrophication restoration goals for Lake Okeechobee (FL) are unachievable, therefore assigning managers a “mission impossible.” Since the 1970s, restoration efforts have focused on reducing pelagic total phosphorus (TP) to ∼40 µg/L. A total daily maximum load (TMDL) of 140 metric tons (t)/yr was adopted by the Florida Department of Environmental Protection in 1999 (effective date 2015) to restore the lake’s balance of flora and fauna. Phosphorus (P) loads (1975–2018) averaged 516 t/yr with no significant change over time, yet average TP significantly increased from 51 µg/L (1974–1977) to 146 µg/L (2015–2019). Greater TP values in 2019 were due to Hurricane Irma and an early June storm event. Annual P-loads and pelagic TP were not significantly correlated. Instead, TP was strongly correlated with turbidity (R 2 = 0.85), which is generated by wave-driven resuspension of P-rich unconsolidated sediments. Since 1973, >13,000 t of TP has been added to Okeechobee’s sediments that have accumulated over the past century due to the lowering of water levels and the construction of the Herbert Hoover Dike. Prior to settlement, high water levels allowed turbid lake waters to flood large areas of adjacent wetlands, where suspended sediments were removed from the lake. With the minimization of this self-cleansing mechanism after construction of the Herbert Hoover Dike, P-rich fine sediments accumulated, and periodic hurricanes disrupted consolidated sediments. Unconsolidated sediments are easily resuspended into the water column, raising TP. Efforts to reduce Okeechobee’s pelagic TP through reductions of P-loads alone will not work due to sediment accumulation and resuspension.

Mercury chemostratigraphy as a proxy of volcanic-driven environmental changes in the Aptian-Albian transition, Araripe Basin, northeastern Brazil

The stratigraphy of mercury (Hg) in sections of the Araripe Basin straddling the Aptian-Albian transition, encompassing the Romualdo, Ipubi, Crato and Barbalha (formerly Rio da Batateira)Formations showed positive excursions of Hg concentrations without correlation with organic carbon (C-org) contents. These incursions occurred during the deposition of the Barbalha Formation, which occurred in the Aptian under warm climate and high bio-productivity; in the Crato Formation, in the Albian, and also during the deposition of the Romualdo Formation. The Hg enrichments suggest external sources of Hg to the basin. The positive Hg excursion in the Ipubi Formation, unlike the others, was shown to be correlated with an increase in the deposition of C-org, suggesting internal processes as major river of Hg accumulation in sediments. The positive Hg excursions independent of C-org accumulation are concomitant to periods of intense volcanic activity in the Kerguelen Large Igneous Provinces (LIP). The excursion observed in the Ipubi Formation, however, seems associated with an event of anoxia, resulting in sediments rich in C-org, scavenging Hg from the water column. The Hg chemostratigraphy helps to understand of the paleoenvironmental changes in the Araripe basin, allowing understanding some of the drivers of such changes as the influence of volcanic activity and events of anoxia, as well as major biological crises.

Assessment of subsurface riverbed clogging by fine sediments in a semi-arid catchment of north-western Algeria

In semi-arid regions, natural and anthropogenic disturbances increase the input of fine particles and their subsequent accumulation in streambeds sediment. The clogging of streambeds sediment is caused by the infiltration of fine particles at depth, reducing hydraulic conductivity (K) and hyporheic flow. Grain-size distribution and streambed vertical K were estimated using hyporheic sediment samples collected from ten stations in the Tafna River catchment during two hydrological periods of high and low water in order to investigate spatiotemporal variations and the variables influencing hydraulic conductivity. During the wet season, the upstream part of the catchment had significantly higher coarse sand content, with K measured to be three times greater than downstream. During low flow periods, there were significantly more fine particles (clay and silt) downstream, which were negatively correlated with K. Increases in clay and silt were the main cause of sediment clogging in the downstream part of catchment. However, within-group PCA showed that geomorphology had no significant influence on hyporheic sediment clogging. This study demonstrated that the process of streambed sediment clogging was influenced by the accumulation of fine particles and organic matter, which significantly contributed to the clogging of the downstream hyporheic zone, thus decreasing hydraulic conductivity despite prevailing geomorphology.

Three North African dust source areas and their geochemical fingerprint

North Africa produces more than half of the world's atmospheric dust load. Once entrained into the atmosphere, this dust poses a human health hazard locally. It also modifies the radiative budget regionally, and supplies nutrients that fuel primary productivity across the North Atlantic Ocean and as far afield as the Amazonian Basin. Dust accumulation in deep sea and lacustrine sediments also provides a means to study changes in palaeoclimate, particularly those associated with rainfall climate change. Systematic analysis of satellite imagery has greatly improved our understanding of the trajectories of long-range North African dust plumes, but our knowledge of the dust-producing source regions and our ability to fingerprint their contribution to these export routes is surprisingly limited. Here we report new radiogenic isotope (Sr and Nd) data for sediment samples from known dust-producing substrates (dried river and lake beds), integrate them with published isotope data and weight them for dust source activation. We define three isotopically distinct preferential dust source areas (PSAs): a Western, a Central and an Eastern North African PSA. More data are needed, particularly from the Western PSA, but our results show a change in PSA dust source composition to more radiogenic Nd- and less radiogenic Sr-isotope values from west to east, in line with the overall decreasing age of the underlying bedrock. Our data reveal extreme isotopic heterogeneity within the Chadian region of the Central PSA, including an extremely distinctive geochemical fingerprint feeding the Bodélé Depression, the most active dust source on Earth. Our new analysis significantly improves the reliability by which windblown dust deposits can be geochemically fingerprinted to their distant source regions.

Multidecadal records of microplastic accumulation in the coastal sediments of the East China Sea

Microplastics are an emerging hazard in the marine environment, and considered to eventually sink into sediments. An investigation into the long-term variation of microplastic accumulation in sediment cores is essential for understanding the historical trend of this contamination and its response to human activities. In this study, the multidecadal changes of microplastic abundances in two sediment cores from the inner shelf of the East China Sea (ECS) were revealed by two methods, i.e., a visual enumeration method based on scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and a quantitative method based on microplastic-derived carbon (MPC) abundances. The features of microplastics were determined via SEM-EDS and micro-Fourier transform infrared spectroscopy (μ-FTIR). The results reveal a multidecadal increasing trend of microplastic accumulation in the coastal sediments of the ECS since the 1960s, which may be jointly governed by the release of plastic wastes and oceanographic dynamics. Meanwhile, the breakpoint of the exponential growth of microplastics in the ECS occurs in 2000 AD, which well matches the rapid increasing of plastic production and consumption in China. Further, based on the MPC contents in sediments, the influence of microplastics on the quantitative evaluation of carbon storage in the ECS has been examined for the first time, revealing an insignificant (<2% before 2014 AD) but potentially-increasing (6.8% by 2025 AD) contribution of microplastics to carbon burial. Our results may provide the important data for evaluating and mitigating the impact of microplastics on the marine environment.