Pb Inventories Research Articles

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

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

Influence of the Keystone Grazer, Sesarma reticulatum, on the Hydrology and Organic Matter Cycling in Salt Marshes of the Southeastern USA

AbstractIn salt marshes of the Southeastern USA, purple marsh crabs (Sesarma reticulatum), hereafter Sesarma, aggregate in grazing and burrowing fronts at the heads of tidal creeks, accelerating creek incision into marsh platforms. We explored the effects of this keystone grazer and sediment engineer on salt marsh sediment accumulation, hydrology, and carbon (C) and nitrogen (N) turnover using radionuclides (210Pb and 7Be), total hydrolyzable amino acids (THAA), and C and N stable isotopes (δ13C and δ15N) in sediment from paired Sesarma-grazed and un-grazed creeks. Sesarma-grazed-creek sediments exhibited greater bioturbation and tidal inundation compared to sediments in un-grazed creeks, as indicated by larger 210Pb and 7Be inventories. Total organic carbon (TOC) to total nitrogen (TN) weight ratios (C:N) were higher and δ15N values were lower in grazed-creek sediments than in un-grazed-creek sediments, suggesting Sesarma remove and assimilate N in their tissues, and excrete N with lower δ15N values into sediments. In support of this inference, the percent total carbon (TC) and percent TOC declined by nearly half, percent TN decreased by ~ 80%, and the C:N ratio exhibited a ~ threefold increase between Sesarma fore-gut and hind-gut contents. An estimated 91% of Sesarma’s diet was derived from Spartina alterniflora, the region’s dominant salt marsh plant. We found that, as Sesarma grazing fronts progress across marsh landscapes, they enhance the decay of Spartina-derived organic matter and prolong marsh tidal inundation. These findings highlight the need to better account for the effects of keystone grazers and sediment engineers, like Sesarma, in estimates of the stability and size of blue C stores in coastal wetlands.

210Pb Deposition Distribution in the Northern Hemisphere Based on a Long-Range Atmospheric Transport and Deposition Model Calculation

This study delves into the long-term atmospheric transport and deposition of 210Pb in the Northern Hemisphere by using the atmospheric transport model HIRAT. The calculation for the four-year (2012–2015) period showed an average deposition flux of 13.0 Bq m−2 month−1 with significant seasonal variations characterized by higher deposition rates during summer and lower during winter. High deposition was found in the Northern Bay of Bengal and Bangladesh regions, Southern China, the Western Philippine Sea, the Eastern Japan Sea, the Northwestern Pacific region, the Eastern and Western coasts of North America, the Caribbean Sea, the Eastern Pacific region off of Central America, the Central Atlantic region between Central America and Africa, and the Northwestern Atlantic Ocean. Deposition patterns varied across latitudinal zones, with tropical areas experiencing the highest deposition and polar/subpolar zones the lowest. This study emphasized the impact of monsoons on the significantly large 210Pb deposition in the Japan Sea region. Furthermore, this study showed that the lower troposphere (0 to 3 km) dominates with about 53%, and the middle troposphere (3 to 6 km) and upper troposphere (above 6 km) also contribute significantly to the total 210Pb inventory with 37% and 10%, respectively. These findings provide essential insights into the characteristics of atmospheric transport and deposition of 210Pb, and their mechanisms.

Widespread Pb contamination in urban backyard soils for >100 years identified in soil cores constrained by 210Pb and 137Cs

Contaminated soil in urban residential areas is often overlooked as a source of childhood exposure to toxic levels of lead (Pb). We document mean Pb concentrations of 1200 ± 1000 mg/kg, three times the now outdated EPA soil hazard standard of 400 mg/kg, for 370 surface soils collected from 76 homes in the boroughs of Brooklyn and Manhattan of New York City. The mean Pb content of 250 ± 290 mg/kg Pb for 571 surface soils collected from tree pits and public parks was much lower. A subset of 22 surface samples analyzed by EPA Method 1340 extracted 86 ± 21 % (±1SD) of total soil Pb, indicating that it the Pb was highly bioavailable. To investigate the origin of backyard contamination, 49 cores were collected to an average depth of 30 cm from a subset of 27 homes. Twelve soil cores were analyzed for 210Pb and 137Cs to constrain processes that impact contaminant distribution and inventories (particle focusing, soil accumulation, loss, and mixing). Concentrations of Pb declined with depth in 60 % of the cores but usually did not reach background. Mean uncorrected Pb inventories of 340 ± 210 g/m2 Pb (mean ± 1SD, n = 12) were more than five times higher than the radionuclide corrected inventory of 57 g/m2 from Central Park soil cores. Average inventories of 210Pbxs (3.5 ± 0.9 kBq/m2) and 137Cs (0.9 ± 0.6 kBq/m2) corresponded to 71 ± 19 % and 50 ± 30 % of the predicted atmospheric inventories. Elevated Pb concentrations were found both in the fine (<1 mm) and coarse (>1 mm) fractions, the latter suggesting a local non-atmospheric source. This was confirmed by individual grains containing up to 6 % Pb and visible pieces of coal, bricks, and ash. Regardless of the source of contamination in backyard soils, systematic testing is needed to identify contaminated areas and reduce child exposure.

The Atmospheric Input of Dissolvable Pb Based on the Radioactive 210Pb Budget in the Equatorial Western Indian Ocean

To estimate the atmospheric deposition flux of 210Pb in the equatorial western Indian Ocean, we determined the dissolved (&lt;0.45 μm) and particulate 210Pb (&gt;0.45 μm) in the water column. In addition, we calculated the atmosphere-derived dissolvable Pb in seawater using the budget of 210Pb. The dissolved 210Pb and total 210Pb were higher in the surface layer and, overall, showed a decreasing distribution with depth. In particular, radioactive 210Pb activities in the surface-to-upper layer (&lt;1000 m depth) were 1.5 to 2 times higher than those reported in the 1970s (in nearby regions), suggesting that there has been additional 210Pb input in recent years. Based on the mass balance of the total 210Pb budget in the water column, we estimated the atmospheric deposition flux of 210Pb and the residence time of Pb for the first time in this region. The atmospheric deposition flux of 210Pb was estimated to be 0.1–0.5 dpm cm−2 yr−1, and these values agreed with the general global estimations for the major oceans (0.1–0.7 dpm cm−2 yr−1). Considering the residence time of 210Pb (29–41 years) in the water column (estimated from the 210Pb inventory and 234Th-based Pb scavenging rate), the atmospheric input of seawater-dissolvable Pb was quantified to be 0.08–0.1 nmol cm−2 yr−1, which is about eight times higher than the estimated input in the early 1990s in the region. Therefore, these results imply that radioactive 210Pb could be a useful tracer for quantifying Pb flux in seawater.

Behaviour of 137Cs and 210Pb inventory at three candidate reference sites for erosion study in the upstream Citarum watershed area, West Java, Indonesia

ABSTRACT The fallout radionuclide (FRN) analysis needs a reference site (RS) inventory to determine erosion and sedimentation in the study area. The investigated area is in the upstream Citarum watershed, West Java, Indonesia. Twenty-seven corings and 22 scrap samples have been prepared well and measured using HPGe gamma spectroscopy. The data below the minimum detectable activity (MDA) was found for 137Cs in RS6 cor 4 and 7 (<0.16 ± 0.08 Bq kg–1). MDA quantification implies that the inventory below MDA eroded greater than its maximum value (76.02 tons ha–1 a–1). The comparison 137Cs inventory in this study is lower than the three estimation models; however, the inventory of Mt. Papandayan is closer to the model. This study found the depth percentage of 20–30 cm using the proportion of 0–20 cm/0–30 cm ratio and predicted the portion of the existence of 137Cs and 210Pbex in the 20–30 cm in the bulk sample. The highest H0 (142.04 kg m–2), the relaxation length λ, and proportion of 20% of 137Cs in 20–30 cm depth imply that 137Cs inventory activity is possibly deeper than 30 cm. This study recommends that Mt. Papandayan could be the alternative RS for the upstream Citarum watershed.

DISTRIBUTIONS OF 210PB, 137CS AND PHYSICAL PROPERTIES IN BOTTOM SEDIMENTS OF WEST NANAO BAY, JAPAN.

This study revealed sedimentation processes based on 137Cs and 210Pb distribution, grain size and magnetic susceptibility of bottom sediments in West Nanao Bay, Japan. Surface sediment concentrations and inventories of these radionuclides were relatively low in the middle and eastern areas of the bay and high in the western area, which has several major river mouths, suggesting that the contribution of riverine input affected only the western area. In the middle and eastern areas, the level of 137Cs inventory was much lower than that of the soils, and the excess 210Pb inventory was at the same level or lower. These results indicate that removal effects are stronger than accumulation effects (riverine input) in these areas. The patterns of radionuclides were consistent with the results, that grain size was relatively large in the middle and eastern areas, implying strong current conditions, and that fine sediment accumulated less in these areas.

Heterogeneous tidal marsh soil organic carbon accumulation among and within temperate estuaries in Australia

The scarcity of data on tidal marsh soil accumulation rates (SAR) and soil organic carbon accumulation rates (CAR) globally precludes a comprehensive assessment of the role of tidal marshes in climate change mitigation and adaptation. Particularly few data exist from the southern hemisphere and for Australia in particular, which contains ~24% of globally recognised tidal marsh extent. Here we estimate SAR and CAR over the last 70 years using 210Pb-based geochronologies in temperate estuarine tidal marsh ecosystems in southern Western Australia (WA). Specifically, we assessed tidal marsh ecosystems situated in two geomorphic settings (marine vs. fluvial deltas) within 10 wave-dominated, barrier estuaries. Overall, average SAR (1.1 ± 0.3 mm yr−1) and CAR (32 ± 9 g m−2 yr−1) estimates were 5-fold lower than global mean estimates. Furthermore, we showed that hotspots of soil organic carbon stocks are not indicative of current hotspots for CAR. The lack of significant differences (P > 0.05) in SAR, CAR, and excess 210Pb inventories between marine and fluvial settings can be explained by the high heterogeneity among and within estuaries throughout the region. The relative stability of recent and Holocene relative sea-levels in WA likely explains the limited CAR potential in tidal marshes under relatively stable sea-level conditions. However, further research exploring interactions among biotic and abiotic factors within estuaries is required to shed more light on the small spatial-scale variability in SAR and CAR across tidal marsh ecosystems in WA and elsewhere. This study provides baseline estimates for the inclusion of tidal marshes in national carbon inventories, identifies hotspots for the development of blue carbon projects, and supports the use of site-specific assessments opposed to regional means for estimating blue carbon resources.

Biogenic matter content in marine sediments in the vicinity of the Antarctic Peninsula: Recent sedimentary conditions under a diverse environment of production, transport, selective preservation and accumulation

Burial fluxes of organic carbon and biogenic silica were determined in 17 continental shelf sediment cores collected from the northern Weddell Sea, the Bransfield Strait, and the southern Drake Passage. Coring sites included open-shelf stations as well as slope and glacial trough environments, with water depths varying from 220 to 760 m. Apparent 210Pb accumulation rates from these cores ranged from 0.04 g m−2y−1 to 0.21 g m−2y−1 (1 to 3 mm y−1), with organic carbon burial rates ranging from 3 to 15 g OC m−2y−1 and biogenic silica accumulation rates ranging from 15 to 126 g SiO2 m−2y−1. OC contents below the surface mixed layer ranged from 0.26 to 1.51 wt. % (avg. 0.64 %). Biogenic silica contents at depth ranged from 2.3 to 11.2 wt. % (avg. 7.5%), with an average bSi/OC ratio (wt. %/wt. %) at depth of 12. Annual OC primary production rates and biogenic silica production rates in the euphotic zone were estimated from satellite chlorophyll-a data in the literature and from a seasonal model for biogenic particle export from surface waters. Based on these biogeochemical data, preservation efficiencies (i.e., mass burial rate/water column production rate) were calculated for organic carbon and biogenic silica. These preservation efficiency values ranged from 2 to 18% (avg. 9%) for OC and 8 to 106% (avg. 54%) for bSi. These relatively high preservation efficiencies resulted from extensive lateral sediment focusing (210Pb Psi (Ψ) values [burial flux/water column production rate] ranging from 2 to 33; avg. of 16), cold bottom water temperatures (2 to −2°C), and relatively high biogenic Si and OC production rates in the euphotic zone. The enhanced preservation efficiency for bSi relative to OC (i.e., 54% vs. 9%) in these Antarctic settings is consistent with the change in the phytoplankton bSi/OC (wt. %/wt. %) value of 2 for this area to the burial bSi/OC value of 12. Excess 210Pb activities in surface sediments varied from 4 to 47 dpm g−1. The surface mixed layer in the seabed varied in thickness from 0 to 4 cm. The penetration of excess 210Pb into these Antarctic Peninsula sediments varied from 6 to 28 cm (avg. 18 cm). The inventory of excess 210Pb in the seabed varied from 13 to 230 dpm cm−2 (avg. 110 dpm cm−2). Although 210Pb was the only radionuclide measured in this study, “apparent” 210Pb sediment accumulation rate (SAR) values from these 17 cores (assuming that deep bioturbation is negligible) are believed to be accurate SAR values because of good agreement between 210Pb and 14C chronologies from nearby cores reported in the literature.

210Po-210Pb distribution and carbon export in the northern Gulf of Mexico continental slope

An important pathway for CO2 sinking in the ocean is via the “biological pump”, driven by the production of particulate organic carbon (POC) in the surface ocean and its subsequent export to the deeper ocean via vertical settling. Here we examine the vertical fluxes of POC in the continental slope of the northern Gulf of Mexico by utilizing the short-lived radionuclide pair 210Po - 210Pb. The total activities of 210Po and 210Pb ranged from 2.5 ± 0.35 to 16.52 ± 1.98 dpm 100 L-1 and from 3.47 ± 0.45 to 24.49 ± 3.42 dpm 100 L-1 respectively with the exception of higher activities of 210Po (87.36 ± 11.38 dpm 100 L-1) and 210Pb (32.25 ± 4.35 dpm 100 L-1) from the near bottom water in the hypersaline anoxic Orca basin. In the upper 150 m of the water column, the inventories of 210Pb were consistently greater than those of 210Po while the total overall water column inventories of 210Po and 210Pb were found to be near equilibrium. The 210Po fluxes varied between 9.8 ± 6.34 dpm m-2 d-1 and 30.7 ± 12.06 dpm m-2 d-1 with corresponding POC fluxes between 8.6 mg C m-2 d-1 and 37.65 mg C m-2 d-1. The fluxes showed a general decreasing trend further offshore, closely following a similar trend in net primary productivity across the slope. The export efficiency ratios “e-ratios” of the biological pump over this slope region was found to vary between 0.027 and 0.11 averaging at 0.05 ± 0.01, which is low. The 210Po based and the model-based e-ratio estimates were different but within the range of previous estimates.

Refined spatio-temporal emission assessment of Hg, As, Cd, Cr and Pb from Chinese coal-fired industrial boilers

Coal-fired industrial boilers (CFIBs) are a significant source of trace metals (TMs) emissions, due to its large number and widespread industry application. In this study, a highly resolved of county-based atmospheric emission inventory of Hg, As, Cd, Cr and Pb for Chinese CFIBs in 2017 is established firstly based on integrated source-specific information of both activity level and air pollution control devices (APCDs) from ~61,000 CFIBs in mainland China. Our results estimated that the total emissions of Hg, As, Cd, Cr and Pb from national CFIBs in 2017 were about 25.46, 115.33, 7.04, 371.40, and 589.76 t, respectively. Hg0 was the majority species of atmospheric Hg, accounting for 71.5% of the total Hg emission. The peak emission intensities of five TMs were mainly concentrated in northern and eastern region of China due to its large demand of coal consumption for winter heating, broad economic activity, as well as high population density. Monthly emission characteristics of TMs exhibited seasonal peak. The overall uncertainties of the newly updated emission inventory were estimated at the ranges of −42.0%–45.5%. Generally, TMs emissions from Chinese CFIBs were effectively controlled through implementing energy substitution, APCDs upgrading, and ultra-low emission (ULE) retrofitting in different regions of China, which contributed to 18.8%–29.4% of five TMs emission reductions. We believe that our highly resolved county-level emission inventory will be comprehensively explored the current tempo-spatial emission characteristics of atmospheric TMs from Chinese CFIBs and the forecast results will be useful for developing effective emission control programs for policy makers in the county levels and improving the regional air quality in the future.

Seawater Pb concentration and isotopic composition response to daily time scale dust storms in the Gulf of Aqaba, Red Sea

Lead (Pb) is a primary tracer of natural and anthropogenic processes in the marine environment, with atmospheric deposition being one of its main sources to open ocean surface waters. However, the impact of short-term (daily) dust storms on the oceanic water column is poorly constrained due to the typically low sampling temporal resolution in deep open ocean settings. The Gulf of Aqaba (GoA), northern Red Sea, is a deep oligotrophic water body surrounded by hyper-arid deserts with no major tributaries, and hence its surface waters receive limited terrigenous input, except from settling atmospheric dust particles. The GoA is highly accessible and therefore provides the opportunity to study the dynamics of seawater Pb chemistry across abrupt and short periods of enhanced atmospheric deposition.Here, we report a highly resolved time series of vertical profiles of dissolved Pb concentrations and isotopic compositions across daily-timescale dust storm events that occurred during 2018. GoA Pb concentrations range between 19 and 85 pmol kg−1, and the isotopic compositions of 206Pb/207Pb and 208Pb/206Pb are in the range of 1.163–1.190 and 2.062–2.093, respectively. These compositions reflect a mixture of multiple end members: seafloor sediments and open Red Sea waters, which modulate the long-term deep-water composition of GoA Pb, and settling aerosols, which shift the seawater composition towards anthropogenic values. The results show that dust storms impose strong perturbations of seawater compositions towards the anthropogenic aerosols end member, inducing increases of up to 54% in the Pb inventory in the upper water column. We propose a short-term dissolution-scavenging mechanism, whereby upon dust-seawater impact, the majority of the aerosol's soluble anthropogenic phases rapidly dissolve. The peak in the aerosol derived isotopic shift in the mixed layer is reached after 3–4 days. Simultaneously, Pb is re-adsorbed onto the sinking dust mineral particulates. Post dust storm Pb leaching and scavenging rates are modeled, yielding quantitative constraints on the connection between increasing dust loads and seawater Pb concentrations and isotopic compositions. Our findings demonstrate the short-term variable Pb response to dust storms and should be applied when interpreting open ocean surface water Pb patterns.

Budget and fate of sedimentary trace metals in the Eastern China marginal seas

To achieve a better understanding of global biogeochemical cycle and budget of trace metals (TM) in the world's ocean, a comprehensive study of the level, fate and burial flux of TM in surface sediment from the Eastern China Marginal Seas (ECMS) was conducted. The results indicated that Pb, Zn, Cu, and Cr were highly concentrated in mud deposits and primarily controlled by the natural processes of sediment composition and regional hydrodynamics, whereas As had a close association with Mn and was mainly derived from anthropogenic activity. The sediment mass inventories of Pb, Zn, Cu, Cr, and As in the ECMS (~220,780 km2) were estimated to be 28,324, 92,192, 23,434, 94,560 and 11,968 t/yr, respectively. A mass budget model revealed that riverine runoff, coastal erosion input and atmospheric deposition (dry and wet) constituted 62–76%, 15–37% and 2–9% of the total Pb, Zn and Cr influxes, respectively, while more than 4,690 t of Cu annually outflowed to the open seas to balance the budget. More importantly, we found that the sum of the estimates of these contributions tended to fall short of the calculated depositional fluxes of As, implying that anthropogenic activities probably have altered the natural geochemical cycle of As. Our results suggest that the ECMS constitutes a major final repository of TM at the Asia scale; however, the burial fluxes of trace metals are expected to decrease due to enhanced environmental investments by the Chinese government and decreased suspended particulate TM loads from the Chinese major rivers.

Reference Inventory of 210Pb in Soils of Chinese Mainland

Naturally occurring fallout 210Pb is strongly adsorbed by soils and has been widely used as a tracer to soil erosion and deposited sediments in various sedimentary environments. The determination of reference inventory is the premise and basis of soil erosion research using this technique,it is directly related to the accuracy of erosion rate calculation. This paper starting reports from the selection of 210Pb reference inventory sampling points, the distribution of 210Pb reference inventory in Chinese mainland is summarized. It is pointed out that the reference inventory is mainly affected by the location of land and sea, climate, topography and other factors.

The distribution and transport of lead over two centuries as recorded by lake sediments from northeastern North America

We evaluated anthropogenic Pb deposition along a west-east transect from the Adirondack Mountains, New York, USA (ADIR) region, the Vermont-New Hampshire-Maine, USA (VT-NH-ME) region, and Nova Scotia, Canada (NS) region using 47 210Pb-dated lake sediment records. We used focus-corrected Pb inventories to evaluate cumulative deposition and breakpoint analysis to evaluate possible differences in timings among regions. Peak Pb concentrations decreased from west to east (ADIR region: 52–378 mg kg−1, VT-NH-ME region: 54–253 mg kg−1, NS: 38–140 mg kg−1). Cumulative deposition of anthropogenic Pb also decreased from west to east (ADIR region: 791–1344 mg m−2, VT-NH-ME region: 209–1206 mg m−2, NS: 52–421 mg m−2). The initiation of anthropogenic Pb deposition occurred progressively later along the same transect (ADIR region: 1869–1900, VT-NH-ME region: 1874–1905, NS region: 1901–1930). Previous lead isotope studies suggest that eastern Canadian Pb deposition over the past ~150 years has originated from a mix of both Canadian and U.S. sources. The results of this study indicate that anthropogenic Pb from sources west of the ADIR region were deposited in lesser amounts from west to east and/or Pb sources reflect less population density from west to east. The timing of the initiation of anthropogenic Pb deposition in the NS region suggests that Pb from gasoline may be an important source in this region.

Mixing depths and sediment accumulation rates on an arid tropical shelf based on fine-fraction 210Pb analysis

Continental shelves in arid tropical settings present particular challenges to 210Pb-based analysis of sedimentation rates and surface mixing owing to the combination of coarse sediment, deep and year-round bioturbation, and lower atmospheric flux of 210Pb. The modern continental shelf at the northern terminus of the hyper-arid Gulf of Eilat/Aqaba (GOE) receives flood-runoff of siliciclastics, producing a mixed seabed with ~20% carbonate that is dominated by larger benthic foraminifera and mollusks. Focusing analysis on only the fine-fraction of deep-penetrating cores (≥70 cm) from 15 to 40 m water depths yields reliable 210Pb profiles, in contrast to analysis of bulk sediment (graphical abstract). Sedimentation rates increase offshore five-fold, from 0.01–0.04 cm/y in 15 m water depth to 0.21–0.27 cm/y in 30–40 m depths, reflecting offshore redistribution of flood-delivered siliciclastic sediments away from the wadi mouth, a result also supported by an offshore increase in the inventory of excess 210Pb. In contrast, the thickness of the surface mixed layer (SML) decreases from >30 cm to ~20 cm with proximity to anthropogenic stressors (channelized flood runoff, historic release of sewage and operation of fish cages), which we attribute to the suppression of macrobenthic burrowers. The rate of sedimentation on the Gulf shelf –away from dynamic bypassing in the 15 m shoreface – is comparable to other tropical carbonate shelves rich in large benthic foraminifera, and is higher than rates documented on the adjacent slope, increasing confidence in this approach to 210Pb analysis using only the fine fraction. Analysis of the fine fraction rather than bulk sediment would be a useful adjustment to 210Pb methodology in any area with scarce fine-grained sediment.

Evaluating the historical sedimentation patterns in two different Mediterranean deep environments (Sardinia and Sicily Channels)

The sediment accumulation rate in the Sardinia and Sicily channels in the central part of the Mediterranean Sea was studied by using short-lived radionuclides (210Pb and 137Cs) in two deep sediment cores. Different sedimentation regimes were identified indicating substantial differences in accumulation rates and historical patterns. The 210Pb-derived mean accumulation rate found in the Strait of Sardinia was 0.05 g.cm-2.y-1, lower than that in Sicily Channel (0.1 g.cm-2.y-1) suggesting an inverse correlation with water depth. Excess 210Pb inventories were 24 ± 1 and 6.0 ± 0.4 kBq.m-2, while the fluxes to the sediment were 745 ± 31 and 188 ± 11 Bq.m-2.y-1 in Sicily and Sardinia channels, respectively. 137Cs failed to use for the validation of the established chronologies, while its inventories found 450 Bq.m-2 and 355 Bq.m-2 in the Sicily and Sardinia channel, respectively.

The Critical Role of Bioturbation for Particle Dynamics, Priming Potential, and Organic C Remineralization in Marine Sediments: Local and Basin Scales

Bioturbation promotes priming and total remineralization of sedimentary organic matter (Corg) in multiple ways. A primary local mode is the injection of reactive Corg from the water column, surface sediment, and mucus secretions into deposits. During feeding, burrowing, and construction activities by benthic fauna, labile substrates are brought into close association with more refractory material over a wide range of time scales, geometries, and depths, enhancing decomposition of the less reactive components (priming). One measure of these local interactions is the particle mixing coefficient, DB, which can be estimated from the averaged penetration of particle-reactive radionuclides into deposits. Patterns of DB in Long Island Sound, an estuarine system with well-defined sources of naturally-occurring radionuclides, show consistent positive correlations between DB and total inventories of 234Th (t1/2 = 24 d) and 210Pb (t1/2 = 22 yr) at local and basin scales. These correlations, maintained seasonally in the case of 234Th, demonstrate not only the penetration of plankton-derived, reactive Corg into deeper regions of deposits during bioturbation over monthly (~ 5 – 10 cm) to decadal timescales (~ 20 – 100 cm) but also the enhanced capture of labile substrates from the water column across basin scales into bioturbated patches as the intensity of reworking increases. In Long Island Sound, sedimentary Chl-a distributions and benthic nutrient regeneration (e.g., NH4+ fluxes) reflect these particle exchange processes. Basin and regional scale capture of labile substrates into bioturbated deposits can be generally demonstrated, for example, along the highly productive Cape Hatteras continental margin. Thus, total and net remineralization necessarily increase with the biogenic enhancement of the quantity of labile particulate substrate in deposits. This capture, intermixing, and close association of reactive and refractory substrates (reductant mixing), and thus the optimization of priming potential, represent important, often overlooked, pathways by which bioturbation generates biogeochemical conditions conducive to maximum efficiency of remineralization.

Comparison of the scavenging intensity, remineralization and residence time of 210Po and 210Pb at key zones (biotic, sediment-water and hydrothermal) along the East Pacific GEOTRACES transect

The contrasting geochemical behavior of two long-lived progeny of 222Rn (daughter product of 226Ra), 210Po and 210Pb, provide valuable insights on the extent of recycling of biogenic particulate matter and their preferential removal from the water column. We collected and analyzed 135 water samples from six vertical profiles for 210Po and 210Pb as well as a suite of aerosol samples for 210Pb along the US GEOTRACES East Pacific Zonal Transect (GP16). Calculated atmospheric depositional flux of 210Pb from the measured 210Pb activity in aerosols exhibits an overall decrease from east to west along the cruise track. The inventories of 210Po and 210Pb and residence times in key zones that include biotic (upper 60 and 300 m), sediment-water (bottom 300 m) and volcanogenic (bottom 300 m at the East Pacific Rise (EPR) station) were calculated and compared. A comparison of inventories of 210Po and 210Pb in 500-m layers (maximum penetration depth of atmospherically-delivered 210Pb was reported to be upper < 500 m) for all stations indicates clearly discernable disequilibrium between total (= particulate + dissolved) 210Po and total 210Pb, with 210Po/210Pb activity ratios less than 0.95 or greater than 1.05, in 63% (26 out of 41) of the 500-m layers. The observed large variations in the 210Po/210Pb activity ratio (AR) in 500 m layers (range: 0.79–1.32) of the whole water column is by far the largest disequilibrium in open ocean water reported when integrated over 500 m depths. However, the whole water-column 210Po/210Pb AR, calculated from the inventory of total 210Po and total 210Pb, varied between 0.97 ± 0.02 and 1.06 ± 0.02 (except in the EPR site, with 1.09 ± 0.02), indicating at or near-equilibrium for the whole water column in all five deep water stations. This contrasts with earlier claims of gross disequilibrium between 210Po and 210Pb in water depths >1000 m and we contend that most of these observations do not take in to account the variable extent of redistribution of 210Po and 210Pb in the water column due to remineralization of biogenic particulate matter and preferential scavenging of 210Po over 210Pb. We observed intense scavenging of 210Po and 210Pb in the bottom 300 m of the EPR site (attributed to discharge of high amounts of dissolved and colloidal Fe and Mn from the hydrothermal vent) and lower scavenging in the upper and bottom 300 m at the most oligotrophic station (ST-36), indicating that the scavenging intensities in bottom waters are likely coupled to the surface waters.

Terrestrial Ecotoxic Impacts Stemming from Emissions of Cd, Cu, Ni, Pb and Zn from Manure: A Spatially Differentiated Assessment in Europe

Metallic elements present in livestock manure as co-contaminants have the potential to cause terrestrial ecotoxic impacts when the manure is used as fertilizer on agricultural soils. The magnitude of this impact at country scale in Europe has, to date, not been quantified. Here, we address this knowledge gap by combining recently developed national emission inventories of Cd, Cu, Ni, Pb and Zn releases from manure with metal- and soil-specific comparative toxicity potentials (CTP) calculated for cropland grid cells at 1 × 1 km resolution for 33 European countries. The CTPs account for speciation in environmental fate, exposure and effects, including reduction in the solid-phase reactivity of a metal when it is associated with organic carbon present in the manure. Given the scarcity of inventory data at sub-national level, it was assumed that each unit area of cropland within a given country has the same probability to receive manure. The resulting CTPs span a range of several orders of magnitude reflecting the influence of soil type and properties on the speciation patterns and resulting CTP values. However, when combined with the use of manure in each European country, the resulting national impact scores were mainly explained by the total mass input of metal released to soil rather than by geographic variability in the CTP values. Simple linear regression is then sufficient to predict terrestrial ecotoxic impacts from input mass. Although some changes in ranking of metals and countries were observed, both mass- and impact-based comparisons between metals agreed that Zn and Cu are dominant contributors to total impacts, and that top contributing countries were those emitting the largest amounts of metals. Our findings show that spatially differentiated impact assessment is important for ranking of countries when differences in national emission inventories between countries are smaller than a factor of two (Ni), a factor of three (Cd, Cu, Zn) or a factor of four (Pb). In other cases, ranking of countries can be based on national emission inventories.