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Abstract Soils are a principal global reservoir of mercury (Hg), a neurotoxic pollutant that is accumulating through anthropogenic emissions to the atmosphere and subsequent deposition to terrestrial ecosystems. The fate of Hg in global soils remains uncertain, however, particularly to what degree Hg is re-emitted back to the atmosphere as gaseous elemental mercury (GEM). Here we use fallout radionuclide (FRN) chronometry to directly measure Hg accumulation rates in soils. By comparing these rates with measured atmospheric fluxes in a mass balance approach, we show that representative Arctic, boreal, temperate, and tropical soils are quantitatively efficient at retaining anthropogenic Hg. Potential for significant GEM re-emission appears limited to a minority of coniferous soils, calling into question global models that assume strong re-emission of legacy Hg from soils. FRN chronometry poses a powerful tool to reconstruct terrestrial Hg accumulation across larger spatial scales than previously possible, while offering insights into the susceptibility of Hg mobilization from different soil environments. 

Nanoparticle-enhanced laser-induced breakdown spectroscopy and Tag-LIBS are two approaches that have been shown to significantly enhance LIBS sensitivity and specificity. In an effort to combine both of these approaches, we have initiated a study on the effect of the presence of Silver nanoparticle concentrations on Europium (Eu) and Ytterbium (Yb) LIBS signals. These elements are part of metal-loaded polymers conjugated to antibodies. We observe a signal enhancement of the emission lines of about 10 and 12 times for the Europium and Ytterbium lines. This study shows that Europium and Ytterbium are enhanced differently; Europium shows enhancement for both neutral and ionized species while the Ytterbium shows enhancement only for ionized species. Additionally, we found that NPs at 0.1 mg/mL and 0.05 mg/mL achieved maximum enhancement for Eu and Yb, respectively. Based on our findings, the temperature and electron density of Eu and Yb are not significantly different for NPs concentrations, but the total signal intensity is significantly higher for optimum NP concentrations for both Eu and Yb. 

Abstract Spatial complexity impacts the resilience of river ecosystems by mediating processes that control the sources and sinks of sediment and organic material. Using four independent geochemical tracers and three morphometric indices, we show that downstream spatial gradients in stream power (Ω) predict storage of material in the channels and margins and/or floodplains. A field test in a 48 km2 watershed demonstrates that reaches with downstream decreases in Ω coincide with wider floodplains and elevated inventories of 137Cs, 210Pbex (ex—excess), and organic matter in locations of the ~3 to 20 yr floodplain. In contrast, reaches with downstream increases in Ω coincide with narrower floodplains and decreased inventories of 137Cs, 210Pbex, and organic matter. The occurrence of in-channel bedrock exposures and the activity of short-lived 7Be in within-channel sediments also correlate with downstream Ω gradients, demonstrating a link, over both short and long time scales, between withinchannel processes and floodplain-forming processes. The combined geochemical and physical characteristics demonstrate the importance of downstream gradients in sediment transport, characterized by downstream changes in stream power rather than at-a-point stream power, in determining spatial complexity in carbon and sediment storage at intermediate scales (102 to 103 m) in river systems. 

Abstract Oxbow lakes are important stores for fine-grained sediment, which potentially makes them critical sinks for sediment-associated pollutants. We leverage an exhaustive public archive of coring data, supplemented by our data collection, to provide a quantitative assessment of the role of oxbows as off-channel sinks. We investigated loading trends of sediment-sorbed polychlorinated biphenyls (PCBs) within oxbows of the Housatonic River, an actively meandering river in western Massachusetts, USA. Our results reveal the efficiency of oxbows as sinks, with average PCB concentrations (14.8 ppm) that are nearly twice that of the surrounding floodplain (7.56 ppm). Even though the 5.83 km2 floodplain is the largest sink of PCB-laden material, storing as much as 14.1 t of PCBs or 2.42 g m−2, oxbows store more than 20% of all PCBs (3.63 t of PCBs or 11.2 g m−2) while making up just over 5% of the floodplain surface area. Nearly 85% of the oxbow storage of PCBs occurs within the first 50 m of floodplain, making clear the significance of regular oxbow production to the off-channel storage of sediment-associated pollutants. 

We applied luminescence dating to a suite of shorelines constructed by pluvial Lake Clover in northeastern Nevada, USA during the last glacial cycle. At its maximum extent, the lake covered 740 km2 with a mean depth of 16 m and a water volume of 13 km3. In the north-central sector of the lake basin, 10 obvious beach ridges extend from the highstand to the lowest shoreline over a horizontal distance of ~1.5 km, representing a lake area decrease of 35%. These ridges are primarily composed of sandy gravel and rise ~1.0 m above the alluvial fan surface on which they are superposed. Single grain luminescence dating of K-feldspar using the pIRIR SAR (post-infrared infrared single-aliquot regenerative dose) protocol, corroborated by SAR dating of quartz, indicates that the highstand shoreline was constructed ca. 16–17 ka during Heinrich Stadial I (Greenland Stadial 2, GS-2), matching 14C age control for this shoreline elsewhere in the basin. The lake regressed rapidly during the Bølling/Allerød (GI-1), before the rate of regression slowed during the Younger Dryas interval (GS-1). The lowest shoreline was constructed ca. 10 ka. Persistence of Lake Clover into the early Holocene may reflect enhanced monsoonal precipitation driven by the summer insolation maximum. 

High concentrations of barium (Ba), strontium (Sr) and radium (Ra) are present in both the liquid and suspended solid portions of wastewater produced from hydraulic fracturing. These high concentrations often require special treatment in which the solid and liquid portions are separated and then independently treated prior to disposal. The solids are typically disposed in landfills while the liquids are further treated, recycled for future hydraulic fracturing, or disposed via injection wells. Finding optimal treatment methods of both the solid and the liquid fractions requires a thorough understanding of potential Ra mobility from both the raw suspended solids and mineral precipitates formed during treatment. Using a sequential extraction procedure, we found that, without treatment, more than 50% of Ra-226 in the suspended solids was associated with soluble salts and readily exchangeable fractions. When the liquid portion of the wastewater was treated by mixing with acid mine drainage (AMD), which contained high sulfate concentrations, approximately 80–97% of the total Ra-226 in the mixture solution is found in the insoluble sulfate fraction of the precipitate. The activity of Ra-226 sequestered in the precipitated solid sulfate fractions is positively correlated with the Sr/Ba ratio of the wastewater-AMD solution. We discuss implications of these findings for effective long-term management of elevated radium in both solid and liquid wastes.