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1. Evidence for multi-decadal fuel buildup in a large California wildfire from smoke radiocarbon measurements

   https://doi.org/10.7280/D1498P  

   Odwuor, Audrey; Moreno, Alondra; Yañez, Cindy Y; Hopkins, Francesca M; Czimczik, Claudia I; Randerson, James T; Xu, Xiaomei (June 2023, Dryad)

   Over the past several decades, the annual burned area in California's Sierra Nevada mountains has increased considerably, with significant social, economic, and ecosystem impacts that provide motivation for understanding how the history of forest management influences the composition of fuels and emissions in wildfires. Here, we measured the carbon concentration and radiocarbon abundance (∆14C) of fire-emitted particulate matter from the KNP Complex Fire, which burned through several groves of giant sequoia trees in the southern Sierra Nevada mountains during California’s 2021 wildfire season. Over a 26-hour sampling period, we measured the concentration of fine airborne particulate matter (PM2.5) along with carbon monoxide (CO) and methane (CH4) dry air mole fractions using a ground-based mobile laboratory. Filter samples of PM2.5 were also collected and later analyzed for carbon concentration and ∆14C. Covariation of PM2.5, CO, and CH4 time series data confirmed that our PM2.5 samples were representative of wildfire emissions. Using a Keeling plot approach, we estimated that the mean ∆14C of PM2.5 was 111.5 ± 2.3‰ (n=12), which is considerably enriched relative to that of atmospheric carbon dioxide in the northern hemisphere in 2021 (-3.4 ± 1.4‰). By combining these ∆14C data with a steady-state one-box ecosystem model, we estimated that the mean age of fuels combusted in the KNP Complex Fire was 40 ± 6 years. This multi-decadal fuel age provides evidence for emissions from woody biomass, coarse woody debris, and larger-diameter fine fuels. The combustion of these larger-size fuel classes is consistent with independent field observations that indicate high fire intensity contributed to widespread giant sequoia mortality. With the expanded use of prescribed fires planned over the next decade in California to mitigate impacts of wildfires, our measurement approach has the potential to provide regionally-integrated estimates of the effectiveness of fuel treatment programs. 

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2. Phosphonate cycling supports methane and ethylene supersaturation in the phosphate-depleted western North Atlantic Ocean: Phosphonate cycling in the N. Atlantic

   https://doi.org/10.1002/lno.11463  

   Sosa, Oscar A.; Burrell, Timothy J.; Wilson, Samuel T.; Foreman, Rhea K.; Karl, David M.; Repeta, Daniel J. (May 2020, Limnology and Oceanography)

   In oligotrophic ocean regions, dissolved organic phosphorus (DOP) plays a prominent role as a source of phosphorus (P) to microorganisms. An important bioavailable component of DOP is phosphonates, organophosphorus compounds with a carbon-phosphorus (C-P) bond, which are ubiquitous in high molecular weight dissolved organic matter (HMWDOM). In addition to being a source of P, the degradation of phosphonates by the bacterial C-P lyase enzymatic pathway causes the release of trace hydrocarbon gases relevant to climate and atmospheric chemistry. In this study, we investigated the roles of phosphate and phosphonate cycling in the production of methane (CH4) and ethylene (C2H4) in the western North Atlantic Ocean, a region that features a transition in phosphate concentrations from coastal to open ocean waters. We observed an inverse relationship between phosphate and the saturation state of CH4 and C2H4 in the water column, and between phosphate and the relative abundance of the C-P lyase marker gene phnJ. In phosphate-depleted waters, methylphosphonate and 2-hydroxyethylphosphonate, the C-P lyase substrates that yield CH4 and C2H4, respectively, were readily degraded in proportions consistent with their abundance and bioavailability in HMWDOM and with the concentrations of CH4 and C2H4 in the water column. We conclude that phosphonate degradation through the C-P lyase pathway is an important source and a common production pathway of CH4 and C2H4 in the phosphatedepleted surface waters of the western North Atlantic Ocean and that phosphate concentration can be an important control on the saturation state of these gases in the upper ocean. 

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3. Dissolved CH4 concentrations and fluxes to the atmosphere from a tropical floodplain lake

   https://doi.org/doi.org/10.1007/s10533-020-00650-1  

   Barbosa, PM; Melack, JM; Amaral, JHF; MacIntyre, S; Kasper, D; Cortes, AC; Farjalla, FV; Forsberg, BR (January 2020, Biogeochemistry)

   Large uncertainties in estimates of methane (CH4) emissions from tropical inland waters reflect the paucity of information at appropriate temporal and spatial scales. CH4 concentrations, diffusive and ebullitive fluxes, and environmental parameters in contrasting aquatic habitats of Lake Janauaca´, an Amazon floodplain lake, measured for two years revealed patterns in temporal and spatial variability related to different aquatic habitats and environmental conditions. CH4 concentrations ranged from below detection to 96 lM, CH4 diffusive fluxes from below detection to 2342 lmol m-2 h-1, and CH4 ebullitive fluxes from 0 to 190 mmol m-2 d-1. Vegetated aquatic habitats had higher surface CH4 concentrations than open water habitats, and no significant differences in diffusive CH4 fluxes, likely due to higher k values measured in open water habitats. CH4 emissions were enhanced after a prolonged low water period, when the exposed sediments were colonized by herbaceous plants that decomposed after water levels rose, possibly fueling CH4 production. Statistical models indicated the importance of variables related to CH4 production (temperature, dissolved organic carbon) and consumption (dissolved nitrogen, oxygenated water column), as well as maximum depth. 

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4. Urban runoff drives titanium dioxide engineered particle concentrations in urban watersheds: field measurements

   https://doi.org/10.1039/d2en00826b  

   Nabi, Md Mahmudun; Wang, Jingjing; Erfani, Mahdi; Goharian, Erfan; Baalousha, Mohammed (March 2023, Environmental Science: Nano)

   Urban runoff is a significant source of pollutants, including incidental and engineered nanoparticles, to receiving surface waters. The aim of this study is to investigate the impact of urbanization on the concentrations of TiO 2 engineered particles in urban surface waters. The study area boundaries are limited to the Lower Saluda and Nicholas Creek-Broad River from upstream, and outlet of upper Congaree River in Columbia, South Carolina, United States from downstream. This sampling area captures a significant footprint of the urban area of the city of Columbia. Water samples were collected daily from four sites during two rain events. All samples were analyzed for total metal concentrations following acid digestion and for particle number concentration and elemental composition using single particle-inductively coupled plasma-time of flight-mass spectrometry (SP-ICP-TOF-MS). The Ti/Nb ratios in the Broad and Congaree River samples are generally higher than those of natural background ratios, indicating contamination of these two rivers with anthropogenic Ti-bearing particles. Clustering of multi-metal nanoparticles (mmNPs) demonstrated that Ti-bearing particles are distributed mainly among three clusters, FeTiMn, AlSiFe, and TiMnFe, which are typical of naturally occurring iron oxide, clay, and titanium oxide particles, indicating the absence of significant number of anthropogenic multi-element Ti-bearing particles. Thus, anthropogenic Ti-bearing particles are attributed to single-metal particles; that is pure TiO 2 particles. The total concentration of anthropogenic TiO 2 in the rivers was determined by mass balance calculation using bulk titanium concentration and increases in Ti/Nb above the natural background ratio. The concentration of anthropogenic TiO 2 increases following the order 0 to 24 μg L −1 in the Lower Saluda River <0 to 663 μg L −1 in the Broad River <43 to 1051 μg L −1 in Congaree River at Cayce <58 to 5050 μg L −1 in the Congaree River at Columbia. The concentration of anthropogenic TiO 2 increases with increases in urban runoff. The source of anthropogenic TiO 2 is attributed to diffuse urban runoff. This study demonstrates that diffuse urban runoff results in high concentrations of TiO 2 particles in urban surface waters during and following rainfall events which may pose increased risks to aquatic organisms during these episodic events. 

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5. Microplastic in riverine fish is connected to species traits

   https://doi.org/10.1038/s41598-018-29980-9  

   McNeish, R. E.; Kim, L. H.; Barrett, H. A.; Mason, S. A.; Kelly, J. J.; Hoellein, T. J. (December 2018, Scientific Reports)

   Abstract Microplastic is a contaminant of concern worldwide. Rivers are implicated as major pathways of microplastic transport to marine and lake ecosystems, and microplastic ingestion by freshwater biota is a risk associated with microplastic contamination, but there is little research on microplastic ecology within freshwater ecosystems. Microplastic uptake by fish is likely affected by environmental microplastic abundance and aspects of fish ecology, but these relationships have rarely been addressed. We measured the abundance and composition of microplastic in fish and surface waters from 3 major tributaries of Lake Michigan, USA. Microplastic was detected in fish and surface waters from all 3 sites, but there was no correlation between microplastic concentrations in fish and surface waters. Rather, there was a significant effect of functional feeding group on microplastic concentration in fish. Neogobius melanostomus (round goby, a zoobenthivore) had the highest concentration of gut microplastic (19 particles fish −1 ) compared to 10 other fish taxa measured, and had a positive linear relationship between body size and number of microplastic particles. Surface water microplastic concentrations were lowest in the most northern, forested watershed, and highest in the most southern, agriculturally dominated watershed. Results suggest microplastic pollution is common in river food webs and is connected to species feeding characteristics. Future research should focus on understanding the movement of microplastic from point-source and diffuse sources and into aquatic ecosystems, which will support pollution management efforts on inland waters. 

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