fluctuations in arsenic concentrations in shallow groundwater. Monitoring of water levels and stable carbon isotope compositions in groundwater from different depths and canal water over a year indicated that terrestrial DOM was the dominant source, accounting for 54.2% - 85.5% of groundwater DOM. Electrospray ionization combined with ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry revealed that canal water infiltration transferred aliphatic, tannin-like and leached aromatic DOM from sediments into groundwater. Therefore, groundwater recharge through irrigation using canal water not only inputs terrestrial DOM, but also accelerates the release of sedimentary DOM. Furthermore, carboxylic-rich alicyclic molecule (CRAM)-like DOM that is derived from biomolecules has the highest proportion (60.1% - 65.5%) among the identified DOM structures. And, it might be reused in biochemical processes during arsenic mobilization, suggesting a third source of groundwater DOM in addition to canal water and sediments. The findings in this study advance the understanding on transport processes and molecular properties of DOM in high arsenic groundwater under extensive anthropogenic influences.

Yu, X., Millet, D.B., Wells, K.C., Griffis, T.J., Chen, X., Baker, J.M., Conley, S.A., Smith, M.L., Gvakharia, A., Kort, E.A., Plant, G., Wood, J.D., 2020. Top-down constraints on methane point source emissions from animal agriculture and waste based on new airborne measurements in the U.S. Upper Midwest. Journal of Geophysical Research: Biogeosciences 125, e2019JG005429.

https://doi.org/10.1029/2019JG005429 Abstract: Agriculture and waste are thought to account for half or more of the U.S. anthropogenic methane source. However, current bottom-up inventories contain inherent uncertainties from extrapolating limited in situ measurements to larger scales. Here, we employ new airborne methane measurements over the U.S. Corn Belt and Upper Midwest, among the most intensive agricultural regions in the world, to quantify emissions from an array of key agriculture and waste point sources. Nine of the largest concentrated animal feeding operations in the region and two sugar processing plants were measured, with multiple revisits during summer (August 2017), winter (January 2018), and spring (May -June 2018). We compare the top-down fluxes with state-of-science bottom-up estimates informed by U.S. Environmental Protection Agency methodology and site-level animal population and management practices. Top-down point source emissions are consistent with bottom-up estimates for beef concentrated animal feeding operations but moderately lower for dairies (by 37% on average) and significantly lower for sugar plants (by 80% on average). Swine facility results are more variable. The assumed bottom-up seasonality for manure methane emissions is not apparent in the aircraft measureme nts, which may be due to on-site management factors that are difficult to capture accurately in national-scale inventories. If not properly accounted for, such seasonal disparities could lead to source misattribution in top- down assessments of methane fluxes. Plain Language Summary: Key agricultural methane sources are quantified using new airborne measurements in the U.S. Corn Belt and Upper Midwest. Measurements spanned multiple seasons and targeted nine of the largest concentrated animal feeding operations in the region along with two sugar processing plants. Compared with bottom-up estimates informed by U.S. Environmental Protection Agency methodology and site-level animal and management data, top-down fluxes agree well with bottom-up estimates for beef but are lower for dairies and sugar plants and suggest a possible mismatch in the timing of emissions.

Yu, Y., Li, G., Wu, D., Liu, J., Chen, J., Hu, N., Wang, H., Wang, P., Wu, Y., 2020. Thiol radical-based chemical isotope labelling for sterols quantitation through high performance liquid chromatography-tandem mass spectrometry analysis. Analytica Chimica Acta 1097, 110-119.

http://www.sciencedirect.com/science/article/pii/S0003267019313509 Enlightened by the high specificity and reactivity of thiol radical toward allyl, here, we first established a rapid thiol radical-based chemical isotope-labelling (CIL) strategy coupled with high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) analysis for the quantitative profiling of sterols. In this strategy, N-(4-(carbazole-9-yl)-phenyl)-N-maleimide labelled derivative of ethylenedithiol (NCPM-d -SH) 0 and its deuterated analogue NCPM-d -SH were employed as a novel pair of CIL reagents to efficiently label 2 sterols. Under lighting condition, the thiol radical obtained from NCPM-d /d -SH attacks one allyl hydrogen in 0 2