Flux and Seasonality of Dissolved Organic Matter From the Northern Dvina (Severnaya Dvina) River, Russia

Pan‐Arctic riverine dissolved organic carbon (DOC) fluxes represent a major transfer of carbon from land‐to‐ocean, and past scaling estimates have been predominantly derived from the six major Arctic rivers. However, smaller watersheds are constrained to northern high‐latitude regions and, particularly with respect to the Eurasian Arctic, have received little attention. In this study, we evaluated the concentration of DOC and composition of dissolved organic matter (DOM) via optical parameters, biomarkers (lignin phenols), and ultrahigh resolution mass spectrometry in the Northern Dvina River (a midsized high‐latitude constrained river). Elevated DOC, lignin concentrations, and aromatic DOM indicators were observed throughout the year in comparison to the major Arctic rivers with seasonality exhibiting a clear spring freshet and also some years a secondary pulse in the autumn concurrent with the onset of freezing. Chromophoric DOM absorbance at a350 was strongly correlated to DOC and lignin across the hydrograph; however, the relationships did not fit previous models derived from the six major Arctic rivers. Updated DOC and lignin fluxes were derived for the pan‐Arctic watershed by scaling from the Northern Dvina resulting in increased DOC and lignin fluxes (50 Tg yr−1 and 216 Gg yr−1, respectively) compared to past estimates. This leads to a reduction in the residence time for terrestrial carbon in the Arctic Ocean (0.5 to 1.8 years). These findings suggest that constrained northern high‐latitude rivers are underrepresented in models of fluxes based from the six largest Arctic rivers with important ramifications for the export and fate of terrestrial carbon in the Arctic Ocean

Glacier meltwater and monsoon precipitation drive Upper Ganges Basin dissolved organic matter composition

Author Posting. © The Author(s), 2019. This is the author's version of the work. It is posted here by permission of Elsevier Ltd. for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 244 (2019): 216-228, doi:10.1016/j.gca.2018.10.012.Mountain glaciers store dissolved organic carbon (DOC) that can be exported to river networks and subsequently respired to CO2. Despite this potential importance within the global carbon cycle, the seasonal variability and downstream transport of glacier-derived DOC in mountainous river basins remains largely unknown. To provide novel insight, here we present DOC concentrations and molecular-level dissolved organic matter (DOM) compositions from 22 nested, glaciated catchments (1.4 – 81.8 % glacier cover by area) in the Upper Ganges Basin, Western Himalaya over the course of the Indian summer monsoon (ISM) in 2014. Aliphatic and peptide-like compounds were abundant in glaciated headwaters but were overprinted by soil-derived phenolic, polyphenolic and condensed aromatic material as DOC concentrations increase moving downstream. Across the basin, DOC concentrations and soil-derived compound class contributions decreased sharply from pre- to post-ISM, implying increased relative contribution of glaciated headwater signals as the monsoon progresses. Incubation experiments further revealed a strong compositional control on the fraction of bioavailable DOC (BDOC), with glacier-derived DOC exhibiting the highest bioavailability. We hypothesize that short-term (i.e. in the coming decades) increases in glacier melt flux driven by climate change will further bias exported DOM toward an aliphatic-rich, bioavailable signal, especially during the ISM and post-ISM seasons. In contrast, eventual decreases in glacier melt flux due to mass loss will likely lead to more a soil-like DOM composition and lower bioavailability of exported DOC in the long term.We thank Britta Voss (WHOI) for assisting with sample collection; Travis Drake (FSU), and Ekaterina Bulygina (Woods Hole Research Center) for laboratory assistance; and the NHMFL ICR user program (NSF-DMR-1157490) for aiding in data acquisition and analysis. This study was partly supported by NSF-DEB-1145932 to R.G.M.S. J.D.H. was partially supported by the NSF Graduate Research Fellowship Program under grant number 2012126152, with additional support in the form of travel grants awarded by the MIT Houghten Fund and NHMFL. All data used in this study are available in the Supporting Information Tables S1 and S2

An international laboratory comparison of dissolved organic matter composition by high resolution mass spectrometry: Are we getting the same answer?

High-resolution mass spectrometry (HRMS) has become a vital tool for dissolved organic matter (DOM) characterization. The upward trend in HRMS analysis of DOM presents challenges in data comparison and interpretation among laboratories operating instruments with differing performance and user operating conditions. It is therefore essential that the community establishes metric ranges and compositional trends for data comparison with reference samples so that data can be robustly compared among research groups. To this end, four identically prepared DOM samples were each measured by 16 laboratories, using 17 commercially purchased instruments, using positive-ion and negative-ion mode electrospray ionization (ESI) HRMS analyses. The instruments identified ~1000 common ions in both negative- and positive-ion modes over a wide range of m/z values and chemical space, as determined by van Krevelen diagrams. Calculated metrics of abundance-weighted average indices (H/C, O/C, aromaticity, and m/z) of the commonly detected ions showed that hydrogen saturation and aromaticity were consistent for each reference sample across the instruments, while average mass and oxygenation were more affected by differences in instrument type and settings. In this paper we present 32 metric values for future benchmarking. The metric values were obtained for the four different parameters from four samples in two ionization modes and can be used in future work to evaluate the performance of HRMS instruments

Comparing individual-based approaches to modelling the self-organization of multicellular tissues.

The coordinated behaviour of populations of cells plays a central role in tissue growth and renewal. Cells react to their microenvironment by modulating processes such as movement, growth and proliferation, and signalling. Alongside experimental studies, computational models offer a useful means by which to investigate these processes. To this end a variety of cell-based modelling approaches have been developed, ranging from lattice-based cellular automata to lattice-free models that treat cells as point-like particles or extended shapes. However, it remains unclear how these approaches compare when applied to the same biological problem, and what differences in behaviour are due to different model assumptions and abstractions. Here, we exploit the availability of an implementation of five popular cell-based modelling approaches within a consistent computational framework, Chaste (http://www.cs.ox.ac.uk/chaste). This framework allows one to easily change constitutive assumptions within these models. In each case we provide full details of all technical aspects of our model implementations. We compare model implementations using four case studies, chosen to reflect the key cellular processes of proliferation, adhesion, and short- and long-range signalling. These case studies demonstrate the applicability of each model and provide a guide for model usage

Stream dissolved organic matter in permafrost regions shows surprising compositional similarities but negative priming and nutrient effects

Permafrost degradation is delivering bioavailable dissolved organic matter (DOM) and inorganic nutrients to surface water networks. While these permafrost subsidies represent a small portion of total fluvial DOM and nutrient fluxes, they could influence food webs and net ecosystem carbon balance via priming or nutrient effects that destabilize background DOM. We investigated how addition of biolabile carbon (acetate) and inorganic nutrients (nitrogen and phosphorus) affected DOM decomposition with 28-day incubations. We incubated late-summer stream water from 23 locations nested in seven northern or high-altitude regions in Asia, Europe, and North America. DOM loss ranged from 3% to 52%, showing a variety of longitudinal patterns within stream networks. DOM optical properties varied widely, but DOM showed compositional similarity based on Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis. Addition of acetate and nutrients decreased bulk DOM mineralization (i.e., negative priming), with more negative effects on biodegradable DOM but neutral or positive effects on stable DOM. Unexpectedly, acetate and nutrients triggered breakdown of colored DOM (CDOM), with median decreases of 1.6% in the control and 22% in the amended treatment. Additionally, the uptake of added acetate was strongly limited by nutrient availability across sites. These findings suggest that biolabile DOM and nutrients released from degrading permafrost may decrease background DOM mineralization but alter stoichiometry and light conditions in receiving waterbodies. We conclude that priming and nutrient effects are coupled in northern aquatic ecosystems and that quantifying two-way interactions between DOM properties and environmental conditions could resolve conflicting observations about the drivers of DOM in permafrost zone waterways

Design and baseline characteristics of the finerenone in reducing cardiovascular mortality and morbidity in diabetic kidney disease trial

Background: Among people with diabetes, those with kidney disease have exceptionally high rates of cardiovascular (CV) morbidity and mortality and progression of their underlying kidney disease. Finerenone is a novel, nonsteroidal, selective mineralocorticoid receptor antagonist that has shown to reduce albuminuria in type 2 diabetes (T2D) patients with chronic kidney disease (CKD) while revealing only a low risk of hyperkalemia. However, the effect of finerenone on CV and renal outcomes has not yet been investigated in long-term trials. Patients and Methods: The Finerenone in Reducing CV Mortality and Morbidity in Diabetic Kidney Disease (FIGARO-DKD) trial aims to assess the efficacy and safety of finerenone compared to placebo at reducing clinically important CV and renal outcomes in T2D patients with CKD. FIGARO-DKD is a randomized, double-blind, placebo-controlled, parallel-group, event-driven trial running in 47 countries with an expected duration of approximately 6 years. FIGARO-DKD randomized 7,437 patients with an estimated glomerular filtration rate >= 25 mL/min/1.73 m(2) and albuminuria (urinary albumin-to-creatinine ratio >= 30 to <= 5,000 mg/g). The study has at least 90% power to detect a 20% reduction in the risk of the primary outcome (overall two-sided significance level alpha = 0.05), the composite of time to first occurrence of CV death, nonfatal myocardial infarction, nonfatal stroke, or hospitalization for heart failure. Conclusions: FIGARO-DKD will determine whether an optimally treated cohort of T2D patients with CKD at high risk of CV and renal events will experience cardiorenal benefits with the addition of finerenone to their treatment regimen. Trial Registration: EudraCT number: 2015-000950-39; ClinicalTrials.gov identifier: NCT02545049

Photodissolution of charcoal and fire-impacted soil as a potential source of dissolved black carbon in aquatic environments

This study investigates the effect of photodissolution on the production of dissolved black carbon (DBC) from particulate charcoal and a fire-impacted soil. A soil sample and a char sample were collected within the burn vicinity of the 2012 Cache La Poudre River wildfire and irradiated in deionized water with artificial sunlight. Photoexposure of the suspended char and soil significantly enhanced production of DBC after 7 days continuous exposure to the simulated sunlight. The increase was coupled with an increase in the DBC polycondensed character. In agreement with this, characterization using Fourier transform-ion cyclotron resonance-mass spectrometry (FT-ICR-MS) showed an increase in the number of BC molecular formulae detected and in their average molecular weight, suggesting that increasing photoexposure is required for dissolution of larger, more polycondenced DBC compounds. An increase in molecular signatures with lower H/C ratio and higher O/C ratio after 7 days photoexposure suggested increasing functionality of newly produced DBC with irradiation time, and therefore photooxidation as a potential mechanism for the photodissolution of BC. The photoproduced DBC was also strongly coupled with the photoproduced bulk dissolved organic carbon (DOC). The results suggest that photodissolution may be a significant and previously unrecognized mechanism of DBC translocation to aquatic systems

Molecular composition and bioavailability of dissolved organic nitrogen in a lake flow-influenced river in south Florida, USA

Dissolved organic nitrogen (DON) represents a large percentage of the total nitrogen in rivers and estuaries, and can contribute to coastal eutrophication and hypoxia. This study reports on the composition and bioavailability of DON along the Caloosahatchee River (Florida), a heavily managed system receiving inputs from Lake Okeechobee as well as agricultural and urban runoff from the surrounding watershed. Water samples were collected bimonthly for 1 year beginning December 2014 at three stations along the river. Treatments included 28-day dark incubations with and without prior photo-irradiation. Concentrations of DON, ammonium, nitrate–nitrite, total hydrolyzable amino acids (THAA), and urea, as well as bacterial numbers, leucine aminopeptidase activity, and fluorescent optical properties were measured. Ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was used to characterize the molecular composition of DON before and after incubation for selective samples. The total dissolved N pool was dominated by DON (61–99%), with low inorganic N (1–39%), and small amounts of THAA-N (0.1–23%) and urea-N (0.6–3.2%). The mean percentage of biologically available DON (BDON) for the study was 15% (−12–61% range) with highest values occurring when water inputs from Lake Okeechobee were the most dominant freshwater source. FT-ICR MS analysis revealed the presence of a wide range of N-containing formulas and the generation of aliphatic and ‘peptide-like’ structures likely due to microbial alteration of the carbon skeleton of DON compounds. Effects of light exposure prior to incubation did not have a measurable effect on %BDON but did affect bacterial biomass and DON composition. These findings may help predict nutrient loading effects to the Caloosahatchee River estuary and may aid in understanding wetland potential as a treatment technology for removing N in this and other freshwater systems sensitive to N loading