Diverse soil carbon dynamics expressed at the molecular level

The stability and potential vulnerability of soil organic matter (SOM) to global change remains incompletely understood due to the complex processes involved in its formation and turnover. Here we combine compound-specific radiocarbon analysis with fraction-specific and bulk-level radiocarbon measurements in order to further elucidate controls on SOM dynamics in a temperate and sub-alpine forested ecosystem. Radiocarbon contents of individual organic compounds isolated from the same soil interval generally exhibit greater variation than those among corresponding operationally-defined fractions. Notably, markedly older ages of long-chain plant leaf wax lipids (n-alkanoic acids) imply that they reflect a highly stable carbon pool. Furthermore, marked 14C variations among shorter- and longer-chain n-alkanoic acid homologues suggest that they track different SOM pools. Extremes in SOM dynamics thus manifest themselves within a single compound class. This exploratory study highlights the potential of compound-specific radiocarbon analysis for understanding SOM dynamics in ecosystems potentially vulnerable to global change

Fatty Acid Signatures from Bacteria at the Freshwater/Seawater Boundary of the Krka Estuary in Winter, Spring and Autumn

Distribution of fatty acids was determined at the halocline and in adjacent brackish and marine waters in the Krka Estuary, on the East coast of the Adriatic Sea, in winter 1987, spring 1988 and fall 1990. Particulate matter (> 0.7 pm) was extracted and analyzed for fatty acids by gas chromatography and gas chromatography/mass spectrometry. Different groups of fatty adds were examined: branched and monounsaturated (vaccenic). Bacterial signatures were highly variable in the estuary, depending on season and the extent of accumulation of organic matter at the halocline. Imprint of branched fatty acids, probably representative for the largest bacterial populations, varied by three orders of magnitude. This imprint was generally low at marine stations with an exception of fall 1990, and high in river/brackish waters. Bacterial signatures were interpreted in terms of relationship between their occurrence and growth conditions expressed as suspended matter, organic carbon and chlorophyll a concentrations, as well as nature of organic matter in various water types, fresh, brackish and marine

Non-aromatic hydrocarbons in recent sediments of Sepetiba and Ilha Grande Bays, Brazil

An investigation was conducted in Ilha Grande and Sepetiba Bays aiming at identifying the nature of non-aromatic hydrocarbons (NAH) in surface sediments. NAH concentrations ranged from 2.5 µg g-1 to 193.8 µg g-1 of which the major fraction (53 to 93%) was composed by unresolved complex mixture (UMC). In most samples n-alkane distribution was dominated by compounds of odd carbon number showing maxima in nC29 and nC31. Mono-olefins were at low concentrations and the polyolefins including highly branched isoprenoids and squalene varied from 0.099 µg g-1 to 1.387 µg g-1 with lower values relative to NAH appearing in areas of strong terrestrial and anthropogenic influence. Hopanes between C27 and C33 were observed in all samples with the predominant configuration 17a(H),21b(H), characteristic of a petrogenic origin

Organic matter characterization in the sea surface microlayers in the subarctic Norwegian fjords region

The top of the ocean, sea surface microlayer (ML), covers more than 70% of the world's surface. It is a sink for natural and anthropogenic material that depends on its chemical composition. This article is aimed at providing novel data on the characterization of organic matter in ML and underlying waters (ULW) in the rarely investigated subarctic, north Norwegian fjords region, in July 2001, August 2002 and June 2003. A multiparameter approach was used, including DOC measurements, characterization of surface active organic substances (SAS), determination of Cu complexing capacity (LT) and specific analysis of fatty acids (FA). The characteristics of organic matter in fjords' sea surface microlayers showed that organic substances in the films were mainly produced in the subsurface water. There was negligible fractionation of hydrophobic substances to the microlayer and even depletion of fatty acids was found in some ML samples. Fjords' surface waters were found to be very rich in fatty acids in July, up to 201 μ g/l, with high contributions of polyunsaturated compounds. The enrichment of DOC and SAS concentrations in ML as compared to the ULW was in the range of 1.2– 2.8, while higher enrichment factors (1.3– 5.1) were determined for copper complexing ligands, indicating increased contribution of hydrophilic, lower molecular weight molecules. The detected characteristics and concentrations of organic substances in the surface microlayer and adjacent subsurface water were dependent on the month of sampling

Constraining instantaneous fluxes and integrated compositions of fluvially discharged organic matter

Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Freymond, C. V., Lupker, M., Peterse, F., Haghipour, N., Wacker, L., Filip, F., et al. (2018). Constraining instantaneous fluxes and integrated compositions of fluvially discharged organic matter. Geochemistry, Geophysics, Geosystems, 19, 2453 2462. doi: 10.1029/2018GC007539.Fluvial export of organic carbon (OC) and burial in ocean sediments comprises an important carbon sink, but fluxes remain poorly constrained, particularly for specific organic components. Here OC and lipid biomarker contents and isotopic characteristics of suspended matter determined in depth profiles across an active channel close to the terminus of the Danube River are used to constrain instantaneous OC and biomarker fluxes and integrated compositions during high to moderate discharges. During high (moderate) discharge, the total Danube exports 8 (7) kg/s OC, 7 (3) g/s higher plant‐derived long‐chain fatty acids (LCFA), 34 (21) g/s short‐chain fatty acids (SCFA), and 0.5 (0.2) g/s soil bacterial membrane lipids (brGDGTs). Integrated stable carbon isotopic compositions were TOC: −28.0 (−27.6)‰, LCFA: −33.5 (−32.8)‰ and Δ14C TOC: −129 (−38)‰, LCFA: −134 (−143)‰, respectively. Such estimates will aid in establishing quantitative links between production, export, and burial of OC from the terrestrial biosphere.This project was funded by the Swiss National Science Foundation SNF. Grant Number: 200021_140850. F.P. acknowledges funding from NWO‐VENI grant 863.13.016. We thank the sampling crews from both field campaigns (Björn Buggle, James Saenz, Alissa Zuijdgeest, Marilu Tavagna, Stefan Eugen Filip, Silvia Lavinia Filip, Mihai, Clayton Magill, Thomas Blattmann, and Michael Albani), Daniel Montluçon for lab support and Hannah Gies for PCGC work. Figures, tables, and equations can be found in supporting information

n-Alkanes, PAHs and surfactants in the sea surface microlayer and sea water samples of the Gerlache Inlet sea (Antarctica)

Sea surface microlayer (SML) and sea water samples (SSW) collected in the Gerlache Inlet Sea (Antarctica) were analysed for n-alkanes and polycyclic aromatic hydrocarbons (PAHs). The SML is a potential enrichment site of hydrophobic organic compounds compared to the underlying water column. Total concentration ranges of n-alkanes and PAHs (dissolved and particulate) in subsurface water (−0.5 m depth) were 272– 553 ng l−1 (mean: 448 ng l−1) and 5.27–9.43 ng l−1 (mean: 7.06 ng l−1), respectively. In the SML, the concentration ranges of n-alkanes and PAHs were 353–968 ng l−1 (mean: 611 ng l−1) and 7.32–23.94 ng l−1 (mean: 13.22 ng l−1), respectively. To evaluate possible PAH contamination sources, specific PAH ratios were calculated. The ratios reflected a predominant petrogenic input. A characterisation of surface active substances was also performed on SML and SSW samples, both by gas bubble extraction, and by dynamic surface tension measurements. Results showed a good correlation between n-alkanes, PAHs and refractory organic matter

Food habits of the farmer damselfish Stegastes nigricans inferred by stomach content, stable isotope, and fatty acid composition analyses

The territorial damselfish, Stegastes nigricans, maintains algal farms by excluding invading herbivores and weeding unpalatable algae from its territories. In Okinawa, Japan, S. nigricans farms are exclusively dominated by Polysiphonia sp., a highly digestible filamentous rhodophyte. This study was aimed at determining the diet of S. nigricans in Okinawa and its dependency on these almost-monoculture algal farms based on stomach content and chemical analyses. Stomach content analyses revealed that all available food items in the algal farms (i. e., algae, benthic animal inhabitants, trapped detritus) were contained in fish stomachs, but amorphous organic matter accounted for 68% of the contents. Therefore, carbon and nitrogen stable isotope ratios and fatty acid (FA) compositions were analyzed to trace items actually assimilated in their bodies. Stable isotope analyses showed that benthic animals were an important food source even for this farmer fish. Two essential fatty acids (EFAs), 20:4n6 and 20:5n3, which are produced only by rhodophytes among available food items, were rich in the muscle tissue of S. nigricans as well as in algal mats and detritus, suggesting that algal mats contribute EFAs to S. nigricans directly and indirectly through the food web. In conclusion, S. nigricans ingested algal mats, detritus, and benthic animals maintained within its farm. Algae and detritus were original sources of EFAs, and benthic animals, which were much more abundant in the farms than in outside territories, provided a nitrogen-rich dietary source for the fish