Rudolf Jaffé

Spatial and temporal variations in DOM composition in ecosystems: The importance of long‐term monitoring of optical properties

[1] Source, transformation, and preservation mechanisms of dissolved organic matter (DOM) remain elemental questions in contemporary marine and aquatic sciences and represent a missing link in models of global elemental cycles. Although the chemical character of DOM is central to its fate in the global carbon cycle, DOM characterizations in long-term ecological research programs are rarely performed. We analyzed the variability in the quality of 134 DOM samples collected from 12 Long Term Ecological Research stations by quantification of organic carbon and nitrogen concentration in addition to analysis of UV-visible absorbance and fluorescence spectra. The fluorescence spectra were further characterized by parallel factor analysis. There was a large range in both concentration and quality of the DOM, with the dissolved organic carbon (DOC) concentration ranging from less than 1 mgC/L to over 30 mgC/L. The ranges of specific UV absorbance and fluorescence parameters suggested significant variations in DOM composition within a specific study area, on both spatial and temporal scales. There was no correlation between DOC concentration and any DOM quality parameter, illustrating that comparing across biomes, large variations in DOM quality are not necessarily associated with corresponding large ranges in DOC concentrations. The data presented here emphasize that optical properties of DOM can be highly variable and controlled by different physical (e.g., hydrology), chemical (e.g., photoreactivity/redox conditions), and biological (e.g., primary productivity) processes, and as such can have important ecological consequences. This study demonstrates that relatively simple DOM absorbance and/or fluorescence measurements can be incorporated into long-term ecological research and monitoring programs, resulting in advanced understanding of organic matter dynamics in aquatic ecosystems.

Global Charcoal Mobilization from Soils via Dissolution and Riverine Transport to the Oceans

Dissolving Charcoal Biomass burning produces 40 to 250 million tons of charcoal per year worldwide. Much of this is preserved in soils and sediments for thousands of years. However, the estimated production rate of charcoal is significantly larger than that of decomposition, and Jaffe et al. (p. 345; see the Perspective by Masiello and Louchouarn) calculate that a large fraction of the charcoal produced by fires is lost from the land through dissolution and transport to the oceans. A larger-than-assumed fraction of charcoal produced by wildfires leaches out of soils and is transported to the oceans. [Also see Perspective by Masiello and Louchouarn] Global biomass burning generates 40 million to 250 million tons of charcoal every year, part of which is preserved for millennia in soils and sediments. We have quantified dissolution products of charcoal in a wide range of rivers worldwide and show that globally, a major portion of the annual charcoal production is lost from soils via dissolution and subsequent transport to the ocean. The global flux of soluble charcoal accounts to 26.5 ± 1.8 million tons per year, which is ~10% of the global riverine flux of dissolved organic carbon (DOC). We suggest that the mobilization of charcoal and DOC out of soils is mechanistically coupled. This study closes a major gap in the global charcoal budget and provides critical information in the context of geoengineering.

Origin and transport of sedimentary organic matter in two subtropical estuaries: a comparative, biomarker-based study

Two sub-tropical estuaries of south Florida, USA, were studied to determine the origin and transport of organic matter between the freshwater and marine end-members of these systems. Sediments, as well as main biomass components (vegetation) were analyzed for lipid composition and content. The molecular distribution of several biomarker compounds, organism-specific biomarkers and bulk sediment characteristics such as %OM, C/N and δ13C were used to assess differences in OM source and transport between a strongly tidally-influenced estuary (Harney River) and one that is only seasonally influenced by estuarine waters (Taylor River). The data show mixing of combined terrestrial and autochthonous freshwater-derived OM, with marine planktonic and seagrass-derived OM in the middle to lower estuary of the Harney River. In contrast, such mixing did not occur to a measurable degree at the Taylor River, where low water discharge and exchange does not allow for any significant mixing of OM from end-member sources. Differences in hydrological conditions and benthic plant biomass and productivity between the two systems results in different OM inputs, which are reflected in the quality and degree of diagenesis of the sedimentary OM. Specific applications and potential limitations of traditional biomarker compounds for OM source assessment are discussed.

Molecular characterization of smoke from campfire burning of pine wood (Pinus elliottii)

Abstract Although campfires are typically enjoyable events, people are exposed to high concentrations of gaseous and particulate pollutants. The combustion conditions of wood burned in campfires are different from those of indoor wood burning in stoves or fireplaces. Typically, wood logs, twigs, and branches with their leaves or needles are burned in campfires, whereas mostly wood logs are burned in indoor settings. Consequently, the molecular source profiles for organic particulate matter emissions may be different from a campfire. For human exposure assessment, there is a need to fingerprint the organic compound compositions in campfire wood smoke. Here we present the detailed biomarker composition of conifer wood smoke from a campfire. The major biomarkers emitted are dehydroabietic acid, the resin acids (pimaric, iso-pimaric, sandaracopimaric and abietic acids), retene, pimanthrene, methylcyclopentenophenanthrene and β-sitosterol, with levoglucosan and lignin phenolics such as vanillic acid in the polar fraction. PAH are minor components. A marker and PAH profile has been generated which can be utilized for tracing emissions from campfire burning and evaluating personal exposure risk.

Determination of organomercury compounds in aqueous samples by capillary gas chromatography-atomic fluorescence spectrometry following solid-phase extraction

A new method based on capillary gas chromatography-atomic fluorescence spectrometry (GC/AFS) is described for the determination of methylmercury (MeHg) and ethylmercury (EtHg) in water samples. An improved sample preparation methodology was developed, which involves preconcentration of the alkylmercury species from water samples, drawn with a 12 channel peristaltic pump, onto sulfhydryl cotton fiber (SCF) adsorbent packed in a screening column, elution of MeHg and EtHg with a mixture of acidic potassium bromide and copper sulfate solution, and back-extraction using methylene chloride. Analysis was performed by capillary GC/AFS with a DB-1 column. Some important parameters, including sample pH, presence of anions and cations, concentration of dissolved organic carbon (DOC), eluent type, and eluent volume were evaluated. With AFS as a detector, the capillary gas Chromatographic technique provides high selectivity, high sensitivity, and a straightforward method for organomercury halide analysis. It eliminates possible spectral interferences to the detector from other sample components and from chemicals used in the sample preparation procedure. The detection limit was 0.01 ng l−1 in a 11 water sample for both MeHg and EtHg. The result for organomercury analysis in a number of natural water samples is shown to illustrate the applicability of this method to real environmental samples.

Dissolved Organic Matter Characteristics Across a Subtropical Wetland’s Landscape: Application of Optical Properties in the Assessment of Environmental Dynamics

Wetlands are known to be important sources of dissolved organic matter (DOM) to rivers and coastal environments. However, the environmental dynamics of DOM within wetlands have not been well documented on large spatial scales. To better assess DOM dynamics within large wetlands, we determined high resolution spatial distributions of dissolved organic carbon (DOC) concentrations and DOM quality by excitation–emission matrix spectroscopy combined with parallel factor analysis (EEM–PARAFAC) in a subtropical freshwater wetland, the Everglades, Florida, USA. DOC concentrations decreased from north to south along the general water flow path and were linearly correlated with chloride concentration, a tracer of water derived from the Everglades Agricultural Area (EAA), suggesting that agricultural activities are directly or indirectly a major source of DOM in the Everglades. The optical properties of DOM, however, also changed successively along the water flow path from high molecular weight, peat-soil and highly oxidized agricultural soil-derived DOM to the north, to lower molecular weight, biologically produced DOM to the south. These results suggest that even though DOC concentration seems to be distributed conservatively, DOM sources and diagenetic processing can be dynamic throughout wetland landscapes. As such, EEM–PARAFAC clearly revealed that humic-enriched DOM from the EAA is gradually replaced by microbial- and plant-derived DOM along the general water flow path, while additional humic-like contributions are added from marsh soils. Results presented here indicate that both hydrology and primary productivity are important drivers controlling DOM dynamics in large wetlands. The biogeochemical processes controlling the DOM composition are complex and merit further investigation.

Chemical ecology of the palm weevil Rhynchophorus palmarum (L.) (Coleoptera: Curculionidae): attraction to host plants and to a male-produced aggregation pheromone.

Attraction to host plants by adultRhynchophorus palmarum (L.) palm weevils was studied in the field and in the laboratory. Chemical analysis revealed the presence of ethanol and ethyl-acetate in stems of coco palms and in pineapple fruits and of pentane, hexanal, and isopentanol in coco stems. In the olfactometer, the first two compounds and isoamyl-acetate were attractive to the insects and the last three compounds, although not attractive by themselves, increased attractiveness when mixed with the first two compounds. Mixtures of these compounds, in proportions similar to the one occurring in attractive plant tissue, were as attractive as natural coconut tissue. In the field, the chemical compounds, either presented alone or as a mixture, did not attract the weevil. Males produce an aggregation pheromone when smelling ethyl-acetate. Rhynchophorol, 2(E)-6-methyl-2-hepten-4-ol, the known active component of the aggregation pheromone, attracts weevils in the olfactometer and in the field only if plant tissue, ethyl-acetate, or the above-mentioned odor mix are present. We propose that a complex mix of ethanol, ethyl-acetate, pentane, hexanal, isolamyl-acetate, and/or isopentanol serve as a short-range orientation cue to fresh wounds on the plant and that additional host odors, attracting weevils from a distance, have still to be discovered. Rhynchophorol can be considered to be a Synergist, having an anemotactic action at a distance. We recommend the use of retention traps baited with rhynchophorol, ethyl-acetate, and sugar cane as an alternative control method for the pest.

Origin and transport of n-alkane-2-ones in a subtropical estuary: potential biomarkers for seagrass-derived organic matter

Abstract n-Alkane-2-ones are lipids commonly found in sediments and soils. This group of compounds, frequently reported in the literature, usually occurs in the form of a homologous series ranging from about C19 to C33 characterized by a strong odd over even carbon number predominance. In this paper we report a different molecular distribution, centered about the C25 homologue as the dominant ketone. The relative abundance of the C25 compared to the C27 homologue in a sediment transect increased from the upper to the lower end of a South Florida estuary, and was found to correlate with surface water salinity in extracts from suspended solids. Analyses of different varieties of seagrasses showed these to be the most likely source of the C25 n-alkane-2-ones, while the C27+ homologues were mainly derived from mangroves and freshwater marsh vegetation. Compound-specific stable isotope measurements and statistical analyses support this finding, suggesting that molecular distributions of n-alkane-2-ones can be used to identify seagrass-derived organic matter in coastal environments.

Molecular characterization of dissolved organic matter in freshwater wetlands of the Florida Everglades.

In this study, the molecular composition of dissolved organic matter (DOM), collected from wetlands of the Southern Everglades, was examined using a variety of analytical techniques in order to characterize its sources and transformation in the environment. The methods applied for the characterization of DOM included fluorescence spectroscopy, solid state 13C CPMAS NMR spectroscopy, and pyrolysis-GC/MS. The relative abundance of protein-like components and carbohydrates increased from the canal site to more remote freshwater marsh sites suggesting that significant amounts of non-humic DOM are autochthonously produced within the freshwater marshes, and are not exclusively introduced through canal inputs. Such in situ DOM production is important when considering how DOM from canals is processed and transported to downstream estuaries of Florida Bay.

Organic geochemistry of seasonally flooded rain forest soils : molecular composition and early diagenesis of lipid components

Ten soil samples from the Orinoco River Basin, Venezuela, were studied in order to characterize the molecular distribution of lipids and to determine early diagenetic degradation processes in these environments. The sample set contained six soil samples that were collected directly adjacent to large tropical rivers, and that were, therefore, subject to seasonal flooding. Molecular evidence for the formation of anaerobic microenvironments in these soils during the flooding period was obtained; this was based on the presence of several ring-A-degraded higher plant triterpenoids, products of the anaerobic degradation of 3-oxy-triterpenoids. The molecular distribution of other lipid classes such as n-alkanes, n-alkanols, fatty acids and sterols are also reported here and compared to the organic matter of rivers from the Orinoco Basin.