Characterisation of sedimentary organic matter from three south-eastern Australian estuaries using solid-state 13C-NMR techniques

Abstract

Solid state 13C-nuclear magnetic resonance (NMR) spectroscopy was used to characterise sedimentary organic matter sampled from three estuaries on the central New South Wales coast (Australia). Cross polarisation (CP) and Bloch decay (BD) experiments were used to determine the chemical composition of the samples. These experiments indicated that, although the natural organic matter is predominately terrestrial in origin, the proportion of carbon existing as aromatic carbon, distinctive of vascular plants, decreases towards the mouth of the estuaries. This suggests that the relative contribution of terrestrial and marine source material largely defines the character of estuarine organic matter. Substantial amounts of charcoal were identified in sedimentary organic matter close to recent bushfire activity. Proton-spin relaxation editing (PSRE) was used to probe the physical structure of the sedimentary organic matter at the sub-micron scale. This technique showed that the organic matter was heterogeneous, providing support for a popular model of sedimentary organic matter structure. However, detailed interpretation of the domain structure of the organic matter was hindered by the presence of multiple components from both terrestrial and marine sources.

Solid-state 13C NMR analysis of size and density fractions of marine sediments: Insight into organic carbon sources and preservation mechanisms

“…8). The rapidly relaxing component is dominated by a strong unsaturated carbon signal, probably derived from aromatic-rich charcoal, which tends to have very short T 1 H values (Golchin et al, 1997a;Smernik et al, 2000;Golding et al, 2004), along with alkyl carbon. The sharp O-aryl and N-alkyl/methoxyl resonances present in the slowly relaxing component, along with a strong unsaturated signal (Fig.…”

“…NMR observabilities are not affected by degradation, and with careful attention to experimental setup, NMR spectra can be acquired quantitatively (Kinchesh et al, 1995;Oades, 2000a,b, 2003). NMR spectroscopy has been applied extensively to study soil organic matter (as reviewed in Preston, 1996;Kö gel-Knabner, 1997) but remains underutilized in studies of marine systems (e.g., Gélinas et al, 2001aGolding et al, 2004).…”

Black (pyrogenic) carbon: a synthesis of current knowledge and uncertainties with special consideration of boreal regions

“…PyC is delivered by atmospheric deposition, and dissolved, colloidal and particulate organic matter of rivers to marine sediments, where it constitutes up to one-third of organic C (Gustafsson and Gschwend, 1998;Masiello andDruffel, 1998, 2001;Middelburg et al, 1999;Mitra et al, 2002;Golding et al, 2004). In addition to BC from biomass combustion, sedimentary BC includes petrogenic graphite (GBC) which can be weathered out of rock, transported and reburied in ocean sediments (Dickens et al, 2004a, b) and soot from fossil fuel combustion (Masiello and Druffel, 2003).…”

Molecular Composition of Humic Acids from Coastal Wetland Soils along a Salinity Gradient

“…While HAs or humic substances in general have been traditionally believed as relatively high molecular-mass polymers formed through secondary synthesis (Stevenson, 1994), recent evidence has suggested that they are more of collections of diverse, relatively low molecular mass components forming dynamic associations stabilized by hydrophobic interactions and H bonds (Hayes, 2009;Sutton and Sposito, 2005). Th e molecular moieties in humic substances refl ect the sources of organic carbon (OC) inputs and are related to degradation/decomposition state and depositional environment (Golding et al, 2004). In addition, humic substances have been shown to contain both amorphous and crystalline domain characteristics, which are expected to have diff erent resistivity to environmental attack .…”