Chemical composition of aquatic dissolved organic matter in five boreal forest catchments sampled in spring and fall seasons

Abstract

The chemical composition and carbon isotope signature of aquatic dissolved organic matter (DOM) in five boreal forest catchments in Scandinavia were investigated. The DOM was isolated during spring and fall seasons using a reverse osmosis technique. The DOM samples were analyzed by elemental analysis, FT-IR, solid-state CP-MAS 13 C-NMR, and C-1s NEXAFS spectroscopy. In addition, the relative abundance of carbon isotopes ( 12 C, 13 C, 14 C) in the samples was measured. There were no significant differences in the chemical composition or carbon isotope signature of the DOM sampled in spring and fall seasons. Also, differences in DOM composition between the five catchments were minor. Compared to reference peat fulvic and humic acids, all DOM samples were richer in O-alkyl carbon and contained less aromatic and phenolic carbon, as shown by FT-IR, 13 C-NMR, and C-1s NEXAFS spectroscopy. The DOM was clearly enriched in 14 C relative to the NBS oxalic acid standard of 1950, indicating that the aquatic DOM contained considerable amounts of organic carbon younger than about 50 years. The weight-based C:N ratios of 31 AE 6 and the d 13 C values of À29 AE 2‰ indicate that the isolated DOM is of terrestrial rather than aquatic origin. We conclude that young, hydrophilic carbon compounds of terrestrial origin are predominant in the samples investigated, and that the composition of the aquatic DOM in the studied boreal forest catchments is rather stable during low to intermediate flow conditions.

Efficient aquatic bacterial metabolism of dissolved low-molecular-weight compounds from terrestrial sources

“…The average water renewal time in the headwater streams was ca. 2 h during spring flood (Laudon, unpublished) and previous studies (Schumacher et al, 2006;Å gren et al, 2007) showed that terrestrial DOM totally dominated the DOM pool of these streams. We also included the outlet of the nearby small humic lake, Stortjärnen, with a 95-ha mixed catchment (ca.…”

Properties of dissolved and total organic matter in throughfall, stemflow and forest floor leachate of central European forests

“…Consequently, solid-state 13 C NMR spectroscopy is widely used for the characterization of a range of organic materials from various natural environments (Baldock et al, 2004). It has been applied to soil OM (Helfrich et al, 2006;Keeler et al, 2006), hot water extracts (Leinweber et al, 1995;Balaria et al, 2009) and DOM in aqueous solutions from aquatic (Schumacher et al, 2006) and terrestrial ecosystems Fröberg et al, 2003;Sanderman et al, 2008). Although the technique has been applied to POM from aquatic systems (McKnight et al, 1997;Lankes et al, 2008), to the best of our knowledge, it has never been applied to POM or TOM in aqueous samples from terrestrial ecosystems such as TF, SF or FF leachates.…”

Organic Carbon Chemistry in Soils Observed by Synchrotron-Based Spectroscopy

“…In this regard, synchrotron radiation has opened new opportunities for the study of C in soils because the high energy provided significantly improves the spectral as well as the spatial resolution. Recent investigations using synchrotron-based scanning transmission X-ray microscopy (STXM), C (1s) near-edge X-ray absorption fine structure (NEXAFS), and Fourier transform infrared (FTIR) spectroscopy have indicated that these techniques are powerful and noninvasive, and can be used to identify and fingerprint the complex structural characteristics of SOC and dissolved organic C (DOC), as well as to investigate the impact of management on the composition and biogeochemical cycling of organic C at the molecular level in terrestrial ecosystems (Jokic et al, 2003;Kinyangi et al, 2006;Lehmann et al, 2005Lehmann et al, , 2007Myneni et al, 1999;Schäfer et al, 2003;Scheinost et al, 2001;Solomon et al, 2005Solomon et al, , 2007aSchumacher et al, 2005Schumacher et al, , 2006. Soils typically have low amounts of C as compared to pure biological organic matter, which is a challenge for obtaining good spectral data from spectroscopy techniques.…”