Allochthonous DOC in floodplain rivers: identifying sources using solid phase microextraction with gas chromatography

Abstract

Models of carbon transport are an important mechanism for conceptualizing and assessing the significance of matter and energy sources in streams. The development of a fingerprinting technique that identifies the origins of dissolved organic carbon (DOC) would be invaluable for the development of more sophisticated carbon budget models and improving our understanding of energy flow in river systems. This study explores the potential for solid phase microextraction – gas chromatography (SPMEGC) as a technique for fingerprinting DOC leached from allochthonous source materials (e.g., red gum leaves, willow leaves, couch grass, alluvial soil) collected from a floodplain river in NSW, Australia. The SPME-GC technique is a portable, solventless extraction technique that can detect semi-volatile and volatile organic compounds (SV and VOC) including terpenes, fatty acids, fatty acid esters, ketones, alcohols, and aldehydes, and, importantly, has detection limits approaching parts-per-trillion. The semi-volatile and volatile organic compounds found in DOC leachate solutions produced complex chromatograms, consisting of over 100 individual DOC compounds from each allochthonous source. Hierarchical cluster analysis based on peak presence-absence revealed that each of the source materials produce different chemical profiles. The results indicate that the SPMEGC technique in conjunction with multivariate analyses has considerable potential for identifying source specific chemotaxonomic markers in DOC from riverine habitats. These markers may then be used to test and validate existing models of river function by identifying the origins of DOC contributing to instream metabolism.