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Source to sink: Evolution of lignin composition in the Madre de Dios River system with connection to the Amazon basin and offshore
Author(s) -
Feng Xiaojuan,
Feakins Sarah J.,
Liu Zongguang,
Ponton Camilo,
Wang Renée Z.,
Karkabi Elias,
Galy Valier,
Berelson William M.,
Nottingham Andrew T.,
Meir Patrick,
West A. Joshua
Publication year - 2016
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2016jg003323
Subject(s) - lignin , dissolved organic carbon , soil water , sink (geography) , organic matter , environmental science , total organic carbon , hydrology (agriculture) , drainage basin , environmental chemistry , mineralization (soil science) , geology , ecology , soil science , chemistry , geography , biology , cartography , geotechnical engineering , organic chemistry
While lignin geochemistry has been extensively investigated in the Amazon River, little is known about lignin distribution and dynamics within deep, stratified river channels or its transformations within soils prior to delivery to rivers. We characterized lignin phenols in soils, river particulate organic matter (POM), and dissolved organic matter (DOM) across a 4 km elevation gradient in the Madre de Dios River system, Peru, as well as in marine sediments to investigate the source‐to‐sink evolution of lignin. In soils, we found more oxidized lignin in organic horizons relative to mineral horizons. The oxidized lignin signature was maintained during transfer into rivers, and lignin was a relatively constant fraction of bulk organic carbon in soils and riverine POM. Lignin in DOM became increasingly oxidized downstream, indicating active transformation of dissolved lignin during transport, especially in the dry season. In contrast, POM accumulated undegraded lignin downstream during the wet season, suggesting that terrestrial input exceeded in‐river degradation. We discovered high concentrations of relatively undegraded lignin in POM at depth in the lower Madre de Dios River in both seasons, revealing a woody undercurrent for its transfer within these deep rivers. Our study of lignin evolution in the soil‐river‐ocean continuum highlights important seasonal and depth variations of river carbon components and their connection to soil carbon pools, providing new insights into fluvial carbon dynamics associated with the transfer of lignin biomarkers from source to sink.