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Erosion of organic carbon from the Andes and its effects on ecosystem carbon dioxide balance
Author(s) -
Clark K. E.,
Hilton R. G.,
West A. J.,
Robles Caceres A.,
Gröcke D. R.,
Marthews T. R.,
Ferguson R. I.,
Asner G. P.,
New M.,
Malhi Y.
Publication year - 2017
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2016jg003615
Subject(s) - total organic carbon , environmental science , amazon rainforest , hydrology (agriculture) , drainage basin , sediment , carbon cycle , carbon sink , biosphere , ecosystem , discharge , geology , ecology , environmental chemistry , geography , chemistry , geomorphology , biology , geotechnical engineering , cartography
Productive forests of the Andes are subject to high erosion rates that supply to the Amazon River sediment and carbon from both recently photosynthesized biomass and geological sources. Despite this recognition, the source and discharge of particulate organic carbon (POC) in Andean Rivers remain poorly constrained. We collected suspended sediments from the Kosñipata River, Peru, over 1 year at two river gauging stations. Carbon isotopes ( 14 C, 13 C, and 12 C) and nitrogen to organic carbon ratios of the suspended sediments suggest a mixture of POC from sedimentary rocks (POC petro ) and from the terrestrial biosphere (POC biosphere ). The majority of the POC biosphere has a composition similar to surface soil horizons, and we estimate that it is mostly younger than 850 14 C years. The suspended sediment yield in 2010 was 3500 ± 210 t km −2 yr −1 , >10 times the yield from the Amazon Basin. The POC biosphere yield was 12.6 ± 0.4 t C km −2 yr −1 and the POC petro yield was 16.1 ± 1.4 t C km −2 yr −1 , mostly discharged in the wet season (December to March) during flood events. The river POC biosphere discharge is large enough to play a role in determining whether Andean forests are a source or sink of carbon dioxide. The estimated erosional discharge of POC petro from the Andes is much larger (~1 Mt C yr −1 ) than the POC petro discharge by the Madeira River downstream in the Amazon Basin, suggesting that oxidation of POC petro counters CO 2 drawdown by silicate weathering. The flux and fate of Andean POC biosphere and POC petro need to be better constrained to fully understand the carbon budget of the Amazon River basin.