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Radiocarbon and stable isotope geochemistry of organic matter in the Amazon headwaters, Peruvian Andes
Author(s) -
TownsendSmall Amy,
Noguera Jorge L.,
McClain Michael E.,
Brandes Jay A.
Publication year - 2007
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2006gb002835
Subject(s) - tributary , hydrology (agriculture) , organic matter , amazon rainforest , streams , δ13c , surface runoff , dissolved organic carbon , environmental science , isotopes of carbon , stable isotope ratio , geology , total organic carbon , environmental chemistry , ecology , oceanography , chemistry , geography , computer network , physics , cartography , geotechnical engineering , quantum mechanics , computer science , biology
We used δ 13 C, δ 15 N, and Δ 14 C to determine the sources of riverine organic matter in the Pozuzo River, a tributary of the Pachitea River located in the mountainous headwaters of the Amazon. Particulate organic matter (POM) Δ 14 C decreased downstream, suggesting that young organic matter (OM) introduced in small headwaters is respired preferentially in rivers or is diluted downstream with older material. The δ 13 C and δ 15 N of POM in headwater rivers were heterogeneous and also isotopically distinct from the main stem, suggesting that differences in landscape processes in small catchments impact the concentration and composition of POM in streams. The δ 13 C of dissolved organic matter (DOM) closely mirrored that of POM in the headwaters, with an apparent decoupling of dissolved and particulate OM in the river main stem. The δ 13 C of POM sampled in 2004 had a much different relationship with altitude than observed during previous years: In 2004, a very dry year, we observed enrichment from the headwaters to the main stem, and the opposite pattern in 2002, when rain fell heavily throughout the sampling campaign. This suggests that during dry conditions, in‐stream processes (such as resuspension or photosynthesis) may control riverine POM composition as opposed to terrestrial processes, which dominate during high runoff. Thus a decrease in runoff in Andean headwaters could result in less terrestrial POM transfer to rivers in the Andes foothills and lowland Amazon with a corresponding decrease in aquatic CO 2 evasion.