Organic matter in the Peruvian headwaters of the Amazon:: compositional evolution from the Andes to the lowland Amazon mainstem - Aufdenkampe, Anthony K; Mayorga, Emilio; Hedges, John I; Llerena, Carlos; Quay, Paul D; Gudeman, Jack; Krusche, Alex Vladimir; Jeﬀrey E. Richey b (Organic Geochemistry, 2007)