The size distribution of organic carbon in headwater streams in the Amazon basin
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Despite the strong representativeness of streams in the Amazon basin, their role in the accumulation of coarse particulate organic carbon (CPOC), fine particulate organic carbon (FPOC), and dissolved organic carbon (DOC) in transport, an important energy source in these environments, is poorly known. It is known that the arboreal vegetation in the Amazon basin is influenced by soil fertility and rainfall gradients, but would these gradients promote local differences in organic matter in headwater streams? To answer this question, 14 low-order streams were selected within these gradients along the Amazon basin, with extensions that varied between 4 and 8 km. The efficiency of the transformation of particulate into dissolved carbon fractions was assessed for each stream. The mean monthly benthic organic matter storage ranged between 1.58 and 9.40 t ha−1 month−1. In all locations, CPOC was the most abundant fraction in biomass, followed by FPOC and DOC. Rainfall and soil fertility influenced the distribution of the C fraction (p = 0.01), showing differentiated particulate organic carbon (POC) storage and DOC transportation along the basin. Furthermore, the results revealed that carbon quantification at the basin level could be underestimated, ultimately influencing the global carbon calculations for the region. This is especially due to the fact that the majority of studies consider only fine particulate organic matter and dissolved organic matter, which represent less than 50 % of the stored and transported carbon in streambeds.
KeywordsBenthic organic matter Coarse particulate organic carbon Fine particulate organic carbon Dissolved organic carbon Tropical streams Global carbon cycle
We are thankful to the following projects and programs for financial and logistical support: Large Scale Program of Biosphere-Atmosphere in the Amazon - LBA, Ecology, Monitoring and Sustainable Use of Flooding Areas - MAUA, Amazon Forest Inventory Network - RAINFOR, Cenários para a Amazônia: Uso da terra, Biodiversidade e Clima, Conselho Nacional de Desenvolvimento Científico e Tecnológico - CNPq/Edital Universal (14/2008), and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – CAPES. We also thank all field assistants: Paulão, Milton, Mr. Robson, Demetrius, Nina, Yamileth, Osmar, and Romilda; to Wallace Costa for helping with the maintenance of equipment, Jonis Souza and Carmen Conrad for carrying out DOC analyses, and Mariana de Paula and Dr. A. Leyva for helping with English editing of the manuscript.
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