LBA-ECO ND-11 Organic Carbon Watershed Exports, Mato Grosso, Brazil: 2003-2004

Resolving the carbon (C) balance in the Amazonian forest depends on an improved quantification of production and losses of particulate C from forested landscapes via stream export. The main goal of this work was to quantify litterfall, the lateral movement of litter, and the export of coarse organic particulate matter (>2 mm) in four small watersheds (1-2 ha) under native forest in southern Amazonia near Juruena, Mato Grosso, Brazil (10°25 S, 58°46 W). Mean litterfall production was 11.8 Mg ha-1 y-1 (5.7 Mg C ha-1 y-1). Litterfall showed strong seasonality, with the highest deposition in the driest months of the year. About two times more C per month was deposited on the forest floor during the 6-mo dry season (0.65 Mg C ha-1 mo-1) compared to the rainy season (0.3 Mg C ha-1 mo-1). The measured C concentration of the litterfall samples was greater in the dry season than in the rainy season (49% vs. 46%, P < 0.05). The lateral movement of litter increased from the plateau (upper landscape position) towards the riparian zone. However, the trend in C concentration of laterally transported litter samples was the opposite, being highest on the plateau (44%) and lowest in the riparian zone (42%) (P < 0.05). Stream-water exports of particulate C were positively correlated with streamflow, increasing in the rainiest months. The export of particulate C in streamflow was found to be very small (less than 1%) in relation to the amount of litterfall produced.