Concentration and fluxes of dissolved carbon in an Amazonian riparian forest

Abstract:

Many rivers experience a season-specific annual pulse that plays an important role in the nutrient dynamics of its riparian forests. Hence one would expect that these forests may undergo seasonally-enhanced inputs with potential to change its nutrient cycling. We studied the concentrations and fluxes of dissolved organic (DOC) and inorganic (DIC) carbon in hydrological flowpaths of a tropical riparian forest in the Brazilian Amazonian state of Rondônia during the rainy seasons 2005-2007. DOC concentrations increased as the rain passed through the forest canopy, reaching its maximum in stemflow, and decreasing steadily after the passage through the forest floor, with minimum concentration in the groundwater (a slow flowpath). DIC exhibited a progressive increase in concentration from rainwater to groundwater. In general, the pattern of dissolved carbon concentrations and fluxes on a riparian forest in Southwestern Amazonia showed DOC to be preferentially controlled by quick flowpaths (throughfall and overland flow) and DIC by slow flowpaths. Seasonality exerts a key role in changing the relative importance of hydrological flowpaths throughout the year with potential to deliver dissolved carbon with distinct sources to the adjacent river. Streamwater DOC concentration exhibited a clockwise hysteresis with discharge, with much higher DOC concentrations for the rising limb, suggesting an important contribution of lateral flow from quick flowpaths. Surprisingly, DIC concentrations did not exhibit hysteresis. Anthropogenic emissions due to biomass burning in the region seems to have the potential to promote changes in precipitation chemistry and therefore in the nutrient cycling for the riparian forest.