Dynamics of Carbon Export to the Atmosphere and Oceans from Fluvial Systems of the Humid Tropics: Southeast Asia

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AbstractThe overall question we are addressing in this proposal is, "What role does the evasion (outgassing) of CO2 from the river system to the atmosphere play relative to fluvial carbon export to the ocean in the carbon cycle of the humid tropics?" We have recently demonstrated that outgassing of CO2 from rivers and wetlands of the central Amazonian basin is 1.2 0.3 Mg C ha -1 y -1 , or, when extrapolated across the entire basin, an order of magnitude greater than fluvial export of organic carbon to the oceans. Such a flux would be an important loss, as it is approximately equal to lower estimates of carbon sequestration in the Amazon. These conclusions lead to the working hypothesis for this proposal, that Surface water CO2 evasion is the dominant source of carbon loss (exceeding export to the oceans by a factor of 10) in fluvial systems of the humid tropics, and in the aggregate reconciles the tropics in the global carbon budget. Evasion is driven primarily by in-stream respiration of organic carbon translocated in space and time from its terrestrial and riparian origins. While estimates are becoming better constrained in the Amazon, they are not elsewhere in the tropics, particularly in regions of much greater anthropogenic impact.With this proposal we intend to extend and test our Amazon-based working hypothesis to another significant region, Southeast Asia. We propose to (1) enhance an existing model with improved water routing and inundation, sediments, and carbon modules as a function of landscape condition, (2) conduct a field sampling campaign to determine region-specific processes and provide data for model validation, and (3) use the resulting improved model to analyze questions concerning the dynamics of carbon in the fluvial environments of Southeast Asia which will test our working hypothesis.The most significant intellectual merit of our proposal is (1) that a significant anomaly in the global carbon cycle is being addressed, and (2) the work represents a convergence of historically separate lines of earth science into a significant "new" view of the global importance of the processes and magnitudes of land-water-atmosphere coupling. The most important broader impact of the work will most likely come via improved tools and information networks for "sustainability" in a region of multiple transboundary environmental pressures.