A preliminary estimate of organic carbon transport by the Ayeyarwady (Irrawaddy) and Thanlwin (Salween) Rivers of Myanmar

Abstract

We report results of a preliminary study of particulate and dissolved organic carbon transport in the Ayeyarwady and Thanlwin Rivers of Myanmar, based on 52 suspended sediment samples and 9 water samples collected during conditions of low and high flow in 2005 and 2006. The Ayeyarwady transports 2.2–4.3 MtC/yr as POC with a weighted average δ13C value of -24.8‰, while the Thanlwin transports an additional 2.4–3.4 MtC/yr with a δ13C value of -25.3‰. In addition, the Ayeyarwady transports ~0.9Mt/yr, and the Thanlwin ~0.23Mt/yr, of DOC with a δ13C value of -26.2‰ and -27.1‰, respectively. The Ayeyarwady and Thanlwin catchments adjoin each other, debouching into the Indian Ocean over a length scale similar to the deltas of the Ganges–Brahmaputra or the Amazon. Therefore, the Ayeyarwady and Thanlwin rivers should be considered a single point source contributing to the global ocean.

This combined river system transports 5.7–8.8 MtC/yr of organic carbon, suggesting that it may be the second largest point source of organic carbon to the global ocean after the Amazon. The implied organic carbon yield from the catchments is 8.4–12.9 t/km2/yr, which is clearly amongst the highest in the world among rivers of similarly large size. The high organic carbon yields are likely to be the result of (i) a strongly monsoonal climate, (ii) the large area of highly productive forest present on steep slopes in a region of active tectonism, and (iii) the comparatively small area of floodplain in the catchments.