VULNERABILITY OF ORGANIC CARBON TRANSPORT IN TROPICAL RIVERS TO GLOBAL CHANGE: A COUPLED TERRESTRIAL-AQUATIC APPROACH

Tropical rivers and streams originating in mountainous areas are a large source of organic matter and nutrients to the coastal ocean. Terrestrial organic matter in streams helps support aquatic productivity in the coastal ocean, and may support carbon sequestration in marine sediments. Tropical watersheds also serve as sites of high reactivity of organic matter and nutrients, with large fluxes of carbon dioxide as a result. However, tropical mountainous watersheds are also highly vulnerable to global change, including climate change and land use change. Warming temperatures can affect biological activity in streams and in riparian soils, potentially accelerating the release of organic matter as carbon dioxide. Warming may also have a disproportionate effect on tropical mountainous streams by accelerating glacier melting and/or sublimation. Changing precipitation regimes will also have a large effect on mountainous streams. Deforestation and urbanization will also affect terrestrial organic C stocks, erosion rates, and discharge patterns, especially when dams are created. In this presentation, I will address the need for a broad approach to understanding the effect of global change on tropical mountainous streams, including measurements of both terrestrial and aquatic processes. I will supplement with examples from headwater streams in the tropical Andes and Himalayas. Broadly, my work has shown that mountainous headwater watersheds can have very high storage rates of organic carbon in soils, but these soils are episodically eroded into streams during extreme precipitation events. Changing precipitation regimes in the Amazon and the Himalayas due to climate change may therefore reduce overall carbon storage in soils in these regions, thus acting as a positive feedback to climate change.