CARBON TRANSFORMATIONS IN THE TROPICAL SILICATE-DOMINATED DEDURU OYA CATCHMENT, SRI LANKA (C-TROPIC-TRANS)

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Carbon transfer and transformations in rivers are important reflectors of land use, weathering and climate effects. Such carbon systematics equally reflect river ecosystem and catchment health in an integral manner. A global uncertainty in this context includes extensive losses of CO2 from rivers that have mostly been budgeted on large river systems. However, smaller rivers and streams have hardly been investigated in this way so far. In particular, this lack of investigations applies to rivers from small catchments that directly discharge to the oceans. Here we propose a new investigation of carbon transformations in the tropical Deduro Oya catchment (Sri Lanka). This study would offer new insights into tropical functioning with respect to carbon transformations of a silicate-dominated lithology. Moreover, the work aims to investigate typical regional agricultural practices such as rice paddy growth that likely influences carbon spiraling within the river. Other factors such as reservoirs and multiple small water retention systems along the river as well as sewage inputs are equally planned for investigation in this monsoon-driven system. Planned geochemical tools include concentration analyses of dissolved and particulate carbon (DOC, DIC and POC) together with their stable isotopes on river and groundwater samples. This will combine with field parameters, water isotopes and major- as well as trace element analyses. Expected data will offer modelling on CO2 degassing from the water phase. Similar approaches on other aquatic systems have helped to outline natural and anthropogenic influences on aquatic carbon balances between important ecological factors such as photosynthesis and respiration. When transposed to the Deduru Oya catchment, these techniques can help to define a so far hardly known endmember of a tropical medium-sized catchment that discharges directly to the ocean with respect to river functioning in the terrestrial carbon cycle.