Publication Date:
2015-08-08
Description:
Globally, Dissolved Inorganic Carbon (DIC) accounts for more than half the annual flux of carbon exported from terrestrial ecosystems via rivers. Here we assess the relative influences of biogeochemical and hydrological processes on DIC fluxes exported from a tropical river catchment characterized by distinct land cover, climate and geology transition from the wet tropical mountains to the low lying savanna plains. Processes controlling changes in river DIC were investigated using dissolved organic carbon (DOC), particulate organic carbon (POC) and DIC concentrations and stable isotope ratios of DIC (δ 13 C DIC ) at two time scales; seasonal and diel. The recently developed Isotopic Continuous Dissolved Inorganic Carbon Analyser (ISO-CADICA) was used to measure diel DIC concentration and δ 13 C DIC changes at a 15 minute temporal resolution. Results highlight the predominance of biologically mediated processes (photosynthesis and respiration) controlling diel changes in DIC. These resulted in DIC concentrations varying between 3.55-3.82 mg/L, and δ 13 C DIC values ranging from -19.7 ± 0.31 to -17.1 ± 0.08 ‰. In contrast, at the seasonal scale we observe wet season DIC variations predominantly from mixing processes, and dry season DIC variations due to both mixing processes and biological processes. The observed wet season increases in DIC concentrations (by 6.81 mg/L) and δ 13 C DIC values of river water (by 5.4 ‰) largely result from proportional increases in subsurface inflows from the savanna plains (C 4 vegetation) region relative to inflows from the rainforest (C 3 vegetation) highlands. The high DIC river load during the wet season results in the transfer of 97% of the annual river carbon load. Therefore, in this gaining river there are significant seasonal variations in both the hydrological and carbon cycles, and there is evidence of substantial coupling between the carbon cycles of the terrestrial and the fluvial environments. Recent identification of a substantial savanna carbon sink in wetter years in the recent past does not take into account the possibility of a substantial, rapid, lateral flux of carbon to rivers and back to the atmosphere. This article is protected by copyright. All rights reserved.
Print ISSN:
0885-6087
Electronic ISSN:
1099-1085
Topics:
Architecture, Civil Engineering, Surveying
,
Geography
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