A seasonal cycle in the carbon-isotope composition of organic carbon in the Sanaga River, Cameroon
Bird, Michael I., Pierre Giresse, and Simon Ngos
Limnol. Oceangr. 43:143-145

We report measurements of the carbon-isotope composition (¹³C value) of particulate organic carbon (POC) in the suspended sediment load of the Sanaga and Mbam Rivers, Cameroon. The results demonstrate that there is a seasonal cycle in ¹³C value of 3.3%0 (-26.6 to -23.3%0) in the Sanaga River and 5.9%0 (-27.1 to -21.2%0) in the Mbam River that is directly related to seasonal changes in the discharge of the rivers. During periods of high discharge, ¹³C values of POC are high, reflecting an increase in the proportion of POC derived from C, plants, including C₄-derived carbon transported overland by wet season rains from savanna regions in the catchment hinterland. During periods of low discharge, the ¹³C values of POC are low, reflecting derivation of the carbon primarily from C₄ plants growing close to the riverbanks. Results suggest that the prime determinant of POC ¹³C values in tropical rivers that carry a significant suspended sediment load is the ¹³C value of the catchment vegetation.