A seasonal cycle in the carbonisotope composition of organic carbon in the Sanaga River, Cameroon
Limnol. Oceanogr., 43(1), 1998, 143-146 | DOI: 10.4319/lo.1998.43.1.0143
ABSTRACT: We report measurements of the carbon-isotope composition (δ13C 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 δ13C 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, δ13C 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 δ13C 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 δ13C values in tropical rivers that carry a significant suspended sediment load is the δ13C value of the catchment vegetation.