Baseflow CO2 fluxes in small tropical rivers driven by hydrological dynamics

Abstract

Dry season CO2 fluxes were estimated for 1418 small rivers and streams in the Upper São Francisco Basin (USFB), Brazil. This first basin-scale estimate revealed a substantial contribution of 1.52 Pg C yr− 1 (95 % confidence interval: 1.40 to 1.64 Pg C yr− 1 ). pCO2 values, calculated from pH and total alkalinity (TA) and subsequently corrected, ranged from 66 to 20,200 μatm (2191 ± 1791 μatm; coefficient of variation of 82 %). Approximately 95 % of rivers exhibited evasive fluxes with bed friction dissipation as the dominant control on turbulence in over 85 %. Analysis of gas transfer velocity (k600) parameterizations revealed significant inter-equation differences, high spatial variability, and strong slope influence. These findings highlight the potentially role of small tropical rivers and streams in global carbon cycling and provide the first CO2 emission estimate for the USFB.