Seasonal and spatial variability of CO2 in aquatic environments of the central lowland Amazon basin

Abstract

Different sources and processes contribute to pCO2 and CO2 exchange with the atmosphere in the rivers and floodplains of the Amazon basin. We measured or estimated pCO2, CO2 fluxes with the atmosphere, planktonic community respiration (PCR), and environmental and landscape variables along the Negro and Amazon-Solimoes rivers during different periods of the fluvial hydrological cycle. Values of pCO2 ranged from 307 to 7527 μatm, while CO2 fluxes ranged from − 9.3 to 1128 mmol m−2 d−1 in the Amazon-Solimoes basin. In the Negro basin, pCO2 values ranged from 648 to 6526 μatm, and CO2 fluxes from 35 to 1025 mmol m−2 d−1. In a general linear model including data from Negro and Amazon-Solimoes basins, seasonal and spatial variation in flooded vegetated habitat area, dissolved oxygen, depth and water temperature explained 85% of surface pCO2 variation. Levels of pCO2 varied with inundation extent, with higher pCO2 values occurring in periods with greater water depth and inundation area, and lower dissolved oxygen concentrations and water temperatures. In a separate analysis for the Amazon-Solimoes river and floodplains, ecosystem type (lotic or lentic), hydrological period, water temperature, dissolved oxygen, depth and dissolved phosphorus explained 83% of pCO2 variation. Our results demonstrate the influence of alluvial floodplains and seasonal variations in their limnological characteristics on the pCO2 levels in river channels of the lowland Amazon.