Inundation, mixing and vegetation influences carbon dioxide concentrations in Amazon floodplains

Abstract:

Tropical lakes and associated wetlands, such as those on Amazon floodplains, often have high rates of carbon dioxide fixation and release. Aquatic habitats throughout the Amazon basin vary seasonally and spatially as a function of inundation. In a representative central Amazon floodplain lake, Lake Janauacá, we measured diel, seasonal and inter-annual variations of carbon dioxide concentrations in open waters of the lake and in an embayment, and in flooded forests and floating herbaceous plants, combined with environmental variables and remote sensing of habitat areas. Carbon dioxide concentrations in surface waters of open water of the lake varied from 0.2 to 280 µM, in open water of an embayment from 3 to 430 µM, in herbaceous plant mats from 8 to 2050 µM, and in flooded forests from 19 to 329 µM. Interannual differences were related to changes in herbaceous plant cover, while diel changes were related to planktonic metabolism, advection and mixing. We developed a statistical model linking measures of inundation, productivity, carbon quality and mixing to carbon dioxide concentrations using a multi-model selection and averaging approach. The strongest model included CO₂ measured within herbaceous plant mats, changes in water level, an indicator of changes in inundation, and Secchi depth, an indicator of optical conditions related to plankton productivity and thermal stratification, as key explanatory variables.