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Large uncertainties in estimates of methane (CH4) emissions from tropical inland waters reflect the paucity of information at appropriate temporal and spatial scales. CH4 concentrations, diffusive and ebullitive fluxes, and environmental parameters in contrasting aquatic habitats of Lake Janauaca´, an Amazon floodplain lake, measured for two years revealed patterns in temporal and spatial variability related to different aquatic habitats and environmental conditions. CH4 concentrations ranged from below detection to 96 lM, CH4 diffusive fluxes from below detection to 2342 lmol m-2 h-1, and CH4 ebullitive fluxes from 0 to 190 mmol m-2 d-1. Vegetated aquatic habitats had higher surface CH4 concentrations than open water habitats, and no significant differences in diffusive CH4 fluxes, likely due to higher k values measured in open water habitats. CH4 emissions were enhanced after a prolonged low water period, when the exposed sediments were colonized by herbaceous plants that decomposed after water levels rose, possibly fueling CH4 production. Statistical models indicated the importance of variables related to CH4 production (temperature, dissolved organic carbon) and consumption (dissolved nitrogen, oxygenated water column), as well as maximum depth.
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Inundation, hydrodynamics and vegetation influences carbon dioxide concentrations in Amazon floodplain lakes
Extensive floodplains and numerous lakes in the Amazon basin are well suited to examine the role of floodable lands within the context of the sources and processing of carbon within inland waters. We measured diel, seasonal and inter-annual variations of carbon dioxide concentrations and related environmental variables in open water and flooded vegetation and estimated the extension of these habitats using remote sensing in a representative central Amazon floodplain lake, Lake Janauacá. Depth-averaged values of CO2 in the open water of the lake, 157± 91 µM (mean ± SD), were less than those in an embayment near aquatic vegetation, 285±116 µM, and were variable over 24-h periods at both sites. Within floating herbaceous plant mats, mean concentration (without one outlier) was 275±77 µM and in flooded forests mean concentration was 217±78 µM. Variability in CO2 concentrations in open water resulted from changes in the extent of inundation and exchange with vegetated habitats. The best statistical model, including CO2 in aquatic plant mats, Secchi depth, rate of change in water level and chlorophyll concentrations, explained around 90% of the variability in CO2 concentration. Three-dimensional hydrodynamic modeling demonstrated that diel differences in water temperature between plant mats and open water and basin-scale motions caused lateral exchanges of CO2 linking vegetated habitats to open water. Our findings extend understanding of CO2 in tropical lakes and floodplains with measurements and models that emphasize the importance of flooded forests and aquatic herbaceous plants fringing floodplain lakes as sources of carbon dioxide to the open waters.
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- Award ID(s):
- 1753856
- PAR ID:
- 10330387
- Date Published:
- Journal Name:
- Ecosystems
- ISSN:
- 1112-3737
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1007/s10021-021-00692-y
