title: High Primary Production Contrasts with Intense Carbon Emission in a Eutrophic Tropical Reservoir.
abstract: Recent studies from temperate lakes indicate that eutrophic systems tend to emit less carbon dioxide (CO2) and bury more organic carbon (OC) than oligotrophic ones, rendering them CO2 sinks in some cases. However, the scarcity of data from tropical systems is critical for a complete understanding of the interplay between eutrophication and aquatic carbon (C) fluxes in warm waters. We test the hypothesis that a warm eutrophic system is a source of both CO2 and CH4 to the atmosphere, and that atmospheric emissions are larger than the burial of OC in sediments. This hypothesis was based on the following assumptions: (i) OC mineralization rates are high in warm water systems, so that water column CO2 production overrides the high C uptake by primary producers, and (ii) increasing trophic status creates favorable conditions for CH4 production. We measured water-air and sediment-water CO2 fluxes, CH4 diffusion, ebullition and oxidation, net ecosystem production (NEP) and sediment OC burial during the dry season in a eutrophic reservoir in the semiarid northeastern Brazil. The reservoir was stratified during daytime and mixed during nighttime. In spite of the high rates of primary production (4858 ± 934 mg C m(-2) d(-1)), net heterotrophy was prevalent due to high ecosystem respiration (5209 ± 992 mg C m(-2) d(-1)). Consequently, the reservoir was a source of atmospheric CO2 (518 ± 182 mg C m(-2) d(-1)). In addition, the reservoir was a source of ebullitive (17 ± 10 mg C m(-2) d(-1)) and diffusive CH4 (11 ± 6 mg C m(-2) d(-1)). OC sedimentation was high (1162 mg C m(-2) d(-1)), but our results suggest that the majority of it is mineralized to CO2 (722 ± 182 mg C m(-2) d(-1)) rather than buried as OC (440 mg C m(-2) d(-1)). Although temporally resolved data would render our findings more conclusive, our results suggest that despite being a primary production and OC burial hotspot, the tropical eutrophic system studied here was a stronger CO2 and CH4 source than a C sink, mainly because of high rates of OC mineralization in the water column and sediments.
authors.affiliation: Laboratory of Aquatic Ecology, Department of Biology, Instituto de Ciências Biológicas, Federal University of Juiz de Fora Juiz de Fora, Brazil.
authors.forename: Rafael M
authors.initials: RM
authors.lastname: Almeida
authors.affiliation: Departamento de Ciência do Solo, Escola Superior de Agricultura Luiz de Queiroz, University of São Paulo Piracicaba, Brazil.
authors.forename: Gabriel N
authors.initials: GN
authors.lastname: Nóbrega
authors.affiliation: Laboratory of Limnology, Federal University of Rio de Janeiro Rio de Janeiro, Brazil.
authors.forename: Pedro C
authors.initials: PC
authors.lastname: Junger
authors.affiliation: Laboratory of Water Resources and Environmental Sanitation, Federal University of Rio Grande do Norte Natal, Brazil.
authors.forename: Aline V
authors.initials: AV
authors.lastname: Figueiredo
authors.affiliation: Laboratory of Limnology, Federal University of Rio Grande do Norte Natal, Brazil.
authors.forename: Anízio S
authors.initials: AS
authors.lastname: Andrade
authors.affiliation: Laboratory of Limnology, Federal University of Rio Grande do Norte Natal, Brazil.
authors.forename: Caroline G B
authors.initials: CG
authors.lastname: de Moura
authors.affiliation: Laboratory of Freshwater Ecology, Federal University of Santa Catarina Florianópolis, Brazil.
authors.forename: Denise
authors.initials: D
authors.lastname: Tonetta
authors.affiliation: Department of Aquatic Ecology and Environmental Biology, Institute for Water and Wetland Research, Radboud University Nijmegen, Netherlands.
authors.forename: Ernandes S
authors.initials: ES
authors.lastname: Oliveira
authors.affiliation: Laboratory of Water Resources and Environmental Sanitation, Federal University of Rio Grande do Norte Natal, Brazil.
authors.forename: Fabiana
authors.initials: F
authors.lastname: Araújo
authors.affiliation: Laboratory of Aquatic Ecology, Department of Biology, Instituto de Ciências Biológicas, Federal University of Juiz de Fora Juiz de Fora, Brazil.
authors.forename: Felipe
authors.initials: F
authors.lastname: Rust
authors.affiliation: Departamento de Ecología Teórica y Aplicada, Centro Universitario Regional Este and Facultad de Ciencias, Universidad de la República Montevideo, Uruguay.
authors.forename: Juan M
authors.initials: JM
authors.lastname: Piñeiro-Guerra
authors.affiliation: Laboratory of Water Resources and Environmental Sanitation, Federal University of Rio Grande do Norte Natal, Brazil.
authors.forename: Jurandir R
authors.initials: JR
authors.lastname: Mendonça
authors.affiliation: Laboratory of Limnology, Federal University of Rio Grande do Norte Natal, Brazil.
authors.forename: Leonardo R
authors.initials: LR
authors.lastname: Medeiros
authors.affiliation: Departamento de Ciências Naturais, Universidade Federal do Estado do Rio de Janeiro Rio de Janeiro, Brazil.
authors.forename: Lorena
authors.initials: L
authors.lastname: Pinheiro
authors.affiliation: Laboratory of Aquatic Ecology, Department of Biology, Instituto de Ciências Biológicas, Federal University of Juiz de Fora Juiz de Fora, Brazil.
authors.forename: Marcela
authors.initials: M
authors.lastname: Miranda
authors.affiliation: Laboratory of Water Resources and Environmental Sanitation, Federal University of Rio Grande do Norte Natal, Brazil.
authors.forename: Mariana R A
authors.initials: MR
authors.lastname: Costa
authors.affiliation: Laboratory of Microbial Processes and Biodiversity, Federal University of São Carlos São Carlos, Brazil.
authors.forename: Michaela L
authors.initials: ML
authors.lastname: Melo
authors.affiliation: Laboratory of Limnology, Federal University of Rio Grande do Norte Natal, Brazil.
authors.forename: Regina L G
authors.initials: RL
authors.lastname: Nobre
authors.affiliation: Laboratory of Limnology, Federal University of Rio de Janeiro Rio de Janeiro, Brazil.
authors.forename: Thiago
authors.initials: T
authors.lastname: Benevides
authors.affiliation: Laboratory of Aquatic Ecology, Department of Biology, Instituto de Ciências Biológicas, Federal University of Juiz de Fora Juiz de Fora, Brazil.
authors.forename: Fábio
authors.initials: F
authors.lastname: Roland
authors.affiliation: Aquatic Ecology and Environmental Sciences, Wageningen University Wageningen, Netherlands.
authors.forename: Jeroen
authors.initials: J
authors.lastname: de Klein
authors.affiliation: Laboratory of Aquatic Ecology, Department of Biology, Instituto de Ciências Biológicas, Federal University of Juiz de Fora Juiz de Fora, Brazil.
authors.forename: Nathan O
authors.initials: NO
authors.lastname: Barros
authors.affiliation: Laboratory of Aquatic Ecology, Department of Biology, Instituto de Ciências Biológicas, Federal University of Juiz de ForaJuiz de Fora, Brazil; Department of Ecology and Genetics, Uppsala UniversityUppsala, Sweden.
authors.forename: Raquel
authors.initials: R
authors.lastname: Mendonça
authors.affiliation: Laboratory of Water Resources and Environmental Sanitation, Federal University of Rio Grande do Norte Natal, Brazil.
authors.forename: Vanessa
authors.initials: V
authors.lastname: Becker
authors.affiliation: Laboratório de Ficologia, Museu Nacional, Universidade Federal do Rio de Janeiro Rio de Janeiro, Brazil.
authors.forename: Vera L M
authors.initials: VL
authors.lastname: Huszar
authors.affiliation: Department of Aquatic Ecology and Environmental Biology, Institute for Water and Wetland Research, Radboud University Nijmegen, Netherlands.
authors.forename: Sarian
authors.initials: S
authors.lastname: Kosten
keywords: Caatinga; carbon dioxide; methane; net ecosystem production; organic carbon burial; semiarid