| Publisher Information: |
Uppsala universitet, Limnologi; Univ Fed Juiz de Fora, Inst Ciencias Biol, Dept Biol, Aquat Ecol Lab, Juiz De Fora, Brazil.; Univ Sao Paulo, Escola Super Agr Luiz de Queiroz, Dept Ciencia Solo, Piracicaba, Brazil.; Univ Fed Rio de Janeiro, Lab Limnol, Rio De Janeiro, Brazil.; Univ Fed Rio Grande do Norte, Lab Water Resources & Environm Sanitat, BR-59072970 Natal, RN, Brazil.; Univ Fed Rio Grande do Norte, Lab Limnol, BR-59072970 Natal, RN, Brazil.; Univ Fed Santa Catarina, Lab Freshwater Ecol, Florianopolis, SC, Brazil.; Radboud Univ Nijmegen, Dept Aquat Ecol & Environm Biol, Inst Water & Wetland Res, NL-6525 ED Nijmegen, Netherlands.; Univ Republica, Dept Ecol Teor & Aplicada, Ctr Univ Reg Este, Montevideo, Uruguay.;Univ Republica, Fac Ciencias, Montevideo, Uruguay.; Univ Fed Estado Rio de Janeiro, Dept Ciencias Nat, Rio De Janeiro, Brazil.; Univ Fed Sao Carlos, Lab Microbial Proc & Biodivers, BR-13560 Sao Carlos, SP, Brazil.; Wageningen Univ, Aquat Ecol & Environm Sci, NL-6700 AP Wageningen, Netherlands.; Univ Fed Juiz de Fora, Inst Ciencias Biol, Dept Biol, Aquat Ecol Lab, Juiz De Fora, Brazil; Univ Fed Rio de Janeiro, Museu Nacl, Lab Ficol, Rio De Janeiro, Brazil. |
| Description: |
Recent studies from temperate lakes indicate that eutrophic systems tend to emit less carbon dioxide (Co-2) 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 ... |