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Biogeosciences An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/bg-2017-108
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
21 Apr 2017
Review status
This discussion paper is a preprint. It has been under review for the journal Biogeosciences (BG). The manuscript was not accepted for further review after discussion.
Biogeochemical diversity and hot moments of GHG emissions from shallow alkaline lakes in the Pantanal of Nhecolândia, Brazil
Laurent Barbiero1,2,3, Marcos Siqueira Neto4, Rosangela Rodrigues Braz1, Janaina Braga de Carmo5, Ary Tavares Rezende Filho6, Edmar Mazzi1, Fernando Antonio Fernandes7, Sandra Regina Damatto8, and Plinio Barbosa de Camargo1 1Laboratorio de Ecologia Isotópica, Centro de Energia Nuclear na Agricultura (CENA), Universidade de São Paulo, Piracicaba-SP, 13416-000, Brazil
2Instituto de Química, Universidade estadual de Campinas, Campinas-SP, 13083-970, Brazil
3Géoscience Environnement Toulouse (GET), IRD, CNRS, Université P. Sabatier de Toulouse, F31400, France
4Laboratorio de Biogeoquímica Ambiental, Centro de Energia Nuclear na Agricultura (CENA), Universidade de São Paulo, Piracicaba-SP, 13416-000, Brazil
5Centro de Ciências e Tecnologias para a Sustentabilidade, Universidade Federal de São Carlos, Sorocaba-SP, 18052-780, Brazil
6Faculdade de Engenharias, Arquitetura e Urbanismo e Geografia (FAENG), Universidade Federal do Mato-Grosso do Sul, Campo Grande-MS, 79070-900, Brazil
7Empresa Brasileira de Pesquisa Agropecuária (EMBRAPA), Embrapa-Pantanal, Corumbá-MS, 79320-900, Brazil
8Departamento de Metrologia das Radiações, Instituto de Pesquisas Energéticas e Nucleares (IPEN), Universidade de São Paulo, São Paulo-SP, 05508-000, Brazil
Abstract. Nhecolândia is a vast sub-region of the Pantanal wetland in Brazil with great diversity in surface water chemistry evolving in a sodic alkaline pathway under the influence of evaporation. In this region, more than 15,000 shallow lakes are likely to contribute an enormous quantity of greenhouse gas to the atmosphere, but the diversity of the biogeochemical scenarios and their variability in time and space is a major challenge to estimate the regional contribution. In this study, we compiled measurements of the physico-chemical characteristics of water and sediments, gas fluxes in floating chambers, and sedimentation rates to illustrate this diversity. Although these lakes have a similar chemical composition, the results confirm an opposition between the black-water and green-water alkaline lakes, corresponding to distinct biogeochemical functioning. Black-water lakes are CO2 and CH4 sources, with fairly constant emissions throughout the seasons. Annual carbon dioxide and methane emissions approach 790 mmol m−2 y−1 and 73 mmol m−2 y−1, respectively. By contrast, green-water lakes are CO2 sinks but significant CH4 sources with fluxes varying significantly throughout the seasons, depending on the development of the cyanobacterial bloom. The results highlight two hot moments for methane emissions. The first one is suspected after the disappearance of the cyanobacterial bloom, which is accompanied by a drop in pH of the upper part of the sediments. The second one is identified when the O2-supersaturation is reached under extreme bloom and sunny weather conditions, which provoke an abrupt O2 purging of the lakes. Taking into account the seasonal variability, annual methane emissions are around 8,850 mmol m−2 y−1, i.e., much higher than reported in previous studies for alkaline lakes in Nhecolândia. Carbon dioxide consumption is estimated about 1,140 mmol m−2 y−1. However, these balances must be better constrained with systematic and targeted measurements around these hot moments.

Citation: Barbiero, L., Siqueira Neto, M., Braz, R. R., Carmo, J. B. D., Rezende Filho, A. T., Mazzi, E., Fernandes, F. A., Damatto, S. R., and Camargo, P. B. D.: Biogeochemical diversity and hot moments of GHG emissions from shallow alkaline lakes in the Pantanal of Nhecolândia, Brazil, Biogeosciences Discuss., https://doi.org/10.5194/bg-2017-108, 2017.
Laurent Barbiero et al.
Laurent Barbiero et al.

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Short summary
Large tropical alkaline wetlands are likely to contribute significantly to the global GHG emissions budget, but little data are available. The study shows the diversity of situations that depend on local biogeochemical processes and their stage of development during the season. Hot moments are identified and must be taken into account for calculating the regional emission budget.
Large tropical alkaline wetlands are likely to contribute significantly to the global GHG...
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