Biogeochemical diversity, O-2-supersaturation and hot moments of GHG emissions from shallow alkaline lakes in the Pantanal of Nhecolandia, Brazil

Author(s)

Barbiero, Laurent ^{[1, 2, 3]} ; Neto, Marcos Siqueira ^[4] ; Braz, Rosangela Rodrigues ^[2] ; do Carmo, Janaina Braga ^[5] ; Rezende Filho, Ary Tavares ^[6] ; Mazzi, Edmar ^[2] ; Fernandes, Fernando Antonio ^[7] ; Damatto, Sandra Regina ^[8] ; de Camargo, Plinio Barbosa ^[2]

Affiliation

^[1] Univ Estadual Campinas, Inst Quim, BR-13083970 Campinas, SP - Brazil

^[2] Univ Sao Paulo, CENA, Lab Ecol Isotop, BR-13416000 Piracicaba, SP - Brazil

^[3] Univ P Sabatier Toulouse, CNRS, IRD, GET, F-31400 Toulouse - France

^[4] Univ Sao Paulo, CENA, Lab Biogeoquim Ambiental, BR-13416000 Piracicaba, SP - Brazil

^[5] Univ Fed Sao Carlos, Ctr Ciencias & Tecnol Sustentabilidade, BR-18052780 Sorocaba, SP - Brazil

^[6] Univ Fed Mato Grosso do Sul, Fac Engn Arquitetura & Urbanismo & Geog FAENG, BR-79070900 Campo Grande, MS - Brazil

^[7] Empresa Brasileira Pesquisa Agr EMBRAPA, BR-79320900 Corumba, MS - Brazil

^[8] Univ Sao Paulo, IPEN, Dept Metrol Radiacoes, BR-05508000 Sao Paulo, SP - Brazil

• Document type: Journal article
• Source: Science of The Total Environment; v. 619, p. 1420-1430, APR 1 2018.
• Web of Science Citations: 3

Abstract

Nhecolandia is a vast sub-region of the Pantanal wetland in Brazilwith great diversity in surface water chemistry evolving in a sodic alkaline pathway under the influence of evaporation. In this region, >15,000 shallowlakes 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. From 4 selected alkaline lakes, we compiled measurements of the physico-chemical characteristics ofwater 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 a difference between the black-water and green-water alkaline lakes, corresponding to distinct biogeochemical functioning. This difference does not appear to affect lake sedimentation rates, but is reflected in gas emissions. Black-water lakes are CO2 and CH4 sources, with fairly constant emissions throughout the seasons. Annual carbon dioxide and methane emissions approach 0.86 mol m(-2) y(-1) and 0.07 mol m(-2) y(-1), respectively, and no clear trend towards N2O capture or emissionwas observed. By contrast, green-water lakes are CO2 and N2O sinks but important CH4 sources with fluxes varying significantly throughout the seasons, depending on the magnitude of the phytoplankton bloom. The results highlight important daily and seasonal variations in gas fluxes, and in particular a hot moments for methane emissions, when the O-2(-) supersaturation is reached during the afternoon under extreme bloom and sunny weather conditions, provoking an abrupt O-2 purging of the lakes. Taking into account the seasonal variability, annual methane emissions are around 10.2 mol m(-2) y(-1), i. e., much higher than reported in previous studies for alkaline lakes in Nhecolandia. Carbon dioxide and nitrous oxide consumption is estimated about 1.9 mol m(-2) y(-1) and 0.73 mmol m(-2) y(-1), respectively. However, these balances must be better constrained with systematic and targeted measurements throughout the seasons. (C) 2017 Elsevier B. V. All rights reserved. (AU)

• FAPESP's process: 16/14227-5 - Climatic changes and environmental impacts in wetlands of Pantanal region (Brazil): quantification, control factors and long term temporal modeling
• Grantee: Adolpho José Melfi
• Support Opportunities: Research Program on Global Climate Change - Thematic Grants
• FAPESP's process: 13/09192-0 - Saline lakes in the Pantanal of Nhecolândia: Hydro-bio-geochemistry of a singular wetland
• Grantee: Laurent Barbiero
• Support Opportunities: Regular Research Grants