Biogeochemical processes and the diversity of Nhecolândia lakes, Brazil

Anais da Academia Brasileira de Ciências

Teodoro I. R Almeida²  Maria Do Carmo Calijuri¹  Patrícia B Falco¹  Simone P Casali¹  Elena Kupriyanova¹  Antonio C Paranhos Filho¹  Joel B Sigolo²  Reginaldo A Bertolo² 

[1] ,Universidade de São Paulo Instituto de Geociências São Paulo SP ,Brasil

关键词: Pantanal;    alkaline lakes;    saline lakes;    cyanobacteria;    alkalinization processes;    Pantanal;    lagos alcalinos;    lagos salinos;    cianobactérias;    processos de alcalinização;   

DOI  :  10.1590/S0001-37652011000200004

来源: SciELO

【 摘 要 】

The Pantanal of Nhecolândia, the world's largest and most diversified field of tropical lakes, comprises approximately 10,000 lakes, which cover an area of 24,000 km² and vary greatly in salinity, pH, alkalinity, colour, physiography and biological activity. The hyposaline lakes have variable pHs, low alkalinity, macrophytes and low phytoplankton densities. The saline lakes have pHs above 9 or 10, high alkalinity, a high density of phytoplankton and sand beaches. The cause of the diversity of these lakes has been an open question, which we have addressed in our research. Here we propose a hybrid process, both geochemical and biological, as the main cause, including (1) a climate with an important water deficit and poverty in Ca2+ in both superficial and phreatic waters; and (2) an elevation of pH during cyanobacteria blooms. These two aspects destabilise the general tendency of Earth's surface waters towards a neutral pH. This imbalance results in an increase in the pH and dissolution of previously precipitated amorphous silica and quartzose sand. During extreme droughts, amorphous silica precipitates in the inter-granular spaces of the lake bottom sediment, increasing the isolation of the lake from the phreatic level. This paper discusses this biogeochemical problem in the light of physicochemical, chemical, altimetric and phytoplankton data.

【 授权许可】

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