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| Author(s): |
Tiago Osorio Ferreira
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Piracicaba. |
| Institution: | Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC) |
| Defense date: | 2006-02-21 |
| Examining board members: |
Pablo Vidal Torrado;
Wilson Thadeu Valle Machado;
João José Granate de Sá e Melo Marques;
Jefferson Mortatti;
Xose Luis Otero Perez
|
| Advisor: | Pablo Vidal Torrado |
| Abstract | |
Due to the important functional role of mangrove forest communities and their transitional position between marine and terrestrial environments, these ecosystems have been the object of study by a variety of scientific disciplines; however, there are only a few published studies on the genesis and biogeochemistry of its soils. Iron and sulfur compounds play a key role on the active biogeochemical cycles in these environments, mainly because sulfate reduction is considered the preponderant respiration process in these sites. The biogeochemical cycles of these elements are, however, ruled by physicochemical variations constantly generated by tide flooding, different climatic seasons and fauna and flora activity. Considering the scarce information about these soils, a detailed biogeochemical study of mangrove sites located in the State of São Paulo was undertaken to generate additional information on the genesis of these soils and also to evaluate the effects of seasonal variations, biological activity (plants and macrofauna) and physiographic positions on Fe and S biogeochemistry. Morphological, chemical and mineralogical data (XRD and SEM) were examined for evidence of pedogenic processes; interstitial water (pH, salinity, concentrations of Mn2+, Fe2+, HS-, SO4 2-e Cl-) and solid phase (TOC, total Fe, total S, total Mn, AVS, microbial biomass C, density of living and dead roots, sand percentage and sequential extraction of Fe) analysis were undertaken in different soil profiles under mangrove vegetation from São Paulo State (Guarujá and Cananéia) to asses Fe and S biogeochemistry. The evidences presented in this study indicate that pedogenic processes (addition of organic material; translocation of Fe2+ and mineral particles; transformation of elements such as Fe and S) have occurred in mangrove substrates and that these substrates are more properly referred to, understood and studied as soils and not sediments. Results also evidence that pyrite and AVS oxidation is taking place in response to plants and macro-fauna activity and that the seasonal cycle of Fe and S biogeochemistry is mostly ruled by plants and macro-fauna. Results indicate important differences between physicochemical conditions of the pore water in the vegetated (soils) and non-vegetated (sediment) zones, which are related to the faster dynamics of the biogeochemical soil processes caused by the effect of plants (oxidation, liberation of the exudates by the roots). Our data also show that the contribution and intensity of each process coupled to organic matter mineralization in mangrove soils may vary significantly between the distinct physiographic positions. These variations are generated by physiographic positions effects on frequency and duration of tidal flooding and grain size composition of soils. In this context, the occurrence, or dominance, of one process over the others, affects, in a significant way, pore water and solid phases chemistry. (AU) | |