Soil processes and properties related to the genesis and evolution of a Pleistocene savanna palm swamp (vereda) in central Brazil

The peat properties of Brazilian palm swamps, or veredas, as they are locally known, lend these environments the character of water reservoirs and carbon stores, in addition to being important archives of past changes. In this paper, we present, in high-resolution, the stratigraphy and morphological, physical, chemical, elemental, and isotopic properties of a deep soil vereda core (Pau Grande, with 283 cm) from the Grande Serta tilde o Veredas National Park, in the state of Minas Gerais, Brazil. The core is constituted by 10 histic horizons in the first 151 cm, and one mineral layer from 151 to 283 cm. Peat sedimentation rates were different along its depth, as follow: 0.0273 cm year(-1) (109-111 cm), 0.0018 cm year(- 1) (85-87 cm), 0.0027 cm year(-1) (59-61 cm), 0.0031 cm year(-1) (45-47 cm), and 0.0042 cm year(-1) (24-26 cm). Mean values of the main peat properties were: 16% for C, 44% for Si,-17.20%o for delta C-13, 3.68%o for delta N-15, 167% for gravimetric moisture, 75% for mineral material, 8% for rubbed fibres, 3.58 for pH, 0.77 Mg m(-3) for bulk density, and 0.15 for bulk density of the organic matter. Principal components analysis was applied to peat properties to assist in the identification of processes/drivers that control the nature of the studied vereda, in addition to providing evidence of changes in the paleoenvironment. The first principal component, PC1, is related to the relative accumulation of organic versus local mineral matter, linked to the evolution of the catchment soils (erosion) and possible associated vegetation (C3 and C4 plants); PC2 is related to the hydromorphism conditions; PC3 is related to the incorporation of inorganic material through the deposition of dust from regional sources; and PC4 is related to the main sources of organic matter. Radiocarbon dating indicates this vereda began its formation during the late Pleistocene. Five phases of changes in the environment were also verified: I) 33,309-26,818 cal BP - formation of a lake or a shallow water body, pre-dominance of algae, and locally and regionally unstable environment; II) 26,818-16,659 cal BP - predominance of terrestrial plants, locally stable but regionally unstable environment; III) 16,659-10,401 cal BP - oxic, drier environment with a predominance of C4 terrestrial plants, and a simultaneous increase in local instability with stabilization of the regional environment at similar to 15.0 kyr cal BP; IV) 10,401-5,052 cal BP - return to being an algal source in even more oxic conditions, and beginning of greater stability in both the local and regional environ-ments; and V) 5,052 cal BP until present - consolidation of the stable environment initiated in the previous phase, characteristic reducing environment to that currently found in the Pau Grande vereda, and changing the contribution of organic matter sources, initially with terrestrial plants and, subsequently, algae. Our results suggest that the Pau Grande vereda is a complex ecosystem. These environments have a large potential for studies on environmental reconstruction and climate changes that have occurred since the late Pleistocene, and they should be fully protected.

Automated summary

This paper presents a study on the stratigraphy and properties of a deep soil core from a vereda in Brazil. The research provides insight into the formation and environmental changes of the vereda, as well as the potential for studying climate changes since the late Pleistocene. The results highlight the importance of protecting these complex ecosystems for further research.