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Flooded ecosystems are conditioned to seasonal floods that promote specific soil conditions, such as low oxygen, hydromorphism, and peculiar chemical reactions. These environments are dependent on flood pulses that determine specific ecological conditions. Ipucas are seasonally flooded discontinuous forest patches that occur exclusively in the Araguaia Plain in Central Brazil. They are located 0.40 to 1.20 m lower than the surrounding plain, which promotes an accumulation of rainwater for five to six months of the year, being entirely or partially dry during the dry season. The aim of this study was to evaluate the horizontal (centre and edge) and vertical (depths: 0–0.20 m and 0.20–0.40 m) variability of physicochemical parameters in Ipucas soils, attempting to establish the importance of flood pulses and the leaching of surrounding areas in soil formation and composition. Samples were collected during the dry season in three Ipucas of similar size and circularity using a Dutch auger. The results reveal that flood pulses promote the deposition of sediments eroded from the surrounding plain, homogenizing the characteristics of the surface soil, from the edge to the centre of the Ipucas. However, biogeochemical processes, also linked to temporary flooding, account for the differences between the surface and deeper soil horizons because anoxic conditions during flooding promote chemical reactions characteristic of anaerobic environments, modifying the pH and organic matter content, in addition to the gleying of soils subjected to flooding, which are then covered by sediments after the dry season. Finally, Ipucas soils are susceptible to anthropic changes and are dependent on seasonal flood pulses.

Abstract Aim The present study investigated the diversity of aquatic macrophytes in the littoral zone of Lajeado Reservoir, Tocantins River. We characterized spatial variations in species richness, composition and abundance along depth gradients. Methods Macrophyte sampling occurred at the end of the dry season (September and October 2014) in four sites of the reservoir. We established transects perpendicular to the shoreline, each 25 m long, divided in 3 sections (plots of 5 x 5 m). Results In total, we recorded 18 taxa of aquatic macrophytes, belonging to nine families and four life forms. Najas microcarpa, Echinodorus tenellus. and Chara sp. were the more frequent and abundant taxa. Considering depth gradients, we recorded 18 taxa in the section closer to the shoreline, 13 in the middle section and 10 in the section more distant to the shoreline. Submerged and emergent species were more frequent and abundant, especially in the section close to the shoreline; epiphytes and free-floating species were rare. Plot species richness (total, emergent and submerged) decreased along the gradient, and a Non-Metric Multidimensional Scaling (NMDS) revealed that the plot close to the shoreline had different composition when compared to adjacent sections. Individual species showed particular behaviors, but most tended to decline in abundance and occurrence along the gradient. Conclusions The present study revealed that small-scale environmental gradients affect the distribution of aquatic plants in Lajeado Reservoir, with greater diversity in habitats close to the shoreline.

Ipucas são ecossistemas de fragmentos florestais naturais, ocorrendo particularmente na planície do Araguaia. Apresenta grande influência dos pulsos de inundação que ocorrem no período chuvoso, pois permanecem inundadas durante este período e como ambientes terrestres no período seco. O estudo objetivou avaliar a variação temporal de fatores limnológicos em uma Ipuca, no município de Lagoa da Confusão, Tocantins, através de coletas mensais entre Dezembro/2014 e Agosto/2015. As variáveis mensuradas foram: transparência através do disco Secchi, turbidez (NTU), oxigênio dissolvido (mg/L), temperatura (°C), potencial hidrogeniônico - pH, sólidos totais dissolvidos (ppm), condutividade elétrica (µS/cm), amônia – NH3 (mg/L), nitrito – NO­2 (mg/L), nitrato – NO3 (mg/L), ortofosfato - P (mg/L), clorofila-? (µg/L) e profundidade da lamina d’água (cm). O total transparência da água e os baixos valores de turbidez demonstram a importância da precipitação nestes parâmetros, assim como a estrutura florestal da “Ipuca” suporta os valores encontrados. A temperatura da água das “Ipucas” foi influenciada pelas estações do ano, principalmente pela quantidade de ventos. O oxigênio dissolvido esteve diretamente relacionado a clorofila-?. A concentração dos nutrientes analisados apresentou grandes oscilações, provavelmente devido à rápida incorporação destes pelas comunidades aquáticas. Contudo, foi observada uma homogeneização dos parâmetros físico-químicos no decorrer do tempo amostral.