Percolação da água no solo e teor de nutrientes lixiviados em função da variação topográfica e sazonal na Amazônia Central

Abstract

In this climate change scenario, we need to seek better answers about the future of the planet and its forests. Understanding the dynamics of soil moisture and transport associated with the chemical elements is a challenge in tropical ecosystems due to the physical nature of tropical soils and the coupled ecohydrological impacts on water flux and nutrient transport. In this study we show the percolation flux of water and nutrients leached during the process of water drainage in the soil, addressing the interaction of water and nutrients. We performed the study in a mature tropical forest in the Central Amazon in space scale "plateau, slope and valley" and over time. We used the fluxmeter passive wick (or drainage lysimeter) containing 60 cm of intact soil and previously configured to make percolation flux measurements every 5 seconds and with a percolated water storage system that had its chemical composition analyzed monthly. Two fluxmeters were installed in each topographic position (plateau, slope and valley) along two transects in the area ZF-2 (Manaus), totaling six installed fluxmeters. The fluxmeters were installed to measure percolation flux 60 cm below the soil surface (which is well below the denser part of the root zone). Our results demonstrate that the flux of percolation is greater in the valley, intermediate in the slope and lower in the plateau. The daily flux to the plateau, slope and valley was 2.18 ± 0.43 mm (95% CI), 2.98 ± 0.59 mm (95% CI) and 5.52 ± 0.82 mm (CI 95%), where accumulated flux for the analyzed period from 01/05/2017 to 10/31/2018 was 1194.83 mm, 1635.18 mm and 3027.83 mm, respectively. The percolation flux results show that the percolation is highly pulsed and seasonally affected. The physical characteristics of the soil (texture and porosity) directly influence the flux of percolation, where in the basin that naturally has larger fractions of sand when compared to other topographic positions, percolated volume corresponded to 81.78% of the total rainfall volume in the period studied. There are substantial variations in ion concentrations (eg, calcium, sodium, magnesium) over time, but the most notable biogeochemical behavior observed in this study is associated with nitrate. Nitrate concentrations are extremely high at all sites, with values exceeding 100 mg / L. Nitrate varies over time, where the slope and valley areas present the highest concentrations. These results demonstrate that the nitrogen cycle is very dynamic and suggests that nitrogen is unlikely to be a co-limiting nutrient in these forests. Phosphate concentrations are often below the limit of detection, although occasionally they exceed.