Dinâmica hidrogeomorfológica em vertente na Floresta Nacional de Piraí do Sul, Paraná

Abstract

The objective of this work is to understand the hydrogeomorphological dynamics and its relation with the losses of materials - water and soil - in a slope in the National Forest of Piraí do Sul, Paraná. This qualitative-quantitative case study was based on methodological procedures that allowed the recognition of the pedological system performed in toposequence, identifying the physical-chemical and water properties of soils. It is added the characterization of the rainfall distribution occurred in the study area between May 2018 and February 2019, contributing to the analysis of soil losses and surface runoff along one slope. Seven surveys were carried out along the study strand to recognize the main characteristics of the soils and their changes along the profile. Subsequently, four trenches were opened to classify the soils in toposequence, which were analyzed by grain size analysis, clay dispersed in water, soil bulk density and routine chemistry, as well as aggregate stability for soils with erosion monitoring. Field measurements of rainfall in the study area were carried out by means of digital and analogue rain gauges that allowed the intensity, duration, kinetic energy and erosivity of rainfall during the period. For the monitoring of soil and water losses, plots were installed, being upper third, middle third and lower middle third, with dimensions of 10m2, with Gerlach type collecting trough of sediments and gallon of 20 liters for collection of the drained volume. In this way, it was possible to obtain sediment loss (g / m2), flow rate (%) and precipitation / flow ratio. Infiltration tests with double-ring infiltrater were performed in the three segments of the slope, the same ones whose plots were installed. The data obtained show that the soils are distinct in the slope and that their development is very much due to the shape of the slope, in which a pedological system composed of Ferralsol-Cambisol-Gleysol. The rains that have the greatest erosive effect were the rains caused by the influence of the frontal systems, with rains below the historical average, except for the month of October with 255mm total. This meant that the plots in the upper third and mid-lower third had little soil loss compared to the middle third plot, with a rate of 365.8 g / m2 in October against 0.5 g / m2 and 0.007 g / m2 in plots 1 and 3, respectively. The low soil loss is mainly due to good aggregation of soils, greater than 86%, and its physical attributes such as clay texture, granular structure, soil density above 0.94g / cm3, high infiltration rate above 29.6 cm.h-1. The soils are acid and poorly fertile and may hinder plant regeneration.