Distribuição espacial dos atributos físico-hídricos do solo em uma área de recarga de nascente

Abstract

The quantity and quality of water produced by a spring are controlled by the interaction between the factors that act in its recharge area, among them, the physical-hydric properties and characteristics of the soil. In this sense, in order to maintain the water production of the springs and to understand the hydrological dynamics of these areas, it is essential to know the behavior of the physical-hydric attributes of the soil and how they are distributed in space. Therefore, the

objective of the present work was to analyze the spatial distribution and to map the physical- water attributes of the recharge area of the main spring that supplies the Federal University of

Lavras, MG. After delimiting the recharge area using GIS tools, a sampling grid was established with points separated by 50 m and, in each one, deformed and undeformed soil samples were collected in the 0 - 20 cm and 20 - 40 cm depths. For the soil's physical-hydric characterization, the saturated soil hydraulic conductivity (K0), bulk density (Ds), particle density (Dp), total pore volume (VTP), drainable porosity (μ), organic matter content (MO) and sand, clay and silt contents were determined in the laboratory. After the exploratory data analysis step, geostatistical analysis was applied to study the spatial structure of the physical-hydrological attributes. After the selection of the best theoretical semivariogram model, the adjusted values of each parameter were used for the generation of maps, adopting ordinary kriging as interpolator. For the 0 - 20 cm depth, the attributes Ds, Dp and VTP were classified as having low variability and μ, MO, sand, clay and silt, as having medium variability. For the depth 20 - 40 cm, the results were similar, except for μ that presented high variability, with a CV of 66.69%. The saturated soil hydraulic conductivity showed high variability for the two depths analyzed, with CV of 128.15% and 217.22%, respectively. Through the analysis of the degree of spatial dependence, for both depths, most of the physical-hydric attributes presented spatial dependence classified as strong and none as weak. By evaluating the of the Mean Standardized Error and the Root Mean Square Standardized Error, generated in the cross validation procedure, the exponential model was considered the best model for most attributes, in both depths. The interpolation through ordinary kriging allowed the identification of areas with favorable conditions for water recharge, such as the lower regions, around the spring, and the higher regions, located to the east. In order to maintain the spring's water production, it is recommended that these areas be considered priority sites for conservation.