Determination of parameters for modeling of soil transport in a small river basin using nuclear techniques (⁷Be)

The purpose of the research was to survey the parameters for the soil transport modeling in the Mato Frio stream basin using the performance of the environmental radioactive tracer ⁷Be. The project proposes to develop and introduce tracer methodologies using nuclear techniques of zero environmental impact in the field of hydrology, with a potential to enhance the environmental management of a micro basin. The use of a model based on ⁷Be measurements in the soil is capable of estimating the redistribution of soil which can be used to calculate both erosion and deposition rates. The study compare soil redistribution rates in working plots and the selected reference site. Approximately 100 soil samples (10 to 50 mm deep) and 15 rainwater samples were collected to establish the concentration of ⁷Be by gamma spectrometry analysis. This fallout is used to evaluate the erosion and deposition processes that occur during extreme rainfall events in short periods of time, but in order to use the ⁷Be as a tracer it is necessary to know its vertical distribution profile of resulting from its penetration, its total inventory on the Reference Site (Aref - Bq.m^-2) and its mass relaxation depth (h0 - kg.m^-2). The results indicated that the total monthly content (inventory) of ⁷Be in the soil at the Reference Site is related to the asymmetric precipitation patterns, and that the said monthly content presents lower values during the dry season. Using the ⁷Be concentration in the rainfall and the amount of daily of precipitation it is possible to obtain the expected theoretical ⁷Be content in the soil and to compare it with the data of the analyzed soil samples. Modeling the soil transport with this tool indicates that the investigated area has an appreciable soil loss for one month of rainfall, which makes it vulnerable to critical erosion processes in case its vegetation cover is lost. (author)