A contribuição da erosão laminar no processo de desertificação no Semiárido Baiano

Abstract

Water erosion associated with land use activities is one of the most destructive environmental degradation processes today, being able to move millions of tons of soil, reducing fertile land and silting up water sources. Laminar water erosion is less noticeable, it occurs in a "silent" way, without many marks on the landscape, but at the same time, it is responsible for the superficial removal of the most fertile layer of the land, moving, in several parts of the slopes, large volumes of soil. The objective of this research work was to evaluate the contribution of laminar water erosion in the removal of soils in a slope in the semi-arid spatial context, in the north of the State of Bahia, with annual rainfall below 500 mm, evapotranspiration around 2000 mm/ year-1 and vegetation of hyperxerophilous Caatinga. It is emphasized that the study area is inside a desertification nucleus. For that, several techniques were developed, from the elaboration of MDE (Digital Elevation Model) from UAV images, spatialization of slope slope classes, to the quantification of soil loss by laminar erosion, from the pin method, in which 36 pins were installed on the slope studied. The local rainfall index was recorded, serving as a basis to correlate the accumulated precipitation to the soil displacement in periods of 30 days. Two soil profiles were studied at the site (morphological description, chemical and granulometric analysis and soil classification). At the end, a map was elaborated, specializing in a prediction model of laminar erosion, made from Kriging in the Quantum Gis 3.22 software. The hypsometry and slope maps of the area showed altitudes that varied from 500 to 507 and slopes that varied mainly between 5 and 14%, which had a direct influence on the potential energy of surface runoff, a crucial factor in triggering the erosive process. The soils found were the Regolithic Neosol and the Haplic Cambisol, both with physical and chemical attributes that indicate high vulnerability to erosion. The accumulated monthly rainfall was recorded from October 2021, with 67.2 mm, in November with 73.7 mm, December with a very high 201.4 mm, and in the following months there was a significant reduction. In the first month of laminar erosion data collection, approximately 0.8 mm of soil removal from the 36 pins (324 points) was observed, the high value of soil loss coincides with the beginning of the rainy season in the region. When the accumulated average of soil loss in the seven monitored months was calculated, a total of 37 mm or 49.21 t/ha-1 was reached. This result is characterized as very high, as the tolerance limit for poorly developed and shallow soils is 16.5 t/ha-1. The laminar erosion data in the analyzed spatial clipping confirm the advanced stage of land degradation, contributing to the composition of the set of information necessary for the recognition of an ongoing process of desertification in the place.