Avaliação experimental e numérica da adequação e disponibilidade de águas subterrâneas aluviais e de reuso para fins agrícolas no semiárido

Abstract

The productive coexistence with water scarcity is a growing challenge, particularly in the semiarid regions, either due to limitations in the quantity or quality of available water. This Dissertation aims to analyze the quantitative and qualitative availability of water resources in the semiarid region, within the context of climate change, and to evaluate the potential and suitability of alternative sources of water for agricultural purposes. Two alternative water sources are investigated in this study: waters from alluvial aquifers, often with moderate to high levels of salts, and waters from treated domestic effluents, which can also cause salts accumulation in the soil and in the environment. Temporal stability for piezometry and salinity was investigated using the Relative Differences Method, based on a monitoring network of piezometers and wells in the alluvial valley of the Mimoso rivulet Basin, Alto Ipanema sub- basin, located in Pesqueira-PE. Trend analysis of potentiometry, salinity and exploitation of groundwater and climatic variables in the region were analyzed by the Mann-Kendall method, and the magnitudes by the Sen’s Slope test, for the period from 2000 to 2020. Spatial variability patterns of electrical conductivity and the sodium adsorption ratio of groundwater, over time, were identified through geostatistics, as well as the suitability for irrigation by means of an indicator variable. The geostatistical technique was also used to evaluate the spatial variability of soil and plant attributes in experimental plots cultivated with corn irrigated with treated domestic effluent and application of sewage sludge in the experimental pilot reuse unit in Pesqueira. It was possible to verify the occurrence of temporal stability for the potentiometric level only. Increasing trends for evapotranspiration (5.74 mm.year-1), exploitation (4450 m3.year-1), mean temperature (0.09 ° C.year-1) and decreasing trends for precipitation (-126 mm. Year-1) and for water level in the aquifer (-0.074 m.year-1). Evaluation of water quality and the mapping of indicator variables allowed the identification of suitable and unsuitable areas for agricultural use, with percentages ranging from 81.4 to 93.7% and 6.3 to 20.5%, respectively, over time. Such variations are linked to the agricultural use of the soil and those correlated to the natural characteristics of the aquifer, supporting decisions about when and where to irrigate. Besides that, the use of treated wastewater for agricultural crops represents an important alternative for the enhancement and maintenance of irrigated agriculture in the semiarid region, providing greater plant growth, and increasing soil moisture and soil organic matter content.