Iniciação do escoamento em microbacia hidrográfica e relações hídricas no sistema solo-planta-atmosfera no Bioma Caatinga

• Autor(a) principal: Figueiredo, José Vidal de
• Data de Publicação: 2018
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Repositório Institucional da Universidade Federal do Ceará (UFC)
• Texto Completo: http://www.repositorio.ufc.br/handle/riufc/40035
• topic: Condutividade hidráulica; Umidade do solo; Semiárido; Caatinga; Transpiração noturna; Ecohidrologia

The main outputs in the soil water balance in a semi-arid basin are: flow, evaporation and transpiration. In the Caatinga biome, located in the Brazilian semi-arid region, vegetation has been observed to affect soil moisture variability considerably and surface runoff events are rare. In addition, investigations into perspiration in Caatinga species under natural conditions are still poorly understood and understanding the use of water by trees is crucial for sustainable ecological restoration and ecohydrological understanding. In this context, the objective was to analyze the conditions that promote the beginning of surface runoff in a semi-arid watershed, and to study the temporal dynamics of transpiration through sap flow measurements in representative plants of the Caatinga biome. The study was developed in the Aiuaba Experimental Basin (AEB, 12 km²). The work is divided in two main chapters: i) Initiation of the drainage in the hydrographic microbasin of the semi-arid under Caatinga preserved in the Brazilian northeast; ii) Transpiration in plants of the Caatinga biome. In the first chapter the necessary conditions for the occurrence of surface runoff were analyzed. Among the data analyzed in the period from 2005 to 2014 (10 years) are: total precipitation; precipitation with five days antecedent; soil moisture; duration of precipitation; and rainfall intensity (average and maximum within 5, 15, 30, 45, 60 and 120 minutes). In all, 118 events with precipitation greater than 10 mm were monitored, providing 45 events with flow, 25 with negligible flow and 49 with no flow. From the results, it was evaluated that the annual flow coefficient was less than 0.5% and the surface runoff occurred only four days per year on average, characterizing the scarcity of surface water of the Caatinga biome. The most relevant variables to explain the onset of runoff were total precipitation and maximum precipitation intensity in 60 min (I60). The runoff occurred whenever the total precipitation exceeded 31 mm, but never occurred for precipitation below 14 mm or for I60 below 12 mm.h-1. The fact that the duration of the critical intensity (60 min) is similar to the basin concentration time (65 min) and that the value of the infiltration threshold approaches the saturated hydraulic conductivity of the riverbed supports the assumption that surface runoff prevails Hortoniano; In the second chapter, the transpiration process of species (P. pyramidalis) representative of the Caatinga was evaluated using the sap flow methodology in the hydrological xylem during the two-year period, covering dry, rainy and transition periods. The influence of climatic factors that interfere with sap flow (SF), such as global radiation, vapor pressure deficit (VPD) and temperature were also evaluated. The sap flow (SF) was measured in situ during 365 uninterrupted days. The daily SF values ranged between 1.4 (May / 2016) and 47.0 L.dia-1 (October / 2016). For analysis of the temporal distribution of SF, the data were grouped in four water regimes: rainy; rainy-dry transition; dry and dry-rainy transition. Sap flow (SF) in P. pyramidalis decreased with increasing soil moisture, since in this period the VPD is small when compared to the dry period. It was observed that SF increased during the rainy-dry and dry transition period compared to the rainy season. This finding indicates that the influence of the low values of vapor pressure deficit (VPD), air temperature and ET0 on the rainwater regime mean that SF is lower during the wet period compared to the dry period. Another interesting result was the occurrence of nocturnal transpiration both in deciduous species (P. pyramidalis) and in evergreen plants (Ziziphus. Joazeiro) in the Caatinga biome. The nocturnal perspiration in the two species ranged from 4% to 36%, according to the thermal dissipation method; and from 10% to 16% by IRGA (infrared gas analyzer) method in relation to daily transpiration. From this result, it is hypothesized that the nocturnal transpiration occurs due to the incomplete closure of the stomata, associated with the high atmospheric evaporative demand in the Caatinga, from low humidity winds. These results highlight some unique aspects in the measurement of transpiration in seasonally dry tropical forests, which are relevant for future studies at several levels. It was also verified that the average annual transpiration of P. pyramidalis corresponds to 44-69% of the annual mean precipitation in the AEB; and that the thermal dissipation probe method proved effective in estimating transpiration in plants of the Caatinga biome.