Recarga subterrânea direta e sua influência sobre a temperatura e a condutividade elétrica em microbacias do rio Vacacaí-Mirim, RS

Abstract

Water is vital to life, essential to the development of humanity in health, social and economic levels, having strategic importance to the productive sectors and thus playing a key role in generating wealth and ecosystem maintenance. The present study aimed to record the variability of electrical conductivity and temperature of groundwater in shallow wells, and estimate direct recharge of the Guarani Aquifer System, in your outcrop zones over a hydrological year, between October 2012 to September 2013. The survey was conducted in two adjacent watersheds of the river Vacacaí-Mirim, in the Santa Maria region, inserted in the Central Depression of Rio Grande do Sul, on the Paraná Sedimentary Basin edge. Was recorded the electrical conductivity, temperature and the fluctuation of water level in three monitoring wells, designated P05, P06 and P07, with depths of 31, 20 and 15 meters respectively. Pressure transducers were configured to perform readings of groundwater level and temperature, often from hour to hour, at 05 and 07 wells. There were 24 measurement campaigns, with fortnightly basis, the three monitoring wells, enrolling in the entire water column, conductivity and water temperature. There was obtained an amplitude variation of the water level in the order of 3.05 m in the well 05, in the highest position, in the order of 1.55 m in the well 06 in an intermediate position, while the well 07, located in alluvial plain, was only 0.82 m in saturated sedimentary rocks all year. For the electrical conductivity of groundwater were obtained yearly averages ranging from 35.9 to 58.8 μS/ cm in wells 05 and 06, while the well 07 yielded higher annual average of up to 106.5 μS/cm. The average temperatures of the water column in the monitoring wells showed a range of variation of 1.0 oC , 2.8 oC and 1.6 oC, correspondingly to the wells 05, 06 and 07. Regarding the estimation of the direct recharge of the aquifer, was used to Water Table Fluctuation method (WTF). Was estimated the recharge of 38.95% in the well 05, and 18.31% in 07 well, considering the total annual rainfall in the period of 1.887 mm. The estimated results of groundwater recharge were similar to those found in previous research. We observed the variability in temperature as the electrical conductivity of the groundwater, possibly related to the position occupied in the landscape wells, as well as characteristics of the constituent materials of the sandstones matrix, formers unconfined aquifer.