Soil moisture and groundwater recharge prediction in an Atlantic Forest-oxisol site

Abstract

The study of soil water dynamics is fundamental for the understanding of hydrological processes, especially those that involved forest environments. In this context, this study aimed to simulate the water movement in soil and groundwater recharging in an Atlantic Forest Oxisol site, through the Richard’s equation solution by means Hydrus-1D model. The study was conducted using eighteen sets of hydrological monitoring, at each point a rain gauge was installed, a stemflow apparatus and a soil moisture measurement tube until 1.0 m depth. After each rainfall event, throughfall, stemflow and soil moisture were measured from January/2016 to February/2018. Throughfall and stemflow were then summed to account the net precipitation (NP). In order to improve the Hydrus calibration, a daily measurement campaign was carried out in January and February/2018, aiming to refine the water breakthrough in the soil profile. On the other hand, the validation period comprehended the years of 2016 and 2017. During the validation, the amount of water drained through in the profile bottom was accounted as groundwater recharge. For periods longer than 15 days without rain the soil moisture measurement was carried out. Further, the exponential model was fitted to the empirical semivariogram to map both observed and simulated soil moisture in order to analyze the Hydrus 1D ability in representing the spatial distribution of moisture throughout the study area. For the calibration period, NS, ER and RMSE precision statistics ranged from 0.34 to 0.86; 0.0237 to 0.0398; and 0.0095 to 0.0185, respectively. In contrast, in validation step these statistics ranged respectively, from -0.35 to 0.63; 0.0368 to 0.0760; and 0.0138 to 0.0315. Despite nine points had presented NS close to zero or even negative, the soil moisture mapping simulated and observed were similar, highlighting the importance of NP and soil hydraulic parameters in relation to the moisture spatial distribution. Finally, the groundwater recharge in the Atlantic Forest-Oxisol site was 386 mm (31%) and 429 mm (39%) for 2016 and 2017, respectively.