Avaliação do efeito da intrusão salina no funcionamento do ecossistema das terras húmidas de Macaneta, considerando o efeito das mudanças climáticas

Abstract

Estuaries are dynamic environments because they are regions where water discharged through continental drainages it meets marine waters. Depending on conditions of this drainage and/or sea level, this mixing region can become move further in or out of the continent. The length of the channel river that is influenced by sea water, measured from the mouth of the estuary is called saline intrusion zone. This phenomenon causes physical-chemical changes of water available in the region, significantly altering ecosystem conditions. In the wetlands of Macaneta, which are located approximately 25 km from the mouth of the Incomáti estuary, various activities are carried out such as agriculture, fishing and pastoralism, which are strongly influenced by saline intrusion. Therefore, in this study the HEC-RAS modeling program was used to evaluate the dynamic behavior of saline intrusion under different conditions of river discharge, tide level and influence of groundwater discharge in the Macaneta wetlands. To do so, the hydrodynamic model was developed, calibrated and validated. Calibration and validation were made using data from 02/20/2021 to 08/08/2021 and from 08/09/2021 to 01/30/2022, having obtained the following statistical values; Skill of 92.61% and 93.52%, R2 of 92.88% and 85.85%, EF of 80.90% and 77.99% and FC of 63.20% and 70.92%, for the calibration and validation, respectively. These values ​​indicate good performance of the model in describing the hydrodynamics of the study area. Then the model was used to simulate saline intrusion in the estuary, for this purpose flow rates of 5, 10, 20, 40, 80, 120, 160 and 200 m3 /s and it was found that the flow rate necessary to preserve the functioning of the Macaneta wetlands is 40 m3 /s. The model also provided answers to the influence of tidal level variation at the mouth of the estuary as a consequence of climate change, showing that saline intrusion varies in approximately 5 and 10 km for tide level rises of 0.55 and 1.10 meters, respectively. The discharge of groundwater along the wetlands of Macaneta proved to be highly relevant for maintaining low salinity in a section close to the dunes that is used for rice cultivation (TRADUÇÃO NOSSA).