Hydro-sedimentological interactions between a tropical fluviokarst system and surface waters in the Brazilian Savannah

Abstract

Karst environments are fragile. Their hydro-sedimentologic flows transport materials from various sources, and their hydrogeological recharge areas are diverse. They also suffer directly from the effects of surface water and soil degradation. In tropical regions, these flows intensify, accelerating hydro-sedimentological dynamics and degradation. This study assessed the hydro-sedimentological interactions between land use, surface water, and the fluviokarst system in the Extrema cave. The karstic system in the Lagoa do Jacaré Formation presents the main land uses and soil management of the Cerrado Biome and karst formations like caves, dolines, sinkholes, and springs. Data collection platforms were installed at the cave’s entrance and exit, recording level, turbidity, physicochemical variables, and sediment during floods, and a three-dimensional model of the area was created to evaluate structural and lithological dispositions. The Extrema cave has a perennial flow transporting materials from distinct sources. The solid discharge ranged from 1,082 Mg per day at the sinkhole to 1,630 Mg per day at the resurgence, indicating that approximately one-third of the material is transported through the karst conduit. This process primarily involves older upper layers of the Tarimba cave and adjacent dolines. Water samples revealed seasonal variations in basicity, indicating contributions of low mineralization water from sandstones of the upper aquifer and dilution processes in carbonate formations in the rainy season. The model indicated flows originate from different areas, elevating contamination susceptibility through sinkholes, caves, and karst fissures, common given the area’s hydrological regime. Thus, priorities were considered for the conservation of these karst systems, their uses, and management with high susceptibility to erosion, and the absence of riparian forests in the streams and surroundings of the sinkholes, given their capacity to affect the hydro-sedimentological dynamics in the Extrema cave.