Subsurface Flow Pathway and Hydrochemistry of a Geographically Isolated Depression Wetland in the Serra Geral Diabase Formation, São Paulo State, Brazil

Abstract

Abstract Connectivity among water bodies is a key of important hydrological and ecological processes and fundamental to water management. Hydrochemistry and potentiometric studies applied on an isolated wetland allow to assess the landscape influence in water, flow pathways, and subsurface connection. This study focus on an isolated wetland developed over diabase on a topographic depression with no visible connection with river and aims to determine the influence of rainfall and landscape on its water composition and to investigate the existence of subsurface flow toward the Santa Gertrudes stream. Water level was monitored, and water samples were collected in the four wells during the wet and dry seasons. Physical and chemical water parameters were measured, and it was determined the concentration of ions of interest. Pearson’s correlations were applied to understand the codependence between physical and chemical parameters and ions and Piper’s diagram allowed to classify the water composition. Six potentiometric maps were generated based on hydraulic loads interpolation derived from each monitoring event. The findings indicate that water levels fluctuate between rainy and dry periods, suggesting direct rainwater influence on water availability. The water composition was categorized as Sodium Bicarbonate, exhibiting seasonal concentration variations. The strong positive correlation between sodium, bicarbonate and carbonate, and sulfate with the electrical conductivity (Ce) and among themselves suggests that these ions are being released simultaneously into water due to the alteration of the rock and soil minerals. Potentiometric data reinforce the hypothesis of a subsurface connection between the studied area and the Santa Gertrudes stream.