Recent Hydrogeomorphological Changes and Their Impacts on Hydrodynamics and Water Quality in the Amazon Basin Estuarine Region—Amapá/Brazil

Over the past fifteen years, the lower Araguari River drainage system has undergone profound hydrogeological reconfiguration, disconnecting its mouth from the Atlantic Ocean and forming two new channels. This study experimentally quantified the impacts of these changes on hydrodynamics and water quality, considering anthropogenic drivers (upstream dam construction) and natural drivers (hyperdynamic erosional processes, Te, downstream). The methodology integrated spatial and seasonal landscape analysis via remote sensing and in situ observations; seasonal quantification of discharge and water quality parameters across semidiurnal tidal cycles; statistical correlation between hydrodynamic variables and water quality indicators; and hypothesis testing to assess the significance of hydrogeomorphological impacts. The results showed significant seasonal variation in turbidity, pH, color, total dissolved solids (TDS), suspended solids, electrical conductivity, nitrate, and instantaneous discharge (Qinst), while temperature, total coliforms, and Escherichia coli showed no significant seasonal difference (p > 0.05). Spatially, TDS and E. coli did not vary significantly, but electrical conductivity showed marked marine influence, increasing up to twenty-twofold during the dry season (p < 0.05). Water balance analysis revealed significant seasonal fluctuations in both liquid discharge (Qliq) and Qinst (p < 0.05), underscoring Te’s critical role in shaping the new channels and reflecting their proximity to the Amazon River and Atlantic Ocean. Maximum discharge (Qmax) correlated significantly with erosional processes (p < 0.05), confirming that Te has measurably impacted basin hydrodynamics and water quality.