THE IMPACT OF ACID MINE DRAINAGE ON THE WATER QUALITY OF THE ODIEL RIVER (HUELVA, SPAIN): EVOLUTION OF PRECIPITATE MINERALOGY AND AQUEOUS GEOCHEMISTRY ALONG THE CONCEPCI ´ON-TINTILLO SEGMENT

The study investigates the impact of acid mine drainage (AMD) on water quality in the Odiel River, Huelva, Spain, focusing on the evolution of precipitate mineralogy and aqueous geochemistry. The objective is to understand how AMD from abandoned mines affects the river's chemistry while examining its mineral precipitates. Methodologically, field studies were conducted in October 2003 and May 2004, analyzing water samples across a 7 km reach of the river that receives AMD discharges. Results indicate the river maintains a near-neutral pH despite significant acidity and metal contamination introduced by the AMD, due to the river's inherent alkalinity. Key metals such as Fe, Al, Mn, and Cu are retained in colloidal forms of poorly crystallized minerals resulting from the precipitation of iron and aluminum oxides. However, downstream convergence with the acidic Tintillo River leads to a drastic decrease in pH and an increase in metal concentrations, evidencing the significant influence of mining activities on the river ecosystem. This research highlights the complex interactions between natural and anthropogenic influences in aquatic systems impacted by mining.