Monitoring the impacts of illegal mining in the Camaná-Majes basin: hydrochemical and benthic macroinvertebrate assessment

Abstract

Water resources are crucial for development, sustainability, and productive activities. Water quality is influenced by natural processes and human activities, affecting river ecosystems. Hydrogeochemical studies aid in understanding water chemistry, detecting contaminants, and assessing surface water quality. The Camaná-Majes river basin, located in the Arequipa region of southern Peru (on the southwestern flank of the Andes), is affected by contamination from intensive mining, excessive chemical fertilizer and pesticide use, untreated wastewater, and informal landfills. This study evaluates the anthropogenic impacts on riparian areas and offers a monitoring tool for illegal mining deposits. Physicochemical parameters (pH, total dissolved solids, dissolved oxygen, salinity, conductivity), cations (Na + > Ca + > Mg + > K + > Li + in 2022; Ca + > Mg + > K + > Na + > Li + in 2023), anions (SO₄²– > Cl– > NO₃- > F- for both years), carbonates (determined through ion chromatography), and heavy metals (Al > Zn > Cu > Ba > V > Mn > Ag > Pb > Se > Ni > Cr > Co > Hg in 2022; Al > Mn > Ba > Cu > Zn > Pb > V > As > Ni > Co > Cr > Mo > Hg in 2023) were analyzed using Inductively Coupled Plasma Mass Spectrometry. This study provides the first report on the benthic macroinvertebrate structure in the Camaná-Majes basin, assessed during the dry season of 2022 and the wet season of 2023. The 2023 evaluations of the Camaná-Majes river basin revealed significant contamination and biological vulnerability linked to illegal mining and other anthropogenic activities. Water quality assessments compared to Environmental Quality Standards, U.S. Environmental Protection Agency, and World Health Organization guidelines, along with biodiversity indices and principal component analyses, indicated heavy metal levels exceeding permissible limits, alterations in ionic composition, and a marked decline in macroinvertebrate biodiversity. These findings underscore a significant decline in water quality and ecosystem health from 2022 to 2023, driven by intensified mining activities.