Impact of Pollution on Physico-Chemical Parameters and Diatom Communities Diversity in the Main Tributaries of the Arieș River, Romania

Human activities in the Apuseni Mountains region, Romania, especially in the Roșia Montană mining area, have significantly impacted water quality in the Arieș River tributaries. This study assessed the main physico-chemical and salinity parameters, along with the contents of trace elements (As, Cd, Co, Cr, Cu, Fe, Mn, and Ni) dissolved in water, as well as in the Abrud, Ștefanca, Valea Seșii, and Sârtaș rivers, the main tributaries of the Arieș River. Maximum concentrations of trace elements were observed in Valea Seșii (e.g., Zn up to 716 µg/L, Fe up to 562 µg/L), while Abrud and Sartăș showed moderate contamination. Diatom analysis revealed a high prevalence of Achnanthidium minutissimum and Planothidium lanceolatum, with teratological forms of A. minutissimum being the most frequent, indicating stress from pollutants. Saprobic index values ranged from 1.21 to 1.91, reflecting water quality from good to moderately impacted. The integration of chemical and biological data highlights the cumulative effects of mining and agricultural activities, demonstrating the utility of combined monitoring for effective freshwater management. Our results showed that numerous diatom taxa are currently present in samples collected from various watercourses within the Aries River basin, reflecting both the biological diversity and the variable influence of environmental factors on aquatic communities.