Spatial patterns and ecological significance of heavy metals in water and sediments of the Drini–Buna river system
The Drini River Basin represents the largest river system in Albania and plays a key role in supporting freshwater resources, biodiversity, hydropower production, and human activities. This study evaluated the distribution, contamination status, and ecological risk of trace metals in water and surface sediments collected from eleven stations covering the basin of the river. Concentrations of metals were determined and interpreted using contamination indices, including the geoaccumulation index (Igeo), Nemerow pollution index (NPI), and potential ecological risk index (PERI). Trace metal concentrations exhibited significant spatial variability, with the highest enrichment observed for Ni, Cr, and Co. Geoaccumulation index results classified these metals as moderately to heavily con - taminated at several stations, particularly in the upper basin and the Zalli River. In contrast, Cu, Mn, Fe, Al, Pb, Cd, and Hg generally remained within the uncontaminated or slightly contaminated categories. The NPI values for water were below 1 at all stations, indicating no significant metal pollution in the water column. PERI values ranged from low to moderate ecological risk, with no station exceeding the threshold for considerable ecological risk. The highest ecological risk was observed at the Zalli stream station, while the Bushtrica River exhibited the lowest contamination and risk levels. The spatial distribution of metals suggests that sediment contamination is controlled predominantly by geogenic factors associated with ultramafic and ophiolitic formations characteristic of northeastern Albania, although localized contributions from historical mining activities cannot be ruled out. Results indicated good water quality with respect to trace metals and low to moderate ecological risk in sediments, providing an important baseline for future monitoring and management of the Drini River Basin.