Effects of Multiple Variables on Epilithic Algal Communities in the Pülümür Stream System

This study evaluates the influence of multiple environmental stressors—including nutrient enrichment, physicochemical variability, and trace metal contamination—on the spatial and seasonal dynamics of epilithic algal communities in the semi-arid Pülümür Stream (Eastern Türkiye). Ten stations were sampled seasonally between February 2022 and January 2023 to characterize gradients in temperature, dissolved oxygen, pH, nutrients, and heavy metals in both water and sediments. Dissolved oxygen ranged from 9.72 to 12.27 mg/L, temperature from 2.76 to 18.03°C, and pH from 8.82 to 9.93. Nitrate (0.43–4.50 mg/L), phosphate (0.38–2.48 mg/L), and metal concentrations (notably Pb, Cd, Zn, Mn, and Fe) exhibited pronounced spatial variability associated with downstream anthropogenic pressures. Multivariate analyses (PCA, CA, CCA) revealed that nutrients (NO₃⁻, PO₄³⁻) and metals—particularly Pb, Cd, Mn, and Zn—were the primary drivers shaping algal composition. Pollution-tolerant taxa such as Nitzschia palea , Gomphonema parvulum , and Achnanthidium minutissimum predominated at nutrient- and metal-rich sites, whereas sensitive species persisted in upstream reaches. These findings demonstrate strong species–environment relationships and highlight epilithic algae as effective bioindicators for detecting early ecological degradation in semi-arid river systems. The study provides essential baseline data to support ecological monitoring and sustainable watershed management strategies in the region..