Résumé
Benthic diatoms are sensitive indicators of freshwater ecosystem health, yet their spatial diversity patterns in tropical rivers remain poorly understood. This study investigated beta-diversity of benthic diatom assemblages along the Sangker River, northwestern Cambodia. beta-Diversity was quantified using the S & oslash;rensen index and partitioned into turnover (beta sim) and nestedness (beta sne) components, based on 7 sampling campaigns from 2018 to 2022. Local (LCBD) and taxa (SCBD) contributions identified unique sites and influential taxa (genera). Twelve environmental variables, including nine physical and chemical and three spatial factors, were analyzed along the upstream-downstream gradient. A total of 78 genera were recorded, dominated by Gomphonema, Nitzschia, Navicula, and Achnanthidium. Alpha diversity declined downstream, reflecting reduced habitat heterogeneity and increasing nutrient enrichment, while evenness remained stable. Overall beta-diversity was high (beta sor = 0.748), driven mainly by species turnover (beta sim = 0.639), indicating distinct assemblages across river sections. Certain sites located in tributaries exhibited high-LCBD values, whereas total phosphorus and total suspended solids significantly influenced LCBD. These findings highlight the strong roles of environmental filtering and longitudinal (upstream-downstream) gradients in structuring diatom assemblages. Targeting high-LCBD sites and key indicator genera can enhance biomonitoring efficiency and guide freshwater conservation under growing anthropogenic pressures in tropical river systems.