Application of Diatom Indices to Monitor Environmental Shifts in the Downstream Tuntang River, Central Java

Abstract

Diatoms are widely recognized as sensitive bioindicators for reconstructing past water quality and ecological changes in aquatic ecosystems. In this study, multiple diatom-based indices were applied to sediment cores collected from three downstream stations of the Tuntang River, Central Java, to infer long-term environmental change in a tropical river system. A total of 38 sediment subsamples were analyzed, with dominant taxa including Fragilaria crotonensis (2.4–18.6%), Nitzschia palea (3.1–22.4%), and Aulacoseira granulata (2.0–15.8%), indicating sustained nutrient enrichment. Diatom indices consistently classified conditions as mesotrophic to eutrophic throughout the sediment profiles. The occurrence of the marine diatom Cylindrotheca closterium (up to 6.3%) at downstream stations suggests episodic seawater intrusion associated with hydrological alterations. Although the indices were originally developed for temperate regions, the pollution sensitivity index (IPS) and generic diatom index (IDG) performed robustly, with >70% species representation across all depths. These results demonstrate that sedimentary diatom indices provide a reliable proxy for reconstructing long-term ecological change and eutrophication trends in tropical river systems where historical water quality data are limited.