Natural and anthropogenic evidence drive macronutrient distribution in the Bengkulu River, Indonesia

Idha Ikhsani, Ilham Ilham, Hanif Budi Prayitno, Rina Elvia, Suci Lastrini, Nurhamidah Nurhamidah, Kuo Hong Wong, Wiwit Wiwit

Abstract


The Bengkulu River, the largest river in Bengkulu Province, discharges into the Indian Ocean and drains a watershed increasingly influenced by agricultural, urban, and industrial activities. Despite its ecological and socio-economic importance, information on nutrient distribution and export along the river–estuary continuum remains limited. This study investigated the distribution, transport, and potential sources of macronutrients (nitrite, nitrate, phosphate, and silicate) and estimated their fluxes to adjacent coastal waters. Surface water samples were collected from 15 stations along the Bengkulu River–estuary system during the dry season (17–19 March 2023). Nutrient concentrations were analyzed using spectrophotometric methods. Concentrations ranged from 0.01–5.17 ppm for nitrite, 0.01–1.94 ppm for nitrate, 0.01–0.35 ppm for phosphate, and 0.79–35.21 ppm for silicate, with mean values of 0.54 ± 1.30, 0.38 ± 0.49, 0.04 ± 0.10, and 11.19 ± 9.92 ppm, respectively. Higher concentrations of nitrite, nitrate, and phosphate were generally observed near areas with intensive agriculture, industrial activities, and dense settlements, suggesting potential anthropogenic influence, although natural hydrodynamic processes may also contribute. In contrast, silicate showed higher concentrations in upstream areas and decreased toward the coast, a pattern that may be associated with dilution during mixing and biological uptake. Estimated nutrient fluxes to the Indian Ocean were ~9.9 × 10? mg day?¹ for silicate, 1.9–6.1 × 10? mg day?¹ for nitrate, 9.1–9.4 × 10? mg day?¹ for nitrite, and 1.8–6.0 × 10? mg day?¹ for phosphate. These results suggest that the Bengkulu River is an important pathway for nutrient transport to adjacent coastal waters. The findings provide baseline information on nutrient dynamics and land–sea nutrient connectivity in tropical river systems.

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DOI: http://dx.doi.org/10.20884/1.oa.2026.22.1.1217

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