Submarine groundwater discharge (SGD) and its influence on coastal acidification and trace-metal enrichment have not been studied in Borneo. This study characterizes SGD from northwest Borneo into the South China Sea, focusing on iron (Fe) and aluminum (Al) inputs, hydrogeochemical controls on their mobility, and SGD’s role in coastal acidification. Samples were collected along transects at Tungku and Empire beaches, spanning the peritidal to subtidal zones, as well as from streams, pools, and beach sand. SGD contained elevated Fe and Al (Tungku: 4.07 mg/L Fe, 1.31 mg/L Al; Empire: 2.12 mg/L Fe, 0.38 mg/L Al), identifying these as key SGD-derived trace metals. pH was near-neutral in many samples (minimum 6.6), rising from 7.72 (Tungku) and 7.48 (Empire) in SGD to 8.11 and 8.01 in adjacent seawater, creating steep pH gradients favoring Al and Fe precipitation. Acid sulfate soils and high dissolved organic matter enhance groundwater acidity and trace-metal mobility. Major-ion chemistry indicates dominance of non-carbonate alkalis (SO₄²⁻ + Cl⁻ >CO₃²⁻ + HCO₃⁻; Na⁺ + K⁺ >Ca²⁺ + Mg²⁺) and low phosphate and nitrate, with mixed freshwater–saline contributions. The combination of low pH, elevated Fe and Al, and anthropogenic disturbance may degrade coastal and groundwater quality, affecting marine biogeochemical cycles, biodiversity, and ecosystem functioning. Overall, SGDs in Brunei deliver acidic, Fe- and Al-enriched water, contributing to coastal acidification and contamination, with implications for regional climate resilience.
Abdelwahab A. A., Abas P. E., Marshall D., Schirmer M., Azffri L. & Gödeke S., 2026. Hydrogeochemistry of submarine groundwater discharge along a Bruneian coastline: iron and aluminum enrichment along with coastal acidification. Environmental Earth Sciences 85: 34. doi: 10.1007/s12665-025-12731-1. Article.
