Water quality of submarine caves and marine karst lakes in Cat Ba Archipelago (Hai Phong, Vietnam)

Submarine caves and marine karst lakes in Vietnam's Cat Ba Archipelago exhibit distinct water quality characteristics, with caves showing higher and more stable salinity but lower dissolved oxygen levels compared to lakes. Research conducted in 2019 revealed that water self-purification improves during the rainy season, though pollution by ammonium was detected in several lakes (Ang Vem, Ba Man, Ba Mat, Ang Gay) during this period. While no evidence of organic contamination was found, elevated nitrate and phosphate concentrations were recorded, along with the presence of H2S gas, which may impact aquatic organisms. The study highlights seasonal variations in water quality, emphasizing the need for monitoring to preserve these unique ecosystems within a UNESCO World Heritage Site.

Cao, T. T. T., Nguyen, D. N., Le, V. N., Pham, T. K., Dinh, H. N., Tran, M. H., Nguyen, V. M., & Dau, V. T. (2025). Water quality of submarine caves and marine karst lakes in Cat Ba Archipelago (Hai Phong, Vietnam). Vietnam Journal of Marine Science and Technology, 25(1), 77–89. https://doi.org/10.15625/1859-3097/18632