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The purpose of this study was to infer changes in water quality from diatom stratigraphy of a sediment core taken from Hebe Haven, New Territories, Hong Kong, China. Diatoms and diatom fragments were counted in the top (0—5 cm) and bottom (20—25 cm) portions of the core. The core was age dated using 210 Pb and these results were used to calculate a mean sedimentation rate(0 69 cm/a). A significant difference in the total number of diatoms and their relative abundance between the top 0—5 cm and the bottom 20—25 cm was found ( p <0 05). Significantly higher diatom species diversity and a more even diatom species composition occurred at 20—25 cm some 40—60 years ago. This difference was interpreted as a reflection of the water quality changes which have occurred over the last 40—60 years in Hebe Haven. Benthic diatoms once flushed in the clear waters of Hebe Haven as reported by individuals who swam and boated there immediately after WW II. Increased turbidity in recent years has apparently increased the relative abundance of planktonic diatoms at the expense of benthic diatoms which today are unable to receive sufficient light to grow on the bottom of the Hebe Haven Harbor (mean depth about 6 m). The observed increase in planktonic diatom abundance in the top 5 cm of the sediment core was attributed to increased nutrient loading to Hebe Haven over the last three decades.
