Changes in the nutrient ratios and phytoplankton community after declines in nutrient concentrations in an eutrophic semi-enclosed bay in Hong Kong

Alle A.Y. Lie (1) , C. Kim Wong (1) , Jackie Y.C. Lam (2) , J.H. Liu (2) , Y.K. Yung (2)

1 Department of Biology
2 Hong Kong Government Environmental Protection Department

Tolo Harbour is a landlocked bay with poor tidal flushings in the northeastern part of Hong Kong. During the 1980s, excessive nutrient loading led to dramatic increase in nutrient concentrations, accompanied by lower N:P ratios, higher algal biomass and shifts in the phytoplankton community. We studied the effects of nutrient loading reduction measures on nutrient concentrations, nutrient ratios and phytoplankton dynamics in Tolo Harbour by comparing data collected before the full implementation of nutrient loading reduction measures (1986-1997) to those after the implementation (1998-2008). Such measures led to declines in nutrient concentrations, changes in N:P and N:Si ratios, lower chlorophyll- concentrations and fewer algal blooms. Diatoms were the most abundant phytoplankton group in Tolo Harbour both before and after declines in nutrient concentrations. The density of dinoflagellates did not change, but substantial increase in other algal group abundance was recorded.

Mots clés: Nutrients; Nutrient ratios; Phytoplankton; Eutrophication; Coastal waters; Tolo Harbour

Domaines: Sciences du Vivant [q-bio]

Alle A.Y. Lie, C. Kim Wong, Jackie Y.C. Lam, J.H. Liu, Y.K. Yung. Changes in the nutrient ratios and phytoplankton community after declines in nutrient concentrations in an eutrophic semi-enclosed bay in Hong Kong. Marine Environmental Research, 2011, 71 (3), pp.178. ⟨10.1016/j.marenvres.2011.01.001⟩. ⟨hal-00673201⟩