Denitrification in Qi'ao Island coastal zone, the Zhujiang Estuary in China

Samples of sediments and the overlying water were collected in the Qi'ao Island coastal zone, the Zhujiang (Pearl River) Estuary (ZE). Denitrification rates, sediment oxygen demand (SOD), and fluxes of inorganic nitrogen compounds were investigated with N₂ flux method, using a self-designed continuous flow through and auto-sampling system. The results indicate that the denitrification rates varied between 222 and 908 μmol/(m²·h) with an average of 499 μmol/(m²·h). During incubation, the sediments absorbed dissolved oxygen in the overlying water with SOD ranging from 300 to 2 363 μmol/(m²·h). The denitrification rates were highly correlated with the SOD (r²=0.77) regardless of the NO₃^-+ NO₂^- concentrations in the overlying water, organ-ic carbon contents in sediments and water temperature, suggesting that the SOD was probably the main environ-mental factor controlling the denitrification in the Qi'ao Island coastal zone. There was a net flux of NO₃^-+ NO₂^- into the sediments from the overlying water. The NH₄⁺ flux from sediments into water as the result of mineraliza-tion was between 12.3 and 210.3 μmol/(m²·h),which seems limited by both organic carbon content in sedi-ment and dissolved oxygen concentration in the overlying water.