Denitrification rates in sediments of Suzhou river and rivers in Chongming Island of Shanghai and their affecting factors

Denitrification rates in the sediments of the Suzhou River and the rivers in Chongming Island of Shanghai were measured with the acetylene inhibition method. Extractable NO₃⁻ and NH₄⁺, sediment organic carbon (SOC), bulk density, moisture content of the sediments, and relevant physicochemical properties of their overlying waters were also determined. Results show that the denitrification rate in the top 10 cm sediment of the Suzhou River is 126. 22 μg · m⁻²· h⁻¹, 1. 2 times higher than that in the rivers in the Chongming Island (105. 57 μg · m⁻²· h⁻¹). Obviously it is much higher in the sediment of a seriously polluted river running through the urban area than in the sediment of a less polluted rural river. Denitrification rate in the sediments varied with sediment depth (0–10 cm), ranging from 0. 15 to 5. 07 ng · g⁻¹· h⁻¹ in the Suzhou River, and from 0. 39 to 2. 80 ng · g⁻¹ · h⁻¹ in the rivers in the Chongming Island, and decreased with the increasing depth. Correlation analysis of sediment denitrification rate with environmental factors demonstrates that the denitrification rate was positively related to extractable NO₃⁻-N in the sediment (Suzhou River: r = 0. 699, P<0. 05; Chongming Island rivers: r = 0. 629, P<0. 05). So extractable NO₃⁻-N is the key factor influencing sediment denitrification rate in the sediment.