Measurement of Denitrification in the Changjiang River

Environmental Context. Rivers are carrying an increased load of nitrogen-based matter (nitrates, nitrites) resulting from, among others, increased use of agricultural fertilizers. This nitrogen enrichment leads to a proliferation of plant life in the receiving water body, which in turn reduces the dissolved oxygen content and can cause the extinction of other organisms. Rivers can reduce their nitrogen levels through denitrification, the bacterially mediated transformation of dissolved nitrates and nitrites to gaseous N₂ and N₂O. This paper reports the first examination of denitrification in China’s largest river, the Changjiang (Yangtze) River, to understand the details of riverine denitrification and its role on controlling nitrogen export.

Abstract. Rivers are an important link between terrestrial and aquatic ecosystems for nitrogen cycling, while denitrification plays a key role in riverine nitrogen removal. Denitrification was first examined in China’s largest river, the Changjiang River, by using a whole-reach method. The production rates of N₂ by means of denitrification were 2.82 ± 1.18 and 5.74 ± 2.92 mmol(N) m⁻² h⁻¹ in October 2002 and March 2003, respectively, and the rates of N₂O production were 1.98 ± 1.48 and 581 ± 1937 nmol(N) m⁻² hr⁻¹ in August and October 2002, respectively. Nitrogen removal through N₂ and N₂O emission accounted for 1–2% of NO₃^–-N flux through October 2002 to March 2003. Continued measurement throughout a whole year period after the construction of the Three Gorges Reservoir will provide more understanding of riverine denitrification and its role on controlling nitrogen export.