Sediment denitrification in waterways in a rice-paddy-dominated watershed in eastern China

• Published in: Journal of soils and sediments 2013-04, Vol.13 (4), p.783-792
• Main Authors: Li, Xiaobo, Xia, Yongqiu, Li, Yuefei, Kana, Todd M., Kimura, Sonoko D., Saito, Masanori, Yan, Xiaoyuan
• Format: Article
• Language: English
• Subjects: Agricultural watersheds; Biogeochemistry; Denitrification; Earth and Environmental Science; Environment; Environmental Physics; Mass spectrometry; Ponds; Reservoirs; Rice; Sec 2 • Physical and Biogeochemical Processes • Research Article; Sediments; Soil Science & Conservation; Soil sciences; Streams; Surface water; Water temperature; Watersheds; Waterways
• ISSN: 1439-0108; 1614-7480
• DOI: 10.1007/s11368-013-0651-0

Purpose Rice-paddy-dominated watersheds in eastern China are intensively cultivated, and lands with two crops receive as much as 550–600 kg ha –1  year –1 of nitrogen (N), mainly through the addition of N-based fertilizers. However, stream N concentrations have been found to be relatively low. Waterways in the watersheds are assumed to be effective “sinks” for N, minimizing its downstream movement. We directly measured net sediment denitrification rates in three types of waterways (ponds, streams/rivers, and a reservoir) and determined the key factors that control net sediment denitrification. Such information is essential for evaluating the impact of the agricultural N cycle on the quality of surface water. Materials and methods The pond–stream–reservoir continuum was sampled every 2 months at nine sites in an agricultural watershed between November 2010 and December 2011. Net sediment N 2 fluxes/net sediment denitrification rates were determined by membrane inlet mass spectrometry and the N 2 /Ar technique. A suite of parameters known to influence denitrification were also measured. Results and discussion Net denitrification rates ranged between 28.2 ± 18.2 and 674.3 ± 314.5 μmol N 2 –N m –2  h –1 for the streams, 23.7 ± 23.9 and 121.2 ± 38.7 μmol N 2 –N m –2  h –1 for the ponds, and 41.8 ± 17.7 and 239.3 ± 49.8 μmol N 2 –N m –2  h –1 for the reservoir. The mean net denitrification rate of the stream sites (173.2 ± 248.4 μmol N 2 –N m –2  h –1 ) was significantly higher ( p