Abstract: The differences in different land-use patterns result in differences in contents of organic matter and total nitrogen in sediments of irrigation and drainage system, so we analyzed the characteristics in sediments in Yongji Irrigation Sub-District of Hetao Irrigation District in Northern China. The results showed that there was s difference in organic matter and total nitrogen contents between the surface sediments in the Canal and Drains. The highest content of organic matter and total nitrogen was in the upstream of the Fifth Drain and the mean value was 3.60% and 0.35%, respectively. The corresponding value was 4.82 times and 2.94 times higher than the average value of organic matter and total nitrogen. The organic indices showed that the contamination standard in sediments in the Fifth Drain was heavy and implied that eutrophication problem was serious; The lowest value in sediment was found in the Yongji Canal, while the mean value was 1.41% and 0.03% for organic matter and total nitrogen, respectively, which was considered as clean category. The content of organic matter and total nitrogen in the upstream of the Forth Drain was moderate, and close to the background value. Organic matter was significantly correlated to the total nitrogen in sediments: y_(TN)=0.141x_(OM)-0.180 (r=0.978,P<0.001).

Key words: Yongji Irrigation District, sediment, organic matter, total nitrogen