Figure 4
[NO3 −–N] (mean ± sd) in the Yellow River from Tongguan (M13) to the downstream in different years. The branch gives the range of the data, and the histogram gives the average value. (a) Samples from Luokou station (M23) during 1980 (n = 24)22; (b) Samples from lower part of river from November 1983 to August 198623; (c)Samples at August 1986 (n = 5)24; (d) Annual average concentration of NO3 − –N in the seven mainstream stations during 199717; (e) Average concentration of DIN in the two mainstream stations (M17 and M23) from 1989 to 200025; (f) Samples in the high flow season in this study (n = 14); (g) Samples in the low flow season in this study (n = 14); (h) Samples collected from Tongdaoguai (M9) to Lijin (M26) during October 2011(n = 13)16; (i) Sample in the high flow season during 2012 (n = 9)26; (j) Average concentration of NO3 − –N in two mainstream stations (M17 and M23) from 2012 to 2014 in this study.
