Spiralling curve characterization of nitrate–nitrogen absorption in a channel at a rural–urban ecotone in Northeast China
2020
Song, Yujia | Song, Shoufa
To determine the dynamic change characteristics of NO₃–N in a rural–urban ecotone channel, five tracer tests were conducted in the Dongda Channel in the suburbs of Changchuan city, Jilin province, China, from October 2016 to April 2017. NaBr was used as conservative tracer and KNO₃ served as an added nutritive salt. The kinetic features of NO₃–N were simulated via the addition of tracers and by employing the spiralling curve characterization approach and the Michaelis–Menten (M–M) equation. The average absorption length of NO₃⁻–N background concentration (Sw₋ₐₘb) is 199 m, which is much less than the discharge channel length (2.5 km), thereby suggesting that the channel has a strong NO₃–N retention potential. Moreover, the M–M equation fits well the kinetic features of NO₃–N adsorption. The average maximum absorption rate and subsaturation constant are 631 μg (m² s)⁻¹ and 1.46 mg L⁻¹, respectively. The correlation analysis reveals that Sw₋ₐₘb and NO₃⁻–N absorption rates (NO₃–Nₐₘb) are significantly negatively correlated whereas the absorption rates of NO₃⁻–N background concentration (Uₐₘb) and NO₃–Nₐₘb are significantly positively correlated. The other spiralling indices show faint correlations with the background concentration of NO₃–N. Meanwhile, the hydrological factors slightly influence NO₃–N retention, but the geomorphic features of the channel, including (width residual) Фw and (cross-sectional area residual) ФA, have significant correlations with most spiralling indices, thereby highlighting the relatively important roles of geomorphic features in NO₃–N retention.
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