农业排水沟渠硝态氮吸收动力学特征及相关性分析

Nitrate Uptake Kinetics and Correlation Analysis in an Agricultural Drainage Ditch

为揭示农业排水沟渠NO_3^--N吸收动态变化特征,选择溴化钠(Na Br)为保守示踪剂、硝酸钾(KNO3)为添加营养盐,于2016年10月至2017年4月在合肥地区某一源头溪流开展5次示踪试验,并以TASCC方法和Michaelis-Menten(M-M)方程模拟NO_3^--N吸收动力学特征,结果表明,背景浓度条件下排水沟渠完全混合子渠段U_(amb)和V_(f-amb)的变化范围分别为11.40~69.13μg·(m^2·s)^(-1)[均值为34.45μg·(m^2·s)-1]、0.07~0.43 mm·s^(-1)(均值为0.24 mm·s^(-1)),相应地Sw-amb变化范围为92.51~405.74 m(均值为199.06 m),明显小于排水沟渠长度(也就是2.5 km),表明沟渠具有较强的NO_3^--N滞留潜力.M-M方程较好地拟合了NO_3^--N吸收动力学特征,参数Umax变化范围为158~1 280μg·(m^2·s)^(-1)[均值为631.13μg·(m^2·s)^(-1)],Km变化范围为0.16~5.52 mg·L^(-1)(均值为1.46 mg·L^(-1)).相关分析表明,Sw-amb与NO_3^--Namb呈显著负相关、Uamb与NO_3^--Namb呈极显著正相关,其它螺旋指标与NO_3^--N背景浓度的相关性均不明显;水文因素对NO_3^--N滞留影响也不显著,而沟渠槽道地貌特征指标Фw、ФA与大部分螺旋指标都呈显著相关性,表明槽道地貌特征对NO_3^--N滞留影响相对较为重要.

To investigate the whole-reach nitrate（ NO3^--N） uptake dynamics in a headwater agricultural stream,we performed five pulse tracer additions of a reactive solute（ as KNO3） and a conservative solute（ as NaBr） in an agricultural drainage ditch in Hefei district,Chaohu Lake basin,from October 2016 to April 2017. The TASCC（ tracer additions for spiraling curve characterization）approach and Michaelis-Menten（ M-M） method were applied for the simulation of NO3^--N uptake dynamics. Results showed that the ambient areal rate of total NO3^--N uptake U（amb） varied from 11. 40 to 69. 13 μg·（ m^2·s）^（-1） with an average of 34. 45 μg·（ m^2·s）^（-1）,and the ambient uptake velocity Vf-ambaveraged 0. 24 mm·s^（-1） and varied from 0. 07 to 0. 43 mm·s^（-1） across three well-mixed sub-reaches in the study. The ambient uptake length Sw-ambaveraged 199. 06 m with a range from 92. 51 to 405. 74 m,which was much smaller than the length of the drainage ditch（ about 2. 5 km）,suggesting that the agricultural drainage ditch had a high potential for NO3^--N retention. Generally,the M-M model fit the NO3^--N uptake dynamics well,and the maximum uptake Umaxranged from 158 to 1280μg·（ m^2·s）^（-1） with a mean of 631. 13 μg·（ m^2·s）^（-1）. The half saturation constant Kmranged from 0. 16 to 5. 52 mg·L^（-1） with a mean of 1. 46 mg·L^（-1）. According to correlation analysis,Sw-ambwas negatively correlated with NO3^--Namb,and Uambwas significantly positively correlated with NO3^--Namb,while other nutrient spiraling metrics were not correlated with the NO3^--N ambient concentration.Hydrological conditions had no distinct effect on the NO3^--N retention,but both the width variability Фwand variability in crosssectional area ФAwere significantly correlated with most of the nutrient spiraling metrics,indicating that geomorphic features in the drainage ditch evidently impacted NO3^--N uptake.