芦苇占优势农田溪流暂态存储特征及影响分析

2014年9月~2015年6月,在合肥市二十埠河流域一长约90m的芦苇占优势农田源头溪流渠段,选择NaCl为示踪剂,采用恒速连续投加的方式,开展8次野外示踪实验.在此基础上,利用OTIS模型对考虑和不考虑暂态存储影响的两种情景开展水质模拟,计算示踪剂氯离子(Cl^-)浓度峰值的相对偏差,并以暂态存储指标定量刻画农田溪流的暂态存储潜力.结果表明,不同季节的暂态存储交换系数α稳定在10^-4数量级;不考虑主流区与暂态存储区交换作用的Cl^-浓度峰值相对偏差HI的变化范围为2.60%~12.54%,平均值为5.35%;HI与流量Q呈现显著的对数函数关系,且随Q的增加而逐步减小;HI与比值A_s/A呈明显的线性关系,并随A_s/A的增加而逐步增大;8次示踪实验对应主流区停留时间T_c、暂态存储区水力停留时间T_s差异均较显著,且春季、初夏的暂态存储能力较秋、冬季更强一些;比值A_s/A变化范围为1.036~1.627, F_med²⁰⁰数值介于8.10%~23.03%,两者均表明该芦苇占优势渠段具有较大的暂态存储潜力.

Transient storage characteristics of an agricultural headwater stream predominated by Phragmites australis

From September 2014 to June 2015, eight field tracer experiments were conducted in a 90-m-length stream reach of an agricultural headwater stream, which is dominant of reeds and belongs to the Ershibu River watershed in Hefei city, using a constant-rate injection of NaCl. Based on the data sets of tracer experiments, the relative deviation of the peak values (HI) of the chloride ion concentrations was calculated with the OTIS model at the condition of ignoring the impact of transient storage or not, and the efficiency for transient storage was interpreted by using multiple transient storage metrics. The results showed that all the values of transient storage exchange coefficient (α) were in the order of magnitude of 10^-4 in different seasons. The values of HI ranged from 2.60% to 12.54% without considering the interaction between the main channel and transient storage zone, with the mean value of 5.35%. There was a significant logarithm function relationship between HI and discharge (Q), which was decreased gradually with the increase of the value of Q. Moreover, HI had obvious linear relationship with the ratio of cross-sectional area of storage zones to main channel cross-sectional area (A_s/A), and which was gradually increased with the increase of the A_s/A. Significant differences were exhibited between the main channel residence time (T_c) and the transient storage residence time (T_s) in all eight tracer experiments, and the transient storage capacity in the spring and early summer was stronger than that in the autumn and winter. The values of A_s/A and F_med²⁰⁰ were respectively in the range of 1.036 to 1.627 and 8.10% to 23.03%. This suggested that the stream with a dominant plant of reeds has a higher capacity for transient storage.