From November 2015 to February 2016, five short-term tracer injections were performed with a conservative tracer (NaCl) in an agricultural headwater stream, Lake Chaohu basin. Thus the data sets of tracer experiments were finally employed for calculating the physical characteristics and transient storage metrics. Through the comparisons between the artificial pool reach and straight reach, characteristics of transient storage for the artificial pool geomorphic structure were interpreted and explored. Study results showed that: ① The ratio of As/A in artificial pool was larger than that in straight reach, whereas its value of exchange coefficient α was lower by an order of magnitude than that of straight reach. ② Artificial pool geomorphic structure had greater influence of transient storage on solute retention than that in straight reach, but its solute retention capacity of flowing water was weaker than that of straight reach. ③ It had a large ratio of As/A for the pool geomorphic structure, whereas its impact on the migration and transformation of solutes was less than that of straight reach. ④ Based on the Fmed200 metric, the transient storage accounted for 18.86% to 26.05% of travel time in artificial pool. For the straight reach, the Fmed200 metric had a range of 5.28% to 33.87%. In most cases, the values of Fmed200 metric in straight reach were higher than those in artificial pool. ⑤ Significant differences existed between artificial pool geomorphic structure and straight reach in the values of φw, φA and Ts, however, the differences were not significant in other indicators.
Keywords: OTIS model; agricultural headwater stream; artificial pool; riffle-pool sequence; transient storage.