Transient storage and nitrogen retention in headwater stream of a suburban watershed in Beijing, China

Abstract

Transient storage refers to a vital process affecting nutrient retention dynamics. To explore how streambed topography, discharge, and nutrient ambient concentration impact the transient storage and nitrogen retention of the headwater stream, tracer experiments were performed in five reaches of the Yanqi watershed. The one-dimensional transport with inflow and storage model (OTIS) was employed to simulate the solute injection. Transient storage potential was evaluated by transient storage metrics. Moreover, the material balance method was adopted to obtain the amount of nitrogen retention in the respective reach, and the nutrient spiraling metrics were determined to assess the nitrogen retention potential. As revealed from this study, improving transient storage under low flow conditions effectively facilitated nitrogen retention (except for the case of low-head weirs reach), while the erosion of high discharge destroyed the transient storage zone, thereby reducing the nitrogen retention potential. Ecological restoration in the Yanqi watershed could rescue nitrogen retention potential to a natural state under low flow, whereas limitations were identified in nitrogen retention potential under high flow and high ambient concentration.