Abstract
Nitrogen migration and transformation in the stormwater bioretention system were studied in laboratory experiments, in which the effects of drying-rewetting were particularly investigated. The occurrence and distribution of nitrogen in the plants, the soil, and the pore water were explored under different drying-rewetting cycles. The results clearly showed that bioretention system could remove nitrogen efficiently in all drying-rewetting cycles. The incoming nitrogen could be retained in the topsoil (0-10 cm) and accumulated in the planted layer. However, the overlong dry periods (12 and 22 days) cause an increase in nitrate in the pore water. In addition, nitrogen is mostly stored in the plants' stem tissues. Up to 23.26% of the inflowing nitrogen can be immobilized in plant tissues after a dry period of 22 days. In addition, the relationships between nitrogen reductase activity in the soil and soil nitrogen content were explored. The increase of soil TN content could enhance the activity of nitrate reductase. Meanwhile, the activity of hydroxylamine reductase (HyR) could be enhanced with the increase of soil NO3- content. These results provide a reference for the future development of nitrogen transformation mechanism and the construction of stormwater bioretention systems.
Highlights
Urban stormwater runoff is a major source of nutrient input to streams and lakes, accounting for more than 50% of the nitrogen in some water bodies (Davidson et al 2010)
It has been reported that the concentrations of total nitrogen (TN) in stormwater runoff was in the range of tens to hundreds mg/L, depending on site characteristics (Jarney et al 2014; Taylor et al 2005)
The death of some plants in December caused by frequent inflows and low temperatures resulted in lower organics content in the planting zone (PZ) than in the submerged zone (SZ)
Summary
Urban stormwater runoff is a major source of nutrient input to streams and lakes, accounting for more than 50% of the nitrogen in some water bodies (Davidson et al 2010). Bioretention (or biofiltration) is one of the efficient stormwater control measures. It has been widely implemented on different scales from rain gardens to retention basins installed in public open space. Nitrogen in surface runoff undergoes a range of complex biogeochemical processes is attenuated, and gradually stored in multiple media such as soil, plants, and microbes. Both the biotic and abiotic transformations involved in these processes are closely related to the media involved (Maltais-Landry et al 2009)
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