Characterizing the flush of stream chemical runoff from forested watersheds

Zhao Zhang,1* Fulu Tao,2 Peijun Shi,1 Wei Xu,1 Yu Sun,3 Takehiko Fukushima4

and Yuichi Onda4

1 State Key Laboratory of Earth Surface Processes and Resource Ecology/Academy of Disaster Reduction and Emergency Management, Beijing

Normal University, Beijing 100875, China

2 Institute of Geographical Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China

3 The Center of Disaster Relief and Donation, Bureau of Civil Administration in Hebei Province, China

4 Graduate School of Life and Environmental Science, University of Tsukuba, Tsukuba 305-8572, Japan

 

A flush can be defined as stream chemical exhibiting higher concentrations during the prophase of a storm event at an event scale, or exhibiting progressively lower concentrations during several successive storms at a seasonal scale. Investigating the flush characteristics of chemical runoff from forested watersheds is important and helpful to understand the chemical dynamics as well as to design a sampling schedule strategy during storm events. Here, three parameters describing the flush characteristic are quantified and the flush characteristics of chemicals from four Japanese forested watersheds (Mie, Kochi, Nagano and Tokyo) were investigated at both event and seasonal levels. We found that the characteristics of the flush were complicated, and depended on the constituents of the hydrochemistry, climate and runoff quality. Generally, the flush occurs more readily for particulate components than for those in solution; the flush on nitrate-nitrogen is weaker in regions of nitrogen saturation, such as Nagano and Tokyo, than in Mie and Kochi. Rainfall feature was the main factor controlling the flush of particulate components. However, the source available in a watershed plays a main role on the flushes of dissolve chemicals.

 

Keywords: flush; stream chemistry; forested watersheds; storm runoff; Japan.