Materials and methods
2.1. The study area
Shenzhen region, at the central coastal area in southern
Guangdong Province, is the passageway from mainland
China to Hong Kong (Fig. 1). It has a total land area of
1948.69 km2. According to soil horizontal zonality, the
main soil types are yellow soil, red soil and lateritic red soil.
Moreover, Shenzhen was once a rural area, so types of soil
being used also include latosol, paddy soil, seashore sand
soil and saline soil. Vegetation covers 50–80% of the land
area. With tropical oceanic monsoon climate, the average
annual precipitation from 1952 to 1992 was 1882.8 mm, and
rainfall in the flood season from April to September made
up 84.5% of the annual total.
In Shenzhen region, there are 160 rivers, among which 13
rivers with drainage basin areas larger than 10 km2 and 5 river
basins larger than 100 km2. We selected Buji River Basin as
the study area. The upper reach of Buji River flows through