2.1 Study area and sampling sites
The Pearl River, the second largest river in China, is in the tropical
and subtropical areas of Southeast Asia and serves as a critical water
source for Guangdong Province and Hong Kong. The water sources of the
Pearl River are essential for supplying drinking water, generating
power, and performing irrigation in Guangdong Province. Thus, the
ecological health of the Pearl River is important for the sustainable
development of the Pearl River Delta. The Pearl River consists of
multiple tributaries – the North, West, East, Liuxi, and Zeng Rivers –
which ultimately merge into the Pearl River Estuary in southern China.
The current survey originated from the Liuxi River and Zeng River (Fig.
1), which are regarded as the water sources with high cultural
significance for Guangzhou, the capital city of Guangdong Province in
southern China. The Liuxi River and Zeng River are the upstream source
waters for the Pearl River, including both upstream wadable and
downstream nonwadable habitats. Thus, they are important for the
comparison between the eDNA
metabarcoding protocol and electrofishing method.
Thirty-eight sampling sites were chosen from the headwaters of the Liuxi
(L1 – L14) and Zeng Rivers (Z1 – Z12) to the mainstream of the Pearl
River (P1 – P12) and then to the Pearl River mouth connected with the
South China Sea (Fig. 1). The landforms within the drainage basin are
dominated by medium-low mountains and hills. The mean annual temperature
and precipitation are 21.6 °C and 2188 mm, respectively. Approximately
83.3% of the runoff is discharged in the flood season (from April to
September). The zonal soil and vegetation are Udic Ferralisols and
southern subtropical evergreen broad-leaved forest, respectively. Forest
coverage is approximately 50%. Arable land accounts for only 8.7% of
the drainage area, with paddy fields accounting for most of this.
Environmental data, including physicochemical parameters of water
quality, habitat characteristics, and bacterial amounts (see Table S1 in
the Supplementary Material), were provided by two nationally accredited
(China Metrology Accreditation) third-party testing agencies (Hainan
Qingxiao Environmental Testing Co., Ltd. and Hainan Qianchao Ecological
Technology Co., Ltd.).