## 2 Materials and Methods
### Sample Collection and Laboratory Analysis  
#### 2.2.1 Vegetation Investigation  
In April 2018, a riparian plant survey of Lingshan River was conducted through establishing monitoring sample plots. The river was divided into three reaches based on the channel gradient: upstream (S), midstream (Z), and downstream (X). In each section, 3-5 typical floodplains were selected according to the morphology, area, bending the degree and flow conditions. The locations of floodplains are shown in Figure 1 and Table 1. Meanwhile, in each floodplain, three lateral sections were set with 2-3 plant sample plots (1 m \(\times\) 1 m) for each section at 5 m intervals. This selection process entailed avoiding low-lying areas, steep slopes, and locations significantly impacted by anthropogenic activities. A total of 120 sample plots were thus acquired.  
Each sample plot underwent scrutiny to document the species' nomenclature, abundance, height, and coverage of all herbaceous plants present. Following this documentation, all plants overground with each species were harvested according to their species and then were transported to the laboratory at \(-\)4 \({}^{\circ}\)C for biomass measurement. The plants that could not be accurately identified in the investigation were prepared and brought back to the laboratory. The identification of each plant species was conducted using references such as the Chinese Plant Image Library and the _Flora of China_.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**River Reach** & **Floodplain Name** & **Longitude** & **Latitude** & **Numbers of Plant Sample Plot** \\ \hline S1 & Xikou Siqiao & 119\({}^{\circ}\)09\({}^{\prime}\)53.68\({}^{\prime\prime}\) & 28\({}^{\circ}\)51\({}^{\prime}\)46.28\({}^{\prime\prime}\) & 8 \\ S2 & Jiangtan & 119\({}^{\circ}\)09\({}^{\prime}\)41.26\({}^{\prime\prime}\) & 28\({}^{\circ}\)51\({}^{\prime}\)54.92\({}^{\prime\prime}\) & 6 \\ S3 & Xiaxuqiao & 119\({}^{\circ}\)09\({}^{\prime}\)46.73\({}^{\prime\prime}\) & 28\({}^{\circ}\)53\({}^{\prime}\)18.95\({}^{\prime\prime}\) & 6 \\ Z1 & Sixia & 119\({}^{\circ}\)09\({}^{\prime}\)33.95\({}^{\prime\prime}\) & 28\({}^{\circ}\)53\({}^{\prime}\)35.25\({}^{\prime\prime}\) & 5 \\ Z2 & Meicun & 119\({}^{\circ}\)08\({}^{\prime}\)51.57\({}^{\prime\prime}\) & 28\({}^{\circ}\)53\({}^{\prime}\)48.08\({}^{\prime\prime}\) & 5 \\ Z3 & Zhoucun & 119\({}^{\circ}\)08\({}^{\prime}\)00.62\({}^{\prime\prime}\) & 28\({}^{\circ}\)54\({}^{\prime}\)00.41\({}^{\prime\prime}\) & 6 \\ X1 & Jiangxiyan & 119\({}^{\circ}\)10\({}^{\prime}\)32.99\({}^{\prime\prime}\) & 28\({}^{\circ}\)57\({}^{\prime}\)56.34\({}^{\prime\prime}\) & 6 \\ X2 & Sihou & 119\({}^{\circ}\)10\({}^{\prime}\)29.33\({}^{\prime\prime}\) & 29\({}^{\circ}\)00\({}^{\prime}\)09.82\({}^{\prime\prime}\) & 6 \\ X3 & Shangyang & 119\({}^{\circ}\)10\({}^{\prime}\)58.23\({}^{\prime\prime}\) & 29\({}^{\circ}\)03\({}^{\prime}\)00.46\({}^{\prime\prime}\) & 6 \\ X4 & Gaotie & 119\({}^{\circ}\)10\({}^{\prime}\)28.31\({}^{\prime\prime}\) & 29\({}^{\circ}\)00\({}^{\prime}\)07.38\({}^{\prime\prime}\) & 9 \\ X5 & Caihongqiao & 119\({}^{\circ}\)11\({}^{\prime}\)00.21\({}^{\prime\prime}\) & 29\({}^{\circ}\)03\({}^{\prime}\)06.41\({}^{\prime\prime}\) & 9 \\ \hline \end{tabular}
\end{table}
Table 1: The sampling point section and monitoring point sample layout.