2.2 Physicochemical analysis
The coordinates (latitude and longitude) of sampling sites were recorded using a Global Positioning System (GPS). Sediment pH and electrical conductivity (EC) were measured using a pH/Conductivity meter (HANNA, HI98129) after creating a slurry, 1:2.5 (v/v) fresh sediment to water ratio. Total carbon (TC) and total nitrogen (TN) contents were measured by a TOC-Vcph analyzer (Shimadzu Corp, Japan). Concentrations of ammonium (NH4+-N), nitrite (NO2--N), nitrate nitrogen (NO3--N), soluble phosphorus (PO43--P), and total phosphorous (TP) were measured with an automatic absorbance microplate reader (Spark 10M, TECAN, Mannedorf, Switzerland) as previously reported (Hernández‐López and Vargas‐Albores, 2003). Sediment particle size distribution (e.g., clay, silt, and sand) were measured using particle size analyzer (Mastersizer 2000, Malvern UK). The land use classification and corresponding proportions were derived from National Earth System Science Data Center, National Science & Technology Infrastructure of China (http://www.geodata.cn).