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).