2.2 Sample collection
The water samples in this study were tested from January 2010 to April
2022, and the frequency of testing was three times per month, at the
beginning, middle, and end of the month. The study selected the average
of the three data as the water sampling data for the month to avoid
chance. And most of the water sampling data were collected under clear
or cloudy weather, reducing the effect of rainfall. Water samples were
collected from three reservoirs in Chuzhou City during the study period,
and when the sampling was completed, the water samples were transported
to the laboratory in an insulated box with ice packs to test the
required indicators. A total of 10 water quality parameters were chosen
for reflecting reservoir water quality in the study, which were Water
Temperature (WT), pH, Secchi Depth (SD),
Dissolved Oxygen (DO), Chemical
Oxygen Demand (CODMn), Biological Oxygen Demand (BOD),
Ammonia Nitrogen (NH3-N), Total Nitrogen (TN), Total
Phosphorus (TP), and Chlorophyll a (Chl-a). Among them, WT, pH, and DO
were measured in situ using a multi-parameter water quality
analyzer (YSI 6600V2, USA)., while the remaining parameters were
measured by the (Editorial Committee, Methods of Analysis for
Water and Wastewater Monitoring , State Environmental Protection
Administration, 2002). However, when the data were finally selected, it
was found that there were large areas of missing data or some key
indicators that were not measured in the previous years. Thus the
indicator data from 2019 to 2021 were selected as the determining
factors for judging the conditions of water quality and the trophic
status of the water bodies in three reservoirs in Chuzhou City.