3.2 Correlation Analysis between water quality parameters
The Pearson correlation coefficient matrix was used to test and analyze the 10 indicators common to the three reservoirs (Fig. 2). As expected, there were similar correlations between some of the parameters in the three reservoirs, for example, WT and DO showed a relatively strong negative correlation in Shahe Reservoir (r = − 0.71, P < 0.001) and Huanglishu Reservoir (r = − 0.69, P < 0.001), and a tremendously stronger negative correlation in Chengxi Reservoir (r = − 0.88, P < 0.001). Additionally, WT was also moderately positively correlated with CODMn in ShaheReservoir (r = 0.48, P <0.01) and Huanglishu Reservoir (r = 0.53, P < 0.001), and highly strongly positively correlated with CODMn in Chengxi Reservoir (r = 0.62, P < 0.001).
In the Shahe Reservoir, pH was statistically significantly different from CODMn (r = 0.41, P < 0.05), showing a moderate positive correlation, as well as positively correlating with WT (r = 0.51, P < 0.01) and BOD (r = 0.43, P < 0.01) at higher confidence levels. In the Huanglishu Reservoir, Chl-a was positively correlated with WT (r = 0.40,P < 0.01) and negatively correlated with DO (r = − 0.34, P < 0.01). In the Chengxi Reservoir, TP was positively correlated with TN at a confidence level of 0.05 with a correlation coefficient of 0.38, and negatively correlated with pH at a much higher confidence level (r = − 0.44, P < 0.01), as well as moderately positively correlated with CODMn (r = 0.42, P < 0.01).