Multivariate statistical analysis of temporal-spatial variations in water quality of a constructed wetland purification system in a typical park in Beijing, China.

Using discriminant analysis (DA) and principal component analysis/factor analysis (PCA/FA), we described the variations in the water quality of a constructed wetland (CW) purification system in Olympic Park supplied with reclaimed water (RW). The analyses were conducted across three seasons (spring, summer, and autumn) and four functional zones (composite vertical flow constructed wetland [CVW], plant oxidation pond [POP], mixed oxidation pond [MOP], and main lake [ML]). The results demonstrated the relatively high water quality of the CW, which was suitable for landscape reuse. The most severe contamination occurred in autumn and in the ML/MOP. Chemical oxygen demand (CODMn), NO₃(-)-N, oxidation-reduction potential (ORP), and total nitrogen (TN) caused 91.8% of the temporal variations while DO, cyanobacteria (PCY), and pH caused 70.8% of the spatial variations. The low accuracy of the DA indicated that the four functional areas exhibited similar pollution characteristics. Internal pollution was the major pollutant source in all selected seasons/functional zones. In spring, the CW was largely affected by organic matters. In summer, the CW was contaminated chiefly by nutrient pollutants (N and P), particularly in the CVW and POP. In autumn, the major threat became eutrophication. Enhancing water circulation and shortening hydraulic retention time can effectively weaken the effect of nutrient salts and organic pollutants.