Spatial and seasonal dynamics of zooplankton functional groups and their relationship with environmental factors in urban rivers in Haikou City, China

The urban rivers, including Changwang, Meishe, and Wuyuan in Haikou City, China, are vital water resources. Despite the rivers experiencing anthropogenic impacts, limited studies have investigated their water quality and ecological community structure. This study assessed zooplankton functional groups' spatial and seasonal dynamics relative to environmental factors in the three urban rivers. The samples were collected and analyzed seasonally between March and December 2019. The environmental factors varied significantly at spatial and seasonal scales (p < 0.05). Meishe and Wuyuan Rivers had higher electrical conductivity, salinity, TN, and TP than Changwang, which had low turbidity. Seasonally, higher TP, TN, NH3-N, and CODMn levels were found in the spring, while summer and autumn experienced high temperatures. Additionally, spring and summer had high Chl-a levels. Likewise, spring had the lowest heavy metal concentrations, while nearly all metals were elevated in winter and summer. Generally, the average metal content followed the order of Mn > Zn > Cu > Ni > As > Cr > Co > Pb > Cd. The environmental parameters were within class III of the China standard for surface waters (GB 3838-2002), suggesting negligible pollution. This study identified 159 zooplankton species, including 62 Rotifers, 50 Protozoans, 31 Cladocerans, and 16 Copepods. They were classified into 11 functional groups, dominated by Rotifers filter feeders (RF), Rotifers carnivores (RC), and small copepods and cladocerans filter feeders (SCF), followed by Middle copepods and cladocera carnivores (MCC) and Middle copepods and cladocerans filter feeders (MCF). Analysis of similarity (ANOSIM) revealed seasonal differences (p < 0.001) in zooplankton functional groups, with RF and RC most dominant in summer, autumn, and winter, while SCF, MCF, and MCC were dominant in spring. Hence, the redundancy analysis (RDA) and Pearson Correlation analysis revealed that temperature, Chl-a, TP, salinity, CODMn, NH3-N, TN, As, Co, and Cd were the main environmental factors influencing zooplankton functional groups. This study helps understand urban rivers' water quality and ecological community structure, bridging the knowledge gap. The findings are essential for water quality monitoring and management.