Ecological health assessment using zooplankton index of biotic integrity (Z-IBI) in urban rivers in Hainan Island, China.

The Changwang, Meishe, and Wuyuan are urban rivers in Haikou City, Hainan Island. They are vital water sources, serving various purposes, from farmland irrigation to domestic and industrial use. Unfortunately, anthropogenic activities have influenced these "rivers," negatively impacting water quality and ecological functions; however, there is limited research on their ecological status. Thus, this study assessed the zooplankton community structure and developed the zooplankton index of biotic integrity (Z-IBI) to evaluate the ecological status. Samples were collected and analyzed seasonally in 2019. Generally, 159 zooplankton species belonging to 85 genera, 55 families, and 3 phyla were identified, dominated by Rotifer and Protozoa, followed by Arthropoda (groups of Copepod and Cladocera). The zooplankton density varied from 0.00 to 126.04 ind L-1, with averages of 19.49 ind L-1, 31.40 ind L-1, and 20.38 ind L-1 in Changwang, Meishe, and Wuyuan, respectively. The zooplankton density varied seasonally as summer > spring > winter > autumn. Analysis of similarity (ANOSIM) indicated a significant seasonal difference (R = 0.070, p < 0.001) in zooplankton community but not spatially (R = 0.004, p = 0.413). Thus, SIMPER revealed that Brachionus forficula, Didinium nasutum, Keratella valga, Nauplius, and Polyarthra vulgaris contributed to the seasonal differences. The redundancy analysis (RDA) revealed environmental factors, including total phosphorus (TP), total nitrogen (TN), ammonia nitrogen (NH3-N), chemical oxygen demand (CODMn), dissolved oxygen (DO), temperature, pH, Chl-a, and electrical conductivity (EC) influenced zooplankton species. The Z-IBI was established using Zooplankton abundance, Protozoa abundance, Copepod abundance, Cladoceran biomass %, and Shannon-Wiener diversity index. Based on Z-IBI evaluation, ecological status was "moderate" in Changwang and Wuyuan, while it was "low" in Meishe. Seasonally, the ecological status in autumn was better than in summer and spring. The Z-IBI showed that parameters, including pH, EC, CODMn, TN, TP, and Chl-a, decreased with improving water quality, while water transparency increased with improved water quality. Thus, the "rivers" ecological status could be adequately assessed using the Z-IBI to guide their water quality monitoring and management.

Spatio-temporal variation in water quality and phytoplankton community structure in Changwang, Meishe, and Wuyuan Rivers in Hainan Island, China.

For the first time, this study explored spatio-temporal variation in water quality and phytoplankton community structure in Changwang, Meishe, and Wuyuan Rivers in tropical Hainan Island, China. Phytoplankton samples and water were collected between March and December 2019 and analyzed using standard methods. Two-way ANOVA revealed significant spatial and seasonal variation in physico-chemical parameters (p < 0.05). Wuyuan had high TP (0.06 ± 0.04 mg L-1), TN (1.14 ± 0.71 mg L-1), NH4+-N (0.07 ± 0.09 mg L-1), Secchi depth (2.28 ± 3.79 m), salinity (3.60±5.50 ppt), and EC (332.50 ± 219.10 µS cm-1). At the same time, Meishe had high TP (0.07 ± 0.03 mg L-1), TN (1.04 ± 0.74 mg L-1), NH4+-N (0.07 ± 0.10 mg L-1), EC (327.61 ± 63.22 µS cm-1), and turbidity (40.25 ± 21.16 NTU). In terms of seasons, spring recorded high average TP, TN, NH4+-N, COD, and DO, while summer had a high temperature, Chl-a, salinity, and EC. Generally, the physico-chemical parameters met the China water quality standard limits (GB 3838-2002). Overall, 197 phytoplankton species belonging to Cyanophyta, Chlorophyta, Cryptophyta, Bacillariophyta, Pyrrophyta, Euglenophyta, Xanthophyta, and Chrysophyta were identified, with Cyanophyta being dominant. Phytoplankton density showed spatial changes varying from 18 × 106 cell L-1 to 84 × 106 cell L-1. The phytoplankton diversity ranged from 1.86 to 2.41, indicating a mesotrophic state. One-way ANOSIM showed no significant spatial dissimilarity in phytoplankton composition (R = 0.042, p = 0.771) but indicated a significant seasonal difference (R = 0.265, p = 0.001). Therefore, SIMPER analysis revealed that Lyngbya attenuata, Merismopedia tenuissima, Cyclotella sp., Merismopedia glauca, Merismopedia elegans, and Phormidium tenue contributed to the seasonal differences. Furthermore, CCA demonstrated that TP, TN, NH4+-N, COD, Chl-a, and Secchi depth greatly influenced the phytoplankton community. This study shows the spatio-temporal variation in water quality and phytoplankton communities, useful for managing riverine quality.

Assessing ecological status using phytoplankton functional groups in three urban rivers in Hainan Island, China.

The urban rivers, including Changwang, Meishe, and Wuyuan in Haikou City, Hainan Island, are vital water sources for agricultural production and support industrial and domestic activities. Despite the rivers experiencing anthropogenic impacts, limited studies have assessed their water quality. Accordingly, this study assessed the phytoplankton community structure, utilized the river phytoplankton assemblage index (Qr index) to evaluate the ecological status, and compared its performance with the comprehensive trophic level index (TLI). Sample collection and microscopy analysis was conducted seasonally in 2019. Two hundred ninety-eight phytoplankton species belonging to 8 phyla were identified, predominated by Chlorophyta, Bacillariophyta, and Cyanophyta. The phytoplankton biomass ranged from 0.04 to 34.98 mg L-1, with averages of 3.06 ± 0.71, 5.16 ± 1.92, and 2.70 ± 0.76 mg L-1 in Changwang, Meishe, and Wuyuan, respectively. The phytoplankton biomass varied seasonally, recording the highest and lowest values in summer and autumn, respectively. The phytoplankton species were classified into 26 functional groups, which exhibited spatial and seasonal differences in their biomass and composition. The redundancy analysis (RDA) revealed that NH3-N, TP, CODMn, Chl-a, salinity, and temperature were the main environmental factors influencing phytoplankton functional groups. The average Qr index values in Changwang, Meishe, and Wuyuan were 3.39 ± 0.61, 3.44 ± 0.51, and 3.22 ± 0.67, and all the rivers were rated "good" in status. Seasonally, the Qr index and TLI revealed that the rivers' ecological condition was better in autumn and winter compared to spring and summer. Generally, the Qr index performed better, indicating that parameters such as NH3-N, CODMn, TP, and Chl-a decreased with improving ecological conditions from "poor" to "excellent" status. In addition, the Qr index exhibited a significant negative relationship with TLI, suggesting that low Qr index values may indicate increased eutrophication or deteriorated water quality. Thus, the ecological condition of the urban rivers could be adequately assessed using the Qr index to guide their water quality monitoring and management.