[Characteristics of Phytoplankton Communities and Key Impact Factors in Three Types of Lakes in Wuhan]

To reveal the characteristics and key impact factors of phytoplankton communities in different types of lakes, sampling surveys for phytoplankton and water quality parameters were conducted at 174 sampling sites in a total of 24 lakes covering urban, countryside, and ecological conservation areas of Wuhan in spring, summer, autumn, and winter 2018. The results showed that a total of 365 species of phytoplankton from nine phyla and 159 genera were identified in the three types of lakes. The main species were green algae, cyanobacteria, and diatoms, accounting for 55.34%, 15.89%, and 15.07% of the total number of species, respectively. The phytoplankton cell density varied from 3.60×10⁶-421.99×10⁶ cell·L^-1, chlorophyll-a content varied from 15.60-240.50 μg·L^-1, biomass varied from 27.71-379.79 mg·L^-1, and the Shannon-Wiener diversity index varied from 0.29-2.86. In the three lake types, cell density, Chla, and biomass were lower in EL and UL, whereas the opposite was true for the Shannon-Wiener diversity index. NMDS and ANOSIM analysis showed differences in phytoplankton community structure (Stress=0.13, R=0.048, P=0.2298). In addition, the phytoplankton community structure of the three lake types had significant seasonal characteristics, with chlorophyll-a content and biomass being significantly higher in summer than in winter (P<0.05). Spearman correlation analysis showed that phytoplankton biomass decreased with increasing N:P in UL and CL, whereas the opposite was true for EL. Redundancy analysis (RDA) showed that WT, pH, NO₃^-, EC, and N:P were the key factors that significantly affected the variability in phytoplankton community structure in the three types of lakes in Wuhan (P<0.05).

Impacts of residual aluminum from aluminate flocculant on the morphological and physiological characteristics of Vallisneria natans and Hydrilla verticillata

Aluminate is generally used as a flocculant in water and wastewater treatment processes, but the residual aluminum (Al) may have toxic effects on aquatic organisms when the concentration accumulates beyond a threshold level. The in situ and laboratory tests were conducted to evaluate the impact of residual Al on submerged macrophytes in West Lake, Hangzhou, China, which receives Al flocculant-purified water diverted from the Qiantang River. The responses of Vallisneria natans and Hydrilla verticillata were investigated based on their morphological and physiological parameters in pot culture and aquarium simulation experiments. In the pot culture experiments, the biomass, seedling number, plant height, stolon number, stolon length, and root weight were significantly higher at a site located 150m from the inlet compared with those at a site located 15m from the inlet (P < 0.05), thereby indicating that the residual Al significantly inhibited the morphological development of V. natans and H. verticillata. The variations in the chlorophyll-a, protein, and malondialdehyde contents of the two species in both the pot culture and aquarium simulation experiments also demonstrated that the two submerged macrophytes were stressed by residual Al. V. natans and H. verticillata accumulated 0.052-0.227mg of Al per gram of plant biomass (fresh weight, mg/g FW) and 0.045-0.205mg Al/g FW in the in situ experiments, respectively, where the amounts of Al were significantly higher in the plants in the treatment aquaria during the laboratory experiments than those in the controls. These results may have important implications for the restoration of submerged macrophytes and ecological risk assessments in Al-exposed lakes. It is recommended that the Al salt concentration used for the control of lake eutrophication should be reduced to an appropriate level.