The Hulan River Wetland (N 45°54'-45°51', E126°139'-127°14') is located in the northeastern part of China, where climate conditions are similar to those in subtropical monsoon regions. The wetland, currently being restored, is China's largest urban wetland. It has three distinct zones: an agricultural area, an industrial area and a reserve area. We recently carried out a survey of phytoplankton in the wetland, during which we collected samples from 10 sites in these three areas. In the survey, we identified 191 phytoplankton species that belonged to 69 genera, 17 families, 14 orders, 9 classes and 7 phyla. Bacillariophyta was the dominant class, followed by Chlorophyta and then Euglenophyta. Quantitative analysis showed that phytoplankton abundance increased from 1.23×10⁷ind/L in summer to 1.98×10⁷ind/L in autumn. The total average phytoplankton abundance in summer and autumn was 1.60×10⁷ ind/L. There were obvious seasonal changes in the phytoplankton community structure, for example Anabaena azotica and Scenedesmus protuberans were the dominant species in summer, while the most abundant species in autumn were Navicula radiosa and Trachelomonas volvocina.
The development of phytoplankton functional groups is an important achievement and has been a popular research topic in recent years. Phytoplankton functional groups simplify phytoplankton classification. They help us to arrange phytoplankton into groups based on ecological function so that we can understand phytoplankton adaptability to the environment. Phytoplankton functional groups may be based on classical taxonomy, morphological structure, physiological characteristics and ecological attributes. Phytoplankton functional groups can help us successfully process and combine changes in habitat and phytoplankton communities, and can explain how some habitat-specific phytoplankton taxa adapt to habitat change. This paper therefore aims to demonstrate how recently developed phytoplankton functional group classifications can effectively explain changes in phytoplankton in an urban wetland in response to environmental conditions.
We arranged the phytoplankton species data from the summer and autumn into 19 functional groups. The dominant assemblages in summer and autumn were from the X1/W2/MP/Lo/J functional groups. Groups such as X1/W2/MP/Lo/J were abundant in summer and autumn, while H1/Y/W1 groups were only detected in certain seasons and habitats. While groups D/P/TB appeared frequently, when compared with other groups, their relative abundance was lower. H1/MP/Lo/TB/J/G were the dominant functional groups in summer, while MP/J/W1/W2/X1/Y were dominant in autumn.
We measured the following environmental variables: specific conductance (SpCond), total phosphorus (TP), water temperature, total nitrogen (TN), dissolved oxygen (DO), ammoniacal nitrogen (NH⁺₄-N), turbidity and pH. Water temperature ranged from 17.08 to 26.64 °C, and there were obvious differences between summer and autumn. pH was less variable than water temperature, and ranged from 6.20 to 7.60, with an average of 6.63, which suggests that the Hulan River wetland is neutral. TP concentrations ranged from 0.14 to 0.84 mg/L; TN concentrations ranged from 0.14 to 0.81 mg/L; SpCond was between 224.77 and 657.50 μS/cm; DO was in the range 3.88-9.46 mg/L; Turb ranged from 80.25 to 343.78 NTU and NH⁺₄-N concentrations were in the range 0.7-3.80 mg/L. Trophic status ranged from mesotrophic to eutrophic.
Canonical correspondence analysis was used to analyze the relationships between environmental variables and the seasonal succession of phytoplankton functional groups. Results showed that succession in the phytoplankton functional groups was largely determined by interactions between SpCond, TP and water temperature. Data suggest that the Hulan River Wetland may have been eutrophic during the study period. Nitrogen and phosphorus concentrations were above water quality standard thresholds, so the dominant indicator species in the wetland were those that were tolerant of polluted water.