Seasonal Variation Characteristics and the Factors Affecting Plankton Community Structure in the Yitong River, China

Abstract

To explore how environmental factors affected the plankton structure in the Yitong River, we surveyed the water environmental factors and plankton population in different seasons. The results showed high total nitrogen concentrations in Yitong River throughout the year, while the total phosphorus, water temperature (WT), and chemical oxygen demand in summer were significantly higher than those in other seasons (p < 0.05), and the dissolved oxygen (DO) concentrations and TN/TP ratio were significantly lower (p < 0.01) than those in other seasons. There was no significant seasonal change in other environmental factors. Cyanophyta, Chlorophyta, and Bacillariophyta were the main phytoplankton phylum, while Protozoa and Rotifera were the main zooplankton phylum. The abundance and biomass of zooplankton and phytoplankton in the summer were higher than those in other seasons. Non-Metric Multidimensional scaling methods demonstrated obvious seasonal variation of phytoplankton in summer compared to spring and winter, while the seasonal variation of the zooplankton community was not obvious. The results of the redundancy analysis showed that WT, DO and nitrate nitrogen were the main environmental factors affecting phytoplankton abundance. In contrast to environmental factors, phytoplankton was the main factor driving the seasonal variation of the zooplankton community structure. Cyanophyta were positively correlated with the changes in the plankton community.

Keywords: Cyanophyta; Yitong River; phytoplankton; plankton community; seasonal variation; zooplankton.

Figure 1

Location of the Yitong River and the sampling sites.

Figure 2

Seasonal variation of water quality indicators (* indicating significant differences at 0.05 level; ** indicating significant differences at 0.01 level). The three horizontal lines from top to bottom in the box plot represent the 75%, 50% and 25% quartiles, respectively. The vertical bar above the box represents the range of values from the 75% quartile to the maximum value, and the vertical bar below the box represents the range of values from the minimum value to the 25% quartile. Blocks of different colors indicate the average values.

Figure 3

Seasonal variation of plankton abundance (a,b), biomass (c) and biodiversity (d,e), and the correlation between Chl-a and zooplankton biomass (f) (different letters on the error bars represent significant seasonal differences at 0.05 or 0.01 level in (a–c). * indicating significant differences at 0.05 level; ** indicating significant differences at 0.01 level in (d,e). ** indicating significant correlation at 0.01 level in (f)). Blocks of different colors in (d,e) indicate the average values.

Figure 4

NMDS ordination plot of phytoplankton (a) and zooplankton (b) abundance.

Figure 5

RDA of phytoplankton (a) and zooplankton (b) abundance with environmental factors.

Figure 6

Linear relationship between log (Cyanophyta abundance), log (plankton biomass) (a,b), log (plankton biodiversity index) (c–f) (H-phytoplankton and H-zooplankton indicate the Shannon-Wiener index of phytoplankton and zooplankton; J-phytoplankton and J-zooplankton indicate the Pielou index of phytoplankton and zooplankton).