Phytoplankton Community Investigation and Water Quality Assessment of M River in winter in Shijiazhuang City

An investigation of phytoplankton community and water quality for M River was conducted in December 2019.The results showed that 38 species of phytoplankton belonging to 6 phyla and 26 genera were collected. Among them, Bacillariophyta is the richest species, which accounted for 34.21%, followed by Cyanophyta with 26.32% and Chlorophyta with 28.95%. The density of phytoplankton was 63.0*106 inds/L which indicated as eutrophic water body. The highest density was Bacillariophyta, accounting for 51.03%. The Shannon-Wiener diversity index (H’) varied from 1.34 to 2.24, the Margalef Species diversity index (d) varied from 2.71 to 3.85, and the Pielou evenness index (J) varied from 0.38 to 0.67. According to the integrative analysis results of H’, d and J, M River water quality belongs to oligo-polluted, but individual sites belong to meso-polluted.


Introduction
The survival of aquatic organisms is closely related to the water environment quality, and the composition of species and their proportion in the community can reflect the water quality [1] . Phytoplankton forms the basic link in the food chain of an aquatic ecosystem and virtually all the dynamic features of lakes such as color, clarity, trophic state, zooplankton, and fish production depend to a large extent on the phytoplankton. Freshwater communities are very much sensitive to environmental variables [2] . The number of species, dominant species and diversity index of phytoplankton community varied greatly in the water environment with different nutrition levels, which often become a biological index of water environmental monitoring and eutrophication [3][4] .
There have been many studies on phytoplankton community investigation and water quality evaluation on surface rivers and watersheds. An investigation was carried out in the Shanxi section of Xiaolangdi Reservoir from May 2014 to November 2015, the result showed that water body of Xiaolangdi Reservoir belongs to medium eutrophication level [5] . Phytoplankton community investigation and water quality evaluated were conducted in the three typical waters of Baiyangdian Lake from April to November in 2013, the conclusion is phytoplankton distribution was significantly affected by three environment factors [6] . However, there is little research on water quality evaluation for the M River. In this paper, the phytoplankton community constitute and water quality evaluation in M River were carried out in December 2019.
Results of phytoplankton composition together with water quality parameters are reported, which provided the basic data for the ecological environment management.

Overview of the study area
M River is located in Shijiazhuang City, Hebei Province, a total length of 56.9 kilometers. It is divided into the east, west, south, north and center five rivers around the city, east line for Century Park, west line for Zhongshan Park, south line for the Ouyun Park , north line for Pearl Park, center line for Binhe Park. In turn named S1, S2, S3, S4, S5. The water system of this river is city landscape water body. In recent years, human activities have made a significant impact on the ecological environment of M River. Therefore, it is necessary to know the water quality of the M River to control and prevent water pollution. In December 2016, samples were collected and analyzed in the S1, S2, S3, S4, S5 (Fig.1).

Phytoplankton samples
The samples for phytoplankton analysis were collected using 5L plexiglass water harvesting device at the depth of 0~0.5m. 4% formalin were then added to the phytoplankton samples for longer preservation [7][8] . Before taxonomic analyses and species enumeration, the samples for phytoplankton analysis were stored in the dark in evacuated 4 L flasks and allowed to supernate for 48 h [9] . According to " The Freshwater Algae of China: Systematics, Taxonomy and Ecology" and "Freshwater plankton map", phytoplankton species were identified and counted [10][11] . All phytoplankton samples were analyzed by the same investigator. The count was counted twice and the density of the phytoplankton was calculated by the following formula: inds/ 400 10 1000(1) After phytoplankton qualitative and quantitative analysis, the phytoplankton community characteristics in Minxin River were analyzed by Dominance index (Y), Shannon-Wiener diversity index (H'), Margalef Species diversity index (d) and Pielou evenness index (J). Assessment criterion of each index were showed in Tab.2. The calculation formula is as follows:  The composition of phytoplankton species mainly is Bacillariophyta, Cyanophyta and Chlorophyta. Bacillariophyta is the richest species of algae, which accounted for 34.21% (Tab.3). The percentage of Cyanophyta and Chlorophyta in the number of species was similar, accounted for 26.32% and 28.95% (Tab.3), respectively. It can be seen from Tab.5 that the density of Bacillariophyta was the largest at 32.1×10 6 , accounting for 50.95% of the total density of phytoplankton, followed by Chlorophyta (27.14%) (Fig.2). Bacillariophyta density was greatest at all sampling sites (Tab.5). Therefore, Bacillariophyta not only occupies an advantage in the number of species, but also occupies a certain advantage in density (Tab.3 and Fig.2). The phytoplankton density of S 3 is the largest, accounted for 46.19% of the total phytoplankton, followed by S 4 (16.67%) and S 5 (14.76%). The total density of phytoplankton was 63.0×10 6 inds/L. According to the evaluation criteria of lake eutrophication [12] , M River belongs to an eutrophic water body, there may be some influence on the composition and distribution of phytoplankton species. In recent years, a large amount of organic pollutants containing nitrogen and phosphorus are discharged into the M River, the degree of water quality eutrophication is aggravated, which directly affects the urban water quality. In general, there is a clear positive correlation between nutrient concentration and biomass in lakes. Algae have some indication effect on water quality [13] .  As can be seen from Fig.3, Shannon-Wiener diversity index of all sites were between 1-2, which indicate that the water quality is meso-polluted. Pielou evenness index of S 1 and S 2 were between 0.5 and 0.8, which indicate that the river is oligo-polluted, but S 3 , S 4 and S 5 were mesopolluted whose index in the range of 0.3-0.5. Margalef Species diversity index of all sites were between 3-4, which indicate that the water quality is oligo-polluted, but S 3 were meso-polluted whose index were between 2 and 3. The change trend of Shannon-Wiener diversity index, Margalef Species diversity index and Pielou evenness index are basically consistent, all of which are the lowest in S 3 . This close relationship between them is reflected in ecological processes such as predation, competition and succession [14] . Among all the sampling sites, S 3 is the most serious pollution. In summary, the M River water quality is meso-polluted.

Conclusions
The main types of phytoplankton in the M River include Bacillariophyta (34.21%), Cyanophyta (26.32%) and Chlorophyta (28.95%). The total density is 63.0 × 10 6 inds/L of phytoplankton, it is indicated that the M River belongs to eutrophic water body. According to the integrative analysis result of Shannon-Wiener diversity index, Margalef Species diversity index and Pielou evenness index, M River water quality belongs to mesopolluted, but individual sites belong to oligo-polluted.