Effect Of Spirulina Aquaculture Effluent Discharge On The Phytoplankton Community Structure Of Hammatai Lake

Hammatai Lake（which locates in Wulan Town,Ordos City,Inner Mongolia）was selected as the research site,the Chaganore Lake as control,sampling surveys were conducted 4 times every year（April,June,August and October）from 2017 to 2018.The difference of water quality and phytoplankton community structure between Hammatai Lake（which was contaminated by spirulina aquaculture wastewater）and Chaganore Lake（control）were analyzed,and the relationship between changes in lake water environment and phytoplankton community structure was analyzed at the same time.Discussing the influence and mechanism of the discharge of spirulina culture waste liquid on the ecological environment of the plateau alkaline lake in arid-semi-arid areas.The main conclusions of the study as follow:（1）A total of 14 genera of phytoplankton in 5 phyla were identified in Hammatai Lake.5 phyla and 13 genera and 4 phyla and 11 genera were identified in H-1 and H-2respectively.A total of 4 phyla of phytoplankton and 12 genera were identified in Chaganore Lake.C-1 has 4 phyla and 11 genera and C-2 has 5 phyla and 10 genera.The dominant species were Spirulina and Chlamydomonas of Cyanophyta and Chlorophyta.The number of phytoplankton genera in Hammatai Lake and Chaganore Lake increased from April to August,however decreased in October.（2）The annual average phytoplankton abundances of H-1,H-2,C-1,and C-2 were0.170 ind./L,0.165 ind./L,0.102 ind./Land 0.151 ind./L,respectively.The higher abundance values were in June and August.The annual average biomass values were 2.677mg/L,3.572 mg/L,2.570 mg/L and 3.470 mg/L,respectively.The biomass of phytoplankton decreased from April to October,with the highest in April and the lowest in October.The Shannon-Wiener diversity index and Pielou evenness index were single-peaked curve,the abundance and Shannon-Wiener diversity index varied obviously,both of which the largest value were in June and August,and the lowest occurred in October.（3）The average p H value and dissolved oxygen（DO）value of Hammatai Lake was significantly higher than that of Chaganore Lake（P<0.05）.There was no significant difference in total phosphorus（TP）,total nitrogen（TN）,nitrate nitrogen（NO₃-N）,ammonium nitrogen（NH₄-N）and chemical oxygen demand（COD）.The concentration of TN and TP was high,but the value of TN/TP was low,so both lakes were restricted by N.The above parameter indicators are one of the important parameters to measure water quality,According to the evaluation standard results of the single factor index evaluation method and the comprehensive pollution index evaluation method,the water environment of Hammatai Lake and Chaganore Lake is of poor water quality.（4）The mainly cations of Hammatai Lake and Chaganore Lake were Na⁺,K⁺,Mg²⁺and Ca²⁺,and the ion concentration was Na⁺>K⁺>Mg²⁺>Ca²⁺.The anions mainly were Cl^-,SO₄^2-and CO₃^2-+HCO₃^-,and the concentration of Mg²⁺,Ca²⁺and NO₃^-was low.The concentration of Na⁺and K⁺in Chaganore Lake was higher than that of Hammatai Lake,and the concentration of Na⁺and K⁺in yellow pool was higher than that of green pool;the anion concentration of Chaganore Lake was higher than that of Hammatai Lake,and yellow pool was higher than that of green pool,but the CO₃^2-+HCO₃^-content was significantly lower than that of Hammatai Lake.The concentration of CO₃^2-+HCO₃^-and p H value increased with the discharge of spirulina culture waste liquid in Hammatai Lake,the concentration of Na⁺,K⁺,Cl^-and SO₄^2-was diluted at the same time.（5）The main factors that promoted the growth of phytoplankton in Hammatai Lake were p H,ammonium nitrogen（NH₄-N）and cations.The main inhibitors of its growth were SO₄^2-and Cl^-.The phytoplankton of Chaganore Lake was affected by Mg²⁺,Ca²⁺,p H,dissolved oxygen（DO）,water temperature（WT）,SO₄^2-and Cl^-;the biomass of Hammatai Lake（H-1,H-2）and Chaganore Lake（C-1,C-2）declined with the increase of water temperature,the abundance of phytoplankton was promoted at the same time.（6）The discharge of spirulina culture waste liquid lead to the concentration of CO₃^2-+HCO₃^-（alkalinity）in the water body of Hammatai Lake to increase,it had a certain dilution effect on the concentration of Na⁺,K⁺,Cl^-and SO₄^2-.The high ion concentration will inhibit the growth of algae.On the contrary,the dilution of the ion concentration of the Hammatai Lake will promote the massive growth of Spirulina and Chlamydomonas,which will increase the probability of algal blooms.