| Baima Lake is one of the ten largest lakes in Jiangsu Province and one of lakes of national priority protection in China.Since Baima Lake restored lakes from diked areas,to curb the environmental issues such as eutrophication of Baima Lake and to restore its ecosystem health as soon as possible,ecological reconstruction technologies for lake restoration will urgently need to be developed.Relying on macrophyte water decomtamination eco-engineering"National Key Lake Ecological Environmental Protection Project-Submerged Macrophytes Planting Area"(referred to as"water decomtamination engineering",WD),Four samplings were conducted to investigate the impact of WD on the plankton of Baima Lake during the growth period of macrophytes(Spring-April 16th,Summer-June 12th,July 26th,Autumn-September 26th).The main results are as follows:(1)Inside the WD,total nitrogen of four samplings in water column were 0.85,1.15,1.13,and1.33 mg/L in turn;and total phosphorus in water column were 0.020,0.102,0.121,and 0.099 mg/L in turn.Outside the WD,total nitrogen of four samplings in water column were 1.60,1.50,1.88,and 2.03 mg/L in turn;and total phosphorus in water column were 0.068,0.124,0.171,and 0.139mg/L in turn.Obviously,total nitrogen and total phosphorus of water column in WD could be reduced.In addition,WD could significantly increase water transparency,decrease water p H,chlorophyll a content and total alkaline phosphatase activity.Correlation analysis showed that there was a significant positive correlation between chlorophyll a and total alkaline phosphatase activity,and there was a significant positive correlation between chlorophyll a and total phosphorus,but no significant correlation with total nitrogen both inside and outside the WD.Therefore,phosphorus was a key factor limiting the primary productivity of Baima Lake.(2)The phytoplankton community characteristics were different between inside and outside the WD.Both abundance and biomass of phytoplankton inside the WD were lower than those outside.Inside the WD,phytoplankton abundance of the four samplings were 4.16,20.22,17.48,and 13.27×10~6/L in turn,and phytoplankton biomass were 4.78,25.40,42.57,and 38.00 mg/L in turn.Outside the WD,phytoplankton abundance of the four samplings were 16.48,23.24,22.40,and 14.48×10~6/L in turn,and phytoplankton biomass were 14.01,29.26,52.07,and 45.07 mg/L in turn.In summer(July 26th)and autumn,Oscillatoria sp.and Melosira granulata were the largest dominant phytoplankton both inside and outside the WD.The behavior of Shannon-Wiener diversity index,Simpson’s diversity index,and Pielou evenness index of phytoplankton all were inconsistent with the Margalef diversity index between inside and outside the WD.Therefore,the phytoplankton diversity indexes could not effectively evaluate the effect of WD.The envfit analysis showed that the environmental factors with good correlation with phytoplankton community were chemical oxygen demand,water temperature,chlorophyll a,total phosphorus,dissolved oxygen,transparency,electrical conductivity,and ammonia nitrogen in turn inside the WD.Meanwhile,the environmental factors with good correlation with phytoplankton community were chemical oxygen demand,water temperature,electrical conductivity,ammonia nitrogen,chlorophyll a,dissolved oxygen,and total phosphorus in turn outside the WD.(3)The characteristics of zooplankton community were different between inside and outside the WD.Abundance of rotifera was much greater than that of cladocera and copepoda,but the relative biomass of rotifera was less.Inside the WD,zooplankton abundance of the four samplings were 75.6,1752.0,4165.4,and 4063.0×1/L in turn,and zooplankton biomass were 0.73,2.60,3.81,4.31 mg/L in turn.Outside the WD,zooplankton abundance of the four samplings were 333.4,1930.1,1511.0,and 3063.5×1/L in turn,and zooplankton biomass were 1.04,1.29,2.61,and 5.12mg/L in turn.Therefore,the abundance and biomass of zooplankton inside the WD were partly higher than those outside the WD.The Shannon-Wiener diversity index,Simpson’s diversity index,Pielou evenness index,and Margalef diversity index of the zooplankton did not reach significant differences between inside and outside the WD.Therefore,the zooplankton diversity index could not effectively evaluate the effect of WD.The envfit analysis showed that the environmental factors with good correlation with zooplankton community were chlorophyll a,chemical oxygen demand,water temperature,transparency,total phosphorus,electrical conductivity,and dissolved oxygen in turn inside the WD.Meanwhile,the environmental factors with good correlation with zooplankton community were were chemical oxygen demand,water temperature,chlorophyll a,total phosphorus,electrical conductivity,and total nitrogen in turn outside the WD.(4)Regarding the relationship between phytoplankton and zooplankton,Correlation analysis showed that both phytoplankton biomass and chlorophyll a had significant positive correlation with biomass of rotifers,copepods,and zooplankton inside the WD,respectively.Rotifera,copepoda,and zooplankton biomass all showed significant positive correlation with phytoplankton biomass,but any groups of zooplankton were significantly correlated with chlorophyll a outside the WD.The zooplankton/phytoplankton biomass ratio(zoop/phyto)inside the WD was a little higher than that outside the WD,indicating that the top-down effect inside the WD was slightly stronger than that outside the WD.Overall,however,total phosphorus and chlorophyll a showed significant positive correlation,and zooplankton biomass and phytoplankton biomass showed a significant positive correlation but not negative correlation both inside and outside the WD.Therefore,bottom-up effect was the main driver to control phytoplankton in the WD.In summary,the study showed that the WD could reduce the total nitrogen and total phosphorus,and total phosphorus was a vital factor affecting the plankton.Using macrophytes to reduce the total phosphorus loading,therefore,could be an effective way to regulate the plankton in the Baima Lake. |
