Studies On Changes Of Ecosystem Services And Phytoplankton Diversity In Typical Lake Wetlands In Shandong Province

Human exploitation and conversion of the ecosystems have caused problems such as biodiversity loss and ecosystem services degeneration,which leads to the reduction of ecosystem services for human well-being.International initiatives to address these impacts,including "Convention on Biological Diversity" and "Millennium Development Goals",which were launched by the United Nations Environment Program.China has also issued various wetland protection and restoration policies,including the "National Wetland Protection",the "Returning Farmland to Wetland",the pilot project of wetland ecological compensation,the "Ecological Red Line".In order to explore the effects of ecological restoration on lake wetlands,this study selected two typical ecological restoration lakes in Shandong Province,discussed the changes of ecosystem service value and the tradeoff between ecosystem services during the ecosystem restoration process,which provided experience and suggestions for subsequent lake restoration.In addition,as important primary productivity in the lake ecosystem,phytoplankton directly affects the geochemical cycle;phytoplankton has the ability to respond quickly to environmental changes,such as changes in water quality and hydrodynamic conditions.During the restoration of the lake wetland ecosystem,changes in the ecosystem environment directly affect the phytoplankton community and further affect changes in zooplankton and fish through phytoplankton,thereby affecting the ecosystem biodiversity and services functions.Therefore,this study further explored the responses of phytoplankton biodiversity to environmental changes during ecosystem restoration,and also analyzed the dynamic changes of phytoplankton communities and their biodiversity,which could provide theoretical support for lake health management and algae blooms prevention.Nansi Lake and Mata Lake are typical freshwater lakes in Shandong Province,which have been included in the national lake ecological environment protection pilot.Both Mata Lake and Nansi Lake have undergone the process of ecological degradation,restoration and water quality improvement.However,they have their own unique restoration characteristics.Mata Lake had obvious land use changes,while Nansi Lake had water quality improvement and had better phytoplankton biodiversity.This study profiled different emphases on different lakes based on preliminary investigations.Changes of land use and ecosystem services value and relationships between ecosystem services were mainly studied in Mata Lake,while research on Nansi Lake focused on the impact of its environmental changes,especially the improvement of water quality and the water supply of the South-to-North Water Transfer Project,on the phytoplankton community and biodiversity.Based on the land cover changes of Mata Lake and Nansi Lake in the process of lake degradation and restoration,this study assessed the changes and tradeoffs between ecosystem services.Results suggested that land cover change fluctuated frequently in Mata Lake from 1984 to 2015,especially water and lakeside wetland.The value of ecosystem services showed a trend of first decreasing and then increasing.The land use changes of Nansi Lake mainly occurred among farmland,forest,open water,and wetlands,while the ecosystem services value increased first and then decreased from 2001 to 2017.The results of Mata Lake suggested that the restoration process of ecosystem service value was slower than that of land cover change,which indicated a time lag between land use change and ecosystem service value change.The tradeoffs in ecosystem services were mainly between provisioning and regulating services.The biodiversity conservation was significantly related to other ecosystem services,indicating the necessity of considering its protection and the evaluation during restoration from an overall perspective.There is a tradeoff relationship between different ecosystem services.The increase in food production by improving food production service function would eventually damage other service functions.Long-term changes in land use to obtain food or raw materials might result in a decrease in total ecosystem service value.Hence,more attention should be paid to changes in biodiversity and total ecosystem services value.In order to further study the changes in biodiversity in wetland restoration,phytoplankton in Nansi Lake was collected and analyzed.There were 153 species of phytoplankton(including variants)in 78 genera and 8 phyla in Nansi Lake during the investigation.The results showed that phytoplankton diversity in Nansi Lake followed annual cycles,which were interrupted by a water diversion in 2013.The disruption of equilibrium was clearly demonstrated by the decrease of Shannon-Wiener' s diversity index,Pielou's evenness index,and Simpson's dominance index.The dominant species were Synedra acus Kutz(Bacillariophyta),Closterium gracile Breb(Chlorophyta),and Scenedesmus quadricauda Breb(Chlorophyta)in summer and autumn.It was also found that the phytoplankton was most widely distributed in summer when conditions were more conducive to phytoplankton growth and reproduction.Redundancy analysis(RDA)indicated that the main drivers for the phytoplankton community varied in different taxonomic units.Generally,total phosphorus,the ratio of nitrogen to phosphorus,and the permanganate index(CODMn)influenced the total phytoplankton community.Specifically,the NP ratio and permanganate index(CODMn)had significant effects on Chlorophyta,whereas pH,dissolved oxygen(DO),and transparency significantly influenced Bacillariophyta.The NP ratio was significantly negatively correlated with the density of algae in Chlorophyta and Cyanophyta phylum,while the CODMn had different effects on different taxa of algae in Cyanophyta and Chlorophyta phylum.In addition,total nitrogen also had a significant negative impact on most cyanobacteria.Dissolved oxygen and pH are negatively correlated with the density of most diatoms,while transparency has different effects on different types of diatoms.The density of most algae in Xanthophyta and Euglenophyta were negatively influenced by pH.Determining the diverse responses of phytoplankton in different taxa to environmental variables can theoretically help predict algae blooms and specifically monitor the health of the aquatic ecosystem.The spring and summer when algae blooms are more likely to occur were selected to study the seasonal phytoplankton dynamics and analyze the seasonal prediction of diversity indices.The results showed the phytoplankton abundance increased more significantly than other indices from spring to summer.The dominant species of phytoplankton decreased in summer,indicating stronger competition among species in summer than in spring.The correlation analysis showed Shannon-Wiener's diversity in spring positively correlated with summer richness,and uncorrelated with summer abundance,Although the ability of Shannon-Wiener's and Simpson's diversity to predict the phytoplankton community structure decreased in summer,the two could be combined with dominance as predictive factors.Through the calculation of targeted species dominance and community diversity,the possibility of harmful algal blooms can be analyzed.Further,specific management of water quality can be adopted to regulate phytoplankton communities and to prevent harmful algal blooms.The insignificant relation between species richness and evenness was also detected,indicating that these two indices were independent in relation to diversity measurement.It was found that Shannon-Wiener's diversity had a stronger correlation with other indices across seasons than Simpson's diversity,suggesting that Shannon-Wiener's diversity was a better predictor of seasonal dynamics for phytoplankton than Simpson's diversity.In conclusion,through the research on the ecosystem service value and tradeoff relationships between different ecosystem services,the increase in food production by improving food production service function will eventually damage other service functions.Therefore,more attention should be paid to changes in biodiversity and total ecosystem services value.Based on the diverse response mechanisms in different taxa of phytoplankton to environmental factors,classified management on algae can be focused on managing lake water quality and monitor water quality changes.The seasonal prediction between phytoplankton diversity indices noticed that more attention should be paid to monitoring the phytoplankton biodiversity.To combine the diversity index(Shannon-Wiener's diversity and Simpson's diversity)and the dominance of related species that may cause harmful algal blooms,environmental factors such as water quality can be adjusted in advance to reduce the possibility of harmful algal blooms.In this way,the balance and health of the lake ecosystem can be maintained.This research helps understand the ecological functions and phytoplankton changes in lake restoration and is of great significance to the scientific management of lake ecosystems.