Effects Of Changes In The Aquatic Environment Under The Contribution Of Sediment Phosphorus Release On Interspecific Relationships Of Plankton

Xingkai Lake Basin（including Xingkai Lake and Xiaoxingkai Lake）is an important waterfowl breeding site,migration corridor,and biodiversity hotspot protection area in Northeast Asia.Still,eutrophication is becoming more severe yearly due to the effects of climate change and human activities,especially under the conditions of endogenous sediment release,which adversely affects the aquatic ecosystem.Planktons are important primary producers and consumers in lake ecosystems and are highly sensitive to changes in aquatic environmental conditions.Therefore,it is necessary to investigate the key environmental factors under the influence of endogenous release from sediment on plankton community structure and interspecific interactions.In this study,the plankton and water environment samples were collected,identified,and analyzed by combining the field in situ experimental phase method with the Russian-Chinese boundary lake,Xingkai Lake,as the research object.The characteristics of the plankton community structure in Xingkai Lake were studied.This study analyzed the driving effect of environmental factors on the plankton community under the influence of endogenous release from sediment.Finally,this study synthesized the correlation between environmental parameters and the planktonic interactions network to reveal the the key factors behind the changes in the interactions between primary producers and consumers.Specific findings are as follows:1.The structural characteristics of the plankton community have spatial and temporal distribution variability.A total of 134 species of phytoplankton from 7 phyla were identified in Xingkai Lake and Xiaoxingkai Lake,with 14 and 15 dominant species,respectively.NMDS analysis showed significant seasonal differences in the plankton community structure between the two lakes in different sampling months.The abundance and biomass of plankton were both highest in summer（July）.And the average f abundance and biomass were more elevated in Xingkai Lake than in Xiaoxingkai Lake.Both lakes’relative abundance of cyanobacterial species was dominant in July and September.The diatom phylum with higher individual weight and the green algae phylum with the highest species diversity had higher relative biomass in all sampling months in both lakes.The relative abundance of the zooplankton was the highest for rotifers and the lowest for cladocerans.The relative biomass of rotifers was significantly lower than that of copepods and cladocerans.Both lakes’Margalef species richness index,Pielou evenness index,and Shannon-Weinner diversity index of phytoplankton were the lowest in July when cyanobacterial blooms occurred.Meanwhile,diversity was generally lower in areas affected by agricultural pollution and fishing activities. 2.Water environmental factors had spatial and temporal distribution variability,and water temperature and nutrient salinity were the primary environmental indicators that significantly affected plankton.The main water quality parameters and nutrient concentrations in Xingkai Lake and Xiaoxingkai Lake were significantly different（P<0.05）between different sampling months and between Xingkai Lake and Xiaoxingkai Lake.RDA analysis showed that TP was the most important explanatory factor for the dominant plankton species in Xingkai Lake,and TN,TP,COD_Mn,p H and turbidity all had significant effects on the dominant plankton species in Xingkai Lake.The Pearson correlation analysis showed that the phytoplankton abundance and biomass were mainly positively correlated with water temperature and TP,and the biomass of metazooplankton was significantly correlated with water,TP and Chla.Mantel analysis showed that the correlation between plankton community composition and DO,water temperature,TDS,ORP,TN,TP,p H and Chla was highly significant.3.Sediments mostly play the role of phosphorus"source"and may promote phytoplankton growth by increasing the TP concentration in the water column.In this study,the release rate of SRP was greater than zero in both Xingkai Lake and Xiaoxingkai Lake,except for some sample points in December.That showed that the corresponding pollutants were released from the sediment to the overlying water,and the sediment played an obvious role as a source of pollution.The SRP release rate and SRP release flux per unit area were affected by TP,OM,Fe²⁺,soil particle size,soil volume,soil water content,and soil moisture content in the sediment.Both of them were significantly and positively correlated with TP and Chla,indicating that endogenous phosphate release may promote the growth and reproduction of phytoplankton by promoting nutrient content in the water column.4.The release of SRP may exacerbate the reduction of TP on the association network complexity of plankton in the Xiaoxingkai Lake.The plankton network in both Xingkai Lake and Xiaoxingkai Lake had a clear modular structure（MD>0.4）,with different modularity indices among different sampling months,and the relatively low connectivity in July（the cyanobacterial bloom period）indicated that the phytoplankton-metazooplankton interactions were weak.Overall,the interactions between zooplankton were dominated by positive and positive interactions,and the relationship between rotifers and phytoplankton was closer and more complex than that between cladocerans and copepods.In Xingkai Lake,TN had a significant effect on the interspecific relationships of plankton,while in Xiaoxingkai Lake,TP made the interspecific relationships of plankton less close,and the release of endogenous SRP might intensify this process.In summary,the spatial and temporal distribution of the plankton community structure in both Xingkai Lake and Xiaoxingkai Lake was different,with the highest plankton abundance and biomass in July,while the plankton diversity was generally lower in the areas that were more affected by human activities.This spatial and temporal variability in community structure was influenced by water environmental factors,especially water temperature and nutrient salinity.At the same time,the release of endogenous SRP from the sediment promoted the change of nutrient salinity in the water column and the reproduction of phytoplankton,which indirectly changed the interspecific interactions between plankton and the stability of the strong and weak biological connections of ecosystem species in Xiaoxingkai Lake.This paper deepens the understanding of the biological community structure of the lake ecosystem under different environmental conditions and the effect of the water environment conditions under the influence of endogenous release on the interspecific interactions between primary producers and consumers.Higher network complexity among plankton implies a higher network stability,which may further indicate a more stable ecosystem.Therefore,the interspecific association complexity indicators extracted from ecological interactions networks can represent network complexity and be used to assess the impact of environmental changes on aquatic ecosystems,which can be used as potential indicators for lake ecosystem health evaluation.Meanwhile,the nutrient input to Xingkai Lake can be regulated in lake management,while the attention to endogenous nutrient release from sediments should be increased.