丰水期东洞庭湖超微型浮游藻类时空分布特征及其影响因子

Temporal and Spatial Variation Patterns of Picophytoplankton and Their Correlations with Environmental Factors During the Wet Season in East Lake Dongting

超微型浮游藻类(<3μm)主要包括超微蓝藻(PCY)和超微真核藻(PPEs),是浮游生态系统的重要组成部分,在水体物质循环和能量流动中起着重要作用.为了解通江湖泊中超微藻动态变化特征及其关键影响因子,于2019年洞庭湖丰水期(5~8月)每月对东洞庭湖进行采样调查,研究了丰水期间东洞庭湖超微藻生物量和丰度的时空演变规律及其与环境因子的关系.结果表明,东洞庭湖丰水期超微藻生物量和丰度均表现出显著的时空演变规律(P<0.05).整个丰水期间,超微藻Chla平均浓度为8.52μg·L^-1,其对总浮游藻类Chla的贡献率平均为41.6%;从5~8月,随着水温的增加,超微藻Chla浓度不断增加,尤其是东洞庭湖北部湖区和南部湖区;东部行洪道超微藻Chla浓度全湖最低.PCY是东洞庭湖超微藻的主要优势藻,其丰度平均是PPEs的3.4倍.PCY和PPEs丰度表现出相似的时空分布规律:时间上,从5~8月均呈现先增加后降低的趋势;空间上,随着丰水期的推移,超微藻丰度峰值由北部湖区向南部湖区迁移,到8月丰水期末期超微藻丰度逐渐降低,北部湖区超微藻丰度最高.分析结果表明,丰水期超微藻表现出了显著的时空分布规律,水位和N∶P比是影响东洞庭湖PCY和PPEs丰度组成比例变化最重要的因子.

Picophytoplankton(<3μm),comprising picocyanobacteria(PCY)and photosynthetic picoeukaryotes(PPEs),are considerably important in the material circulation and energy flow of aquatic ecosystems.To explore the temporal and spatial variation patterns of picophytoplankton and their correlations with environmental factors in lotic Yangtze-connected lakes,field in-situ investigations were performed on a monthly basis during the wet season(May to August)in 2019 in East Lake Dongting,a Yangtze-connected lake.The results indicated that both the Chla biomass and abundances of picophytoplankton exhibited significant spatial and temporal variability(P<0.05).The picophytoplankton Chla biomass showed an average concentration of 8.52μg·L^-1 and accounted for 41.6%to total phytoplankton on an average.From May to August,Chla biomass of picophytoplankton kept increasing with increasing temperature,especially in the north and south of the lake,and it was the lowest in the east of the lake.PCY dominated picophytoplankton abundance in East Lake Dongting and was 3.4 times the abundance of PPEs on an average.Similar spatial and temporal variation patterns were observed between PCY and PPEs.The abundances of PCY and PPEs both increased first and then decreased during the wet season.Spatially,picophytoplankton showed a trend to migrate from the northern lake to the southern lake from May to July,and the abundance significantly declined in August and peaked mainly in the north of the lake.The analysis results showed that picophytoplankton in East Lake Dongting exhibited significant spatial and temporal variability during the wet season;the water level and N∶P ratio were determined to be the most important factors explaining the variation of the abundance proportion of PCY and PPEs.