18S rRNA gene sequencing reveals significant influence of anthropogenic effects on microeukaryote diversity and composition along a river-to-estuary gradient ecosystem

Abstract

Microeukaryotes play key roles in the structure and functioning of lotic ecosystems; however, little is known about the relative importance of the processes that drive planktonic microeukaryotic biogeography in rivers, especially the effects of anthropogenic inputs (e.g., wastewater discharge and pesticide and fertilizer use) on the taxonomic and functional diversity of microeukaryotes. Herein 18S ribosomal RNA sequencing was used to examine the assembly of microeukaryotes in samples from Xiaoqing River, a mid-sized river in north China that runs through urban and agricultural areas and then discharges into the Bohai Sea. We found that diversity of microeukaryote declined obviously due to the excessive disturbance of the urban and agricultural activities in the midstream of the river. Our results support the concept that species sorting caused by local pollution can largely determine microeukaryotic community structure when significant environmental gradients exist in polluted running-water ecosystems and that compositional dissimilarity increased with increases in the Euclidean distance of environmental variables. Variation of microeukaryotic diversity was mainly determined by changes in levels of nutrients, dissolved oxygen, turbidity, and salinity and they can affect the rare subcommunities significantly. Furthermore, zooplankton were dominated in rare taxa, meanwhile phytoplankton was composed by the abundant taxa mainly. These findings confirmed the dynamic character of riverine ecosystems and the significance of human activities in shaping microeukaryote diversity in rivers.