Land use types, basin characteristics and water quality together shape riverine phytoplankton community composition...

Exploring the combined effects of basin characteristics, land use types, and human activities on phytoplankton biomass, community composition and diversity is important for developing effective river protection strategies. In the present study, 182 phytoplankton samples were collected in the Hanjian and Danjiang River basins and the explanation rate of the above factors was analyzed. Water quality was the primary factor affecting riverine phytoplankton biomass, with an explanation rate to Chl a reaching 59.8%. Water quality was also the primary factor affecting phytoplankton diversity but the contribution of land use types and basin characteristics was also high. In addition to affecting phytoplankton communities and diversity by affecting water quality, diverse land use can increase the taxa of algae discharged through soil erosion processes. Elevation and slope were the main basin characteristics regulating phytoplankton community and diversity because they can determine the retention time of phytoplankton in rivers. The results also showed that land use types were the primary factor affecting the critical relative abundance of extinction (a), competition coefficient (k), environmental taxa capacity (N), but water quality was the primary factor affecting Shannon index, Simpson index, and Pielou index. This difference indicated that index a, k, and N could reflect specific characteristics of phytoplankton diversity that were not reflected by the latter indices. Our results implied that land use types and basin characteristics affected the discharge of exotic algal taxa, retention time, and other factors, thereby influencing the composition and diversity of riverine phytoplankton communities.