Eutrophication as a homogenizer process of phytoplankton β-diversity in lowland streams

Phytoplankton diversity was assessed in subtropical lowland streams in two regions (Espinal and Islas) with different land uses to determine if eutrophication homogenized diversity. We sampled phytoplankton and took relevant information on several environmental variables across twelve streams in two sampling periods (April and November). We partitioned the β-diversity into its components (richness difference and turnover) to describe the diversity variation. Furthermore, we performed redundancy analyses and regression models to approach the relevance of environmental and spatial variables (geographical distance) on such variation. We identified low β-diversity values, and turnover was the dominant component of β-diversity for both regions. In the most eutrophic region (Espinal), eutrophication (inferred from total phosphorus concentration) appeared as a homogenizing process of total β-diversity while in the less eutrophic (Islas), variations in soluble reactive phosphorus among sites appeared as the main driver. The turnover component at both regions was regulated by other processes (e.g., biological oxygen demand and temperature). We conclude that eutrophication acts as a homogenizing process of phytoplankton β-diversity in lowland streams linked to agriculture (Espinal). Still, it is not the same on Islas, where other factors not revealed in this study could determine low β-diversity values.