Threshold responses of phytoplankton species and morphofunctional groups to multiple environmental gradients in an Amazon floodplain lake

Abstract

Determining ecological thresholds for natural communities has implications for biodiversity conservation and for identifying reference conditions. Among aquatic communities’ phytoplankton is an important indicator of environmental changes and is highly susceptible to physical, chemical, and biological variations in aquatic ecosystems. This study shows multiple ecological thresholds of the phytoplankton community associated with rainfall, turbidity, water temperature, pH, particulate organic carbon, and total nitrogen, which were key factors influencing the phytoplankton community throughout the hydrological year in Lago Grande do Curuai. Among the six gradients evaluated, five (turbidity, temperature, pH, total nitrogen, and precipitation) influenced the distribution and biovolume of phytoplankton. This influence was associated with multiple points of change in the phytoplankton community along these gradients, phytoplankton species and morphofunctional groups (MBFG). The structure of the phytoplankton community in this system showed great variation throughout the year, as multiple ecological thresholds of the community were detected, which are associated with variations in habitat conditions. The MBFG ecological classification indicated a certain degree of loss of responses, potentially due to the weaker signal and lower amplitude threshold response. In conclusion, both classification methods have the potential to be effective biomonitoring and ecological management tools for this environment.