Driving factors of the phytoplankton functional groups (RFG) in subtropical reservoir (SP, Brazil)

Resumen

Subtropical reservoirs are susceptible to the eutrophication process, largely due to their watershed's irregular uses and occupations. Changes in the composition of the phytoplankton community occur according to the sensitivity and environmental tolerances of the species. According to Functional Reynolds Groups (RFGs), phytoplankton is an excellent model of a multispecies system to answer ecological questions at different scales in space and time. The Itupararanga reservoir is located in the upper Sorocaba river basin, (Sorocaba, SP, Brazil). It is used to supply drinking water to approximately one million people and for agricultural and recreational purposes. The objective of this research was to analyze the relationship between environmental variables and the composition of the phytoplankton community, identifying the main functional groups (RFGs), in a spatial gradient (longitudinal) in the reservoir, during a period of one year. Five samplings were carried out at seven points in the reservoir, in the rainy and dry seasons (2016 to 2017). The effects of spatial heterogeneity influenced the formation of different biomass gradients for each functional group. The most abundant RFGs were Sn, H1 and Lo, which responded to the spatial heterogeneity of the reservoir. Thus, in the direction from the upstream sampling point (P1) to the point on the dam (P7), the biomass gradient was increasing for the Sn codon, while for H1 it was decreasing. The factors that most influenced the phytoplankton composition of the reservoir were total nitrogen, nitrite and the N/P ratio, with phosphorus being the limiting nutrient. This research showed the effectiveness of using RFGs as environmental descriptors, being an important tool in studies in a subtropical reservoir.