Productivity–diversity relationships in reservoir phytoplankton communities in the semi-arid region of northeastern Brazil

• We analyze the PDR of phytoplankton in local and regional scale.
• We tested concentrations of nutrients and algal biomass as descriptors of diversity.
• Eutrophication affects the scale dependence of the PDR.
• The PDR is locally affected by environmental conditions of the semi-arid.

The aims of study were to 1) evaluate the productivity–diversity relationships (PDR) in reservoir phytoplankton communities in the semi-arid of northeastern Brazil on the local and regional scales; 2) determine the association between regional dissimilarity in species composition and regional mean productivity; 3) test the potential of productivity as well as physical and chemical factors of the water as descriptors of phytoplankton diversity using generalized linear models. Nutrient availability (total nitrogen and total phosphorus) and phytoplankton biomass were used as measures of productivity, whereas species richness as measure of diversity. Unimodal PDR was found when total phosphorus and biomass were considered as measure of productivity. Regional dissimilarity diminished with regional mean productivity. This finding may be attributed to the effect of eutrophication on diminishing the differences in the composition of species between compartments within each reservoir, leading to a loss of diversity in these ecosystems. Moreover, the analysis of the models demonstrated evidence that PDR may be influenced by environmental factors, such as electrical conductivity, total dissolved solids and pH in reservoirs located in semiarid regions of northeastern Brazil.