Effects of water level, abiotic and biotic factors on bacterioplankton abundance in lagoons of a tropical floodplain (Paraná River, Brazil)

The purpose of this paper was to assess the influence of basic limnological variables on bacterioplankton abundance in twenty lagoons in the Upper Paraná River floodplain, Brazil. Twelve abiotic (depth, total nitrogen, total phosphorus, dissolved organic carbon (DOC), water transparency, temperature, dissolved oxygen, alkalinity, pH, turbidity, electrical conductivity and total inorganic carbon), and two biotic (chlorophyll-a and rotifers abundance) limnological factors were used as independent variables to explain bacterial countings. Principal component analysis (PCA) was used to reduce the dimensionality of the abiotic data and chlorophyll-a. Subsequently, multiple regression analysis was used to examine the relationship between bacterial abundance and the principal component axes and rotifer densities. Bacterioplankton abundance fluctuated from 1.8 to 5.9 × 106 cells.ml−1 during the high water phase and from 1.4 to 4.0 × 106 cells.ml−1 during the low water phase and they were significantly higher during the former phase (t=3.06; p=0.007). Bacterial abundance was not significantly correlated with chlorophyll-a and rotifers abundance. On the other hand, it was positively correlated with principal components 1 and 2, indicating that DOC, total nitrogen and phosphorus concentration, temperature and pH are important to explain bacteria abundance. These results indicate that the input of different sources of DOC and inorganic nutrients from the floodplain into the lagoons during the high water phase is more important to explain bacterial abundance than autochthonous phytoplanktonic organic matter or predation by rotifers.