Relationships among nitrogen and total phosphorus, algal biomass and zooplankton density in the central Amazonia lakes

Abstract

The relationship among concentrations of total nitrogen (TN), total phosphorus (TP), algal biomass (Chl) and the density and size of individuals of the zooplankton community were studied for the dry season (November 1999-January 2000) at 20 lakes of the Central Amazonia. The study was conducted along a productivity gradient to identify the existence of resource or predator-dependent patterns on the primary producers of the trophic web. A strong positive relationship was observed between the log Chl and TN (r 2 = 0.88, P = 0.000) and to log Chl and log TP (r2 = 0.85, P = 0.000) in a simple linear regression. However, when both variables were running together in a multiple regression, TN alone explained every variation of algal biomass (r2 = 0.89, PTN = 0.022, PTP = 0.233). The total density of the zooplankton showed a positive correlation with log Chl (r2 = 0.53, P = 0.000) and the large zooplankton (>0.5 mm) was found to be a more positive function of the phytoplankton (r2 = 0.65) than the density of the small ones (<0.5 mm, r2 = 0.44). Results show that complex food web interactions could be responsible for patterns in tropical systems. We contend that Chl variation in tropical lake systems is controlled by TN and TP, but the predictor power of the TN increase the fit of the model in analysis and can be use alone to access the variability in algae biomass to Amazonian tropical lakes. We also agree that the density of large zooplankton individuals is regulated by the biomass of primary producers. Hence we concluded that the resource-dependent hypothesis is supported in these systems. © 2007 Springer Science+Business Media B.V.