Role of submerged macrophytes in sediment phosphorus stabilization in shallow lakes from the Brazilian semiarid region

Abstract

ABSTRACT Allochthonous or autochthonous disturbances may change waterbodies from a clear to a turbid state, increasing the availability of nutrients and promoting blooms of harmful cyanobacteria. Submerged macrophytes may play an important role in alleviating the adverse effects of phosphorus resuspension and release from bottom sediments. We assessed the effects of allochthonous disturbances (rainfall and wind) on phosphorus release by constructing models using data from 2 shallow lakes with contrasting steady states. Using partial least squares path modeling, we examined submerged macrophytes, phytoplankton, and possible drivers of their abundance. In the clear-water lake, the concentrations of total phosphorus (TP) had the greatest direct influence on the macrophyte percentage of volume infested and phytoplankton biomass, followed by concentrations of TP in the sediment. In the turbid lake, the TP concentration in the water was the most important factor affecting phytoplankton biomass directly, followed by disturbances on TP concentration in the sediment and euphotic zone. Our models support the hypothesis that submerged macrophyte coverage acts as a stabilizing force to prevent the proliferation of cyanobacteria and stabilize the clear-water phase in semiarid lakes. However, potential mutual inhibition mechanisms between the submerged macrophyte Nitella cernua and the cyanobacterium Microcystis aeruginosa need to be better addressed for restoration purposes in lakes with shallow clear waters.