Influence of nitrogen species (NH4+ and NO3-) on the dynamics of P in water-sediment-Salvinia herzogii systems

Water - Salvinia herzogii - sediment systems were exposed to different phosphorus and nitrogen combinations in outdoor experiments. The aim was to estimate the amounts of P immobilized in macrophytes and sediments, as well as to elucidate whether or not the presence of N affects the retention of P. The following components were added: o-P, o-P + NH4+, o-P + NO3- + NH4+, o-P + NO3-. The concentration of nutrients was periodically determined throughout the experiment ( 28 days). The concentrations of P and N in plant tissues and sediments were determined at the beginning and the end of the experiment. Sequential extractions of P-fractions in sediment were performed using the EDTA method ( Golterman, 1996). The removal efficiency of P in water was 95-99%. The removal of NH4+ (97 - 98%) was more effective than that of NO3- (44 - 86%). The presence of nitrogen species increased the removal velocity of o-P from water, NH4+ was the most effective species. Sediments not only had higher P removal rates than macrophytes but, in the control treatment without macrophytes, they reached the values obtained by macrophytes plus sediments in the other treatments. The adsorption of P takes place at the surface layer of the sediment ( 1 cm). Most of the P incorporated into the sediment during the experiment was sorbed by the fraction Fe(OOH)approximate toP. The addition of nutrients to water modified the leaves/lacinias weight ratio.