Decomposition rate of plant material in the Parana Medio River (Argentina)

The degradation of plant material in the centre of two plain streams (the Parana Medio River main channel – 0.6 m.s^–1 - and the Colorado River – 0.03 m.s.^–1) was studied in order to obtain a degradation coefficient for the species Panicum prionitis, Paspalum repens and Eichhornia crassipes, representative of the vegetation of the area of the future man-made lake of the Parana Medio, Dam. The experimental sites were chosen at the limit (minimum and maximum) velocities of the two streams in the valley to be flooded.The plant samples (submerged at different depths) were periodically analysed during 80 days, the experimental data being fitted to an exponential decomposition model. Degradation coefficients ranged from 0.0357 to 0.0682 day^–1 (P. prionitis); from 0.0182 to 0.0643 day^–1 (P. repens) and from 0.0120 to 0.0425 day^–1 (E. crassipes). The incidence of leaching and fragmentation on the decomposition of plant materials was also studied.