Fluctuaciones anuales en la composición fitocenótica y biomasa de la hidrofitia en lagunas isleñas del Paraná medio

Resumen

The present paper deais with the seasonal changes of the aquatic vegetation in two shallow lentic water bodies belonging to the flood plain of the middle Paraná River, located nearly Santa Fe city (Rep. Argentina), throughout and annual cyde.
Distribution, structure and variations of the community were studied by longitudinal and cross sections according to the mean morphological pond featurés. The observations and sampling were performed bimonthly complemented by aditional fleld operations related to the vegetation development. The population dinamic was studied by the analysis of hieght, cover, biomass, frequence, abundance and density in each section.
The normal vegetation growth period reaches its máximum at the end of the summer. Another particular and even more important growing period was registered in some rooted species during the flood because of the rapid raise of water level. The higher standing crop was obtained during the summertime with 3,11 tm/ha (dry weight) and 12,7 tm/ha (fresh weight) in the “La Guardia” pond, and 2,09 tm/ha (dry weight) and 22,2 tm/ha (fresh weight) in the “Don Felipe” ox-bow. The smaller standing crop was registered after the flood, when the raise of water overeante the growing capacity of the rooted vegetation an the floating plants were washed to the shore and downstream.
Therefore, the more important changes in the aquatic vegetation of these ponds were related to the climate cyde and to the Paraná rivers hydrological regime, with their variable influence in the water level of these ponds.