Resumo

QUIROZ-FLORES, Agustín; MIRANDA-ARCE, María Guadalupe  e  LOT-HELGUERAS, Antonio. Comparative study of some physicochemical variables of water at secondary channels of Xochimilco with and without Eichhornia crassipes (Martius) Solms-Laubach. Polibotánica [online]. 2008, n.25, pp.127-133. ISSN 1405-2768.

When aquatic vascular plants show excessive growth, they have the capacity to modify certain physical and chemical properties of the water bodies in which they become established, affecting the balance of the aquatic ecosystem. Eichhornia crassipes, water hyacinth, is regarded as a weed because of its capacity to adapt to various habitats. In the Xochimilco Lake zone (México, D.F.), where water hyacinth can completely obstruct secondary channels that surround the parcels, it is extracted mechanically on a permanent basis and used as green manure. These channels, locally called as "apantles," are very important to the peasants, because they give constant humidity to the soil. The aim of our study was to determine if there are significant differences in physico-chemical properties of the water between secondary channels due the presence of water hyacinth. Physical and chemical data obtained from water samples collected in these channels showed that the presence of water hyacinth significantly decreased hydrogen potential, subsurface temperature and dissolved oxygen levels, the latter causing oxidized chemical compounds to diminish, therefore decreasing nitrate levels and increasing ammonium levels. Dissolved reactive phosphorus, together with the rest of the parameters considered in this study, did not show any significant differences. Nevertheless, it is necessary to point out the high levels of dissolved reactive phosphorus quantified.

Palavras-chave : water hyacinth; Xochimilco; hydrophytes; nitrogen; phosphorus.