Effect on the planktonic community of the chemical program used to control water hyacinth (Eichhornia crassipes) in Guadalupe Dam, Mexico

Abstract

Guadalupe Dam is a reservoir located into the Metropolitan area of Mexico City, which had been infested with water hyacinth (Eichhornia crassipes) for more than 12 years. In 1993 a management program was conducted in the reservoir. The main activities included the use of aquatic herbicides and mechanical control. The goal of this study was to monitor the composition and fluctuation of the planktonic community during the chemical control program. Five sampling stations were selected. Six samplings were made during the period of herbicides applications (July to November 1993) and one sampling more, used as control, was performed four months after the last application (March 1994). Herbicides diquat and 2,4-D amine were used in the chemical control program. Variables measured included temperature, dissolved oxygen, pH, chlorophyll a and numbers of phytoplankton, ciliates, rotifers, cladocerans and copepods. The reservoir is eutrophic, with high concentrations of chlorophyll a and low values of Secchi disc depth. Thermally, the dam seems to be warm monomictic. The infestation of aquatic weeds at the beginning of the program reached 95% of surface area. Two main effects of the herbicide application were observed. The first was the direct toxic effect of the chemicals on the growth and density of phytoplanktonic species, which lead to a reduction in zooplankton density related to food shortage. The second effect was indirect caused by the decomposing hyacinths which depleted dissolved oxygen concentrations. The oxygen deficit greatly affected the biological community. Although the chemical control program of Guadalupe Dam water hyacinth had a notable effect on the planktonic community, it recovered promptly. After the weed control program, the Guadalupe dam remained eutrophic. Although water hyacinth was eliminated, it was replaced by a large phytoplankton bloom.

Effect of mechanical removal of water hyacinth (Eichhornia crassipes) on the water quality and biological communities in a Mexican reservoir

“…However, there were no significant thermal differences between the two cyles studied. Similar thermal conditions were found by Lugo et al (1998) in the Guadalupe reservoir. Measurements of pH ( Figure 2B) showed a tendency from neutrality to acidic readings.…”

“…After hyacinth removal values were more variable but no significant differences were found in both periods of sampling (see Figure 3J). Lugo et al (1998) found a slight increase of pH after water hyacinth removal, probably due to algal blooms.…”

“…According to their data, in three Mexican dams no noticeable effects were found in the benthos and plankton communities after weed control measures were taken. Lugo et al (1998) studied changes after use of diquat and 2.4-D amine in a reservoir of Mexico City to eliminate the water hyacinth Eichhornia crassipes. The main effect was a decline of all planktonic communities and dissolved oxygen levels, as a secondary effect of the decomposing residual biomass from the weeds.…”

Cladocers, Copepods and Rotifers in rice-fish culture handled with metsulfuron-methyl and azimsulfuron herbicides and carbofuran insecticide

“…Evidences indicate that natural stressors can modify the sensitivity of the zooplankton community exposed to agrochemicals, so that these organisms are more sensitive to agrochemicals at natural environments than if they are cultivated at controlled conditions in laboratory (LUGO et al, 1998). This could take place because at the natural environment the organisms are exposed to mixtures of chemical compounds, which when combined can cause behavioral, physiological and biochemical changes, death or other adverse effects (HERBRANDSON et al, 2003).…”

Efeitos do manejo de Eichhornia crassipes sobre a qualidade da água em condições de mesocosmos

“…Lugo et al (1998) comprovaram que, na prática, os efeitos deletérios do controle do aguapé no zooplâncton ocorreram em virtude da redução na concentração de oxigênio dissolvido, provocada pela morte da planta, e não diretamente pelos herbicidas diquat e 2,4-D, utilizados na aplicação.…”