Environmental Engineering Reference
In-Depth Information
luazinam) at 0.2, 1, and 5% of the respective recommended application rates.
Most effects were observed at the 5% treatment level, which resulted in short-term
changes to pH and oxygen levels; phytoplankton responded in a manner that was
consistent with expected compound-speciic results. These study results showed
that the successive impact of repeated treatments by the various pesticides did not
produce extensive harm, since most substances dissipated rapidly, avoiding simul-
taneous exposure for most combinations. In a similar experiment, van Wijngaarden
et al. (
2004
) mimicked an application scenario in tulip-cultivation practice. They
made successive treatments of the fungicide luazinam, the insecticide lambda-
cyhalothrin and the herbicides asulam and metamitron to indoor microcosms at
estimated spray-drift concentrations varying from 0.2 to 5% of recommended label
rates. The 0.5% treatment regime resulted in short-term effects, whereas the 2 and
5% treatment levels triggered marked effects. Although effects were detected at
the ecosystem level, the two highest herbicide application levels had only minimal
effects on phytoplankton and periphyton. Phytoplankton biomass increased from
indirect effects; these effects resulted from the decrease of the macrophyte
E. nut-
tallii
after asulam application (decreased competition for nutrients), and from the
decrease of zooplankton after lambda-cyhalothrin application (reduced grazing
pressure). Treatments had no direct or indirect effects on the abundance of per-
iphyton. Nevertheless, using the same pesticide application procedure, Wendt-
Rasch et al. (
2004
) showed that the inal effect of pesticide exposure was greatly
inluenced by the structure of the ecosystems. In mesotrophic microcosms, domi-
nated by submerged macrophytes, periphyton biomass increased and species com-
position varied at the 0.5% treatment level and higher. However, there was no
effect on these two parameters in eutrophic microcosms, characterized by a high
Lemna
surface coverage.
3
Field Studies
3.1
Effect of In Situ Exposure on Community Structure
and Primary Production
Lotic ecosystems, especially in agricultural areas, are often highly exposed to herbi-
cide pollution. A common way to assess the resulting effects on aquatic communities
is to compare biological parameters at different sampling sites that received different
herbicide levels (ideally including a clean reference point). This strategy was success-
fully used by Dorigo et al. (
2002
) to measure changes to phytobenthic community
species composition in river sections, mainly contaminated by atrazine and isopro-
turon. Using partial 18S rRNA cloning and sequencing, they showed that the propor-
tion of diatoms was lower at the unpolluted site than at polluted ones. In an agricultural
area, Pesce et al. (
2008
) observed a sharp drop in free algal biomass during the main
pollution period, which suggested a strong herbicide impact on phototrophic
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