Environmental Engineering Reference
In-Depth Information
communities. However, Dorigo et al. (
2002
) and Pesce et al. (
2008
) urged caution in
interpreting these results, because of the complexity in distinguishing between effects
of pollutants vs
.
other environmental variables. Morin et al. (
2009
) have also recently
stressed the dificulties in accurately linking diatom community structure to pesticide
inputs in lotic environments. However, Ricart et al. (
2010
) revealed a potential
relationship between triazine-type herbicides and diatom community distribution in a
contaminated river (Llobregat river, Spain). Their study also showed that the metrics
most sensitive to the presence of pesticides were chl
a
and photosynthetic activity.
A series of in situ studies have recently been conducted in a small river that
drains a vineyard watershed (Morcille River, France; Montuelle et al.
2010
). Various
surveys revealed that bioilm phototrophic community composition varied from
upstream to downstream locations, in parallel with increased nutrient and pesticide
concentrations. Changes in phototrophic community composition along this river
have been recorded using several end points: pigment distribution, eukaryotic gene
structure, and diatom taxonomic composition (Dorigo et al.
2007, 2009, 2010a, b
;
Morin et al.
2010
; Pesce et al.
2010a, b
).
3.2
PICT Approaches
Among the various methods and tools available to evaluate microbial community
responses to toxicant exposure, the PICT approach makes it possible to partially
isolate the effects of individual toxicants within an ecosystem that is subjected to
multiple stressors, by studying shifts in community sensitivity (Schmitt-Jansen
et al.
2008
). In the river Morcille, PICT was, therefore, applied to verify that
structural changes in phototrophic communities were related to pesticide contami-
nation. In all surveys, all bioilms exhibited an upstream-to-downstream increase in
tolerance to diuron, which is the most often detected herbicide in this river (Dorigo
et al.
2007, 2009, 2010a, b
; Pesce et al.
2010a, b
). Pesce et al. (
2010a
) identiied
three possible inluences that constituted covarying environmental variables
(i.e., nitrates, conductivity, and temperature) in the tolerance induction. However,
statistical analysis demonstrated that the main factor affecting diuron sensitivity
was the mean in situ diuron exposure level during the bioilm colonization periods.
Nevertheless, ield studies conducted by Guasch et al. (
1998a
, b, 2003) in various
European streams and rivers clearly indicated that the sensitivity of phototrophic
bioilms to organic herbicides in lotic systems may be highly dependent on light
conditions during colonization. Indeed, they observed higher atrazine toxicity to
natural bioilms that were adapted to high-light conditions, and were dominated by
green algae or cyanobacteria, than that to diatom-dominated bioilms adapted to
low-light conditions.
Dorigo et al. (
2004
) assessed seasonal changes in the sensitivity of river microal-
gae to atrazine and isoproturon along a contamination gradient, and showed that
both free and ixed algal communities responded positively to the PICT approach.
The positive response occurred despite the fact that free algae are mobile and can
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