Environmental Engineering Reference
In-Depth Information
qualitative and quantitative ecological status of all surface waters, and there is now
growing interest in studying recovery trajectories. Ecosystem recovery is deined
as the potential for a disturbed ecosystem to return to a state similar to that before
a stress was imposed on it, which basically revolves around the notion of ecosys-
tem and community resilience. Despite the importance of studying and under-
standing the resilience processes employed by autotrophic microbial communities
following pesticide exposure, even basic knowledge on these processes remains
scarce (e.g., Morin et al.
2010
; Dorigo et al.
2010a, b
; Rotter et al.
2011
).
5
Summary
Over the past 15 years, signiicant research efforts have been channeled into assess-
ing the effects of organic herbicides on freshwater phototrophic microbial commu-
nities. The results of this research are reviewed herein. The main conclusions we
have reached after performing this review can be summarized into ive points:
•
Most relevant assessments have dealt with the effects of triazine and phenylurea
herbicides. Herbicides from these chemical classes are often considered to be
model compounds when photosystem-II inhibitors are studied.
Until the early 2000s, the vast majority of investigations conducted to evaluate
•
herbicide effects on phototropic microbes were performed in microcosms or
mesocosms. In such studies, herbicides were usually applied alone, and often at
concentrations much higher than those detected in the environment. More
recently, the trend has been toward more realistic and relevant studies, in which
lower herbicide concentrations were considered, and compound mixtures or suc-
cessive treatments were tested. Increasingly, in situ studies are being designed to
directly evaluate microbial community responses, following chemical exposures
in contaminated aquatic environments.
Several biological end points are used to evaluate how organisms in the pho-
•
totrophic microbial community respond to herbicide exposure. These end points
allow the detection of quantitative changes, such as chl
a
concentrations, total
cell counts or periphytic biomass, qualitative changes such as community struc-
ture to algal diversity, or functional changes such as photosynthesis and respira-
tion, among others. They may give different and complementary information
concerning the responses of microbial communities.
PICT approaches, which have generally combined functional and structural mea-
•
surements, may prove to be valuable for assessing both an immediate impact, and
for factoring in the contamination history of an ecosystem at the community level.
Finally, any relevant assessment of pesticide effects should incorporate a detailed
•
environmental characterization that would include abiotic parameters (light, low
speed, nutrient content), or biotic parameters (diversity and structure of bioilms),
because these control the bioavailability of pesticides, and thereby the exposure
of microbial communities.
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