Effects of chronic copper exposure on fluvial systems: Linking structural and physiological changes of fluvial biofilms with the in-stream copper retention
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Abstract
Long-term metal exposure is known to be responsible for a large variety of structural
and functional changes in periphyton communities which allow these communities to
adapt to metal-polluted conditions. This study aimed to link the changes that chronic
copper (Cu) exposure causes on the structure and physiology of fluvial biofilms with
the efficiency of the river systems in retaining phosphate and Cu. The effects of
a chronic Cu exposure on the structure, physiology and induction of Cu tolerance of
the community were evaluated by comparing this community with a non-exposed one. Results
showed that periphyton chronically exposed to Cu had lower algal biomass, higher proportion
of green algae, lower proportion of brown algae, and higher EPS content per unit of
biomass than the un-exposed community. In addition, the chronically-exposed community
showed a Cu content (both total and intracellular Cu content) ten times higher than
the un-exposed community. While in-stream phosphate retention was not markedly influenced
by chronic Cu exposure; Cu retention was clearly reduced, as was shown by a reduction
in Cu retention efficiency (Cu-S(w)) and demand (Cu-Vf). The chronically-exposed periphyton,
in spite of having high intracellular Cu concentration, showed similar photosynthetic
efficiency than the un-exposed community and showed a higher Cu tolerance. It indicated
that this community was acclimatized to Cu exposure and that this acclimatization
was probably linked to the ability to detoxify and immobilize metals. These observations
suggest that the fate of Cu in fluvial ecosystems will be influenced by the exposure
history of the system. The results from this study indicate that metals will travel
longer distances in metal-polluted streams compared to pristine systems having effects
on water quality farther downstream.