Phototrophic biofilm activity and dynamics of diurnal Cd cycling in a freshwater stream.
Diel cycles of dissolved cationic metal concentrations commonly occur in freshwater streams in apparent response to coincident cycles in water quality parameters (pH, O2, temperature). Hourly sampling of the Cd-contaminated Riou Mort (France) revealed large diel cycles in "total" dissolved Cd (232-357 nM; < 0.45 microm) and "truly" dissolved Cd (56-297 nM; < 0.02 microm) which were strongly correlated with changes in water pH. Using measured fluxes, a dissolved O2 model was constructed that indicated that benthic metabolic activities, respiration and photosynthesis, were responsible for the diel O2 (and thus, CO2 and pH) variation in the stream. However, microsensor measurements also showed that the pH changes occurred at the biofilm interface earlier than in the bulk water column. This difference in timing was reflected in the Cd dynamics, where pH-controlled sorption effects caused Cd partitioning from the truly dissolved pool onto the biofilm in the morning, and from the truly dissolved pool onto large colloids (0.02-0.45 microm) later in the day. Because this process causes large changes in the bioavailable Cd fraction, it has significant implications for Cd toxicity in freshwater streams. This study demonstrates the profound control of benthic microbiological processes on the cycling of heavy metals in aquatic systems.
Beck
Aaron J
AJ
Microsensor Group, Max Planck Institute for Marine Microbiology, Celsiusstrasse 1, D-28359 Bremen, Germany. abeck@mpi-bremen.de
Janssen
Felix
F
Polerecky
Lubos
L
Herlory
Olivier
O
De Beer
Dirk
D
D018441:Biofilms; D002104:Cadmium / Q000737:chemistry* / Q000378:metabolism*; D002940:Circadian Rhythm; D004784:Environmental Monitoring; D005618:Fresh Water / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008027:Light; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000737:chemistry / Q000378:metabolism
D014874:Water Pollutants, Chemical; D002104:Cadmium; D010100:Oxygen