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Sediment-water interface nitrogen transformations in Missisquoi Bay, Lake Champlain (Québec): potential impacts on cyanobacteria community structure

Mark J. Mccarthy
David F. Bird
W. S. Gardner
MM

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Mark J. Mccarthy

Résumé de la communication

Nitrogen transformations at the sediment-water interface were evaluated in Missisquoi Bay, Lake Champlain, using sediment core incubations and stable isotopes. Sampling occurred in June and Aug 2007. Potential denitrification (DNF) rates at two sites ranged from 160 to 560 µmol N m-2 h-1. Higher DNF rates versus net N2 fluxes suggest that denitrifiers may be limited by substrate, a surprising result given the high water column NO3- concentrations (up to 78 µM) in most cases. Sediment-water interface N2 fixation rate estimates determined from isotope pairing cannot account for this difference. Dissimilatory NO3- reduction to NH4+ (DNRA) was observed at the nearshore site, but rates were only ~4-5% of DNF, suggesting that DNRA does not compete effectively with DNF for available NO3-. However, NO3- induced NH4+ flux (NIAF) at both sites suggests that DNRA may be underestimated. NH4+ cation exchange in the sediments may explain this phenomenon. Isotope pairing results indicate that anaerobic NH4+ oxidation (anammox) may have occurred and, if so, accounts for 3-6% and 11-27% of total sediment N2 flux at the nearshore and offshore sites, respectively. Microbial techniques may be necessary to confirm the presence and activity of DNRA and anammox. These and future results, combined with water quality and phytoplankton monitoring data, will provide insights into mechanisms responsible for phytoplankton ecological observations, including cyanobacteria community succession and toxicity.

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Section :
Les causes et les conséquences de la prolifération et de la toxicité des cyanobactéries.
news icon Thème du colloque :
Les causes et les conséquences de la prolifération et de la toxicité des cyanobactéries.
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Philippe Juneau
host icon Hôte : Institut national de la recherche scientifique

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Thème du colloque :

Les causes et les conséquences de la prolifération et de la toxicité des cyanobactéries.
Sediment-water interface nitrogen transformations in Missisquoi Bay, Lake Champlain (Québec): poten…
Mark J. Mccarthy
Sediment-water interface nitrogen transformations in Missisquoi Bay, Lake Champlain (Québec): poten…
Mark J. Mccarthy