INFLUENCE OF SHELLFISH FARMING ACTIVITIES ON NITRIFICATION, NITRATE REDUCTION TO AMMONIUM AND DENITRIFICATION AT THE WATER-SEDIMENT INTERFACE OF THE THAU LAGOON, FRANCE
F. Gilbert et al., INFLUENCE OF SHELLFISH FARMING ACTIVITIES ON NITRIFICATION, NITRATE REDUCTION TO AMMONIUM AND DENITRIFICATION AT THE WATER-SEDIMENT INTERFACE OF THE THAU LAGOON, FRANCE, Marine ecology. Progress series, 151(1-3), 1997, pp. 143-153
The seasonal patterns of nitrification, denitrification and dissimilat
ory ammonium production (DAP) rates were studied in the sediment of 2
stations in the Thau lagoon (south of France). The station ZA was loca
ted within the shellfish farming zone and the station B was the refere
nce site. A marked effect of shellfish fanning on bacterial activities
was observed. Spatial differences were associated with discrepancies
in the organic content and the reduction state of sediments, i.e. high
est reductive processes (denitrification and DAP) were noted in shellf
ish farming area, whereas the oxidative process (nitrification) was pr
edominant outside the farming zone. At both stations, the DAP activity
increased in September (autumn) concomitant with an increase of the C
/N ratio in the sediment due to the sedimentation of the summer phytop
lanktonic production. Nitrification and denitrification rates exhibite
d maxima in November (winter) corresponding to dissolved inorganic nit
rogen inputs from the surrounding land. In the shellfish farming site,
98 % of nitrate was reduced to NH4+ and 2 % to N2O showing that the m
ost of the NO3- was reduced to ammonium and remained available for the
ecosystem.