FN Archimer Export Format
PT J
TI Biogeochemical aspects of bottom anoxia in a Mediterranean lagoon (Thau, France)
BT 
AF SOUCHU, Philippe
   GASC, Anne
   COLLOS, Y
   VAQUER, A
   TOURNIER, Henri
   BIBENT, B
   DESLOUS-PAOLI, Jean-Marc
AS 1:1;2:1;3:2;4:2;5:1;6:2;7:1;
FF 1:;2:;3:;4:;5:;6:;7:;
C1 IFREMER, Ecol Lab, F-34200 Sete, France.
   Univ Montpellier, UMR 5556 CNRS, Lab Hydrobiol, F-34095 Montpellier 5, France.
C2 IFREMER, FRANCE
   UNIV MONTPELLIER, FRANCE
IN WOS Ifremer jusqu'en 2018
   copubli-france
   copubli-univ-france
IF 1.928
TC 71
UR https://archimer.ifremer.fr/doc/00070/18142/15694.pdf
LA English
DT Article
DE ;anoxia;nitrogen;phosphorus;eutrophication;Thau lagoon;Mediterranean Sea
AB Physical and chemical characteristics (temperature, salinity, dissolved oxygen), nutrients [dissolved inorganic nitrogen (DIN), soluble reactive phosphorus (SRP) and silicate], dissolved organic nitrogen (DON) and phosphorus and particulate matter [particulate organic carbon (POC) and nitrogen (PON) and chlorophyll a] were measured at a station located in the deepest part of the Thau lagoon (8.5 m), France, during a 10 d period of bottom anoxia in summer 1994. The upper 8 cm of sediment were also analyzed for ammonium (NH(4)(+)) and SRP concentrations in the porewater. The study period was characterized by mean wind speed under 4 m s(-1) which induced an increase of surface temperature from 18 to 29 degrees C with the formation of a thermocline. The correlation (p < 10(-4)) between the wind speed averaged over the previous day and the difference between bottom and surface temperatures showed that the wind constituted the main vector of vertical mixing. The lack of wind led to dissolved oxygen depletion in the bottom 2 m and to a strong porosity increase in the upper 10 cm of sediment (80 to >95%). Anoxic conditions increased NH(4)(+) and SRP concentrations in porewater from 231 +/- 89 to 1305 +/- 305 (+/- SD) mu M and from 6.6 +/- 0.8 to 108 +/- 43 mu M respectively. The potential increase of NH(4)(+) concentrations in porewater estimated from the mineralization of the microphytobenthos explained 30% of the measured increase in the upper 8 cm of porewater. The study period was characterized by an increase in NH(4)(+) SRP and dissolved Si concentrations in the bottom water column (maxima respectively 24.2, 4.9 and 57 mu M). Linear regressions between nutrient concentrations in the water column and temperature revealed a strong enhancement of bottom fluxes during anoxia. Nitrate + nitrite (NO(3)(-) + NO(2)(-)) were absent in anoxic waters and remained below 0.5 mu M in oxic waters. Monthly concentrations of SRP in the water column of the Thau lagoon from 1970 to 1994 revealed anoxia events by summer peak values corresponding to strong bottom anoxia. Nevertheless, the general trend was a decrease due to the gradual control of eutrophication which should lead to the disappearance of bottom anoxia within the next decade. A fraction of the nutrients of benthic origin was transformed into planktonic particulate matter via primary production which increased the concentrations of chi a from about 1 to 15 mu g l(-1). Concentrations of DON and PON in the water column were significantly correlated, suggesting that DON compounds were released by the pelagic food web but not directly by the sediment. The increase of total nitrogen (DIN + DON + PON), considering the water column as a closed box during 10 d of winds under 5 m s(-1), was estimated at 1.7 mu mol N l(-1) d(-1) and would correspond to a benthic flux of 600 mu mol N m(-1) h(-1) for 10 d.
PY 1998
SO Marine Ecology-progress Series
SN 0171-8630
PU Inter-research
VL 164
UT 000073460100012
BP 135
EP 146
DI 10.3354/meps164135
ID 18142
ER

EF