Ml. Decasabianca et al., SEASONAL-CHANGES OF NUTRIENTS IN WATER AND SEDIMENT IN A MEDITERRANEAN LAGOON WITH SHELLFISH FARMING ACTIVITY (THAN LAGOON, FRANCE), ICES journal of marine science, 54(5), 1997, pp. 905-916
The French Mediterranean lagoon of Thau is characterized by an importa
nt eutrophication dominated by shellfish farming(ca. 15 times the terr
estrial inputs). On the basis of increasing eutrophication; three area
s were identified and monitored for one year (overlying and sediment p
ore water nutrients, macrophytic biomass and water column chlorophyll
a). Though some parameters show similar changes in the three areas (sa
linity, temperature), others are elevated in eutrophicated sites; e.g.
organic content and siltation of the sediments, dissolved inorganic n
itrogen (136.1 mu mol l(-1) overlying water, and 1185 mu mol l(-1) por
e water), dissolved reactive phosphorus (DRP) (20.9 mu mol l(-1) overl
ying water), the summer oxygen depletion (1.1 mg l(-1)), the peak of m
acrophytic biomass (8 kg w . wt m(-2)) and phytoplanktonic bloom (14 m
u g l(-1)). Differences in DRP levels arise from sediment release duri
ng the summer anoxia: DRP appeared to play a key role as a limiting fa
ctor, and regulates competition between macrophytes and phytoplankton
in spring. The macrophytes (seagrass Zostera and seaweeds Gracilaria a
nd Ulva) may sustain the environment they are living in, acting as add
itional eutrophication sources. (C) 1997 International Council for the
Exploration of the Sea.