E. Donali et al., Carbon flow patterns in the planktonic food web of the Gulf of Riga, the Baltic Sea: a reconstruction by the inverse method, J MAR SYST, 23(1-3), 1999, pp. 251-268
We used the inverse method to reconstruct a carbon flux model for the plank
tonic food web of the southern part of the Gulf of Riga, the Baltic Sea. Th
e model was based on data from three field campaigns (3-12 May 1995; 28 Jun
e-7 July 1994; 26 August-3 September 1993). The carbon flow model indicated
very different channelling of gross primary production (GPP) in the three
different periods. In spring 55% of GPP was channelled to detritus, while i
n summer 35% was exudated and channelled to dissolved organic carbon (DOC).
In autumn, 42% of GPP was channelled to the zooplankton compartments. The
model suggested high bacterial respiration rates and low bacterial growth e
fficiencies (6%) in spring and autumn. During these periods large decreases
in DOC were anticipated to occur due to bacterial respiration. In summer t
he model suggested that bacterial respiration rate was low and that the bac
terial growth efficiency was high (60%). During this period a net accumulat
ion of DOC apparently occurred. Respiration was the most important loss of
organic carbon in all seasons, corresponding on average to 152, 59 and 391%
of GPP daily in spring, summer and autumn, respectively. Daily sedimentati
on rates of particulate organic carbon (POC) were consistently low (< 3% d(
-1)), removing 13-29% of GPP daily. The sedimented material consisted mainl
y of amorphous detritus. This indicates that in spite of the relatively hig
h level of eutrophication, the planktonic system in the Gulf of Riga has a
high short-term carbon retention and recycling capacity, and little POC is
lost from the upper water column through sedimentation. (C) 1999 Elsevier S
cience B.V. All rights reserved.