0 < salinity < 2 2003 2004 2005 2006 2007 2008 4000 4500 5000 5500 6000 pCO2 pCO2@13°C p C O2 o r p C O2 @ 1 3 °C ( p p m ) 0 2000 4000 6000 8000 10000 Jan. 2008 Jan.1998 Winter p C O2 ( p p m ) April 2008 April 1997 Spring 0 5 10 15 20 25 30 35 0 2000 4000 6000 8000 10000 June 2008 June 1997 Summer salinity p C O2 ( p p m ) 0 5 10 15 20 25 30 35 Sept. 2008 Sept. 1997 salinity Fall
Decadal changes of carbon dioxide in the Scheldt estuary
Borges A.V. 1,*, Middelburg2
1University of Liège (BE) 2Centre for Estuarine and Marine Ecology (NL)
* alberto.borges@ulg.ac.be
European Geosciences Union General Assembly, 2-7 May 2010
The seasonality and spatial variability in theScheldt estuary of pCO2 measured with an
equilibrator coupled to an infra-red gas
analyser was investigated by monthly cruises in 2008. Whatever the season, pCO2 values are higher upstream and decrease downstream as salinity increases. Upstream, two seasonal
maxima of pCO2 coinciding with oxygen
saturation level (%O2) minima occur in May and October. This corresponds to the periods of high O2 consumption and CO2 production due to bacterial respiration and nitrification. In mid-summer (July-August), light availability is maximum upstream leading to a phytoplankton bloom in the freshwater reaches (as indicated by the increase of chlorophyll-a (Chla) and %O2 and decrease of pCO2). Downstream, the major seasonal feature is the marked spring increase of Chla and %O2and a decrease of pCO2(below atmospheric equilibrium ~380 ppm).
•
Seasonal variations of pCO
2in the whole estuary
•
Decadal changes of pCO
2in the upper estuary and in the whole estuary
0 10 20 30 40 50 60 70 80 90 100 110 D is ta n c e f ro m e s tu a ry m o u th ( k m ) 0 2 4 6 8 10 12141618 20222426 28 3032 J F M A M J J A S O N D Salinity 0 10 20 30 40 50 60 70 80 90 100 110 D is ta n c e f ro m e s tu a ry m o u th ( k m ) 0 1500 3000 4500 6000 7500 J F M A M J J A S O N D pCO (ppm)2 0 10 20 30 40 50 60 70 80 90 100 110 D is ta n c e f ro m e s tu a ry m o u th ( k m ) 0 20 40 60 80 100 J F M A M J J A S O N D Chla (µg L )-1 0 10 20 30 40 50 60 70 80 90 100 110 D is ta n c e f ro m e s tu a ry m o u th ( k m ) 0 20 40 60 80 100 120 140 J F M A M J J A S O N D %O (%)2
This feature extends from the mouth of the estuary to about salinity 5 where is located the downstream limit of the estuarine maximum turbidity zone. In fall, there is a slight decrease of %O2 and an increase of pCO2 downstream related to the collapse of primary production due to light limitation, and degradation of organic matter.
pCO2 was measured continuously with an equilibrator coupled to an infra-red gas analyser in the upper Scheldt
estuary (Ste Anna Station, city of
Anvers) since late 2002. Data-set shows
that annual average pCO2 values
remained stable from 2003 to 2006, and strongly declined in 2007 and 2008, at salinities < 2. This corresponds to the response of carbon cycling in the upper Scheldt estuary to the on-set on the Brussels North sewage treatment plant. To check the impact of the response of C cycling in the upper Scheldt estuary downstream we carried out a monthly monitoring in the whole salinity gradient
of the estuary, and results were
compared with data obtained in the late 1990’s during the BIOGEST project. Data show that pCO2 values from freshwaters to about salinity 15 were systematically higher in 1997/1998 than 2008. Hence the impact of changes in carbon cycling in the upper estuary seem to impact pCO2dynamics down to salinity 15.
