Chou, Lei

Van Der Zee, Clara

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Phosphorus speciation in the Scheldt estuary and the Belgian coastal zone

Phosphorus speciation was studied in the Scheldt estuary and the Belgian coastal zone from November 2002 to December 2003. Monthly surveys were performed at 10 coastal stations and seasonal campaigns (winter, spring and summer) were conducted in the Scheldt estuary. Weekly to monthly samples were also taken in the upper freshwater reaches of the Scheldt and in tributaries at stations under the tidal influence.Phosphorus was measured as soluble reactive phosphorus (hereafter called PO4), dissolved inorganic phosphorus (DIP), total dissolved phosphorus (TDP), particulate inorganic phosphorus (PIP), total particulate phosphorus (TPP) and total phosphorus (TP). Dissolved organic phosphorus (DOP) was determined by difference between TDP and DIP. Likewise, particulate organic phosphorus (POP) was determined by difference between TPP and PIP.In the freshwater part of the Scheldt estuary practically all dissolved P is in the PO4 pool and the concentration shows a seasonal trend, whereas little variation in the DOP pool is observed. The concentration of particulate P is usually higher than that of the dissolved P pool. During July and August in the upper freshwater reaches of the Scheldt where intensive diatom blooms have been developed resulting in a depletion of dissolved silicate, the PO4 concentration remains above 3µM. In contrast, at the mouth of the Scheldt estuary, the PO4 concentration drops below 0.30µM in April-May.Phosphate versus salinity plots show conservative mixing in the Belgian coastal zone from November 2002 until February 2003 and again from July/August onwards. In March, the PO4 concentration decreases and the chlorophyll a content in the water reaches maximal values in March-April. The DOP concentration is usually low compared to the PO4 concentration, except in this period. At the more off-shore stations, the dissolved P pool is larger than the particulate P pool. Closer to the coast particulate and dissolved P contribute about equally to the total P, whereas near the mouth of the Scheldt particulate P is the dominant P pool. The % POP of the TPP shows a seasonal trend for the coastal stations with maxima around April. Biogeochemical cycling of phosphorus will be discussed in terms of the relative contribution of biological versus inorganic processes

van der Zee, C.

Chou, L.

Open Marine Archive

Geophysical Research Abstracts, Vol. 6, 06119, 2004
SRef-ID: 1607-7962/gra/EGU04-A-06119
c© European Geosciences Union 2004
PHOSPHORUS SPECIATION IN THE SCHELDT
ESTUARY AND THE BELGIAN COASTAL ZONE
C. van der Zee and L. Chou
Laboratoire d’Océanographie Chimique et Géochimie des Eaux, Université Libre de Bruxelles,
Campus Plaine - CP 208, B-1050 Brussels, Belgium (cvdzee@ulb.ac.be; lei.chou@ulb.ac.be)
Phosphorus speciation was studied in the Scheldt estuary and the Belgian coastal
zone from November 2002 to December 2003. Monthly surveys were performed at 10
coastal stations and seasonal campaigns (winter, spring and summer) were conducted
in the Scheldt estuary. Weekly to monthly samples were also taken in the upper
freshwater reaches of the Scheldt and in tributaries at stations under the tidal influence.
Phosphorus was measured as soluble reactive phosphorus (hereafter called PO4),
dissolved inorganic phosphorus (DIP), total dissolved phosphorus (TDP), particulate
inorganic phosphorus (PIP), total particulate phosphorus (TPP) and total phosphorus
(TP). Dissolved organic phosphorus (DOP) was determined by difference between
TDP and DIP. Likewise, particulate organic phosphorus (POP) was determined by
difference between TPP and PIP.
In the freshwater part of the Scheldt estuary practically all dissolved P is in the PO4
pool and the concentration shows a seasonal trend, whereas little variation in the DOP
pool is observed. The concentration of particulate P is usually higher than that of
the dissolved P pool. During July and August in the upper freshwater reaches of the
Scheldt where intensive diatom blooms have been developed resulting in a depletion
of dissolved silicate, the PO4 concentration remains above 3µM. In contrast, at
the mouth of the Scheldt estuary, the PO4 concentration drops below 0.30µM in
April-May.
Phosphate versus salinity plots show conservative mixing in the Belgian coastal zone
from November 2002 until February 2003 and again from July/August onwards.
In March, the PO4 concentration decreases and the chlorophyll a content in the
water reaches maximal values in March-April. The DOP concentration is usually
low compared to the PO4 concentration, except in this period. At the more off-shore
stations, the dissolved P pool is larger than the particulate P pool. Closer to the
coast particulate and dissolved P contribute about equally to the total P, whereas
near the mouth of the Scheldt particulate P is the dominant P pool. The % POP of
the TPP shows a seasonal trend for the coastal stations with maxima around April.
Biogeochemical cycling of phosphorus will be discussed in terms of the relative
contribution of biological versus inorganic processes.


Phosphorus speciation in the Scheldt estuary and the Belgian coastal zone

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