Md. Doval et al., DISSOLVED ORGANIC-MATTER IN A TEMPERATE EMBAYMENT AFFECTED BY COASTALUPWELLING, Marine ecology. Progress series, 157, 1997, pp. 21-37
From September 1994 to September 1995 a time-series station in the Ria
de Vigo (NW Spain) was monitored fortnightly. Dissolved organic carbo
n (DOC) was analysed by high temperature catalytic oxidation. Dissolve
d organic nitrogen (DON) was determined by the Kjeldahl method, after
removal of inorganic nitrogen from the sample. The time courses of DOC
and DON changes were parallel. The average C/N molar ratio of dissolv
ed organic matter (DOM) was similar to 15. DOM was strongly influenced
by physical and biological processes. During the upwelling season, th
e entry of DOM-poor Eastern North Atlantic Central Water (ENACW) contr
olled DOM levels in subsurface waters. Biologically produced DOM exces
s in surface waters was uncoupled with chlorophyll a on a daily time-s
cale. A tentative partitioning of DOM during the upwelling season has
been inferred from mixing of oceanic and freshwater endmembers. The re
fractory pool, similar to 70% of total DOC in surface water, was carri
ed by upwelled ENACW (60%, 10% of which was semi-refractory) and conti
nental water (10%). Net production of semi-labile DOC occurred in the
bottom layer (similar to 10 mu M C). The average DOC excess in surface
waters compared to bottom waters was 21 mu M C, with a C/N molar rati
o of 12. The excess was a mixture of labile and semi-labile material w
ith a recycling time >5 d, which represented similar to 23 and similar
to 13 % of the net primary production for C and N respectively. The a
verage DOM excess/[POM (particulate organic matter) + DOM excess] rati
o in surface waters was similar to 0.4 and similar to 0.3 for C and N
respectively, indicating that POM was the most important pool of organ
ic matter net produced in the inner ria. During the downwelling season
DOM was balanced by the external inputs and the DOM excess in surface
waters was due to the freshwater contribution.