The Ecology of Tijuana Estuary, California: An Estuarine Profile

calculated from chlorophyll a measurements, so
that other plankton could be estimated by
subtract~on from totals Dead biomass was
calculated by subtracting the live fraction from total
POC. The difficult but precise analyses were
necessary to quantify tidal water composition
Over 1,850 samples were processed for carbon
analysis in the 2-year study (Winfield 1980)
Most studles of carbon flux ignore the DOC
component. Yet at Tijuana Estuary, thts was the
major form of carbon export (Figure 56)
Concentratrons oi DOC in ebb ttde water often
exceeded concentrations in flood tide water (Figure
57). Furthermore, concentrattons of C In the
drssolved form averaged much higher than In the
part~culate form (Figure 58). DOC ranged from 1 to
11 mg C/I, whrle POC ranged from 04 to 1 8 mg
C/I of creek water. Thus, the ultimate removal of
organic mater~als produced in the marsh results
from processes such as leaching of DOC from both
trve and dead plants and anbmals and excretion of
organic molecules by piants and an~mals
Detrltal carbon dominated the particulate
component In t~dai waters, sarnetirnes making up
98% of the PQC, and never less than 3tYU (Winfield
1980). Live organisms made up the majority of the
particulate matter only in June 1977 and April
1978. Both times the live POC was largely algae,
as indicated by chlorophyll concentrations. In
contrast with DOC results, the POC data suggested
that the salt marsh entrains particulate materials.
although this is the net result of frequent import
and occasior~al export.
What fraction of marsh product~vrty is exported
to tidal creeks' Based on his 10-month study
penod, W~nfield (1980) estimated an annual export
of 40 g C/m2/yr as DOC for the area domfnated by
succulents and 110 g C/m2/yr for the area of
mixed cordgrass and succulents A net import of
partlcuiate carbon was determ~ned for POC, wrth
annual estimates at 5-6 g C/m2/yr for the areas
included in his two sampling statrons At most,
then, there was a net removal of 105 g C/m7/yr,
which is well below the net amount produced by
vascular plants (approximately 220 g C/m2/yr.
Secttan 4 3) and eptbenthlc algae (185-340 g
C/ine'/yr) Add~t~onal fluxes of debris probably
occurred on the water surface and as wind-borne
mater~als, ne~ther was measured because of
enormous difficulties in sampling Because
temporal variab~lity in all of these processes IS
Figure 56. Net flux of parttculate (left) and dissofved (right! organic carbon in tidal waters of (a) the succulentdominated
and fb) mtxed cordgrass-succulent study s~tes of Wtnfield (1980). Reprinted with pernissron from
Winfieid (18801.