DISTRIBUTIONS OF DISSOLVED MANGANESE AND FLUORESCENT DISSOLVED ORGANIC-MATTER IN THE COLUMBIA RIVER ESTUARY AND PLUME AS DETERMINED BY IN-SITU MEASUREMENT
Gp. Klinkhammer et al., DISTRIBUTIONS OF DISSOLVED MANGANESE AND FLUORESCENT DISSOLVED ORGANIC-MATTER IN THE COLUMBIA RIVER ESTUARY AND PLUME AS DETERMINED BY IN-SITU MEASUREMENT, Marine chemistry, 56(1-2), 1997, pp. 1-14
We deployed an instrument package consisting of a SeaBird 911 plus CTD
, SeaTech 25-cm transmissometer, Chelsea AquaTracka fluorometer/nephel
ometer, Seapoint turbidity meter and ZAPS UV fluorometer/chemical sens
or during a series of tows and lowerings within the Columbia River plu
me and estuary in 1994 and 1995. Simultaneous in situ measurements of
Chi a, light attenuation, light scattering, and fluorescent dissolved
organic matter (FDOM) or dissolved Mn collected along with CTD informa
tion provided new insight into the effects of mixing and non-conservat
ive processes on riverine input to the coastal ocean. Inter-relationsh
ips among these parameters proved to be effective at delineating three
coastal water masses: Columbia River Plume Water (CRPW), Shelf Deep W
ater (SDW), and Shelf Bottom Water (SEW). CRPW had variable amounts of
FDOM, dissolved Mn, and Chi a as the plume mixed with coastal water.
SEW was characterized by high concentrations of Chi a and low concentr
ations of dissolved Mn, suggesting a surface or near-surface source. T
he properties of SDW were intermediate between humic-rich plume water
and turbid bottom water. FDOM displayed a quasi-linear and inverse rel
ationship with salinity inside the estuary and nearshore coastal plume
which supports previous work relating this parameter to the humic-ric
h terrestrial component of dissolved organic matter (DOM). There was,
however, considerable evidence of lower FDOM levels within the estuari
ne turbidity maximum (ETM) and near the seaward boundary of the plume.
There were also elevated levels of FDOM near the bottom at some locat
ions on the shelf, suggesting that there may be a significant benthic
flux of this material. Thus FDOM appears to be more reactive than prev
iously thought when looked at in detail. Dissolved Mn also displayed n
on-conservative behavior in the estuary and across the plume showing s
ignificant input into surface waters. The sharpest Mn gradient on the
shelf occurred near the seaward edge of the plume in an area of relati
vely high turbidity and Chi a, and relatively low FDOM. These distribu
tions are consistent with the presence of a chemical front near the pl
ume boundary where Mn-oxides are reduced during the oxidation of humic
ligands. This process would release dissolved Mn and promote producti
vity in the turbid zone associated with the leading edge of the plume
jet. This study demonstrates that chemical sensors can provide highly
resolved, detailed information on trace substance distribution and var
iability in marine environments.