Publication Date:
2024-03-15
Description:
The Amazon and the Pará are two major rivers that carry dissolved and suspended particulate trace metals to the
Atlantic Ocean. In the dynamic mixing zone of the estuary, competing processes of trace metal sorption and
release play a role, which might affect transport to the open ocean. Here we investigate the behavior of dissolved
(〈0.2 μm), soluble (〈0.015 μm) and truly dissolved (〈10 kDa and 〈 1 kDa) molybdenum (Mo), uranium (U),
and vanadium (V) during estuarine mixing between river water (S 〈 1) and seawater (S 〉 35) end members
during the high discharge period, as well as during aging of the plume in its northward flow along the coast.
Molybdenum behaved conservatively during estuarine mixing and showed no colloidal fraction, suggesting Mo is
solely present in the soluble or even truly dissolved fraction. Uranium behaved mostly conservatively but showed
removal in the low salinity range (ca. S 〈 9). This is potentially due to colloidal flocculation at low salinities, as
indicated by colloidal (0.015–0.2 μm) fractions of up to 30% for U but decreasing with increasing salinity until
no significant difference could be discerned at S 〉 10. Vanadium shows a general conservative mixing, but with
more scatter in the data than for Mo and U and potential removal at low to mid-salinities. Removal of V to the
sediments is also indicated by surface sediment data from the mid-salinity region of the estuary but no size
fractionation in the dissolved phase could be observed. Hence, V seems to be predominantly present in the
soluble or even truly dissolved phase and export to the sediments might take place through particles 〉0.2 μm. No
considerable removal or release of Mo, U and V was observed in their water column depth profiles, indicating a
conservative behavior in the water column of the estuaries studied here. Additionally, we present a comparison
of differential pulse adsorptive stripping voltammetry and inductively coupled plasma – mass spectrometry
analyses for Mo and V, which showed excellent agreement within analytical uncertainty in this challenging
sample material covering the full salinity range from freshwater to seawater.
Type:
Article
,
PeerReviewed
Format:
text
Format:
text
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