『Abstract
We report Zn isotopic ratios (δ66Zn) of river suspended
particulate matter (SPM) and floodplain deposits (FD) from the
Seine basin, France, with a precision ≦0.05‰. A decrease in δ66Zn
from 0.30‰ to 0.08‰ is observed in SPM from the upstream to downstream
parts of the fluvial system, associated with an increase in Zn
concentration from 100 ppm to 400 ppm. The Zn/Al of SPM at the
river mouth is up to five times greater than the Zn/Al of the
natural background, and by normalizing to the later value we define
a Zn enrichment factor. Suspended sediments from a temporal series
of samples collected in Paris display a similar variation in δ66Zn
of between 0.08‰ and 0.26‰, while showing an inverse relationship
between the Zn enrichment factor and δ66Zn. The amount
of Zn transported as suspended load varies from 10％ to 90％, as
a function of increasing discharge. The δ66Zn of SPM
and the dissolved load are correlated, suggesting that adsorption
processes are probably not the dominant process by which the Zn
enrichment of SPM takes place. Instead, we interpret our data
as reflecting the mixture of two main populations of suspended
particles with distinct δ66Zn. The first is characteristic
of natural silicate particles transported by erosion processes
to the river, while the second likely represents anthropogenic
particles derived from wastewater treatment plants or combined
sewer overflows. Based on isotopic ratios, we calculate that 70％
of Zn in SPM of the Seine River in Paris is of anthropogenic origin.』
1. Introduction
2 Analytical methods
3. Results
3.1. Zn concentrations and enrichment factors in suspended
particulate matter
3.2. Zn isotope ratios in the Seine River SPM and flood deposits
3.3. Zn isotopic ratios and concentrations in geological and
anthropogenic samples
3.4. Mineralogy, POC content and granulometry of SPM
4. Discussion
4.1. Carbonate dilution and grain-size effects on Zn enrichment
4.2. Effects of in situ biological process on Zn concentration
and isotopic composition
4.3. Relationships between dissolved and suspended loads and
adsorption effects
4.3.1. Zn partition between dissolved and suspended loads
4.3.2. Adsorption effects on isotopic relationships between
dissolved and suspended loads
4.4. Natural sources of Zn in the Seine River sediments
4.5. The anthropogenic end-members
4.5.1. Combined sewer overflow
4.5.2. Plant-treated wastewaters
4.5.3. Contribution from atmosphere and agricultural compositing
4.6. Main mixing process aspect
4.7. Proportions of natural and anthropogenic Zn in the Seine
sediments
5. Conclusions
Acknowledgments
References