 |
| Titel |
Seven centuries of atmospheric Pb deposition recorded in a floating mire from Central Italy |
| VerfasserIn |
Claudio Zaccone, Daniela Lobianco, Valeria D'Orazio, Teodoro M. Miano, William Shotyk |
| Konferenz |
EGU General Assembly 2016
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250125990
|
| Publikation (Nr.) |
 EGU/EGU2016-5657.pdf |
|
|
|
|
|
| Zusammenfassung |
| Floating mires generally consist of emergent vegetation rooted in highly organic buoyant
mats that rise and fall with changes in water level. Generally speaking, the entire
floating mass (mat) is divided into a mat root zone and an underlying mat peat
zone.
Floating mires are distributed world-wide; large areas of floating marsh occur along rivers
and lakes in Africa, the Danube Delta in Romania, the Amazon River in South America, and
in the Mississippi River delta in USA, whereas smaller areas occur also in The Netherlands,
Australia and Canada.
While peat cores from ombrotrophic bogs have been often (and successfully) used to
reconstruct changes in the atmospheric deposition of several metals (including Pb), no
studies are present in literature about the possibility to use peat profiles from floating
mires.
To test the hypothesis that peat-forming floating mires could provide an exceptional tool
for environmental studies, a complete, 4-m deep peat profile was collected in July 2012 from
the floating island of Posta Fibreno, a relic mire in the Central Italy. This floating island has a
diameter of ca. 30 m, a submerged thickness of about 3 m, and the vegetation is organized in
concentric belts, from the Carex paniculata palisade to the Sphagnum palustre
centre.
The whole core was frozen cut each 1-to-2 cm (n =231), and Pb determined by
quadrupole ICP-MS (at the ultraclean SWAMP lab, University of Alberta, Canada) in each
sample throughout the first 100 cm, and in each odd-numbered slice for the remaining
300 cm. The 14C age dating of organic sediments (silty peat) isolated from the
sample at 385 cm of depth revealed that the island probably formed ca. 700 yrs
ago.
Lead concentration trend shows at least two main zones of interest, i.e., a clear peak
(ranging from 200 to 1600 ppm) between 110-115 cm of depth, probably corresponding to
early 1960’s – late 1970’s, and a broad band (80-160 ppm) between 295-320 cm of depth,
corresponding to approximately AD 1480-1650.
Lead concentrations were normalized to those of Th, a conservative, lithophile element
often used as an indicator of the abundance of mineral particles. Crustal enrichment factor
values, calculated by normalizing the Pb/Th ratio in peat samples to the corresponding ratio
for the Upper Continental Crust, clearly show that almost all the Pb reaching this floating isle
in the last seven centuries is of anthropogenic origin. In particular, while the big peak
around 100-115 cm of depth is associated with that of Sb, the band around 300 cm
characterized also the trend of several other major and trace elements (i.e., Ag, Al, Ba,
Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sr, Th, Tl, U, V, Y, Zn) with the exception of
Sb.
Although γ-spectrometry measurement (210Pb, 137Cs and 241Am) for the first 100 cm of
this core is still on-going, at the best of our knowledge, this work may provide the first Pb
chronology obtained from a (4 m) deep floating mire.
Furthermore, it is to note that a) this floating mire could consist of the southernmost
European population of Sphagnum, and b) this core shows a great potential to be used as
archive of environmental changes, especially considering its high resolution (1 cm = 0.5 yr in
the first 100 cm, and 2-2.5 yrs in the remaining 300 cm of depth).
The Authors thank the Municipality of Posta Fibreno, Managing Authority of the
Regional Natural Reserve of Lake Posta Fibreno, for allowing peat cores sampling. |
|
|
|
|
|
|