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| Titel |
Organic matter evolution throughout a 100-cm ombrotrophic profile from an Italian floating mire |
| VerfasserIn |
Claudio Zaccone, Valeria D'Orazio, Daniela Lobianco, Teodoro M. Miano |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250114739
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| Publikation (Nr.) |
 EGU/EGU2015-15552.pdf |
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| Zusammenfassung |
| The curious sight of an island floating and moving on a lake naturally, already described by
Pliny the Elder in his Naturalis historia (AD 77-79), fascinated people from time
immemorial. Floating mires are defined by the occurrence of emergent vegetation rooted in
highly organic buoyant mats that rise and fall with changes in water level. Peat-forming
floating mires could provide an exceptional tool for environmental studies, since much of
their evolution, as well as the changes of the surrounding areas, is recorded in their peat
deposits.
A complete, 4-m deep peat core 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
centre. Here, some of the southernmost Italian populations of Sphagnum palustre
occur. The 14C age dating of macrofossils removed from the sample at 360 cm of
depth revealed that the island probably formed more than 500 yrs ago (435±20 yr
BP).
In the present work, we show preliminary results regarding the evolution of
the organic matter along the first, ombrotrophic 100 cm of depth, hoping also to
provide some insight into the possible mechanism of the evolution of this floating
island.
The 100 cm monolith was collected using a Wardenaar corer and cut frozen in 1-cm
layers. It consists almost exclusively of Sphagnum mosses, often spaced out, in the top 20-30
cm, by leaves of Populus tremula that annually fell off. This section shows a very low bulk
density, ranging from 0.017 and 0.059 g cm-3 (avg. value, 0.03±0.01 g cm-3),
an average water content of 96.1±1.1%, and a gravimetric water content ranging
between 14.3 and 41.5 gwater gdrypeat-1. The pH of porewaters was in the range
5-5.5.
The C content along the profile ranged between 35 and 47% (avg., 41±1%), whereas the
N between 0.3 and 0.9% (avg., 0.6±0.1%). Main atomic ratios seem to confirm
what found during the visual inspection of the core, i.e., Sphagnum material so
well preserved that it is hard to classify it as “peat”. In fact, the F14C age dating
suggests that the first 95 cm of Sphagnum material accumulate in less than 55 yrs,
thus resulting in an average growing rate of ca. 1.7-1.8 cm yr-1. At the same time,
C/N, H/C and O/C ratios show their lowest values between 20 and 55 cm of depth,
corresponding to the section with highest bulk density (0.025-0.059 g cm-3). This
seems to suggest a slightly more decomposed material. Consequently, the depth of
55-60 cm could represent the emerged (i.e., less anaerobic) section of this floating
mire.
Finally, the first 100 cm of the core show a great potential to be used as archive of
environmental changes, especially considering their high resolution (1 cm = 0.5 yr ca.),
although the short time-space covered could be a limiting factor.
The Authors thank the Municipality of Posta Fibreno (FR), Managing Authority of the
Regional Natural Reserve of Lake Posta Fibreno, for allowing peat cores sampling. C.Z. is
indebted to the Staff of the Regional Natural Reserve for the help during samplings and for
their continuous feedbacks. |
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