Late Holocene pollen record from Fiume Morto (Dead River), a palaeomeander of Tiber River near Ancient Ostia (central Italy)
Résumé
Pollen and non pollen palynomorph analyses
were carried out in a sediment core (MO2) drilled
in the southern lobe of a palaeomeander, Fiume Morto
(Dead River), in the Tiber delta area, near Ancient
Ostia (central Italy). Since the Roman period, the
Tiber River flowed close to Ancient Ostia and its
saltworks, Salinae Ostiensis. The Tiber meander was
cut off during the Tiber River flood of 1557 AD and
transformed into an oxbow lake. During the nineteenth
century the Fiume Morto pond was reclaimed and at
present the area is about 3 km distant from the present
shoreline and intensely transformed by human settlements.
According to radiocarbon dates, the pollen
record, not continuous, spans from the fourth century
BC to the nineteenth century AD. It shows first a
riverine phase before the meander cut off of sixteenth
century AD and probably only the last centuries BC
were preserved from erosion. The river deposits record
riparian vegetation (mainly tamarisk and alder) with
mesophilous (mainly deciduous oaks) and Mediterranean
(mainly evergreen oaks, heather and olive tree)
elements. The human presence is clear, probably
related to the development of Ancient Ostia and
evidenced by synanthropic taxa. The second phase
corresponds to the oxbow lake formed after the
meander cut off. Several peaks of pine pollen are
tentatively ascribed to Tiber flood events: the first peak
is found just in correspondence with the meander cut
off at 1557 AD. The numerous floods we interpret in
the following part of the diagram could be linked to the
increase in extreme events and precipitation that
occurred during the Little Ice Age. The last phase, in
which freshwater plants are present and chenopods
decrease, shows the saltworks abandonment that
occurred in nineteenth century. This study turned out
to be of key relevance to reconstruct the palaeoenvironmental
evolution of the ancient Holocene Tiber
meander during the last two and a half millennia.
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