Late Holocene pollen record from Fiume Morto (Dead River), a palaeomeander of Tiber River near Ancient Ostia (central Italy)

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Pollen and non pollen palynomorph analyseswere carried out in a sediment core (MO2) drilledin the southern lobe of a palaeomeander, Fiume Morto(Dead River), in the Tiber delta area, near AncientOstia (central Italy). Since the Roman period, theTiber River flowed close to Ancient Ostia and itssaltworks, Salinae Ostiensis. The Tiber meander wascut off during the Tiber River flood of 1557 AD andtransformed into an oxbow lake. During the nineteenthcentury the Fiume Morto pond was reclaimed and atpresent the area is about 3 km distant from the presentshoreline and intensely transformed by human settlements.According to radiocarbon dates, the pollenrecord, not continuous, spans from the fourth centuryBC to the nineteenth century AD. It shows first ariverine phase before the meander cut off of sixteenthcentury AD and probably only the last centuries BCwere preserved from erosion. The river deposits recordriparian vegetation (mainly tamarisk and alder) withmesophilous (mainly deciduous oaks) and Mediterranean(mainly evergreen oaks, heather and olive tree)elements. The human presence is clear, probablyrelated to the development of Ancient Ostia andevidenced by synanthropic taxa. The second phasecorresponds to the oxbow lake formed after themeander cut off. Several peaks of pine pollen aretentatively ascribed to Tiber flood events: the first peakis found just in correspondence with the meander cutoff at 1557 AD. The numerous floods we interpret inthe following part of the diagram could be linked to theincrease in extreme events and precipitation thatoccurred during the Little Ice Age. The last phase, inwhich freshwater plants are present and chenopodsdecrease, shows the saltworks abandonment thatoccurred in nineteenth century. This study turned outto be of key relevance to reconstruct the palaeoenvironmentalevolution of the ancient Holocene Tibermeander during the last two and a half millennia.