Climate vs. anthropogenic changes in North Adriatic shelf sediments influenced by freshwater runoff

Land-ocean coupling was investigated for the Adige River-Adriatic Shelf system by analyzing precipitation, water discharge and suspended load records over the period 1922-2000 and by comparing them with the 210Pbex and porosity depth profiles of 4 marine cores taken along the riverborne sediment transport pathway on the shelf. The results show that precipitation was affected only by minor variations in yearly and seasonal amounts but was accompanied by a significant decrease (increase) in the number of wet days (precipitation intensity). River discharge which is strongly influenced by total precipitation as well as by the number of wet days (in contrast to the quantitatively less important precipitation intensity) shows a continuous decrease throughout the whole period. A significant decrease in suspended load is recorded after the 1940s, and meteorological and hydrological data suggest a major discontinuity over the same period, which was also recorded by marine sediments as a significant decrease in accumulation rates of fine materials. After the 1970s a further change in water discharge is observed in the river-system lowlands, recorded on the Adriatic shelf as intermittent sediment accumulation, and probably related to major floods. Changes seem to be mostly anthropogenic, such as progressive withdrawal of water and sediment for agricultural and civil uses, as well as damming for irrigation purposes and for generation of electricity.