Outcome of environmental change from historical sediment discharge in a Mediterranean fluvial basin, 1500 - 2019 CE

Soil loss is a challenge for sustainable river management, not the least in the Mediterranean region, with climate extremes altering erosion and overland sediment transport. The dynamics of these processes, and their ecological consequences, are poorly documented in the Mediterranen region. For the Arno River Basin (ARB), located by the Tyrrhenian coast of Italy, we estimated changes in annual sediment discharge (SD) as a function of the landscape characteristics within the basin, the seasonal distribution of precipitation and flooding, and the vegetation cover. Owing to a semi-empirical modelling framework, we identified critical erosion-/deposition-prone periods from 1500 to 2019 CE. The long-term estimated mean gross soil erosion in the ARB was ∼900 Mg km−2 yr−1, whereas mean net erosion was ∼200 Mg km−2 yr−1. The results revealed that during the Little Ice Age (ending ∼1850 CE), increased storms and SD had a large impact on the landscape and agricultural activity of the ARB. The downward trend in SD observed after ∼1903 CE occurred with high soil movement, along with environmental change and basin reforestation. The basin area thus experienced, on average, only slight soil losses, with ∼76% of the eroded soil being trapped along the stream reaches, on gently sloping areas as well as in the foot slopes and the valley terrains which divide the basin area. Relying on credible information regarding SD and its hydrological drivers, we showed how historical climatology and parsimonious modelling can be implemented to obtain basin-wide estimates of soil loss, and are appropriate tools for sustainable river basin management.