Man made deltas

Abstract

The review of geochronological and historical data documents that the largest southern European deltas formed almost synchronously during two short intervals of enhanced anthropic pressure on landscapes, respectively during the Roman Empire and the Little Ice Age. These growth phases, that occurred under contrasting climatic regimes, were both followed by generalized delta retreat, driven by two markedly different reasons: after the Romans, the fall of the population and new afforestation let soil erosion in river catchments return to natural background levels; since the industrial revolution, instead, flow regulation through river dams overkill a still increasing sediment production in catchment basins. In this second case, furthermore, the effect of a reduced sediment flux to the coasts is amplified by the sinking of modern deltas, due to land subsidence and sea level rise, that hampers delta outbuilding and increases the vulnerability of coastal zone to marine erosion and flooding.D eltas are strongly three-dimensional lithosomes that represent one of the most complex, fragile and densely populated landscapes of mid-latitude modern coastal systems. Understanding the life cycle of modern deltas since their embryonic stages is crucial for disentangling the role of natural vs. anthropic forcing, an open issue that bears substantial implications on our full awareness on the management of the entire coastal zone. By underpinning the timing of the main phases of delta growth it is possible to define how pervasively have human populations modified landscapes and to predict threats to delta stability during forthcoming, and possibly abrupt, environmental changes. The growth of deltas reflects the forcing by eustatic oscillations, which determines the available space for sediment accumulation, the riverine input, defined by water and sediment discharge, and the oceanographic regime, responsible for sediment dispersal 1 . The lithology and morphology of the drainage basin and the climatic regime govern sediment production and delivery to the coast, while the power of marine processes (storms, waves and tides) and local vertical movements of the delta plain controls sediment accumulation and the final shape of the delta 2 .The evolution of modern deltas can be reconstructed combining complementary information from multiproxy analyses, at core scale, and from geomorphological reconstructions of the growth of delta plains, channel avulsion and delta lobe progradations 3 . The comparative study of the Ebro, Rhone, Po and Danube deltas, representing the four main deltas of the northern Mediterranean and Black Sea regions (Fig. 1), is favored by the following circumstances: 1-the oceanographic regime of the receiving basins has allowed delta formation and substantial preservation; 2-the four catchments present comparable climate conditions having contiguous watersheds (comprised between 40u and 48u N) impacted by human diffusion since the Neolithic; 3-the ages of the main progradation phases are constrained by robust chronol...

Palaeoenvironments and palaeotopography of a multilayered city during the Etruscan and Roman periods: early interaction of fluvial processes and urban growth at Pisa (Tuscany, Italy)

“…The geoarchaeological analysis of the Pisa landscape not only confirmed the strong inclination of past human communities to settle on topographically elevated areas close to river courses, as recorded in other Mediterranean alluvial and coastal plains (Arnaud-Fassetta et al, 2000;Bini et al, 2009Bini et al, , 2012Bruno et al, 2013;Castaldini et al, 2009;Cremaschi et al, 2006;Cremonini et al, 2013;Maselli and Trincardi, 2013;Mele et al, 2013;Mozzi et al, 2010;Ninfo et al, 2011;Russo Ermolli et al, 2014), but also clearly documented the mutual reliance between palaeotopography and urban tissue evolution (Fig. 11).…”

Deltaic and Coastal Sediments as Recorders of Mediterranean Regional Climate and Human Impact Over the Past Three Millennia

“…Human activities such as forest clearing and exploitation of wood for construction are reflected by low forest cover. Comparison with our southern Adriatic records (Figures b and d) suggests a notable human influence on soil erosion and subsequent offshore delivery of land‐derived material during the past five centuries (Maselli & Trincardi, ). This is attested by the very low forested fraction of usable land as a consequence of forest clearance (Figure e) at ~1500 C.E.…”

Ephemeral rollover points and clinothem evolution in the modern Po Delta based on repeated bathymetric surveys

“…The modern Po Delta is one of the largest Mediterranean deltas (Maselli & Trincardi, ). Following the end of the Little Ice Age, a growth rate of 47 m/year is reported for the Po di Pila lobe, after 1886 AD (Correggiari, Cattaneo, & Trincardi, ; Correggiari et al, ), when the anthropic E‐W straightening of the main branch of the Po River was carried out to protect the delta plain from flooding (Visentini & Borghi, ).…”