The Pontine Marshes: An integrated study of the origin, history, and future of a famous coastal wetland in Central Italy

The Pontine Marshes (Central Italy) are known for their long drainage history starting early in Roman times and culminating in their reclamation (bonifica integrale) by the Fascist's regime under Mussolini, mostly in the 1930s of past century. The geology of this coastal wetland and causes for its drainage problems received limited attention till recently. We reviewed results from recent studies, identified still existing knowledge gaps and performed additional research to fill these, to produce a full description of the Holocene history and drainage of these marshes. Massive coring data that served to map the soils and surficial geology, observations in archaeological excavations, analytical data on soil and sediment characteristics, and radiocarbon datings allowed us to distinguish several phases in this history, with a main break in the early Roman Republican period with the first systematic drainage works. Earlier, natural processes brought about by sea level rise largely controlled its drainage. Once artificial drainage started, soil subsidence became an important process, aggravating the drainage problems. The bonifica introduced mechanical drainage, temporarily masking the impacts of subsidence. We quantified the historical subsidence using DTMs and developed scenarios for the impacts of sea level rise and subsidence in 2100 and 2200, assuming that this rise will be mitigated by a coastal defence system and enhanced capacity of the mechanical drainage. Our results demonstrate the important role of soil subsidence throughout the history of this wetland and need to include subsidence in scenarios for the impacts of sea level rise.