Vulnerability of tidal morphologies to relative sea-level rise in the Venice Lagoon.

The rise in sea level and land subsidence are seriously threatening the diversity of tidal morphologies that have made the Venice Lagoon such a distinctive landscape. Here, we assess the vulnerability of tidal morphologies to relative sea-level rise based on a new conceptual framework that accounts for both above- and below-sea-level zones, sedimentary architecture, and surface morphology. Around 80 % of the lagoon area will face moderate to severe vulnerability by 2050, doubling compared to the 1990s. While the subtidal zone may be relatively less threatened compared to past conditions, the drastic decline in intertidal morphologies is alarming. This contributes to the flattening and deepening of the lagoon topography and thus to the loss of lagoon landscape diversity, likely leading to a decrease in the ecosystem services the tidal morphologies provide. The interconnection of intertidal and subtidal morphologies is crucial for maintaining the overall health and functionality of the lagoon's ecosystem. Any disruption to one aspect can have ripple effects throughout the entire system.

Salinity origin in the coastal aquifer of the Southern Venice lowland.

Groundwater salinization can be natural and anthropogenic in origin, although it often results from a combination of both, especially in low-lying coastal regions that are hydraulically controlled. This study proposes a method to assess the origin of salinity using environmental tracers in porewater, like Cl- and Br-, combined with depositional facies associations detected in sediment cores. Such integrated approach was tested in a target area south of the Venice Lagoon (Italy), where groundwater salinization is triggered by multiple mechanisms due to the complexity of the hydro-geomorphological environment. Batch tests were performed on sediment core samples from boreholes to quantify major anions and total inorganic N. Cl- and Br- porewater concentrations coupled with sedimentary facies association provided insights into the origin of groundwater salinity from a variety of sources, including past and present seawater intrusion, agricultural leaching, and evaporites. The strengths and limitations of the integrated approach are discussed to provide a pathway for improving water resource management and planning measures to prevent groundwater salinization in coastal areas.

The Crotone Megalandslide, southern Italy: Architecture, timing and tectonic control.

Large-scale submarine gravitational land movements involving even more than 1,000 m thick sedimentary successions are known as megalandslides. We prove the existence of large-scale gravitational phenomena off the Crotone Basin, a forearc basin located on the Ionian side of Calabria (southern Italy), by seismic, morpho-bathymetric and well data. Our study reveals that the Crotone Megalandslide started moving between Late Zanclean and Early Piacenzian and was triggered by a contractional tectonic event leading to the basin inversion. Seaward gliding of the megalandslide continued until roughly Late Gelasian, and then resumed since Middle Pleistocene with a modest rate. Interestingly, the onshore part of the basin does not show a gravity-driven deformation comparable to that observed in the marine area, and this peculiar evidence allows some speculations on the origin of the megalandslide.

Land subsidence in the Friuli Venezia Giulia coastal plain, Italy: 1992-2010 results from SAR-based interferometry.

Land subsidence is a concern in many coastal plains worldwide, particularly in the low-lying areas already facing sea level rise due to climate change, and much still needs to be done, with respect to both mapping land subsidence and gaining a comprehensive understanding of the relevant cause-effect relationships. Land subsidence of the northern coastal plain encompassing the Friuli Venezia Giulia (FVG) region in Italy, remains, to the authors' knowledge, poorly investigated. This coastland includes low-lying agricultural and urban areas and highly valuable lagoon environments, archaeological and touristic sites, and industrial zones. Here, we resolve land subsidence in the coastal plain between the Tagliamento River delta and the Isonzo River mouth over the period 1992-2010 using Envisat ASAR and ERS1/2 interferometric datasets. We identify a large variability of the land subsidence and a spatial gradient that ranges from less than 1mm/year in the high southwestern plain toward the littoral to more than 5mm/year close to the Tagliamento River delta. A comparison between the 2003-2010 and 1992-2000 sinking rates depicts quite similar behaviors of the process over the two time spans. The analysis indicates unclear correlations between ground movements and the typical driving mechanisms acting in the north Adriatic coastal plains, such as the variability of the morphological setting, the subsoil characteristics and the land use. We reason that multi-component mechanisms contribute to the observed image of the subsidence in the FVG coastland. Specifically, anthropogenic activities, e.g., groundwater exploitations, hydraulic reclamations and the development of newly built-up areas, are superposed to natural mechanisms related to the spatial variability of the subsoil characteristics, typical of transitional coastal environments.

Paleochannel and beach-bar palimpsest topography as initial substrate for coralligenous buildups offshore Venice, Italy.

We provide a model for the genesis of Holocene coralligenous buildups occurring in the northwestern Adriatic Sea offshore Venice at 17-24 m depth. High-resolution geophysical surveys and underwater SCUBA diving reconnaissance revealed meandering shaped morphologies underneath bio-concretionned rocky buildups. These morphologies are inferred to have been inherited from Pleistocene fluvial systems reactivated as tidal channels during the post- Last Glacial Maximum transgression, when the study area was a lagoon protected by a sandy barrier. The lithification of the sandy fossil channel-levee systems is estimated to have occurred at ca. 7 cal. ka BP, likely due to the interaction between marine and less saline fluids related to onshore freshwater discharge at sea through a sealed water-table. The carbonate-cemented sandy layers served as nucleus for subsequent coralligenous buildups growth.

Saltwater contamination in the managed low-lying farmland of the Venice coast, Italy: An assessment of vulnerability.

The original morphology and hydrogeology of many low-lying coastlands worldwide have been significantly modified over the last century through river diversion, embankment built-up, and large-scale land reclamation projects. This led to a progressive shifting of the groundwater-surficial water exchanges from naturally to anthropogenically driven. In this human-influenced hydrologic landscape, the saltwater contamination usually jeopardizes the soil productivity. In the coastland south of Venice (Italy), several well log measurements, chemical and isotope analyses have been performed over the last decade to characterize the occurrence of the salt contamination. The processing of this huge dataset highlights a permanent variously-shaped saline contamination up to 20km inland, with different conditions in relation with the various geomorphological features of the area. The results point out the important role of the land reclamation in shaping the present-day salt contamination and reveal the contribution of precipitation, river discharge, lagoon and sea water to the shallow groundwater in the various coastal sectors. Moreover, an original vulnerability map to salt contamination in relation to the farmland productivity has been developed taking into account the electrical conductivity of the upper aquifer in the worst condition, the ground elevation, and the distance from salt and fresh surface water sources. Finally, the study allows highlighting the limit of traditional investigations in monitoring saltwater contamination at the regional scale in managed Holocene coastal environments. Possible improvements are outlined.

The secret gardener: vegetation and the emergence of biogeomorphic patterns in tidal environments.

The presence and continued existence of tidal morphologies, and in particular of salt marshes, is intimately connected with biological activity, especially with the presence of halophytic vegetation. Here, we review recent contributions to tidal biogeomorphology and identify the presence of multiple competing stable states arising from a two-way feedback between biomass productivity and topographic elevation. Hence, through the analysis of previous and new results on spatially extended biogeomorphological systems, we show that multiple stable states constitute a unifying framework explaining emerging patterns in tidal environments from the local to the system scale. Furthermore, in contrast with traditional views we propose that biota in tidal environments is not just passively adapting to morphological features prescribed by sediment transport, but rather it is 'The Secret Gardener', fundamentally constructing the tidal landscape. The proposed framework allows to identify the observable signature of the biogeomorphic feedbacks underlying tidal landscapes and to explore the response and resilience of tidal biogeomorphic patterns to variations in the forcings, such as the rate of relative sea-level rise.

Vegetation engineers marsh morphology through multiple competing stable states.

Marshes display impressive biogeomorphic features, such as zonation, a mosaic of extensive vegetation patches of rather uniform composition, exhibiting sharp transitions in the presence of extremely small topographic gradients. Although generally associated with the accretion processes necessary for marshes to keep up with relative sea level rise, competing environmental constraints, and ecologic controls, zonation is still poorly understood in terms of the underlying biogeomorphic mechanisms. Here we find, through observations and modeling interpretation, that zonation is the result of coupled geomorphological-biological dynamics and that it stems from the ability of vegetation to actively engineer the landscape by tuning soil elevation within preferential ranges of optimal adaptation. We find multiple peaks in the frequency distribution of observed topographic elevation and identify them as the signature of biologic controls on geomorphodynamics through competing stable states modulated by the interplay of inorganic and organic deposition. Interestingly, the stable biogeomorphic equilibria correspond to suboptimal rates of biomass production, a result coherent with recent observations. The emerging biogeomorphic structures may display varying degrees of robustness to changes in the rate of sea level rise and sediment availability, with implications for the overall resilience of marsh ecosystems to climatic changes.

The secret gardener: vegetation and the emergence of biogeomorphic patterns in tidal environments.

The presence and continued existence of tidal morphologies, and in particular of salt marshes, is intimately connected with biological activity, especially with the presence of halophytic vegetation. Here, we review recent contributions to tidal biogeomorphology and identify the presence of multiple competing stable states arising from a two-way feedback between biomass productivity and topographic elevation. Hence, through the analysis of previous and new results on spatially extended biogeomorphological systems, we show that multiple stable states constitute a unifying framework explaining emerging patterns in tidal environments from the local to the system scale. Furthermore, in contrast with traditional views we propose that biota in tidal environments is not just passively adapting to morphological features prescribed by sediment transport, but rather it is 'The Secret Gardener', fundamentally constructing the tidal landscape. The proposed framework allows to identify the observable signature of the biogeomorphic feedbacks underlying tidal landscapes and to explore the response and resilience of tidal biogeomorphic patterns to variations in the forcings, such as the rate of relative sea-level rise.