Loss of geomorphic diversity in shallow tidal embayments promoted by storm-surge barriers

Abstract

Coastal flooding prevention measures, such as storm-surge barriers, are being widely adopted globally because of the accelerating rise in sea levels. However, their impacts on the morphodynamics of shallow tidal embayments remain poorly understood. Here, we combine field data and modeling results from the microtidal Venice Lagoon (Italy) to identify short- and long-term consequences of flood regulation on lagoonal landforms. Artificial reduction of water levels enhances wave-induced sediment resuspension from tidal flats, promoting in-channel deposition, at the expense of salt marsh vertical accretion. In Venice, we estimate that the first 15 closures of the recently installed mobile floodgates operated between October 2020 and January 2021 contributed to a 12% reduction in marsh deposition, simultaneously promoting a generalized channel infilling. Therefore, suitable countermeasures need to be taken to offset these processes and prevent significant losses of geomorphic diversity due to repeated floodgate closures, whose frequency will increase as sea levels rise further.

Statistical characterization of erosion and sediment transport mechanics in shallow tidal environments. Part 1: erosion dynamics

“…The WWTM has been widely tested against field observations not only in the Venice Lagoon (e.g., Carniello et al, 2005Carniello et al, , 2011Tognin et al, 2022) but also in other shallow microtidal environments worldwide, for example in the back-barrier lagoons of the Virginia Coast Reserve (Mariotti et al, 2010) and the Cádiz Bay (Zarzuelo et al, 2018(Zarzuelo et al, , 2019.…”

“…However, at the same time, increased SSC, typically occurring during storm surges, can support sedimentation on salt marshes, thus helping them to keep pace with sea level rise (Goodbred and Hine, 1995;Tognin et al, 2021). Therefore, understanding BSS dynamics is fundamental to describe to morphodynamic evolution of tidal flats and to indicate long-term sustainable management strategies for shallow tidal systems (Zhou et al, 2022), which is crucial under the increasing pressure of relative sea level rise (Nicholls et al, 2021) and human interventions (Tognin et al, 2022).…”

“…Opting for such a simplified approach, long-term models ideally should be tested in tidal systems where information on the morphological evolution is available for a sufficiently long time. From this point of view, the Venice Lagoon, Italy (Figure 1) represents an almost unique opportunity to test long-term models, because several bathymetric surveys are available for the last four centuries (Carniello et al, 2009;Tommasini et al, 2019;Finotello et al, 2022).…”

Analysis of Organic Matter Decomposition in the Salt Marshes of the Venice Lagoon (Italy) Using Standard Litter Bags

“…Despite their importance, coastal ecosystems are some of the most heavily used and threatened natural systems globally, experiencing widespread loss or degradation (Barbier et al, 2011;Duarte et al, 2005;Valiela et al, 2001). Marsh ecosystems are seriously exposed to the effects of climate changes and human interferences, sea level rise and lack of available sediments being the key factors in determining salt-marsh drowning and disappearance (D'Alpaos et al, 2011;Kirwan et al, 2010;Marani et al, 2007;Morris et al, 2002;Mudd, 2011;Tognin et al, 2021Tognin et al, , 2022. Therefore, understanding of the processes regulating OM accumulation and C sequestration in salt marshes is critical to better estimate their resilience to climate change, as well as their contribution to the global carbon cycle, providing valuable information to improve management and conservation strategies (Cahoon & Guntenspergen, 2010;Couvillion et al, 2013;C.…”

Developing a framework for the assessment of current and future flood risk in Venice, Italy

“…As such, no risk assessment framework is accessible that captures the flood dynamics or allows for a comprehensive adjustment of exposure and vulnerability due to urban developments for potential long-term use of such frameworks. Flood dynamics might be altered in the future because of the operation of the MOSE barrier influencing the bathymetry and thus hydrodynamics of floods in the Venetian Lagoon (Tognin et al, 2022).…”