Salt marshes are important coastal habitats and provide ecosystem services to surrounding communities. They are, however, threatened by accelerating sea-level rise and sediment deprivation due to human activity within upstream catchments, which result in their drowning and a reduction in their extent. Rising seas are also leading to an expansion of coastal flooding protection infrastructures, which might also represent another serious if poorly understood threat to salt marshes due to effects on the resuspension and accumulation of sediment during storms. Here, we use observations from the Venice Lagoon (Italy), a back-barrier system with no fluvial sediment input recently protected by storm-surge barriers, to show that most of the salt-marsh sedimentation (more than 70% in this case) occurs due to sediment reworking during storm surges. We also prove that the large, yet episodic storm-driven sediment supply is seriously reduced by operations of storm-surge barriers, revealing a critical competition between the objectives of protection against coastal flooding and preservation of natural ecosystems. Without complementary interventions and management policies that reduce barrier activations, the survival of coastal wetlands is even more uncertain.
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All data are available at http://researchdata.cab.unipd.it/id/eprint/416. Meteorological data are also available at https://www.comune.venezia.it/content/dati-dalle-stazioni-rilevamento and https://www.venezia.isprambiente.it/rete-meteo-mareografica.
We used the program MATLAB (R2020b) to generate all the results. Analysis scripts are available at http://researchdata.cab.unipd.it/id/eprint/416.
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The authors thank the technical staff of the Department of Biology and the Department of Geosciences, University of Padova, for fieldwork and laboratory analysis support. This scientific activity was performed as part of the Research Programme Venezia2021, with contributions from the Provveditorato for the Public Works of Veneto, Trentino Alto Adige and Friuli Venezia Giulia, provided through the concessionary of State Consorzio Venezia Nuova and coordinated by CORILA, Research Line 3.2 (PI A.D.) and by the 2019 University of Padova project (BIRD199419) ‘Tidal network ontogeny and evolution: a comprehensive approach based on laboratory experiments with ancillary numerical modelling and field measurements’ (PI L.C.).
The authors declare no competing interests.
Peer review information Nature Geoscience thanks Tracy Elsey-Quirk and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary Handling Editor: James Super.
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(a-c-e) organic matter accumulation (bars) and organic matter accumulation rate (solid circles); (b-d-f) organic matter as percentage of weight. The cloud symbol indicates storm periods. Data are grouped for study area: SF (a-b), SE (c-d) and CO (e-f). Alternate white and grey background indicates different observation periods.
Percentage of sedimentation (a) and percentage of time (b) related to storm events and to fair-weather conditions. Categories refer to the study areas (SF, SE and CO) and their mean (darker colour); subscripts indicate the beginning of the grouping period: O18, from October 2018 to October 2019, J19 from January 2019 to January 2020 and O19 from October 2019 to October 2020.
Comparison between measured data (grey bars), sediment accumulation modelled in the non-regulated (teal bars) and regulated scenario (yellow bars) for each study area: SF (a), SE (b) and CO (c). Alternate white and grey background indicates different observation periods, hatched background indicates periods with actual closures of flood barriers. The cloud symbol indicates storm-dominated periods.
Comparison between measured data (grey bars), vertical accretion modelled in the non-regulated (teal bars) and regulated scenario (yellow bars) for each study area: SF (a), SE (b) and CO (c). Lines represent cumulative accretion rates and black solid circles are yearly horizon marker measurements. Alternate white and grey background indicates different observation periods, hatched background indicates periods with actual closures of flood barriers. The cloud symbol indicates storm-dominated periods.
Extended Data Fig. 5 Sediment accumulation changes in the flood-regulated scenario at yearly time scale.
Change in sediment accumulation between the non-regulated (teal bars) and regulated scenario (yellow bars). Categories refer to the study areas (SF, SE and CO) or their mean. Subscripts indicate the beginning of the grouping period: O18, from October 2018 to October 2019, O19, from October 2019 to October 2020. Percentages indicate the relative change in the flood-regulated scenario with respect to the non-regulated one (see also Supplementary Tables 3 and 4).
Comparison between measured data (grey bars), modelled data in the non-regulated (teal bars) and regulated scenario (yellow bars) summed for autumnal months (October, November and December) for each study area: SF (a), SE (b), CO (c) and their mean (d). In autumn 2020 the flood barriers were used, so measurements refer to the flood-regulated condition.
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Tognin, D., D’Alpaos, A., Marani, M. et al. Marsh resilience to sea-level rise reduced by storm-surge barriers in the Venice Lagoon. Nat. Geosci. 14, 906–911 (2021). https://doi.org/10.1038/s41561-021-00853-7
Nature Geoscience (2021)