Return periods of extreme sea levels: From magnitude to frequency, duration and seasonality. Implications in a regulated coastal lagoon.

Extreme sea levels (ESLs) affect coastal ecosystems worldwide. Protection and adaptation strategies rely on the characterization of the extreme's occurrence probability in the future. However, knowledge on the occurrence rate and duration of ESLs is also needed to properly characterize the associated future risk. In this paper, we focus on the Venice lagoon, where a system of storm surge barriers can disconnect the lagoon from the sea to mitigate ESLs. Using long-term (96 years) sea level records, we model occurrence rate and duration of ESLs while accounting explicitly for seasonality and mean sea level rise. While historically ESLs occurred in the winter season, we project a significant increase (up to 10-fold with a mean sea level increase of +100 cm) of the occurrence rate also in the summer season, when disconnections from the sea can have profound impacts on the lagoon's ecosystem. We also predict an increase in ESLs durations up to 200 h, leading to longer disconnections of the lagoon from the sea in the future. Therefore, several adaptation strategies will be needed to limit the adverse effects of storm surge barriers on the lagoon ecosystem.

Changes in Macrozoobenthos Community after Aquatic Plant Restoration in the Northern Venice Lagoon (IT).

Responses of the macrozoobenthic community to an ecological restoration activity in the northern Venice lagoon were studied, within the scope of the project LIFE SEagrass RESTOration aimed at recreating aquatic phanerogam meadows largely reduced in recent decades. Transplants were successful in almost all project areas. Macrozoobenthos was sampled in eight stations before (2014) and after (2015, 2016, 2017) transplanting activities. An increase in abundance and fluctuations in richness and univariate ecological indices (Shannon's, Margalef's, Pielou's indices) resulted during the years. Comparing non-vegetated and vegetated samples in 2017, every index except Pielou's increased in the latter. Multivariate analysis (hierarchical cluster analysis, MDS, PERMDISP, SIMPER) grouped samples by localization rather than years, with differences between stations due to the abundance of common species. In 2017, results were also grouped by the presence or absence of aquatic plants, with differences in the abundance of grazer and filter-feeding species. Results of ecological index M-AMBI depicted conditions from moderate to good ecological status (sensu Dir.2000/60/EC) with similar fluctuations, as presented by univariate indices from 2014 to 2017. Responses of the macrozoobenthic community were more evident when comparing vegetated and non-vegetated samples, with the vegetated areas sustaining communities with greater abundance and diversity than non-vegetated samples, thus demonstrating the supporting function of aquatic plants to benthic communities.

Environmental restoration by aquatic angiosperm transplants in transitional water systems: The Venice Lagoon as a case study.

The paper reports the results obtained after 4 years of aquatic angiosperm transplants in areas of the Venice Lagoon (North Adriatic Sea, Mediterranean) where meadows almost disappeared due to eutrophication, pollution and overexploitation of clam resources. The project LIFE12 NAT/IT/000331-SeResto, funded by the European Union, allowed to recolonize the Habitat 1150* (coastal lagoons) in the northernmost part of the lagoon, by extensive manual transplants of small sods or single rhizomes of Zostera marina, Zostera noltei, Ruppia cirrhosa and, in some stations also of Cymodocea nodosa. Over the 4 years of the project more than 75,000 rhizomes were transplanted in 35 stations with the support of local stakeholders (fishermen, hunters and sport clubs). Plants took root in 32 stations forming extensive meadows on a surface of approx. 10 km2 even if some failures were recorded in areas affected by outflows of freshwater rich in nutrients and suspended particulate matter. The rapid recovery of the ecological status of the involved areas was the result of this meadow restoration, which was in compliance with Water Framework Directive (WFD 2000/60/EC) objectives. Moreover, the monitoring of environmental parameters in the water column and in surface sediments allowed to identify the best conditions for successful transplants. Small, widespread interventions and the participation of local stakeholders in the environmental recovery, make this action economically cheap and easily transposable in other similar environments.