Interplay between natural drivers and human activities in two Northern Adriatic lagoons

Coastal wetlands are important transitional environments, providing several ecosystem services such as carbon sequestration, water filtration and habitat provision for diverse plant and animal species. At the same time, various human activities, such as fishing, aquaculture, tourism and industrial operations, are centred around coastal wetlands. Therefore, the morphological evolution of many coastal transitional systems is not only influenced by natural processes, namely tidal currents and wind waves, but also anthropogenic interventions have been playing a pivotal role in adapting the morphological features to meet the needs of human activities. For instance, extensive areas are usually confined by artificial levees for aquacultural activities, large channels are dredged and inlets are stabilized for navigation purposes. However, the long-term effects of these modifications on the morphological evolution of shallow tidal systems are still unclear and can potentially affect the ecosystem as a whole.

The aim of this work is to investigate the consequences of natural and anthropogenic drivers on two back-barrier lagoons in the northern Adriatic Sea: the Venice Lagoon and Marano-Grado Lagoon. Despite sharing a similar microtidal regime and meteorological conditions, the morphology of these systems exhibits distinct characteristics. The Venice Lagoon is about 550 km² and it is connected to the Adriatic Sea with three inlets. Its evolution has been strongly affected by human interventions, such as the construction of jetties at the inlets at the beginning of the 20^th century, the excavation of navigable channels between 1930 and 1970 and, more recently, the installation of a storm-surge barrier system, named Mo.S.E., to prevent flooding of the city of Venice. Instead, the Marano-Grado Lagoon is smaller, covering an area of 160 km², and it is relatively more pristine than the Venice Lagoon. It is connected to the Adriatic Sea with six inlets, of which only two were provided with jetties in the 20^th century, and it experienced fewer modifications of channels for navigation purposes.

We applied a 2D, finite-element model to describe the hydrodynamic flow field and the wind-wave generation and propagation in these two environments. The computational grids were built upon the most recent bathymetric survey available for each system, that is the 2017 survey for the Venice Lagoon and the 2011 survey for the Marano-Grado Lagoon. We then performed an extensive calibration of the model with water level and discharge data available. Results allowed us to investigate similarities and differences in the hydrodynamics of the two tidal systems, highlighting the effects of specific anthropogenic interventions on the ecosystems.