Integrated assessment of climate change impacts on transitional waters and the role of nature-based solutions in regulating water quality

Transitional environments are particularly susceptible to multiple pressures like climate change, land use or pollution that can lead to the deterioration of their water quality (WQ) and ecosystem services. Nature-based solutions (NBS) can be implemented as adaptation strategies essential for maintaining WQ regulation. Numerical models offer valuable support to understand the WQ dynamics of transitional environments and the influence of NBS, together with the evaluation of the effects induced by interacting stressors and different management schemes. The Venice lagoon is a transitional environment of great ecological and socio-economic value where NBS are at play through salt marsh restoration programs. A literature review revealed that current assessments and modelling approaches of the effects of NBS on WQ are characterized by the analysis of short-term observations, lack of integration of multiple ecosystem processes, as well as limited consideration of catchment scale management strategies. Considering these challenges, a new WQ modelling system will be developed for the Venice Lagoon by integrating a vegetation module for saltmarshes into an existing coupled hydrodynamic-biogeochemical model. The vegetation module will represent the effects of NBS, i.e. saltmarshes restoration measures, in order to evaluate their role and effectiveness in regulating WQ through their influence on the hydrodynamics, as well as the nutrient and carbon cycle associated with the distribution, growth, and mortality of saltmarsh vegetation. Onsite monitoring of WQ indicators linked to eutrophication processes in relation to climate-related stressors, hydro-morphodynamic processes, and implementation of restoration activity will be utilized to support and validate the modeling methodology. For this purpose, automatic recording instruments with high temporal resolution have already been placed providing data on different WQ parameters that can be related to hydrodynamic conditions and the ongoing restoration activities. Furthermore, the designed model will support the evaluation of WQ changes in the Lagoon against future climate change scenarios and several ‘what-if’ scenarios representing different NBS, thereby informing management and adaptation decision-making processes.  Keywords Climate change impacts, multi-hazards, transitional ecosystem, water quality, eutrophication, integrated modelling, nature-based solutions, salt marshes, biogeochemistry, Venice Lagoon