Conceptualizing a multi-risk Bayesian Network model to identify nature-based management solutions to face water quality degradation in a changing climate

Water quality (WQ) deterioration in marine-coastal areas (MCA) is among the main threats affecting socio-economic systems and ecosystem functioning, calling for urgent actions to preserve ecosystems’ resilience. Nature-based Solutions (NBS) improve ecosystem resilience and biodiversity, transforming nature management while providing environmental and societal benefits. Yet, little is known on NBS capacity in reducing WQ deterioration due to climate and human-induced pressures in MCA. Understanding this nexus requires establishing functional relationships between marine ecosystems status and climate and human drivers exerting pressures over them. In this study, the relationship between climate change (CC) impacts on marine-coastal ecosystems is unravelled through a spatio-temporal Bayesian Network (BN) model, which allows estimating the adverse effects of human-induced and climate pressures on seagrass meadows (Posidonia oceanica) along the Apulia region coast (Italy). To this aim, both anthropogenic (e.g., land use, MPAs) and environmental data (e.g., nutrients, temperature, transparency, depth, etc.) were integrated in the BN model, and jointly combined at the coastal water bodies scale, as framed within the WFD, and elicited by expert knowledge. Baseline environmental conditions were compared against multiple ‘what-if’ scenarios, representing different climate conditions, under RCP4.5 and 8.5, and nature-based management schemes. Key results emphasize the main variables (and the spatial extent) affecting the status of seagrass meadows, primarily depth, water transparency, and the presence/absence of protection actions along MCA, both on land and sea. On the other hand, results from scenario analysis highlight that under RCP4.5 the environmental conditions remain more suitable for seagrass habitat survival and growth, compared to RCP8.5 in both short (2050) and long (2100) term. Furthermore, the integration of management actions, primarily linked to land-use changes and widening of MPAs, would benefit WQ conditions for Posidonia oceanica health status, while contributing to achieve the Sustainable Development Goals (as part of Agenda 2030), and the Good Environmental and Ecological Status as required by relevant EU acquis.