Water Quality Assessment in the Venice Lagoon Watershed with Multiple Modelling Approaches

Over the last 20 years a series of research projects analysed water quality issuesof the Venice Lagoon and its watershed (VLW). The policy framework was relatedto the implementation of the Italian special law for the safeguarding of Venice anda series of European regulations, including the Nitrate and the Water Frameworkdirectives and the Common Agricultural Policy (CAP). The main focus was ondiffuse pollution from agricultural sources - nitrogen and phosphorous in particular -with the aim of assessing the impacts of current and alternative cultivation andlivestock practices. Many different modelling approaches were adopted, rangingfrom cognitive mapping for expert knowledge elicitation, to deterministicmechanistic models at different scales and Bayesian Belief Networks.One general evidence of the long term research efforts is that there is not a singleor best modelling solution to the water management issues of the VLW. Instead,trade-offs between different approaches are always evident, for example in thedata needs, management of complexity and uncertainty, on one side, andknowledge transfer, communication and policy support on the other. Therefore,integration of multiple models is required. In particular a two step procedure issuggested for combining qualitative and quantitative knowledge and tools within aparticipatory process for policy and decision making.