Modellizzazione delle condizioni di riferimento

The Guidance Documents for setting reference conditions for rivers and lakes states that in the case of a small number of water bodies, mainly affected by human impact, reference condition should preferably be modeled. However, in the ECOSTAT activity and in the Italian legislation, the (discouraged) spatial approach was adopted. To verify if there are differences in the results given by those two approaches, in this report we used two general models of lake eutrophication to evaluate phosphorus reference conditions for all relevant Italian lakes. Furthermore, we used the relationships between phosphorus concentration and two quality index (chlorophyll concentration and PTI index) to estimate reference conditions for phytoplankton. The results of the exercise showed that the spatial approach was realistic, but one of the Italian phytoplankton indices (PTIspecies) is probably too stringent for the large deep lakes. For the Mediterranean shallow lakes, we also suggest a case-by-case evaluation of the reference conditions using specific models or paleolimnological tools, in order to avoid unrealistic restoration targets. Finally, the relationships between phosphorus concentration and the indices based on other biological quality elements (macrophytes, benthic invertebrates and fish fauna) were not strong enough to allow their prediction using these simple models, because these communities have complex response to multiple stressors, such as water quality, shore integrity and water level modifications.