The guidelines for the evaluation of reference conditions of water bodies indicate that when few water bodies, mostly impacted by human activity are present, as in the case of the Italian lakes, it is not appropriate to use a spatial approach for the estimation of reference conditions, but it is preferable a modeling approach. However, the European Working Group ECOSTAT used the spatial approach for the definition of reference conditions of lakes, and these values were also adopted by the Italian law.
In the INHABIT project we used two simple statistical models to assess the reference level of phosphorus in all relevant Italian natural lakes. Then, appropriate regression equations were used to infer reference conditions for the concentration of chlorophyll and for phytoplankton-based quality indices.
This exercise showed that, at least in the case of phytoplankton, the spatial approach can be considered as correct. However, our results suggest to use the PTIot index for all the Italian lakes, discouraging the use of the PTIspecies index for large deep lakes.
In addition, in the case of Mediterranean shallow lakes of the types ME- 1 and ME -2, reference conditions should be checked lake by lake, using more complex models or paleolimnological techniques, to avoid the setting of too strict quality targets.
For the other biological quality elements, considering the lack of a direct and simple relationship between the values of the indices and the concentrations of phosphorus, it is not possible to use these simple models for the validation of reference conditions.
These results are presented in detail in deliverable D1d3.
The WFD states that the qualitative classification of water bodies should include an estimate of its accuracy and precision. We assessed the temporal variability of reference conditions by comparing the multi-decadal variability obtained from monitoring data with the paleolimnological inferences obtained through the analysis of sediment cores. In the case of the fish fauna, the spatial variability within a single water body was also examined in detail.
As regards the temporal variability of reference conditions, we found a strong sensitivity of the phytoplankton-based indices to meteorological conditions. This variability can affect lake classification and can be assessed, for example, through the activation of a network of continuously monitored reference sites, to be used for adjusting the values of the biological indices, in order to prevent natural fluctuations of trophic levels, linked to interannual weather variability, from driving fluctuations in the quality classification of lake waterbodies.
The macrophyte-based index, however, resulted less sensitive to changes in the trophic status, although the intercalibrated class boundaries appear to be too strict. In the case of fish fauna, we compared the results obtained in the classification using electrofishing and nets, and we found that the use of different tools may affect the classification of ecological status in different ways, depending on lake type.
These results are presented in detail in deliverable D1d4.