摘要：The ultimate aim of the Water Framework Directive (WFD 00/60/EC) is the achievement of good water status for all waters by 2015. The WFD requires water bodies to be differentiated according to types determined using either System A or System B. Both systems are based on morphometric descriptors and the predominant composition of the geological substratum. Then, for each type, reference sites regarding their ecological status must be identified through the analysis of different elements, primarily by evaluating pressures and impacts on water bodies. This paper discusses the characterization of 190 Italian lake-types (selected on the basis of size, i.e. surface area >0,5 km2) using both systems, and a method for determining their potential reference sites by analysing the pressure factors involved. The results show that System A is not suitable for Italian lakes; too high a number of types (36) emerges, and the distribution of the lakes into the various types is not homogeneous, making it difficult to identify reference sites. In contrast, the application of System B, including optional (i.e. conductivity and origin) as well as obligatory factors, makes it possible to group together the types and reduce their number. Thirteen different types, containing between 1 and 44 lakes, were identified using System B . The method developed to identify reference sites is based on the analysis of anthropogenic pressure. It was estimated from the equivalent population density (inhab. km-2) in topographic catchments and calculated using census data from ISTAT (Italian National Statistics Institute) (population, industry, animal husbandry). The equivalent population density, related to total phosphorus concentrations, enabled us to identify 5 potential reference sites, representative of 3 of the 13 types characterized (23%). The method can be regarded as a preliminary approach to identifying reference sites, but must be refined through the addition of other pressure factors and other quality elements. Another approach to identifying reference sites is based on the relation between altitude (indirect index of anthropogenic pressures) and phosphorus concentration: high-altitude lakes (above 1000 m a.s.l.) have high or good quality status and can be regarded as potential reference sites. However, the development of a suitable method for identifying reference sites must consider the receptive capacity of a water body and its specificity; the identification of reference conditions must be specific for each type, and the analysis must be based on both spatial and temporal factors.
