A biotic index using benthic macroinvertebrates for Italian lakes

A trophic status index was calculated ranking percentage oxygen saturation (O2 %sat), transparency (transp) and total phosphorus (TP). The means of O2 %sat, transp and TP weighted by the species abundances were calculated to have optimum values for each species; a benthic quality index was then obtained by multiplying the weighted means of O2 %sat, transp and TP by species abundances and dividing the product by the total number of specimens present at each station. A significant correlation was observed between trophic status and the benthic quality index. A good agreement was also observed between the indexes calculated using the large database and the second dataset on small lakes.