Dept. of Animal and Human Biology, Univ. "La Sapienza" Viale dell'Università 32, 00185, Rome Italy

*Corresponding author: luciana.mastrantuono@uniroma1.it

Abstract

   Lake Nemi was subjected from the 1970s to organic pollution due to domestic wastes, which led to a severe eutrophication process. Local authorities consequently planned a gradual waste diversion programme completed in 1990. Comparison between data on plant-associated invertebrates in the period of maximum eutrophication (1981/82) and twenty years after the total waste diversion (2001/02) was carried out with the aim of demonstrating the performance of this littoral community for the purpose of lake recovery assessment. Following the water clarity improvement characterizing the 2001/02 period, the macrophyte community displayed an amelioration in plant diversification, an enlargement of the colonized area, and an appearance of Charales, important bioindicators of oligotrophic conditions. In complete agreement with this new situation, the invertebrate fauna extended its colonization, and the species composition and quantitative structure changed completely. A considerable increase in species richness and diversity, and significant modifications of percentages and densities of bioindicator taxa (cladocerans, gastropods and acari) showed a very appreciable recovery, which can be defined as a phase of “oligotrophication”. This trophic state is closely related to nutrient reduction in the water, enhanced by a drift of organic materials from littoral to profundal bottoms due the remarkable water level reduction of about five meters occurred in the lake in recent times.