Stato attuale delle ricerche bio-ecologiche sui laghi vulcanici dell'Italia centrale

The volcanic lakes constitute the major part of the lacustrine environments in Central Italy. In the last century these lakes were exposed to various disturbances caused by urbanization, agricultural activities, domestic discharges and recreational use. Due to their small watershed and great water renewal time, they can be considered as very sensitive to degradation and their major suffering problems are eutrophication, hypolimnetic deoxygenation, meromixis and lowering of water level. We report here some biological data collected in the last decades on five volcanic lakes with the aim of evaluating their present trophic status by means of some biological parameters of all the lacustrine communities useful to detect water quality changes and suggesting some monitoring guidelines to enhance conservation and managing policies of the lakes. In a trophic scale, Lake Bracciano revealed the most oligotrophic characteristics, due to the presence of an o-ring waste water collecting system, its large size and depth, and the strong hydrodynamism. Lake Martignano follows in the rank, with some symptoms of stress in the hypolimnion due to a marked summer deoxygenation. Lake Vico, which showed in the past decades a mesotrophic condition with clear signals of increasing trophy and oxygen depletion in the profundal, have a trend towards meso-eutrophy. Lake Albano showed meso-eutrophic conditions with the total absence of fauna below 120 m depth due to a meromictic status, also evidentiated by palaeolimnological studies. Finally, in the 70ies Lake Nemi was subject to domestic waste water discharges which led to heavy eutrophication with dramatic algal blooms and fish kills. In the last decade a partial improvement in many ecological characteristics of the lake seemed to take place, following the discharges diversion.