Chironomids Insecta, Diptera as Indicators of Ecological Status In Lakes

Benthic communities are used in biological assessment and monitoring in lakes. Chironomids are considered indicators of oxygen level and trophic state. The taxocoenosis of 42 Italian lakes with different volume, depth, annual minimum hypolimnetic oxygen concentration, transparency and phosphorous concentration were investigated. Larvae were collected with a Petersen grab at different depths, pupal exuviae with a drift net near the outlet of lakes and adults with a sweep net along the shore. 334 species were identified: 41 Tanypodinae, 17 Diamesinae, 3 Prodiamesinae, 118 Orthocladiinae, 155 Chironominae (61 Tanytarsini, 93 Chironomini and 1 Pseudochironomini). Drift samples included many more taxa than grab samples, adult samples often included terrestrial species. Lake Garda, Como and Maggiore were the richest in species (78, 72 and 66 respectively), as expected because of their large size. Species richness did not result as good indicator: both oligotrophic (Monate 52 species, Toblino 33) and eutrophic lakes (Annone 57, Pusiano 42) were characterized by similar species numbers. Different species were indicator of different oxygen concentration more than nutrients. A comparison of different lakes is limited because of: 1. different morphometric and trophic conditions; 2. different sampling effort; 3. lack of knowledge of species optima and tolerance.