Share Stelvio - Case Study 2

L. Rosole (Forni Glacier – 2441m)

Another lake was considered in detail, Lake Rosole, located in the vicinity of the Shelter Branch at the foot of Forni Glacier. The lake is shallow (<2 m) and is therefore subject to silting due to lack of water supply, with turbid waters during the ice-free period and maximum measured temperatures reaching ~23°C, unusual for alpine lakes.

Macroinvertebrates are mainly constituted by Oligochaetes (94% ± 2.6%), chironomid larvae (4% ± 1.5%) and Coleopterans (2.3% ± 1.1%), with different abundances along the littoral or in the deep zone. Among Oligochaetes, the genera Cognettia and Nais dominated, while Chironomus prevailed among chironomids. The stronger presence of oligochaetes, as well as the almost exclusive presence of chironomini tribu, is clearly due to the high RP (23 µg P L^-1), TP (54 µg P L^-1), and TOC (1,5 mg C L^-1) values and to the considerable temperatures that the lake maintains during summer.

Notable the presence of Paranais litoralis, euryhaline species able to withstand considerable variations in salinity, and therefore characteristic of brackish and marine waters. Its presence at these altitudes suggests salinity variations related to climate change with strong fluctuation level due to rising temperatures and evapo-transpiration, which tends to concentrate water solutes. Pristinella idrensis (o Pristina (P.) jenkinae) is, on the other hand, indicator of allochthonous organic matter accumulation, associated with muddy and sandy substrates, and of the presence of submerged vegetation.

These last findings are in agreement with the dominance of Microcostatus krasskei (38%) in the epilithic diatom community. This is an aerophilic species that occurs primarily on lithic pseudoaerial substrates and that seems to prefer acidic habitats in cool temperate climates.