Share Stelvio - Case Study 1

L. Bianco (Gavia mountain Pass – 2608m): past and present situation

Lake Bianco was one of the few lakes on which the interest of researchers was addressed since 1975, both as regards macroinvertebrates and hydrochemistry. The lake, of glacial origin, is located near the Gavia mountain Pass below the former Glacier of L. Bianco, who supply waters to the lake throughout the year. In this lake, researches were conducted aimed at deepening knowledges on benthic fauna and on hydrochemistry, to compare current with past data to identify any influence of the Glacier and of its retreat with time. A comparison was conducted among macroinvertebrates’ densities, belonging to samples taken at the maximum depth (~8 m) in 1975 and in 2011. Compared to the past, chironomids show remarkably high density (6500 ind m^-2), while oligochaetes, caddis flies and beetles have lower values.

The present situation is certainly index of a trophic increase, justified by the organic matter enrichment derived from the catchment, and by the natural evolution of the lake (lake ontogeny) toward a terrestrial condition due to vegetation, which affects in particular the western shore, as well as by the increase in temperatures not any more influenced by the glacier. The dominance of chironomids over Oligochaetes, is typical of oligotrophic lakes and makes clear that, although the lake is silting, its waters still remain in a low trophic level, even if higher than in the past. The increasing export of solutes from the catchment is confirmed by chemical analysis: previous data available for this lake (1981) showed remarkably lower concentrations of the major ions (calcium, magnesium, bicarbonates) with respect to recent years (2011-2012).

	1981	2011
-	-	-
pH	6,9	7,6
Cond. (µS cm-1)	24	72
Alk (µeq L-1)	90	250
Ca (mg L-1)	2,5	7,1
Mg (mg L-1)	0,8	3
Na (mg L-1)	0,3	0,7
K (mg L-1)	0,6	1,2
RSi (mg L-1)	0,6	0,8