Figure from:Different performances of independent sediment biological proxies in tracking ecological transitions in a small sub-alpine lake since the Little Ice Age

See full PDF downloadDownload figure

Table 2 Major environmental and socio-economical events which affected Lake Ledro and its catchment during the study period (1689+9 - 2011).

Related Figures (12)

Lake Ledro (45° 52’ N, 10° 45’ E, 652 m a.s.l.) is a small lake (area = 3.7 km? » Lina = 49 m, Table 1) of glacial origin located in the Italian Alps, close to Lake Garda (Fig. 1). The large catchment area (111 km’) includes mountains culminating at 2254 m a.s.l.. The bedrock is composed of Triassic dolomite and Jurassic and Cretaceous limestones, while alluvial deposits of calcareous and siliceous composition fill the bottom of the tributary valleys. Two temporary tributaries feed the lake: the Massangla and the Pur rivers (Fig. 1). The combination between _ torrential forced through a pumped-storage power plant RPS as eee: ae oe ee a oe last one in AD 1920, possibly in relation to climate change, land use, and protective interventions on the main lake tributaries (Simonneau et al., 2013). The lake outlet, River Ponale, originally flowed into nearby Lake Garda (65 m a.s.l.), while it is inactive since AD 1929 due to the lake hydroelectric exploitation (Table 2). Lake water enters an underwater pipe located at 25 m depth, is forced through a pumped-storage power plant

and its catchment. Table 1 Geo-morphological features of Lake Ledro and its catchment.

Fig. 2 Depth profiles of geochemical proxies and subfossil pigment concentrations in the master core collected from Lake Ledro in 2011. PI1-PI4 = homogeneous pigment zones, Sed. rate = sedimentation rate, H2O = water content, WD = wet density, OM = organic content, CD = chlorophyll derivates, IsoBac = ¥-carotene (often associated to bacteria), Car-pH and Car-TP = past lake water pH and TP concentrations as inferred from the ratio of spectrophotometric absorbances at 430 and 410 nm, and from total carotenoid concentrations, respectively. “Am), and a minor one at 10.25 cm, which

minimum values concomitant with the major Fig. 3 Depth profiles of diatom concentration, key species, ecological classification, Shannon index and inferred TI concentrations in the master core collected from Lake Ledro in 2011. DI1-DIS = homogeneous pigment zones, } DW-1 = number of valvae per unit of dry matter DAR = diatom accumulation rate, unic cent = unicellular centrics fil cent = filamentous centrics, unic penn = unicellular penntes, colo penn = colony forming pennates, Oligo - oligortraphentic, Meso = meso to meso-eutraphentic, Eu = eu- to hypertraphentic, Tol = tolerant, N. Cl. = no classified. DI-TP = diatom based lake TP concentrations obtained respectively from the NW-European (NW-Eu Bennion et al., 1996) and Combined (Comb-eu, Battarbee et al., 2001) calibration sets by applying a weightec average model with inverse deshrinking and downweighting of species tolerance. Range standard error of TI reconstruction = 1.2-2.0 ug L’! for the NW-Eu and 1.2-2.2 ug L" for the Comb-Eu models, respectively. between 83 and 24 cm depth concentration and water content (Fig. 2). In the core section

Fig. 4 Depth profiles of subfossil Cladocera total abundance, key species, ecological classification, and Shannon Index in the master core collected from Lake Ledro in 2011. LC1-LC3b = homogeneous Cladocera zones. Alona affinis (Leydig) were identified in this

period total cladocera abundance reached its

Fig. 5 Samples scores on the two dimensions (DIM1 and DIM2) of the NMDS ordinations based on subfossil pigments, diatoms and Cladocera plotted against air temperature and atmospheric precipitation recorded at the station of Riva del Garda since 1870 and at the station of Bezzecca since 2002. DI-TP = diatom inferred lake TP concentrations. WWI = World War I, Stars indicate the floods event of 1920 and 1966, the rainy 1996 and the hot 2003. Vertical lines mark major changes in NMDS samples scores.

Table 4. Spearman correlation coefficients between samples score on the two dimensions (DIMI and DIM2) of the NMDS ordinations relative to subfossil pigments (PI), diatoms (DI) and Cladocera (CL) and independent sediment proxies (n = 113) and climatic variables (n = 50) recorded at the station Riva del Garda (HISTALP webpage, 2013), respectively. WD = wet density, PI-pH = pigment inferred water pH, DI-TP = diatom inferred lake total phosphorus concentration, Ann. Air Temp. = Annual average air temperature, Air Temp MM and AS = mean air temperature for the periods March-May and April-September, Ann. Precipitation = cumulative annual precipitation, Precip. JA = precipitation in the period June-August. ** = p<0.001, * = p<0.1, n.s. = not significant. Ann. Air Temp. = Annual average air temperature, Air

Discussion Table 5. Level of significance of environmental and longispina, while all the most abundant key