Different performances of independent sediment biological proxies in tracking ecological transitions and tipping points of a small sub-alpine lake since the Little Ice Age

• A comparative study of independent geochemical and biological proxies was carried out on a short (83 cm) sediment core collected in 2011 from the deepest point of a small subalpine Lake Ledro (Trentino, N-Italy). The aim of the study is to compare the capability of subfossil photosynthetic pigments, diatoms and Cladocera in tracking lake ecological transitions and tipping points related to major environmental perturbations occurred during the last three centuries, i.e. after the culmination of the Little Ice Age in the Alpine region. In relation to the sparse neo-limnological and climate data available for the lake, the study aims also at defining of the lake trophic and ecological reference conditions, at improving the reconstruction of the nutrient enrichment process during the last decades, and at evaluating the effects of restoration measures initiated in the 1990s. The analysis of the selected proxies outlined a pronounced sensitivity of Lake Ledro to hydrological variability throughout the whole time span considered, especially during the 18th and 19th century, and revealed two major stages in the ecological evolution of the lake, which were mainly controlled by climate related hydrological variability and lake nutrients. The results largely agree with the hypothesis that responses of sediment biological proxies to different natural and human stressors may differ in type, timing and magnitude. Subfossil pigments, diatoms and Cladocera showed a comparable capability in tracking ecological transitions and tipping points related to lake hydrology and nutrient variability, while only diatoms demonstrated a certain capability to track changes in water temperature of the lake studied. The strong response of planktonic organisms to hydrological variability depends on the peculiar catchment and lake morphology, and confirmed that planktonic organism principally respond to climate variability in an indirect way. The reconstruction of the trophic development of Lake Ledro during the last decades revealed that the vulnerability of the lake toward climate and land use driven hydrological variability is congenital for the lake, though at present it is masked by nutrients. This stresses the necessity to maintain and improve the control of nutrient inputs also in reoligotrophicated subalpine lakes, in relation to the present context of human use and climate change, and paying particular attention to the lake-specific sensitivity to local forcings.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences (hsv//eng)

NATURVETENSKAP  -- Biologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences (hsv//eng)

Nyckelord

Paleoecology

Multi-proxy

Diatoms

Cladocera

Subfossil pigments

Ecological transitions

Lake Ledro

Publikations- och innehållstyp

vet (ämneskategori)

ovr (ämneskategori)