Tracing recent geochemical sediment properties in subalpine lakes using wavelength-dispersive X-ray fluorescence spectroscopy (XRF): understanding regional patterns of recent lake development
(English)Manuscript (preprint) (Other academic)
The sedimentary geochemical records of two subalpine lakes (Lake Garda and Lake Ledro) in northern Italy were analyzed and explored using wavelength-dispersive X-ray fluorescence spectroscopy (XRF). The aim of the study was to investigate how human impact and environmental changes have affected the geochemical record of the two lakes and their catchments, in comparison to existing paleolimnological evidence based on biological proxies. Sediment cores were collected from the deepest points of the two basins of Lake Garda (Brenzone and Bardolino) and Lake Ledro, and chronologies were established using radioisotopic dating (210Pb and 14C). In Brenzone, the main basin of Lake Garda, a pronounced shift in elemental composition occurred in the mid-1900s, when major elements (Mg, Al, K) and lithogenic tracers (Ti) start to decrease, while some elements related to redox conditions (Mn, P) and other (contaminant) trace elements (Pb) increase. Bardolino, the shallower and smaller basin of Lake Garda, shows to some extent comparable shifts (Mg, Al, K, Ti, Pb), but some elements show deviating patterns such as those influenced by changing redox (Mn, P). Lake Ledro shows in general higher short-term variability for most elements, even though some features are comparable (Pb) to Brenzone and Bardolino. Overall, the geochemical record reveals a general change in Lake Garda since the mid-1900s, which is in good agreement with the biological records (diatoms, Cladocera, pigments). The differences recorded in the two basins of Lake Garda reflect the effects of local conditions, both related to hydrology and sedimentation patterns. In contrast, the more variable geochemical record of Lake Ledro is mainly affected by human-induced lake-level fluctuations and the effects of the relatively large catchment. This study reveals the importance of the ratio between lake area and catchment area on the lake geochemical records. The sediment records from large and deep lakes seem to be more affected by direct impacts of nutrient enrichment and/or climate change than the changes within the catchment area. On the other hand, small lakes with larger catchment areas are to a larger extent influenced by the modifications occurring in the drainage basin.
Paleolimnology, Geochemistry, Wavelength-dispersive X-ray fluorescence spectroscopy, Lake Garda, Lake Ledro
Earth and Related Environmental Sciences
IdentifiersURN: urn:nbn:se:umu:diva-115193OAI: oai:DiVA.org:umu-115193DiVA: diva2:899043