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Natural and anthropogenic changes in a lake-forest system in Bukovina (Romania) since 1340 AD documented by sedimentary organic geochemistry (C, N and n-alkanes)

Karlik, Máté, Fekete, József, Mindrescu, Marcel, Grădinaru, Ionela, Bozsó, Gábor, Bíró, Lóránt, Kern, Zoltán
Quaternary international 2018 v.493 pp. 166-175
C3 plants, afforestation, algae, alkanes, anthropogenic activities, carbon, cold, deforestation, embryophytes, geochemistry, ice, lakes, landscapes, nitrogen, nitrogen content, organic matter, pastures, sediments, stable isotopes, vegetation, watersheds, Carpathian region, Romania
Lake Bolătău-Feredeu is a small (surface: 0.3 ha; catchment area: 31 ha) landslide-dammed lake in Bukovina (Eastern Carpathians, Romania). Elemental concentration, stable isotope composition of carbon and nitrogen, and n-alkane composition of the saturated hydrocarbon fraction of the organic material were analyzed along the sediment profile from Lake Bolătău-Feredeu covering the past ∼700 years. The ranges of δ¹³C values (−30.5 to −26.6‰) and C/N atomic ratios (10.5 and 15.4) placed the organic material of the recent Bolătău-Feredeu sediment between the C3 Land Plants and the lacustrine algae. The n-alkane proxies provide better distinction between organic matter inputs. Detected major shifts in the n-alkane composition and the C and N concentrations along with the stable isotope compositions pointed towards three distinct stages in the environmental history of the lake-catchment system. The proxy information indicate a substantial landscape change characterized by deforestation and an increase in open pastureland with herbaceous vegetation from ∼1820. The C/N, δ¹⁵N, and δ¹³C values showed the highest variability probably linked to a variable lacustrine environment and decreased productivity in the catchment between ∼1640 and 1760. It can be assumed that the extended periods of lake ice cover during the cold decades experienced at the turn of the 17ᵗʰ-18th centuries resulted in diminished biological productivity both in the lake and its catchment. Finally, afforestation and the decline in lake productivity have been reconstructed for the period of ∼1470–1560.