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ABSTRACTThe carbon isotope distribution and its relationship with stable N and S isotope ratio values were investigated within a fish assemblage from the shallow lake Tapeliai, which is constantly affected by inflows of 14C depleted water from the surrounding watershed mires. The “conventional” radiocarbon age within the fish from this lake varied from 119 to 693 yr. The 14C/12C and δ13C values correlated significantly (r=0.85 p<0.001), which is not typical in lakes of the temperate zone. There were no observed statistical differences (Kruskal–Wallis ANOVA tests) in the 14C/12C values among different fish species. The radiocarbon dating values and 15N/14N measurements did not correlate. The radiocarbon measurement values also did not correlate with δ34S, however, the distribution of these isotopes in carp (119 yr and 1.3‰, respectively) and roach (344 yr and 4.5‰, respectively) indicated that fish may include allochthonous food sources in their diet.

ABSTRACTIn this study, we examined how land use and urbanization changes in adjacent areas affected biological productivity and carbon cycling in a lake ecosystem over 100 years and how these changes are reflected in carbon isotope variations. We performed radiocarbon (14C) activity and stable carbon isotope ratio analysis in two organic fractions: humin and humic acids of lake sediment. Additionally, we performed pigment and diatom analysis and determined the carbonate and organic matter (OM) content in sediments. Over the last century, the estimated 14C reservoir age in both sediment organic fractions varied from 1136 ± 112 yr to 5733 ± 122 yr. The increase in the reservoir age by 1175 ± 111 yr was related with higher inputs of pre-aged organic carbon and 14C depleted hard water due to the opening of the channel connecting two lakes. Nuclear weapons tests caused an increase in the reservoir age of up to 5421 ± 135 yr and 5733 ± 122 yr in humin and humic acids, respectively. 13C values in the humic acid fraction showed a tendency to decrease, depending on the content of autochthonous versus allochthonous OM in sediments, while changes in the sources of OM had a minor impact on the stable carbon isotope composition in the humin fraction.

The distribution of metals (Pb, Cu, Cd, Ni, Cr, Zn) in surface sediments and the potential pollution sources in the south-eastern part (SE) of the Baltic Sea (Lithuanian zone) were investigated in relation to the environmental characteristics (amount of fine-grained particles, TOC content in sediments, origin of sedimentary organic matter, salinity, water depth) in 2011–2014. The higher metal concentrations were measured in sediments of the Curonian Lagoon and in the open waters. An approach using various environmental indices (enrichment factor EF, geoaccumulation index Igeoand contamination factor CF) was used to quantitatively assess a contamination degree. The principal component analysis (PCA) was applied in order to further scrutinize pollution from metal sources. The values of the contamination indices showed no/very low sediment contamination with Ni and Cr, minor–moderate contamination with Cu, Zn and Pb and moderate–considerable pollution with Cd. The strong relationships among metals suggested their similar distribution pattern and a combination of natural and anthropogenic sources. The higher metal concentrations coincided with an increasing amount of fine-grained fraction and organic carbon. In the territorial waters, the distribution of elements was related to the water depth. In addition, the binding of metals with insoluble iron sulphides might explain their high concentrations at the most remote and deepest stations.