Kimmo Tolonen

The use of fallout 137Cs and 239,240Pu for dating of lake sediments

The distribution of 137Cs and 239,240Pu in sediment core samples of the Finnish lakes Laukunlampi, Lovojärvi and Pääjärvi were determined. The sediment samples were collected using dry ice and liquid nitrogen freezing methods. The sediments of these lakes are annually laminated. A clear maximum concentration of 137Cs and 239,240Pu was found in sediment layers formed during 1962–1964, the years of maximum fallout, and the middle of the 1950s can be estimated from the 137Cs and 239,240Pu profiles. The highest concentrations, 11 500 and 820 pCi kg−1 dry wt for 137Cs and 239,240Pu, respectively, were found in the sediment of Laukunlampi. The vertical distribution was similar for 137Cs and 239,240Pu in the lakes investigated. A slight migration of 239,240Pu and 137Cs was found and the migration of 137Cs seems to be higher than that of 239,240Pu. The advantages of 137Cs dating method are rapidity and simplicity. 239,240Pu is preferable when the sample size is small. The agreement found between 137Cs and 239,240Pu dates and the annual laminae show that these fallout radio isotopes can be used for dating sediments formed during the past 25 years.

Long-term fire frequency in the spruce-dominated forests of the Ulvinsalo strict nature reserve, Finland

Abstract The long-term fire history of the spruce-dominated forests of the Ulvinsalo strict nature reserve in Kuhmo, eastern Finland (63°58′N, 30°22′E), was studied by means of charcoal particle layer records and macroscopic charcoal particles in peat and by pollen analysis. The data suggest that spruce forest sites in the area burned at a mean interval of a few centuries over a period of almost 6000 years prior to the beginning of slash-and-burn cultivation in the area. This low forest fire frequency can be attributed to the fragmented landscape pattern, which restricted the spread of fires ignited by lightning. Because a similar landscape pattern predominates over large areas of boreal Fennoscandia, it is possible that natural fire frequencies may also have been considerably lower than expected in these areas. It may well have been the case that, at least in spruce forests located in fragmented landscapes, small-scale disturbances were more important for the forest dynamics than fires.

The history of airborne polycyclic aromatic hydrocarbons (PAH) and perylene as recorded in dated lake sediments

Polycyclic aromatic hydrocarbons (PAH) were analyzed in sediment cores from five small forest lakes in Finland. The catchments of the lakes were undisturbed (2 lakes) or only very slightly disturbed by human activity (3 lakes). None of the lakes had runoff delivery of PAH from their shores.Lead-210 dating of four lakes enabled the calculation of individual PAH fluxes over the past 100 to 150 yr. The sedimentary distribution of abiotic PAH in these lakes appears to be indicative of the development of combustion-generated energy production in Finland and adjacent countries. This development is reflected in an overall increase in sedimentary PAH since about 1850. After World War II the rate of accumulation of PAH continues to increase. The large variation between the PAH fluxes of different lakes indicates different trapping efficiencies and/or different preservation of the PAH compounds due to limnological differences between the lakes.

Effects of recent acidification on Cladocera in small clear-water lakes studied by means of sedimentary remains

Cladoceran populations, as revealed by sedimentary remains, were studied in six lakes which by diatom evidence have become strongly acidified during the past 30 years. The accumulation rates of cladoceran remains and in two of the most strongly acidified lakes both relative and absolute numbers of Bosmina greatly increased during this period. Species numbers were not reduced, but there were shifts in relative abundances of cladoceran species. Bosmina longispina dominated all the lakes. Low pH (4.7) seemed not to be straightforwardly harmful to Daphnia longispina, but the relative abundances of this taxon were reduced because of Bosmina.

Lead-210 and heavy metal contents in dated ombrotrophic peat hummocks from Finland

Abstract Two Sphagnum fuscum hummock cores, core 1, Karpansuo bog and core F9, Kunonniemensuo bog, from Finland were used in this study. The peats are ombrotrophic and were dated using the moss-increment method. The mosses in both cores were carefully examined for their botanical composition, degree of humification, ash percentage and bulk density. The total accumulated dry peat-matter in the Kunonniemensuo core was almost double that in the Karpansuo core. The total 210 Pb and the supported 210 Pb were measured by isotope dilution and the radon emanation technique. Materials in the same peat samples were analysed for their 210 Pb content at the Institute of Physics, Uppsala, Sweden and the Technical Research Centre of Finland, Espoo, Finland. The annual content of unsupported 210 Pb in the dated peat-layers showed that peat materials are effective traps which could yield information on atmospheric-fluxes both chronologically and regionally. Lead, copper, zinc, iron and manganese were also measured by flame atomic absorption spectrometry (AAS). The total accumulated amounts over the past 150 y of the heavy metals investigated are almost identical for both cores apart from manganese which is considerably higher in the Kunonniemensuo core. However, the metal profiles studied exhibit discontinuity zones more pronounced in the Kunonniemensuo core. The 210 Pb data indicate that growth rate and bulk density variations in ombrotrophic peat bogs affect the accumulation of 210 Pb and similar trace metals.

Sedimentary chemistry of a small polluted lake, Gallträsk, S. Finland

Macro nutrients N, P, K, Ca, Mg, Na and S as well as heavy metals Pb, Cu, Zn, Co, Cr, Ni, Fe and Mn were analysed from a sediment core representing a 7000-year long history of a lake including the preceding brackish (Litorina Sea) and freshwater (Ancylus Lake) stages. Sediments were also analysed for sedimentary pigments, algal growth potential (AGP) of the interstitial water, phosphorus fractions, pH, specific conductivity and redox potential. The annual accumulation values of several chemical elements were interpreted in light of other paleolimnological data from the same core. In the uppermost sediment stratum the influence of sewage pollution is clearly reflected by increases in total electrolyte content, pH, AGP and sedimentary pigments including myxoxanthophyll. Nickel, copper and manganese only slightly increase in the recent sediment, whilst other heavy metals (especially Cr and Zn) and sulphur, phosphorus, nitrogen and total organic matter are heavily concentrasted in the polluted surface sediment. The interpretation of the chemostratigraphy of the lake accords with evidence of lake development based on biological analyses.

Changes in diatom flora deposited annually during the freshening of the impounded, sea-bay of Gennarbyviken in southern Finland

Diatoms have been studied in an annually laminated sulphide mud which was deposited after the impoundment of the sea-bay of Gennarbyviken. It was possible to follow how the measured decrease in salinity in the basin was reflected by the diatom flora of the sediment which had been deposited concurrently