Pentti Alhonen

Holocene lake-level changes in the Fennoscandian tree-line region, western Finnish Lapland: diatom and cladoceran evidence

Lithostratigraphical, diatom and cladoceran evidence were used to demonstrate Holocene lake-level changes in two closed-basin lakes in western Finnish Lapland, north of the coniferous tree- line. The lake levels were significantly lower than present in early to mid-Holocene times, from about 8000 until about 4000BP, after which they rose to the present level. The changes are believed to be climatically controlled and regionally representative. The proposed mid-Holocene dryness in Lapland contrasts with the evidence from southern Sweden and Finland, where past lake levels indicate humid conditions during much of the mid-Holocene (Atlantic) time.

Cladoceran and diatom evidence of lake-level fluctuations from a Finnish lake and the effect of acquatic-moss layers on microfossil assemblages

We studied Holocene lake-level fluctuations from a small lake, Iso Lehmälampi, southern Finland, utilizing cladoceran and diatom analyses. We report data from a sediment core (A) taken from the deepest part of the lake (8.1 m) where two layers of moss, mixed with gyttja, were found. These layers were formed in situ during the early Holocene (1. ca. 8100-7900, 2. ca. 7300 BP). Lake-level fluctuations were inferred also from another core C, which did not have moss layers. According to the ratio of planktonic/littoral Cladocera, the water level was high around 9000 BP and started to fall before 8000 BP. The lowering continued until 7000 BP and the moss layers were formed during this lowering. Water level was high again ca. 6000 BP and lowered towards ca. 4000 BP. The late Holocene is characterized by several rapid fluctuations of lake-level. The ratio of planktonic/littoral Cladocera and the diatom species composition in core A showed drastic changes between the moss layers and the non-moss gyttja sections of the core. We suggest that they reflect changes in sedimentary facies between the local moss environment and the pelagic bottom. Thus, cores which contain moss layers may lead to erroneous interpretations of lake-level fluctuations.

The trophic history of Enäjärvi, SW Finland, with special reference to its restoration problems

The eutrophicated Enäjärvi was studied by paleolimnological analyses and sediment mapping. The sedimentary record indicates that the lake nutrient balance had deteriorated due to lowering of the lake water level in the year 1928. From that event onwards Chironomus plumosus and Cyclotella astraea characterize the chironomid and diatom communities. The concentrations of sedimentary total and mobile phosphorus show that since then the internal load of phosphorus has controlled the nutrient cycle of the lake. The areal distribution of mobile phosphorus can be explained by dominant wind directions and wind resuspension of the sediment is the key factor in the nutrient cycle. Restoration of Enäjärvi must be based on actions which stabilize the surface sediment and improve its natural phosphorus-binding capacity. They include the regulation of lake water to as high a level as possible and the removal of the majority of roach.

Bacterial weathering of rapakivi granite

Rapakivi granite samples were incubated with Pseudomonas aeruginosa culture solutions in order to elucidate the possible role of bacteria in rapakivi (crumbling stone) disintegration. SEM micrographs showed micromorphological alterations on the incubated rapakivi surface at 21 to 23°C for 20 days. Elevated concentrations of Na, Ca, K, Fe, and Mg were detected in the culture solutions after incubation. Elemental oxide ratios [K2O : (Na2O + CaO)] in culture solutions were similar to those in rapakivi ovoids, suggesting a proportional dissolution pattern of these elements.

Palaeolimnological and limnogeochemical features in the sedimentary record of the polluted Lake Lippajärvi in Southern Finland

Abstract A sediment core from Lake Lippajarvi, sampled by freezing it in situ , was investigated. The sedimentary sequence was dated using the 137 Cs method and the 210 Pb content of the core was also determined. It seems that, during the recent history of the lake, increasing eutrophication is the main factor controlling fluctuations in lake ecosystems. This increase is clearly reflected in the changes in the diatom stratigraphy of the core investigated. Sequential extraction analysis was performed for speciation of elements in the sediment. Ammonium acetate and hydroxylammonium chloride plus acetic acid were used as extractants; acid digestion and extraction by NaClO and NaDDTC/MIBK were also performed. An increase in sedimentation rate is apparent for the upper part of the lithostratigraphy of Lake Lippajarvi. The increased nutrient load and heavy metal input have led to cultural eutrophication and pollution effects in the lake, and black bands of Fe monosulphides have emerged in sediments as a sign of oxygen deficit in the hypolimnion. The eutrophication of Lake Lippajarvi is also accompanied by biogeochemical cycles and limnogeochemical processes apparently responsible for the leaching of chemical elements from sediments and their subsequent redeposition in more loosely bound forms. Fe has been redeposited mainly as Fe oxyhydroxides and monosulphides, and Cu and Zn also seem to be associated with these precipitates. Ca, Mn and Zn are present to relatively large degrees as very loosely bound and sorbed forms. Fe, Mn, Cu and Zn are also associated with sulphides, and Fe and Cu with biogenic matter. There is a clear difference between man-made airborne forms of Pb and natural mineral-bound forms in the sediment column of the lake. In the polluted part of the investigated lithostratigraphy, Pb is mainly present in loosely bound reducible forms. Al and Si also seem to show leaching and redeposition in the sediments of Lake Lippajarvi.

Diatoms as indicators of provenance in Finnish sub-neolithic pottery

Abstract The clays of Finland originated from glacial deposits formed during the deglaciation of the Weichselian ice-sheet and during the different stages of the Baltic Sea. The analysis of the fossil diatom flora is of central importance in the study of its developmental history. The diatoms in the clay indicate its sedimentary environment, which can be linked to the stages of the Baltic Sea. The siliceous valves of diatoms tolerate heating up to 1400°C and can consequently be identified in ceramics fired at lower temperatures. Several diatom analyses have been made in Finnish Sub-Neolithic comb ware pottery in order to determinate the origin of their clay materials. According to the results of these studies, prehistoric potteries used clays deposited during the Yoldia and the Ancylus stages. The criteria used in selecting raw materials were identical to those of modern ceramic industries. Further details as to provenance of clay materials have been illustrated in connection with research on pottery from the Aland Islands. In the example from Kymi, South-eastern Finland, changes in the composition of the diatom flora have been found to correlate with changes in pottery decoration styles.

Relationships between the prevalence of multiple sclerosis and some physical and chemical properties of soil

The prevalence of multiple sclerosis (MS) and some physical and chemical properties of soil in two counties of Finland have been compared. In the county where the MS prevalence rate was significantly higher, the pH of the soil was lower, the organic carbon content higher, the concentration of soluble iron, zinc, chromium and aluminium higher and those of soluble potassium, calcium, magnesium, strontium and total selenium lower than in the county with the lower MS-prevalence rate. According to the literature, areas of a high MS prevalence correspond rather closely to the global distribution of mires, particularly to raised bogs in the northern hemisphere.

Biostratigraphy of Lake Spitaalijärvi: an ultraoligotrophic small lake in Lauhanvuori, western Finland

The Early and Middle Flandrian geological development and paleolimnology of Lake Spitaalijarvi was studied using pollen, diatom and cladoceran analysis and 14C dating. Spitaalijarvi was isolated from the Ancylus Lake about 9000 B.P., at which time birch and pine and plants typical of open habitat communities grew on the solitary island. The rational limits for Alnus and Picea were ca. 8300 B.P. and 3700 B.P., respectively. During the first few hundred years after isolation Spitaalijarvi was probably fairly eutrophic, with a low water level. Water level began to rise before the Alnus rise (A°) and the lake became oligotrophic. After another transgression, which started before the Picea rise (P°), Tabellaria binalis and Semiorbis hemicyclus appear in the diatom stratigraphy indicating ultra-oligotrophic conditions.

Aspects of the developmental history and paleolimnology of lakes in Finland

The developmental history of Finnish lakes can be studied both morphologically and stratigraphically. Former water levels are indicated by raised beaches and outlet channels, and fluctuations in water level can be inferred from the lithostratigraphy of the sediments. The stratigraphic system is also the starting point for studies concerned with the changing biodynamics of lake ecosystems. Consequently, sediment stratigraphy is the fundamental basis of paleolimnology.

The sediment history of a 100 year old pond near Lake Höytiäinen, Eastern Finland

Hyvarinen, H., and Alhonen, P.: The sediment history of a 100 year old pond near Lake Hoytiainen, Eastern Finland. Geologiska Foreningens i Stockholm For‐handlingar, Vol. 92, pp. 410–414, Stockholm, September 30, 1970. The pond investigated was formed in connexion with the drainage of Lake Hoytiainen in 1859. In the sediment record the drainage is represented by a 5 cm layer of sand. This is overlain by about 6 cm of sandy mud deposited in the pond during the 100 years since its isolation. A thin sulphide‐rich horizon occurs at the isolation contact.