Suo - Mires and peat vol. 56 no. 2 | 2005

Timo Silver, Samuli Joensuu. Ojien kunnon säilymiseen vaikuttavat tekijät kunnostusojituksen jälkeen.
English title: The condition and deterioration of forest ditches after ditch network maintenance.
Avainsanat: ditch network maintenance
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The study deals with the dimensions and condition of ditches five and ten years after ditch network maintenance in southwest Finland. The deterioration of ditches was very fast, averaging 20 cm five years and 30 cm ten years after ditch network maintenance. The shallowing of the ditches depended on the type of soil at the bottom of the ditch. There are several factors related to the deterioration of ditch condition, including: falling stones and erosion just after digging, moose paths, growth of vegetation in ditches and litterfall, clogging of culverts and shallow main ditches and unevenness of ditch bottom. The growth of vegetation in ditch bottoms is rapid and vigorous. Vegetation cover in the ditch bottoms averaged 68% five years and 100% ten years after ditch network maintenance. Our results indicate that about 25% of the ditches in southwest Finland should be cleaned again during the rotation period. We recommend the drainage ditches be re-dug to 0.9–1.1 m depth and that the main ditches be dug 20–30 cm deeper. In this way it should be possible to reduce the number of ditch maintenance operations needed at a site.
  • Silver, Lounais-Suomen metsäkeskus (Lounais-Suomi Forestry Centre) Kuralankatu 2 FIN-20540 Turku, Finland Sähköposti: ei.tietoa@nn.oo (sähköposti)
  • Joensuu, Sähköposti: ei.tietoa@nn.oo
Päivi Picken. Suonpohjien turpeen alaisen mineraalimaan ominaisuudet eri geologisilla alueilla.
English title: The characteristics of mineral subsoils of Finnish cut-away peatlands related to different geological areas.
Avainsanat: cut-away peatlands; after-use; mineral subsoil; geochemical province; Litorina zone
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In Finland, the whole peat layer of a peat production area is used due to the value of the basal peat as energy peat. In this situation the properties of the mineral subsoil below the peat layer are significant when choosing the form of after-use. The geochemical provinces are based on the chemical features of the fine material in till, related to differences found in the bedrock, defined by Geological Survey of Finland. The study of peat production areas (1998-1999, covering 9800 ha) shows that the characteristics of the provinces affects the subsoil sediments. In Lake Ladoga–Bothnian Bay zone subsoils were rich in sulphur and iron. The amount of water soluble sulphur was 3-6 times higher than that in the Granitoid area of Central Finland and the Archaean gneiss areas (calculated as mg kg-1). Below the highest shoreline of the ancient Litorina Sea the average content of the water soluble sulphur in subsoil sediments was ca. seven fold compared to the content found above the highest shoreline, (calculated as mg kg-1). There was also a difference in soil acidity between these areas. Nutrient content varied between sediments, which have the same fine material percentage. In the Lake Ladoga–Bothnian Bay geological zone and in the zones of Svecocarelian schists and gneisses, natural nutrient levels are high when compared to the Granitoid areas.
  • Picken, Kekkilä Oyj, P.O. Box 67, 04300 Tuusula, Finland Sähköposti: ei.tietoa@nn.oo (sähköposti)
Anna-Kaisa Ronkanen, Bjørn Kløve. Turpeen hydrauliset ominaisuudet kunnallisten jätevesien ja turvetuotantoalueen valumavesien puhdistukseen rakennetuissa kosteikkopuhdistamoissa.
English title: Hydraulic soil properties of peatlands treating municipal wastewater and peat harvesting runoff.
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Peat hydraulic conductivity (K), specific yield (S), degree of humification and shear strength were measured at two wetland treatment systems constructed on natural peatlands receiving different wastewater quality and loading in Northern Finland. Peat K was measured with a falling head piezometer test in situ and by taking soil cores in horizontal and vertical directions using Eijkelkamp cylinders. Peat S was obtained from pF-curves and drainage tests. The K in situ was 5.2x10-7 - 2.9x10-3m s-1, the horizontal K was 6.1x10-6 - 3.8x10-2 m s-1 and the vertical K was 4.2x10-6 - 2.6x10-2m s-1. The highest K value was usually found in the vertical direction. The estimated acrotelm layer with high K reached 40 - 60 cm at Kompsasuo wetland and 10 - 60cm at Ruka wetland. There was an agreement between different measurement methods for S when pF values corresponding to relevant negative pressure were used. S varied from 0.023 to 0.23. After several years of wastewater loading, the peat hydraulic conductivity was still sufficient to maintain wastewater flow in the top 50 cm of the peatland.
  • Ronkanen, Sähköposti: ei.tietoa@nn.oo (sähköposti)
  • Kløve, Sähköposti: ei.tietoa@nn.oo

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