Artikkelit jotka sisältää sanan 'runoff'
Kunnostusojituksen pitkän ajan vaikutus valumaveden ominaisuuksiin.
English title: Long-term effects of maintaining ditch networks on runoff water quality.
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The effects of ditch network maintenance on runoff water quality was studied at 23 sites in different parts of Finland. The study included a calibration period of 1–3 years before maintaining the ditches and six years after. No observations were made during winter. After ditch maintenance, which involves either cleaning of old ditches and/or digging of complementary new ditches, the concentrations of suspended solids in runoff water increased immediately. At sites where the ditches cut into fine-textured subsoil, runoff continued to have increased suspended solids concentrations throughout the whole six-year period. However, if the bottom of the ditches consisted of coarse mineral subsoil or peat, the annual mean concentration of suspended solids returned to pre-treatment levels in 5–6 years. Concentrations of mineral nitrogen, especially NH4-N, increased while the concentration of organic nitrogen decreased after ditch network maintenance. These changes persisted for the whole six-year period. The overall effect of these changes resulted in a slight lowering of total dissolved nitrogen concentrations. With the exception of a few sites, runoff water pH increased after ditch maintenance and remained high during the 6-year period. Concentrations of DOC decreased at all sites after ditch maintenance and was still at a low level after six years. Concentrations of base cations (Ca, Mg, K, Na) increased significantly after ditch maintenance and were still high after six years. High concentrations of Al and Fe immediately after the digging operations were observed in a few sites. Concentration of total dissolved P did not change much and tended to decrease rather than increase.
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Joensuu,
Forestry Development Centre Tapio, Soidinkuja 4, FIN-00700 Helsinki, Finland
Sähköposti:
ei.tietoa@nn.oo
- Ahti, Sähköposti: ei.tietoa@nn.oo
- Vuollekoski, Sähköposti: ei.tietoa@nn.oo
Effect of peat harvesting on peat hydraulic properties and runoff generation.
Avainsanat:
peatlands;
Drainage;
runoff generation;
hydrological pathways;
hydraulic conductivity;
shear strength;
soil loss;
subsidence;
peak runoff
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Peat hydraulic conductivity, shear strength, plant composition and runoff at seven peat harvesting sites in Central Finland were measured. A large variation in hydraulic conductivity (10–8–10–6 m s–1 ), peat shear strength (302–413 kPa), and peak runoff (97–898 l s–1 km–2 ) was observed between different harvesting sites. The hydraulic conductivity showed a clear correlation with peat shear strength (r = –0.89), which has not been previously observed. The correlation between hydraulic conductivity and degree of humification was weak (r = 0.60). Soil lowering decreased the hydraulic conductivity and the peat shear strength. These reductions, with reduced drainage depths, increased peak flow and changed runoff generation patterns by increasing the possibility of Horton and saturation excess overland flow.
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Kløve,
Jordforsk, Norwegian Centre for Soil and Environmental Research, 1432 Ås, Norway
Sähköposti:
ei.tietoa@nn.oo
Leaching of organic carbon and nitrogen from peatland-dominated catchments.
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The area of 13 study catchments is 2.5-56.3 km2 and 37-87% of the catchments is covered by peatlands. Ditching intensities varied from 0 to 100%. Median total organic carbon (TOC) in runoff waters from the catchments was 10-30 mg l-1 and median total nitrogen (Ntot) 380-1 000 µg l-1. The annual leaching of TOC and N tot was calculated for five catchments for which daily runoff data was available. The range for mean annual leaching of TOC and Ntot from the catchments was 4 700 to 7 300 kg km-2 a-1 and 190-250 kg km-2 a-1, respectively. The variation between different years was high and annual leaching was closely related to annual runoff. The regional variation in the leaching of TOC and N tot was small compared to the annual variation.
Keywords: Hydrology, leaching, organic carbon, peatlands, runoff
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Kortelainen,
National Board of Waters and the Environment, Water and Environment Research Institute, P.O. Box 250, FlN-00101 Helsinki, Finland S
Sähköposti:
ei.tietoa@nn.oo
- Saukkonen, Sähköposti: ei.tietoa@nn.oo
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