Samuli Joensuu , Erkki Ahti, Martti Vuollekoski

Kunnostusojituksen pitkän ajan vaikutus valumaveden ominaisuuksiin

Joensuu S., Ahti E., Vuollekoski M. Kunnostusojituksen pitkän ajan vaikutus valumaveden ominaisuuksiin.

Tiivistelmä

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.

Avainsanat
peatland; ditch maintenance; runoff quality

Vastaanotettu 31.10.2017 Julkaistu 1.1.2001

Katselukerrat 3806

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