Liettyneiden metsäpurojen kunnostaminen

Tieteen tor

Bäck inventering i Ijo älv flodområde under år 1998-2003

Alueelliset ympäristöjulkaisut 403Iijoen valuma-alueella inventoitiin 257 metsäpuroa vuosina 1998-2003. Inventoinneilla kerättiin tietoa purojen luonnontilaisuudesta ja sitä muuttaneista tekijöistä sekä laadittiin tarvittaessa alustavat kunnostusehdotukset. Inventoinneissa kerättyjä tietoja voidaan käyttää purojen kunnostussuunnittelun pohjana. Inventointien tuloksena todettiin, että täysin luonnontilaisia puroja ei ollut juuri lainkaan: vain 2 % tutkituista puroista. Lähes kaikissa puroissa oli kuitenkin sekä luonnontilaisia että muutettuja purojaksoja, ja kaikkiaan 22 % purojaksoista arvioitiin luonnontilaisiksi. Eniten purojen luonnontilaa olivat muuttaneet metsäojat ja niistä puroihin kulkeutunut kiintoaine eli hiekka tai muta. Muita yleisiä luonnontilaa muuttaneita tekijöitä olivat rantametsien hakkuut ja purouomien perkaukset. Yleisimpiä ehdotettuja kunnostustoimenpiteitä olivat suisteet, vesiensuojelurakenteiden kunnostaminen ja kiveämiset. Tutkituista puroista vain 17 %:lla ei havaittu kunnostustarvetta ja erittäin suuressa kunnostustarpeessa oli jopa 39 % tutkituista puroista. Jokaisesta inventoidusta purosta koottiin perustiedot taulukoihin ja kirjoitettiin lyhyt yleiskuvaus. Käytettyä inventointimenetelmää tulisi testata tieteellisesti, koska ei tiedetä, kuinka hyvin menetelmällä saadaan esille todelliset biologiset haitat ja purojen biodiversiteetti

Data from: Differential responses by stream and riparian biodiversity to in-stream restoration of forestry-impacted streams

1. Forestry can have detrimental impacts on stream ecosystems, particularly via excessive sedimentation. A key challenge to stream management is therefore to identify the best restoration practices to mitigate the harmful impacts of fine sediments on stream biodiversity and ecosystem functioning. 2. We studied the effects of restoration of sediment-impacted headwater streams on the habitat structure, hydrologic retention, biodiversity (microbes, bryophytes, benthic macroinvertebrates, riparian plants) and ecosystem functions (periphyton accrual rate and leaf breakdown) by comparing four treatments: wood-restored, boulder-restored, impacted (by fine sediments) and near-natural streams. The restored streams were sampled three to seven years post restoration. Restoration by wooden or boulder structures aimed to reduce deposited sediments and increase channel heterogeneity and hydraulic retention. 3. Wooden structures were ineffective in removing fine bed sediments and did not induce positive responses in aquatic biota. Boulder additions reduced substrate limitation and thereby proved beneficial for aquatic bryophytes. Benthic macroinvertebrates were clearly impaired by sedimentation but responded weakly to restoration. Leaf-decomposing microbes and ecosystem functions were unresponsive to restoration but neither did they differ between near-natural and impacted streams, suggesting that they were little harmed by sedimentation. 4. Wood addition enhanced hydraulic retention, and riparian plant assemblages along wood-restored streams resembled those in near-natural streams, suggesting that increased retention re-established a more natural flood regime. By contrast, riparian plant assemblages in boulder-restored streams did not differ from those in impacted streams. Synthesis and applications. Restoration improved several aspects of stream and/or riparian biodiversity, but had limited effects on ecosystem functions. Different restoration measures resulted in differing biodiversity outcomes: boulder addition was more effective at restoring in-stream heterogeneity and aquatic biodiversity, whereas wooden structures helped restore channel hydrology and retentiveness, and, consequently, riparian vegetation. Therefore applying both measures in the restoration of forested headwater streams with naturally stony substrates enhances stream habitat variability at the watershed scale, providing the most promising scenario for biodiversity benefits in broad-scale restoration designs. In-stream restoration that increases hydraulic retention has impacts that extend beyond ecosystem boundaries, reinforcing the need to restore, manage and protect streams and their riparian forests in an integrated effort

Restoration increases transient storages in boreal headwater streams

Abstract Bed siltation can drastically alter the physical conditions of headwater streams and is therefore a stressor for stream ecosystems. We studied 32 headwater streams that represented near‐natural (reference; N = 11), sediment‐impacted (N = 12), or wood‐ (N = 4) or stone‐restored (N = 5) streams to quantify how extensive siltation and restoration with either large woody debris (LWD) or boulder structures influence transient storage conditions. We carried out repeated stream tracer experiments, field measurements of habitat characteristics, and numerical simulations to determine the effects of siltation and restoration on total transient storage. Compared with reference streams, impacted streams had a smaller storage zone cross‐sectional area (As/A) ratio and fraction of median travel time due to transient storage (F200), whereas restored streams had transient storage conditions similar to near‐natural conditions. Both of the two restoration methods had positive but differing impacts on bed sediment and transient storage properties. The LWD restoration created diverse total transient storage conditions, whereas boulder restoration decreased fine sediment cover. Addition of both LWD and boulders could thus aid the recovery of headwater streams from excessive sediment input and increase transient storage and in‐stream habitat complexity

Turunen_etal_2017_Journal_of_Applied_Ecology

Environmental and biological variables