６９０：環境政策の科学から（河川修復）

プロポ作成中だがいろいろ情報が各地から入る。取りあえず転記しておく。

今回はお馴染みECから。10年ぐらい前からだろうか、アメリカのriver restorationが流行っていて結構フォローしたものだ。サマリーだけ下記に示す。本文を見るのはまたいずれにしよう。

European river restoration projects need to widen their scope

A new study of European river restoration projects has indicated that their impact on the physical characteristics of rivers depends on the region, river type and restoration approach. However, regardless of the river, region or approach, impacts on the biodiversity of riverbed species is limited. Larger scale projects could be more effective.

There is increasing interest in restoring degraded rivers back to a more natural form, partly driven by biodiversity targets set by legal frameworks, such as the EU Water Framework Directive and EU Habitats Directive. Green (Blue) Infrastructure covers the restoration of rivers when enhancing the functioning of floodplain ecosystems and enhancing their connectivity. However, there currently seems to be a mismatch between the small scale at which restoration measures take place and the larger catchment-level scale of these targets.

River restoration projects aim to improve the composition of habitats and biodiversity of species by changing the physical characteristics of rivers. The research analysed the impacts of restoration projects on mesohabitats, on microhabitats and on the biodiversity of benthic invertebrates. Mesohabitats are habitats described at the medium scale, such as islands, floodplains and embankments, whereas microhabitats are described at the level of the river bed, such as large woody debris and coarse gravel. Benthic invertebrates live on the riverbed and are considered good indicators of the ecological status of water.

The study evaluated the success of restoration projects by comparing 26 pairs of non-restored and restored river sections in Austria, Czech Republic, Germany, Italy and the Netherlands. It was funded under the EU Euro-limpacs scheme.

Restoration had significantly improved the diversity of mesohabitats in 83 per cent of the studied river sections. For microhabitats, restoration had a significant positive effect on diversity at 69 per cent of sites but a significant negative effect at 15 per cent of sites. More specifically, the impacts of restoration on river site characteristics such as shore length, habitat width and the actual number of mesohabitats and microhabitats were greater in Southern Europe and mountainous regions.

Active restoration projects, such as removing banks and placing logs in the river channel, had a greater effect on the characteristics of mesohabitats and microhabitats, particularly for Southern European sites and Central European mountain rivers. The impact of passive restoration projects, such as abandoning river maintenance and removing livestock, was smaller and mainly restricted to mountain rivers in Central Europe.

The effect of restoration on the biodiversity of benthic invertebrates was small or not detectable. This supports the results of previous studies which have found that enhanced habitat diversity has little or no effects on benthic invertebrate biodiversity.

The results indicated that, while restoration can have an impact at the level of habitats, it does not produce significant changes in biodiversity of benthic invertebrates when applied to relatively short river sections, several hundred metres in length. Passive river restoration, which is less expensive and easier to apply to longer stretches of river, may lead to the same impact on the catchment area as expensive active restoration techniques. Efforts at the larger catchment scale which tackle wider problems, such as water quality, could have greater effects on the invertebrate community.

Source: Jähnig, S.C., Brabec, K., Buffagni, A. et al. (2010). A comparative analysis of restoration measures and their effects on hydromorphology and benthic invertebrates in 26 central and southern European rivers. Journal of Applied Ecology. 47: 671-680.