Title: From Natural Design to Degraded Rivers and Back Again: A Test of Restoration Ecology Theory and Practices
Authors: Feld, C.K., Birk, S., Bradley, D.C., Hering, D., Kail, J., Marzin, A., Melcher, A., Nemitz, D., Pedersen, M.L., Pletterbauer, F., Pont, D., Verdonschot, P.F.M., & Friberg, N.
Journal: NA
Year: 2011
DOI: NA
Species or groups: Fish, benthic macroinvertebrates, aquatic macrophytes
Other sources of evidence: https://www.conservationevidence.com/actions/840
Abstract: Extensive degradation of ecosystems, combined with the increasing demands
placed on the goods and services they provide, is a major driver of biodiversity
loss on a global scale. In particular, the severe degradation of large rivers, their
catchments, floodplains and lower estuarine reaches has been ongoing for
many centuries, and the consequences are evident across Europe. River restoration
is a relatively recent tool that has been brought to bear in attempts to
reverse the effects of habitat simplification and ecosystem degradation, with a
surge of projects undertaken in the 1990s in Europe and elsewhere, mainly
North America. Here, we focus on restoration of the physical properties (e.g.
substrate composition, bank and bed structure) of river ecosystems to ascertain
what has, and what has not, been learned over the last 20 years.
First, we focus on three common types of restoration measures- riparian
buffer management, instream mesohabitat enhancement and the removal of
weirs and small dams- to provide a structured overview of the literature. We
distinguish between abiotic effects of restoration (e.g. increasing habitat
diversity) and biological recovery (e.g. responses of algae, macrophytes,
macroinvertebrates and fishes).
We then addressed four major questions: (i) Which organisms show clear
recovery after restoration? (ii) Is there evidence for qualitative linkages
between restoration and recovery? (iii) What is the timescale of recovery?
and (iv) What are the reasons, if restoration fails?
Overall, riparian buffer zones reduced fine sediment entry, and nutrient and
pesticide inflows, and positive effects on stream organisms were evident. Buffer
width and length were key: 5-30 m width and > 1 km length were most effective.
The introduction of large woody debris, b,oulders and gravel were the most
commonly used restoration measures, but the potential positive effects of such
local habitat enhancement schemes were often likely to be swamped by largerscale
geomorphological and physico-chemical effects. Studies demonstrating
long-term biological recovery due to habitat enhancement were notable by their
absence. In contrast, weir removal can have clear beneficial effects, although
biological recovery might lag behind for several years, as huge amounts affine
sediment may have accumulated upstream of the former barrier.
Three Danish restoration schemes are provided as focal case studies to
supplement the literature review and largely supported our findings. While
the large-scale re-meandering and re-establishment of water levels at River
Skjern resulted in significant recovery of riverine biota, habitat enhancement
schemes at smaller-scales in other rivers were largely ineffective and failed to
show long-term recovery.
The general lack of knowledge derived from integrated, well-designed and
long-term restoration schemes is striking, and we present a conceptual
framework to help address this problem. The framework was applied to the
three restoration types included in our study and highlights recurrent causeeffect
chains, that is, commonly observed relationships of restoration measures
(cause) and their effects on abiotic and biotic conditions (effect). Such
conceptual models can provide useful new tools for devising more effective
river restoration, and for identifying avenues for future research in restoration
ecology in general.
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