The River Gelså restoration revisited: Habitat specific assemblages and persistence of the macroinvertebrate community over an 11-year period

Abstract

Please cite this article in press as: Friberg, N., et al., The River Gelså restoration revisited: Habitat specific assemblages and persistence of the macroinvertebrate community over an 11-year period. Ecol. Eng. (2013) b s t r a c tThe study was undertaken on the River Gelså, Denmark, where a 1.8 km meandering course was established in 1989 to replace a channelized river reach. This restoration project was the first of its kind in Denmark and has the longest time-series of post-intervention data of any restoration project conducted world-wide. Additionally, a 0.5 km upstream (control) reach that remained channelized has been sampled since 1989. In this paper, we examined macroinvertebrate assemblages in distinct habitats in 2008, 19 years after the restoration, and community persistence between two years, 1997 and 2008, to investigate the longer-term effects of restoration on the biota. We found that habitat type influenced macroinvertebrate community composition to some degree, while there were no clear effects on ␣-and ␤-diversity of habitat or reach type. Stony substrate habitats introduced as part of the restoration could, however, still be separated from other habitat types and were much more frequent in the restored reach. Furthermore, very little change had occurred over the 11-year period from 1997 to 2008, suggesting a high degree of community persistence. Our results suggest that the local species pool was already close to saturation in 1997 and that only limited immigration of new species occurred in the intervening period until 2008. The lack of long term benefits could be attributed to the simultaneous cessation of weed cutting (which had almost as big a positive impact as restoration), other types of stress on the river (eutrophication) and dispersal limitations. However, it might also reflect that River Gelså is still functionally channelized and is far from exhibiting a dynamic river morphology governed by natural processes that create a range of habitats for the biota and this might explain why there has not been a more pronounced increase in macroinvertebrate diversity in River Gelså.

The role of benthic microhabitats in determining the effects of hydromorphological river restoration on macroinvertebrates

“…These results are consistent with other restoration studies, which indicated that hydromorphological restoration measures increasing structural heterogeneity or restoring natural flow regimes did not generally promote macroinvertebrate biodiversity, even if habitat changes were considerable (Lepori et al, 2005;Jähnig et al, 2010;Palmer et al, 2010;Haase et al, 2013;Friberg et al, 2014). Nonetheless, by employing an alternative approach based on quantification of microhabitat diversity and patchiness rather than restoration per se, we were able to identify some important cases where restoration did have positive effects on macroinvertebrate metrics.…”

“…However, evidence for strong and long-term positive ecological effects of these measures on macroinvertebrates remains generally limited (e.g. Palmer et al, 2010;Feld et al, 2011;Friberg et al, 2014), despite some notable exceptions (Miller et al, 2010;Kail et al, 2015). These findings partly reflect the lack of robust scientific assessments of restoration measures, but even where such assessments have been carried out, changes in invertebrate diversity and community composition have often been minimal (e.g.…”

Long‐term performance of in‐stream restoration measures in boreal streams

“…Kondolf and Micheli (1995) suggested that the minimum monitoring period to judge the sustainability of a restoration scheme is at least 10 years, based on the argument that a restored site should experience variable climatic events and discharge conditions during the monitoring period. Consequently, monitoring that exceeds 5 years is relatively rare, and a monitoring period of more than 10 years is exceptional (Friberg et al, 2014). Consequently, monitoring that exceeds 5 years is relatively rare, and a monitoring period of more than 10 years is exceptional (Friberg et al, 2014).…”

“…Unfortunately, the volume of long-term studies able to identify the performance trajectory of stream restoration projects is low, owing primarily to limited project funding that often ceases soon after the restoration work is completed (Champoux et al, 2003;Buchanan et al, 2014). Consequently, monitoring that exceeds 5 years is relatively rare, and a monitoring period of more than 10 years is exceptional (Friberg et al, 2014).…”

Hydromorphological restoration stimulates river ecosystem metabolism

“…The assessment of restoration effects has mainly focused on responses of aquatic organisms, such as fish (e.g., Roni et al, 2008;Haase et al, 2013;Schmutz et al, 2016), benthic invertebrates (e.g., Jähnig et al, 2010;Friberg et al, 2014;Verdonschot et al, 2016), and macrophytes (e.g., Lorenz et al, 2012;Ecke et al, 2016). Recently, increasing attention has also been given to the response of floodplain organisms (e.g., Hering et al, 2015;Göthe et al, 2016;Januschke and Verdonschot, 2016), while functional characteristics, i.e., the rates and patterns of ecosystem processes, have rarely been addressed.…”