Twenty years of stream restoration in Finland: little response by benthic macroinvertebrate communities

Abstract

The primary focus of many in-stream restoration projects is to enhance habitat diversity for salmonid fishes, yet the lack of properly designed monitoring studies, particularly ones with pre-restoration data, limits any attempts to assess whether restoration has succeeded in improving salmonid habitat. Even less is known about the impacts of fisheries-related restoration on other, non-target biota. We examined how restoration aiming at the enhancement of juvenile brown trout (Salmo trutta L.) affects benthic macroinvertebrates, using two separate data sets: (1) a before-after-control-impact (BACI) design with three years before and three after restoration in differently restored and control reaches of six streams; and (2) a space-time substitution design including channelized, restored, and near-natural streams with an almost 20-year perspective on the recovery of invertebrate communities. In the BACI design, total macroinvertebrate density differed significantly from before to after restoration. Following restoration, densities decreased in all treatments, but less so in the controls than in restored sections. Taxonomic richness also decreased from before to after restoration, but this happened similarly in all treatments. In the long-term comparative study, macroinvertebrate species richness showed no difference between the channel types. Community composition differed significantly between the restored and natural streams, but not between restored and channelized streams. Overall, the in-stream restoration measures used increased stream habitat diversity but did not enhance benthic biodiversity. While many macroinvertebrates may be dispersal limited, our study sites should not have been too distant to reach within almost two decades. A key explanation for the weak responses by macroinvertebrate communities may have been historical. When Fennoscandian streams were channelized for log floating, the loss of habitat heterogeneity was only partial. Therefore, habitat may not have been limiting the macroinvertebrate communities to begin with. Stream restoration to support trout fisheries has strong public acceptance in Finland and will likely continue to increase in the near future. Therefore, more effort should be placed on assessing restoration success from a biodiversity perspective using multiple organism groups in both stream and riparian ecosystems.

Acid mine drainage and stream recovery: Effects of restoration on water quality, macroinvertebrates, and fish

“…Biological recovery can be highly variable and contingent on factors other than water chemistry (e.g. Louhi et al, 2011;Sundermann et al, 2011, Johnson et al, 2014, but the results of our study also show large improvements in most aspects of the biological community of our study system. Local macroinvertebrate taxonomic richness, mean macroinvertebrate density, mean live biomass, and Shannon Wiener diversity index were all significantly higher in 2011 (post-restoration) than in 1967 (pre-restoration), and regional taxonomic richness throughout the watershed more than doubled after remediation efforts were implemented.…”

“…Given the large effort expended on restoration, there are relatively few studies in the peer reviewed literature evaluating the success of restoration efforts (Brooks and Lake, 2007;Louhi et al, 2011). Furthermore, published studies of restoration often encompass only limited spatial and temporal scales (Palmer, 2009).…”

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

“…Limited availability of key microhabitats in restored rivers might hinder colonization by additional species (Lorenz et al, 2009). Restoring these microhabitats, such as stones covered by aquatic mosses and large woody debris, might render relatively large effects because they can be regarded as key habitat elements for a relatively large number of (specialized) species (McKie & Cranston, 1998, 2001Feld & Hering, 2007;Miller et al, 2010;Louhi et al, 2011). Here also a disparity in the effects of microhabitat types was found; of all microhabitat types investigated, positive effects on EPT richness or diversity were found for cobbles, sand and especially coarse particulate organic matter.…”

“…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. Louhi et al, 2011;Ernst et al, 2012).…”

“…Although in most restoration projects, diversity of habitats, including microhabitats, increases considerably, this does not automatically result in a strong positive response by macroinvertebrate assemblages Louhi et al, 2011). It is unclear to what extent this is the result of an overriding effect of catchment-scale hydromorphological, physicochemical or biological factors.…”