Forecasting Environmental Responses to Restoration of Rivers Used as Log Floatways: An Interdisciplinary Challenge

Abstract

Log floating in the 19th to mid 20th centuries has profoundly changed the environmental conditions in many northern river systems of the world. Regulation of flow by dams, straightening and narrowing of channels by various piers and wing dams, and homogenization of bed structure are some of the major impacts. As a result, the conditions for many riverine organisms have been altered. Removing physical constructions and returning boulders to the channels can potentially restore conditions for these organisms. Here we describe the history of log driving, review its impact on physical and biological conditions and processes, and predict the responses to restoration. Reviewing the literature on comparable restoration efforts and building upon this knowledge, using boreal Swedish rivers as an example, we address the last point. We hypothesize that restoration measures will make rivers wider and more sinuous, and provide rougher bottoms, thus improving land-water interactions and increasing the retention capacity of water, sediment, organic matter and nutrients. The geomorphic and hydraulic/hydrologic alterations are supposed to favor production, diversity, migration and reproduction of riparian and aquatic organisms. The response rates are likely to vary according to the types of processes and organisms. Some habitat components, such as beds of very large boulders and bedrock outcrops, and availability of sediment and large woody debris are believed to be extremely difficult to restore. Monitoring and evaluation at several scales are needed to test our predictions.

Demonstration Restoration Measures in Tributaries of the Vindel River Catchment

“…For example, in some stream reaches, the current best-practice methods have been shown to enhance biodiversity (Helfield et al 2007), whereas in others there has been no effect (Lepori et al 2005). It may be that best-practice restoration does not produce the best possible result because the original channel material available to be placed back in the channels was broken up (boulders) or eliminated (large wood) as a result of channelization (Nilsson et al 2005a). By adding large structures from adjacent upland areas, more heterogeneous morphologic and hydraulic channel conditions are created, hopefully leading to a clearer biotic response.…”

“…This, in turn, is predicted to retain drifting matter (Nilsson et al 2005a, Rosenfeld et al 2011, offer fish shelter from predators and fast flows, as well as provide hydraulically suitable feeding locations ). In small streams, large wood has been shown to be an important channel-forming agent, affecting channel morphology by trapping sediment, creating steps and pools, and triggering avulsions (Faustini and Jones 2003, Dahlström and Nilsson 2004, Gurnell et al 2005.…”

“…Growing awareness of the value of healthy ecosystems and the need to adapt to future changes in climate has put a focus on restoration of ecosystems, especially rivers (Bernhardt et al 2005, Palmer et al 2008, Arthington et al 2010. Recent river restoration approaches include renaturalization of flows; that is, environmental flows (Tharme 2003) and flood protection (Nardini and Pavan 2012); reconfiguration of channels (Nilsson et al 2005a); defragmentation, that is, dam removal (Bednarek 2001, Lejon et al 2009), and rebuilding of populations (Luhta et al 2012). There is a dearth of detailed, scientifically based guidelines for stream restoration.…”

The Future of Baltic Sea Populations: Local Extinction or Evolutionary Rescue?

“…On top of natural stress from low salinity, the Baltic Sea biota is exposed to high levels of anthropogenic contaminants (nutrients, oil, heavy metals, and toxins) (Jansson and Dahlberg 1999;Ducrotoy and Elliott 2008), and commercial fish species in particular are affected by intense fisheries and physical exploitation of migration routes and spawning sites (Nilsson et al 2005). In addition, deep benthic habitats are fragmented owing to increasing occurrence of large oxygen-depleted areas (Conley et al 2009).…”

Social success of in-stream habitat improvement: from fisheries enhancement to the delivery of multiple ecosystem services

“…These changes are expected to increase species diversity and the production of the target fish species. Although in-stream restorations have generally overlooked the riparian ecosystems and the river landscape (Nilsson et al 2005), their effects on ecosystem service delivery reach far beyond the stream banks.…”