(Dis)connectivity in hydro-geomorphic systems - emerging concepts and their applications

In geomorphology, connectivity has emerged as a framework for understanding the transfer of water and sediment through landscapes. Over the past decade, sessions on (dis)connectivity at the General Assembly of the European Geosciences Union (EGU), and more recently, three mini-conferences in 2020 and 2021 called “Connectivity Conversations“, organized by the International Association of Geomorphologists (IAG) working group on “Connectivity in Geomorphology”, have created a space for the exchange of ideas relating to (dis)connectivity in geomorphology and related disciplines. The result of these initiatives has been a collection of research articles related to a special issue (SI) entitled “(Dis)connectivity in hydrogeomorphic systems - emerging concepts and their applications”. In this paper we provide a synthesis that embraces the SI contributions related to the application of the connectivity concept in different environments and geomorphic process domains, spatial and temporal scales, types and spatial dimensions of connectivity and the role of human impacts and associated river and catchment management aspects

Riparian and in-stream restoration of boreal streams and rivers: success or failure?

We reviewed follow-up studies from Finnish and Swedish streams that have been restored after timber floating to assess the abiotic and biotic responses to restoration. More specifically, from a review of 18 case studies (16 published and 2 unpublished), we determined whether different taxonomic groups react differently or require different periods of time to respond to the same type of restoration. Restoration entailed returning coarse sediment (cobbles and boulders) and sometimes large wood to previously channelized turbulent reaches, primarily with the objective of meeting habitat requirements of naturally reproducing salmonid fish. The restored streams showed a consistent increase in channel complexity and retention capacity, but the biotic responses were weak or absent in most species groups. Aquatic mosses growing on boulders were drastically reduced shortly after restoration, but in most studies, they recovered after a few years. Riparian plants, macroinvertebrates and fish did not show any consistent trends in response. We discuss seven alternative explanations to these inconsistent results and conclude that two decades is probably too short a time for most organisms to recover. We recommend long-term monitoring using standardized methods, a landscape-scale perspective and a wider range of organisms to improve the basis for judging to what extent restoration in boreal streams has achieved its goal of reducing the impacts from timber floating