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Ecological and geomorphic theory assume longitudinal connectivity; here, we test whether these concepts apply in naturally disconnected paraglacial stream networks with lakes and coarse glacial sediment. We determined downstream hydraulic geometry relationships (DHG) for channel width; riparian vegetation was inventoried across process domains (rapids, flats, lakes) over 10 km in two northern Swedish catchments—one above and one below the former highest coastline (FHC). Below the FHC, finer sediment from marine/deltaic deposition may allow more stream self-adjustment. DHG relationships were weak overall, with large local width variation, but slightly stronger in the FHC-below catchment, where a lake-effect was found, with wider channels downstream of lakes. Riparian vegetation species density did not substantially increase downstream as in connected stream networks, and vegetation similarity between reaches was weakly related to distance, suggesting disrupted dispersal. These findings indicate that formerly glaciated catchments are highly fragmented, with local factors dominating geomorphic and ecological patterns.

Water is an important dispersal vector for seeds of riparian plants, but little is known on how this form of dispersal, called hydrochory, varies throughout seasons and through geomorphically different areas. Therefore, we trapped seeds in 25 x 25 Astroturf mats along a free-flowing boreal river for an entire year. Sites mirrored the full range of geomorphic variation in the area and traps were emptied before and after the annual peak flow. The traps collected 2,062 seeds before the spring flood and 16,157 during the spring flood. While most of the seeds were deposited in the summer-low water traps (from now on “water edge”) before the spring flood, they were distributed more equally in the riparian traps (defined as the level 40 cm above the water edge; from now on “riparian zone”) during the spring flood. We found 77 species in total, of which 71 were at least recorded during the spring flood. Species numbers were higher at the water edge than at the riparian zone before and during the spring flood. Only 6.6% of the seeds, from 26 species, were viable. Most viable seeds were found in the water edge traps and, during the spring flood, in the riparian zone traps. While species that are primarily dispersed by water were not the most abundant among the viable seeds, they were the most species-rich group. This means that hydrochory is an important dispersal mechanism for riparian vegetation and an important contributor to riparian plant diversity in free-flowing rivers, and that changes in flow regimes, such as by flow regulation, can affect riparian vegetation composition.

Technological advances continue to improve our ability to detect landforms and landscape changes. Remote sensing can provide geomorphological information at larger scales than previously possible but interpreting this information can be more challenging than for field data. Measuring and mapping roughness elements, such as boulders and large wood, is essential for understanding geomorphic processes and restoration in many landscapes where these are abundant. Mapping roughness elements from aerial orthoimagery is common but could produce different results than field measurements due to the 2D nature of the imagery and the variable ability to detect boulders through water and vegetation. We compared measurements of river boulders from aerial imagery collected by uncrewed aerial vehicles (UAVs) to direct measurements in the field. We surveyed boulder size, density and spatial distributions using both approaches at eight river reaches in northern Sweden. We found that the density, coverage and size of boulders mapped from UAVs were strongly correlated with those from field measurements, giving confidence in UAV methods. However, the UAV approach consistently resulted in fewer boulders (30% lower density), lower boulder coverage and smaller boulders (7% smaller mean b-axis) compared to field measurements. The difference between field and UAV measurements was strongly associated with river bankfull depth. Therefore, we conclude that UAV measurements should be restricted to sites with low depth or high visibility through the water column and where bias in boulder detection with depth is not likely to influence study conclusions. In reaches with many boulders, overlap of boulders also likely reduces the suitability of aerial imagery. We conclude that aerial imagery has high potential for mapping landforms in rivers but is not directly equivalent to field studies and the implications of hiding by water, sediment and vegetation need to be considered.

Lateral connectivity between rivers and terrestrial landscapes is critical for both river and landscape health. Due to widespread anthropogenic degradation of riverscapes, river management is aiming to connect rivers to floodplains, riparian zones, and wetlands, putting a spotlight on lateral connectivity. However, there is currently no consensus on how to conceptualize and study lateral connectivity in rivers across disciplines. Here, we review lateral connectivity between riverscapes and terrestrial landscapes. We focus on the natural sciences, considering hydrology, geomorphology, ecology and biogeochemistry, but also consider social connectivity and the management and restoration of lateral connectivity. We emphasize the importance of considering the bidirectional nature of lateral connectivity, operating both into and out of river channels and the balance between these directions. The resulting “lateral connectivity balance” provides a framework to understand natural spatial and temporal variability in connectivity. Anthropogenic impacts have swung the balance of lateral connectivity, enhancing the transport of materials into and through river networks while suppressing fluxes from rivers to adjacent landscapes. We conclude that further research at the interfaces between the aquatic and terrestrial components of riverscapes is critical to advance our conceptual understanding of river and catchment systems. We propose that such research should be framed within the paradigm of “rebalancing” lateral connectivity, explicitly recognizing the natural bidirectionality of laterally connecting processes, the significance of the hydrologic, geomorphic, and biologic functions they support, and the value to society of the ecosystem services and climate change resilience they provide.

In the present climate, almost all high-latitude rivers in northern regions freeze every winter. In the future, however, climate change may cause shifts in freezing, duration and breakup of river ice cover, runoff, and sediment transport. The main aim of the study is to determine changes in surface flow velocity during river ice freezing and melting periods. We also examine the interplay between surface flow velocity and the initiation and progress of freezing and break-up. The study was performed in three Nordic rivers: the Pulmanki (northern Finland), the Koita (eastern Finland), and the Sävar (northern Sweden). They represent different slope and depth conditions and are representative of boreal and sub-arctic channel types. The flow characteristics were measured and remote sensing data for video-based surface velocimetry analyses (STIV) were collected during one season in each river during autumn ice-formation and spring ice break-up. STIV enabled analyses of surface flow velocities, which were compared to direct flow measurements and against freezing (incl. frazil ice, and partial ice cover) and break-up characteristics. Notable variations were observed in the interaction between ice cover and flow velocities among the three rivers. The Pulmanki River showed the most rapid decrease in flow velocities during freezing due to increased friction from the ice cover. Continuous frazil ice formation occurred in the Sävar and Pulmanki Rivers, while the Koita River experienced intermittent episodes. Temperature was key in accelerating freezing during colder days and causing ice break-up during warmer days. During the melting period, the Pulmanki River had the highest flow velocities during melting, while the Koita and Sävar Rivers showed a steady increase as the ice melted. Regression models showed that higher flow velocities reduced ice cover, with air temperature also influencing ice behavior. The STIV method enabled effective detection of flow and ice rafting and proved useful for tracking river ice with affordable time-lapse cameras. These findings provide valuable insights for managing river systems in cold climates.

Geomorphic-based solutions for land rehabilitation in areas transformed by human activities such as mining, civil engineering, or urbanisation focus on designing and constructing landforms and landscapes that replicate the morphology and dynamics of natural systems.

The GeoFluv method is the most widely used approach for geomorphic landform design, combining the design of stream channels and upland hillslope areas into stable landforms. Its widespread application in various climatic environments has led users to consider how it could be better adapted to replicate the geomorphic features and dynamics found in these different climate regions.

The objective of this study is to assess the characteristics of drainage networks in the Norrbotten region (northern Sweden) and provide recommendations applicable to geomorphic landform design projects in mine sites within such climatic environments. Using a combination of remote sensing tools and fieldwork, 67 first-order channels and four drainage networks developed on quaternary moraine and glacial till deposits were identified around Kiruna, Abisko and Svappavaara. The identified channels had low-flow to moderate-flow, with varying degrees of sinuosity and a clearly identifiable stream bed. Channel morphometric parameters such as the width/depth ratio, channel reach length, drainage density, distance from ridgeline to channel’s head, and sinuosity were measured using remote sensing tools and mobile Global Positioning System (GPS) stations.

A compilation of morphometric characteristics of the measured channels is presented in this study. The results show that glacial legacy landforms and materials strongly influence channel geometry by constraining fluvial processes. Morphometric characteristics of the channels such as the width/depth ratio and overland flow path length show a clear deviation compared with the same characteristics in channels dominated by fluvial processes. Suggestions that can be incorporated in geomorphic landform design software are presented according to the observed results in order to adapt design outcomes for the northern Sweden climate and achieve more stable landforms.

Boulders are globally widespread and influence processes across many landscapes including hillslopes, coasts, rivers and extra-terrestrial settings. Boulders are described as particles, sufficiently large, that they have a disproportionate effect on the surrounding landscape. Moving beyond this conceptual definition, however, requires a somewhat arbitrary decision of how to define a minimum boulder size. The implications of boulder definition on study findings are rarely considered. We investigate the suitability of five boulder definitions, two based on fixed sizes: (1) 0.26 m and (2) 1 m, and three definitions which vary based on system characteristics: (3) grain mobility, (4) grain protrusion and (5) surface grain size distribution (> 84th percentile, D84). We consider the impact of definition on calculated boulder metrics, and, for the >1m and >D84 definitions, their association with channel and catchment characteristics across 20 boulder-bed streams in northern Sweden. We also surveyed river managers responsible for restoring these rivers, to gain a practitioner insight on boulder size definition. We found that boulder definition matters; for metrics relating to the number or density of boulders, the >D84 and >1m size definitions were negatively correlated. Surveys indicated the importance of communicating boulder definition. We conclude that, whilst the best choice of boulder size definition will vary based on the questions of interest and techniques employed, evaluating the implications of the chosen boulder size definition and communicating the reasoning behind boulder definition choice is crucial.

Riparian buffers are commonly used to mitigate the negative effects of forestry operations near water, particularly sediment transport to streams. In Sweden, current practices typically involve 5-7 m wide riparian buffers along small streams. Historical forest management, which favored conifers up to the channel edge, has resulted in these narrow buffers having a simplified tree species composition and structure, making them prone to windthrow. While windthrow can contribute large wood (LW) to streams, windthrow also risks increasing sediment inputs if rootwads are exposed near stream edges. This disturbance affects sediment connectivity, or the movement of particles through the fluvial system, but the interaction between LW dynamics and sediment connectivity in small boreal streams is not well understood. We investigated sediment connectivity at the Trollberget Experimental Area in northern Sweden, where six 100 m stream reaches had either 5 m or 15 m wide riparian buffers. Pre-harvest and one-year post-harvest data on windthrow, hydrology, and sediment yields were collected. Forest harvesting increased sediment connectivity in the streams regardless of buffer width, indicating that buffers wider than 15 m are necessary to reduce sediment input impacts in small headwater streams. Windthrow affecting stream channels was more common in the 5 m buffers, leading to significantly higher deposition of very fine sediments (<250 μm) compared to the 15 m buffers. Coarse (>1 mm) and fine sediments (250 μm – 1 mm) were also higher in the 5 m buffers. We found that sediment connectivity in streams was closely linked to LW dynamics, negatively before harvest but positively after harvest. Before harvest, LW trapped sediment and prevented downstream transport, but after harvest, the increased sediment input overwhelmed this function. Our results highlight a trade-off between the recruitment of LW and minimizing sediment connectivity, two key objectives in riparian buffer management.

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 hydro-geomorphic systems – emerging concepts and their applications’. In this article, 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.

River management is founded on predictable self-organisation between river form and catchment controls in alluvial rivers. However, a substantial proportion of rivers are not fully alluvial. In previously glaciated landscapes, boulder-rich glacial till influences river channel form and process. Increasing interest in nature- and process-based river restoration requires knowledge of pre-disturbance natural processes, which does not exist for semi- and non-alluvial rivers in Fennoscandia. We aimed to determine the role of Pleistocene glaciation and subsequent deglaciation versus Holocene fluvial processes in controlling channel form of boulder-bed rivers in Fennoscandia. We quantified morphological characteristics of northern Swedish boulder-bed rivers, in which channel morphology was minimally impacted by humans, and used the degree of alluvial signatures to infer fluvial and legacy glacial controls. We conducted surveys of reach-scale channel geometry, boulder and wood distributions and catchment characteristics for 20 reference reaches (drainage area: 11–114 km2). Reaches ranged in slope from 1% to 8% and were extremely diverse in channel geometry. Rivers showed little self-organisation at the reach scale; no association exists between channel width and channel slope or bed sediment size. Boulders were rarely clustered into bedforms (e.g., step-pools) typical of boulder-bed mountain rivers. Drainage area was positively correlated with channel capacity but not channel width, slope or sediment size. Channel boulder density was best predicted by surveys of terrestrial boulders. Consequently, channel geometry, boulder size and the distribution of boulders were primarily controlled by legacy glacial conditioning rather than current fluvial processes, with some alluvial adjustment of smaller particles within the boulder template. Therefore, restoration of semi-alluvial rivers should take into account local sediment and geomorphic conditions rather than use management principles built for fully alluvial rivers.