Modification of river corridors, particularly deforestation and the removal of large wood, has greatly altered the abundance and influence of large wood in most rivers in the temperate latitudes. The conceptual framework of large wood process domains can assist in both directing research and facilitating large wood-related management and restoration in rivers. Large wood process domains are spatially or temporally distinct portions of a river network or region with distinct processes of wood recruitment, transport, and storage. Previous research has shown wood to be unevenly distributed across space and time. We use a data set of logjam distribution density (# of channel-spanning logjams/100 m length of channel) in 304 spatially distinct reaches of mountain streams in the Colorado Front Range, and up to 11 years of repeat measurements at some reaches, to (a) statistically evaluate whether a priori designated process domains for logjam distribution density are distinctly different and (b) evaluate the sensitivity of process domain delineations to spatial and temporal sample size. Our results indicate that the major spatial controls on logjam process domains for logjam distribution density in the Southern Rockies are drainage area, reach morphology, and wildfire disturbance history. Greater logjam distribution densities were present in wide reaches and undisturbed catchments. Using subsets of the data set composed of under 100 reaches created similar results. The relationship between geomorphic and hydrologic characteristics and their ability to describe logjam distribution density was minimally affected when using fewer than 10 years of data.

Arctic rivers transport water, sediment and carbon, playing a central role in coastal stability and biogeochemical cycling. Although freshwater discharge to the Arctic Ocean has increased in recent decades, limited observations have hindered system-wide assessment of long-term, reach-level sediment dynamics. Here we develop a pan-Arctic-specific, satellite- and machine learning-based framework to reconstruct four decades of suspended sediment concentration dynamics for 4,331 river reaches. Our analysis reveals a significant increase in suspended sediment concentration in 40

Forests cover nearly one third of Earth’s land. Dead, downed wood plays a critical role in the planet's physical, biogeochemical, evolutionary, and ecological processes. Wood from terrestrial source areas moves into freshwater and marine environments in wood cascades. Cascades embody a ‘source-to-sink’ approach emphasizing the details of connectivity between production and eventual recycling and can be applied at local to global scales. We lack quantitative studies of specific source-to-sink wood movement, including volumes of wood involved in the cascade, timespans of transport and storage, or partitioning of terrestrial wood from a particular forested area into diverse potential sinks. Characterizing wood cascades can highlight differences in wood dynamics from source to sink and identify geographically specific wood cascades disrupted by human activities, the potential consequences associated with this disruption, and strategies for mitigating the disruption. We review existing understanding of wood production at terrestrial sources, transport processes and rates in freshwater and marine settings, and wood abundance in sinks, and highlight knowledge gaps. Wood dynamics in forests and rivers are the best understood components of wood cascades. Global deforestation and freshwater and coastal management have drastically altered wood cascades. Despite the documented importance of wood, contemporary understanding of wood abundance and quantitative prediction of transport processes and pathways or wood accumulation sites is limited. An integrative conceptualization of wood from source to sink and research targeted at known gaps can advance our understanding of the importance of wood and inform efforts to manage wood for human and environmental benefits.

Abstract Riparian vegetation and wood play crucial roles in enhancing spatial heterogeneity in rivers. Historical removal of large wood and cutting of streamside forests around the world have simplified rivers and substantially reduced aquatic habitat complexity. To understand how natural rivers sustain geomorphic and hydrologic complexity and support aquatic diversity, we carried out an interdisciplinary field study in a stream flowing through a natural forest in Hokkaido, Japan. We mapped a total of 631 large wood pieces, including 77 log jams, as well as 65 side channels (total 10.1 km) along a 9.2‐km length of the main channel. More avulsions (channel divergence) and side channels were present in stream sections with a greater density of large wood and logjams. At flood stage, 90% of the side channels were inundated with through‐flowing river water, while the other 10% remained disconnected from the main channel and harbored stagnant water. At base flow, only 20% of the side channels had flow from the mainstem river, 46% contained stagnant water, and 34% were dry. The cumulative areas of permanent, transient, and disconnected side channels were 20%, 9%, and 6% of the main channel area, respectively. We estimated the contribution of each habitat type with different hydrological regimes to the entire population of aquatic animals in the study area. The analysis demonstrated that 4 out of 11fish taxa, 5 out of 26 benthic macroinvertebrate taxa, 3 out of 3 plankton taxa, and 2 out of 2 amphibian taxa primarily utilized transient or disconnected channels. Furthermore, cohort analysis of the dominant fish Salvelinus leucomaenis showed that they exhibit ontogenetic habitat shifts from channels with transient flow as juveniles to channels with permanent flow, indicating the need for both types of habitats and for connectivity between these habitats. Our results demonstrate forms and processes characteristic of the mostly lost and forgotten baseline of rivers in Japan; how geomorphologically and hydrologically complex a natural river can be; and how aquatic organisms rely on such complexity. Large wood potentially plays important roles in sustaining such complexity, and further studies should investigate these mechanisms.

Abstract Logjams in streams create complex morphologic features such as pools, bars, and branching channels that enhance stream water storage and force water through the streambed. We examine how these features alter solute retention in stream corridors as discharge increases, backwaters expand, new channels activate, and jams become more submerged. Using numerical experiments informed by a well‐studied field site (Little Beaver Creek, Colorado, USA), we simulate coupled surface water and groundwater flow in stream reaches with logjams. Model results indicate that solute retention declines with increasing stream discharge, although the magnitude of decline depends on the metric used to quantify retention. We do not observe threshold‐like changes when dry channels reactivate but only modest deviations from the overall trend, suggesting that reactivation does not produce strong threshold‐like changes in retention behavior in already complex reaches. As discharge increases, backwater pools enlarge and hyporheic exchange volumes increase, but backwaters comprise a diminishing fraction of total channel storage, leading to reduced overall retention. Hyporheic zone volume and the turnover length both increase with discharge, indicating a larger but weakly connected hyporheic zone. Taken together, we expect substantially greater biogeochemical transformation at low flows in complex mountain streams. This research offers new insights into potential reach‐scale changes in solute transport through complex mountain streams as streamflow changes, which can be expected with the loss of snowpack under a warming climate.

Headwater streams include first- and second-order channels with ephemeral, intermittent, or perennial flow. Delineation depends on accurate mapping of channel heads, which remains challenging. Consequently, headwaters are underrepresented in river network maps. Hydrology is governed by processes in adjacent uplands. Proportions of surface and groundwater contributions vary spatially and temporally, partly because of impeding layers. The wetted expanse varies seasonally and flows are likely to decline with climate warming. Morphology is temporally and spatially variable. Channels tend to be < 2 m wide but may not exhibit downstream hydraulic geometry. Headwaters can exhibit greater episodicity in sediment transport. Water chemistry is strongly influenced by factors external to the channel and can be variable or stable. The influence of riparian zones on biogeochemistry depends on the strength and location of hydrological connectivity. Hyporheic exchange typically affects a larger proportion of total stream flow, although this may be only 2% of discharge. Headwater gaseous emissions remain poorly quantified but have been estimated at more than 70% of global riverine CO2, CH4, and N2O emissions. Headwaters may be particularly vulnerable to diverse stressors because their small catchment areas, close coupling to uplands, short channel lengths, and lack of floodplains limit buffering of inputs. Their small size and inaccurate delineation also limit regulatory protection and makes headwaters prone to obliteration. Headwater stream flows are likely to decline in magnitude and spatial extent as climate warms. Despite substantial gaps in understanding of headwaters, existing research clearly indicates their importance to the functioning of larger rivers.

The 2023 drought in the Amazon triggered overlapping socioecological impacts across diverse riverine settings. We integrate hydrological indicators, remote sensing-based surface water mapping and media documented testimonies from communities in the Lower Amazon region to examine how environmental context mediates vulnerability. Communities were grouped into six hydro-geomorphic types across major river and floodplain environments. Statements were coded into eleven impact categories and normalized to avoid overweighting. Satellite comparisons between high water and the drought peak revealed surface-water losses of up to 76

Ecosystems associated with rivers are intricately connected to their entire watershed. The river ecosystem includes the channel of active water flow, floodplain, and riparian and hyporheic zones. This ecosystem is shaped by interactions among the natural flow of water, sediments within the river and entering the river, and large wood regimes within the riparian zone. River integrity describes the ability of a river ecosystem to adjust to changes in these elements and through these adjustments maintain the habitat, disturbance regime, and connectivity necessary to sustain native biotic communities. Riverine food webs conceptualize the coupling between the physical environment and biotic communities and can be used to examine recovery from disturbance, variation in the structure of communities, and sources of energy that fuel metabolism within the ecosystem.

Log jams enhance hydraulic and geomorphic diversity in river corridors. Channel-spanning log jams induce backwatering, increase local flow heterogeneity, promote sediment deposition, and improve aquatic habitat diversity. Despite their increasing popularity in river restoration, predicting their hydraulic effects remains a challenge. We developed a model to predict dimensionless head loss through log jams for sub-bankfull flows as traditional backwater methods are limited in variable natural channels. We developed the model from historical flume studies and tested the model application on field data from natural jams. As solid volume fraction increased, we found that dimensionless head loss also increased. Field application of our model successfully predicted head loss in naturally occurring log jams. Roughness values (Manning's and Darcy-Weisbach ) varied but generally decreased with increased unit discharge. Our approach for determining head loss and roughness allows for better prediction and design of the localized hydraulic impacts of log jams.

The wood regime describes the recruitment, transport, and retention of wood in rivers. While there are data-intensive methods for understanding these processes, such as wood budgeting and transport modeling, it remains difficult to holistically assess the wood regime, especially over large spatial and temporal scales. To address this difficulty, we present the conceptual framework of wood equilibrium. Like sediment equilibrium, wood equilibrium posits that wood load can be in equilibrium with supply, a state characterized by a consistently positive correlation between wood load and wood retention capacity (i.e., the capability of a reach to retain wood). Likewise, there also exist transport-limited and supply-limited states, in which wood retention is greater or less than capacity, respectively. We apply the wood equilibrium framework to understand the wood regime of two large, lowland rivers in Washington State, USA by comparing wood load to retention capacity and the spatial distribution of wood recruitment. We find evidence for wood equilibrium state varying in both space and time in response to changes in wood recruitment, transport, and retention capacity. We discuss how the wood equilibrium framework can be used to understand the wood regime and potential responses to wood reintroduction and river restoration.

Storage-dominated alluvial reaches of river corridor in mountain streams, known as river beads, provide disproportionately important attenuation of downstream fluxes of diverse materials at local- to network-scales. We refer to attenuation as bead functionality. We evaluated potential controls on functionality in beads by statistically evaluating relationships between 28 driver and 5 response variables. Driver variables represent inputs of water and sediment and biophysical interactions that could influence bead functionality. Geomorphic driver variables represent water inputs to the stream corridor (e.g., drainage area, catchment slope, elevation, land cover, precipitation metrics), sediment inputs (catchment slope, the metric of normalized burn index), and bead geometry (e.g., bead size, floodplain/channel width ratio). Biotic driver variables within each bead include wood load, beaver modifications, and type of riparian vegetation. Response variables are proxies for attenuation and storage within river beads. Response variables include greenness (normalized difference vegetation index), wetness (normalized difference water index), patch density, patch count, and total sinuosity. Driver and response variables were measured through a mixture of fieldwork and remote data for 52 beads in 27 catchments in the Colorado Front Range, USA. Statistical analyses examined relationships between drivers and responses and the effectiveness of grouping the beads by dominant vegetation and by elevation zone. Analyses suggest that bead functionality is most strongly linked to bead ratio, or the ratio of bead size to catchment size. Functional beads are larger relative to catchment size. In addition, bead types grouped by dominant vegetation reflect significant differences in catchment geometry, geomorphic inputs, and biotic inputs, and display significant differences in bead geometry. Although functionality is the complex result of numerous factors and may require case-by-case assessment efforts, restoration of channel-floodplain connectivity and facilitating greater retention of water will enhance bead functionality by increasing the width of the active floodplain. Investigating drivers of functionality provides a crucial link between system inputs, restoration action, and desired response, allowing plans to be tailored to address targets. Because bead position and geometry cannot be feasibly modified, the functionality framework can be used to identify sites with the greatest potential for restoration.

There has been a growing interest in integrating geological and ecological processes for sustainable river management and restoration. Lotic systems are shaped by diverse physical processes, including geology, geomorphology, hydrology, and interactions with terrestrial processes. However, restoration practices often prioritize specific habitats or river forms without fully considering the underlying physical processes that support biological communities and ecosystem functions. In this paper, we synthesize studies that integrally examine geological and ecological processes across different scales and components of riverscapes, including geohydrological processes, which have been less investigated in riverscape studies. We begin by examining processes at broader spatial scales, including river–watershed and river–riparian interactions, and gradually narrow our focus to the dynamics that occur among habitats within river channels, through which we highlight the significance of conceptualizing rivers as dynamic “networks” rather than linear features. Finally, we identify both scientific and practical challenges that can be addressed to bridge the gap between basic-science implications and their implementation in riverscape restorations.

Semiarid grassland streams are sensitive to land use, climate, extreme discharges, and internal geomorphic thresholds that drive episodic erosion. Rooted in a process-based philosophy and commonly applied to historically wood-rich, beaver-modified systems, low-tech process-based restoration using structures is increasingly being extended to other geomorphic settings, including grasslands. In these wood-poor systems with fine-grained substrate, channel adjustment depends primarily on subsurface soil piping and asynchronous responses to changing boundary conditions. We evaluate post-grazing recovery and structural restoration outcomes at transect-to-landscape scales in southeastern Colorado. Following grazing cessation, soil compaction decreased after roughly a decade of rest, as indicated by a multivariate linear regression analysis of 238 bulk density samples. In contrast, visible above-ground upland vegetation recovers on timescales longer than the observation window (> 10 years), based on analyses of growing-season composite Landsat imagery from 2013 to 2024. Logistic regression models indicate that the performance of restoration structures depends strongly on drainage area, slope, local vegetation cover, and the recency of large-scale commercial grazing. In total, only similar to 30% of the 92 in-channel structures evaluated (mostly <= 4 years old) were both intact and produced visible geomorphic change. Structures in piping-dominated headwaters remained intact but rarely trapped sediment, whereas those in larger catchments were more likely to initiate local geomorphic change, despite having higher odds of destruction during peak flows. These findings highlight the need to match restoration strategies with the geomorphic processes driving channel adjustment and call into question the extent to which commonly implemented structure-based interventions in grassland systems are truly process-based.

In‐channel wood, a critical component of forested rivers, has the capacity to enhance hyporheic flow. This process facilitates the continuous exchange of gases, solutes, and nutrients across the sediment‐water interface, regulating pollutant transport and biogeochemical cycles in rivers. When two wood structures are in close proximity, the hyporheic flows induced by each log can interact, yet such effects remain largely uncharacterized. In this study, we investigated the impact of two in‐line channel‐spanning logs with a vertical gap above the sediment‐water interface on hyporheic flow through laboratory experiments conducted under various conditions. Specifically, we measured water surface profiles, surface flow fields, and hyporheic flow fields around logs with different center‐to‐center distances (). Our results demonstrated that when the center‐to‐center distance between two logs was less than 10 times the log diameter, the wakes of the two logs interfered with each other, resulting in a decrease in both hyporheic flow rates and the difference in water surface elevation. Furthermore, we demonstrated the relationship between the pattern of log‐induced hyporheic flow and the surface flow regime. Our results suggest that the hyporheic flow pattern induced by logs can be inferred from measurements of the surface flow patterns. Our findings will contribute to an improved estimation of hyporheic flow induced by logs distributed along river channels.

The ecology of forests, their losses, and terrestrial wood decomposition dynamics have been intensively studied and reviewed. In the aquatic realm, reviews have concentrated on large wood (LW) in rivers and the transition from freshwater to marine environments in the Pacific Northwest of North America. However, a comprehensive global synthesis of LW dynamics, including decomposition processes and human influences across the freshwater-marine continuum, is lacking. Here, we review the role of LW and its fate across the entire freshwater-to-marine gradient and synthesise our findings in an integrative conceptual overview. LW has been exported by rivers to sea for hundreds of millions of years. During this journey, LW acts as an ecosystem engineer by modifying its environment and the landscape. In rivers, LW alters hydrodynamics, resulting in sediment retention and changes to riverbed and shoreline morphology. Along coastlines, driftwood initiates dunes, prevents erosion, retains moisture, and provides lignocellulose-based nutrients. Important habitats provided by floating rafts and sunken 'islands' of wood are found across estuarine, shelf and open/deep seas. Wood degradation gradually transitions from mechanical to biomechanical and chemotrophic. In rivers, degradation is primarily mechanical due to abrasion and impacts. In estuaries, salinity increases, allowing marine wood borers to begin biomechanical degradation; their activity remains the main degradation cause across marine environments. On the seafloor, chemotrophic micro-organisms finalise decomposition of small fragments. LW accumulations act as biodiversity hotspots across the freshwater-to-marine gradient. River communities rely on induced abiotic changes such as meanders, pools, and riffles, while log jams and dams serve as velocity and predation shelters, and create pools with cooler, deeper water. The wood itself acts as attachment substrate for eggs and larvae. From estuaries seaward, the focus fully shifts to LW itself: driftwood provides lignocellulose for wood-boring organisms and stable substrate for sessile animals and macroalgae. In shelf seas and open oceans, floating LW rafts provide shade, shelter, and attachment substrate. Humans have greatly decreased export of LW from river to sea by clearing forests for agriculture and urbanisation, damming rivers, and removing LW 'debris' that is often deemed a hazard or nuisance in developed areas. Indeed, the annual export of LW >3 m long to marine environments has decreased by 5,000,000 m3 compared to the pre-landscape-domestication period. Any wood that reaches the sea washes up on shore or sinks, where it is often removed by bottom trawling. Restoring historic levels of LW is implausible, but reintroductions can restore ecosystem functions along the freshwater-to-marine gradient. Thus far, restoration research has focused on freshwater systems, while such work is in its infancy in coastal and marine environments. We argue that managers should consider incorporating LW reintroductions at scale, as a natural and cost-effective restoration measure across freshwater and marine environments.

As beavers (Castor spp.) are reintroduced to streams in the northern hemisphere and nature-based and process-based river restoration emphasizes human-built analogues for beaver dams, it is reasonable to ask how beaver dams and ponds compare to different types of small dams constructed by humans for diverse purposes. We use published research as a basis for comparing the effects of beaver dams and four types of human dams-beaver dam analogues, earthen embankments perpendicular to flow that are used to create stock ponds, check dams, and mill dams. We compare these dams with respect to water balance and three-dimensional hydrologic connectivity, sediment, particulate organic matter and carbon, nutrients, habitat, and biota. These assessments inform us in ranking small dams from generally most beneficial with respect to providing ecosystem services (beaver meadows with multiple dams) to least beneficial (mill dams), recognizing that beaver meadows may not be beneficial at some sites for infrastructure and human property within the river corridor, and mill dams may be beneficial at some sites where they impede upstream migration by invasive species or provide lentic habitat in the river corridor. This comparison among dam types highlights the need for research on the cumulative effects of multiple small dams along a river corridor and across a river catchment, as well as identifying gaps in our understanding of the effects of specific types of dams, including the effects of stock ponds and check dams on carbon and nutrient dynamics.

The ordinary high water mark (OHWM) defines the lateral extent of nontidal aquatic features in the absence of adjacent wetlands in the United States. The federal regulatory definition of the OHWM, 33 CFR 328.3(c)(7), states the OHWM is “that line on the shore established by the fluctuations of water and indicated by physical characteristics such as [a] clear, natural line impressed on the bank, shelving, changes in the character of soil, destruction of terrestrial vegetation, the presence of litter and debris, or other appropriate means that consider the characteristics of the surrounding areas.” This is the first manual to present a methodology for nationwide identification and delineation of the OHWM. A two-page data sheet and field procedure outline a weight-of-evidence (WoE) methodology to organize and evaluate observations at stream sites. This manual presents a consistent, science-based method for delineating the OHWM in streams. It also describes regional differences and challenges in identifying the OHWM at sites disturbed by human-induced or natural changes and illustrates how to use remote data to structure field inquiries and interpret field evidence using the principles of fluvial science. The manual demonstrates that, in many landscape settings, the OHWM may be located near the bankfull elevation.

Wide, low-gradient segments within river networks (i.e., beads) play a critical role in absorbing and morphologically adapting to disturbances, including wildfires and debris flows. However, the magnitude and rate of morphological adjustment and subsequent hydraulic conditions provided by beads compared to pre-disturbance conditions are not well understood. This study analysed trajectories of river morphology, flood attenuation and hydraulic fish habitat following the 2020 Cameron Peak Fire and July 2022 debris flow and flood at Little Beaver Creek, Colorado, USA. Using repeat aerial imagery, ground-based surveys and hydrodynamic modelling, we assessed morphological changes in a 600-m-long bead of Little Beaver Creek. Metrics of floodplain destruction and formation and channel migration greatly increased in magnitude after the first post-fire runoff season but returned to the historical range of these metrics three years after the fire. The 2022 flood deposited sediment, infilled side channels, reduced pool area and increased the area of bars and islands. Flood wave attenuation and hydraulic habitat conditions did not show clear improvement or impairment despite more rapid changes in system geometry, geomorphic unit abundance and geomorphic unit location. The ability of the site to attenuate peak flows changed minimally and inconsistently over the studied floods. Various lotic habitat conditions changed-namely a reduction in floodplain access and deepening of certain pools-but the overall flow-type diversity of the system was not largely impacted. The resilience of the active channel of Little Beaver Creek to the fire and flood disturbances while retaining key services demonstrates the importance of river beads for enhancing river-floodplain resilience to large disturbance events and highlights river beads as key areas for preservation and restoration.