River Segments Research Articles

The Influence of Sediment Transport on Stationary and Mobile Knickpoints in River Profiles

AbstractThe analysis of stationary and mobile knickpoints has been one of the most powerful concepts in tectonic geomorphology for decades. While several models combining bedrock incision and sediment transport are available, the existing theory of knickpoints focuses on detachment‐limited erosion without consideration of sediment transport. On the other hand, fully transport‐limited systems do not maintain distinct knickpoints. This study addresses the existence and the properties of slope‐break knickpoints in fluvial systems between the two extremes with the help of the shared stream‐power model, which allows for a continuous shift between detachment‐limited and transport‐limited erosion. The most important result is that both stationary and mobile knickpoints remain sharp and are not smeared by sediment transport. The system responds to tectonic signals in two phases where the first phase is similar to the detachment‐limited model. Comparing rivers with the same equilibrium profile at a given uplift rate, the velocity of knickpoint migration increases toward transport‐limited conditions. The second phase of the response is dominated by changes in sediment flux and affects the entire river segment downstream of the mobile knickpoint including the fault where the tectonic signal was initiated. During this phase, the mobile knickpoint is flattened in the sense that the difference in steepness index across a slope‐break knickpoint decreases through time. It is also shown that large parts of the theory for the nonlinear model, in particular knickpoint sharpening and stretching, remain valid, but the effect of nonlinearity decreases with increasing contribution of sediment transport.

Geomorphology variables predict fish assemblages for forested and endorheic rivers of two continents.

Stream fishes are restricted to specific environments with appropriate habitats for feeding and reproduction. Interactions between streams and surrounding landscapes influence the availability and type of fish habitat, nutrient concentrations, suspended solids, and substrate composition. Valley width and gradient are geomorphological variables that influence the frequency and intensity that a stream interacts with the surrounding landscape. For example, in constrained valleys, canyon walls are steeply sloped and valleys are narrow, limiting the movement of water into riparian zones. Wide valleys have long, flat floodplains that are inundated with high discharge. We tested for differences in fish assemblages with geomorphology variation among stream sites. We selected rivers in similar forested and endorheic ecoregion types of the United States and Mongolia. Sites where we collected were defined as geomorphologically unique river segments (i.e., functional process zones; FPZs) using an automated ArcGIS‐based tool. This tool extracts geomorphic variables at the valley and catchment scales and uses them to cluster stream segments based on their similarity. We collected a representative fish sample from replicates of FPZs. Then, we used constrained ordinations to determine whether river geomorphology could predict fish assemblage variation. Our constrained ordination approach using geomorphology to predict fish assemblages resulted in significance using fish taxonomy and traits in several watersheds. The watersheds where constrained ordinations were not successful were next analyzed with unconstrained ordinations to examine patterns among fish taxonomy and traits with geomorphology variables. Common geomorphology variables as predictors for taxonomic fish assemblages were river gradient, valley width, and valley slope. Significant geomorphology predictors of functional traits were valley width‐to‐floor width ratio, elevation, gradient, and channel sinuosity. These results provide evidence that fish assemblages respond similarly and strongly to geomorphic variables on two continents.

Prioritizing dams for removal to advance restoration and conservation efforts in the western United States

Dams are socio‐ecological structures fundamentally serving human population growth and economic development. Yet, dams have significantly reduced landscape connectivity, altered hydrologic and geomorphic dynamics, and are a leading cause of freshwater biodiversity decline. As dams age and are no longer used for their original intended purpose, they increasingly threaten both humans and ecosystems. Consequently, dam removal is an increasingly accepted strategy to restore river systems across the United States; since the 1970s, more than 1,400 dams have been removed. As the removal trend continues, important decisions must be made regarding which dams are still ecologically and economically viable and which are optimal for removal to facilitate restoration and subsequent protection. Therefore, it is critical to prioritize dams for removal where rivers, freshwater resources, and ecosystem services will benefit most. To that end, this study uses geospatial analysis and a multi‐criteria decision framework to evaluate dams suitable for removal in the western United States in watersheds with existing conservation priorities, and to examine watershed dynamics in which they are situated. Results reveal 24 top‐ranked dams no longer performing essential ecological and social functions as optimal sites for removal to restore waterways. Of these top‐ranked dams, four are already in the planning process for removal, indicating the model is performing as intended. These results are critical for managers and policymakers to understand where dam removals could enhance overall riverine connectivity and where river restoration could result in subsequent protection of newly free‐flowing river segments in the National Wild and Scenic Rivers System.

Population status of the American crocodile, <em>Crocodylus acutus</em> (Reptilia: Crocodylidae) and the spectacled caiman, <em>Caiman crocodilus</em> (Reptilia: Alligatoridae) in the Costa Rican North Caribbean

Along the Costa Rican Caribbean shoreline, it is possible to find two species of crocodilians, the American crocodile (Crocodylus acutus) and the spectacled caiman (Caiman crocodilus). This region can be divided geographically into three subregions: North, Central, and South Caribbean. We conducted this research in the North Caribbean, between October 6, 2018 and August 31, 2019. Specifically, we worked in the area lying between the Jalova Station of the Tortugero National Park (TNP) and Agua Dulce Lake situated in the northern tip of Machuca Island, at the mouth of the Colorado River inside the Barra del Colorado National Wildlife Refuge (BACORE), which includes other connecting wetlands as well (Sierpe River, Samay Lake). Overall, this study area had an approximate extension of 408 km2 characterized by large, wide and deep canals, as well as wetlands, meanders, and adjacent lakes. The sampling was performed along 10 segments that varied in length from 7.5 km up to 29.49 km, located in the nearby zones of TNP and BACORE. In these zones, nightly counts were carried out using dazzling lamps. Individuals of C. acutus and C. crocodilus were classified into eight and six body size classes, respectively (both with 50 cm intervals). A relative abundance of 0.55 crocodiles and 1.37 caimans per linear kilometer was estimated during these spotlight surveys. The capture of 39 caimans let us to estimate a ratio of 30 males to 9 females (3.3:1 M:F). In stark contrast, only 1 male and 1 female crocodile were captured. A total of 85 C. acutus and 205 C. crocodilus were observed. Regarding the number of caiman sightings in the TNP, a statistically significant difference was found (Χ2=5.62, p≤0.05) for the distribution by sizes between the zones of BACORE and TNP, whereas no such difference was found for C. crocodilus sightings (Z=–1.22, p≥0.222). Some segments had a higher probability of caiman occurrence than did others in the surveys performed during the monitoring period (X2=8.36, p≤0.05), especially the Jalova-Sierpe River, Caño Negro-Tortuguero, and Tortuguero-Samay Lake (Tortuguero subarea) segments. Ninety percent of the sightings occurred in the BACORE zone, and this was significantly different (Χ2=7.34, p≤0.026) from the studied subareas. The number of crocodile sightings in the Colorado River segment was significantly different and higher than the other segments (X2=7.28, p≤0.05). There was a significant statistical difference among the sizes in all areas of study (X2=5.529, p≤0.026). The abundance of C. acutus and C. crocodilus in the north Caribbean part is lower than in the central Caribbean part of Costa Rica, where this species could use the resources available in more urbanized areas.

Nested analysis of macroinvertebrate diversity along a river continuum: Identifying relevant spatial scales for stream communities

AbstractBenthic macroinvertebrates are important for stream ecosystem function and are considerable food resources for vertebrate consumers such as fish. The diversity, composition, and distribution of stream macroinvertebrate taxa are affected by factors that act at different spatial scales, from microhabitat to watershed‐level effects. While comparative studies of watershed‐level and between stream influences on benthic diversity are common, the effects of scale are less investigated within individual river segments. Benthic macroinvertebrates were systematically sampled across nested spatial scales along a 2.2‐km near‐pristine stretch of the Upper Black River (MI, USA), and analyzed in relation to near‐bed flow and substrate features. Responses of community diversity metrics to near‐bed conditions were quantified, and diversity was modeled to determine the contribution of each spatial scale to total diversity. Near‐bed conditions, especially Froude number and substrate size, were positively associated with macroinvertebrate diversity and abundance. Larger (e.g., 100 m stream reach) and finer scales (e.g., individual samples) accounted for a greater proportion of variation in taxon richness and abundance, respectively. Longitudinal variation in environmental conditions was an important driver of macroinvertebrate diversity, with replacement between sites (i.e., turnover) contributing a considerably greater proportion of variation in total diversity than nestedness. Results demonstrate that macroinvertebrate communities were shaped by both local flow and substrate conditions as well as taxa replacement over larger spatial scales. This emphasizes the importance of maintaining the hydro‐morphological integrity along stream courses as a requisite condition to further watershed and fisheries conservation and management.

Determination of load capacity of BOD pollutant in Cisadane River with Qual2kw model & its effect on DO parameters

The research to determine the carrying capacity of pollutant loads in the middle to downstream Cisadane River segment started from Jl. Teuku Umar, Tangerang and ends at Muara Tanjung Burung, Tangerang Regency with a research time starting from March – June 2021. Increased land-use change due to human and industrial activities so that population growth and limited residential land make watersheds a target for land conversion. The purpose of this study is to identify sources of pollutants that have the potential to contaminate the Cisadane River in the middle to downstream segments, analyze water quality and pollutant load capacity, the Cisadane River in the middle to downstream segments along 34 km. The method used for identification of pollutant sources is carried out by conducting field surveys, water quality analysis is carried out by SNI and compared with quality standards according to Peraturan Pemerintah No. 22 of 2021, as well as analysis of the Pollutant Load Capacity (PLC) BOD and DO using the QUAL2Kw model. The results of identifying potential pollutant sources in the middle to a downstream segment of the Cisadane River are dominated by settlements, agriculture, industry, and other domestic activities, namely restaurants and stalls. The results of water quality analysis for BOD parameters ranged from 2.51 mg/L - 5.1 mg/L, and DO range from 5.4 mg/L – 7,2 mg/L. BOD parameters from all points 1-2 meet the quality standard class 2 (3 mg/L) & points 4-6 do not meet the quality standard. The DO parameter is still in good condition because the more significant the DO value, the waters are in good condition. The high levels of BOD in the Cisadane River are influenced by domestic waste that enters the river, and the land is dominated by built-up spaces as settlements, schools, hotels and malls. Land use around the river is very influential on the load of pollutants that enter the river. The lowest DTBP of the Cisadane River for BOD is 22497,9 kg/day, and the highest is 33201,6 kg/day. The decrease in the concentration of BOD load must be lowered in the Cisadane River by 29% - 42%.

What Have We Lost? Modeling Dam Impacts on American Shad Populations Through Their Native Range

American shad (Alosa sapidissima) are native to the east coast of North America from the St. Johns River, Florida, to the St. Lawrence River region in Canada. Since the 1800s, dams have reduced access to spawning habitat. To assess the impact of dams, we estimated the historically accessed spawning habitat in coastal rivers (485,618 river segments with 21,113 current dams) based on (i) width, (ii) distance from seawater, and (iii) slope (to exclude natural barriers to migration) combined with local knowledge. Estimated habitat available prior to dam construction (2,752 km2) was 41% greater than current fully accessible habitat (1,639 km2). River-specific population models were developed using habitat estimates and latitudinally appropriate life history parameters (e.g., size at age, maturity, iteroparity). Estimated coast-wide annual production potential was 69.1 million spawners compared with a dammed scenario (41.8 million spawners). Even with optimistic fish passage performance assumed for all dams (even if passage is completely absent), the dam-imposed deficit was alleviated by fewer than 3 million spawners. We estimate that in rivers modeled without dams, 98,000 metric tons of marine sourced biomass and nutrients were annually delivered, 60% of which was retained through carcasses, gametes and metabolic waste. Damming is estimated to have reduced this by more than one third. Based on our results, dams represent a significant and acute constraint to the population and, with other human impacts, reduce the fishery potential and ecological services attributed to the species.

Basin‐wide hydromorphological analysis of ephemeral streams using machine learning algorithms‡

AbstractSustainable river management now encompasses a much wider concept that includes hydromorphological and fluvial habitat studies. In ephemeral streams, the geomorphological characterization of channels is complex due to episodic flows and riparian vegetation dynamics. Stream channel survey and classification at the watershed scale provide the basis for geomorphological conservation, process interpretation, assessing sensitivity to disturbance, and identifying reaches that supply and store sediment. Here, we present a stream classification based on a two‐step approach: (1) automatic river segmentation based on spatial variability in channel/valley morphology from topographic measurements (LiDAR, light, detection and ranging), and (2) fluvial landform and vegetation density mapping derived from multispectral open‐source satellite images (Sentinel‐2) using support vector machine (SVM) and Random Forest (RF) algorithms. These analyses provide continuous, quantitative spatial values of geometric (channel/valley width, slope gradient, and route distance), landform (active channel and gravel bars with five densities of vegetation cover), and hydraulic (specific stream power) variables. Four stream types were identified in the Rambla de la Viuda catchment (~1500 km2), an ephemeral gravel‐bed river in eastern Spain. The spatial distribution of channel types is explained by differences in geometry (active channel width, valley width, and slope gradient) and a hydraulic parameter (specific stream power). The landforms/vegetation patterns provided insight on causal relationships between erosion and deposition processes during high flow periods and the time since the most recent large disruptive flood event. Channel type distribution provided first‐order predictions about the location of reaches that supply and store sediment and thus information on sediment continuity along the river. Dam effects on downstream reaches resulted in geomorphological disequilibrium, producing narrowing of the active channel, slope reduction, and a decrease of gravel bar areal extension. The proposed catchment scale analysis provides a comprehensive and replicable methodology for environmental planning in Mediterranean ephemeral streams to guide further hydromorphological surveys at the reach scale.

Dazed and confused: Behavioural constraints impose major challenges to fish passage in the neotropics

Abstract The role of fish translocation upstream of dams, for the conservation of migratory species, is controversial. An important but still unaddressed question is whether migratory patterns are affected, after the translocation events, by a hydropower dam. In existing dams, a useful means to test this might be to compare the behaviour of translocated fish with those in undammed river segments in the same region. The objective of this study was to evaluate the effectiveness of fish translocation in promoting access to spawning areas through a behavioural approach using Prochilodus costatus as a study model in the São Francisco River, south‐east Brazil. The reservoir acted as a barrier to the dispersal of translocated individuals with only a small fraction of the population able to locate lotic stretches in the tributaries. Individuals translocated to undammed stretches of river upstream of the reservoir exhibited movement behaviour that was markedly different from that of individuals native to this region. Translocated individuals mainly displayed an erratic pattern of movement between upstream and downstream stretches of river with no specific route. In contrast, local individuals made long‐distance upstream spawning migrations and downstream return migrations to feeding sites during specific periods of the year. The results indicate that translocating individuals upstream of Três Marias dam tends to be ineffective for the conservation of P. costatus in the region. The study showed that the behaviour of translocated individuals, a largely neglected factor for the tropical region, may be an additional barrier to the success of conservation programmes based on fish passage systems. For the population studied, the maintenance of a free‐flowing stretch where fish are able to complete their life cycle is a more viable and effective alternative for conservation.

Are Genomic Updates of Well-Studied Species Worth the Investment for Conservation? A Case Study of the Critically Endangered Magdalena River Turtle.

As genomic-scale data sets become economically feasible for most organisms, a key question for conservation biology is whether the increased resolution offered by new genomic approaches justifies repeating earlier studies based on traditional markers, rather than investing those same time and monetary resources in less-known species. Genomic studies offer clear advantages when the objective is to identify adaptive loci that may be critical to conservation policy-makers. However, the answer is far less certain for the population and landscape studies based on neutral loci that dominate the conservation genetics research agenda. We used Restriction-site Associated DNA sequencing (RADseq) to revisit earlier molecular studies of the IUCN Critically Endangered Magdalena River turtle (Podocnemis lewyana), documenting the conservation insights gained by increasing the number of neutral markers by several orders of magnitude. Earlier research indicated that P. lewyana has the lowest genetic diversity known for any chelonian, and little or no population differentiation among independent rivers. In contrast, the RADseq data revealed discrete population structure with isolation-by-distance within river segments and identified precise population breaks clearly delineating management units. It also confirmed that the species does not have extremely low heterozygosity and that effective population sizes are probably sufficient to maintain long-term evolutionary potential. Contrary to earlier inferences from more limited population genetic markers, our genomic data suggest that management strategies should shift from active genetic rescue to more passive protection without extreme interventions. We conclude with a list of examples of conservation studies in other vertebrates indicating that for many systems a genomic update is worth the investment.

Geomorphic assessment of longitudinal profile of the Kanchi river basin, India: Recognition of dynamic equilibrium condition

ABSTRACT The Kanchi, an eastward flowing river, traverses through the Ranchi plateau of the Proterozoic Chhotanagpur granite gneissic complex to meet its trunk stream, the Subarnarekha River. The present study analyzed longitudinal profiles and associated geomorphic indices of the Kanchi River and its tributaries to identify spatial variation in profile form and fluvial response to prevailing controls. This work was carried out using a digital dataset and maps, which were processed in a GIS environment to obtain longitudinal profiles, and different data required in best-fit modelling and geomorphic investigation of longitudinal profiles. The analyses indicate that the rivers are in dynamic equilibrium condition. Spatial distribution of geomorphic indices values reveals that longitudinal profile forms vary from one segment to another along river channels, and these irregularities in the form of prominent and minor knickpoints are highly concentrated in middle river basin areas. The absence of lithological variation and active tectonics, and close association of anomalously steep river segments with structural lineaments and landforms demonstrates structural control on river channel development. PCA denotes strong similarities between geomorphic indices. This understanding of longitudinal variation in river nature may help to formulate strategies for the sustainable development and management of river related resources.

Hot spot of CH4 production and diffusive flux in rivers with high urbanization

Rivers and streams play a central role in global carbon budget, but our knowledge is limited on the magnitude and extent of urbanization influence on riverine methane (CH4) dynamics. In this study, we investigated dissolved CH4 (dCH4) concentration and CH4 diffusive fluxes in 27 river segments of two 4th-order and three 3rd-order tributary rivers to the Yangtze River in China, which drained land areas with varied urbanization intensities. We found that urban development was the key factor responsible for high fluvial dCH4 concentration and diffusive flux, exceeding the influence of agricultural farming, and these headwater rivers were over-saturated in CH4 with respect to atmospheric equilibrium. dCH4 concentration (3546 ± 6770 nmol L−1) in the river segments draining higher urban area (20% ≤ urban land proportion ≤ 46%) was 5-6 times higher than those (615 ± 627 nmol L−1 and 764 ± 708 nmol L−1) in the river segments draining less urban area (0.1% ≤ urban land proportion < 2% and 2 ≤ urban land proportion < 20%). River segments draining higher urban area also acted as important sources of CH4 to the atmosphere (8.93 ± 14.29 mmol m−2 d−1). Total nitrogen (TN) concentration in river water showed the best prediction capacity when compared to other water parameters. Based on urban land use grouping, nutrient elements could predict dCH4 well in rivers draining higher urban areas (urban ≥ 2%), which also reflected the lateral input of pollutants (TN, ammonia nitrogen, and total phosphorus). River bottom sediment fraction contributed to trapping organic matter and nutrients as well as to oxic and anoxic conditions, thereby determining reach-scale spatial patterns of dCH4 concentration. These findings highlight that combining distal geomorphic and hydrologic drivers can be effective in determining the relationship between riverine CH4 and the proximal controls (e.g., nutrients, dissolved oxygen, dissolved organic carbon), as well as in identifying their key drivers. Being rapid urbanization a common feature of catchments worldwide, our results suggest riverine CH4 emissions will increase into the future.

남강 상류 유역 시설하우스 유출수의 하천 오염기여도 평가

This study was done to address the effect of greenhouse cultivation effluents on river waters in the Upper Nam River Basin. We measured flow rate and six water quality parameters at the final outlet of the greenhouse cultivation during eight rainfall events randomly occurred between October 2019 and April 2021 which were provided as input to a popular watershed modeling tool SWAT. The years 2012-2014, 2015-2016, and 2017-2018 were set as the warm-up, calibration and validation periods, respectively. Our findings showed that a good model performance was achieved for discharge prediction reaching minimum R² values of 0.65, which was followed by sediments, NO₃, ORGP, and BOD. Annual pollutant loads estimated from the monitoring data were slightly lower than the land-based (unit) pollutant loads. Accordingly, the pollutant load contributions to receiving waters were underestimated by 6.35 % (for BOD), 1.86 % (for T-N), and 3.09 % (for T-P). In addition, pollutant movement, described as the delivery ratio of pollutant loads, varied largely across 18 river segments for BOD and but to only a small extent for T-N and T-P. This calls for more sophisticated monitoring and modeling efforts to develop customized water management strategies along the river segments.

A deep learning model for predicting river flood depth and extent

This paper presents an innovative deep learning (DL) framework to (a) automatically identify river geometry and flood extent, and (b) predict river flooding depth. To do that, U-Net, an advanced convolutional neural network (CNN), was modified and given the designation of U-NetRiver. With the modification, the model received an input composite image with two bands of ground elevation and flooding discharge, and the output was water depth. The model was trained and validated based on the outputs from iRIC (a two-dimensional hydraulic model) for a segment of the Green River in the state of Utah. The results showed that the U-NetRiver could identify the river shape and wetted areas for flooded regions automatically. The maximum difference of predicted river depth obtained from U-NetRiver and the one obtained from the hydraulic model was 2.7 m. This result suggests a 29% improvement in prediction of the maximum flood depth in the river.

Forcing uncertainty and salinity response to dredging in a tidal freshwater river

ABSTRACT This study evaluates the salinity response to dredging under different forcing regimes for a 75-kilometer segment of the flood-prone Vermilion River located in coastal Louisiana, USA. The Vermilion is a tidal freshwater river affected by baseflow regulation, rapid urbanization, and hydromodification. This river also serves as major freshwater resource for the region. An efficient one-dimensional model calibrated previously for stage and water temperature is used to analyse the salinity impacts due to a large-scale flood control dredging. The analysis is based on 200 alternative scenarios based on combinations of uncertain key forcing variables for a critical 13-day intrusion period. The analysis reveals a nonlinear effect on mean salinities and position of the brackish water limit as a function of uncertain forcing variables. Dredging also increases the variability of salinity encroachment effects due to uncertainty in future forcing conditions (e.g. relative sea level rise, baseflow diversion volumes, and salinities at the river mouth). The robust analysis presented here provides a foundation for future model-based assessments of under-studied tidal freshwater rivers and provides key insights for coastal management and sustainability efforts in general.

Risks to Fish Populations in Dryland Rivers From the Combined Threats of Drought and Instream Barriers

In dryland rivers, flow intermittency means fish populations are often subjected to drought disturbance. The viability of these fish populations depends on the availability of waterhole refuges for individuals to survive drought (resistance) and the ability of surviving fish to repopulate the rivers by recruitment and dispersal once flow returns (resilience). In this study we combined remote-sensed mapping of the locations of waterholes that lasted through an extreme drought in the northern Murray Darling Basin, Australia, with an assessment of the impacts of in-stream barriers on limiting the opportunities for fish to move and repopulate after drought. We found that at the peak of this 2018–2020 drought, the worst on record for some rivers and the most spatially synchronous recorded across the region, waterholes were few and generally small – representing only 11% of the total river channel network. All the fish in the region that survived the drought were concentrated into this limited waterhole refuge habitat. Even small instream structures, such as minor weirs, caused large reductions in the opportunities for fish to move between river segments when there is flow. Almost all the 104 instream structures assessed reduced long-term fish movement opportunities, measured as days with discharge greater than calculated barrier drown out thresholds, by more than 70% and up to 100%, when compared to opportunities for movement if the barrier was not present. This large impact from small instream barriers is a consequence of flow intermittency and is likely to reduce fish population resilience and impact the capacity of fish populations to recover after drought. Combining information on the risks posed by limited refuge habitat availability during drought and from reduced movement opportunity following drought allowed us to identify river segments where these combined threats are the greatest risk to viability of local fish populations. Considering the spatial arrangements of these risks provides a means to systematically prioritize mitigation measures such as weir removal to improve fish movement opportunities and local management of key waterholes to increase drought resistance. The approach used here provides a guide for assessing and prioritizing the management of fish population viability risks from drought and fragmentation by barriers in any non-perennial river setting.

High-resolution remote sensing and multistate occupancy estimation identify drivers of spawning site selection in fall chum salmon (Oncorhynchus keta) across a sub-Arctic riverscape

Groundwater upwellings provide warmer, stable overwinter temperatures for developing salmon embryos, which may be particularly important in cold, braided, gravel-bed sub-Arctic rivers. We used a three-year time series of aerial counts and remote sensing to estimate the distribution of low and high aggregations of spawning fall chum salmon (Oncorhynchus keta), classify approximately 0.5 km long river segments by geomorphic channel type, and map thermal variability along a 25.4 km stretch of the Teedriinjik River, Alaska. We used a dynamic multistate occupancy model to estimate detectability, occupancy, and the dynamics of spawning aggregations among river segments. Detectability was higher for large (&gt;150) relative to smaller aggregations. Unoccupied segments were likely to remain so from year to year; low abundance spawning segments were dynamic and rarely remained in that state for multiple years, while ∼20%–35% of high abundance segments remained stable, indicating the presence of high-quality spawning habitat. Spawning habitat use was associated with warmer water temperatures likely caused by groundwater upwellings. We identified spawning habitat characteristics and trends in usage by fall chum salmon, which will inform land management decisions and assist in evaluating impacts of shifting climate conditions and resource management on Arctic salmon populations.

Large-Scale River Mapping Using Contrastive Learning and Multi-Source Satellite Imagery

River system is critical for the future sustainability of our planet but is always under the pressure of food, water and energy demands. Recent advances in machine learning bring a great potential for automatic river mapping using satellite imagery. Surface river mapping can provide accurate and timely water extent information that is highly valuable for solid policy and management decisions. However, accurate large-scale river mapping remains challenging given limited labels, spatial heterogeneity and noise in satellite imagery (e.g., clouds and aerosols). In this paper, we propose a new multi-source data-driven method for large-scale river mapping by combining multi-spectral imagery and synthetic aperture radar data. In particular, we build a multi-source data segmentation model, which uses contrastive learning to extract the common information between multiple data sources while also preserving distinct knowledge from each data source. Moreover, we create the first large-scale multi-source river imagery dataset based on Sentinel-1 and Sentinel-2 satellite data, along with 1013 handmade accurate river segmentation mask (which will be released to the public). In this dataset, our method has been shown to produce superior performance (F1-score is 91.53%) over multiple state-of-the-art segmentation algorithms. We also demonstrate the effectiveness of the proposed contrastive learning model in mapping river extent when we have limited and noisy data.

Research on the impact of ship traffic flow on the restricted channel segment of the middle Yangtze River based on traffic wave theory

On the basis of the influence of dry season on ship traffic flow, the gathering and dissipating process of ship traffic flow was researched with Greenshields linear flow—density relationship model, the intrinsic relationship between the ship traffic congestion state and traffic wave in the unclosed restricted channel segment was emphatically explored when the ship traffic flow in a tributary channel inflows, and the influence law of multiple traffic waves on the ship traffic flow characteristics in unclosed restricted segment is revealed. On this basis, the expressions of traffic wave speed and direction, dissipation time of queued ships and the number of ships affected were provided, and combined with Monte Carlo method, the ship traffic flow simulation model in the restricted channel segment was built. The simulation results show that in closed restricted channel segment the dissipation time of ships queued is mainly related to the ship traffic flow rate of segments A and C, and the total number of ships affected to the ship traffic flow rate of segment A. And in unclosed restricted channel segment, the dissipation time and the total number of ships affected are also determined by the meeting time of the traffic waves in addition to the ship traffic flow rate of segments. The research results can provide the theoretical support for further studying the ship traffic flow in unclosed restricted channel segment with multiple tributariesArticle HighlightsThe inflow of tributaries' ship traffic flows has an obvious impact on the traffic conditions in the unenclosed restrictedchannel segment.The interaction and influence between multiple ship traffic waves and the mechanism of generating new traffic waves are explained.The expression of both dissipation time of queued ships and the total number of ships affected in the closed and unclosed restricted channel segment are given.

Quantile regression illuminates the successes and shortcomings of long-term eutrophication remediation efforts in an urban river system

Despite massive financial investment in mitigation, eutrophication remains a major water quality problem and management priority. Eutrophication science—well established for lakes—is not as well developed for rivers, and scientific understanding of how rivers respond to eutrophication management is far more limited. Long-term data are required to evaluate progress, but such datasets are relatively rare for rivers. We analyzed 23 years of water quality data for the Charles River, a major urban river system in the northeastern U.S.A., to examine nutrient and phytoplankton biomass (chl-a) responses to decades of phosphorus (P) management. Using the more novel and robust approach of quantile regression, we identified statistically and ecologically significant declines in both total phosphorus (TP) and chl-a over time, but only for middle percentiles. Statistically high concentrations of TP and chl-a persist—the segments of the data of greatest concern to managers and the public—and yet this critical result is concealed by statistical tests often employed in eutrophication studies that only evaluate mean changes. TP, temperature, precipitation, and river segment jointly explain the most chl-a variation observed at the decadal scale. Spatial variation is also considerable: despite a significant decline in TP, the impounded lower river exhibits no long-term trend in chl-a and continues to experience annual blooms of harmful cyanobacteria—a lagging response comparable to that of a recovering eutrophic lake. Despite long-term successes in reducing P, chl-a, and cyanobacteria in the Charles River system, we did not detect any significant, long-term change in the attainment of statutory compliance, illustrating the protracted and complex nature of the river's response. Our analysis demonstrates the need for high-frequency, long-term water quality data to evaluate the progress of eutrophication management in urban rivers, and the utility of quantile regression for detecting critical trends in the occurrence of statistically low-frequency but ecologically high-impact events, including blooms of harmful cyanobacteria.