River Ecological Restoration Research Articles

Removal characteristics of heavy metals from polluted river water purified by hybrid constructed wetlands.

Heavy metal pollution in urban rivers has become a global issue. In this study, hybrid constructed wetlands (HCWs) were used to comprehensively evaluate the effectiveness of field wetland projects in removing heavy metals, with evaluation metrics including seasonal variations, plant contributions, and structure compositions. The experimental results showed that the synergistic system of root-microorganism-substrate formed in the combined process well realized the high efficiency of heavy metal removal, in which the removal rate in the warm season was higher than that in the cold season. The average removal rates of Cu, Zn, Cr, and Pb were 44.62%, 43.12%, 40.59% and 45.18%, respectively. In the effluent, Zn and Cr can better meet the corresponding standards of the US, EU, and CN, and the biotoxicity of Cu and Pb was also greatly reduced. Compared to Cu, Cr, and Pb, the removal of Zn was less affected by influent loads and stable removal was achieved. In HCWs, the primary contribution to heavy metal removal is attributed to sediment deposition, subsequently followed by the uptake by plant roots and stems, with adsorption onto fillers being the least significant. These results of the study show that HCWs can effectively treat heavy metal pollution in water bodies, and are a highly efficient process for ecological remediation of urban river water. Most importantly, HCWs have demonstrated strong adaptability during the operation of actual ecological restoration projects. Additionally, HCWs can adjust the component structure according to the specific conditions of the process to realize the highest efficiency, which provides a new idea for urban river ecological restoration.

Impacts of mining on the diversity of benthic macroinvertebrates - A case study of molybdenum mining area in Luanchuan county

Mineral exploitation is one of the human activities that seriously affect freshwater ecosystems. It is of great significance to study the impact of mining on the α and β diversity of macroinvertebrates. This study reveals the response of taxonomic and functional α and β diversity of macroinvertebrates to mining activities in the Luanchuan molybdenum mining area. A total of 40 sets of macroinvertebrates, sediment and water samples in the Taowan North River (TR), Yu River (UR) and Hongluo River (HR) in the molybdenum mining area were collected. The results show that: 1) the mining activities led to obvious differences in the environmental factors of the three rivers. The heavy metals in the sediments and water bodies of TR and UR showed different degrees of exceedance, while there was no exceedance of heavy metals in HR; 2) The taxonomic and functional α diversity was much lower in the TR and the UR than in the HR. The concentrations of heavy metals in sediments and water bodies were significantly negatively correlated with the taxonomic and functional α diversity; 3) Mineral extraction resulted in significant differences in macroinvertebrate β diversity among the three rivers. The taxonomic and functional β diversity of the macroinvertebrate communities in TR and UR was much higher than that in HR. The turnover and nestedness of functional β diversity showed significant differences. Functional β diversity was more obviously affected by heavy metal exceedance than taxonomic β diversity. Nestedness were more sensitive to exceedance of heavy metals than turnover. The results of this study can provide a theoretical basis for ecological restoration and protection of rivers in mining areas.

The Study of Nitrogen and Phosphorus Removal Efficiency in Urbanized River Systems Using Artificial Wetland Systems with Different Substrates

This study evaluated the effectiveness of five commercial substrates (zeolite, volcanic rock, gravel, magic rack, and ceramic pellets) in removing nitrogen (N) and phosphorus (P) from urban river systems using constructed wetlands. By employing X-ray CT and NGS technologies, we analyzed the physical structure of the substrates and the microbial communities they harbor. The results indicated that volcanic rock and ceramic pellets, due to their high porosity and specific surface area, performed exceptionally well in nitrogen and phosphorus removal. Specifically, the microbial systems with these two substrates achieved ammonia nitrogen removal rates of 89.86% and 88.45%, total nitrogen removal rates of 78.78% and 74.97%, and total phosphorus removal rates of 92.67% and 80.82%, respectively, within a 7-day period. Furthermore, the microbial communities on volcanic rock and ceramic pellets were more diverse, which correlated with their high pollutant removal efficiency. The study further elucidated the synergistic role of substrate characteristics and microbial community structure and function in nitrogen and phosphorus removal, enhancing the understanding of the purification mechanisms in constructed wetlands. These findings provide a scientific basis for the ecological restoration of urban rivers and are significant for improving the quality of urban water environments.

Evaluation of acoustic environmental effects and improvement method of ecological fish-nest bricks in the Yangtze River Basin: A model-based case study

With the rapid development of the Yangtze River Basin, the issue of underwater noise pollution has become increasingly severe, which has adversely affected aquatic creatures, particularly fish. Ecological fish-nest bricks (EFNBs), a new type of eco-friendly revetment, can provide a favorable habitat for fish. However, its effects on the acoustic environment remain unclear. The finite element numerical simulation method of acoustic-structure coupling is adopted to explore the acoustic environment of EFNBs, analyzing the impact of sound source frequency (within 300 Hz), structural forms, and arrangement of these bricks on the internal sound pressure level. The sound pressure level distribution of A-EFNBs were also analyzed at a distance of 0–0.5 m from the opening. A method of acoustic environment improvement is proposed, which utilizes porous polyurethane sponge (PPS) sound-absorbing material to establish a conducive acoustic environment for fish in EFNBs. The study results indicate that at low frequencies of sound source (f ≤ 150 Hz), the sound pressure level within EFNBs slightly decreases compared to the adjacent areas without EFNBs. The sound pressure level variation within the bricks increases with sound source frequency. The peak sound pressure increases with the number of openings. Interval arrangements can in general decrease sound pressure by less than 20 dB. At higher frequencies(f＞200 Hz), the sound pressure level at the opening of the A-EFNBs tends to increase. However, the PPS sound-absorbing material substantially reduces the sound pressure level by 15 –55 dB, rendering it an effective method for improving the acoustic environment for fish. The PPS sound-absorbing material is more suitable for habitat improvement of black carp (Mylopharyngodon piceus) and grass carp (Ctenopharyngodon idellus) with relatively low hearing thresholds among the four famous Chinese carps. The research findings can serve as a reference for designing and implementing river ecological restoration projects.

The deployment of spur dike group improves physical habitats in urban meandering rivers: Insight from a 2D habitat suitability model

Although channel meandering is currently a popular approach for river ecological restoration, the spiral flow formed in bends may lead to fragmentation of aquatic habitats due to the concave bank erosion and convex bank sedimentation. The aforementioned issue motivated this study, which aims to mitigate the adverse effects of curved flow on aquatic habitats within bends. We proposed a placement strategy of dike group within the curved channel to adjust the water–sediment structure of meandering rivers, thereby safeguarding against bank erosion and the fragmentation of river habitats. The effectiveness of this strategy has been validated by the development of numerical models based on 2D depth-averaged water–sediment equations, coupled with the IFIM method. These models investigate the mechanism of aquatic habitat enhancement achieved by deploying groups of submerged and non-submerged dikes on the convex and concave banks of the Fuhe River in Chengdu, China. The findings indicate that the implementation of dike groups resulted in an enhancement of approximately 30% in the weighted usable area (WUA) of the specific river. This improvement was accompanied by a 25% decrease in the ecological flow threshold (WUAmax). Furthermore, subsequent comprehensive comparative analyses under various conditions revealed that the fluctuations in enhancement effects were mitigated by flow increases. The degree of submergence parameter exhibits heightened sensitivity to enhancement effects, especially when the flow remains below the ecological threshold. The findings of this study can serve as a reference for the ecological restoration of river systems.

River Ecological Restoration and Groundwater Artificial Recharge II

The depletion of rivers and groundwater caused by climate change and human activity is threatening water security and ecosystems [...]

Urban river recovery: a systematic review on the effectiveness of water clean-up programs.

Urban rivers are affected at different levels by the intensification of human activities, representing a serious threat to the maintenance of terrestrial life and sustainable urban development. Consequently, great efforts have been dedicated to the ecological restoration of urban rivers around the world, as a solution to recovering the environmental functionality of these environments. In this sense, the present work aimed to investigate the effectiveness of interventions carried out aimed at the recovery of urban rivers, through a systematic review of the literature between 2010 and 2022, using the search term "rivers recovery." The results showed that there have been notable advances in the implementation of river recovery programs in urban areas around the world between the years analyzed. The ecosystems studied were affected, for the most part, by the increase in the supply of nutrients from domestic and industrial effluents, in addition to having highly urbanized surroundings and with several changes in land use patterns. The preparation of this literature review made it possible to demonstrate that the effectiveness of river recovery is extremely complex, since river recovery projects are developed for different reasons, as well as being carried out in different ways according to the intended objective.

Water quality and habitat drive phytoplankton taxonomic and functional group patterns in the Yangtze River

BackgroundAlthough phytoplankton are important primary producers in food webs, they are relatively less studied in large rivers compared to other types of systems. To fill this research gap, we studied phytoplankton taxonomic and functional composition and their relationships with water quality, habitat, climate, and land use across 30 river sections in the middle and lower reaches of the Yangtze River during 2017–2018.ResultsMajor observed phytoplankton groups were cyanobacteria, bacillariophyta, and chlorophyta. Phytoplankton total abundance, total biomass, and species richness significantly decreased in the dry season compared to the wet season, with the species and functional composition differing significantly between seasons. Phytoplankton species differences between seasons were mainly contributed by Oscillatoria sp., Pseudanabaena sp., and Melosira granulata. The dfferences in phytoplankton functional groups between seasons were mainly contributed by P (including Closterium sp., Melosira sp.), Lo (including Merismopedia sp., Peridinium sp., Ceratium sp., and Gymnodinium sp.), and J (including Pediastrum sp., Tetraedron sp., Crucigenia sp., Scenedesmus sp., and Coelastrum sp.). The variance partitioning showed that water quality (NO3-N, total suspended solids, turbidity) and habitat (water flow, river bank and river channel conditions) were critical factors in shaping phytoplankton patterns, followed by climate and land use.ConclusionsResults indicated that there was significant seasonal variation of phytoplankton in the Yangtze River, with water quality and habitat primarily driving phytoplankton patterns. Our study contributes to the understanding of natural and anthropogenic factors that drive seasonal successional processes of phytoplankton in the Yangtze River. These findings have important implications for environmental management as well as towards the ecological restoration of large rivers.

Hyporheic exchange in a compound channel under unsteady flow: Numerical simulations

Hyporheic exchange (HE) within compound channels under unsteady surface water flow conditions plays an important role in the river-floodplain ecosystem. Numerical simulations were applied to investigate the HE in a compound channel under unsteady flow. High velocity regions were observed in the hyporheic zone near the banks of the floodplain and of the main channel, and the distribution of the pore water velocity in this region was seen to significantly change under the unsteady conditions. The velocity peaked during the rising and falling phases and had the smallest value when the inlet discharge of surface water had the maximum and minimum values. The changes in the relationship between surface groundwater recharge and discharge were observed in the context of a lateral water level threshold of approximately 1.2 m. About 75 % of the hyporheic exchange flux was due to the dynamic pressure. Comparing the hyporheic exchange in the compound channel driven by static pressure with that in a rectangular channel, it was found that the floodplain decreased the hyporheic exchange. These findings provide a better understanding of the HE driven by unsteady flow in a compound channel and may be applied in combined flood management and river ecological restoration.

Eukaryotic plankton species diversity and community structure in the Xiao Jiang River (the primary tributary of Upper Yangtze River), Yunnan.

The Xiao Jiang River, as a crucial element of ecological restoration in the upper reaches of the Yangtze River, plays an indispensable role in agricultural water utilization and water ecology within its watersheds. The water quality status of the Xiao Jiang River not only impacts local water-ecological equilibrium and economic benefits but also holds paramount importance for sustaining ecosystem health in the Yangtze River basin. Plankton surveys and environmental physicochemical detection were conducted in the major channel region of the Xiao Jiang River in dry and wet periods in 2022 to better understand the diversity of eukaryotic plankton and its community structure characteristics. Environmental DNA is an emerging method that combines traditional ecology with second-generation sequencing technology. It can detect species from a single sample that are difficult to find by traditional microscopy, making the results of plankton diversity studies more comprehensive. For the first time, environmental DNA was used to investigate eukaryotic plankton in the Xiao Jiang River . The results showed that a total of 881 species of plankton from 592 genera in 17 phyla were observed. During the dry period, 480 species belonging to 384 genera within17 phyla were detected, while, during the wet period, a total of 805 species belonging to 463 genera within 17 phyla were recorded. The phylum Ciliophora dominated the zooplankton, while the phylum Chlorophyta and Bacillariophyta dominated the phytoplankton. The presence of these dominant species indicate that the water quality conditions in the study area are oligotrophic and mesotrophic. Principal coordinate analysis and difference test showed that the number of plankton ASVs, abundance, species richness, dominating species, and diversity indices differed between the dry and wet periods. Spearman correlation analysis and redundancy analysis (RDA) of relative abundance data with environmental physicochemical factors revealed that water temperature (WT), dissolved oxygen (DO), potential of hydrogenacidity (pH), ammonia nitrogen (NH3-N), total nitrogen (TN), electrical conductivity (EC) and the determination of redox potential (ORP) were the main environmental physicochemical factors impacting the plankton community structure. The results of this study can serve as a provide data reference at the plankton level for water pollution management in the Xiao Jiang River, and they are extremely important for river ecological restoration and biodiversity recovery in the Yangtze River basin.

Health Assessment of the Stream Ecosystem in Beijing, China

With economic development, the health of river ecosystems is becoming severely threatened because of the increasing effects of human activities on river ecosystems. Here, 101 sites along regional river systems in Beijing rivers were investigated from autumn 2020 to summer 2021. A total of 34 metrics, including aquatic organisms, hydrology, water quality, and habitat, were calculated to be the candidate indicators. Principal component and correlation analyses were used to select the core metrics from the candidate indicators, and the weight of each core metric was estimated using the entropy method. The integrated index of stream ecological health was constructed to assess the health condition of the Beijing rivers. The results of the PCA and correlation analyses revealed that eleven metrics were selected as the core metrics to construct the integrated index of stream ecological health, including water temperature, flow velocity, BOD5, NH4+-N, Cu, the density of phytoplankton and zooplankton, the Shannon-Wiener diversity index of macroinvertebrates and fish, the BMWP index, and the qualitative habitat evaluation index. According to the health assessment results, 4.95% of the sampling sites were healthy, 23.76% were subhealthy, and 71.29% were in a fair or below healthy state. The river health status showed strong spatial heterogeneity, and the river health statuses in the northern and western regions were relatively good, whereas the river health status in the central and southeastern regions were relatively poor. The results of four aspects stream ecosystem assessment showed that the overall water quality of the rivers was "subhealthy" and the aquatic organisms and habitat were "general poor," but the hydrology was "poor." The evaluation results of five water systems demonstrated that the Chaobai River had the best health status, followed by that of the Yongding River, Daqing River, and Jiyun River, and the Beiyun River had the worst health status. Maintaining river ecological baseflow, ensuring river system connectivity, and improving and restoring the river habitat environment are the key aspects of river ecological restoration and protection in Beijing in the future.

Evaluation of Restoration Effect of Submerged Plant Community in Urban Rivers Replenished by Reclaimed Water

Submerged plant community construction is extensively used in the field of urban river ecological restoration, but it is sometimes difficult to establish a large area of survival or a stable community after restoration. Therefore, there is some uncertainty in determining the restoration effect. To verify the restoration effect of urban rivers replenished by reclaimed water through the application of a submerged plant community, this paper takes the typical urban rivers with reclaimed water in Beijing, the Liangshui River and the Dalong River, as the research objects and takes the Yongding River, a river replenished by natural water, as the comparison to establish a water eco-environment quality index and carry out the restoration effect evaluation of a submerged plant community based on field monitoring. In a comparison of the water eco-environment quality index of rivers and the coverage of submerged plants, the evaluation results indicate that the Yongding River and Liangshui River have the same number of submerged plant species, yet their plant coverage is different. The ecological environment quality condition of the Yongding River is superior to that of the Liangshui River and the Dalong River. The ecological environment quality of the reclaimed water river segment with an average coverage of submerged plants greater than or equal to 50% is relatively better, with relatively more sensitive species. This suggests that for rivers replenished by reclaimed water, the construction of submerged plant communities will improve the water ecological conditions on the premise of ensuring a certain degree of submerged plant species and coverage. By calculating the correlation coefficients relating to the coverage of submerged plants by 32 environmental factors including the indicators of water quality, hydrology and sediment, the paper initially screens out water depth, ammonia nitrogen, nitrite nitrogen, BOD, permanganate index, and total nitrogen and organic carbon in the sediment as the major environmental factors affecting the coverage status of submerged plants. It can provide a reference for the control of environmental factors in the construction and maintenance of submerged plants to guarantee a restoration effect in the future.

Historical Spatial Radiation Range of the Yongding River Corridor in Beijing Plain Section: Implications for Landscape Patterns and Ecological Restoration

The radiation range of the corridor effect holds great significance for the ecological restoration, planning, and sustainable development of river corridors. This study focuses on the Beijing plain section of the Yongding River, which has been cut off for half a century, and improves the research methodology. Utilizing land use data from 1967 and 1980, ArcGIS and Fragstats were employed to establish 5 km buffer zones on both sides of the Yongding River corridor. The buffer zone analysis method was then applied to investigate landscape pattern changes. Through SPSS correlation analysis and curve fitting, sensitive landscape indices were identified, and their change characteristics were analyzed to unveil the historical spatial radiation range and characteristics of the Yongding River corridor. The findings of this research are as follows: First, as the buffer width increases, the landscape pattern changes, showing a decrease in heterogeneity, an increase in aggregation and spread, and a good connection between dominant patches. Forest land exhibited higher levels of fragmentation and dispersion, cultivated land demonstrated improved dominance, and construction land became more regular and dispersed. Second, the spatial radiation range of the landscape level within the river corridor was approximately 4 km. The inflection point for the radiation range on forest land was found at 3.5–4 km, while for construction land, it occurred at 4.5 km. The outcomes of this study can be utilized to evaluate the impact of river corridors on landscape patterns in the period of good historical ecology. They also provide more targeted measures and scientific basis for landscape pattern protection and river ecological restoration planning after the restoration of water flow in the Yongding River plain.

Willingness to Pay for Urban Inland River Restoration: Case of Nanyang, China

Ecologically rational restoration of urban inland rivers is crucial for sustainable development of modern cities. The research purpose is to assess and compare the value of urban inland rivers by identifying the willingness of Nanyang residents to pay for each of two types of rivers restoration — ecological (improving the ecological quality of rivers) and recreational (ensuring rivers to meet cleanliness requirements for residents’ recreational areas) as well as to identify the factors that determine the difference in the obtained estimates. The novelty of the study consists in the willingness to pay (WTP) for ecological and recreational restoration of urban inland rivers identification and comparison by using the two dichotomous choice questionnaires and in the determination of factors explaining the difference in ecological and recreational value estimates. A questionnaire survey was conducted in Nanyang City, and data was collected from a sample of 326 respondents. The results of the questionnaire survey revealed quite significant difference between the willingness of urban residents to pay for ecological and recreational restoration of the river — CNY109.56 (USD16.8) and CNY255.12 (USD39.84) per person annually, respectively. Factors influencing differences in WTP for ecological and recreational restoration of urban inland rivers — income level, gender, education level, environmental awareness, need for recreation, and distance to urban inland rivers — were identified. The study’s results indicate that urban inland rivers hold a significant economic value and highlight the importance of implementing measures for targeted ecological and recreational restoration as part of the overall urban river restoration system.

Quantifying the Impact of Changes in Sinuosity on River Ecosystems

To quantitatively study the hydrodynamic changes in different river morphologies and clarify the impact of morphological changes on river ecosystems, this study examined a section of the Nansha River near Laoniuwan in the Haidian District, Beijing, and characterized different river morphologies by river sinuosity. The River 2D model was used for simulation and analysis, and the depth and velocity diversity indices were introduced to quantify the distribution of depth and velocity under different sinuosities. Cyprinus carpio was selected as the target fish in this study, and its suitability curve was determined using literature and field surveys. Combined with the simulation results, a weighted usable area curve was established to identify its inflection point and maximum value and determine the ecological flow in the river under different sinuosities, that is, to clarify the relationship between sinuosity and ecological flow. The results showed that the lower the sinuosity, the worse the depth and velocity diversity, but a greater sinuosity did not lead to better depth and velocity diversity. The depth and velocity diversity of a sinuosity of 1.5 were better than those of 1.89 in general, except for low flow conditions (Q = 5 m3/s). For rivers with water use restricted by nature and society and where ecological needs exist, ecological engineering that appropriately changes the planform of rivers can be considered to increase the diversity of river/channel geometry and provide a basis for the ecological restoration of rivers.

River Ecological Protection and Restoration Using Multi-source Remote Sensing Data

River Ecological Protection and Restoration Using Multi-source Remote Sensing Data

Predictive Simulation Study on the Effect of Small and Medium River Basin Outfall Treatment Measures on Water Quality Improvement

In recent years, the problem of water pollution in middle and small river basins has become increasingly serious. In order to control the water pollution of small- and medium-sized rivers, based upon the hydrodynamic module and the water quality module in MIKE21, this paper established a numerical computing model for middle and small river basins by taking the Xiyong River Basin as a typical representative. The excessive levels of nitrogen in the Xiyong River have significantly impaired the quality of the water in terms of the river status, so seven different scenario hypotheses of treatment measures are proposed, based on which the hydrodynamic simulation on the total nitrogen (TN) concentration’s movement was implemented and the time of the nitrogen concentration to reach the standard was predicted. The results showed that the water quality of the Xiyong River improved significantly after the treatment measure, and the annual mean of the TN concentration will decrease by 0.496 mg/L. The results will help the government to control the pollution sources of small and medium river basins. The research of Xiyong River based on the MIKE21 model can be used as the basis for pollution reduction and water quality improvement, which provides an example for the ecological restoration of small and medium rivers.

Ecological Health Assessment of an Urban River: The Case Study of Zhengzhou City, China

Urban river ecological health assessment is an effective means to manage urban rivers, and combining principles of landscape ecology can provide new help for the ecological restoration of urban rivers and improving their ecosystem service value. From the perspective of important functions of ecosystems, based on typical sample site investigations of different river sections, questionnaire surveys, and remote sensing technology, a fuzzy comprehensive evaluation model based on the factor analysis method was used to construct an indicator system that can quantitatively reflect the ecological health of urban rivers. This comprehensive evaluation index system includes five major functions: social function, habitat and corridor function, water ecological function, water landscape function, and spatial enclosure function. The study identified key areas, key rivers, key river sections, and main indicator projects for the ecological restoration of the urban river landscape corridors in Zhengzhou. The study results also showed that the urban river landscape corridors in Zhengzhou have prominent problems in social function, water ecological function, and habitat and corridor function, and 62.1% of the river sections are currently in a sub-healthy state. The flood control function, eutrophication of water body, naturalization rate of revetment, and five other indicators in the old city district are significantly lower than those in the new city district, and the old city district should be the focus of the ecological restoration of urban river corridors. From the evaluation of the ecological health status of typical river sections, the Jinshui River and Xionger River have a larger number of river sections that urgently need restoration. This study provides a reference for the ecological restoration of urban rivers in Zhengzhou, a rapidly urbanizing region, and has reference significance for the construction of water landscapes in small and medium-sized cities with low levels of urbanization.

Inhibition of sediment erosion and phosphorus release by remediation strategy of contaminated sediment backfilling

The management of sediment-water interfaces, especially bed stability, is essential for controlling accumulated contaminants in the sediment. In this study, the relationship between sediment erosion and phosphorus (P) release under the remediation strategy of contaminated sediment backfilling (CSBT) was explored through a flume experiment, i.e. the dredged sediment was calcined into ceramsite after dewatering and detoxification and then backfilled to the dredged area for sediment capping, thus avoiding the introduction of foreign materials via in-situ remediation and the large-scale land occupation associated with ex-situ remediation. Acoustic Doppler velocimeter (ADV) and optical backscatter sensor (OBS) were used to measure the vertical distributions of flow velocity and sediment concentration in the overlying water, respectively, and diffusive gradients in thin films (DGT) was used to measure the P distribution in the sediment. The results revealed that improving bed stability from CSBT can considerably improve the robustness of sediment-water interface and reduce sediment erosion by more than 70%. The corresponding P release from the contaminated sediment could be inhibited with an inhibition efficiency as high as 80%. CSBT is a potent strategy for managing contaminated sediment. This study provides a theoretical reference for controlling sediment pollution, further supporting river and lake ecological management and environmental restoration.

Diverse portfolios: Investing in tributaries for restoration of large river fishes in the Anthropocene

Rehabilitation of large Anthropocene rivers requires engagement of diverse stakeholders across a broad range of sociopolitical boundaries. Competing objectives often constrain options for ecological restoration of large rivers whereas fewer competing objectives may exist in a subset of tributaries. Further, tributaries contribute toward building a “portfolio” of river ecosystem assets through physical and biological processes that may present opportunities to enhance the resilience of large river fishes. Our goal is to review roles of tributaries in enhancing mainstem large river fish populations. We present case histories from two greatly altered and distinct large-river tributary systems that highlight how tributaries contribute four portfolio assets to support large-river fish populations: 1) habitat diversity, 2) connectivity, 3) ecological asynchrony, and 4) density-dependent processes. Finally, we identify future research directions to advance our understanding of tributary roles and inform conservation actions. In the Missouri River United States, we focus on conservation efforts for the state endangered lake sturgeon, which inhabits large rivers and tributaries in the Midwest and Eastern United States. In the Colorado River, Grand Canyon United States, we focus on conservation efforts for recovery of the federally threatened humpback chub. In the Missouri River, habitat diversity focused on physical habitats such as substrate for reproduction, and deep-water habitats for refuge, whereas augmenting habitat diversity for Colorado River fishes focused on managing populations in tributaries with minimally impaired thermal and flow regimes. Connectivity enhancements in the Missouri River focused on increasing habitat accessibility that may require removal of physical structures like low-head dams; whereas in the Colorado River, the lack of connectivity may benefit native fishes as the disconnection provides refuge from non-native fish predation. Hydrologic variability among tributaries was present in both systems, likely underscoring ecological asynchrony. These case studies also described density dependent processes that could influence success of restoration actions. Although actions to restore populations varied by river system, these examples show that these four portfolio assets can help guide restoration activities across a diverse range of mainstem rivers and their tributaries. Using these assets as a guide, we suggest these can be transferable to other large river-tributary systems.