River Mainstem Research Articles

Survival implications of diversion entrainment for out‐migrating juvenile Chinook Salmon and steelhead

AbstractObjectiveEfforts to ameliorate the negative effects of diversion dams on aquatic species of concern are important in rivers where water withdrawal supports agricultural economies, and they are likely to become increasingly important with impending climate change. A multi‐year study was conducted to evaluate the survival consequences of diversion dam passage for juvenile Chinook Salmon Oncorhynchus tshawytscha and steelhead O. mykiss in the highly managed Yakima River, Washington. Canal entrainment and passage were evaluated at four diversion dams in the lower Yakima River where seaward‐migrating juvenile salmon and steelhead either pass dams via spill bays or enter canals with downstream fish‐screening facilities designed to collect entrained fish and return them to the main‐stem river.MethodsWe used acoustic telemetry to monitor the downstream migration behavior of 4403 juvenile Chinook Salmon and steelhead during 2018–2021.ResultPercent entrainment into canals was substantial (6–59%) at three of the four diversion dams studied, and entrainment probability was positively associated with the proportion of streamflow diverted into canals. Survival probability estimates for groups of tagged fish that were entrained into canals were lower than survival probability estimates for tagged fish that passed through spill bays on the dams. Absolute differences in survival probabilities between routes ranged from 0.099 to 0.369, demonstrating that canal entrainment reduced the survival of outmigrating juvenile Chinook Salmon and steelhead. We also found that entrainment resulted in migration delays, which could further affect survival because fish are increasingly exposed to predation and decreased water quality as water temperature increases throughout the migration season.ConclusionCanal entrainment resulted in increased mortality and travel time through the study area, highlighting the need to limit the entrainment of juvenile salmon and steelhead at diversion dams in rivers where salmon recovery is important.

Quantifying the contributions of tributaries to large‐river fish populations through mark‐recapture modeling

AbstractObjectiveTributaries may play a vital role in maintaining populations of large river fishes, although the specific contributions of tributaries toward recruitment of river‐wide populations are not often understood. Tributaries may experience fewer cumulative anthropogenic impacts relative to main‐stem rivers and may offer more natural conditions supportive of native fish populations, which may provide opportunities for fish population restoration. Thus, an improved understanding of tributary–main‐stem population dynamics may inform targeted conservation actions for spatially structured populations of large‐river fishes. Colorado River tributaries in the Grand Canyon, Arizona, USA, are a focus of imperiled Humpback Chub Gila cypha conservation, which includes translocations to enhance population redundancy and to expand the overall population. However, the fate of fish dispersed to the main stem has not been thoroughly quantified.MethodsUsing open population mark–recapture models, we quantified the relative contribution of three groups of Humpback Chub, including fish of confirmed tributary origin that were either translocated or produced in situ, and others presumed to be Colorado River main‐stem‐origin fish, to three main‐stem populations. Our specific study objectives were to (1) estimate Colorado River abundances of tributary and main‐stem‐origin fish over time, (2) compare relative group‐specific contributions to three main‐stem populations, and (3) compare group‐specific survival rates of Humpback Chub in the Colorado River and in a tributary where a recent translocation has occurred.ResultTributaries contributed 26% and 43% of the overall abundance in two tributary inflow reach populations and zero in a third, which we attributed to uncharacteristically low tributary survival immediately following translocation. In the main stem, survival of tributary‐origin fish was higher compared to main‐stem‐origin fish, suggesting an advantage of tributary residence.ConclusionOur contrasting results from three different tributary inflow populations highlight the potential role for tributaries in sustaining large‐river fish populations, which may have important implications for long‐term maintenance of river metapopulations.

Restored off‐channel pond habitats create thermal regime diversity and refuges within a Mediterranean‐climate watershed

Cool‐water habitats provide increasingly vital refuges for cold‐water fish living on the margins of their historical ranges; consequently, efforts to enhance or create cool‐water habitat are becoming a major focus of river restoration practices. However, the effectiveness of restoration projects for providing thermal refuge and creating diverse temperature regimes at the watershed scale remains unclear. In the Klamath River in northern California, the Karuk Tribe Fisheries Program, the Mid‐Klamath Watershed Council, and the U.S. Forest Service constructed a series of off‐channel ponds that recreate floodplain habitat and support juvenile coho salmon (Oncorhynchus kisutch) and steelhead (O. mykiss) along the Klamath River and its tributaries. We instrumented these ponds and applied multivariate autoregressive time series models of fine‐scale temperature data from ponds, tributaries, and the mainstem Klamath River to assess how off‐channel ponds contributed to thermal regime diversity and thermal refuge habitat in the Klamath riverscape. Our analysis demonstrated that ponds provide diverse thermal habitats that are significantly cooler than creek or mainstem river habitats, even during severe drought. Wavelet analysis of long‐term (10 years) temperature data indicated that thermal buffering (i.e. dampening of diel variation) increased over time but was disrupted by drought conditions in 2021. Our analysis demonstrates that in certain situations, human‐made off‐channel ponds can increase thermal diversity in modified riverscapes even during drought conditions, potentially benefiting floodplain‐dependent cold‐water species. Restoration actions that create and maintain thermal regime diversity and thermal refuges will become an essential tool to conserve biodiversity in climate‐sensitive watersheds.

Reliability of trans-generational genetic mark-recapture (tGMR) for enumerating Pacific salmon.

As Pacific salmon (Oncorhynchus spp.) decline across much of their range, it is imperative to further develop minimally invasive tools to quantify population abundance. One such advancement, trans-generational genetic mark-recapture (tGMR), uses parentage analysis to estimate the size of wild populations. Our study examined the precision and accuracy of tGMR through a comparison to a traditional mark-recapture estimate for Chilkat River Chinook salmon (O. tshawytscha) in Southeast Alaska. We examined how adult sampling location and timing impact tGMR by comparing estimates derived using samples collected in the lower river mainstem to those using samples obtained in upriver spawning tributaries. Results indicated that tGMR estimates using a representative sample of mainstem adults were most concordant with, and 3% more precise than, the traditional mark-recapture estimate for this stock. Importantly, the timing and location of adult sampling were found to impact abundance estimates, depending on what proportion of the population dies or moves to unsampled areas between downriver and upriver sampling events. Additionally, we identified potential sources of bias in tGMR arising from violations of key assumptions using a novel individual-based modeling framework, parameterized with empirical values from the Chilkat River. Simulations demonstrated that increased reproductive success and sampling selectivity of older, larger individuals, introduced negative bias into tGMR estimates. Our individual-based model offers a customizable and accessible method to identify and quantify these biases in tGMR applications (https://github.com/swrosenbaum/tGMR_simulations). We underscore the critical role of system-specific sampling design considerations in ensuring the precision and accuracy of tGMR projects. This study validates tGMR as a potentially useful tool for improved population enumeration in semelparous species.

Major fluvial erosion and a 500‐Mt sediment pulse triggered by lava‐dam failure, Río Coca, Ecuador

AbstractThe failure of a 144‐m‐high lava‐dam waterfall on the Río Coca, Ecuador, in February 2020 initiated a catastrophic watershed reset—regressive erosion upstream and a massive sediment pulse downstream—as the river evolves towards a new equilibrium grade. The evolution of this river corridor after a sudden base‐level fall embodies the “complex response” concepts long understood through laboratory experiments, numerical modelling and smaller‐scale field studies, but that have not been observed in the field before on this scale. This paper presents geomorphic and geotechnical data to characterize the evolution of the Río Coca since 2020. In the three years after the lava‐dam failure, the erosion front migrated almost 13 km upstream along the mainstem river and triggered secondary headcuts that began migrating up tributaries. Erosion of the mainstem and tributary valleys generated a sediment pulse estimated to be 277 million m3 and ~500 million tonnes (Mt) over three years, depositing sediment tens of meters thick over tens of kilometres downstream from the former waterfall. This sediment pulse is one of the largest in modern times, comparable to the annual sediment load of a major continent‐draining river but with orders‐of‐magnitude greater sediment yield. Geomorphic adjustment of the Río Coca represents a highly unusual natural disaster threatening life, property, water quality, the regional economy, major infrastructure and energy security. However, this event also provides a rare opportunity to learn how a large autogenic watershed disturbance and recovery evolve, with important lessons for interpreting the sedimentary record of volcanic landscapes.

Ecological health assessment of the Yellow River mainstem based on benthic macroinvertebrate index of biological integrity

Ecological health assessment of the Yellow River mainstem based on benthic macroinvertebrate index of biological integrity

Spatiotemporal change in vegetation cover in the Yellow River Basin between 2000 and 2022 and driving forces analysis

In this paper, we investigate the features of spatiotemporal change in fractional vegetation cover (FVC) throughout the Yellow River Basin between 2000 and 2022 and identify the driving factors behind the change using the MODIS normalized difference vegetation index (NDVI) as a data source. On that basis, our research involves trend analysis and the center migration model to examine the correlation between vegetation cover changes and various factors, such as climates, topographies, soils, and human activities. In this way, we aim to uncover how such correlation contributed to the reduction in suspended sediment concentration (SSC) in surface runoff. Results suggest that (1) the FVC of the Yellow River Basin has been trending upward over the past 23 years, and vegetation growth has been remarkably improved; (2) the center of medium-high and denser vegetation cover has progressively migrated from the upper reaches of the Yellow River down to its middle-lower segments; (3) soil erosion control measures are critical to improve vegetation cover, given the great impact of the shifting natural elements on vegetation cover changes on a local basis; (4) an improvement in vegetation cover leads to considerable positive change in the runoff and SSC of the Yellow River mainstem. This study has yielded noteworthy contributions in correctly understanding the current vegetation changes and related factors in the Yellow River Basin. Furthermore, it has laid the groundwork for further research in improving the accuracy of basic data and deepening the correlation between factors.

Diets of Native and Non-Native Piscivores in the Stanislaus River, California, Under Contrasting Hydrologic Conditions

The fish communities of the Sacramento–San Joaquin Delta and its tributaries in California’s Central Valley have been irreparably altered through introductions of numerous fish species, including Striped Bass (Morone saxatilis), black bass (Micropterus spp.), and catfishes (Ameiurus spp. and Ictalurus spp.). Research into how predation by non-native piscivores affects native anadromous species has focused on the Sacramento and San Joaquin river mainstems and Delta habitats, through which all anadromous species must pass. Yet, the ranges of non-native fishes extend into upstream tributaries. We collected diets from native and non-native piscivores in the Stanislaus River, a tributary to the San Joaquin River and a remaining stronghold for native fishes. Piscivorous fishes primarily consumed invertebrates and the native species fall-run Chinook Salmon (Oncorhynchus tshawytscha) and Pacific Lamprey (Entosphenus tridentatus). Juvenile Chinook Salmon and Pacific Lamprey were consumed at higher frequencies than any other potential fish prey species, particularly by Striped Bass and black bass. The frequency of native fishes in predator diets was similar across years, despite contrasting hydrologic conditions; 2019 (wet year), 2020 (dry year), and 2021 (critically dry year). Our results show that Pacific Lamprey were frequently consumed by native and non-native piscivores, and that juvenile Chinook Salmon experience substantial predation early in their migration, regardless of hydrologic conditions.

Dissolved polycyclic aromatic compounds in Canada’s Athabasca River in relation to Oil Sands from 2013 through 2019

The Canada-Alberta Oil Sands Monitoring (OSM) Program began long-term surface water quality monitoring on the lower Athabasca River in 2012. Sampling of low level, bio-accumulative polycyclic aromatic compounds (PACs) targeted a suite of parent and alkylated compounds in the Athabasca River (AR) mainstem using semi-permeable membrane devices (SPMDs). Samples were collected along a gradient from upstream reference near Athabasca, Alberta, through exposure to the Athabasca oil sands deposit (AOSD), various tributary inflows, and mining activities within the OSMA, to downstream recovery near Wood Buffalo National Park (WBNP) and reference on the Slave River. The program adapted over the years, shifting in response to program review and environmental events. The AOSD chemical fingerprint was present in samples collected within the AOSD, through the oil sands mineable area (OSMA), downstream to recovery from 2013 to 2019. PACs were dominated by alkylated phenanthrenes/anthracenes (PAs) and dibenzothiophenes (Ds), with elevated levels of alkylated fluorenes (Fs), naphthalenes (Ns), fluoranthenes/pyrenes (FlPys) and benzo[a]anthracenes/chrysenes (BaACs), increasing in concentration from C1 < C2 < C3 < C4. Concentrations of these petrogenic PACs were at their highest within the OSMA and downstream of tributaries. The AOSD fingerprint was absent from sites located outside of the influence of the AOSD and downstream of the Peace-Athabasca Delta on the Slave River. PAC concentrations in the AR increased with mainstem discharge and loadings from tributaries, were moderated by the PAD, and diluted by the Peace River. This work bolsters the baseline PAC information previously reported for the Athabasca River and waters downstream, reporting 7 years of data, from all sites within the mainstem monitoring program, and exploring potential regional and hydrological drivers of these between sites and over time.

Study of the Ecosystem Service Value Gradient at the Land–Water Interface Zone of the Xijiang River Mainstem

The ecosystem service value (ESV) gradient-evolution pattern of a river basin’s land and water-intertwined zones has a variety of ecosystem service values, such as biodiversity conservation, water conservation, water purification, etc. The study of the ecosystem service value (ESV) gradient-evolution pattern of a river basin’s land and water-intertwined zones will provide a scientific basis for the construction and protection of the ecological security pattern of the river basins. In this study, we combined the unit area equivalent factor method and geographically weighted regression (GWR) model to classify and analyze the gradient change pattern of ESV upstream, downstream, and along the river of the Guangdong mainstream section of the Xijiang River in China, and the conclusions are as follows: (1) The corresponding ESV share of each land use type was in the following order: water bodies &gt; broad-leaved forest &gt; artificial wetland &gt; scrub &gt; paddy field &gt; coniferous forest &gt; natural wetland &gt; grassland. The level of each type of ESV does not depend entirely on the size of the area but is determined by the ecosystem service functions it can provide and the level of ESV per unit area; (2) the relationship between land use types along both sides of the river in the Guangdong section of the Xijiang River Basin shows a tendency to shift from water ecosystems to terrestrial ecosystems, and the ESV gradually decreases with the increase in distance from the water. (3) The upstream to the downstream area showed a trend of changing from terrestrial ecosystems to aquatic ecosystems, such as broad-leaved forests, scrublands, water bodies, artificial wetlands, etc., and the mean land ESV showed a general trend of undulating change and decline with the reduction in the distance from the downstream area. (4) Natural factors, such as the topography and geomorphology of the basin and the socio-economic factors of power consumption, influence the spatial distribution characteristics of the ESV in the region; among them, socio-economic factors, such as total power consumption, industrial exhaust gas emissions, industrial wastewater emissions, etc., in the economically developed areas of the Xijiang River Basin are the determinants of the changes in ESV, which are generated by human living and production activities, and these indirectly affect the magnitude of the ESV by influencing the factors of temperature and gas.

Detection efficiency of adult Pacific lamprey passage counts at Leaburg Dam and upstream distribution in the McKenzie River (Oregon, USA)

AbstractAdult Pacific lamprey (Entosphenus tridentatus) were counted using consistent methodology since 2005 with a video monitoring system as they passed Leaburg Dam (McKenzie River, Oregon, USA) en route to upstream spawning areas. In this study we evaluated the detection efficiency of the video system and upstream distribution of Pacific lamprey using the video counts of lamprey passage (herein, “dam counts”), passive integrated transponder (PIT) tags, and radio telemetry. In 2019–2020 we collected, tagged and tracked 32 adult lamprey (4 from the McKenzie River and 28 that were translocated from Willamette Falls). All fish were tagged and released into the tailrace of Leaburg Dam in June 2019. Oregon Department of Fish and Wildlife employees and volunteers from the local community conducted mobile radiotracking above and below the dam in drift boats (114 mainstem river kilometers) and on foot (several tributaries). The estimated detection efficiency for dam counts was 92% (95% confidence interval: 67%–99%). Fifty percent (16 of 32) of the tagged lamprey passed the dam, including 13 of 28 that were translocated. Thirty‐seven percent (6 of 16) of lamprey that passed Leaburg Dam were detected in a restored reach of the South Fork McKenzie, 32.6 river kilometers upstream of the dam.

Migration timing and tributary use of spawning flannelmouth sucker (Catostomus latipinnis).

Spawning phenology and associated migrations of fishes are often regulated by factors such as temperature and stream discharge, but flow regulation of mainstem rivers coupled with climate change might disrupt these cues and affect fitness. Flannelmouth sucker (Catostomus latipinnis) persisting in heavily modified river networks are known to spawn in tributaries that might provide better spawning habitat than neighboring mainstem rivers subject to habitat degradation (e.g., embedded sediments, altered thermal regimes, and disconnected floodplains). PIT tag data and radio telemetry were used to quantify the timing and duration of flannelmouth sucker tributary spawning migrations in relation to environmental cues in McElmo Creek, a tributary of the San Juan River in the American Southwest. We also tested the extent of the tributary migration and assessed mainstem movements prior to and after tributary migrations. Additionally, multiyear data sets of PIT detections from other tributaries in the Colorado River basin were used to quantify interannual and cross-site variation in the timing of flannelmouth sucker spawning migrations in relation to environmental cues. The arrival and residence times of fish spawning in McElmo Creek varied among years, with earlier migration and a 3-week increase in residence time in relatively wet years compared to drier years. Classification tree analysis suggested a combination of discharge- and temperature-determined arrival timing. Of fish PIT tagged in the fall, 56% tagged within 10 km of McElmo Creek spawned in the tributary the following spring, as did 60% of radio-tagged fish, with a decline in its use corresponding to increased distance of tagging location. A broader analysis of four tributaries in the Colorado River basin, including McElmo Creek, found photoperiod and temperature of tributary and mainstem rivers were the most important variables in determining migration timing, but tributary and mainstem discharge also aided in classification success. The largest tributary, the Little Colorado River, had more residential fish or fish that stayed for longer periods (median = 30 days), whereas McElmo Creek fish stayed an average of just 10 days in 2022. Our results generally suggest that higher discharge, across years or across sites, results in extended use of tributaries by flannelmouth suckers. Conservation actions that limit water extraction and maintain natural flow regimes in tributaries, while maintaining open connection with mainstem rivers, may benefit migratory species, including flannelmouth suckers.

Using Multiscale Environmental and Spatial Analyses to Understand Natural and Anthropogenic Influence on Fish Communities in Four Canadian Rivers

Science-based conservation of riverine fishes can be best targeted with specific information about spatial-ecological controls on the community, including anthropogenic stressors. Because anthropogenic stressors can originate at multiple spatial scales, we investigated the influence of natural and anthropogenic variables summarized within the reach, valley, and catchment on fish community composition along four river mainstems in Ontario, Canada. We used Redundancy Analyses (RDA) to explore models with multi- and single-scale variables on fish community composition. We used partial RDAs to differentiate the relative effects of variable types in multiscale models and to determine if spatial variables explained additional variation in fish community composition. Catchment variables accounted for the majority of explained variation in fish community composition in three of the four rivers, but instream habitat variables accounted for considerable variability in fish community composition in the two rivers that are highly fragmented by dams or naturally occurring rapids. Natural and human-derived fragmentation in rivers may reduce the influence of catchment controls, disrupt longitudinal gradients, and increase the influence of local instream habitat. Environmental variables that explained fish distribution had longitudinal or patchy spatial pattern within rivers, but spatial variables representing impediments to fish dispersal and proximity to receiving waterbodies failed to explain additional variation in fish community composition.

The Impact of Inter-Basin Water Transfer Schemes on Hydropower Generation in the Upper Reaches of the Yangtze River during Extreme Drought Years

The Yangtze River Basin experiences frequent extreme heatwaves and prolonged droughts, resulting in a tight supply demand balance of electricity and negatively impacting socioeconomic production. Meanwhile, ongoing inter-basin water diversion projects are planned that will divert approximately 25.263 billion cubic meters of water from the Yangtze River Basin annually, which may further affect the power supply in the region. In this study, the CLHMS-LSTM model, a land-surface hydrological model coupled with a long short-term memory (LSTM)-based reservoir operation simulation model, is used to investigate the impact of water diversions on the power generation of the Yangtze River mainstream reservoirs under extreme drought conditions. Two different water diversion schemes are adopted in this study, namely the minimum water deficit scheme (Scheme 1) and minimum construction cost scheme (Scheme 2). The results show that the land surface–hydrological model was able to well characterize the hydrological characteristics of the Yangtze River mainstem, with a daily scale determination coefficient greater than 0.85. The LSTM reservoir operation simulation model was able to simulate the reservoir releases well, with the determination coefficient greater than 0.93. The operation of the water diversion projects will result in a reduction in the power generation of the Yangtze River mainstem by 14.97 billion kilowatt-hours. As compared to the minimum construction cost scheme (Scheme 2), the minimum water deficit scheme (Scheme 1) reduces the loss of power generation by 1.38 billion kilowatt-hours. The research results provide new ideas for the decision-making process for the inter-basin water diversion project and the formulation of water diversion plans, which has implications for ensuring the security of the power supply in the water diversion area.

The Ohio River Ecological Research Program (ORERP): History and Accomplishments

The Ohio River Ecological Research Program (ORERP), sponsored by multiple power plants along the river's main stem, was in existence for 50 years. Its goals were to collect fish community data to evaluate possible impacts to Ohio River fish communities because of either power plant discharges (i.e., thermal effects) or cooling water intakes. Studies by the ORERP have shown that thermal avoidance of discharge areas often occurs during the summer, but this avoidance is temporary and reversible, and long‐term disruptions of the fish communities have not been detected. Impingement studies conducted at 13 plants from 2005 to 2007 showed that impingement was highly episodic and dominated by clupeids and Freshwater Drum Aplodinotus grunniens. Impinged fish were mainly (&gt;90%) young of the year; as a result, impingement numbers strongly reflected year‐class strength. Entrainment of ichthyoplankton was conducted under the ORERP at seven plants in 2015 and 2016. Annual entrainment estimates ranged from 43 million to 3.5 billion (i.e., 3.5 × 109) ichthyoplankton depending on the plant. The principal benefit of this collaborative effort was that these data allowed the sponsoring facilities and others to access an extensive database upon which fact‐based regulatory, resource management, and plant operating decisions could be based. Most importantly, the ORERP is a collaborative model for private and public organizations to collect, share, and analyze data and make resource management decisions for a large, multi‐use aquatic resource.

Particulate organic matter in the Lena River and its delta: from the permafrost catchment to the Arctic Ocean

Abstract. Rapid Arctic warming accelerates permafrost thaw, causing an additional release of terrestrial organic matter (OM) into rivers and, ultimately, after transport via deltas and estuaries, to the Arctic Ocean nearshore. The majority of our understanding of nearshore OM dynamics and fate has been developed from freshwater rivers despite the likely impact of highly dynamic estuarine and deltaic environments on the transformation, storage, and age of OM delivered to coastal waters. Here, we studied particulate organic carbon (POC) dynamics in the Lena River delta and compared them with POC dynamics in the Lena River main stem along a ∼ 1600 km long transect from Yakutsk, downstream to the delta. We measured POC, total suspended matter (TSM), and carbon isotopes (δ13C and Δ14C) in POC to compare riverine and deltaic OM composition and changes in OM source and fate during transport offshore. We found that TSM and POC concentrations decreased by 70 % during transit from the main stem to the delta and Arctic Ocean. We found deltaic POC to be strongly depleted in 13C relative to fluvial POC. Dual-carbon (Δ14C and δ13C) isotope mixing model analyses indicated a significant phytoplankton contribution to deltaic POC (∼ 68 ± 6 %) and suggested an additional input of permafrost-derived OM into deltaic waters (∼ 18 ± 4 % of deltaic POC originates from Pleistocene deposits vs. ∼ 5 ± 4 % in the river main stem). Despite the lower concentration of POC in the delta than in the main stem (0.41 ± 0.10 vs. 0.79 ± 0.30 mg L−1, respectively), the amount of POC derived from Yedoma deposits in deltaic waters was almost twice as large as the amount of POC of Yedoma origin in the main stem (0.07 ± 0.02 and 0.04 ± 0.02 mg L−1, respectively). We assert that estuarine and deltaic processes require consideration in order to correctly understand OM dynamics throughout Arctic nearshore coastal zones and how these processes may evolve under future climate-driven change.

Distinct drivers of two size fractions of operationally dissolved iron in a temperate river

AbstractRiverine dissolved iron (Fe) affects water color, nutrients, and marine carbon cycling. Fe size and coupling with dissolved organic matter (DOM), in part, modulates the biogeochemical roles of riverine Fe. We used size fractionation to operationally define dissolved Fe (&lt; 0.22 μm) into soluble (&lt; 0.02 μm) and colloidal (0.02–0.22 μm) fractions in order to characterize the downstream drivers, concentrations, and fluxes of Fe across season and hydrologic regime at the freshwater Connecticut River mainstem, which we sampled bi‐weekly for 2 yrs. Drivers of colloidal and soluble Fe concentrations were markedly different. The response of colloidal Fe concentration to changes in discharge was modulated by water temperature; colloidal Fe decreased with increasing discharge at temperatures &lt; 10.5°C, but increased with increasing discharge at temperatures &gt; 10.5°C. Conversely, soluble Fe concentrations were only positively correlated to discharge at high temperatures (&gt; 20°C). Soluble Fe was strongly positively correlated to a humic‐like DOM fluorescence component, suggesting coupling with DOM subsets, potentially through complexation. While average colloidal Fe fluxes varied twofold seasonally, soluble Fe fluxes varied ninefold; therefore, soluble Fe variability was more important to the overall dissolved Fe variability than colloidal Fe, despite lower concentrations. Seasonal Fe fluxes were decoupled from discharge: dissolved and soluble Fe fluxes were greatest in the fall, whereas discharge was greatest in the spring. Fluxes of soluble Fe, which may be more bioavailable and more likely to be exported to the ocean, were lowest in the summer when downstream biological demand is high, having implications for primary productivity and iron uptake.

Are temperature time series measured at hydrometric stations representative of the river’s thermal regime?

River temperature is a key variable for water quality assessment. It can alter different chemical water properties. Indeed, it is considered as determining criterion in the adequacy of cold water fish habitat, and the overall health of the river ecosystem and aquatic biota. Consequently, monitoring this variable and understanding the river thermal variation are highly important. Temperature monitoring along the rivers is often done by deploying autonomous temperature loggers. However, recently, temperature sensors were installed at hydrometric stations in conjunction with water level gauges for monitoring the river temperature, thereby providing an opportunity to expand the temperature network across the region and eventually, the country. In this study, a comparative analysis was conducted to find if the temperatures at the hydrometric station are representative of the river thermal variation upstream and downstream of that location. This comparative analysis was completed using a number of different statistical tools: entropy analysis, Gaussian function fit, and thermal sensitivity analysis. These statistical analyses confirm that temperature loggers that are collocated with the level gauges at hydrometric stations are generally representative of the thermal variation of the river main stem over a distance of a few tens of kilometres. However, the thermal variation observed in temperature loggers located at distances of the order of 100 km or in a different river reach than the hydrometric station, is different from that of the temperature logger located at the hydrometric station.

Assessment of the genetic diversity of Chinese freshwater mussels and refuge areas in the Yangtze River floodplain

Abstract Freshwater mussels are one of the most diverse and endangered faunas worldwide. Owing to the continuing global biodiversity loss, it is essential to identify and protect populations that are not severely affected by human disturbances and ensure that natural genetic diversity is not inevitably lost. The generation of baseline genetic diversity data will help guide species conservation and restoration plans in the Yangtze River Basin where freshwater mussels are facing multiple threats and where strong declines have been observed. The genetic diversity of freshwater mussels was assessed using 818 mtDNA cytochrome c oxidase subunit 1 (COI), 565 28S rRNA and 509 COI + 28S datasets, and refuge areas in the Yangtze River floodplain were predicted using a Maxent habitat suitability model. The results showed that the genetic diversity of Aculamprotula spp., Sinosolenaia carinata, Cuneopsis rufescens, Lamprotula cornuumlunae, Lanceolaria lanceolata, Ptychorhynchus pfisteri, Schistodesmus spp. and Sinohyriopsis cumingii was lower than that of other freshwater mussels, which indicated that the conservation status of these species should be prioritized. The habitat suitability modelling showed that Poyang Lake and Dongting Lake basins (lakes and tributary rivers connected to the Yangtze River mainstem) present the most suitable habitats for freshwater mussels, indicating that lateral hydrological connectivity may be the most important factor in maintaining the genetic diversity of Chinese freshwater mussels. Consequently, Poyang Lake and Dongting Lake basins should be established as protected areas. This study provides valuable information for the conservation and management of freshwater mussel biodiversity in the Yangtze River basin, which will not only help conserve this vulnerable group but will also provide wider benefits to freshwater ecosystems.

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.