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Incorporating societal considerations into decisions related to invasive species management is desirable, but can be challenging because it requires a solid understanding of the ecological functions and socio- cultural and economic benefits and values of the invaded environment before and after invasion. The ecosystem service (ES) concept was designed to facilitate such decision-making by establishing direct connections between ecosystem properties and human well-being, but its application in invasive species management has not been systematic. In this Discussion paper, we propose the adoption of the ES cascade model as a framework for understanding the environmental effects, costs and benefits associated with controlling an invasive shrub (Tamarix spp.) in riparian systems of the western United States. The cascade model has the advantage of explicitly dissecting social-ecological systems into five components: ecosystem structure and processes, ecological functions, ecosystem services, benefits and the economic and socio-cultural valuation of these services and benefits. The first two have received significant attention in the evaluation of Tamarix control effectiveness. The last three have long been implicitly acknowledged over decades of Tamarix management in the region, but have not been formally accounted for, which we believe would increase the effectiveness, accountability and transparency of management efforts. [ABSTRACT FROM AUTHOR]

The loose‐equilibrium concept (LEC) predicts that ecological assemblages change transiently but return towards an earlier or average structure. The LEC framework can help determine whether assemblages vary within expected ranges or are permanently altered following environmental change.Long‐lived, slow‐growing animals typically respond slowly to environmental change, and their assemblage dynamics may respond over decades, which transcends most ecological studies. Unionid mussels are valuable for studying dynamics of long‐lived animals because they can live >50 years and occur in dense, species‐rich assemblages (mussel beds). Mussel beds can persist for decades, but disturbance can affect species differently, resulting in variable trajectories according to differences in species composition within and among rivers.We used long‐term data sets (10–40 years) from seven rivers in the eastern United States to evaluate the magnitude, pace and directionality of mussel assemblage change within the context of the LEC.Site trajectories varied within and among streams and showed patterns consistent with either the LEC or directional change. In streams that conformed to the LEC, rank abundance of dominant species remained stable over time, but directional change in other streams was driven by changes in the rank abundance and composition of dominant species.Characteristics of mussel assemblage change varied widely, ranging from those conforming to the LEC to those showing strong directional change. Conservation approaches that attempt to maintain or create a desired assemblage condition should acknowledge this wide range of possible assemblage trajectories and that the environmental factors that influence those changes remain poorly understood. [ABSTRACT FROM AUTHOR]

Water treatment plant operators need to understand federal and state laws as well as the standards that apply to water treatment systems. They should also understand how drinking water regulations are administered and why compliance is essential to providing safe drinking water to the public. [ABSTRACT FROM AUTHOR]

Eutrophication is one of the largest threats to aquatic ecosystems and chlorophyll a measurements are relevant indicators of trophic state and algal abundance. Many studies have modeled chlorophyll a in rivers but model development and testing has largely occurred at individual sites which hampers creating generalized models capable of making broad‐scale predictions. To address this gap, we compiled a large data set of chlorophyll a concentrations matched to other water quality, meteorological, and reach characteristic data for a diverse set of 82 streams and rivers across the United States. We used this data set and extreme gradient boosting, a tree‐based machine learning algorithm, to predict daily chlorophyll a concentrations. Furthermore, we tested several practical considerations of broad‐scale models, such as making predictions at sites not included in model training or the utility of in situ water quality data versus universally available remotely estimated model inputs. Predictions were very strongly correlated to observations when compared against a randomly withheld subset of days; however, the model had lower accuracy when applied to completely novel sites withheld from model training. Turbidity and total nitrogen were the two most important variables for predicting chlorophyll a. Although in situ variables improved modeled estimates and were identified as more important during model interpretation, using only remote inputs still resulted in highly correlated predictions with small bias. Testing a model across many sites allowed for identification of common variables relevant to chlorophyll a and highlighted several challenges for applying data‐driven models to new sites or at larger spatial scales. Plain Language Summary: One of the largest threats to freshwater and marine ecosystems is excess primary productivity stimulated by increased nutrient availability. An overabundance of algae can cause degradation of ecosystems and risks for public health. Chlorophyll a routinely collected as a proxy measure for algal abundance and provides a common currency to compare across aquatic ecosystems. We compiled a data set of chlorophyll a, additional in situ water quality variables, reach characteristics, and broadscale meteorology to model daily chlorophyll concentrations at 82 rivers across the United States. Machine learning was used to predict daily chlorophyll concentrations and several challenges of broad‐scale modeling were investigated, such as extrapolating predictions to new sites or tradeoffs between data quality and quantity. While the model performed well against a withheld set of days for testing, it performed noticeably worse when entire sites were withheld for model testing. Turbidity and total nitrogen were the two most important predictors, and although in situ data resulted in better predictions, estimates solely made from remote data sets have potential for use in widespread predictions. Testing a model across many sites allowed us to identify variables that are commonly relevant to chlorophyll a and highlighted needs for future improvement of broad‐scale models. Key Points: Predicted daily chlorophyll a concentrations across a diverse set of streams and rivers using a decision tree machine learning algorithmModel estimates performed well at sites that contributed some data to model training but not at sites totally withheld from model trainingUsing in situ data for model inputs increased accuracy but ubiquitous remote data sets can provide reasonable estimates at many more places [ABSTRACT FROM AUTHOR]

Late Quaternary fluvial channel deposits are notoriously difficult to date. In the midwestern United States, shells of aquatic mollusks can be found within many fluvial channel sediments and therefore can be radiocarbon (14C) dated to determine the age of the deposits. However, carbonate platform rocks are abundant in this region, potentially causing freshwater 14C reservoir effects (FRE) in mollusk shells. We 14C dated 11 aquatic gastropod and bivalve shell samples from specimens collected live from a stream in southwestern Ohio during three different years to assess the modern 14C reservoir effect. Modern samples yielded an average 14C FREmodern of 518 ± 65 14C yrs for 2020 (n=5), 640 ± 34 14C yrs for 2021 (n=2), and 707 ± 76 14C yrs for 2022 (n=4). We also 14C dated matched pairs of organic wood or charcoal and aquatic mollusk shells from late Pleistocene and Holocene deposits in the Four Mile Creek floodplain to determine the FREfossil. These samples, free of any potential influence from nuclear bomb testing, yielded an overall weighted mean FREfossil of 1029 ± 345 14C yrs. We then assess the advantages and limitations of both the FREmodern and FREfossil methods for determining freshwater reservoir effects. Finally, we apply the FREfossil correction to a series of shell ages from fluvial terrace deposits as a case study. The results indicate that although there is a 14C FRE in streams from the midwestern United States, aquatic shells can provide robust age control on fluvial channel deposits. More research is needed to understand the spatial and temporal variability of FREs, as well as any species effects, among various watersheds across the midwestern United States. [ABSTRACT FROM AUTHOR]

We use the five landscape ecology metrics of aggregation index, percentage of like adjacencies, interspersion and juxtaposition index, patch density, and Shannon's evenness index to assess spatial heterogeneity at 15 floodplains in the continental United States. Assessments are based on floodplain classes and patches delineated remotely using topography and vegetation. Floodplain reaches examined here represent diverse drainage areas, flow regimes, valley geometries, channel planforms, and biomes. We selected sites with minimal direct human alteration. Our objectives are to quantify floodplain spatial heterogeneity; evaluate whether statistically significant patterns are present; and interpret the statistical analyses with respect to the influence of lateral channel mobility and valley‐floor space available. We develop a conceptual model of the influences on lateral mobility and space available, and then test specific hypotheses derived from this conceptual model. These natural floodplains have a median aggregation index of 58.8%, median percentage of like adjacencies of 58.5%, median interspersion and juxtaposition index of 74.9%, median density of 1,241 patches/ha, and median Shannon's evenness index of 0.934 (n = 15). In other words, natural floodplains have moderate aggregation of classes, high evenness and intermixing of classes, and a wide range of patch densities. Drainage area, the ratio of floodplain/channel width, elevation, precipitation, total sinuosity, large wood volume, planform, and flow regime emerge as important variables to floodplain heterogeneity. These results highlight the influence of biotic‐abiotic interactions in shaping floodplain heterogeneity across diverse river corridors. Plain Language Summary: As river channels move across their valley floors, they create diverse topography including natural levees, cutoff meanders, secondary channels, and floodplain wetlands. These features increase the spatial variability of the floodplain. Many studies indicate that this variability strongly influences habitat abundance and diversity, storage of flood waters and excess nitrate or phosphate, and other floodplain functions. However, no one has systematically measured floodplain variability across multiple rivers and different geographic regions. We measured the variability of natural floodplains at 15 sites in the continental United States using metrics developed by landscape ecologists. We find that natural floodplains have distinctive variability signatures that relate to drainage area, the size of the floodplain, and other characteristics. Key Points: Natural floodplains have moderate aggregation of classes, high evenness and intermixing of classes, and a wide range of patch densitiesFloodplain heterogeneity reflects space available on the valley floor and lateral channel mobility [ABSTRACT FROM AUTHOR]

Maintaining regional‐scale freshwater connectivity is challenging due to the dendritic, easily fragmented structure of freshwater networks, but is essential for promoting ecological resilience under climate change. Although the importance of stream network connectivity has been recognized, lake‐stream network connectivity has largely been ignored. Furthermore, protected areas are generally not designed to maintain or encompass entire freshwater networks. We applied a coarse‐filter approach to identify potential freshwater corridors for diverse taxa by calculating connectivity scores for 385 lake‐stream networks across the conterminous United States based on network size, structure, resistance to fragmentation, and dam prevalence. We also identified 2080 disproportionately important lakes for maintaining intact networks (i.e., hubs; 2% of all network lakes) and analyzed the protection status of hubs and potential freshwater corridors. Just 3% of networks received high connectivity scores based on their large size and structure (medians of 1303 lakes, 498.6 km north–south stream distance), but these also contained a median of 454 dams. In contrast, undammed networks (17% of networks) were considerably smaller (medians of six lakes, 7.2 km north–south stream distance), indicating that the functional connectivity of the largest potential freshwater corridors in the conterminous United States currently may be diminished compared with smaller, undammed networks. Network lakes and hubs were protected at similar rates nationally across different levels of protection (8%–18% and 6%–20%, respectively), but were generally more protected in the western United States. Our results indicate that conterminous United States protection of major freshwater corridors and the hubs that maintain them generally fell short of the international conservation goal of protecting an ecologically representative, well‐connected set of fresh waters (≥17%) by 2020 (Aichi Target 11). Conservation planning efforts might consider focusing on restoring natural hydrologic connectivity at or near hubs, particularly in larger networks, less protected, or biodiverse regions, to support freshwater biodiversity conservation under climate change. [ABSTRACT FROM AUTHOR]

Stream drying is increasing globally, with widespread impacts on stream ecosystems. Here, we investigated how the impacts of drying on stream ecosystem connectivity might depend on stream network size and the location of drying within the stream network. Using 11 stream networks from across the United States, we simulated drying scenarios in which we varied the location and spatial extent of drying. We found that the rate of connectivity loss varied with stream network size, such that larger stream networks lost connectivity more rapidly than smaller stream networks. We also found that the rate of connectivity loss varied with the location of drying. When drying occurred in the mainstem, even small amounts of drying resulted in rapid losses in ecosystem connectivity. When drying occurred in headwater reaches, small amounts of drying had little impact on connectivity. Beyond a certain threshold, however, connectivity declined rapidly with further increases in drying. Given the increasing stream drying worldwide, our findings underscore the need for managers to be particularly vigilant about fragmentation when managing at large spatial scales and when stream drying occurs in mainstem reaches., (© 2024 The Ecological Society of America.)

The Colorado River has experienced a significant streamflow reduction in recent decades due to climate change, resulting in pronounced hydrological droughts that pose challenges to the environment and human activities. However, current models struggle to accurately capture complex drought patterns, and their accuracy decreases as the lead time increases. Thus, determining the reliability of drought forecasting for specific months ahead presents a challenging task. This study introduces a robust approach that utilizes the Beluga Whale Optimization (BWO) algorithm to train and optimize the parameters of the Regularized Extreme Learning Machine (RELM) and Random Forest (RF) models. The applied models are validated against a KNN benchmark model for forecasting drought from one- to six-month ahead across four hydrological stations distributed over the Colorado River. The achieved results demonstrate that RELM-BWO outperforms RF-BWO and KNN models, achieving the lowest root-mean square error (0.2795), uncertainty (U 95  = 0.1077), mean absolute error (0.2104), and highest correlation coefficient (0.9135). Also, the current study uses Global Multi-Criteria Decision Analysis (GMCDA) as an evaluation metric to assess the reliability of the forecasting. The GMCDA results indicate that RELM-BWO provides reliable forecasts up to four months ahead. Overall, the research methodology is valuable for drought assessment and forecasting, enabling advanced early warning systems and effective drought countermeasures., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Various measures are available to help utilities mitigate drought as well as support water supply, quality, and reliability. [ABSTRACT FROM AUTHOR]

This study aimed to identify the importance of ecological factors to distribution patterns of the invasive Clam (Corbicula fluminea) relative to native mussels (family: Unionidae) across seven rivers within the Mobile and Tennessee basins, Southeast United States. We quantitatively surveyed dense, diverse native mussel aggregations across 20 river reaches and estimated mussel density, biomass, and species richness along with density of invasive C. fluminea (hereafter Corbicula). We measured substrate particle size, velocity, and depth in quadrats where animals were collected. Additionally, we characterized reach scale environmental parameters including seston quantity and quality (% Carbon, % Nitrogen, % Phosphorous), water chemistry (ammonium [NH4+], soluble reactive phosphorous [SRP]), and watershed area and land cover. Using model selection, logistic regression, and multivariate analysis, we characterized habitat features and their association to invasive Corbicula within mussel beds. We found that Corbicula were more likely to occur and more abundant in quadrats with greater mussel biomass, larger substrate size, faster water velocity, and shallower water depth. At the reach scale, Corbicula densities increased where particle sizes were larger. Mussel richness, density, and biomass increased with watershed area. Water column NH4+ increased at reaches with more urban land cover. No land cover variables influenced Corbicula populations or mussel communities. The strong overlapping distribution of Corbicula and mussels support the hypothesis that Corbicula are not necessarily limited by habitat factors and may be passengers of change in rivers where mussels have declined due to habitat degradation. Whether Corbicula is facilitated by mussels or negatively interacts with mussels in these systems remains to be seen. Focused experiments that manipulate patch scale variables would improve our understanding of the role of species interactions (e.g., competition, predation, facilitation) or physical habitat factors in influencing spatial overlap between Corbicula and native mussels. [ABSTRACT FROM AUTHOR]

Sunlight can oxidize dissolved organic carbon (DOC) to dissolved inorganic carbon (DIC) in freshwaters. The importance of complete photooxidation, or photomineralization, as a sink for DOC remains unclear in temperate rivers, as most estimates are restricted to lakes, high latitude rivers, and coastal river plumes. In this study, we construct a model representing over 75,000 river reaches in the Connecticut River Watershed (CRW), USA, to calculate spectrally resolved photomineralization. We test the hypothesis that photomineralization is a negligible DOC sink across all reaches and flow conditions relative to DOC fluxes. Our model quantifies reaction rates and transport drivers within the river reaches for the ranges of flow conditions, incoming solar irradiance, and canopy cover shading observed throughout the year. Our model predicts average daily areal photomineralization rates ranging from 1.16 mg‐C m−2 day−1 in low flow river reaches in the winter, to 18.33 mg‐C m−2 day−1 in high flow river reaches during the summer. Even for high photomineralization fluxes, corresponding photomineralization uptake velocities are typically at least an order of magnitude smaller than those reported for other instream processes. We calculate DOC elimination by photomineralization relative to DOC fluxes through individual stream reaches as well as the entire riverine portion of the CRW. We find that relative photomineralization fluxes are highest in summer drought conditions in low order streams. In median flows and mean light intensities, for an average watershed travel distance, 3%–5% of the DOC fluxes are eliminated, indicating that photomineralization is a minor DOC sink in temperate rivers. Plain Language Summary: Rivers are an important part of the carbon cycle, moving carbon compounds from land to the ocean. Within rivers, dissolved organic carbon molecules can be broken down into inorganic carbon molecules, including the greenhouse gas carbon dioxide. Sunlight shining into rivers can cause these organic molecules to break down in a process called photomineralization, but it is not clear if this process is important compared to the total amount of organic carbon that travels through rivers every day. In this paper, we build a model for the river sections of temperate Connecticut River Watershed, which calculates photomineralization for possible river flow conditions, dissolved organic carbon concentrations, and seasons, and compares the size of the sunlight‐driven breakdown of dissolved organic carbon to the amount of dissolved organic carbon in the river. This is the first model that puts photomineralization rates in the context of a flowing temperate river network. We show that compared with the dissolved organic carbon amounts present in the river at any time of the year or any flow conditions, photomineralization is essentially an unimportant process, removing on average 3%–5% of the dissolved organic carbon through an average watershed river route. Key Points: We build a model calculating reaction and transport drivers for photomineralization in 75,000 temperate river reachesPhotomineralization is a negligible dissolved organic carbon (DOC) sink relative to DOC fluxesDOC elimination by photomineralization in temperate rivers is limited by short water residence times and canopy cover [ABSTRACT FROM AUTHOR]

Solar radiation is a fundamental driver of ecosystem productivity, but widespread estimates of light available for primary producers in rivers are lacking. We developed a model to predict light available for river primary producers and used it to estimate river primary production across the contiguous United States (CONUS). Successively accounting for riparian and water column processes improved predictions of primary production as a function of light. We calculated the ratio of river width to riparian tree height and used this metric to predict whether riparian zones or water column processes most limit productivity for over 2 million reaches. Water column processes limited productivity for 50% of the nation's river length and 80% of its surface area, with variations across ecoregions related to riparian forest cover. Our findings facilitate large‐scale predictions of stream and river ecosystem productivity, as well as understanding the processes controlling productivity across networks. Plain Language Summary: The conversion of solar energy to organic matter through photosynthesis is an important component of global carbon cycling. While there are global estimates of solar radiation at the Earth's surface, primary producers in rivers often only receive a small percentage of incoming light due to reductions from riparian shading, water depth, and water clarity. We developed a model to predict light available for river primary producers so that we could make estimates of productivity based solely on light. We predicted light and primary productivity for 173 rivers across the United States and also examined the degree to which riparian zones or water column processes limited productivity. Our model allowed us to make first approximations of productivity across many sites with varying conditions based solely on light availability. We also developed a metric to predict whether river productivity was most limited by riparian zones or water column processes and calculated this metric for over 2 million rivers in the United States. Our results suggested that riparian zones and water column process limit an equal percentage of river length nationally; however, these results varied across ecoregions and appear to be driven by changes in forest cover. Key Points: Riparian zones limit light availability, and thus primary productivity, until channel width is 1.7 times the height of riparian treesLight attenuation from water depth and clarity limit productivity for 50% of river length and 80% of river surface areaThe percentage of river length and surface area limited by riparian zones and water column processes varies across ecoregions [ABSTRACT FROM AUTHOR]

When multiple species of fish coexist there are a host of potential ways through which they may interact, yet there is often a strong focus on studies of single species without considering these interactions. For example, many studies of forestry-stream interactions in the Pacific Northwest have focused solely on the most prevalent species: Coastal cutthroat trout. To examine the potential for interactions of other fishes with coastal cutthroat trout, we conducted an analysis of 281 sites in low order streams located on Washington's Olympic Peninsula and along the central Oregon coast. Coastal cutthroat trout and juvenile coho salmon were the most commonly found salmonid species within these streams and exhibited positive associations with each other for both presence and density. Steelhead were negatively associated with the presence of coastal cutthroat trout as well as with coho salmon and sculpins (Cottidae). Coastal cutthroat trout most frequently shared streams with juvenile coho salmon. For densities of these co-occurring species, associations between these two species were relatively weak compared to the strong influences of physical stream conditions (size and gradient), suggesting that physical conditions may have more of an influence on density than species interactions. Collectively, our analysis, along with a review of findings from prior field and laboratory studies, suggests that the net effect of interactions between coastal cutthroat trout and coho salmon do not appear to inhibit their presence or densities in small streams along the Pacific Northwest. [ABSTRACT FROM AUTHOR]

Climate signatures recorded in the geometry of branching streams provide insight into climate and landscape histories on Earth and other planetary bodies. Recent findings establish that branching angles are narrower and stream profiles are straighter in more arid climates. However, these two observations have been attributed to different mechanisms. Here we demonstrate that for US watersheds the difference in slope between confluent streams increases with humidity, and streams with a greater difference in slope tend to branch at wider angles. Our observations suggest a branching angle endmember of 90° when stream slopes are most different. Using a simple model of runoff erosion, we show how this variation in relative stream slopes can be explained by a shift in streamflow accumulation across climate regimes. These findings connect previously observed climate signatures in branching angles and stream profiles, suggesting that both record the same control of aridity on surface flow. Plain Language Summary: Spatial patterns in stream networks have emerged as a promising tool for interpreting climate and landscape histories on Earth, as well as other planets and moons. Recent findings establish that in wetter environments, branching angles between confluent streams tend to be wider, and stream slopes flatten out more rapidly downstream. However, it remains unclear how these two observations are connected. Here we study watersheds across the contiguous United States, demonstrating that confluent streams tend to have a greater difference in slope in more humid climates. We show how greater differences in slope with increasing humidity link directly to wider average branching angles and downstream shallowing of slope. Variation in relative stream slopes across climates may be produced by climate‐driven changes in drainage. We find that the area of a drainage basin has a stronger influence on erosion—and stream steepness—in wetter landscapes, supporting the theory that water flowing downstream accumulates less efficiently in drier landscapes. Our findings connect previously observed 'signatures' of climate in stream networks and offer a unifying view of how climate shapes the landscape. Key Points: Confluent streams in more humid climates are less likely to share a common slope and orientationThe relative influence of drainage area and stream slope on erosion acts as a climate‐sensitive control on slope ratio and stream profilesThe branching angle of confluent streams varies systematically with climatic aridity in concert with slope ratio [ABSTRACT FROM AUTHOR]

The effectiveness of submerged vanes for stabilizing streamside bluffs varied over a 10-year monitoring period in a tributary to Lake Superior, United States. Submerged vanes are a river training device used to divert river flows away from eroding banks along meander bends and ultimately hold constant or reverse the direction of lateral migration. At the study site, the relatively steep slope, large substrate size, and flashy flow regime pushed the upper end of the design limitations of submerged vanes. Changes in channel location and morphology due to the vanes were monitored using repeat channel cross-section surveys along a 110-m reach. The vanes experienced 15 floods over the monitoring period. The two most damaging floods happened in the summer and fall of 2005 with annual exceedance probabilities of 7% and 6% respectively. A new data analysis method for rivers, using centroids of cross sections, was useful to track channel migration rapidly and objectively and, along with calculations of changes in bankfull channel size, provide metrics to describe channel change. [ABSTRACT FROM AUTHOR]

Freshwater darters belonging to the orangethroat darter species complex, or Ceasia, are widely distributed in the Central and Southern United States, with ranges that span both glaciated and unglaciated regions. Up to 15 species have been recognized in the complex, with one, Etheostoma spectabile, having a widespread northern distribution and another, Etheostoma pulchellum, having a sizeable southern distribution. The other species in the complex have much more restricted distributions in unglaciated regions of the Central Highlands. We sampled 384 darters from 52 sites covering much of the range of Ceasia and evaluated patterns of genetic diversity, genetic structure, and pre- and post-glacial patterns of range contraction and expansion. We anticipated finding much stronger signals of genetic differentiation and diversification in unglaciated regions, given the higher species diversity and levels of endemism reported there. Surprisingly, microsatellite genotyping revealed two well-differentiated genetic clusters of E. spectabile in samples from glaciated regions, one confined to the Illinois River basin and another found in the Wabash drainage and Great Lakes tributaries. This suggests that there was expansion from two isolated glacial refugia, with little subsequent post-glacial gene flow. Fish collected from throughout the unglaciated region were less genetically differentiated. Fish assigned to Etheostoma burri and Etheostoma uniporum based on collection sites and morphological characters were not genetically differentiated from E. spectabile samples from the region. Hybridization and introgression occurring in the Central Highlands may confound genetic delineation of species in this region of high endemism and diversity., (© 2023 The Authors. Journal of Fish Biology published by John Wiley & Sons Ltd on behalf of Fisheries Society of the British Isles.)

An initial and comprehensive map of ecological regions across the conterminous United States was provided by Omernik in 1987. Because that paper was the most-cited published by the Annals of the American Association of Geographers, we sought to assess and quantify its contribution to science. To do so, we conducted a scientometric analysis to address the following main questions: 1) What are the temporal and spatial citation trends? We expected that Omernik's paper would still be employed 36 years after its publication, and mostly in the United States of America. 2) For what types of environments and organisms has it been applied? Based on its generality, we expected that it had been applied to both terrestrial and aquatic ecosystems. 3) What are the main applications of Omernik's article? We predicted that it would mostly be used for describing and delineating study sites and management areas, as well as for selecting regional reference sites. The number of citations presented a positive temporal increase, indicating its continued applicability. Most papers dealt with aquatic environments, mainly in streams carried out predominantly in the United States of America, as was one of its earliest applications. The usefulness of ecoregions for assessing and managing biotic and abiotic patterns and distributions were the main topics addressed by scientists. Ecoregions have offered a general framework for developing regional expectations and rational regional management policies across large areas, as was their original intent. In addition, ecoregion maps were used for communicating patterns-or the lack of them-to interested scientists, citizens, and decision-makers. That comprehensiveness of Omernik's ecoregion approach has led to its widespread applicability and continued usefulness to a diverse set of scientific and management disciplines., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Water table depth (WTD) has a substantial impact on the connection between groundwater dynamics and land surface processes. Due to the scarcity of WTD observations, physically-based groundwater models are growing in their ability to map WTD at large scales; however, they are still challenged to represent simulated WTD compared to well observations. In this study, we develop a purely data-driven approach to estimating WTD at continental scale. We apply a random forest (RF) model to estimate WTD over most of the contiguous United States (CONUS) based on available WTD observations. The estimated WTD are in good agreement with well observations, with a Pearson correlation coefficient (r) of 0.96 (0.81 during testing), a Nash-Sutcliffe efficiency (NSE) of 0.93 (0.65 during testing), and a root mean square error (RMSE) of 6.87 m (15.31 m during testing). The location of each grid cell is rated as the most important feature in estimating WTD over most of the CONUS, which might be a surrogate for spatial information. In addition, the uncertainty of the RF model is quantified using quantile regression forests. High uncertainties are generally associated with locations having a shallow WTD. Our study demonstrates that the RF model can produce reasonable WTD estimates over most of the CONUS, providing an alternative to physics-based modeling for modeling large-scale freshwater resources. Since the CONUS covers many different hydrologic regimes, the RF model trained for the CONUS may be transferrable to other regions with a similar hydrologic regime and limited observations., (© 2023 The Authors. Groundwater published by Wiley Periodicals LLC on behalf of National Ground Water Association.)

Biological assemblages are commonly used for assessing stream health, but there is increased interest among the freshwater research community in incorporating measures of stream function, such as metabolism, to strengthen stream-health assessments. Presently, there is limited information about the relationships between stream metabolism and biological assemblages, along with the measurement period required to relate metabolism with stream biota. Our study assessed which environmental factors explained stream metabolism and to what degree stream metabolism and minimum dissolved oxygen (DOmin) were related to invertebrate and fish metrics in streams distributed across several regions of the United States. Furthermore, we evaluated the number of metabolism monitoring days required for maximizing the ability to detect relationships between stream metabolism and biological assemblage metrics. We sampled 17 sites distributed among reference, agricultural, and urban areas for stream metabolism, nutrients, habitat, and biological assemblages (invertebrates and fishes). Overall, sites were heterotrophic with gross primary production (GPP) and ecosystem respiration (ER) related primarily to days since last high flow, canopy cover, maximum water temperature, and total phosphorus. DOmin was related to days since last high flow, canopy cover, and maximum water temperature. We were unable to determine a clear statistical relationship between invertebrate metrics (invertebrate richness; Ephemeroptera, Plecoptera, and Trichoptera richness; and scraper-taxa richness) and GPP, ER, or DOmin. In contrast, we found that 2 fish-assemblage metrics were associated with stream metabolism and DOmin. A fish multimetric index (FMMI) was negatively correlated with GPP (r = −0.5, p = 0.048) and positively correlated with DOmin (r = 0.47, p = 0.06). Percentage of omnivorous fish taxa was positively correlated with GPP (r = 0.72, p = 0.001) and ER (r = 0.55, p = 0.02) and negatively correlated with DOmin (r = −0.67, p = 0.003). The lack of detected relationships for most of the biological-assemblage metrics with stream metabolism may be partially due to 1 or more factors, including high variability, low sample size, limited range in metabolism values, assemblage metrics used, and geographic distribution of sites. Comparing stream-metabolism measurement periods (in days) to biological-assemblage metrics indicated that optimum correlations occurred at 2 d for DOmin, 3 d for GPP, and 14 d for ER. Although our study found limited relationships of stream metabolism and DOmin with biological assemblages, future studies should consider a larger sample size (≥30), 14-d or longer metabolism measurement period, and assessment of other taxa-specific or assemblage metrics. [ABSTRACT FROM AUTHOR]

Catchments are complex systems containing channel networks and hillslopes. Channel networks interact with hillslopes and are pathways for transporting water, sediment, and nutrients. Understanding the branching and flux transport patterns of channel networks is critical for predicting the response of catchments to external forcing such as climate and tectonics. However, factors creating complexities in catchments are not fully understood. Here, we propose a new framework based on multiscale entropy approach to evaluate complexity of catchments using two different representations of channel networks. First, we investigate the structural complexity using the width‐function, which characterizes the spatial arrangement of channels. Second, we utilize the incremental area‐function along the main channel to study the functional complexity that captures the patterns of transport of fluxes. Our analysis reveals stronger controls of topological connectivity on the functional complexity than on structural complexity, indicating unchannelized surface (hillslope) contribution to the increase of heterogeneity in transport processes. Plain Language Summary: Catchments are complex natural landscape systems that contain hillslopes and channel networks. Understanding and quantifying features and processes that result in catchment complexity is important for predicting their response to changing human and climatic conditions. In this paper, we use an entropy‐based approach to explore the role of channel network and hillslope toward the contribution to catchment's complexity. Based on 40 natural catchments with minimum human impact across the United States in different climatic and geologic conditions, our results show that hillslopes add significant complexity to the catchments and suggest the amount of hillslope information one needs to account for in accurate predictive modeling of hydrologic processes at the catchment scale. Key Points: Topology controls structural and functional complexityFunctional complexity is higher than structural complexity due to contribution from hillslope processesScale of peak difference between the impact of topology on functional and structural complexity indicates the average hillslope length scale [ABSTRACT FROM AUTHOR]

Thermal regimes of rivers and streams profoundly affect aquatic ecosystems, but are poorly described and classified in many areas due to the limited availability of annual datasets from extensive and representative monitoring networks. By mining a new temperature database composed of >23,000 site records that spans the western United States (U.S.), we extract annual monitoring records at 578 sites on perennial streams to describe regimes in this diverse region. Records were summarized using 34 metrics that described regime aspects related to magnitude, variation, frequency, duration, and timing. The metrics were used in a multivariate cluster analysis to classify streams into seven distinct regime types and in a principal components analysis (PCA) to examine patterns of redundancy among metrics. The PCA indicated that 2–5 orthogonal PC axes accounted for 74%–89% of the variation in thermal regimes at the monitoring sites. Most of the variation in PC scores that defined the two dominant axes was in turn predictable from a suite of geospatial covariates in multiple linear regressions that included elevation, latitude, riparian canopy density, reach slope, precipitation, lake prevalence, and dam height. Our results have parallels to previous flow regime analyses that describe the utility of small numbers of PCs or allied metrics in regime characterization, and can be used to better understand and parsimoniously represent thermal regimes in the western U.S. [ABSTRACT FROM AUTHOR]

In the eastern United States, existing paleo-reconstructions in fluvial environments consist primarily of site-specific investigations of climate and human impacts on riverine processes. This paper presents the first meta-analysis of fluvial reconstructions focused on regional watersheds of the eastern United States, including the Lower Mississippi, Tennessee, South Atlantic–Gulf Coast, Ohio, Mid-Atlantic, and New England regional watersheds. Chronologies of fluvial activity (i.e. alluvial deposition) and stability (i.e. landscape stability) were developed by synthesizing data from existing, published, and site-specific fluvial reconstruction studies conducted across the eastern United States. Overall, regional watersheds show variable patterns of synchronicity across watersheds and did not demonstrate cyclic behavior through the Holocene. During the last millennium, only the Lower Mississippi and Ohio regional watersheds exhibit high rates of fluvial activity active during the 'Medieval Climate Anomaly' (650–1050 yr BP), while nearly all other regional watersheds in the eastern United States were active during the 'Little Ice Age' (100–500 yr BP). These findings imply that fluvial activity may be more spatially restricted during warmer/drier climatic conditions than during cooler/wetter periods. We find an increase in fluvial activity during the era of Euro-American colonization (400 yr BP to present) in the southeastern United States but not the northeastern United States, implying a heterogeneous response of fluvial systems to human activities in the eastern United States related to climatic, cultural, and/or physiographic variability. These new insights gained from fluvial chronologies in the eastern United States demonstrate the utility of regionally synthesized paleo-records to understand large-scale climate variation effect on rivers. [ABSTRACT FROM AUTHOR]

The restoration economy has seen significant growth in the United States in recent decades, especially within the context of rural economic development. This paper traces the establishment of the restoration economy in the Mattole River Watershed, USA. Through semi-structured interviews and participant observation, we identified cultural, social, human, financial and political capitals as important components in the creation and maintenance of the restoration economy. This study seeks to highlight the socioeconomic benefits of restoration: how it can create employment and economic diversification, (re)connect people to their landscapes, promote skill and knowledge development, and build trust and reciprocity among community stakeholders. We end with a discussion of the important contributions of the restoration economy in a rural place, and key lessons for potential stakeholders in the development of restoration economies in other communities. [ABSTRACT FROM AUTHOR]

We used a recently published, open‐access data set of U.S. streamwater nitrogen (N) and phosphorus (P) concentrations to test whether watershed land use differentially influences N and P concentrations, including the relative availability of dissolved and particulate nutrient fractions. We tested the hypothesis that N and P concentrations and molar ratios in streams and rivers of the United States reflect differing nutrient inputs from three dominant land‐use types (agricultural, urban and forested). We also tested for differences between dissolved inorganic nutrients and suspended particulate nutrient fractions to infer sources and potential processing mechanisms across spatial and temporal scales. Observed total N and P concentrations often exceeded reported thresholds for structural changes to benthic algae (58, 57% of reported values, respectively), macroinvertebrates (39% for TN and TP), and fish (41, 37%, respectively). The majority of dissolved N and P concentrations exceeded threshold concentrations known to stimulate benthic algal growth (85, 87%, respectively), and organic matter breakdown rates (94, 58%, respectively). Concentrations of both N and P, and total and dissolved N:P ratios, were higher in streams and rivers with more agricultural and urban than forested land cover. The pattern of elevated nutrient concentrations with agricultural and urban land use was weaker for particulate fractions. The % N contained in particles decreased slightly with higher agriculture and urbanization, whereas % P in particles was unrelated to land use. Particulate N:P was relatively constant (interquartile range = 2–7) and independent of variation in DIN:DIP (interquartile range = 22–152). Dissolved, but not particulate, N:P ratios were temporally variable. Constant particulate N:P across steep DIN:DIP gradients in both space and time suggests that the stoichiometry of particulates across U.S. watersheds is most likely controlled either by external or by physicochemical instream factors, rather than by biological processing within streams. Our findings suggest that most U.S. streams and rivers have concentrations of N and P exceeding those considered protective of ecological integrity, retain dissolved N less efficiently than P, which is retained proportionally more in particles, and thus transport and export high N:P streamwater to downstream ecosystems on a continental scale. [ABSTRACT FROM AUTHOR]

The article discusses several researchers have challenged a study conducted by professors Robert Walter and Dorothy Merritts, who have claimed that mud has smothered many streams in the U.S. It mentions Grove Karl Gilbert, a storied geologist has revealed that gold mining in the late 1800s had caused sediment to fill and reshape deep river valleys in the California Sierra; and geomorphologist Jim Knox and hydrologist Stanley Trimble documented thick beds of legacy sediments beneath waterways.

In streams, gross primary production (GPP) and ecosystem respiration (ER) (i.e., stream metabolism) control the transport and fate of nutrients and organic carbon and vice versa. The importance of short-term and local factors in driving these processes is well known in the literature. However, little information exists regarding the extent of temporal variability of stream metabolism and how both local physicochemical and broad-scale climatic drivers affect this variability. We used 7 years of field data from an open-canopy headwater stream ecosystem in the southwestern United States to quantify the extent of seasonal and inter-annual variability in stream metabolism (GPP, ER, and net ecosystem production [NEP]) and to assess if temporal variation in these processes was related to the magnitude of snowmelt runoff. In spring, seasonal mean ER (p = 0.025, r 2 = 0.67) and NEP (p = 0.004, r 2 = 0.83) were more strongly related to discharge (Q) than GPP (p = 0.19, r 2 = 0.32), potentially because of an increased influx of nutrients and organic carbon during years with higher snowmelt runoff. There were no strong relationships between seasonal mean GPP and Q , light, temperature, turbidity, and specific conductance (p ≥ 0.27, r 2 ≤ 0.18). Our long-term data revealed unanticipated shifts from autotrophic to heterotrophic status within and across years. However, this variability was not strongly associated with environmental factors at either local (i.e., Q or photosynthetically-active radiation) or global (i.e., El Niño-Southern Oscillation) scales. Previous paradigms hold that local attributes dictated by geographic and landscape positioning (e.g., light and temperature regimes) control the trophic status of streams, but our findings suggest that complex combinations of spatiotemporally-variable factors, such as snow accumulation and melting, and their role in connecting terrestrial and aquatic ecosystems can lead to substantial within-stream variation in autotrophic or heterotrophic status. [ABSTRACT FROM AUTHOR]

River otter Lontra canadensis populations in the United States have expanded during the past 50 y as a result of improvements in habitat quality and effective management programs implemented by state and federal agencies and native tribes. Periodic assessments of river otter status, population trends, and geographic distribution are needed to detect changes in populations, assess management approaches, and to identify and prioritize conservation efforts. We surveyed state wildlife agency experts to assess the current population and regulatory status of river otters in their jurisdictions. River otters were legally harvested in 40 states as of 2016. Twenty-two states reported increasing populations while 25 reported stable populations. Most states used multiple methods to monitor river otter populations including harvest-based surveys, presence–absence surveys, and empirically derived population model predictions; harvest-based surveys were the most commonly used monitoring approach. As populations have expanded, river otter reintroduction efforts have become less frequent; two additional states had conducted reintroductions since 1998 and only one state had conducted a reintroduction since 2010. We estimated that river otter distribution increased by 10.2% in the continental United States and by 13.7% in the contiguous United States during an 18-y period. Although populations may continue to increase numerically, river otters may be approaching their potential maximum geographic distribution in the United States. [ABSTRACT FROM AUTHOR]

The article discusses work and life of Benjamin Henry Boneval Latrobe, who was a British-American neoclassical architect and influence of rivers on his work. It reports that he was a professional architects in the U.S., drawing on influences from his travels in Italy, as well as British and French Neoclassical architects such as Claude Nicolas Ledoux.

Anthropogenic activities have altered biogeochemical cycles and the fate of organic carbon (OC) and nutrients in freshwater ecosystems. To investigate coupled OC and nutrient cycling and fate in streams, we compared the spiraling lengths (S) and uptake velocities (vf) of OC and nitrate (NO3−) in headwater streams (n = 72) across different land uses (i.e., agricultural, urban, natively vegetated) and regions (n = 8) in the United States. We did these comparisons with data collected for the second Lotic Intersite Nitrogen eXperiment (LINX II; Mulholland et al. 2009). OC spiraling lengths (S OC) in reference (21–4180 m) were shorter than in agricultural streams (89–37,156 m) and urban streams (104–12,605 m). OC mineralization velocities (v f −OC) and NO3− uptake velocities (v f −NO3) were weakly positively correlated across all sites (r = 0.33, p = 0.008). The strongest correlations between OC mineralization and NO3− uptake were in streams with gross primary production (GPP) similar to ecosystem respiration (ER) and human-altered streams (all agricultural streams: r = 0.56, p = 0.008, GPP∶ER = 0.6; all urban streams: r = 0.73, p < 0.001, GPP∶ER = 0.5). Additionally, the distances traveled by OC and NO3− before they were permanently removed from the stream by mineralization (S OC) or denitrification (Sw–den) were similar in magnitude, although S OC was shorter than Sw–den in most streams. This study demonstrates how OC and NO3− spiraling can be used to investigate how region and land use influence coupled OC-NO3− interactions and fate. [ABSTRACT FROM AUTHOR]

Headwater streams impacted by surface coal mining in the central Appalachian region of the eastern USA have characteristics not shared by reference-quality streams. These include elevated salinity, often measured using specific conductance (SC) and cited as a primary stressor of benthic macroinvertebrate communities. The study objective was to assess influence by mining-origin stressors on benthic macroinvertebrate community structure in headwater streams. Stream habitat characteristics were measured and benthic macroinvertebrates were sampled from 12 central Appalachian streams, 9 of which were influenced by mining. Multiple benthic macroinvertebrate community metrics, including Ephemeroptera density, richness, and composition were correlated negatively with watershed mining extent and with SC. Predator density and scraper richness were correlated negatively with watershed mining, stream-water selenium, and SC. Clinger richness was correlated positively with stream substrate characteristics including large cobble-to-fines ratios and relative bed stability, and was correlated negatively with watershed mining and SC. Relationships of predator density and scraper richness with selenium concentrations, and relationships of clinger richness with stream substrate characteristics, are consistent with stress mechanisms revealed by prior studies. Improved understanding of how habitat features are altered by mining and influence community structure in headwater streams can inform water resource management in mining areas. [ABSTRACT FROM AUTHOR]

A total of 71 stream sites representing a gradient of urban land use were sampled across the Piedmont of the south‐eastern United States in 2014. Fish data collected (observed) at each site were compared to an expected community based on georeferenced historical (~1950 ‐ ~1990) species occurrence records for stream segments (1:100,000 scale) containing the sampled stream sites. Loss of expected fish species (per cent of fish species expected to occur but not observed) and homogenization (difference in Jaccard's similarity of the fish community among sites observed and expected) were determined. On average, there was a 13.2% increase in the similarity of fish communities across sites, demonstrating evidence of community homogenization. Occurrence of Redbreast Sunfish (Lepomis auritus), Green Sunfish (L. cyanellus) and Bluegill (L. macrochirus) increased more than 50% over time (between observed and expected). Species loss increased significantly with urbanization, whereas homogenization was not related to urbanization. Random forest analysis indicated that herbicides, insecticides and centrarchid species richness were significant predictors of species loss. Of these, generalized additive model regression indicated that herbicides represented the most parsimonious model based on a single predictor. Stream base flow, elevation and total nitrogen were significant predictors of homogenization. Generalized additive model regression indicated that decreased stream base flow was the single most important factor associated with increased homogenization. Chemical contaminants and associated ecosystem alteration and changes in streamflow may represent important regional influences on changes in fish communities in urban streams in the south‐eastern United States. [ABSTRACT FROM AUTHOR]

Aim: Present a hybrid biogeographic and environmentally constrained clustering approach to classify ~853,000 stream reaches in the eastern United States. Examine the frequency of stream typologies in the landscape relative to anthropogenic stressors to identify potential stream conservation needs. Location: Eastern United States. Methods: Fish communities at 956 least‐disturbed sampling reaches were characterized using taxonomic and functional composition of native species. Environmental variables summarized within stream reaches included stream discharge, channel gradient, hydrologic regime, summer water temperature and boundaries of freshwater ecoregions. Multivariate regression trees were used to relate environmental variables to fish communities while simultaneously developing taxa‐ and trait‐specific biogeographic classifications. We then overlaid stream classifications with indices of anthropogenic disturbances to evaluate rarity and risk of complete loss of natural representation of stream types. Results: Taxonomically based classes represented a combination of ecoregional boundaries and environmental gradients, whereas temperature gradients were most important in differentiating functional composition. An optimal taxonomy‐based classification contained 13 classes and explained 26.4% of community variation, and the optimal trait‐based classification contained 6 classes, explaining 25.2% of community variation. Overlaying class maps with an anthropogenic disturbance index revealed substantial variation in the severity of degradation among classes relative to their abundance in the landscape, especially rare classes (i.e., large rivers and cold headwater systems). Main conclusions: We demonstrate the value of integrating local, regional and historical biogeographic factors with taxonomic and functional characteristics of freshwater biota to classify ecosystems based on mechanistic biota–environment relationships. This approach is important to addressing the challenge of developing stream classifications that reconcile the environmental drivers of community trait composition with the constraints of biogeographic regionality at large spatial scales. Furthermore, the spatially explicit and high‐resolution maps disseminated here can uniquely inform management decisions regarding anthropogenic threats to the biodiverse freshwaters of the eastern United States. [ABSTRACT FROM AUTHOR]

To assess potential impacts on receiving systems, associated with storm water contaminants, laboratory 10‐d amphipod (Eohaustorius estuarius) survival toxicity tests were performed using intact sediment cores collected from Paleta Creek (San Diego Bay, CA, USA) on 5 occasions between 2015 and 2017. The approach included deposition‐associated sediment particles collected from sediment traps placed at each of 4 locations during the 2015 to 2016 wet seasons. The bioassays demonstrated wet season toxicity, especially closest to the creek mouth, and greater mortality associated with particles deposited in the wet season compared with dry season samples. Grain size analysis of sediment trap material indicated coarser sediment at the mouth of the creek and finer sediment in the outer depositional areas. Contaminant concentrations of metals (Cd, Cu, Hg, Ni, Pb, and Zn) and organic compounds (polycyclic aromatic hydrocarbons [PAHs], polychlorinated biphenyls [PCBs], and pesticides) were quantified to assess possible causes of toxicity. Contaminant concentrations were determined in the top 5 cm of sediment and porewater (using passive samplers). Whereas metals, PAHs, and PCBs were rarely detected at sufficient concentrations to elicit a response, pyrethroid pesticides were highly correlated with amphipod toxicity. Summing individual pyrethroid constituents using a toxic unit approach suggested that toxicity to E. estuarius could be associated with pyrethroids. This unique test design allowed delineation of spatial and temporal differences in toxicity, suggesting that storm water discharge from Paleta Creek may be the source of seasonal toxicity. Environ Toxicol Chem 2019;39:229–239. © 2019 SETAC [ABSTRACT FROM AUTHOR]

The Matanuska--Susitna Borough is the fastest growing region in the State of Alaska and is impacted by a number of human activities. We conducted a multiscale assessment of the stressors facing the borough by developing and mapping the Index of Watershed Integrity (IWI) and Index of Catchment Integrity (the latter considers stressors in areas surrounding individual stream segments exclusive of upstream areas). The assessment coincided with the borough's stormwater management planning. We adapted the list of anthropogenic stressors used in the original conterminous United States IWI application to reflect the borough's geography, human activity, and data availability. This analysis also represents an early application of the NHDPlus High Resolution geospatial framework and the first use of the framework in an IWI study. We also explored how remediation of one important stressor, culverts, could impact watershed integrity at the catchment and watershed scales. Overall, we found that the integrity scores for the Matanuska--Susitna basin were high compared to the conterminous United States. Low integrity scores did occur in the rapidly developing Wasilla--Palmer core area. We also found that culvert remediation had a larger proportional impact in catchments with fewer stressors. [ABSTRACT FROM AUTHOR]

Mussel distributions are often described as clumped or patchy. However, few surveys of mussel populations have been designed to quantify these spatial patterns. We used indicators of spatial autocorrelation to quantify spatial patterns of adult and juvenile (≤5 y old) freshwater mussels at local (fine) spatial scales (i.e., <300 m) within 14 sites along ~700 km of the Upper Mississippi River, USA. Juveniles were patchily distributed in 43% of the sites, whereas adults were patchily distributed in 50% of the sites. Juveniles and adults displayed the same spatial pattern in 64% of the sites. Hotspots, areas with locally-high densities, for adults overlapped with juvenile hotspots at ½ of the sites, suggesting that the spatial and temporal mechanisms that structure mussel distributions persist over long periods of time. A comparison of our results with a similar study focused at a coarser spatial scale suggests that patchiness in mussel distributions can occur at multiple scales and that the detection of such patchiness is a function of sampling extent and spatial grain. Mussels play an important ecological role in rivers, so information on their spatial patterns aids our understanding of the spatial structure and function of riverine ecosystems as well as the ecological consequences of their population declines. [ABSTRACT FROM AUTHOR]

Stream fish assemblages in small streams are often less diverse than those in larger streams. Two models to explain this have emerged, one which focuses on local habitat conditions derived from processes related to discharge, and the other which links patterns of network connectivity to dispersal ability and network position in the watershed. Both models now have some support in stream fishes, but how they might interact is not well studied. We draw on observations from stream invertebrates to propose that stream size will affect niche specialization and network position will affect functional trait-based diversity. We test this hypothesis using data from the Interior Highlands, USA. Diversity of upland-adapted groups and trait-based assemblage metrics tied to strategies dependent on depth, flow, and stream width showed strong relationships to stream size. Diversity of lowland-adapted groups and metrics of assemblage morphological diversity showed strong relationships to network position. Examination of patterns of spatial b-diversity supports the idea that dispersal of lowland-adapted groups is linked to network connectivity. Responses to both network position and stream size included longer, later reproductive seasons with more species exhibiting parental care. We support that both stream size and network position interact to lower fish diversity in small streams, but that they do so in different manners. We further discuss the ecological uniqueness and need for research and conservation efforts of small streams low in watershed networks. [ABSTRACT FROM AUTHOR]

The use of PIT tags has rapidly proliferated since their introduction, and new mobile detection methods have been developed. However, the presence of ghost tags (i.e., PIT tags left in the system after a fish dies) creates uncertainty about the status (live or dead) of tags detected. Herein, we describe our raft‐based mobile PIT tag antenna system, which was used to evaluate the movements of "seeded tags" (i.e., PIT tags that we placed in the river as ghost tag analogs) and their interactions with habitat features. We deployed 5,000 seeded tags in the San Juan River, a large sand‐bed river in the southwestern USA. Total distances moved by PIT tags ranged from 0.8 to 4,124 m, but 75% of movements were less than 100 m. Flow conditions causing the smallest to largest movements were (1) base flows, (2) spring runoff flows, (3) flash flood flows, and (4) a combination of spring runoff and flash flood flows. Based on Ivlev's electivity index, tags were more likely to be detected in riffles than in runs. These findings will help to classify mobile PIT tag detections as ghost tags or live fish, a critical data gap limiting the accurate estimation of demographic rates, population status metrics, and descriptions of the habitat use of fishes. [ABSTRACT FROM AUTHOR]

Dams, increasingly common in riverine systems worldwide, are particularly prevalent on the Columbia River (CR) in the United States. Hydroelectric projects, including both storage and run‐of‐river (i.e., minimal storage) structures, on the mainstem CR highly manage water flow, often by releasing water over (rather than through) dams as "spill." To test the effects of run‐of‐river dam spill on microplankton abundance and composition, we sampled above and below two dams in the lower CR before and during spill conditions in spring 2016 and during and after spill conditions in late summer 2007. We tested the effects of location (i.e., above vs. below dams), spill condition (i.e., before, during, and after spill), and their interaction on microplankton abundance. Generally, diatoms were most abundant during springtime, whereas cyanobacteria were most abundant in late summer. Most taxa were not significantly different in abundance above and below dams, regardless of spill status; although cyanobacteria abundance was marginally higher below dams in summer 2007 (p = .04). Abundances of all taxa were significantly different between pre‐spill and spill periods in spring 2016, whereas only diatom and flagellate abundances were significantly different between spill and post‐spill periods in summer 2007. We conclude that spill conditions may influence microplankton abundance, but are not likely to affect microplankton communities on either side of run‐of‐river dams on the CR. This is important information for dam managers concerned about ecosystem impacts of spill. [ABSTRACT FROM AUTHOR]

Emergent aquatic insects transport aquatic-derived resources into terrestrial ecosystems but are rarely studied at landscape or regional scales. Here, we investigate how stream network geometry constrains the spatial influence of aquatic insect subsidies in terrestrial ecosystems. We also explore potential factors (i.e., climate, topography, soils, and vegetation) that could produce variation in stream network geometry and thus change the extent of aquatic insect subsidies from one region to another. The stream signature is the percentage of aquatic insect subsidies traveling a given distance into the terrestrial ecosystem, relative to what comes out of the stream. We use this concept to model the spatial extent (area) and distribution (spatial patterning) of aquatic subsidies in terrestrial ecosystems across the contiguous United States. Our findings suggest that at least 8% of the subsidies measured at the aquatic-terrestrial boundary (i.e., the 8% stream signature) are typically transferred throughout the entire watershed and that variation in this spatial extent is largely influenced by the drainage density of the stream network. Moreover, we found stream signatures from individual stream reaches overlap such that the spatial extent of the 8% stream signature often includes inputs from multiple stream reaches. Landscapescale stream network characteristics increased the area of overlapping stream signatures more than reach-scale channel properties. Finally, we found runoff was an important factor influencing stream network geometry suggesting a potential effect of climate on aquatic-to-terrestrial linkages that have been understudied. [ABSTRACT FROM AUTHOR]

Future land-use development has the potential to profoundly affect the health of aquatic ecosystems in the coming decades. We developed regression models predicting the loss of sensitive fish (R2 = 0.39) and macroinvertebrate (R2 = 0.64) taxa as a function of urban and agricultural land uses and applied them to projected urbanization of the rapidly urbanizing Piedmont ecoregion of the southeastern USA for 2030 and 2060. The regression models are based on a 2014 investigation of water quality and ecology of 75 wadeable streams across the region. Based on these projections, stream kilometers experiencing >50% loss of sensitive fish and invertebrate taxa will nearly quadruple to 19,500 and 38,950 km by 2060 (16 and 32% of small stream kilometers in the region), respectively. Uncertainty was assessed using the 20 and 80% probability of urbanization for the land-use projection model and using the 95% confidence intervals for the regression models. Adverse effects on stream health were linked to elevated concentrations of contaminants and nutrients, low dissolved oxygen, and streamflow alteration, all associated with urbanization. The results of this analysis provide a warning of potential risks from future urbanization and perhaps some guidance on how those risks might be mitigated. [ABSTRACT FROM AUTHOR]

Phosphorus (P) fertilizer has contributed to the eutrophication of freshwater ecosystems. Watershed-based conservation programs aiming to reduce external P loading to surface waters have not resulted in significant water-quality improvements. One factor that can help explain the lack of water-quality response is remobilization of accumulated legacy (historical) P within the terrestrial-aquatic continuum, which can obscure the beneficial impacts of current conservation efforts. We examined how contemporary river P trends (between 1992 and 2012) responded to estimated changes in contemporary agricultural P balances [(fertilizer + manure inputs)-- crop uptake and harvest removal] for 143 watersheds in the conterminous United States, while also developing a proxy estimate of legacy P contribution, which refers to anthropogenic P inputs before 1992. We concluded that legacy sources contributed to river export in 49 watersheds because mean contemporary river P export exceeded mean contemporary agricultural P balances. For the other 94 watersheds, agricultural P balances exceeded river P export, and our proxy estimate of legacy P was inconclusive. If legacy contributions occurred in these locations, they were likely small and dwarfed by contemporary P sources. Our continental-scale P mass balance results indicated that improved incentives and strategies are needed to promote the adoption of nutrient-conserving practices and reduce widespread contemporary P surpluses. However, a P surplus reduction is only 1 component of an effective nutrient plan as we found agricultural balances decreased in 91 watersheds with no consistent water-quality improvements, and balances increased in 52 watersheds with no consistent water-quality degradation. [ABSTRACT FROM AUTHOR]

Aim: To determine the role of flow intermittence and species origin in shaping freshwater fish beta diversity across dryland riverscapes. Location: Verde and Little Colorado River basins, United States. Methods: Fish beta diversity was investigated in two large rivers with marked differences in basin‐wide flow intermittence. Local site (continually flowing perennial vs. periodically flowing intermittent) and species (native vs. non‐native) contributions to beta diversity were compared within each basin and over multiple decades (1987–2013) in relation to changing hydrologic conditions. Metacommunity dynamics were quantified using changes in alpha‐ (local), beta‐ and gamma‐ (regional) diversity through time. Results: Beta‐diversity patterns varied in relation to basin‐wide intermittence. Intermittent sites were most influential to beta diversity where basin‐wide intermittence was lower (Verde River), whereas perennial sites were most influential where basin‐wide intermittence was higher (Little Colorado River). In intermittent sites, native fish species contributions to beta diversity tended to be higher than non‐native species contributions. The relative contributions of perennial and intermittent sites to β‐diversity within each basin were invariant to annual flow regimes, whether atypically lower or higher than average flows, but somewhat related to intra‐annual flow variation. Native species contributions to β‐diversity increased in years with high flow conditions in the Verde River. Over time, beta diversity decreased in the lower intermittence Verde River, indicating taxonomic homogenization, but remained relatively unchanged in the Little Colorado River. Main Conclusions: Investigations of beta‐diversity components over time are considered pivotal for conservation prioritization and planning. We found that both intermittent and perennial streams play complementary roles in supporting fish beta diversity, and that their relative contributions increase as basin wide availability of the habitat type decreases. Moreover, contributions of intermittent streams to overall beta diversity were relatively consistent through time and supported native fish diversity. Despite weakening policy protections of intermittent streams, these habitats are critical for supporting local species persistence and regional biodiversity. [ABSTRACT FROM AUTHOR]

Considerable effort towards conservation has contributed to the recovery of historically depleted pinniped populations worldwide. However, in several locations where pinnipeds have increased, they have been blamed for preventing the recovery of commercially valuable fish species through predation. Prompted by increasing pinniped abundance within the Columbia River (CR), USA, over a 6-year period, we used passive integrated transponder tags to measure the survival of adult spring-run Chinook salmon (Oncorhynchus tshawytscha) through the estuary and lower CR to Bonneville Dam (river kilometre 234). We estimated 51 751 – 224 705 salmon died annually within this reach from sources other than harvest. Mixed-effects logistic regression modelling identified pinniped predation as the most likely source of this mortality. The odds of survival was estimated to decrease by 32% (95% CI: 6%–51%) for every additional 467 sea lions (Zalophus californianus and Eumetopias jubatus) present within the CR and to increase by 32% (95% CI: 8%–61%) for every increase of 1.5 in the log of American shad (Alosa sapidissima), a potential prey item for sea lions. [ABSTRACT FROM AUTHOR]

Dams challenge Atlantic salmon (Salmo salar) conservation, while hatcheries are a common but poorly evaluated recovery tool. We developed a spatially explicit smolt survival model for the Penobscot River, Maine, USA, population. By partitioning survival through dams (with flow dependency), free-flowing river reaches, and the estuary (with dam dependency), the model quantified how these factors influenced the number of fish entering the ocean. Given historical impounded conditions, 74%–22% of hatchery smolts released entered the ocean annually from 1970 to 2012. Of 19.7 million smolts stocked, 7.7 million entered the ocean (39%). Survival was most variable at dams (range 95% to 63%), followed by in-river (range 98% to 70%) and estuary (range 88% to 82%). Overall, lower-river stocking sites resulted in significantly higher numbers at ocean entry because of fewer dam encounters and shorter migrations. Higher flows also resulted in reduced losses. By reconstructing these freshwater and estuary dynamics, the model provides a more accurate estimate of ocean recruitment annually and can be used for scenario planning of future stocking locations relative to predicted flows while being adaptable to new survival rates. [ABSTRACT FROM AUTHOR]

The purpose of hydrologic modeling of a watershed is to gain valuable information about the processes occurring within watershed. With increasing temperature of the earth atmosphere, the snow fed mountainous river basins are going to get impacted severely. Lack of adequate weather station limits the scope of researches in these mountainous basins which are critical source of water resource for the country. However, improvement of satellite-based weather products has been able to nullify this barrier to great extent. In this study, a semi distributed hydrologic model of Upper Alaknanda river basin has been developed using gridded meteorological input data sourced from India Meteorological Department (IMD), National Aeronautics and Space Administration (NASA) Power, and The SWAT (Soil and water Assessment Tool) model. The calibration and validation of the model reflected satisfactory performance with the validation period (2013-2017) showing better match between simulated and observed flow than calibration period (2005-2012). The values of Nash-Sutcliffe efficiency, coefficient of determination, and Percent of bias for calibration period are 0.65, 0.67, and 14% respectively. Adoption of semi distributed approach for modeling enables to analyze the basin while preserving the heterogeneous nature of the basin. The spatiotemporal evaluation of snowmelt reveals that highest snowmelt was generated during month of April which also causes highest snowmelt contribution to runoff for April (59.76 %). The outcomes of this study reveals that satellite-based meteorological product can be adopted satisfactorily with SWAT model for estimation of snowmelt in upper Himalayan regions which gives a new direction of research in SWAT diaspora., (© 2023. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

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., (© 2023 Fisheries Society of the British Isles.)

Fluvial fishes are threatened globally from intensive human landscape stressors degrading aquatic ecosystems. However, impacts vary regionally, as stressors and natural environmental factors differ between ecoregions and continents. To date, a comparison of fish responses to landscape stressors over continents is lacking, limiting understanding of consistency of impacts and hampering efficiencies in conserving fishes over large regions. This study addresses these shortcomings through a novel, integrative assessment of fluvial fishes throughout Europe and the conterminous United States. Using large-scale datasets, including information on fish assemblages from more than 30,000 locations on both continents, we identified threshold responses of fishes summarized by functional traits to landscape stressors including agriculture, pasture, urban area, road crossings, and human population density. After summarizing stressors by catchment unit (local and network) and constraining analyses by stream size (creeks vs. rivers), we analyzed stressor frequency (number of significant thresholds) and stressor severity (value of identified thresholds) within ecoregions across Europe and the United States. We document hundreds of responses of fish metrics to multi-scale stressors in ecoregions across two continents, providing rich findings to aid in understanding and comparing threats to fishes across the study regions. Collectively, we found that lithophilic species and, as expected, intolerant species are most sensitive to stressors in both continents, while migratory and rheophilic species are similarly strongly affected in the United States. Also, urban land use and human population density were most frequently associated with declines in fish assemblages, underscoring the pervasiveness of these stressors in both continents. This study offers an unprecedented comparison of landscape stressor effects on fluvial fishes in a consistent and comparable manner, supporting conservation of freshwater habitats in both continents and worldwide., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

Excess sediment is a common reason water bodies in the USA become listed as impaired resulting in total maximum daily loads (TMDL) that require municipalities to invest millions of dollars annually on management practices aimed at reducing suspended-sediment loads (SSLs), yet monitoring data are rarely used to quantify SSLs and track TMDL progress. A monitoring network was created to quantify the SSL from the City of Roanoke, Virginia, USA (CoR), to the Roanoke River and Tinker Creek and help guide TMDL assessment and implementation. Suspended-sediment concentrations were estimated between 2020 and 2022 from high-frequency turbidity data using surrogate linear-regression models. Sixty-one percent of the total three-year SSL resulted from five large storm events. The average suspended-sediment yield from the CoR (58.1 metric tons/km 2 /year) was similar to other urban watersheds in the Eastern United States; however, the yield was nearly five times larger than the TMDL allocation (12.2 metric tons/km 2 /year). The TMDL allocated load was modeled based on a predominantly forested reference watershed and may not be a practical target for highly impervious watersheds within the CoR. The TMDL model used daily input data which likely does not capture the full range of SSLs during storm events, particularly from flashy urban streams. The average SSL following the five large storm events doubled that of the CoR's annual allocated load from the TMDL. The results of this study highlight the importance of using high-frequency monitoring data to accurately estimate SSLs and evaluate TMDLs in urban areas., (© 2023. This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply.)