A history of industrialization, oil spills, fires, and silt pollution from agriculture and urbanization led to the Ohio River being listed as one of the most polluted rivers in the USA. The Ohio River Valley Water Sanitation Commission (ORSANCO) and its members responded and conducted monitoring programs for pollutants to monitor water quality. ORSANCO collected annual macroinvertebrate samples at multiple locations using Hester–Dendy samplers. Collections using Hester–Dendy samplers from 1968 to 2004 resulted in 2,934,984 macroinvertebrates in 75 families and 321 species. We tested for temporal variation in trait (functional feeding groups) and taxonomic abundances of Ohio River macroinvertebrates. Our PCA analysis using trophic and tolerance traits resulted in significant temporal patterns. Macroinvertebrate richness increased following implementation of the federal Clean Water Act of 1972. Most trophic traits increased in abundance more recently. We interpreted these patterns as evidence for improvements in water quality and associated macroinvertebrate assemblages.

Fish assemblages, defined by taxonomy or functional traits, -respond to regional and local habitat variation. Our hypothesis was that fish assemblages could be best predicted using reach-scale (RS) hydrology variables over valley-scale (VS) hydrogeomorphology variables for US and Mongolian rivers. We further predicted that fish traits were predicted better by RS than VS variables. We evaluated the FS and VS hydrogeomorphologies of rivers in the United States and Mongolia in each of three ecoregions: grassland, forest and endorheic. Fishes were collected using a backpack electrofisher, following standard protocols. Constrained ordination analyses were conducted at three scales: among continents, by continents and by individual ecoregions within continents. We found no significant difference in mean variation explained by VS versus RS or by taxonomy versus traits. Ecoregions differed in factors contributing to fish assemblage patterns, likely a result of differences in hydrogeomorphology, hydrological connectivity and historical influences. We found that fish assemblages were structured by hydrogeomorphic processes occurring at VS and RS, and that variables predicting fish assemblages varied with scale and whether fishes were classified by taxonomy or traits. Although anthropogenic impacts were substantially higher for western US rivers than for Mongolian rivers, we were unable to detect strong differences in our ability to predict fish assemblage variation from RS and VS habitat variables.

Lotic systems in mountain regions have historically provided secure habitat for native fish populations because of their relative isolation from human settlement and lack of upstream disturbances. However, rivers of mountain ecoregions are currently experiencing heightened levels of disturbance due to the introduction of nonnative species impacting endemic fishes in these areas. We compared the fish assemblages and diets of mountain steppe fishes of the stocked rivers in Wyoming with rivers in northern Mongolia where stocking is absent. Using gut content analysis, we quantified the selectivity and diets of fishes collected in these systems. Nonnative species had more generalist diets with lower levels of selectivity than most native species and native species had high levels of dietary specificity and selectivity. High abundances of nonnative species and high levels of dietary overlaps in our Wyoming sites is a cause of concern for native Cutthroat Trout and overall system stability. In contrast, fish assemblages characterizing Mongolia mountain steppe rivers were composed of only native species with diverse diets and higher selectivity values, suggesting low probability for interspecific competition.

Quantifying the trophic basis of production for freshwater metazoa at broad spatial scales is key to understanding ecosystem function and has been a research priority for decades. However, previous lotic food web studies have been limited by geographic coverage or methodological constraints. We used compound-specific stable carbon isotope analysis of amino acids (AAs) to estimate basal resource contributions to fish consumers in streams spanning grassland, montane and semi-arid ecoregions of the temperate steppe biome on two continents. Across a range of stream sizes and light regimes, we found consistent trophic importance of aquatic resources. Essential AAs of heterotrophic microbial origin generally provided secondary support for fishes, while terrestrial carbon did not seem to provide significant, direct support. These findings provide strong evidence for the dominant contribution of carbon to higher-order consumers by aquatic autochthonous resources (primarily) and heterotrophic microbial communities (secondarily) in temperate steppe streams.

Management actions intended to benefit fish in large rivers can directly or indirectly affect multiple ecosystem components. Without consideration of the effects of management on non-target ecosystem components, unintended consequences may limit management efficacy. Monitoring can help clarify the effects of management actions, including on non-target ecosystem components, but only if data are collected to characterize key ecosystem processes that could affect the outcome. Scientists from across the U.S. convened to develop a conceptual model that would help identify monitoring information needed to better understand how natural and anthropogenic factors affect large river fishes. We applied the conceptual model to case studies in four large U.S. rivers. The application of the conceptual model indicates the model is flexible and relevant to large rivers in different geographic settings and with different management challenges. By visualizing how natural and anthropogenic drivers directly or indirectly affect cascading ecosystem tiers, our model identified critical information gaps and uncertainties that, if resolved, could inform how to best meet management objectives. Despite large differences in the physical and ecological contexts of the river systems, the case studies also demonstrated substantial commonalities in the data needed to better understand how stressors affect fish in these systems. For example, in most systems information on river discharge and water temperature were needed and available. Conversely, information regarding trophic relationships and the habitat requirements of larval fishes were generally lacking. This result suggests that there is a need to better understand a set of common factors across large-river systems. We provide a stepwise procedure to facilitate the application of our conceptual model to other river systems and management goals.

Silver carp (Hypophthalmichthys molitrix) dispersed to the Wabash River, Indiana in the mid-1990s. These fish compete with native, filter-feeding fish species in other central US rivers but relatively little information is available for impacts in the Wabash River. We collected fishes by boat electrofisher on the Wabash River as part of a long-term study. Abundances of six Wabash River species varied temporally, and three had stronger relationships with year than the other species: common carp (Cyprinus carpio) decreased before and after silver carp introduction, freshwater drum (Aplodinotus grunniens) increased prior to silver carp introduction, and gizzard shad (Dorosoma cepedianum) decreased before silver carp introduction. Silver carp abundance was significantly correlated only with abundance of gizzard shad. Nonmetric multidimensional scaling analysis of long-term Wabash River fish assemblages resulted in distinctive temporal and spatial patterns. Silver carp abundance increased from zero in the early 1990s to 28 individuals/km in recent years. Gizzard shad declined to low abundance simultaneous to silver carp increases, yet we did not detect significant patterns for silver carp with other Wabash River fishes.

Abstract River hydrogeomorphology is a potential predictor of ecosystem and assemblage variation. We tested for fish assemblage variation as a function of hydrogeomorphology in a Midwestern US large river, the Wabash River. Fish data were classified by taxonomy and traits and we tested if assemblages varied with river hydrogeomorphology or river distance, defined into 10‐km distinct reaches. Three unique geomorphological units, Functional Process Zones (FPZ), were identified using an ArcGIS hydrogeomorphic model, based primarily on channel width, floodplain width, and down valley slope. Five locations were identified as FPZ A with narrow stream channel, high down valley slope, and an expansive floodplain. Ten locations were identified as FPZ B with a wide river channel and wide floodplain. Thirty‐five locations were identified as FPZ C with wide river channel and a constrained floodplain. The sites were categorized into three stream orders: 5, 6, and 7. We found hydrogeomorphology classified by unique FPZs or by river distance influenced taxonomic and functional fish assemblages for the Wabash River. There was high overlap among fish occurrences among FPZs, but nine species resulted as significant indicators of specific FPZs. Five traits were significant indicators of FPZs: an intermediate Swim Factor score, medium tolerance to silt, small‐large stream size preference, and two Shape Factor categories. Our conclusions are that fish assemblages respond strongly to local geomorphology and river distance, fitting the riverine ecosystem synthesis and the river continuum concept.

86 Motivation: We compiled a global database of long-term riverine fish surveys from 46 regional 87 and national monitoring programs as well as individual academic research efforts upon which 88 numerous basic and applied questions in ecology and global change research can be explored.

Abstract River hydrogeomorphology is a major driver shaping biodiversity and community composition. Here, we examine how hydrogeomorphic heterogeneity expressed by Functional Process Zones (FPZs) in river networks is associated with fish assemblage variation. We examined this association in two distinct ecoregions in Mongolia expected to display different gradients of river network hydrogeomorphic heterogeneity. We delineated FPZs by extracting valley‐scale hydrogeomorphic variables at 10 km sample intervals in forest steppe (FS) and in grassland (G) river networks. We sampled fish assemblages and examined variation associated with changes in gradients of hydrogeomorphology as expressed by the FPZs. Thus, we examined assemblage variation as patterns of occurrence‐ and abundance‐based beta diversities for the taxonomic composition of assemblages and as functional beta diversity. Overall, we delineated 5 and 6 FPZs in river networks of the FS and G, respectively. Eight fish species were found in the FS river network and seventeen in the G, four of them common to both ecoregions. Functional richness was correspondingly higher in the G river network. Variation in the taxonomic composition of assemblages was driven by species turnover and was only significant in the G river network. Abundance‐based taxonomic variation was significant in river networks of both ecoregions, while the functional beta diversity results were inconclusive. We show that valley‐scale hydrogeomorphology is a significant driver of variation in fish assemblages at a macrosystem scale. Both changes in the composition of fish assemblages and the carrying capacity of the river network were driven by valley‐scale hydrogeomorphic variables. River network hydrogeomorphology as accounted for in the study has, therefore, the potential to inform macrosystem scale community ecology research and conservation efforts.

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

. We analyze here the nature of research in freshwater macrosystem biology (especially lotic studies) from both conceptual and current research perspectives. The boundaries of permanent and transi-tional lotic macrosystems from the smallest to largest spatial extents are described. We contrast ecosystem vs. macrosystem research and macroecology vs. macrosystems ecology and provide some examples of rep-resentative aquatic macrosystems ecology projects in the USA. We recommend approaches for incorporating certain large-scale lotic concepts developed over the last 40 yr as the bases for lotic macrosystem studies. Of these, the three most appropriate in chronological order are the River Continuum Concept, the Riverine Ecosystem Synthesis, and the Stream Biome Gradient Concept. Four other concepts would be suit-able for testing macrosystem hypotheses after incorporating small to large conceptual or geographic expansions of the models. We suggest future research directions in lotic macrosystem research in areas of climate change and teleconnections among distant organisms and systems and include general recommendations for conducting macrosystem-level research.

We tested for effects of two dams on fish assemblages in the St. Joseph River, Indiana. Fishes were collected by boat electrofisher twice annually, at 23 sites from 1998 to 2018. Fish collection data were aggregated into CPUE counts of species per 500 m, and CPUE were pooled across sites above and below the dams. We used multivariate analyses to test for spatial and temporal variation for assemblages above and below dams. Assemblages above and downstream of the dams differed significantly when examined by collection year. The effects (abundances of fish species) of the dams on fish assemblages were different at the South Bend dam from those at the Elkhart dam. Trajectories of temporal change in fish assemblages above and below dams were all gradual and directional. Temporal variation in fish abundance categorised into trophic traits (guilds) differed by location. We suggest that moderate to high stress from anthropogenic impacts on the St. Joseph River appears to result in high assemblage variation above and below dams. The St. Joseph River fish community appears to be unstable, likely from multiple anthropogenic impacts to water quality, habitat degradation and hydrologic alteration. We found that 25 of 33 hydrologic variables in four of five Indicators of Hydrological Alteration groups were significantly altered from 1931 to 2019. However, hydrology variation as potential disturbance events did not visually match observed temporal assemblage variation.

Floodplain lakes are important aquatic resources for supporting ecosystem services, such as organismal habitat, biodiversity, and the retention of nutrients and sediment. Due to geomorphic alteration of river channels and land‐cover change, degradation to floodplain lakes in the Ohio River basin is occurring at a rate that will escalate as climate change causes increased flood intensity and the seasonal redistribution of rainfall. A better understanding of the local drivers that affect oxbow lakes is needed for targeted floodplain restoration efforts designed to slow degradation. We examined the effects of land cover, topography, and hydrologic connectivity on water quality and fish diversity and abundance in nine floodplain lakes with potentially high remnant ecological function in the Wabash‐White watershed (Indiana, Ohio, and Illinois). Data collection included water‐quality parameters; stable water isotopes; total phosphorus, total nitrogen, and chlorophyll‐a; and fish community diversity and abundance. Results indicate that hay/pasture land cover and decreased topographic relief in the local oxbow watersheds, along with reduced river hydrologic connectivity, were related to an increase in total phosphorus, total nitrogen, and chlorophyll‐a. Greater biodiversity and abundance in fish assemblages were evident in oxbow lakes that were more disconnected from the main channel. The results of this study suggest that hydrologic connectivity of oxbow lakes with the contributing drainage area and the main channel influence nutrients and fish communities. Knowing the influencing factors can help ecosystem managers better protect these valuable floodplain lake ecosystems and prioritize restoration efforts amidst increasing stressors due to climate and land‐use changes.

Abstract The invasion of freshwater ecosystems by non‐native species can constitute a significant threat to native species and ecosystem health. Non‐native trouts have long been stocked in areas where native trouts occur and have negatively impacted native trouts through predation, competition, and hybridization. This study encompassed two seasons of sampling efforts across two ecoregions of the western United States: The Great Basin in summer 2016 and the Yellowstone River Basin in summer 2017. We found significant dietary overlaps among native and non‐native trouts within the Great Basin and Yellowstone River Basin ecoregions. Three orders of invertebrates (Ephemeroptera, Trichoptera, and Diptera) composed the majority of stomach contents and were responsible for driving the observed patterns. Great Basin trout had higher body conditions (k), and non‐native Great Basin trout had higher gut fullness values than Yellowstone River Basin trout, indicating a possible limitation of food in the Yellowstone River Basin. Native fishes were the least abundant and had the lowest body condition in each ecoregion. These findings may indicate a negative impact on native trouts by non‐native trouts. We recommend additional monitoring of native and non‐native trout diets, regular invertebrate surveys to identify the availability of diet items, and reconsidering stocking efforts that can result in overlap of non‐native fishes with native cutthroat trout.

Buck Creek is a spring-fed, cool-water tributary of the West Fork White River, Indiana.The Muncie Bureau of Water Quality sampled fishes and monitored water temperature in Buck Creek annually from 1986-2018.For this study, we utilized long-term fish data from the Bureau of Water Quality to evaluate spatial and temporal changes in the fish assemblages of Buck Creek in Delaware County, Indiana, USA.Non-metric multidimensional scaling (NMDS) was used to describe changes in the fish assemblages over space and time.Linear mixed effects models were used to evaluate the relationship between environmental factors and the fish assemblages.The spatial NMDS results were separated in distinct groups of upstream and downstream assemblages.This was characterized by a shift of headwater specialists shifting to large-river species.The temporal NMDS results were separated into distinct annual assemblages.This was characterized by a drop in pollution-tolerant species and an increase in intolerant species.Our findings indicate that the fish assemblages have improved in Buck Creek over space and time.

We tested macroinvertebrate assemblages collected from 1979–2015 for temporal variation in structure and for impacts of the Clean Water Act of 1974. Collections were at ten sites on the mainstem of the West Fork White River. We used family-level taxonomy for macroinvertebrates that resulted in 77 families and 92,477 individuals. Macroinvertebrate families were further classified by trophic and tolerance traits and tested for temporal variation. We defined river reaches as upstream, urban, and downstream of Muncie, Indiana for analyses. Taxonomic richness increased over the study. A nonmetric multidimensional scaling (NMDS) analysis identified high temporal variation as assemblage structure differed among decades. Spatial analyses using NMDS indicated significant differences by river location upstream, urban, and downstream. NMDS and Analysis of Similarities (ANOSIM) by trophic relationship and tolerance values did not result in significant temporal or spatial patterns. Our results show the macroinvertebrate assemblages of the West Fork White River improved, likely due to implementation of the Clean Water Act.