Blackwater rivers and streams have stained or tea-colored water from tannins released by decaying plant matter. Natural conditions in these waters often differ from non-blackwater systems. For example, the pH and oxygen levels in waters can be very low, but completely natural. We examined an existing USEPA data set and found that blackwaters existed across the contiguous United States but were most common in the east. Water chemistry showed differences between blackwater and non-blackwater sites, but differences were not consistent across ecoregions making national scale generalizations difficult. Physical habitat data analysis did not show dramatic differences between blackwater and non-blackwater sites. Blackwater typically arises from streams that drain tannin-rich bogs/muskeg and wetlands, so as expected blackwater sites had a shorter Euclidean distance to wetlands than non-blackwater sites and existed in watersheds with a higher percentage of wetland habitat. Blackwaters in Northern and Temperate Plains tended to have higher acid neutralizing capacity, conductivity, and lower True Color; a visual color scale used for water purity. We posit that differences were because Color and Dissolved Organic Carbon at these sites were from buried wetland deposits rather than contemporary wetland habitats. Research needs that may increase our understanding and management of blackwaters include development of an operational definition that includes a classification framework and reference conditions for different blackwater types, identification of stressors and their associated dynamics that negatively impact blackwater systems, and development of data-driven, consistent, and repeatable assessment methods, including development of targets, protective of unique conditions in blackwater rivers and streams.

Continued large-scale public investment in declining ecosystems depends on demonstrations of “success”. While the public conception of “success” often focuses on restoration to a pre-disturbance condition, the scientific community is more likely to measure success in terms of improved ecosystem health. Using a combination of literature review, workshops and expert solicitation we propose a generalized framework to improve ecosystem health in highly altered river basins by reducing ecosystem stressors, enhancing ecosystem processes and increasing ecosystem resilience. We illustrate the use of this framework in the Mississippi-Atchafalaya River Basin (MARB) of the central United States (U.S.), by (i) identifying key stressors related to human activities, and (ii) creating a conceptual ecosystem model relating those stressors to effects on ecosystem structure and processes. As a result of our analysis, we identify a set of landscape-level indicators of ecosystem health, emphasizing leading indicators of stressor removal (e.g., reduced anthropogenic nutrient inputs), increased ecosystem function (e.g., increased water storage in the landscape) and increased resilience (e.g., changes in the percentage of perennial vegetative cover). We suggest that by including these indicators, along with lagging indicators such as direct measurements of water quality, stakeholders will be better able to assess the effectiveness of management actions. For example, if both leading and lagging indicators show improvement over time, then management actions are on track to attain desired ecosystem condition. If, however, leading indicators are not improving or even declining, then fundamental challenges to ecosystem health remain to be addressed and failure to address these will ultimately lead to declines in lagging indicators such as water quality. Although our model and indicators are specific to the MARB, we believe that the generalized framework and the process of model and indicator development will be valuable in an array of altered river basins.

The tolerance of aquatic organisms to stressors is widely used to monitor and evaluate the condition of freshwater ecosystems. Tolerance values (TV) derived from analyses of the relationship between species and their environment are considered to be more objective than those that rely on expert opinion. We used principal component analysis (PCA) to derive a generalized stressor gradient based on physicochemical characteristics and physical habitat quality and structure. Scores of the first principal component axis (PC1) were used to estimate TV for 37 fish species collected from 54 sites in the Karun River basin, Iran. PCA of 17 variables identified stressors that were influential such as total phosphate, total nitrogen, total coliform, and habitat and morphological score. The species were separated into three categories on the stressor gradient: sensitive (18.9%), semi-tolerant (48.6%), and tolerant species (32.4%). Based on these results we developed the Karun Fish Tolerance Index (KFTI) and demonstrated that it performed well in separating the least, moderate, and most disturbed sites in the study area. The discrimination efficiency of the KFTI was 82.5%, which makes it a robust management tool for the protection and conservation of streams and rivers in the Karun River watershed. TV developed here reflect objective characteristics of the sensitivity of fish species to the predominant stressors in the Karun and similar systems.

Nonliving organic matter, including organic carbon, in freshwater systems provides energy inputs to food webs and supports various ecosystem functions. Unusually high organic carbon levels can occur naturally in aquatic habitats such as wetlands and blackwater rivers and streams. However, values may also be high due to anthropogenic influences. In recent years, increasing levels of organic carbon have been observed and suggested as drivers of brownification and increased observation of foam on surface waters. Total organic carbon (TOC) and dissolved organic carbon (DOC) are not commonly included in field studies of aquatic ecosystems because of sampling logistics and resources required for laboratory measurement. As a potential alternative to laboratory analysis, we evaluated the effectiveness of a portable field meter by comparing laboratory results to data collected in situ. Comparisons were made at 43 surface water sites across northern West Virginia. At each of these sites, a field measurement was recorded using a Real TOC/DOC Field Meter, and a water sample was collected and transported for laboratory measurement using a Shimadzu TOC-V analyzer. Data from the laboratory and field for each site were compared using bivariate analysis and concordance correlation on matched pairs. Poor agreement existed between field and lab measurements, so a novel data model was created using laboratory-derived data for further comparison. Substantial accuracy was achieved using the new data model. This suggests that the Real TOC/DOC Field Meter is a viable instrument for field measurement of organic carbon in aquatic ecosystems and may aid in monitoring and management decisions.

Blackwater rivers and streams are a distinct resource type in multiple ecoregions of the United States, including the Coastal Plains. Given the unique nature of blackwaters, they may not be fully protected if using typical water quality standards. Information provided by State agencies was used to identify specific research needs that would directly enhance current assessment approaches. Protection of blackwater rivers and streams would be aided by (1) development of an operational definition; (2) development of a classification framework that distinguishes among blackwater system types; (3) identification of undisturbed or minimally disturbed blackwater systems; (4) identification of stressors that challenge blackwater condition and resilience; and (5) development of criteria that are more suited to the unique conditions of blackwater rivers and streams. Benefits stemming from addressing these research needs may include identification of sites that are unrecognized as impaired and the re-evaluation of sites that may be erroneously listed as impaired when they are not. This would improve reporting by states for Clean Water Act (CWA) Section 305(b) and, for some states, could represent a significant resource savings by reducing the number of sites on CWA Section 303d lists.

We assessed the distribution of alien fishes in the Karun River Basin, Iran. Fish were collected from 39 sites during the November-December 2018 low-flow period. In total, 39 fish species from nine orders and 14 families were documented. Among these, 10 species were alien to the basin (986 individuals; 15.7%). Four species were the most abundant alien species and primarily in impounded, downstream reaches. Redundancy analysis (RDA) was conducted to identify the extent of changes in alien fish assemblages with environmental parameters. RDA1 and RDA2 accounted for 36.24% and 25.33% of the variation of alien species, respectively. Altitude, depth, electrical conductivity, water temperature, turbidity, dissolved oxygen, and river width were the most significant parameters affecting alien species distributions. We present a dual-pathway cause-and-effect hypothesis proposing that alien fish species presence causes declines in the ecological status of native fish communities. We then explore how human-induced aquatic ecosystem degradation creates opportunities for alien species to invade new ecosystems, further impacting native fish communities. Our study contributes insight into the cause and effect of the presence of alien fish species in the Karun River Basin and emphasizes the urgency of conservation measures to protect this critically endangered watershed.

We analyzed spatial variation in fish species richness and community composition in the Karun River basin, Iran. Knowledge about fish diversity in the basin is incomplete and varies widely along spatial and temporal scales: The Karun is the longest river in Iran (950 km) with the largest drainage area (about 67,000 km2). Fish samples were collected from 54 sites from July through August 2019 using a backpack electro-fisher. Physico-chemical and habitat parameter data collected at each site included pH, conductivity (μS/cm), dissolved oxygen (mg/L), water temperature (°C), turbidity (NTU), stream width (m), stream depth (m), water velocity (m/s) and elevation (m). In total, 37 species were collected (5241 individuals weighing 110.67 kg). The species collected represented 12 families and 27 genera. A total of 13 endemic species (35.14%), 16 native species (43.24%), and eight non-native species (21.62%) were recorded. Diversity indices were calculated and used to measure the spatial variation in community composition. Relationships between native and endemic species assemblage structure and environmental descriptors were assessed using canonical correspondence analysis (CCA). The first two axes of the canonical correspondence analysis explained 62.57% of the variation in the data. Of the nine environmental descriptors analyzed, eight significantly affected species distribution; however, electrical conductivity and elevation were most influential. Our study provides up-to-date status information on the distribution of freshwater fishes in the Karun River basin. This information is essential for developing conservation and management strategies to support the long-term sustainability of fish populations in the Karun River basin.

Large river systems are one of the most important water resources for human societies. However, the ecological integrity of large rivers has been altered greatly by human activities. To monitor and manage these ecosystems, multimetric indices (MMI) are considered as efficient tools. This study aimed to develop and validate a fish-based multimetric index for the Karun River basin, Iran (Karun fish-based multi-metric index [KFMMI]). Eighteen rivers and 54 sites in the basin were sampled in July-August 2019, and physico-chemical and habitat characteristics were used to identify reference sites based on principal components analysis (PCA). Of the 54 sites, 14, 26, and 14 sites were classified as least, moderate, and most disturbed sites, respectively. Fifty-four candidate metrics were evaluated for range, responsiveness, and redundancy with other metrics. This resulted in the identification of eight metrics (relative abundance of native and endemic taxa, relative richness of migratory taxa, relative richness of Leuciscidae taxa, relative richness of herbivorous taxa, relative abundance of cyprinid taxa, relative richness of vegetative inhabitant taxa, relative abundance of slow water flow, and relative richness of edge inhabitant taxa) that informed on species richness and composition, migratory status, functional feeding groups, and habitat preferences. The KFMMI showed excellent performance in separating least, moderate, and most disturbed sites in our study area. Regarding water quality, the KFMMI was classified 16, 5, and 29 sites as good, moderate, and bad, respectively. The discrimination efficiency of KFMMI was 81.6%, which makes it an effective management tool for directing restoration actions at most disturbed sites and intensifying protection of least disturbed sites.

Abstract We assessed the distribution of alien fishes in one of the most ecologically and economically important aquatic ecosystems in Iran, the Karun River Basin. Fish samples were collected from 35 sites in the Karun River Basin during the low-flow period from November to December 2018. We documented the occurrence of 37 species of fishes from nine orders and 14 families. Amongst these, 10 species were alien (986 individuals; 15.7%). The relative abundance of native, endemic, and alien species estimated as 54.8%, 29.5% and 15.7%, respectively. Total length of alien species ranged from 0.4 to 25.5 cm and their total weight from 0.17 to 350 g. The ten alien species belonged to seven families including, Cyprinidae, Cichlidae, Xenocyprididae, Gobiidae, Poeciliidae, Gobionidae, and Salmonidae. Carassius gibelio, Oreochromis aureus, and Coptodon zillii were found to be the most abundant alien species in the downstream region. We applied redundancy analysis (RDA) as a direct stressor method to identify the extent of changes in alien fish assemblages with environmental parameters. The first two axes (RDA1 and RDA2) accounted for 36.24% and 25.33% of the variation of five alien species, respectively. Altitude, depth, electrical conductivity, water temperature, turbidity, dissolved oxygen, and river width were the most significant parameters affecting the distribution of alien species. Our results propose that management practices are needed in the downstream sections of the Basin to recover native and endemic species. Monitoring of presence and extent of alien species is a key to measuring the success of these efforts.

Biological monitoring is important for assessing the ecological condition of surface waters. However, there are challenges in determining what constitutes reference conditions, what assemblages should be used as indicators, and how assemblage data should be converted into quantitative indicator scores. In this study, we developed and applied biological condition gradient (BCG) modeling to fish and macroinvertebrate data previously collected from large, sandy bottom southwestern USA rivers. Such rivers are particularly vulnerable to altered flow regimes resulting from dams, water withdrawals and climate change. We found that sensitive ubiquitous taxa for both fish and macroinvertebrates had been replaced by more tolerant taxa, but that the condition assessment ratings based on fish and macroinvertebrate assemblages differed. We conclude that the BCG models based on both macroinvertebrate and fish assemblage condition were useful for classifying the condition of southwestern USA sandy bottom rivers. However, our fish BCG model was slightly more sensitive than the macroinvertebrate model to anthropogenic disturbance, presumably because we had historical fish data, and because fish may be more sensitive to dams and altered flow regimes than are macroinvertebrates.

A physical, chemical and biological characterization of river systems is needed to evaluate their ecological quality and support restoration programs. Herein, we describe an approach using water chemistry, physical structure and land use for identification of a disturbance gradient existing in the Karun River Basin. For this purpose, at each site, physical structure and physico-chemical data were collected once in each season for a total of 4 samples during the period (October 2018 - September 2019). Principal components analysis (PCA) of 17 variables identified five variables that were influential across all seasons: conductivity, total habitat score, stream morphology, clay & silt, and sand. Of the 54 sites, 14, 26 and 14 sites were classified as least, moderate and most disturbed sites, respectively. The metric Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa was used for validation of the classification. Results in different seasons showed that all the least disturbed sites (n = 14) were significantly different from moderate and most disturbed sites (p < 0.01). In this study the validation process presented good confirmation of a priori reference sites selection, showing that the proposed criteria could be considered as appropriate tools for characterization of the existent disturbance gradient in the Karun River Basin.

Length‐weight relationships (LWR) for seven species from the Karun River system in Iran were provided. These species include Alburnus doriae , Alburnus sellal , Barbus karunensis , Capoeta coadi , Squalius berak , Turcinoemacheilus saadii and Rhinogobius lindberg . Fishes were collected in November and December 2018 and LWR is based on total length and weight of 2867 specimens calculated by equation W= aL b . The b value ranged from 2.92 to 3.25 and r 2 from 0.94 to 0.99. The length and weight range is presented for each species collected in the Karun River Basin.

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.

While factors influencing perceptions of drinking water have been well studied, those of aquatic ecosystems have been to lesser extent. We conducted a review to improve awareness of these factors. Environmental factors found to influence public perceptions of aquatic ecosystems were presence/absence of water plants and algae, presence/absence of floating debris, the odor, movement (for flowing waters) and clarity/turbidity of the water, and the type, condition, setting, naturalness, and overall aesthetic appeal of the ecosystem. Sociocultural factors found to influence public perceptions of aquatic ecosystems included age, education, gender, and place-based knowledge. We provide perspectives of how managers can better meet the diverse social demands placed on aquatic ecosystems. The importance and benefits of considering these perspectives may be especially beneficial where significant multi-generational and culturally relevant place-based knowledge exist.

Sustainable development supports watershed processes and functions. To aid the sustainable development of the western Balkans’ transboundary river and lake basins, the Regional Environmental Center for Central and Eastern Europe and the US Environmental Protection Agency (EPA) adapted the EPA’s Index of Watershed Integrity (IWI) following the devasting 2014 floods in Albania, Bosnia and Herzegovina, Kosovo, North Macedonia, Montenegro, and Serbia. The IWI evaluates six watershed functions based on a suite of anthropogenic stressors (e.g., impervious surfaces, reservoirs). A key feature of the IWI is its ability to accumulate the impact of upstream activities of any specific location in a river network. A novel feature of the IWI, compared with other watershed assessment tools, is its capacity to provide actionable information at the local scale. IWI scores—ranging from 0 (low integrity) to 1 (high integrity)—calculated for the 1084 catchments of the study area indicated highest integrity in the Alpine geographic region (mean = 0.55, standard deviation (SD) = 0.11) and intermediate to lowest integrity within the Mediterranean (mean = 0.49, SD = 0.12) and Continental (mean = 0.40, SD = 0.10) geographic regions. The IWI results are presented hierarchically for data analysts (stressor, functional component, Index of Catchment Integrity and IWI), ecologists (stream/catchment, watershed, basin), and managers (local, national, international). We provide real-world examples for managers, and suggestions for improving the assessment.

Aquatic ecosystems provide services essential to human health and economies. Therefore, resource management programs aim to ensure the sustainable flow of these services. Stakeholder engagement is often a critical tool in learning what services are of priority to the public and may be integral to the success of aquatic ecosystem management because public participation in planning and decision making can generate broader support, e.g., financial, intellectual, and labor, for the management plan. The collection of such information may even be statutorily mandated, such as in the Clean Water Act of the United States, which requires that water bodies be classified for the beneficial uses, e.g., fisheries, drinking water, or recreation, they provide. Past evaluations of stakeholder engagement with aquatic ecosystems have considered a wide range of factors influencing engagement. We conducted a critical review of the literature on characteristics of stakeholders and characteristics of the environment that influence stakeholder engagement and participation with aquatic ecosystems. Our objective was to identify factors that should be considered in the creation of surveys to help encourage the inclusion of ecological and social beneficial uses data in large-scale water monitoring programs. Factors identified in our review were, extent and influence of place-based knowledge; proximity to, and frequency of visitation of the resource(s) being considered; basic demographics such as age, gender, education, and income; home community type; aesthetic appeal of the resource; and primary reason for engagement with the resource. We propose these factors, with subfactors, as a template for survey development.

River flows connect people, places, and other forms of life, inspiring and sustaining diverse cultural beliefs, values, and ways of life. The concept of environmental flows provides a framework for improving understanding of relationships between river flows and people, and for supporting those that are mutually beneficial. Nevertheless, most approaches to determining environmental flows remain grounded in the biophysical sciences. The newly revised Brisbane Declaration and Global Action Agenda on Environmental Flows (2018) represents a new phase in environmental flow science and an opportunity to better consider the co-constitution of river flows, ecosystems, and society, and to more explicitly incorporate these relationships into river management. We synthesize understanding of relationships between people and rivers as conceived under the renewed definition of environmental flows. We present case studies from Honduras, India, Canada, New Zealand, and Australia that illustrate multidisciplinary, collaborative efforts where recognizing and meeting diverse flow needs of human populations was central to establishing environmental flow recommendations. We also review a small body of literature to highlight examples of the diversity and interdependencies of human-flow relationships-such as the linkages between river flow and human well-being, spiritual needs, cultural identity, and sense of place-that are typically overlooked when environmental flows are assessed and negotiated. Finally, we call for scientists and water managers to recognize the diversity of ways of knowing, relating to, and utilizing rivers, and to place this recognition at the center of future environmental flow assessments. This article is categorized under: Water and Life > Conservation, Management, and Awareness Human Water > Water Governance Human Water > Water as Imagined and Represented

Many conceptual syntheses in ecology and evolution are undergirded by either a patch- or continuum-based model. Examples include gradualism and punctuated equilibrium in evolution, and edge effects and the theory of island biogeography in ecology. In this study, we sought to determine how patch- or continuum-based analyses could explain variation in concentrations of stream macronutrients and system metabolism, represented by measures of productivity and respiration rates, at the watershed scale across the Kanawha River Basin, USA. Using Strahler stream order (SSO; continuum) and functional process zone (FPZ; patch) as factors, we produced statistical models for each variable and compared model performance using likelihood ratio tests. Only one nutrient (i.e., PO43- ) responded better to patch-based analysis. Both models were significantly better than a null model for ecosystem respiration; however, neither outperformed the other. Importantly, in most cases, a combination model, including both SSO and FPZ, best described observed variation in the system. Our findings suggest that several patch- and continuum-based processes may simultaneously influence the concentration of macronutrients and system metabolism. Nutrient spiral- ing along a continuum and the patch mosaic of land cover may both alter macronutrients, for example. Similarly, increases in temperature and discharge associated with increasing SSO, as well as the differences in light availability and channel morphology associated with different FPZs, may influence system metabolism. For these reasons, we recommend a combination of patch- and continuum-based analyses when modeling, analyzing, and interpreting patterns in stream ecosystem parameters.

Fluvial geomorphology provides the basis for characterizing complex river networks and evaluating biophysical processes within watersheds. Understanding the spatial organization of morphological features, their influencing processes, and resultant geomorphic diversity in stream networks are important for efficient restoration, river health assessment, and improving our knowledge of the resilience of riverine landscapes. River characterization is a means to determine the biophysical character of river networks but many methods are fraught with pitfalls, such as the use of incorrect variables and limited acknowledgment of the hierarchical organization of rivers. In this paper, a top-down geographic information system-based approach for determining the physical typology of river networks is outlined. A suite of multivariate analyses are used to develop a nomenclature for functional process zones (FPZs) large tracts of the river network with similar hydro-geomorphological character. Applied to the Little Miami River, Ohio, six distinct FPZs emerged, which had a nonuniform distribution along the river network. Some FPZs repeated downstream; others were rare in terms of total length and number of FPZ segments. The physical structure of the Little Miami River network was analyzed using a series of community metrics. Application of this approach for river monitoring, establishing reference conditions, as well as management of threatened and endangered species and asset trading is highlighted.