A Synopsis of Global Mapping of Freshwater Habitats and Biodiversity: Implications for Conservation

Accurately mapping freshwater habitats and biodiversity at high-resolutions across the globe is essential for assessing the vulnerability and threats to freshwater organisms and prioritizing conservation efforts. Since the 2000s, extensive efforts have been devoted to mapping global freshwater habitats (rivers, lakes, and wetlands), the spatial representation of which has changed dramatically over time with new geospatial data products and improved remote sensing technologies. Some of these mapping efforts, however, are still coarse representations of actual conditions. Likewise, the resolution and scope of global freshwater biodiversity compilation efforts have also increased, but are yet to mirror the spatial resolution and fidelity of mapped freshwater environments. In our synopsis, we find that efforts to map freshwater habitats have been conducted independently of those for freshwater biodiversity; subsequently, there is little congruence in the spatial representation and resolution of the two efforts. We suggest that global species distribution models are needed to fill this information gap; however, limiting data on habitat characteristics at scales that complement freshwater habitats has prohibited global high-resolution biogeography efforts. Emerging research trends, such as mapping habitat alteration in freshwater ecosystems and trait biogeography, show great promise in mechanistically linking global anthropogenic stressors to freshwater biodiversity decline and extinction risk

Digital Mapping and Environmental Characterization of National Wild and Scenic River Systems

Spatially accurate geospatial information is required to support decision-making regarding sustainable future hydropower development. Under a memorandum of understanding among several federal agencies, a pilot study was conducted to map a subset of National Wild and Scenic Rivers (WSRs) at a higher resolution and provide a consistent methodology for mapping WSRs across the United States and across agency jurisdictions. A subset of rivers (segments falling under the jurisdiction of the National Park Service) were mapped at a high resolution using the National Hydrography Dataset (NHD). The spatial extent and representation of river segments mapped at NHD scale were compared with the prevailing geospatial coverage mapped at a coarser scale. Accurately digitized river segments were linked to environmental attribution datasets housed within the Oak Ridge National Laboratory s National Hydropower Asset Assessment Program database to characterize the environmental context of WSR segments. The results suggest that both the spatial scale of hydrography datasets and the adherence to written policy descriptions are critical to accurately mapping WSRs. The environmental characterization provided information to deduce generalized trends in either the uniqueness or the commonness of environmental variables associated with WSRs. Although WSRs occur in a wide range of human-modified landscapes, environmental data layers suggest that they provide habitats important to terrestrial and aquatic organisms and recreation important to humans. Ultimately, the research findings herein suggest that there is a need for accurate, consistent, mapping of the National WSRs across the agencies responsible for administering each river. Geospatial applications examining potential landscape and energy development require accurate sources of information, such as data layers that portray realistic spatial representations

Session B2: A Quantitative, Traits-based Approach for Choosing and Prioritizing Study Species for Evaluating the Impacts of Turbine Passage

Abstract: The choice of study species when conducting environmental assessments of hydropower facilities is of great importance from a licensing and policy perspective. Power analyses are commonly used to provide quantitative backing for the numbers of study organisms and trials used, but there is not frequent use of quantitative methods for choosing appropriate study species. Species choice can be especially important when measuring the impacts of ecosystem alteration, such as in a hydropower system, when study species must be chosen that are both sensitive to the alteration and of sufficient abundance for study. In this study, we step through two examples using a combination of GIS, a fish traits database, and multivariate statistical analyses to present a quantitative, traits-based approach for designating study species. In our first example, we present a case study where we select broadly-representative fish species for understanding the effects of turbine passage on fishes based on traits that suggest sensitivity to turbine passage. In our second example, we build off of our first example and present a framework for selecting a surrogate species for an endangered species. We suggest that our traits-based framework can provide quantitative backing and added justification to selection of study species while also delineating the expanded inference space of study results

Emerging Themes and Future Directions of Multi-Sector Nexus Research and Implementation

Water, energy, and food are all essential components of human societies. Collectively, their respective resource systems are interconnected in what is called the “nexus”. There is growing consensus that a holistic understanding of the interdependencies and trade-offs between these sectors and other related systems is critical to solving many of the global challenges they present. While nexus research has grown exponentially since 2011, there is no unified, overarching approach, and the implementation of concepts remains hampered by the lack of clear case studies. Here, we present the results of a collaborative thought exercise involving 75 scientists and summarize them into 10 key recommendations covering: the most critical nexus issues of today, emerging themes, and where future efforts should be directed. We conclude that a nexus community of practice to promote open communication among researchers, to maintain and share standardized datasets, and to develop applied case studies will facilitate transparent comparisons of models and encourage the adoption of nexus approaches in practice

Emerging Themes and Future Directions of Multi-Sector Nexus Research and Implementation

Water, energy, and food are all essential components of human societies. Collectively, their respective resource systems are interconnected in what is called the “nexus”. There is growing consensus that a holistic understanding of the interdependencies and trade-offs between these sectors and other related systems is critical to solving many of the global challenges they present. While nexus research has grown exponentially since 2011, there is no unified, overarching approach, and the implementation of concepts remains hampered by the lack of clear case studies. Here, we present the results of a collaborative thought exercise involving 75 scientists and summarize them into 10 key recommendations covering: the most critical nexus issues of today, emerging themes, and where future efforts should be directed. We conclude that a nexus community of practice to promote open communication among researchers, to maintain and share standardized datasets, and to develop applied case studies will facilitate transparent comparisons of models and encourage the adoption of nexus approaches in practice

Revisiting the homogenization of dammed rivers in the southeastern US

For some time, ecologists have attempted to make generalizations concerning how disturbances influence natural ecosystems, especially river systems. The existing literature suggests that dams homogenize the hydrologic variability of rivers. However, this might insinuate that dams affect river systems similarly despite a large gradient in natural hydrologic character. In order to evaluate patterns in dam-regulated hydrology and associated ecological relationships, a broad framework is needed. Flow classes, or groups of streams that share similar hydrology, may provide a framework to evaluate the relative effects of dam regulation on natural flow dynamics. The purpose of this study was to use a regional flow classification as the foundation for evaluating patterns of hydrologic alteration due to dams and to determine if the response of rivers to regulation was specific to different flow classes. We used the US Geological Survey (USGS) database to access discharge information for 284 unregulated and 117 regulated gage records. For each record, we calculated 44 hydrologic statistics, including the Indicators of Hydrologic Alteration. We used a sub-regional flow classification for eight states as a way to stratify unregulated and regulated streams into comparable units. In general, our results showed that dam regulation generally had stronger effects on hydrologic indices than other disturbances when models were stratified by flow class; however, the effects of urbanization, withdrawals, and fragmentation, at times, were comparable or exceeded the effects of dam regulation. In agreement with the existing literature, maximum flows, flow variability, and rise rates were lower whereas minimum flows and reversals were higher in dam regulated streams. However, the response of monthly and seasonal flows, flow predictability, and baseflows were variable depending on flow class membership. Principal components analysis showed that regulated streams occupied a larger multivariate space than unregulated streams, which suggests that dams may not homogenize all river systems, but may move them outside the bounds of normal river function. Ultimately, our results suggest that flow classes provide a suitable framework to generalize patterns in hydrologic alterations due to dam regulation

Species depletion profiles as an alternative to streamflow alteration thresholds in a hydroecological risk assessment

Tradeoffs between human demands and ecological consequences of water resources necessitate setting limits to the hydrologic alteration of rivers – these limits or thresholds are required to prescribe environmental flows to maintain the ecological integrity of river ecosystems. Ideally, water managers could derive these thresholds empirically from hydroecological studies. Unfortunately, recent synthesis studies suggest that clear thresholds for terrestrial and aquatic ecosystems are elusive – if they exist at all. The field of ecological risk assessment (ERA) offers many approaches to describe and manage the prevalence and threat of an environmental stressor and establish limits of that stressor. This study introduces a hydroecological risk assessment (HERA) to identify thresholds of hydrologic alteration using an approach from ecological risk assessment and a stressor derived from publicly available hydrologic data. Rather than a single threshold value for ecological responses to hydrologic alteration, this study found that species exhibit variable patterns of response to depletion across their ranges – what we term Species Depletion Profiles (SDPs). These SDPs correlate with population health of the species in question, with similarities in conservation status and distribution evident among species with similar SDPs. Our results suggest that a well-used approach common to aquatic ecotoxicology has potential application in developing environmental flow guidelines for protection and remediation of riverine systems subject to anthropogenic influences where specific flow-ecology relationships are unknown

Global hydropower expansion without building new dams

Reducing global carbon emissions will require large-scale transitions from fossil fuels to renewable energy resources. Hydropower will likely play a role in those transitions as it provides reliable energy storage while counter-balancing intermittent renewables. However, the construction of new dams comes at significant environmental costs to river ecosystems. An optimal future considers how to maximize the benefits of hydropower while minimizing environmental impact through revitalizing existing infrastructures. Herein, we quantify this potential using a spatially comprehensive global inventory of geolocated dams used for purposes other than hydropower, and augment these results with modelled estimates of small, unmapped dams. Furthermore, we examine increases in hydropower potential from efficiency upgrades at existing hydro-plants. These opportunities afford non-invasive increases in hydropower in populated areas neighbouring biodiversity hot spots. Overall, we estimate that these contributions could potentially provide up to a 9% increase to current global hydropower, potentially reducing the costs of construction and transmission, all while offsetting impacts to biodiversity and river ecosystems incurred by planned new hydropower construction

Appendix A. An examination of the distribution of North American fishes within the 3-point life-history continuum and an evaluation of differences between trait values for lotic and lentic fish.

An examination of the distribution of North American fishes within the 3-point life-history continuum and an evaluation of differences between trait values for lotic and lentic fish