Henriette Jager - Academia.edu (original) (raw)

Papers by Henriette Jager

Frontiers in Ecology and the Environment, 2018

Risk and resilience in an uncertain world E cological disturbances are occurring with greater fre... more Risk and resilience in an uncertain world E cological disturbances are occurring with greater frequency and intensity than in the past. Under projected shifts in disturbance regimes and patterns of recovery, societal and environmental impacts are expected to be more extreme and to span larger spatial extents. Moreover, preexisting conditions will require a longer time to re-establish, if they do so at all. The word "unprecedented" is appearing more often in news reporting on droughts, fires, hurricanes, tsunamis, ice storms, and insect outbreaks. The causes and effects of these events are often exacerbated by human modifications of natural environments and influenced by technological developments. At the same time, multiple events or different types of disturbances can undermine the ability of environmental systems to recover, and interacting disturbances can cause these systems to transition to new and undesirable states. For example, the combination of an expansion of impervious surface area, changes to hydrology and drainage systems, and wetland losses can interact to amplify the frequency and severity of flooding. In addition, actions that seek to manage individual rather than combined risks may induce unintentional consequences, increase the magnitude of impacts, or decrease resilience (the ability of an ecosystem to withstand or recover quickly from a disturbance). Furthermore, re-establishment may be to a new state or to what some call an "emerging ecosystem", whose properties then influence risks of and resilience to subsequent disturbances. The need to proactively address risk and resilience is more pressing than ever. Managing complex ecosystems to maintain essential characteristics in the face of an uncertain future is challenging. Therefore, we offer a perspective on risk and resilience that encompasses interactions among ecosystems, social systems, infrastructure, and evolving technological capabilities. Management decisions need to concentrate on three topic areas: (1) risk assessment, monitoring, and mitigation; (2) natural resource use and ecosystem service management; and (3) linkages among humans, technologies, and emerging ecosystems. More effectively managing natural resources and the ecosystem services they provide requires that scientists and managers anticipate shifts in disturbance regimes and analyze risk and resilience from broader perspectives. Whether and when risks and associated losses in ecosystem services are amplified or attenuated by future disturbances depends on how the environment, society, the economy, and technology respond. We cannot assume that practices that have worked in the past will be effective in the future. Just as future disturbance regimes differ from those of the past, tools to analyze, monitor, and manage them are also changing. Ecologists have much to offer in this regard, because of their knowledge of how disturbances can affect ecosystems. Furthermore, ecologists are using new tools for detecting environmental change at different temporal, spatial, and organizational scales. For instance, the development of smartphones has led to an explosion of information sharing via apps and citizen-science initiatives. Information collected by individuals can be uploaded into mobile or web-based applications to help scientists assess change at regional and global scales. Technological advances in genomics and remote sensing have made it possible to study environments from the molecular to the ecosystem level using biomonitoring tools such as environmental DNA (eDNA) and instruments affixed to drones, submersibles, and satellites. Scientific understanding of the interactive effects of multiple disturbances is also evolving. Together, new technologies and new scientific concepts can help to address the interfaces between human and ecological systems. Combining these new tools and perspectives is essential for science, management, and planning. We urge environmental scientists to design research that analyzes the effects of shifts in disturbance regimes and identifies ways to minimize adverse impacts. The kinds of information that we believe will be useful include mechanisms or conceptual models of impact, risk maps that identify susceptible areas, means to monitor and assess current conditions, indicators of pending change, potential influences on mitigation interventions, and data on the interactions between human and ecological systems. Case studies that focus on multiple scales-including local analyses of interest to landowners and regional analyses useful to watershed, state, and federal planners-are also valuable. Because the future is uncertain and to some extent unknowable, it is imperative that ecologists become involved in the discussion and planning of future infrastructure and protection from the effects of altered disturbance regimes. Research can test and demonstrate the benefits of protecting or proactively managing important features and places, and processes that enhance provisioning of ecosystem services such as flood control and fire mitigation. It is time to demonstrate how ecological science, when applied to human-environmental systems, can reduce risks and enhance resilience in a complex, changing world.

Ecological Modelling, 2014

Using models to represent relationships between flow and fishes has important practical applicati... more Using models to represent relationships between flow and fishes has important practical applications for managing reservoir releases. Attempts to model such relationships often neglect indirect mechanisms by which flow influences fish. For example, growth of salmon juveniles is measurably faster when flows inundate floodplain and promote higher production of invertebrate prey, but out-of-channel flows have not yet been incorporated into models. The QUANTUS model developed here represents indirect linkages between flow and freshwater survival, mediated by temperature and prey availability, for fall Chinook salmon (Oncorhynchus tshawytscha). Quantiles of spawning time and place were used to define cohorts of salmon in a regulated Central Valley, California river. Survival of these quantile-cohorts was simulated through incubation, juvenile growth, and eventual downstream migration. A genetic algorithm was used to optimize the seasonal timing of pulse flows. Simulated survival was highest for flow regimes that provided a modest, temperature-moderating pulse flow in early summer and, for wetter years, a second, larger pulse of over-bank flow in late winter. For many rivers of the Pacific coast that support fall Chinook salmon, the thermal window of opportunity for spawning and rearing is narrow. Optimized flows made the most of this window by providing access to accelerated juvenile growth and early survival in floodplain habitat, a result that should be verified with field experiments. Timing of optimized pulse flows differed in some respects from the region's natural hydrograph, dominated by spring runoff. This suggests that understanding the mechanisms by which flow influences fishes can be important when shaping flows in the changed context of a regulated river.

Military landscapes represent a mixture of undisturbed natural ecosystems, developed areas, and l... more Military landscapes represent a mixture of undisturbed natural ecosystems, developed areas, and lands that support different types and intensities of military training. Research to understand water-quality influences of military landscapes usually involves intensive sampling in a few watersheds. In this study, we developed a survey design of accessible headwater watersheds intended to improve our ability to distinguish land-water relationships in general, and training influences, in particular, on Fort Stewart, GA. We sampled and analyzed water from watershed outlets. We successfully developed correlative models for total suspended solids (TSS), total nitrogen (TN), organic carbon (OC), and organic nitrogen (ON), which dominated in this blackwater ecosystem. TSS tended to be greater in samples after rainfall and during the growing season, and models that included %Wetland suggested a ''build-and-flush'' relationship. We also detected a positive association between TSS and tank-training, which suggests a need to intercept sediment-laden runoff from training areas. Models for OC showed a negative association with %Grassland. TN and ON both showed negative associations with %Grassland, %Wetland, and %Forest. Unexpected positive associations were observed between OC and equipmenttraining activity and between ON and %Bare ground ? Roads. Future studies that combine our survey-based approach with more intensive monitoring of the timing and intensity of training would be needed to better understand the mechanisms for these empirical relationships involving military training. Looking beyond local effects on Fort Stewart streams, we explore questions about how exports of OC and nitrogen from coastal military installations ultimately influence estuaries downstream.

The thread posed to Pacific salmon by competing water demands is a great concern to regulators of... more The thread posed to Pacific salmon by competing water demands is a great concern to regulators of the hydropower industry. Finding the balance between fish resource and economic objectives depends on our ability to quantify flow effects on salmon production. Because field experiments are impractical, simulation models are needed to predict the effects of minimum flows on chinook salmon during their freshwater residence. We have developed a model to simulate the survival and development of eggs and alevins in redds and the growth, survival, and movement of juvenile chinook in response to local stream conditions (flow, temperature, chinook and predator density). Model results suggest that smolt production during dry years can be increased by raising spring minimum flows.

This paper describes a simulation study of reconnection options for white sturgeon Acipenser tran... more This paper describes a simulation study of reconnection options for white sturgeon Acipenser transmontanus subpopulations in adjacent river segments above and below CJ Strike Dam on the Snake River, Idaho, USA. In contrast to the downstream river segment, the upstream river segment is long and has areas that are suitable for spawning during normal and wet hydrologic conditions. We evaluated demographic and genetic consequences of upstream and downstream passage using different model assumptions about trashrack spacing and density-dependent effects on the spawning interval. Our genetic results predict that, although reconnection would introduce new alleles to the upstream subpopulation, it would also preserve alleles from the downstream subpopulation by propagating them in the larger subpopulation above the dam. Our demographic results predict that halving the space between trashracks would have large and unequivocal benefits, whereas the predicted effects of reconnection were smaller and more sensitive to model assumptions. Simulated upstream passage tended to benefit both subpopulations only in the absence of density-dependent limitation. In the presence of density dependence, the combination of halved trashrack spacing and upstream and downstream passage produced the best results. Narrower trashracks kept spawning adults in the upstream segment with spawning habitat, while allowing their progeny to migrate downstream. Screening appears to be the best option for such a species in this configuration of a long river segment acting as a demographic source above a short one acting as a demographic sink.

Environmental Management, 2007

Regulated rivers in the United States are required to support human water uses while preserving a... more Regulated rivers in the United States are required to support human water uses while preserving aquatic ecosystems. However, the effectiveness of hydropower license requirements nationwide has not been demonstrated. One requirement that has become more common is ''run-of-river'' (ROR) operation, which restores a natural flow regime. It is widely believed that ROR requirements (1) are mandated to protect aquatic biota, (2) decrease hydropower generation per unit flow, and decrease energy revenue. We tested these three assumptions by reviewing hydropower projects with licensemandated changes from peaking to ROR operation. We found that ROR operation was often prescribed in states with strong water-quality certification requirements and migratory fish species. Although benefits to aquatic resources were frequently cited, changes were often motivated by other considerations. After controlling for climate, the overall change in annual generation efficiency across projects because of the change in operation was not significant. However, significant decreases were detected at one quarter of individual hydropower projects. As expected, we observed a decrease in flow during peak demand at 7 of 10 projects. At the remaining projects, diurnal fluctuations actually increased because of operation of upstream storage projects. The economic implications of these results, including both producer costs and ecologic benefits, are discussed. We conclude that regional-scale studies of hydropower regulation, such as this one, are long overdue. Public dissemination of flow data, license provisions, and monitoring data by way of on-line access would facilitate regional policy analysis while increasing regulatory transparency and providing feedback to decision makers.

Southern populations of the federally endangered Shortnose Sturgeon Acipenser brevirostrum are co... more Southern populations of the federally endangered Shortnose Sturgeon Acipenser brevirostrum are considered to be at greater risk of extirpation than northern populations. Our study focused on the Ogeechee River, Georgia, a small, undeveloped, coastal river that supports a population with fewer than 300 Shortnose Sturgeon. We designed a population viability analysis (PVA) model to represent and quantify the demographic influences of three factors (poor water quality, intrusion of saline water via rice canals, and incidental harvest) on the viability of this population. As an isolated population, only 75% of simulated populations persisted beyond a 20-year time horizon with all factors simulated. However, immigration from the Altamaha River may help to support the population. We quantified population persistence with and without simulating each factor and found that (1) incidental harvest had no effect on simulated persistence, (2) poor water quality decreased simulated persistence by 29%, primarily due to low oxygen conditions in summer, and (3) roughly one-third of this effect was attributed to rice canals (premature exposure of juveniles to high salinities). Simulated recruitment to age 1 was limited by a habitat squeeze between densitydependent starvation upstream near the spawning grounds and premature exposure to salinity downstream. These results highlight a need for research on availability of summer refuge and freshwater rearing habitat. As these results derived from a PVA model, which required many assumptions, they should be considered preliminary. Further field research is needed to confirm those results where it is possible to test intermediate predictions. We conclude by suggesting that efforts to maintain or increase the number of viable populations of Shortnose Sturgeon in southern U.S. rivers will probably require an understanding of (1) source-sink dynamics between populations in rivers with access to adequate freshwater rearing habitat and those without, and (2) the effects of climate change.

Ecological Modelling, 1997

We developed a simulation model to predict instream flow effects on smolt production for fall chi... more We developed a simulation model to predict instream flow effects on smolt production for fall chinook salmon (Oncorhynchus tshawytscha) in regulated rivers. The principal purpose of this model is to serve as a management tool to evaluate effects on salmon of instream releases from upstream reservoirs. The dramatic decline in chinook salmon in California rivers suggests a need for such a tool. We developed an individual-based and spatially explicit model to simulate the influences of riverine habitat on each lifestage leading to successful outmigration of chinook salmon. Model predictions of development, growth and survival showed good agreement with four years of field data collected on the Tuolumne River, California. Our analysis of parameter sensitivities identified flow-related redd mortality and temperature-related juvenile mortality as limitations on smolt production. © 1997 Elsevier Science B.V.

Environmental Toxicology and Chemistry, 1999

Spatial distribution of contaminants in the sediments and biota of a large reservoir ecosystem we... more Spatial distribution of contaminants in the sediments and biota of a large reservoir ecosystem were related to a variety of biological responses in fish populations and communities to determine possible relationships between contaminant loading in the environment and fish health. Much of the contaminant inventory in the Clinch River/Watts Bar Reservoir (CR/WBR) system has originated from three U.S. Department of Energy facilities on the Oak Ridge Reservation, which borders this system in its upper reaches. Fish sampled from areas of the CR/WBR system with the highest levels of contaminants in the sediments and biota, primarily mercury and PCBs, had the most dramatic bioindicator responses. The major changes observed were induction of detoxification enzymes, organ dysfunction, increased frequency of histopathological lesions, impaired reproduction, and reduced fish community integrity. Mercury, the dominant contaminant, displayed a decreasing concentration gradient from the upper reaches of Poplar Creek to the lower Clinch River, which was consistent with a downstream gradient in several of the biological responses. A multivariate analysis using all of the individual fish health responses at each site in a discriminant analysis procedure also revealed a downstream gradient in integrated fish health. In Poplar Creek where contaminant concentrations were the highest, statistical correlations were observed between individual bioindicator responses such as contaminant exposure indicators, organ dysfunction, histopathological damage, and reproductive impairment. Relationships between contaminant loading and fish community indices such as species richness and relative abundance, however, were more difficult to establish in Poplar Creek because of the possible dominating influence of food and habitat availability on fish community dynamics. Using a suite of bioindicators that encompass a range of levels of biological organization and response-sensitivity scales improves the probability of identifying cause (contaminant) and effect (biological response) and helps in distinguishing between natural and anthropogenic sources of stress in aquatic ecosystems.

In order to mitigate the environmental effects of hydropower development and operation, the Feder... more In order to mitigate the environmental effects of hydropower development and operation, the Federal Energy Regulatory Commission requires environmental compliance by private owners of hydropower facilities. The environmental issues considered are usually within the vicinity of hydropower facilities because many, if not all, are a direct result of dam construction or operation. “On-site” mitigation techniques typically include fish passage, flow and water quality improvement, habitat enhancement, and recreation improvements. We question whether more environmental benefits could be achieved outside the project boundary (“off-site”). Off-site benefits include the above listed mitigations, but also land acquisition, wetland mitigation, and riparian restoration. Determining optimal win-win scenarios between energy and the environment requires identifying the most cost-effective route to increase energy production while also identifying environmental improvements with the highest benefit/...

Environmental Management, 2011

Military landscapes represent a mixture of undisturbed natural ecosystems, developed areas, and l... more Military landscapes represent a mixture of undisturbed natural ecosystems, developed areas, and lands that support different types and intensities of military training. Research to understand water-quality influences of military landscapes usually involves intensive sampling in a few watersheds. In this study, we developed a survey design of accessible headwater watersheds intended to improve our ability to distinguish land-water relationships in general, and training influences, in particular, on Fort Stewart, GA. We sampled and analyzed water from watershed outlets. We successfully developed correlative models for total suspended solids (TSS), total nitrogen (TN), organic carbon (OC), and organic nitrogen (ON), which dominated in this blackwater ecosystem. TSS tended to be greater in samples after rainfall and during the growing season, and models that included %Wetland suggested a "build-and-flush" relationship. We also detected a positive association between TSS and tank-training, which suggests a need to intercept sediment-laden runoff from training areas. Models for OC showed a negative association with %Grassland. TN and ON both showed negative associations with %Grassland, %Wetland, and %Forest. Unexpected positive associations were observed between OC and equipment-training activity and between ON and %Bare ground + Roads. Future studies that combine our survey-based approach with more intensive monitoring of the timing and intensity of training would be needed to better understand the mechanisms for these empirical relationships involving military training. Looking beyond local effects on Fort Stewart streams, we explore questions about how exports of OC and nitrogen from coastal military installations ultimately influence estuaries downstream.

The global recognition of the importance of natural flow regimes to sustain the ecological integr... more The global recognition of the importance of natural flow regimes to sustain the ecological integrity of river systems has led to increased societal pressure on the hydropower industry to change plant operations to improve downstream aquatic ecosystems. However, a complete reinstatement of natural flow regimes is often unrealistic when balancing water needs for ecosystems, energy production , and other human uses. Thus, stakeholders must identify a prioritized subset of flow prescriptions that meet ecological objectives in light of realistic constraints. Yet, isolating aspects of flow regimes to restore downstream of hydropower facilities is among the greatest challenges of environmental flow science due, in part, to the sheer volume of available environmental flow tools in conjunction with complex negotiation-based regulatory procedures. Herein, we propose an organizational framework that structures information and existing flow paradigms into a staged process that assists stakeholders in implementing environmental flows for hydropower facilities. The framework identifies areas where regulations fall short of the needed scientific process, and provide suggestions for stakeholders to ameliorate those situations through advanced preparation. We highlight the strengths of existing flow paradigms in their application to hydropower settings and suggest when and where tools are most applicable. Our suggested framework increases the effectiveness and efficiency of the e-flow implementation process by rapidly establishing a knowledge base and decreasing uncertainty so more time can be devoted to filling knowledge gaps. Lastly, the framework provides the structure for a coordinated research agenda to further the science of environmental flows related to hydropower environments.

Ecological Modelling, Feb 1, 2006

Brine spills associated with petroleum extraction can reduce the amount of suitable habitat and i... more Brine spills associated with petroleum extraction can reduce the amount of suitable habitat and increase habitat fragmentation for many terrestrial animals. We conducted a simulation study to quantify the effects of habitat loss and fragmentation on a solitary mammal predator. To provide focus, we adopted biological attributes of the American badger (Taxidea taxus) and environmental attributes of the Tallgrass Prairie Preserve in Oklahoma. We simulated badger activities on landscapes with different degrees of habitat loss and fragmentation using a spatially explicit and individual-based population model. Both habitat loss and fragmentation increased the incidence of habitat-related mortality and decreased the proportion of eligible females that mated, which decreased final population sizes and the likelihood of persistence. Parameter exploration suggested that steep, threshold-like, responses to habitat loss occurred when animals included high-risk habitat in their territories. Badger populations showed a steeper decline with increasing habitat loss on landscapes fragmented by spills than on less fragmented landscapes. Habitat fragmentation made it difficult for badgers to form high-quality territories, and exposed individuals to higher risk while seeking to establish a territory. Our simulations also suggest that an inability to find mates (an Allee effect) becomes increasingly important for landscapes that support a sparse distribution of territories. Thus, the presence of unmated females with territories may foreshadow population decline in solitary species that do not normally tolerate marginal adults. Published by Elsevier B.V.

North American Journal of Fisheries Management, Feb 1, 2003

Widespread declines in stocks of Pacific salmon in the genus Oncorhynchus highlight the need for ... more Widespread declines in stocks of Pacific salmon in the genus Oncorhynchus highlight the need for research to find new and effective management strategies for recovery. Two recovery objectives are (1) to ensure that recruitment is adequate to rebuild self-sustaining populations and (2) to maintain phenotypic diversity. This study seeks to understand how seasonal flow patterns in a flow-regulated California river might be managed to attain each of these recovery objectives, specifically for the fall and late-fall runs of chinook salmon O. tshawytscha. We ask two questions:

Transactions of the American Fisheries Society, 2010

Damming of large rivers in the U.S. Pacific Northwest and Canada has divided the historical popul... more Damming of large rivers in the U.S. Pacific Northwest and Canada has divided the historical population of white sturgeon Acipenser transmontanus into more than 36 fragmented populations, few of which are thriving. We now face the challenge of managing these populations to avoid extirpation. Two goals of this study were to identify extinction thresholds related to small size and inadequate habitat for this species. The minimum viable population size (MVP) is the threshold size above which populations support recruitment and grow and below which populations fail to support recruitment and decline. We estimated a single, cross-population MVP using data from multiple populations and quantile regression, which removed the effects of factors other than population size. Only two populations (those in the Bonneville and Dalles reservoirs on the Columbia River), both with significant increasing trends, were larger than our MVP estimate. We detected significant decreasing trends in two populations-those below Bonneville Dam and in the Kootenai River. To discover how site-specific differences in river habitat influence MVP, we used a population viability analysis (PVA) model that incorporated Allee mechanisms. The PVA model identified a river segment length below which extinction was certain regardless of initial population size. Above this threshold, simulated populations in river segments that were longer or that provided more frequent recruitment opportunities were able to persist with smaller initial sizes. Two priorities emerged for white sturgeon: monitoring age structure and understanding the circumstances preventing recruitment to age 1. Our results ultimately guided us toward thresholds in rearing habitat and age structure that promise to develop into more useful conservation tools than MVP for this and similar long-lived species.

Although optimization is often used to establish rules for timing flow releases below reservoirs,... more Although optimization is often used to establish rules for timing flow releases below reservoirs, environmental concerns are rarely incorporated as objectives and are relegated to minimum flow constraints. Here, we review studies that derived rules for hydropower operation by solving optimization problems driven by environmental and other competing water uses. We discuss the challenges of selecting environmental objectives amidst ecosystem complexity and consider how hydro system optimization and environmental optimization are modeled with differing uncertainty, time scales, and hierarchy. We explore how specific objectives may vary with the time scale of operations and discuss examples of environmental models that could be compatible with hydropower optimization. Given the increasing value placed on the ecological sustainability of human activities, we suggest that new approaches are needed to identify essential features of flow variation as it promotes river health and find quantitative methods for bringing ecological sustainability into the multi-objective problem of sustainable reservoir operation.

Frontiers in Ecology and the Environment, 2018

Risk and resilience in an uncertain world E cological disturbances are occurring with greater fre... more Risk and resilience in an uncertain world E cological disturbances are occurring with greater frequency and intensity than in the past. Under projected shifts in disturbance regimes and patterns of recovery, societal and environmental impacts are expected to be more extreme and to span larger spatial extents. Moreover, preexisting conditions will require a longer time to re-establish, if they do so at all. The word "unprecedented" is appearing more often in news reporting on droughts, fires, hurricanes, tsunamis, ice storms, and insect outbreaks. The causes and effects of these events are often exacerbated by human modifications of natural environments and influenced by technological developments. At the same time, multiple events or different types of disturbances can undermine the ability of environmental systems to recover, and interacting disturbances can cause these systems to transition to new and undesirable states. For example, the combination of an expansion of impervious surface area, changes to hydrology and drainage systems, and wetland losses can interact to amplify the frequency and severity of flooding. In addition, actions that seek to manage individual rather than combined risks may induce unintentional consequences, increase the magnitude of impacts, or decrease resilience (the ability of an ecosystem to withstand or recover quickly from a disturbance). Furthermore, re-establishment may be to a new state or to what some call an "emerging ecosystem", whose properties then influence risks of and resilience to subsequent disturbances. The need to proactively address risk and resilience is more pressing than ever. Managing complex ecosystems to maintain essential characteristics in the face of an uncertain future is challenging. Therefore, we offer a perspective on risk and resilience that encompasses interactions among ecosystems, social systems, infrastructure, and evolving technological capabilities. Management decisions need to concentrate on three topic areas: (1) risk assessment, monitoring, and mitigation; (2) natural resource use and ecosystem service management; and (3) linkages among humans, technologies, and emerging ecosystems. More effectively managing natural resources and the ecosystem services they provide requires that scientists and managers anticipate shifts in disturbance regimes and analyze risk and resilience from broader perspectives. Whether and when risks and associated losses in ecosystem services are amplified or attenuated by future disturbances depends on how the environment, society, the economy, and technology respond. We cannot assume that practices that have worked in the past will be effective in the future. Just as future disturbance regimes differ from those of the past, tools to analyze, monitor, and manage them are also changing. Ecologists have much to offer in this regard, because of their knowledge of how disturbances can affect ecosystems. Furthermore, ecologists are using new tools for detecting environmental change at different temporal, spatial, and organizational scales. For instance, the development of smartphones has led to an explosion of information sharing via apps and citizen-science initiatives. Information collected by individuals can be uploaded into mobile or web-based applications to help scientists assess change at regional and global scales. Technological advances in genomics and remote sensing have made it possible to study environments from the molecular to the ecosystem level using biomonitoring tools such as environmental DNA (eDNA) and instruments affixed to drones, submersibles, and satellites. Scientific understanding of the interactive effects of multiple disturbances is also evolving. Together, new technologies and new scientific concepts can help to address the interfaces between human and ecological systems. Combining these new tools and perspectives is essential for science, management, and planning. We urge environmental scientists to design research that analyzes the effects of shifts in disturbance regimes and identifies ways to minimize adverse impacts. The kinds of information that we believe will be useful include mechanisms or conceptual models of impact, risk maps that identify susceptible areas, means to monitor and assess current conditions, indicators of pending change, potential influences on mitigation interventions, and data on the interactions between human and ecological systems. Case studies that focus on multiple scales-including local analyses of interest to landowners and regional analyses useful to watershed, state, and federal planners-are also valuable. Because the future is uncertain and to some extent unknowable, it is imperative that ecologists become involved in the discussion and planning of future infrastructure and protection from the effects of altered disturbance regimes. Research can test and demonstrate the benefits of protecting or proactively managing important features and places, and processes that enhance provisioning of ecosystem services such as flood control and fire mitigation. It is time to demonstrate how ecological science, when applied to human-environmental systems, can reduce risks and enhance resilience in a complex, changing world.

Ecological Modelling, 2014

Using models to represent relationships between flow and fishes has important practical applicati... more Using models to represent relationships between flow and fishes has important practical applications for managing reservoir releases. Attempts to model such relationships often neglect indirect mechanisms by which flow influences fish. For example, growth of salmon juveniles is measurably faster when flows inundate floodplain and promote higher production of invertebrate prey, but out-of-channel flows have not yet been incorporated into models. The QUANTUS model developed here represents indirect linkages between flow and freshwater survival, mediated by temperature and prey availability, for fall Chinook salmon (Oncorhynchus tshawytscha). Quantiles of spawning time and place were used to define cohorts of salmon in a regulated Central Valley, California river. Survival of these quantile-cohorts was simulated through incubation, juvenile growth, and eventual downstream migration. A genetic algorithm was used to optimize the seasonal timing of pulse flows. Simulated survival was highest for flow regimes that provided a modest, temperature-moderating pulse flow in early summer and, for wetter years, a second, larger pulse of over-bank flow in late winter. For many rivers of the Pacific coast that support fall Chinook salmon, the thermal window of opportunity for spawning and rearing is narrow. Optimized flows made the most of this window by providing access to accelerated juvenile growth and early survival in floodplain habitat, a result that should be verified with field experiments. Timing of optimized pulse flows differed in some respects from the region's natural hydrograph, dominated by spring runoff. This suggests that understanding the mechanisms by which flow influences fishes can be important when shaping flows in the changed context of a regulated river.

Military landscapes represent a mixture of undisturbed natural ecosystems, developed areas, and l... more Military landscapes represent a mixture of undisturbed natural ecosystems, developed areas, and lands that support different types and intensities of military training. Research to understand water-quality influences of military landscapes usually involves intensive sampling in a few watersheds. In this study, we developed a survey design of accessible headwater watersheds intended to improve our ability to distinguish land-water relationships in general, and training influences, in particular, on Fort Stewart, GA. We sampled and analyzed water from watershed outlets. We successfully developed correlative models for total suspended solids (TSS), total nitrogen (TN), organic carbon (OC), and organic nitrogen (ON), which dominated in this blackwater ecosystem. TSS tended to be greater in samples after rainfall and during the growing season, and models that included %Wetland suggested a ''build-and-flush'' relationship. We also detected a positive association between TSS and tank-training, which suggests a need to intercept sediment-laden runoff from training areas. Models for OC showed a negative association with %Grassland. TN and ON both showed negative associations with %Grassland, %Wetland, and %Forest. Unexpected positive associations were observed between OC and equipmenttraining activity and between ON and %Bare ground ? Roads. Future studies that combine our survey-based approach with more intensive monitoring of the timing and intensity of training would be needed to better understand the mechanisms for these empirical relationships involving military training. Looking beyond local effects on Fort Stewart streams, we explore questions about how exports of OC and nitrogen from coastal military installations ultimately influence estuaries downstream.

The thread posed to Pacific salmon by competing water demands is a great concern to regulators of... more The thread posed to Pacific salmon by competing water demands is a great concern to regulators of the hydropower industry. Finding the balance between fish resource and economic objectives depends on our ability to quantify flow effects on salmon production. Because field experiments are impractical, simulation models are needed to predict the effects of minimum flows on chinook salmon during their freshwater residence. We have developed a model to simulate the survival and development of eggs and alevins in redds and the growth, survival, and movement of juvenile chinook in response to local stream conditions (flow, temperature, chinook and predator density). Model results suggest that smolt production during dry years can be increased by raising spring minimum flows.

This paper describes a simulation study of reconnection options for white sturgeon Acipenser tran... more This paper describes a simulation study of reconnection options for white sturgeon Acipenser transmontanus subpopulations in adjacent river segments above and below CJ Strike Dam on the Snake River, Idaho, USA. In contrast to the downstream river segment, the upstream river segment is long and has areas that are suitable for spawning during normal and wet hydrologic conditions. We evaluated demographic and genetic consequences of upstream and downstream passage using different model assumptions about trashrack spacing and density-dependent effects on the spawning interval. Our genetic results predict that, although reconnection would introduce new alleles to the upstream subpopulation, it would also preserve alleles from the downstream subpopulation by propagating them in the larger subpopulation above the dam. Our demographic results predict that halving the space between trashracks would have large and unequivocal benefits, whereas the predicted effects of reconnection were smaller and more sensitive to model assumptions. Simulated upstream passage tended to benefit both subpopulations only in the absence of density-dependent limitation. In the presence of density dependence, the combination of halved trashrack spacing and upstream and downstream passage produced the best results. Narrower trashracks kept spawning adults in the upstream segment with spawning habitat, while allowing their progeny to migrate downstream. Screening appears to be the best option for such a species in this configuration of a long river segment acting as a demographic source above a short one acting as a demographic sink.

Environmental Management, 2007

Regulated rivers in the United States are required to support human water uses while preserving a... more Regulated rivers in the United States are required to support human water uses while preserving aquatic ecosystems. However, the effectiveness of hydropower license requirements nationwide has not been demonstrated. One requirement that has become more common is ''run-of-river'' (ROR) operation, which restores a natural flow regime. It is widely believed that ROR requirements (1) are mandated to protect aquatic biota, (2) decrease hydropower generation per unit flow, and decrease energy revenue. We tested these three assumptions by reviewing hydropower projects with licensemandated changes from peaking to ROR operation. We found that ROR operation was often prescribed in states with strong water-quality certification requirements and migratory fish species. Although benefits to aquatic resources were frequently cited, changes were often motivated by other considerations. After controlling for climate, the overall change in annual generation efficiency across projects because of the change in operation was not significant. However, significant decreases were detected at one quarter of individual hydropower projects. As expected, we observed a decrease in flow during peak demand at 7 of 10 projects. At the remaining projects, diurnal fluctuations actually increased because of operation of upstream storage projects. The economic implications of these results, including both producer costs and ecologic benefits, are discussed. We conclude that regional-scale studies of hydropower regulation, such as this one, are long overdue. Public dissemination of flow data, license provisions, and monitoring data by way of on-line access would facilitate regional policy analysis while increasing regulatory transparency and providing feedback to decision makers.

Southern populations of the federally endangered Shortnose Sturgeon Acipenser brevirostrum are co... more Southern populations of the federally endangered Shortnose Sturgeon Acipenser brevirostrum are considered to be at greater risk of extirpation than northern populations. Our study focused on the Ogeechee River, Georgia, a small, undeveloped, coastal river that supports a population with fewer than 300 Shortnose Sturgeon. We designed a population viability analysis (PVA) model to represent and quantify the demographic influences of three factors (poor water quality, intrusion of saline water via rice canals, and incidental harvest) on the viability of this population. As an isolated population, only 75% of simulated populations persisted beyond a 20-year time horizon with all factors simulated. However, immigration from the Altamaha River may help to support the population. We quantified population persistence with and without simulating each factor and found that (1) incidental harvest had no effect on simulated persistence, (2) poor water quality decreased simulated persistence by 29%, primarily due to low oxygen conditions in summer, and (3) roughly one-third of this effect was attributed to rice canals (premature exposure of juveniles to high salinities). Simulated recruitment to age 1 was limited by a habitat squeeze between densitydependent starvation upstream near the spawning grounds and premature exposure to salinity downstream. These results highlight a need for research on availability of summer refuge and freshwater rearing habitat. As these results derived from a PVA model, which required many assumptions, they should be considered preliminary. Further field research is needed to confirm those results where it is possible to test intermediate predictions. We conclude by suggesting that efforts to maintain or increase the number of viable populations of Shortnose Sturgeon in southern U.S. rivers will probably require an understanding of (1) source-sink dynamics between populations in rivers with access to adequate freshwater rearing habitat and those without, and (2) the effects of climate change.

Ecological Modelling, 1997

We developed a simulation model to predict instream flow effects on smolt production for fall chi... more We developed a simulation model to predict instream flow effects on smolt production for fall chinook salmon (Oncorhynchus tshawytscha) in regulated rivers. The principal purpose of this model is to serve as a management tool to evaluate effects on salmon of instream releases from upstream reservoirs. The dramatic decline in chinook salmon in California rivers suggests a need for such a tool. We developed an individual-based and spatially explicit model to simulate the influences of riverine habitat on each lifestage leading to successful outmigration of chinook salmon. Model predictions of development, growth and survival showed good agreement with four years of field data collected on the Tuolumne River, California. Our analysis of parameter sensitivities identified flow-related redd mortality and temperature-related juvenile mortality as limitations on smolt production. © 1997 Elsevier Science B.V.

Environmental Toxicology and Chemistry, 1999

Spatial distribution of contaminants in the sediments and biota of a large reservoir ecosystem we... more Spatial distribution of contaminants in the sediments and biota of a large reservoir ecosystem were related to a variety of biological responses in fish populations and communities to determine possible relationships between contaminant loading in the environment and fish health. Much of the contaminant inventory in the Clinch River/Watts Bar Reservoir (CR/WBR) system has originated from three U.S. Department of Energy facilities on the Oak Ridge Reservation, which borders this system in its upper reaches. Fish sampled from areas of the CR/WBR system with the highest levels of contaminants in the sediments and biota, primarily mercury and PCBs, had the most dramatic bioindicator responses. The major changes observed were induction of detoxification enzymes, organ dysfunction, increased frequency of histopathological lesions, impaired reproduction, and reduced fish community integrity. Mercury, the dominant contaminant, displayed a decreasing concentration gradient from the upper reaches of Poplar Creek to the lower Clinch River, which was consistent with a downstream gradient in several of the biological responses. A multivariate analysis using all of the individual fish health responses at each site in a discriminant analysis procedure also revealed a downstream gradient in integrated fish health. In Poplar Creek where contaminant concentrations were the highest, statistical correlations were observed between individual bioindicator responses such as contaminant exposure indicators, organ dysfunction, histopathological damage, and reproductive impairment. Relationships between contaminant loading and fish community indices such as species richness and relative abundance, however, were more difficult to establish in Poplar Creek because of the possible dominating influence of food and habitat availability on fish community dynamics. Using a suite of bioindicators that encompass a range of levels of biological organization and response-sensitivity scales improves the probability of identifying cause (contaminant) and effect (biological response) and helps in distinguishing between natural and anthropogenic sources of stress in aquatic ecosystems.

In order to mitigate the environmental effects of hydropower development and operation, the Feder... more In order to mitigate the environmental effects of hydropower development and operation, the Federal Energy Regulatory Commission requires environmental compliance by private owners of hydropower facilities. The environmental issues considered are usually within the vicinity of hydropower facilities because many, if not all, are a direct result of dam construction or operation. “On-site” mitigation techniques typically include fish passage, flow and water quality improvement, habitat enhancement, and recreation improvements. We question whether more environmental benefits could be achieved outside the project boundary (“off-site”). Off-site benefits include the above listed mitigations, but also land acquisition, wetland mitigation, and riparian restoration. Determining optimal win-win scenarios between energy and the environment requires identifying the most cost-effective route to increase energy production while also identifying environmental improvements with the highest benefit/...

Environmental Management, 2011

Military landscapes represent a mixture of undisturbed natural ecosystems, developed areas, and l... more Military landscapes represent a mixture of undisturbed natural ecosystems, developed areas, and lands that support different types and intensities of military training. Research to understand water-quality influences of military landscapes usually involves intensive sampling in a few watersheds. In this study, we developed a survey design of accessible headwater watersheds intended to improve our ability to distinguish land-water relationships in general, and training influences, in particular, on Fort Stewart, GA. We sampled and analyzed water from watershed outlets. We successfully developed correlative models for total suspended solids (TSS), total nitrogen (TN), organic carbon (OC), and organic nitrogen (ON), which dominated in this blackwater ecosystem. TSS tended to be greater in samples after rainfall and during the growing season, and models that included %Wetland suggested a "build-and-flush" relationship. We also detected a positive association between TSS and tank-training, which suggests a need to intercept sediment-laden runoff from training areas. Models for OC showed a negative association with %Grassland. TN and ON both showed negative associations with %Grassland, %Wetland, and %Forest. Unexpected positive associations were observed between OC and equipment-training activity and between ON and %Bare ground + Roads. Future studies that combine our survey-based approach with more intensive monitoring of the timing and intensity of training would be needed to better understand the mechanisms for these empirical relationships involving military training. Looking beyond local effects on Fort Stewart streams, we explore questions about how exports of OC and nitrogen from coastal military installations ultimately influence estuaries downstream.

The global recognition of the importance of natural flow regimes to sustain the ecological integr... more The global recognition of the importance of natural flow regimes to sustain the ecological integrity of river systems has led to increased societal pressure on the hydropower industry to change plant operations to improve downstream aquatic ecosystems. However, a complete reinstatement of natural flow regimes is often unrealistic when balancing water needs for ecosystems, energy production , and other human uses. Thus, stakeholders must identify a prioritized subset of flow prescriptions that meet ecological objectives in light of realistic constraints. Yet, isolating aspects of flow regimes to restore downstream of hydropower facilities is among the greatest challenges of environmental flow science due, in part, to the sheer volume of available environmental flow tools in conjunction with complex negotiation-based regulatory procedures. Herein, we propose an organizational framework that structures information and existing flow paradigms into a staged process that assists stakeholders in implementing environmental flows for hydropower facilities. The framework identifies areas where regulations fall short of the needed scientific process, and provide suggestions for stakeholders to ameliorate those situations through advanced preparation. We highlight the strengths of existing flow paradigms in their application to hydropower settings and suggest when and where tools are most applicable. Our suggested framework increases the effectiveness and efficiency of the e-flow implementation process by rapidly establishing a knowledge base and decreasing uncertainty so more time can be devoted to filling knowledge gaps. Lastly, the framework provides the structure for a coordinated research agenda to further the science of environmental flows related to hydropower environments.

Ecological Modelling, Feb 1, 2006

Brine spills associated with petroleum extraction can reduce the amount of suitable habitat and i... more Brine spills associated with petroleum extraction can reduce the amount of suitable habitat and increase habitat fragmentation for many terrestrial animals. We conducted a simulation study to quantify the effects of habitat loss and fragmentation on a solitary mammal predator. To provide focus, we adopted biological attributes of the American badger (Taxidea taxus) and environmental attributes of the Tallgrass Prairie Preserve in Oklahoma. We simulated badger activities on landscapes with different degrees of habitat loss and fragmentation using a spatially explicit and individual-based population model. Both habitat loss and fragmentation increased the incidence of habitat-related mortality and decreased the proportion of eligible females that mated, which decreased final population sizes and the likelihood of persistence. Parameter exploration suggested that steep, threshold-like, responses to habitat loss occurred when animals included high-risk habitat in their territories. Badger populations showed a steeper decline with increasing habitat loss on landscapes fragmented by spills than on less fragmented landscapes. Habitat fragmentation made it difficult for badgers to form high-quality territories, and exposed individuals to higher risk while seeking to establish a territory. Our simulations also suggest that an inability to find mates (an Allee effect) becomes increasingly important for landscapes that support a sparse distribution of territories. Thus, the presence of unmated females with territories may foreshadow population decline in solitary species that do not normally tolerate marginal adults. Published by Elsevier B.V.

North American Journal of Fisheries Management, Feb 1, 2003

Widespread declines in stocks of Pacific salmon in the genus Oncorhynchus highlight the need for ... more Widespread declines in stocks of Pacific salmon in the genus Oncorhynchus highlight the need for research to find new and effective management strategies for recovery. Two recovery objectives are (1) to ensure that recruitment is adequate to rebuild self-sustaining populations and (2) to maintain phenotypic diversity. This study seeks to understand how seasonal flow patterns in a flow-regulated California river might be managed to attain each of these recovery objectives, specifically for the fall and late-fall runs of chinook salmon O. tshawytscha. We ask two questions:

Transactions of the American Fisheries Society, 2010

Damming of large rivers in the U.S. Pacific Northwest and Canada has divided the historical popul... more Damming of large rivers in the U.S. Pacific Northwest and Canada has divided the historical population of white sturgeon Acipenser transmontanus into more than 36 fragmented populations, few of which are thriving. We now face the challenge of managing these populations to avoid extirpation. Two goals of this study were to identify extinction thresholds related to small size and inadequate habitat for this species. The minimum viable population size (MVP) is the threshold size above which populations support recruitment and grow and below which populations fail to support recruitment and decline. We estimated a single, cross-population MVP using data from multiple populations and quantile regression, which removed the effects of factors other than population size. Only two populations (those in the Bonneville and Dalles reservoirs on the Columbia River), both with significant increasing trends, were larger than our MVP estimate. We detected significant decreasing trends in two populations-those below Bonneville Dam and in the Kootenai River. To discover how site-specific differences in river habitat influence MVP, we used a population viability analysis (PVA) model that incorporated Allee mechanisms. The PVA model identified a river segment length below which extinction was certain regardless of initial population size. Above this threshold, simulated populations in river segments that were longer or that provided more frequent recruitment opportunities were able to persist with smaller initial sizes. Two priorities emerged for white sturgeon: monitoring age structure and understanding the circumstances preventing recruitment to age 1. Our results ultimately guided us toward thresholds in rearing habitat and age structure that promise to develop into more useful conservation tools than MVP for this and similar long-lived species.

Although optimization is often used to establish rules for timing flow releases below reservoirs,... more Although optimization is often used to establish rules for timing flow releases below reservoirs, environmental concerns are rarely incorporated as objectives and are relegated to minimum flow constraints. Here, we review studies that derived rules for hydropower operation by solving optimization problems driven by environmental and other competing water uses. We discuss the challenges of selecting environmental objectives amidst ecosystem complexity and consider how hydro system optimization and environmental optimization are modeled with differing uncertainty, time scales, and hierarchy. We explore how specific objectives may vary with the time scale of operations and discuss examples of environmental models that could be compatible with hydropower optimization. Given the increasing value placed on the ecological sustainability of human activities, we suggest that new approaches are needed to identify essential features of flow variation as it promotes river health and find quantitative methods for bringing ecological sustainability into the multi-objective problem of sustainable reservoir operation.