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At least 1,279 records · Page 71Linked to original sources
USGS1991

Depositional patterns of the Mississippi Fan surface: Evidence from GLORIA II and high-resolution seismic profiles

GLORIA long-range side-scan sonar imagery and 3.5-kHz seismic-reflection profiles depict a series of nine elongate deposits with generally high-backscatter surfaces covering most of the latest fanlobe sequence of the Mississippi Fan in the eastern Gulf of Mexico. The youngest deposit is a “slump” that covers a 250 by 100 km area of the middle and upper fan. The remaining mapped deposits, termed depositional lobes, are long (as much as 200 km) and relatively thin (less than 35 m thick) bodies. Small channels and lineations on the surface of many of these depositional lobes radiate from a single, larger main channel that is the conduit through which sediment has been supplied to these surficial deposits on the fan. The 3.5-kHz profiles show that adjacent depositional lobes overlap one another rather than interfingering, indicating that only one lobe was an active site of deposition at a time. Shifting of the depositional sites appears to be caused by both aggradation and avulsion. The chronology developed from the overlapping relations indicates the oldest of the mapped depositional lobes are on the lowermost fan, and the youngest are further up the fan. Depositional lobes on the lower fan consist of a series of smaller, elongate features with high-backscatter surfaces (540 km in length) located at the ends of previously unrecognized small channels (< 5 m deep). These small channels extend as much as 120 km from the main channel. Small channelized turbidity currents and/or debris flows, sand flows, or mud flows appear to be the dominant transport process constructing these depositional lobes. Channelized flow is an important mechanism for transporting sediment away from the main channel on this fan and the resulting facies created by these small flows are laterally discontinuous.

Mississippi↗
USGS1985

Ground-water and surface-water interactions in Minnesota and Wisconsin wetlands

The interaction between ground water and surface water in wetlands is complex and depends on the hydrologic setting of the particular wetland. Hydrologic characteristics have been used in Wisconsin to classify wetlands into four categories; surface-waterdepression wetlands, surface-water-slope wetlands, ground-waterdepression wetlands, and ground-water-slope wetlands, as described by Novitzki (1978). The degree of ground- and surface-water interactions differs between the four categories.

Minnesota, Wisconsin↗
USGS1979

The use of habitat structure preferenda for establishing flow regimes necessary for maintenance of fish habitat

The pursuit of simplicity in the complex management of instream and out-of-stream water uses very early led to the minimum , or “base,” flow concept and the myth that a consistent methodology could be used to establish the desired minimum flow. Such a single flow value has not proven to be practical. As water becomes fully appropriated to upstream use and storage, the minimum flow, if not violated, tends to become the average condition. This situation is manifest in a flat or stepped but fixed hydrograph throughout the stream reach of concern for much of the year.

Book chapter↗
USGS1976

Inhibition of mallard salt gland function by DDE and organophosphates

The effects of selected environmental pollutants on avian salt gland function were studied in the mallard duck, Anas pZatyrhynchos . DDE and several organophosphates were found to have an inhibitory effect on the ability of these glands to concentrate and secrete salt from the body. DDE significantly reduced secretion rates from the salt glands. More severe effects were observed following exposure to organophosphate insecticides; reduction in gland size, reduced ability of the birds to secrete Na+ via the salt glands, and reductions in cholinesterase activities in the salt gland and hypothalamus all contributed to elevated mortality levels in treatment birds over controls.

Book chapter↗
USGS1997

Effects of fire on bird populations in mixed-grass prairie

The mixed-grass prairie is one of the largest ecosystems in North America, originally covering about 69 million ha (Bragg and Steuter 1995). Although much of the natural vegetation has been replaced by cropland and other uses (Samson and Knopf 1994, Bragg and Steuter 1995), significant areas have been preserved in national wildlife refuges, waterfowl production areas, state game management areas, and nature preserves. Mixed-grass prairie evolved with fire (Bragg 1995), and fire is frequently used as a management tool for prairie (Berkey et al. 1993).

Book chapter↗
USGS1983

Uptake and transport of heavy metals by heated seawater: A summary of the experimental results

In general, the chemistry of seawater experimentally reacted with basalt is in accord with the observed chemistry of the 350°C vent waters from 21°N on the East Pacific Rise. Experiments at 350°C, 500 bar, and a water/rock ratio of ≤10 reproduce most of the major components in the vent waters, in particular the low Mg and SO 4 and high Si0 2 , Ca, and K. In comparison with the vent waters however the experimental fluids are deficient in H + and heavy metals. Experiments with natural and evolved seawater (Mg and SO 4 depleted) at ≥400 C and 500 bars or 375°C and ~375 bars under rock-dominated conditions more closely reproduce the vent-water chemistry.

Book chapter↗
USGS2014

Wildlife friendly roads: the impacts of roads on wildlife in urban areas and potential remedies

Roads are one of the most important factors affecting the ability of wildlife to live and move within an urban area. Roads physically replace wildlife habitat and often reduce habitat quality nearby, fragment the remaining habitat, and cause increased mortality through vehicle collisions. Much ecological research on roads has focused on whether animals are successfully crossing roads, or if the road is a barrier to wildlife movement, gene flow, or functional connectivity. Roads can alter survival and reproduction for wildlife, even among species such as birds that cross roads easily. Here we examine the suite of potential impacts of roads on wildlife, but we focus particularly on urban settings. We report on studies, both in the literature and from our own experience, that have addressed wildlife and roads in urban landscapes. Although road ecology is a growing field of study, relatively little of this research, and relatively few mitigation projects, have been done in urban landscapes. We also draw from the available science on road impacts in rural areas when urban case studies have not fully addressed key topics.

Book chapter↗
USGS2014

Threshold concepts: implications for the management of natural resources

Threshold concepts can have broad relevance in natural resource management. However, the concept of ecological thresholds has not been widely incorporated or adopted in management goals. This largely stems from the uncertainty revolving around threshold levels and the post hoc analyses that have generally been used to identify them. Natural resource managers have a need for new tools and approaches that will help them assess the existence and detection of conditions that demand management actions. Recognition of additional threshold concepts include: utility thresholds (which are based on human values about ecological systems) and decision thresholds (which reflect management objectives and values and include ecological knowledge about a system) as well as ecological thresholds. All of these concepts provide a framework for considering the use of threshold concepts in natural resource decision making.

Book chapter↗
USGS2014

Getting the message across: using ecological integrity to communicate with resource managers

This chapter describes and illustrates how concepts of ecological integrity, thresholds, and reference conditions can be integrated into a research and monitoring framework for natural resource management. Ecological integrity has been defined as a measure of the composition, structure, and function of an ecosystem in relation to the system’s natural or historical range of variation, as well as perturbations caused by natural or anthropogenic agents of change. Using ecological integrity to communicate with managers requires five steps, often implemented iteratively: (1) document the scale of the project and the current conceptual understanding and reference conditions of the ecosystem, (2) select appropriate metrics representing integrity, (3) define externally verified assessment points (metric values that signify an ecological change or need for management action) for the metrics, (4) collect data and calculate metric scores, and (5) summarize the status of the ecosystem using a variety of reporting methods. While we present the steps linearly for conceptual clarity, actual implementation of this approach may require addressing the steps in a different order or revisiting steps (such as metric selection) multiple times as data are collected. Knowledge of relevant ecological thresholds is important when metrics are selected, because thresholds identify where small changes in an environmental driver produce large responses in the ecosystem. Metrics with thresholds at or just beyond the limits of a system’s range of natural variability can be excellent, since moving beyond the normal range produces a marked change in their values. Alternatively, metrics with thresholds within but near the edge of the range of natural variability can serve as harbingers of potential change. Identifying thresholds also contributes to decisions about selection of assessment points. In particular, if there is a significant resistance to perturbation in an ecosystem, with threshold behavior not occurring until well beyond the historical range of variation, this may provide a scientific basis for shifting an ecological assessment point beyond the historical range. We present two case studies using ongoing monitoring by the US National Park Service Vital Signs program that illustrate the use of an ecological integrity approach to communicate ecosystem status to resource managers. The Wetland Ecological Integrity in Rocky Mountain National Park case study uses an analytical approach that specifically incorporates threshold detection into the process of establishing assessment points. The Forest Ecological Integrity of Northeastern National Parks case study describes a method for reporting ecological integrity to resource managers and other decision makers. We believe our approach has the potential for wide applicability for natural resource management.

Book chapter↗
USGS2014

Identifying objectives and alternative actions to frame a decision problem.

In this chapter, we discuss the role of objectives and alternative actions in framing a natural resource management decision problem, with particular attention to thresholds. We outline a number of considerations in developing objectives and measurable attributes, including when utility thresholds may be needed to express the decision-makers&rsquo; values.We also discuss the development of a set of alternative actions, and how these might give rise to decision thresholds, particularly when the predictive models contain ecological thresholds. Framing of a decision problem plays a central role in decision analysis because it helps determine the needs for a predictive ecological model, the type of solution method required, and the value and structure of a monitoring system.

Book chapter↗
USGS2014

Application of threshold concepts to ecological management problems: Occupancy of Golden Eagles in Denali National Park, Alaska

In this chapter, we demonstrate the application of the various classes of thresholds, detailed in earlier chapters and elsewhere, via an actual but simplified natural resource management case study. We intend our example to provide the reader with the ability to recognize and apply the theoretical concepts of utility, ecological and decision thresholds to management problems through a formalized decision-analytic process. Our case study concerns the management of human recreational activities in Alaska’s Denali National Park, USA, and the possible impacts of such activities on nesting Golden Eagles, Aquila chrysaetos. Managers desire to allow visitors the greatest amount of access to park lands, provided that eagle nesting-site occupancy is maintained at a level determined to be acceptable by the managers themselves. As these two management objectives are potentially at odds, we treat minimum desired occupancy level as a utility threshold which, then, serves to guide the selection of annual management alternatives in the decision process. As human disturbance is not the only factor influencing eagle occupancy, we model nesting-site dynamics as a function of both disturbance and prey availability. We incorporate uncertainty in these dynamics by considering several hypotheses, including a hypothesis that site occupancy is affected only at a threshold level of prey abundance (i.e., an ecological threshold effect). By considering competing management objectives and accounting for two forms of thresholds in the decision process, we are able to determine the optimal number of annual nesting-site restrictions that will produce the greatest long-term benefits for both eagles and humans. Setting a utility threshold of 75 occupied sites, out of a total of 90 potential nesting sites, the optimization specified a decision threshold at approximately 80 occupied sites. At the point that current occupancy falls below 80 sites, the recommended decision is to begin restricting access to humans; above this level, it is recommended that all eagle territories be opened to human recreation. We evaluated the sensitivity of the decision threshold to uncertainty in system dynamics and to management objectives (i.e., to the utility threshold).

Alaska↗
USGS2014

Applying threshold concepts to conservation management of dryland ecosystems: Case studies on the Colorado Plateau

Ecosystems may occupy functionally distinct alternative states, some of which are more or less desirable from a management standpoint. Transitions from state to state are usually associated with a particular trigger or sequence of triggers, such as the addition or subtraction of a disturbance. Transitions are often not linear, rather it is common to see an abrupt transition come about even though the trigger increases only incrementally; these are examples of threshold behaviors. An ideal monitoring program, such as the National Park Service’s Inventory and Monitoring Program, would quantify triggers, and be able to inform managers when measurements of a trigger are approaching a threshold so that management action can avoid an unwanted state transition. Unfortunately, both triggers and the threshold points at which state transitions occur are generally only partially known. Using case studies, we advance a general procedure to help identify triggers and estimate where threshold dynamics may occur. Our procedure is as follows: (1) Operationally define the ecosystem type being considered; we suggest that the ecological site concept of the Natural Resource Conservation Service is a useful system, (2) Using all available a priori knowledge to develop a state-and-transition model (STM), which defines possible ecosystem states, plausible transitions among them and likely triggers, (3) Validate the STM by verifying the existence of its states to the greatest degree possible, (4) Use the STM model to identify transitions and triggers likely to be detectable by a monitoring program, and estimate to the greatest degree possible the value of a measurable indicator of a trigger at the point that a state transition is imminent (tipping point), and values that may indicate when management intervention should be considered (assessment points). We illustrate two different methods for attaining these goals using a data-rich case study in Canyonlands National Park, and a data-poor case study in Wupatki National Monument. In the data-rich case, STMs are validated and revised, and tipping and assessment points are estimated using statistical analysis of data. In the data-poor case, we develop an iterative expert opinion survey approach to validate the degree of confidence in an STM, revise the model, identify lack of confidence in specific model components, and create reasonable first approximations of tipping and assessment points, which can later be refined when more data are available. Our goal should be to develop the best set of models possible given the level of information available to support decisions, which is often not much. The approach presented here offers a flexible means of achieving this goal, and determining specific research areas in need of study.

Book chapter↗
USGS2014

Using natural range of variation to set decision thresholds: a case study for great plains grasslands

Natural range of variation (NRV) may be used to establish decision thresholds or action assessment points when ecological thresholds are either unknown or do not exist for attributes of interest in a managed ecosystem. The process for estimating NRV involves identifying spatial and temporal scales that adequately capture the heterogeneity of the ecosystem; compiling data for the attributes of interest via study of historic records, analysis and interpretation of proxy records, modeling, space-for-time substitutions, or analysis of long-term monitoring data; and quantifying the NRV from those data. At least 19 National Park Service (NPS) units in North America’s Great Plains are monitoring plant species richness and evenness as indicators of vegetation integrity in native grasslands, but little information on natural, temporal variability of these indicators is available. In this case study, we use six long-term vegetation monitoring datasets to quantify the temporal variability of these attributes in reference conditions for a variety of Great Plains grassland types, and then illustrate the implications of using different NRVs based on these quantities for setting management decision thresholds. Temporal variability of richness (as measured by the coefficient of variation, CV) is fairly consistent across the wide variety of conditions occurring in Colorado shortgrass prairie to Minnesota tallgrass sand savanna (CV 0.20–0.45) and generally less than that of production at the same sites. Temporal variability of evenness spans a greater range of CV than richness, and it is greater than that of production in some sites but less in other sites. This natural temporal variability may mask undesirable changes in Great Plains grasslands vegetation. Consequently, we suggest that managers consider using a relatively narrow NRV (interquartile range of all richness or evenness values observed in reference conditions) for designating a surveillance threshold, at which greater attention to the situation would be paid, and a broader NRV for designating management thresholds, at which action would be instigated.

Book chapter↗
USGS2015

Managing the Mississippi River floodplain: Achieving ecological benefits requires more than hydrological connection to the river: Chapter

Floodplains are vital to the structure and function of river-floodplain ecosystems. Among the many ecological services provided by floodplains are nutrient cycling and seasonal habitats for fish, including spawning, nursery, foraging and wintering habitats. Connections between the river channel and floodplain habitats are essential to realize these ecological services, but spatial and temporal aspects of the connection and contemporary geomorphology must also be considered in restoration efforts. This chapter synthesizes available information to compare floodplain function and needed management strategies in two extensive reaches (upper impounded and lower free-flowing) of the Mississippi River, USA. The upper impounded reach is the 523-km reach from about Minneapolis, Minnesota to Clinton, Iowa. This reach has been impounded and channelized for navigation. Mean annual water-level fluctuation ranges from 1 to 2 m in the navigation pools in this reach. Floodplain environmental conditions that affect nitrogen cycling and fish production vary seasonally and longitudinally within and among navigation pools. Significant issues affecting ecological services include sedimentation, constrained water level fluctuations, island erosion and seasonal hypoxia. The lower free-flowing reach, the 1570-km reach from the confluence of the Ohio and Mississippi rivers to the Gulf of Mexico, has no dams and average annual fluctuations of 7 m throughout most of the reach. Despite the substantial flood pulse, floodplain inundation is often brief and may not occur annually. Significant issues affecting floodplain ecological function are the short duration and thermal asynchrony of the flood pulse, sedimentation and loss of connection between the river channel and permanent/semi-permanent floodplain water bodies due to channel incision. Needs and strategies for floodplain enhancement to increase ecological services, particularly nitrogen cycling and fish production, differ along the longitudinal gradient of the Mississippi River and provide informative contrasts to guide floodplain management. Prediction of the effects of climate change on this system will be complicated by the magnitude of the watershed that encompasses 41 % of the continental USA and multiple climatic regions.

Mississippi River floodplain↗
USGS2015

The role of floodplain restoration in mitigating flood risk, Lower Missouri River, USA

Recent extreme floods on the Lower Missouri River have reinvigorated public policy debate about the potential role of floodplain restoration in decreasing costs of floods and possibly increasing other ecosystem service benefits. The first step to addressing the benefits of floodplain restoration is to understand the interactions of flow, floodplain morphology, and land cover that together determine the biophysical capacity of the floodplain. In this article we address interactions between ecological restoration of floodplains and flood-risk reduction at 3 scales. At the scale of the Lower Missouri River corridor (1300 km) floodplain elevation datasets and flow models provide first-order calculations of the potential for Missouri River floodplains to store floods of varying magnitude and duration. At this same scale assessment of floodplain sand deposition from the 2011 Missouri River flood indicates the magnitude of flood damage that could potentially be limited by floodplain restoration. At the segment scale (85 km), 1-dimensional hydraulic modeling predicts substantial stage reductions with increasing area of floodplain restoration; mean stage reductions range from 0.12 to 0.66 m. This analysis also indicates that channel widening may contribute substantially to stage reductions as part of a comprehensive strategy to restore floodplain and channel habitats. Unsteady 1-dimensional flow modeling of restoration scenarios at this scale indicates that attenuation of peak discharges of an observed hydrograph from May 2007, of similar magnitude to a 10 % annual exceedance probability flood, would be minimal, ranging from 0.04 % (with 16 % floodplain restoration) to 0.13 % (with 100 % restoration). At the reach scale (15–20 km) 2-dimensional hydraulic models of alternative levee setbacks and floodplain roughness indicate complex processes and patterns of flooding including substantial variation in stage reductions across floodplains depending on topographic complexity and hydraulic roughness. Detailed flow patterns captured in the 2-dimensional model indicate that most floodplain storage occurs on the rising limb of the flood as water flows into floodplain bottoms from downstream; at a later time during the rising limb this pattern is reversed and the entire bottom conveys discharge down the valley. These results indicate that flood-risk reduction by attenuation is likely to be small on a large river like the Missouri and design strategies to optimize attenuation and ecological restoration should focus on frequent floods (20–50 % annual exceedance probability). Local stage reductions are a more certain benefit of floodplain restoration but local effects are highly dependent on magnitude of flood discharge and how floodplain vegetation communities contribute to hydraulic roughness. The most certain flood risk reduction benefit of floodplain restoration is avoidance of flood damages to crops and infrastructure.

Iowa, Kansas, Minnesota, Missouri, Nebraska, South↗
USGS2016

Expert elicitation of population-level effects of disturbance

Expert elicitation is a rigorous method for synthesizing expert knowledge to inform decision making and is reliable and practical when field data are limited. We evaluated the feasibility of applying expert elicitation to estimate population-level effects of disturbance on marine mammals. Diverse experts estimated parameters related to mortality and sublethal injury of North Atlantic right whales ( Eubalaena glacialis ). We are now eliciting expert knowledge on the movement of right whales among geographic regions to parameterize a spatial model of health. Expert elicitation complements methods such as simulation models or extrapolations from other species, sometimes with greater accuracy and less uncertainty.

Book chapter↗
USGS2018

Sediment erosion and delivery from Toutle River basin after the 1980 eruption of Mount St. Helens: A 30-year perspective

Exceptional sediment yields persist in Toutle River valley more than 30 years after the major 1980 eruption of Mount St. Helens. Differencing of decadal-scale digital elevation models shows the elevated load comes largely from persistent lateral channel erosion across the debris-avalanche deposit. Since the mid-1980s, rates of channel-bed-elevation change have diminished, and magnitudes of lateral erosion have outpaced those of channel incision. A digital elevation model of difference from 1999 to 2009 shows erosion across the debris-avalanche deposit is more spatially distributed compared to a model from 1987 to 1999, in which erosion was strongly focused along specific reaches of the channel.

Book chapter↗
USGS2018

Geomorphic response of the Muddy River Basin to the 1980 eruptions of Mount St. Helens, 1980–2000

The 18 May 1980 eruption of Mount St. Helens produced a mosaic of primary landscape disturbances that decreased in intensity with distance from the volcano across the headwaters of Muddy River and its tributaries. Subsequent geomorphic responses were influenced by evolving hillslope and channel conditions that affected fluxes of water, sediment, and wood, as well as by an exceptional storm in February 1996. Sediment fluxes have generally decreased, but downed wood in channels remains episodically mobile. Geomorphic change and biotic activity in the basin continue to interact in terrestrial, riparian, and aquatic ecosystems and in many cases diversify ecosystem conditions.

Washington↗