Geology topics

Seth J. Wenger

Publications and source records attributed to Seth J. Wenger.

At least 19 recordsLinked to original sources

USGS2024

How low is too low? Partnering with stakeholders and managers to define ecologically based low-flow thresholds in a perennial temperate river

Managing aquatic ecosystems for people and nature can be improved by collaboration among scientists, managers, decision-makers, and other stakeholders. Many collaborative and interdisciplinary approaches have been developed to address the management of freshwater ecosystems; however, there are still barriers to overcome. We worked as part of a regional stakeholder group comprising municipal water utility operators, conservation organizations, academic partners, and other stakeholders to understand the effects of low-flow and drought on ecological functions of the upper Flint River, Georgia (USA), a free-flowing river important for municipal water supply, recreation, and native biota. We used published literature and locally targeted studies to identify quantitative flow targets that could be used to inform water management and drought planning. Drawing from principles of Translational Ecology, we relied on an iterative process to develop information needs for the group and maintained communication and engagement throughout data collection, analysis, and synthesis. We identified three quantitative flow benchmarks to evaluate the ecological impacts of drought in the river. The results were valuable to both the water utilities represented in the working group and State regional water planning, which is used to guide water management strategies and permitting for the basin. We identified principles that were important for the successful engagement in the working group and helped to overcome the challenge of working across sectors and without direct authority guiding the implementation of our work. Interdisciplinary work and creative solutions are crucial to plan for and adapt to greater pressure on our water resources.

River Research and Applications↗

USGS2024

Life-history connections to long-term fish population trends in a species-rich temperate river

Fishes exhibit a diverse range of traits encompassing life-history strategies, feeding behaviours and spawning behaviours. These traits mediate fish population responses to changing environmental conditions such as those caused by anthropogenic stressors. The Conasauga River, located in northwestern Georgia and southeastern Tennessee, USA, hosts a diverse assemblage of over 75 species of freshwater fish, some of which are locally or regionally endemic, and many of which are imperilled. Annual monitoring data have shown population declines in multiple fish species of conservation concern in the Conasauga River since at least the 1990s, raising the possibility that other taxa could be declining as well. We quantified temporal changes in fish communities at six shoal sites sampled annually in most years from 1996 to 2022, and asked whether species traits hypothesized to underlie population vulnerability to environmental alteration were correlated with species-specific trends for 32 taxa. We estimated that total counts of fish in annual samples declined by ~2% per year, although declines were uneven among species and generally greater for less abundant taxa. Tests for species traits corresponding to temporal population trends provided evidence that crevice-spawning minnows and smaller-bodied taxa had steeper declines compared with broadcast spawners and larger, longer-lived, more fecund taxa. Lower abundance, reliance on a particular habitat feature, and life-history traits that may limit population resilience to disturbance may all prove useful for identifying riverine fishes at particular risk of future population decline.

Georgia↗

USGS2024

Elemental composition and potential toxicity of the riverine macrophyte Podostemum ceratophyllum Michx. reflects land use in eastern North America

Land use influences surface water quality, often alleviating stoichiometric constraints on primary production and altering biogeochemical cycling. However, land use effects on nutrient content and potential trace metal accumulation in aquatic plants remain unclear, and high concentrations of metals and altered nutrient ratios could impact the health of herbivores and detritivores. We tested for land use effects on nutrient and trace metal accumulation in a widespread riverine macrophyte, Podostemum ceratophyllum , collected from 91 locations from Georgia to Maine, USA in 2014–2016. We quantified carbon (C), nitrogen (N), phosphorus (P), their molar and mass ratios, N and C stable isotopes, and 17 additional elements in dried plants collected from each location to estimate relationships between plant tissue content and watershed land use, which we quantified as agriculture, forest, and development. Decreasing forest cover was correlated with increasing δ 15 N, Mg, Mn, and P in Podostemum tissue. Increasing urban development was correlated with increasing δ 15 N, Mg and P, while increasing agriculture was correlated with a decrease in C: P and the concentrations of multiple metals, along with increases in P, Mg and δ 15 N. Decreases in ratios of N: P and C:P with increasing agriculture and urban development in the watershed indicate more rapid P storage relative to C and N in plant tissue, and increased resource quality of the plant to consumers in these watersheds. We also observed potentially toxic dietary concentrations of some trace metals (B, Cd, Tl, Zn) in plant tissue which could be related to the plant's natural herbivory defense system or to land use. We conclude that land use influences the elemental composition of P. ceratophyllum , and potentially the quality and toxicity of the plant to herbivores and detritivores in eastern North American rivers.

Science of the Total Environment↗

USGS2023

Patterns, drivers, and a predictive model of dam removal cost in the United States

Given the burgeoning dam removal movement and the large number of dams approaching obsolescence in the United States, cost estimating data and tools are needed for dam removal prioritization, planning, and execution. We used the list of removed dams compiled by American Rivers to search for publicly available reported costs for dam removal projects. Total cost information could include component costs related to project planning, dam deconstruction, monitoring, and several categories of mitigation activities. We compiled reported costs from 455 unique sources for 668 dams removed in the United States from 1965 to 2020. The dam removals occurred within 571 unique projects involving 1–18 dams. When adjusted for inflation into 2020 USD, cost of these projects totaled \$1.522 billion, with per-dam costs ranging from $1 thousand (k) to \$268.8 million (M). The median cost for dam removals was \$157k, \$823k, and \$6.2M for dams that were< 5 m, between 5–10 m, and > 10 m in height, respectively. Geographic differences in total costs showed that northern states in general, and the Pacific Northwest in particular, spent the most on dam removal. The Midwest and the Northeast spent proportionally more on removal of dams less than 5 m in height, whereas the Northwest and Southwest spent the most on larger dam removals > 10 m tall. We used stochastic gradient boosting with quantile regression to model dam removal cost against potential predictor variables including dam characteristics (dam height and material), hydrography (average annual discharge and drainage area), project complexity (inferred from construction and sediment management, mitigation, and post-removal cost drivers), and geographic region. Dam height, annual average discharge at the dam site, and project complexity were the predominant drivers of removal cost. The final model had an R 2 of 57% and when applied to a test dataset model predictions had a root mean squared error of $5.09M and a mean absolute error of \$1.45M, indicating its potential utility to predict estimated costs of dam removal. We developed a R shiny application for estimating dam removal costs using customized model inputs for exploratory analyses and potential dam removal planning.

Frontiers in Ecology and Evolution↗

USGS2023

Stream restoration produces transitory, not permanent, changes to fish assemblages at compensatory mitigation sites

There is inconsistent evidence that stream restoration projects lead to recovery of ecosystem attributes, especially stream biota. While some assessments have documented desired changes in fish community metrics in the first years following restoration, longer-term studies have not always corroborated these findings. In this study, we used data and monitoring reports submitted to federal regulators by stream mitigation consultants to examine whether in-stream restoration activities led to changes in fish community attributes at 23 compensatory mitigation projects representing 53 sampling sites in Georgia, United States over 7 years of post-restoration monitoring. Modeling results indicated that abundance and species richness of fishes generally increased in the first years after restoration before decreasing to baseline levels by the seventh year. This pattern was consistent for models considering sensitive fish taxa, as well as at sites across a range of agricultural and forested land cover percentages. However, the effect of restoration on species richness was dampened in larger streams and at more urbanized locations. A community trajectory analysis supported the findings that fish community change was transitory at most sites. Remote estimation of canopy cover change at restoration sites suggested that the hump-shaped response may be driven by increased light availability during the immediate-post restoration period, followed by subsequent re-shading of stream channels by riparian plantings. Our analysis indicates that reach-level manipulation of streams should not be expected to induce long-term changes in fish communities, and that publicly available monitoring reports may be leveraged to address questions of stream restoration efficacy.

Restoration Ecology↗

USGS2023

Persistence of native riverine fishes downstream from two hydropower dams with contrasting operations

Identifying hydropower dam operations that lessen detrimental effects on downstream fauna could inform conservation strategies for native fishes. We compared occurrence of native fishes in 20 shoal habitats downstream from two differently operated hydropower dams in the Coosa River system, Georgia, USA. Species richness averaged 7 and 11, respectively, in surveys downstream from (1) a hydropeaking dam and (2) a dam with a re-regulation structure that stabilized downstream flows. In contrast, surveys in two nearby reference communities averaged 19 and 24 species. Species persisting downstream from the dams tended toward water-column orientation, larger body size, longer life-span, and greater prevalence in tributary stream collections, compared with missing or rarely captured species. We observed no evidence of recovery toward reference conditions when operations were paused for 28 months at the hydropeaking dam. Our observations suggest that (1) strongly contrasting dam operations can result in similar alterations to native fish assemblages, potentially reflecting effects of thermal alteration by hypolimnetic water release, and (2) periodic dispersal from tributary streams may enhance fish persistence in flow-altered rivers.

Canadian Journal of Fisheries and Aquatic Sciences↗

USGS2022

Habitat associations of riverine fishes among rocky shoals

Understanding species' associations with physical habitat conditions is a fundamental goal of ecology. For organisms that occupy lotic ecosystems, relationships to streamflow are of particular importance, but these associations are unstudied for most species. We tested the predictability of fish–microhabitat relationships in river shoals (shallow, rocky areas with relatively swift water flow) using a large data set from the Conasauga River in Georgia, USA. Our objective was to assess the consistency of species-specific relationships with flow-dependent variables (depth, velocity, Reynolds number and Froude number) while accounting for other microhabitat variables (e.g. vegetation). We used data from 8285 seine-sets collected during late summer or autumn at 26 sites over 12 years to relate occurrence and counts of 22 fish species to habitat variables using generalised linear multiple regression models. Results showed that microhabitat models explained a substantial amount of the variation in counts for some species, although other species were poorly predicted. We classified 16 species as velocity specialists and nine species as depth specialists, with six species specialised for depth and velocity and three species classified as depth and velocity generalists. The variability in habitat associations that we observed suggests that species will be unevenly affected by anthropogenic activities that alter flows.

Georgia↗

USGS2022

Seasonal variability in macroinvertebrate assemblages in paired perennial and intermittent streams in Costa Rica

Ecological effects of flooding and drying events are relatively understudied in the Neotropics and less is known about these hydrological extremes in intermittent streams. Neotropical headwater streams in Costa Rica provide opportunities to evaluate the response of macroinvertebrate communities to seasonal changes in flow regime in relatively human undisturbed systems. We quantified the effects of seasonal flow variation on aquatic macroinvertebrate assemblages (i.e., density, richness, and functional traits) within two headwater streams with differing hydrological regimes (i.e., intermittent versus perennial), in the Pacific North of Costa Rica. We sampled macroinvertebrates monthly over a year in riffle and pool habitats. Non-metric multidimensional scaling (NMDS) analyses indicated differences in macroinvertebrate taxonomic richness and density between the two streams and riffle and pool habitats. We found that macroinvertebrates in the intermittent stream riffles had significantly higher richness during the dry season. We also found higher macroinvertebrate functional trait richness in the intermittent stream riffle habitats during the dry season. Our results may be explained by life history traits related to stream velocity preference or tolerance, short life cycles that limit exposure to disturbances, and dispersal capacities and feeding mechanisms that are dependent on water movement.

Hydrobiologia↗

USGS2022

Simple statistical models can be sufficient for testing hypotheses with population time series data

Time-series data offer wide-ranging opportunities to test hypotheses about the physical and biological factors that influence species abundances. Although sophisticated models have been developed and applied to analyze abundance time series, they require information about species detectability that is often unavailable. We propose that in many cases, simpler models are adequate for testing hypotheses. We consider three relatively simple regression models for time series, using simulated and empirical (fish and mammal) datasets. Model A is a conventional generalized linear model of abundance, model B adds a temporal autoregressive term, and model C uses an estimate of population growth rate as a response variable, with the option of including a term for density dependence. All models can be fit using Bayesian and non-Bayesian methods. Simulation results demonstrated that model C tended to have greater support for long-lived, lower-fecundity organisms (K life-history strategists), while model A, the simplest, tended to be supported for shorter-lived, high-fecundity organisms (r life-history strategists). Analysis of real-world fish and mammal datasets found that models A, B, and C each enjoyed support for at least some species, but sometimes yielded different insights. In particular, model C indicated effects of predictor variables that were not evident in analyses with models A and B. Bayesian and frequentist models yielded similar parameter estimates and performance. We conclude that relatively simple models are useful for testing hypotheses about the factors that influence abundance in time-series data, and can be appropriate choices for datasets that lack the information needed to fit more complicated models. When feasible, we advise fitting datasets with multiple models because they can provide complementary information.

Ecology and Evolution↗

USGS2022

Toward improved prediction of streamflow effects on freshwater fishes

Understanding the effects of hydrology on fish populations is essential to managing for native fish conservation. However, despite decades of research illustrating streamflow influences on fish habitat, reproduction and survival, biologists remain challenged when tasked with predicting how fish populations will respond to changes in flow regimes. This uncertainty stems from insufficient understanding of the context-dependent mechanisms underlying fish responses to, for example, periods of reduced flow or altered frequency of high-flow events. We aim to address this gap by drawing on previous research to hypothesize mechanisms by which low- and high-flows influence fish populations and communities, identifying challenges that stem from data limitations and ecological complexity, and outlining research directions that can advance an empirical basis for prediction. Focusing flow-ecology research on testing and refining mechanistic hypotheses can help narrow management uncertainties and better support species conservation in changing flow regimes.

Fisheries Magazine↗

USGS2022

Community-powered urban stream restoration: A vision for sustainable and resilient urban ecosystems

Urban streams can provide amenities to people living in cities, but those benefits are reduced when streams become degraded, potentially even causing harm (disease, toxic compounds, etc.). Governments and institutions invest resources to improve the values and services provided by urban streams; however, the conception, development, and implementation of such projects may not include meaningful involvement of community members and other stakeholders. Consequently, project objectives may be misaligned with community desires and needs, and projects may fail to achieve their goals. In February 2020, the 5 th Symposium on Urbanization and Stream Ecology, an interdisciplinary meeting held every 3 to 5 y, met in Austin, Texas, USA, to explore new approaches to urban stream projects, including ways to maximize the full range of potential benefits by better integrating community members into project identification and decision making. The symposium included in-depth discussion about 4 nearby field case studies, participation of multidisciplinary urban stream experts from 5 continents, and input from the Austin community. Institutional barriers to community inclusion were identified and analyzed using real-world examples, both from the case studies and from the literature, which clarified disparities in power, equity, and values. Outcomes of the symposium have been aggregated into a vision that challenges the present institutional approach to urban stream management and a set of strategies to systematically address these barriers to improve restoration solutions. Integrating community members and other stakeholders throughout the urban restoration process, and a transparent decision-making process to resolve divergent objectives, can help identify appropriate goals for realizing both the ecological and social benefits of stream restoration.

Texas↗

USGS2021

Slow recovery of headwater-stream fishes following a catastrophic poisoning event

Accidental spills of chemicals and other pollutants can decimate populations of stream-dwelling species. Recovery from such accidents can be relatively fast and complete when the affected stream reaches can be recolonized from upstream and downstream sources. However, faunal recoveries from accidental spills that extirpate populations from entire headwater streams have not been extensively documented, and understanding resilience of headwater-stream biota is relevant for assessing threats to at-risk species. We assessed recovery of fish populations in a 5.7-km long headwater stream in the southeastern United States following a complete, or nearly complete, fish-kill caused by a chemical spill near the source of the stream. We sampled for fishes at five stream locations, two downstream and three upstream from a perched, culverted road-crossing located 2.4 km upstream from the stream mouth, over a period of 18.5 months following the poisoning event. We observed 11 fish species, representing <65% of the fish species expected based on occurrences in nearby tributary streams. In post-poisoning sampling, only three of these taxa were observed upstream of the culvert; all 11 species, including the federally threatened Cherokee Darter Etheostoma scotti, were found downstream of the culvert but were mostly represented by a few, large individuals. In contrast, dead individuals of at least eight taxa including the Cherokee Darter were observed upstream of the culvert at the time of the fish-kill. These observations provide evidence of slow recovery of a headwater fish fauna, and especially upstream of a barrier to fish movement, where the recolonization sources are primarily downstream. Additional case studies may reveal whether this result applies generally to headwater streams. Slow recovery could make species that primarily inhabit or maintain greatest abundances in headwaters, including multiple at-risk fishes, particularly vulnerable to the threat of accidental spills that result in local population extirpation.

Journal of Fish and Wildlife Management↗

USGS2021

Do crayfish affect stream ecosystem response to riparian vegetation removal?

1. Riparian vegetation management alters stream basal resources, but stream ecosystem responses partly depend on top-down interactions with in-stream consumers. Large-bodied omnivores can exert particularly strong influences on stream benthic environments through consumption of food resources and physical disturbance of the benthos. Trophic dynamics studies conducted within the context of reach-scale riparian vegetation manipulations can provide insights into the interactions and relative importance of top-down and bottom-up controls that determine ecosystem response to riparian change. 2. Here, we examine how top-down control by crayfish omnivores (Cambarus spp.) interacts with abiotic conditions created by reach-scale removal of riparian rhododendron (Rhododendron maximum) in the southern Appalachian Mountains. We conducted 32-day trophic experiments by nesting 5 pairs of electrified (crayfish excluded) and non-electrified (crayfish access) plots within each of two 300-m stream reaches (one control and one rhododendron-removed) for one year pre-removal and two years post-removal. 3. Algal growth only responded positively to the reduced canopy cover (post-rhododendron removal) under low flow conditions and in the absence of top-down control by crayfish during the post-treatment year 2. Leaf decomposition rates were reduced by ~40% in the absence of crayfish, but higher inputs of rhododendron leaf litter during the summer following rhododendron removal reduced the effect of crayfish presence on decomposition. Riparian rhododendron removal also significantly increased benthic sediment and fine benthic organic matter, but macroconsumer exclusion did not affect these stream properties. 4. Potential long-term reductions in crayfish abundance could reduce the top-down effects of crayfish and ultimately lead to higher algal growth and reduced leaf decomposition rates in streams where rhododendron is managed through removal.

North Carolina↗

USGS2021

Mixed evidence for biotic homogenization of southern Appalachian fish communities

Anthropogenic impacts on the landscape can drive biotic homogenization, whereby distinct biological communities become more similar to one another over time. Land-use change in the Southern Appalachian region is expected to result in homogenization of the highly diverse freshwater fish communities as in-stream habitat alterations favor widespread cosmopolitan species at the expense of more narrowly distributed highland endemic species. We compiled four datasets spanning 25 years to (1) evaluate the effects of environmental factors on relative abundance and richness of highland endemic vs. cosmopolitan species in this region and (2) test for taxonomic homogenization, measured as a change in beta diversity over time. We found that several environmental factors differentially affected highland endemic and cosmopolitan species, with the proportion of forested land cover in a watershed most strongly predicting higher relative abundance and richness of highland endemic species. Our analysis of beta diversity change, however, shows mixed evidence of taxonomic homogenization, depending on how common species are weighted. Shifts in community composition, with or without homogenization, may warrant attention in biodiversity conservation planning.

Georgia, North Carolina↗

USGS2020

Freshwater crabs (Decapoda: Pseudothelphusidae) increase rates of leaf breakdown in a neotropical headwater stream

Freshwater crabs are the largest macroconsumers in many neotropical headwater streams, but few studies have examined their roles in ecosystem processes such as leaf litter breakdown. As omnivorous macroconsumers, freshwater crabs affect multiple trophic levels. They may directly increase leaf breakdown through fragmentation and consumption or indirectly decrease breakdown by consuming other macroinvertebrates, including shredders and detritivores. In a headwater stream in Monteverde, Costa Rica, we conducted an in‐stream experiment with 40 enclosures to quantify the effects of pseudothelphusid crabs on both leaf breakdown and macroinvertebrate colonisation of leaves. Half of the enclosures were randomly selected to contain two crabs (mean carapace width = 30 mm) and half were controls without crabs. We sampled mixed leaf packs from the enclosures on days 11, 19, 28, 34, and 42. We found the leaves of one species ( Koanophyllon pittieri ) almost completely decomposed by day 28 in both treatments (crab versus no crab). The other two leaf species ( Meliosma idiopoda , Quercus brenesii ) composed the remaining leaf mass at the end of the experiment. At 42 days, enclosures with crabs had faster rates of leaf breakdown than those without crabs (with crabs: k = −0.020; without crabs: k = −0.016; p = 0.034). This suggests that the magnitude of direct leaf breakdown by crabs, due to fragmentation, consumption, or manipulation of leaves, was greater than any indirect effects on leaf breakdown via crab consumption of other leaf‐consuming species. Macroinvertebrate composition based on taxa abundances or biomasses did not significantly differ between treatments (ANOSIM; p = 0.73 and p = 0.65, respectively). Shredder and detritivore abundances and biomasses increased significantly through time (ANOVA; p ≤ 0.001), but there was no evidence of an effect of crab presence ( p > 0.2), nor were there significant interactions between crab presence and time ( p > 0.3). This is one of the first studies to quantify the effects of pseudothelphusid freshwater crabs on leaf breakdown rates. Our results suggest that these crabs can play a significant role in detrital processing in neotropical headwater streams. This study has also demonstrated that short‐term enclosure experiments are useful in measuring in‐stream effects of crab activity on leaf breakdown.

Quebrada Máquina↗

USGS2020

Incorporating spatial synchrony in the status assessment of a threatened species with multivariate analysis

Spatial synchrony—correlated abundance fluctuations among distinct populations—is associated with increased extinction risk but is not a component of widely-used extinction risk assessments (e.g., IUCN Red List, U.S. Fish and Wildlife Service’s Species Status Assessment). Alongside traditional viability metrics (i.e., the number of populations, their spatial extent, the status of each population), consideration of spatial synchrony in these assessments may provide additional insight into extinction risk as well as the relative importance of intrinsic and extrinsic factors on population dynamics. We demonstrate a method for estimating abundance trends in populations of the endangered freshwater fish, the amber darter (Percina antesella), while simultaneously assessing support for spatial synchrony among its two populations in the Conasauga and Etowah rivers in Georgia, U.S.A. Our analysis was performed using multivariate autoregressive state-space (MARSS) models with annual sampling data from 1996-2018 at 16 sites distributed between the two populations. Our results indicate that amber darter populations have declined substantially, with 9% annual losses in both the Conasauga and Etowah rivers, suggesting rangewide imperilment. Furthermore, model selection indicated little support for models with independent dynamics between rivers, which may compound overall extinction risk. This analysis demonstrates the utility of tools such as MARSS models for assessing spatial synchrony and long-term population trajectories of imperiled species, resulting in improved vulnerability assessments that do not assume independence among separate populations.

Georgia↗

USGS2020

Rethinking foundation species in a changing world: The case for Rhododendron maximum as an emerging foundation species in shifting ecosystems of the southern Appalachians

“Foundation species” are widespread, abundant species that play critical roles in structuring ecosystem characteristics and processes. Ecosystem change in response to human activities, climate change, disease introduction, or other environmental conditions may promote the emergence of new foundation species or the decline of previously important foundation species. We present rhododendron ( Rhododendron maximum ) as an example of an emerging foundation species in riparian forest and headwater stream ecosystems of the southern Appalachian Mountains and use its example to propose a dynamic approach to recognizing foundation species. As other species have declined, rhododendron has increased in abundance, biomass, and ecosystem importance, and now dominates the riparian zones and mesic uplands of much of the region. Rhododendron structures, stabilizes, and modulates functions within both terrestrial and aquatic ecosystems. Studies of forest ecosystem response to environmental conditions indicate that rhododendron may increase the resistance and resilience of its associated ecosystems to predicted anthropogenic stress, including climate change, nitrogen enrichment, and invasive species. A more dynamic conception of foundation species as dependent on ecosystem states will help ecologists to focus on ecosystem processes and services, rather than on historically dominant species, for restoration strategies.

Alabama, Georgia, North Carolina, South Carolina, ↗

USGS2019

Application of multiple-population viability analysis to evaluate species recovery alternatives

Population viability analysis (PVA) is a powerful conservation tool, but one that remains unapproachable for many species. This is particularly true for species with multiple, broadly-distributed populations for which collecting suitable data can be challenging. A recently-developed method of multiple population viability analysis (MPVA), however, addresses many limitations of traditional PVA. We build on previous development of MPVA for Lahontan cutthroat trout (LCT), a species listed under the US Endangered Species Act which is distributed broadly across habitat fragments in the Great Basin, USA. We simulated potential management scenarios and assessed their effects on population sizes and extinction risks in 211 streams where LCT exist or may be reintroduced.

Conservation Biology↗