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USGS2019

Spatial sampling bias and model complexity in stream-based species distribution models: A case study of Paddlefish (Polyodon spathula) in the Arkansas River basin, USA

Leveraging existing presence records and geospatial datasets, species distribution modeling has been widely applied to informing species conservation and restoration efforts. Maxent is one of the most popular modeling algorithms, yet recent research has demonstrated Maxent models are vulnerable to prediction errors related to spatial sampling bias and model complexity. Despite elevated rates of biodiversity imperilment in stream ecosystems, the application of Maxent models to stream networks has lagged, as has the availability of tools to address potential sources of error and calculate model evaluation metrics when modeling in nonraster environments (such as stream networks). Herein, we use Maxent and customized R code to estimate the potential distribution of paddlefish ( Polyodon spathula ) at a stream-segment level within the Arkansas River basin, USA, while accounting for potential spatial sampling bias and model complexity. Filtering the presence data appeared to adequately remove an eastward, large-river sampling bias that was evident within the unfiltered presence dataset. In particular, our novel riverscape filter provided a repeatable means of obtaining a relatively even coverage of presence data among watersheds and streams of varying sizes. The greatest differences in estimated distributions were observed among models constructed with default versus AIC C -selected parameterization. Although all models had similarly high performance and evaluation metrics, the AIC C -selected models were more inclusive of westward-situated and smaller, headwater streams. Overall, our results solidified the importance of accounting for model complexity and spatial sampling bias in SDMs constructed within stream networks and provided a roadmap for future paddlefish restoration efforts in the study area.

Arkansas, Colorado, Kansas, Missouri, Nebraska, Ne↗

USGS2017

Genomics of Arctic cod

The Arctic cod (Boreogadus saida) is an abundant marine fish that plays a vital role in the marine food web. To better understand the population genetic structure and the role of natural selection acting on the maternally-inherited mitochondrial genome (mitogenome), a molecule often associated with adaptations to temperature, we analyzed genetic data collected from 11 biparentally-inherited nuclear microsatellite DNA loci and nucleotide sequence data from from the mitochondrial DNA (mtDNA) cytochrome b (cytb) gene and, for a subset of individuals, the entire mitogenome. In addition, due to potential of species misidentification with morphologically similar Polar cod (Arctogadus glacialis), we used ddRAD-Seq data to determine the level of divergence between species and identify species-specific markers. Based on the findings presented here, Arctic cod across the Pacific Arctic (Bering, Chukchi, and Beaufort Seas) comprise a single panmictic population with high genetic diversity compared to other gadids. High genetic diversity was indicated across all 13 protein-coding genes in the mitogenome. In addition, we found moderate levels of genetic diversity in the nuclear microsatellite loci, with highest diversity found in the Chukchi Sea. Our analyses of markers from both marker classes (nuclear microsatellite fragment data and mtDNA cytb sequence data) failed to uncover a signal of microgeographic genetic structure within Arctic cod across the three regions, within the Alaskan Beaufort Sea, or between near-shore or offshore habitats. Further, data from a subset of mitogenomes revealed no genetic differentiation between Bering, Chukchi, and Beaufort seas populations for Arctic cod, Saffron cod (Eleginus gracilis), or Walleye pollock (Gadus chalcogrammus). However, we uncovered significant differences in the distribution of microsatellite alleles between the southern Chukchi and central and eastern Beaufort Sea samples of Arctic cod. Finally, using ddRAD-Seq data, we identified species-specific markers and in conjunction with mitogenome data, identified an Arctic cod x Polar cod hybrid in western Canadian Beaufort Sea. Overall, the lack of genetic structure among Arctic cod within the Bering, Chukchi and Beaufort seas of Alaska is concordant with the absence of geographic barriers to dispersal and typical among marine fishes. Arctic cod may exhibit a genetic pattern of isolation-by-distance, whereby populations in closer geographic proximity are more genetically similar than more distant populations. As this signal is only found between our two fartherest localities, data from populations elsewhere in the species’ global range are needed to determine if this is a general characteristic. Further, tests for selection suggested a limited role for natural selection acting on the mitochondrial genome of Arctic cod, but do not exclude the possibility of selection on genes involved in nuclear-mitogenome interactions. Unlike previous genetic assessment of Arctic cod sampled from the Chukchi Sea, the high levels of genetic diversity found in Arctic cod assayed in this study, across regions, suggests that the species in the Beaufort and Chukchi seas does not suffer from low levels of genetic variation, at least at neutral genetic markers. The large census size of Arctic cod may allow this species to retain high levels of genetic diversity. In addition, we discovered the presence of hybridization between Arctic and Polar cod (although low in frequency). Hybridization is expected to occur when environmental changes modify species distributions that result in contact between species that were previously separated. In such cases, hybridization may be an evolutionary mechanism that promotes an increase in genetic diversity that may provide species occupying changing environments with locally-adapted genotypes and, therefore, phenotypes. Natural selection can only act on the standing genetic variation present within a population. Therefore, given its higher levels of genetic diversity in combination with a large population size, Arctic cod may be resilient to current and future environmental change, as high genetic diversity is expected to increase opportunities for positive selection to act on genetic variants beneficial in different environments, regardless of the source of that genetic variation.

OCS Study↗

USGS2025

Causal networks to inform decisions for ecological restoration

The release of contaminants into the environment can occur from anthropogenic activities, such as oil extraction and transportation, mining, and industrial processes. Remediation associated with reducing contaminant concentrations, and restoration that improves animals and supporting habitat, are often needed to restore ecosystems to their pre-release, baseline condition. We demonstrated the application of Bayesian Decision Networks (BDNs) with two Natural Resource Damage Assessment and Restoration (NRDAR) case studies. We use a stylized case study of riparian restoration following the remediation of a mine-impacted site to evaluate proposed restoration actions aimed at restoring Song Sparrow ( Melospiza melodia ) populations to baseline conditions. We then use a settled NRDAR case with implemented restoration in the Upper Arkansas River (UAR, Colorado, USA) to demonstrate the application of BDNs to evaluate and forecast restoration effectiveness for Brown Trout ( Salmo trutta ) (i.e., restoration effectiveness assessment). The riparian restoration model showed differences in the effects of restoration actions on Song Sparrow populations, with the time to reach baseline generally reduced with increased restoration costs, indicating trade-offs between costs and expected recovery. The UAR model showed recovery of Brown Trout populations (i.e., uplift) in response to improved instream habitat restoration, along with forecasted improvements. While the BDNs we developed were specific to two case studies, the structure is adaptable to a diversity of sites, resources, and actions. We suggest that causal network modeling can provide restoration practitioners with a decision advisory tool useful for a wide range of projects.

Environmental Management↗

USGS2008

Relationship between remotely-sensed vegetation indices, canopy attributes and plant physiological processes: What vegetation indices can and cannot tell us about the landscape

Vegetation indices (VIs) are among the oldest tools in remote sensing studies. Although many variations exist, most of them ratio the reflection of light in the red and NIR sections of the spectrum to separate the landscape into water, soil, and vegetation. Theoretical analyses and field studies have shown that VIs are near-linearly related to photosynthetically active radiation absorbed by a plant canopy, and therefore to light-dependent physiological processes, such as photosynthesis, occurring in the upper canopy. Practical studies have used time-series VIs to measure primary production and evapotranspiration, but these are limited in accuracy to that of the data used in ground truthing or calibrating the models used. VIs are also used to estimate a wide variety of other canopy attributes that are used in Soil-Vegetation-Atmosphere Transfer (SVAT), Surface Energy Balance (SEB), and Global Climate Models (GCM). These attributes include fractional vegetation cover, leaf area index, roughness lengths for turbulent transfer, emissivity and albedo. However, VIs often exhibit only moderate, non-linear relationships to these canopy attributes, compromising the accuracy of the models. We use case studies to illustrate the use and misuse of VIs, and argue for using VIs most simply as a measurement of canopy light absorption rather than as a surrogate for detailed features of canopy architecture. Used this way, VIs are compatible with “Big Leaf” SVAT and GCMs that assume that canopy carbon and moisture fluxes have the same relative response to the environment as any single leaf, simplifying the task of modeling complex landscapes.

Arizona↗

USGS2022

The silence of the clams: Forestry registered pesticides as multiple stressors on soft-shell clams

Contaminants are ubiquitous in the environment, often reaching aquatic systems. Combinations of forestry use pesticides have been detected in both water and aquatic organism tissue samples in coastal systems. Yet, most toxicological studies focus on the effects of these pesticides individually, at high doses, and over acute time periods, which, while key for establishing toxicity and safe limits, are rarely environmentally realistic. We examined chronic (90 days) exposure by the soft-shell clam, Mya arenaria , to environmentally relevant concentrations of four pesticides registered for use in forestry (atrazine, 5 μg/L; hexazinone, 0.3 μg/L; indaziflam, 5 μg/L; and bifenthrin, 1.5 μg/g organic carbon (OC)). Pesticides were tested individually and in combination, except bifenthrin, which was tested only in combination with the other three. We measured shell growth and condition index every 30 days, as well as feeding rates, mortality, and chemical concentrations in tissue from a subset of clams at the end of the experiment to measure contaminant uptake. Indaziflam caused a high mortality rate (max. 36%), followed by atrazine (max. 27%), both individually as well as in combination with other pesticides. Additionally, indaziflam concentrations in tissue (61.70–152.56 ng/g) were higher than those of atrazine (26.48–48.56 ng/g), despite equal dosing concentrations, indicating higher tissue accumulation. Furthermore, clams exposed to indaziflam and hexazinone experienced reduced condition index and clearance rates individually and in combination with other compounds; however, the two combined did not result in significant mortality. These two compounds, even at environmentally relevant concentrations, affected a non-target organism and, in the case of the herbicide indaziflam, accumulated in clam tissue and appeared more toxic than other tested pesticides. These findings underscore the need for more comprehensive studies combining multiple compounds at relevant concentrations to understand their impacts on aquatic ecosystems.

Science of the Total Environment↗

USGS2015

Sequential decision making in computational sustainability via adaptive submodularity

Many problems in computational sustainability require making a sequence of decisions in complex, uncertain environments. Such problems are generally notoriously difficult. In this article, we review the recently discovered notion of adaptive submodularity, an intuitive diminishing returns condition that generalizes the classical notion of submodular set functions to sequential decision problems. Problems exhibiting the adaptive submodularity property can be efficiently and provably near-optimally solved using simple myopic policies. We illustrate this concept in several case studies of interest in computational sustainability: First, we demonstrate how it can be used to efficiently plan for resolving uncertainty in adaptive management scenarios. Secondly, we show how it applies to dynamic conservation planning for protecting endangered species, a case study carried out in collaboration with the US Geological Survey and the US Fish and Wildlife Service.

AI Magazine↗

USGS2009

Thatcher Bay, Washington, Nearshore Restoration Assessment

The San Juan Archipelago, located at the confluence of the Puget Sound, the Straits of Juan de Fuca in Washington State, and the Straits of Georgia, British Columbia, Canada, provides essential nearshore habitat for diverse salmonid, forage fish, and bird populations. With 408 miles of coastline, the San Juan Islands provide a significant portion of the available nearshore habitat for the greater Puget Sound and are an essential part of the regional efforts to restore Puget Sound (Puget Sound Shared Strategy 2005). The nearshore areas of the San Juan Islands provide a critical link between the terrestrial and marine environments. For this reason the focus on restoration and conservation of nearshore habitat in the San Juan Islands is of paramount importance. Wood-waste was a common by-product of historical lumber-milling operations. To date, relatively little attention has been given to the impact of historical lumber-milling operations in the San Juan Archipelago. Thatcher Bay, on Blakely Island, located near the east edge of the archipelago, is presented here as a case study on the restoration potential for a wood-waste contaminated nearshore area. Case study components include (1) a brief discussion of the history of milling operations. (2) an estimate of the location and amount of the current distribution of wood-waste at the site, (3) a preliminary examination of the impacts of wood-waste on benthic flora and fauna at the site, and (4) the presentation of several restoration alternatives for the site. The history of milling activity in Thatcher Bay began in 1879 with the construction of a mill in the southeastern part of the bay. Milling activity continued for more than 60 years, until the mill closed in 1942. Currently, the primary evidence of the historical milling operations is the presence of approximately 5,000 yd3 of wood-waste contaminated sediments. The distribution and thickness of residual wood-waste at the site was determined by using sediment coring and GIS-based interpolation techniques. Additionally, pilot studies were conducted to characterize in place sediment redox, organic composition, and sulfide impacts to nearshore flora and fauna. We found that the presence of wood-waste in Thatcher Bay may alter the quality of the benthic habitat by contributing to elevated levels of total organic composition (TOC) of the sediment. Increased TOC favors anaerobic respiration in marine sediments, and sulfide, a toxic by-product of this process, was found at levels as high as 17.5 mg L-1 in Thatcher Bay. The Thatcher Bay sulfide levels are several orders of magnitude higher than those known to impact benthic invertebrates. Eelgrass, Zostera marina, located on the western margin of Thatcher Bay, was surveyed by using underwater video surveys. This baseline distribution will in part be used to measure the impact of any future remediation efforts. Additionally, the distribution and survey data can provide an estimate of propagule source for future colonization of restored sediment. Three restoration alternatives were considered, and a ranking matrix was developed to score each alternative against site-specific and regional criteria. The process identified the removal of wood-waste from a water-based platform as the preferred alternative. Our multidisciplinary investigation identified the location, thickness, and potential impacts of wood-waste that has persisted in the nearshore environment of Thatcher Bay since at least 1942. We also provide a process to efficiently evaluate alternatives to remediate the impact of this historical disturbance and to potentially contribute to an increase of nearshore diversity and productivity at this site. Elements of this approach could inform restoration planning at similarly impacted sites throughout the region.

Open-File Report↗

USGS2021

Comparing sample bias correction methods for species distribution modeling using virtual species

A key assumption in species distribution modeling (SDM) with presence‐background (PB) methods is that sampling of occurrence localities is unbiased and that any sampling bias is proportional to the background distribution of environmental covariates. This assumption is rarely met when SDM practitioners rely on federated museum records from natural history collections for geo‐located occurrences due to inherent sampling bias found in these collections. We use a simulation approach to explore the effectiveness of three methods developed to account for sampling bias in SDM with PB frameworks. Two of the methods rely on careful filtering of observation data—geographic thinning (G‐Filter) and environmental thinning (E‐Filter)—while a third, FactorBiasOut, creates selection weights for background data to bias locations toward areas where the observation dataset was sampled. While these methods have been assessed previously, evaluation has emphasized spatial predictions of habitat potential. Here, we dig deeper into the effectiveness of these methods by exploring how sampling bias not only affects predictions of habitat potential, but also our understanding of niche characteristics such as which explanatory variables and response curves best represent species–environment relationships. We simulate 100 virtual species ranging from generalist to specialist in their habitat preferences and introduce geographic and environmental bias at three intensity levels to measure the effectiveness of each correction method to (1) predict true probability of occurrence across a study area, (2) recover true species–environment relationships, and (3) identify true explanatory variables. We find that the FactorBiasOut most often showed the greatest improvement in recreating known distributions but did no better at correctly identifying environmental covariates or recreating species–environment relationships than G‐Filter or E‐Filter methods. Narrow niche species are most problematic for biased calibration datasets, such that correction methods can, in some cases, make predictions worse.

Ecosphere↗

USGS2019

A Bayesian life-cycle model to estimate escapement at maximum sustained yield in salmon based on limited information

Life-cycle models combine several strengths for estimating population parameters and biological reference points of harvested species and are particularly useful for those exhibiting distinct habitat shifts and experiencing contrasting environments. Unfortunately, time series data are often limited to counts of adult abundance and harvest. By incorporating data from other populations and by dynamically linking the life-history stages, Bayesian life-cycle models can be used to estimate stage-specific productivities and capacities as well as abundance of breeders that produce maximum sustained yield (MSY). Using coho salmon ( Oncorhynchus kisutch ) as our case study, we show that incorporating information on marine survival variability from nearby populations can improve model estimates and affect management parameters such as escapement at MSY. We further show that the expected long-term average yield of a fishery managed for a spawner escapement target that produces MSY strongly depends on the average marine survival. Our results illustrate the usefulness of incorporating information from other sources and highlight the importance of accounting for variation in marine survival when making inferences about the management of Pacific salmon.

Washington↗

USGS2010

Enumeration of viruses and prokaryotes in deep-sea sediments and cold seeps of the Gulf of Mexico

Little is known about the distribution and abundance of viruses in deep-sea cold-seep environments. Like hydrothermal vents, seeps support communities of macrofauna that are sustained by chemosynthetic bacteria. Sediments close to these communities are hypothesized to be more microbiologically active and therefore to host higher numbers of viruses than non-seep areas. Push cores were taken at five types of Gulf of Mexico habitats at water depths below 1000 m using a remotely operated vehicle (ROV). The habitats included non-seep reference sediment, brine seeps, a microbial mat, an urchin field, and a pogonophoran worm community. Samples were processed immediately for enumeration of viruses and prokaryotes without the addition of a preservative. Prokaryote counts were an order of magnitude lower in sediments directly in contact with macrofauna (urchins, pogonophorans) compared to all other samples (10 7 vs. 10 8 cells g -1 dry weight) and were highest in areas of elevated salinity (brine seeps). Viral-Like Particle (VLP) counts were lowest in the reference sediments and pogonophoran cores (10 8 VLP g -1 dry wt), higher in brine seeps (10 9 VLP g -1 dry wt), and highest in the microbial mats (10 10 VLP g -1 dry wt). Virus-prokaryote ratios (VPR) ranged from <5 in the reference sediment to >30 in the microbial mats and >60 in the urchin field. VLP counts and VPR were all significantly greater than those reported from sediments in the deep Mediterranean Sea and in most cases were higher than recent data from a cold-seep site near Japan. The high VPR suggest that greater microbial activity in or near cold-seep environments results in greater viral production and therefore higher numbers of viruses.

Gulf Of Mexico;Green Canyon;Atwater Valley;Alamino↗

USGS1979

Arctic stream processes--an annotated bibliography

This bibliography selectively summarizes investigations to date (1978) dealing with the physical processes of streams in the Arctic. The specialized annotations include aspects of stream processes described in subordinate parts of general papers on the arctic environment and therefore not evident in author-abstract bibliographies. Foreign contributions--Canadian, Scandinavian, and Russian--are summarized, in the case of Russian literature primarily by means of papers in translation journals. Until 1970 the role of streams in development of the arctic landscape was commonly considered subordinate to that of glacial and frost-related processes. This conclusion changed, however, with the findings of the many new studies begun in response to oil and gas discoveries in the late 1960's. The conclusions of these studies, made to provide both the engineering data for resource development and the information to assess the impacts of that development, were in general agreement that stream processes throughout most of the Arctic were significantly more important than previously had been thought.

Water Supply Paper↗

USGS2006

Integration of coral reef ecosystem process studies and remote sensing

Worldwide, local-scale anthropogenic stress combined with global climate change is driving shifts in the state of reef benthic communities from coral-rich to micro- or macroalgal-dominated (Knowlton, 1992; Done, 1999). Such phase shifts in reef benthic communities may be either abrupt or gradual, and case studies from diverse ocean basins demonstrate that recovery, while uncertain (Hughes, 1994), typically involves progression through successional stages (Done, 1992). These transitions in benthic community structure involve changes in community metabolism, and accordingly, the holistic evaluation of associated biogeochemical variables is of great intrinsic value (Done, 1992). Effective reef management requires advance prediction of coral reef alteration in the face of anthropogenic stress and change in the global environment (Hatcher, 1997a). In practice, this goal requires techniques that can rapidly discern, at an early stage, sublethal effects that may cause long-term increases in mortality (brown, 1988; Grigg and Dollar, 1990). Such methods would improve our understanding of the differences in the population, community, and ecosystem structure, as well as function, between pristine and degraded reefs. This knowledge base could then support scientifically based management strategies (Done, 1992). Brown (1988) noted the general lack of rigor in the assessment of stress on coral reefs and suggested that more quantitative approaches than currently exist are needed to allow objective understanding of coral reef dynamics. Sensitive techniques for the timely appraisal of pollution effects or generalized endemic stress in coral reefs are sorely lacking (Grigg and Dollar, 1990; Wilkinsin, 1992). Moreover, monitoring methods based on population inventories, sclerochronology, or reproductive biology tend to myopic and may give inconsistent results. Ideally, an improved means of evaluating reef stress would discriminate mortality due to natural causes from morality to anthropogenic causes (Brown, 1988). Models of coral reef ecosystems, parameterized by process measurements and scaled in time-space using remote sensing, have the potential to address pressing research questions that are central to devising valid management strategies (Grigg el al., 1984; Hatcher, 1997b). To attain this goal, ecosystem-level models that integrate studies of physical and chemical forcing with observed biological and geological responses are required. This interdisciplinary approach to understanding reef biogeochemical dynamics can allow investigations that integrate the scales of time and space (Hatcher, 1997a), thereby enabling prediction of coral reef change (Andréfouët and Payri, 2001). In turn, prediction of holistic ecosystem function within various environmental focusing scenarios has substantial promise in mitigating future disturbance. Indeed, management of coral reefs at the ecosystem level has been suggested as the only meaningful approach to preserving coral reefs (Bohnsack and Ault, 1996; Christensen et al., 1996).

Florida↗

USGS2006

Historical record of Landsat global coverage

The long-term, 34+ year record of global Landsat remote sensing data is a critical resource to study the Earth system and human impacts on this system. The National Satellite Land Remote Sensing Data Archive (NSLRSDA) is charged by public law to: “maintain a permanent, comprehensive Government archive of global Landsat and other land remote sensing data for long-term monitoring and study of the changing global environment” (U.S. Congress, 1992). The advisory committee for NSLRSDA requested a detailed analysis of observation coverage within the U.S. Landsat holdings, as well as that acquired and held by International Cooperator (IC) stations. Our analyses, to date, have found gaps of varying magnitude in U.S. holdings of Landsat global coverage data, which appear to reflect technical or administrative variations in mission operations. In many cases it may be possible to partially fill these gaps in U.S. holdings through observations that were acquired and are now being held at International Cooperator stations.

Photogrammetric Engineering and Remote Sensing↗

USGS2024

Guidelines for the use of automatic samplers in collecting surface-water quality and sediment data

The importance of fluvial systems in the transport of sediment, dissolved and suspended contaminants, nutrients, and bacteria through the environment is well established. The U.S. Environmental Protection Agency (EPA) identifies sediment as the single most widespread water contaminant affecting the beneficial uses of the Nation’s rivers and streams. The evaluation of water-quality as it relates to agriculture, urbanization, highway and residential construction, mining, industrial and human wastes, and other activities requires an extensive data and sample-collection effort. This is especially the case when studying urbanized river basins, where during hydrologic events, concentration of suspended sediment and contaminants can vary rapidly and over large ranges. Where synoptic studies of watersheds are called for, sampling may be needed at many sites throughout the basin; a complicated and difficult task in some settings. Automatic pumping samplers (autosamplers) are one method for conducting intensive time-varying sampling throughout watersheds. This report presents guidelines for the use of autosamplers for collecting surface-water samples by the U.S. Geological Survey. An autosampler is an automatic, pump-based sampler that collects a prescribed volume of water from streams, lakes, reservoirs, storm drains, or other bodies of water after receiving a command from an internal or external control unit. It deposits this sample into a specified container for later analysis of physical, chemical, or biological constituents. This report provides a general background on types of autosamplers and how they work; guidance for designing, selecting, installing, servicing, and calibrating autosamplers; guidance on standardized operating procedures, and guidance on quality-assurance and quality-control efforts when using an autosampler.

Techniques and Methods↗

USGS2022

Value of information and decision pathways: Concepts and case studies

Information used in decision making arises from the structuring of observations and data. The collection, dissemination, and use of information has monetary and non-monetary costs (e.g., competition for attention) and necessitates trade-offs. Understanding the benefits of having information (i.e., the value of information, VOI), including resulting societal outcomes, is useful to information producers/funders and decision makers. Using theory, use cases, and hypotheticals, we describe how information (e.g., geospatial information) is valued and incorporated in decisions and actions related to managing natural resources, environments, and the impacts of natural and anthropogenic hazards. We discuss the nature of information and how it relates to models (conceptual, mental, scientific), beliefs, knowledge, and economic analyses. VOI approaches and behavioral factors that potentially affect information use and value are summarized. Framing of information and VOI through data to decision pathways (DDPs) at first simplifies understanding, then illustrates the benefits of information, and the human and societal challenges encountered in valuing and using it. We present approaches to overcome these challenges. Our transdisciplinary analysis concludes with a summary of critical issues affecting DDPs and VOI, and suggestions for improving both economic analyses and the actionability and use of information.

Frontiers in Environmental Science (Environmental ↗

USGS2017

The added value of time-variable microgravimetry to the understanding of how volcanoes work

During the past few decades, time-variable volcano gravimetry has shown great potential for imaging subsurface processes at active volcanoes (including some processes that might otherwise remain “hidden”), especially when combined with other methods (e.g., ground deformation, seismicity, and gas emissions). By supplying information on changes in the distribution of bulk mass over time, gravimetry can provide information regarding processes such as magma accumulation in void space, gas segregation at shallow depths, and mechanisms driving volcanic uplift and subsidence. Despite its potential, time-variable volcano gravimetry is an underexploited method, not widely adopted by volcano researchers or observatories. The cost of instrumentation and the difficulty in using it under harsh environmental conditions is a significant impediment to the exploitation of gravimetry at many volcanoes. In addition, retrieving useful information from gravity changes in noisy volcanic environments is a major challenge. While these difficulties are not trivial, neither are they insurmountable; indeed, creative efforts in a variety of volcanic settings highlight the value of time-variable gravimetry for understanding hazards as well as revealing fundamental insights into how volcanoes work. Building on previous work, we provide a comprehensive review of time-variable volcano gravimetry, including discussions of instrumentation, modeling and analysis techniques, and case studies that emphasize what can be learned from campaign, continuous, and hybrid gravity observations. We are hopeful that this exploration of time-variable volcano gravimetry will excite more scientists about the potential of the method, spurring further application, development, and innovation.

Earth-Science Reviews↗

USGS2026

Response of juvenile Chinook Salmon to an experimental reservoir operation to facilitate downstream migration

Objectives High-head dams and storage reservoirs impact ecological processes, impeding recovery efforts of Pacific salmon Oncorhynchus spp. in the western United States. These projects can delay migration, increase risks of predation and disease, and induce mortality for juvenile Pacific salmon during downstream passage. To mitigate these negative effects, large-scale changes to dam operations have been proposed as interim measures or alternatives to engineered fish passage solutions. A novel deep drawdown operation of the Lookout Point Project (two dams and reservoirs) in Oregon serves as a case study for learning from a large-scale management experiment. Beginning in July 2024, Lookout Point Reservoir was slowly lowered to attain minimal levels from mid-November to mid-December with the intent of expediting downstream passage through the project for juvenile Chinook Salmon Oncorhynchus tshawytscha . We evaluated the impacts of the months-long operation on two life histories of juvenile Chinook Salmon with different rearing environments and growth rates. Methods Acoustic telemetry was used to monitor juvenile Chinook Salmon in the Lookout Point Project. Environmental data, including water temperature and hydrological conditions, were collected. We fitted a time-integrated migration survival model to these data to estimate the effects of management-influenced covariates and fish length on apparent survival and residence time in each reach of the Lookout Point Project. Results Larger fish had higher survival than smaller fish in each reach of the Lookout Point Project. Apparent survival through each dam of the Lookout Point Project was highest and forebay residence times lowest during the latter part of the drawdown (late November). However, early periods of the drawdown (September) were associated with a transition from a thermally stratified reservoir to a warm isothermal reservoir that negatively impacted reservoir survival. Conclusions The deep drawdown of the Lookout Point Project achieved the management intent to improve downstream passage for juvenile Chinook Salmon at the lowest reservoir elevations but also caused unintended changes in the reservoir rearing environment prior to full drawdown. Further research could resolve remaining uncertainties regarding the overall effectiveness of drawdown operations with respect to the population dynamics of different juvenile life history strategies. Understanding these factors would help optimize future management actions aimed at Pacific salmon recovery above the Lookout Point Project.

Oregon↗

USGS1996

Fish egg injection as an alternative exposure route for early life stage toxicity studies: Description of two unique methods: Chapter 4

In the environment, lipophilic contaminants such as halogenated aromatic hydrocarbons (HAHs, e.g., polychlorinated biphenyls, PCBs) and polycyclic aromatic hydrocarbons (PAHs, e.g., benzo[a]pyrene) readily bioaccumulate in fish, and the bioaccumulation of these lipophilic chemicals by adult fish may have significant consequences on the development and survival of their offspring. Halogenated and polycyclic aromatic hydrocarbons translocate from adult female body stores into eggs during oocyte maturation, and early life stages of fish are often more sensitive than adults to the toxicity of these chemicals. Thus, the presence of persistent, bioaccumulative contaminants in the environment may pose a risk to fish early life stage survival and ultimately reduce recruitment into the adult population. Typically, standard early life stage toxicity studies exposed embryos, larvae, and juveniles to graded concentrations of waterborne toxicants, and dose-response relationships are based on the concentrations of chemicals in the water. However, use of waterborne exposure to assess the toxicity of persistent, bioaccumulative contaminants, such as HAHs and PAHs, has two significant drawbacks. First, uptake of hydrophobic chemicals, such as HAHs and PAHs, into the developing embryo from water is not a significant route of exposure in the environment since concentrations of these chemicals freely dissolved in water are extremely low. Rather, maternal deposition into developing oocytes is the most significant source of these chemicals to the embryo. Second, the dose received by the target tissue, in this case the developing embryo, is the most accurate predictor of the toxic response, and since extrapolation from water concentrations of the chemical to egg concentrations is required, the exact dose received by the embryo can only be estimated, often with large uncertainty. Due to these drawbacks, it is important to develop an alternative exposure method that will directly expose the developing embryo without the need to chronically expose adult fish with subsequent natural deposition of hydrophobic chemicals into the oocytes. Fish egg injection provides this exposure route. Embryos are exposed directly after fertilization with known doses of contaminants, the dose is delivered prior to critical developmental events, and extrapolation of the dose received by the embryo is not needed. We have developed two unique fish egg injection methods as alternative routes of exposure for fish early life stage toxicity studies of lipophilic environmental contaminants. With either method, individual fish eggs are injected with a known dose of chemical. The first approach, a microinjection method, originally developed to assess the developmental toxicity of HAH congeners to early life stages of salmonids, utilizes micro-syringes, 30- gauge stainless steel injection needles, and micro- to nanoliter injection volume. The second approach, a nano-injection method, utilizes glass capillary micropipettes with 2 to 10 µm tips as injection needles, and nano- to picoliter injection volume, allowing injection of nearly any size of fish egg. Both of these egg injection methods allow an investigator to assess the toxicity of lipophilic environmental contaminants to early life stages of fish in a manner that realistically reflects environmental exposure and allows accurate quantitation of the dose to the developing embryo. These injection techniques, however, are not limited to use with only lipophilic chemicals. Since the developmental toxicity of many environmental contaminants ultimately depends on the dose received by the embryo, these egg injection methods could serve as a realistic exposure route in many fish early life stage toxicity studies.

Book chapter↗