Geology topics

Research about Canada, United States

Source-linked reports with geographic coverage including Canada, United States.

At least 73 records · Page 4Linked to original sources

USGS2026

Magnitude conversion relations create substantial differences in seismic hazard models

Earthquake catalogs are essential data inputs for seismic hazard modeling. Because earthquake magnitudes are reported in a variety of types (e.g., local magnitudes and moment magnitudes), magnitude conversion relationships must be used to convert the different magnitude types present in a catalog to a uniform magnitude type to avoid biases in the hazard computation. However, these conversion relationships are often uncertain and have been shown to sometimes perform poorly. Here, we investigate the sensitivity of the gridded seismicity component of the National Seismic Hazard Model (NSHM) to the catalog conversion equations in the Eastern United States. In the 2023 NSHM, magnitudes of various types were converted to moment magnitudes using equations developed by the Central and Eastern United States Seismic Source Characterization for Nuclear Facilities (CEUS‐SSCn), based on least‐squares (LS) regressions made using data from a catalog containing events up through 2008. We recompute these equations using events in the Advanced National Seismic System Comprehensive Earthquake Catalog with multiple magnitudes from 2000 to 2023. Although we prefer the use of orthogonal regressions for our datasets, LS regressions produce broadly similar results, with both approaches exhibiting large deviations from the CEUS‐SSCn conversions, especially at smaller magnitudes. We compare the spatial distribution of annual rates using three different models: (1) the 2023 NSHM conversions, (2) our updated conversions, and (3) no conversions. We find that the choice of conversions leads to substantial differences in the rate forecasts, which can greatly impact the seismic hazard model, particularly in regions with low‐seismicity rates such as the Eastern United States, where the hazard is dominated by gridded seismicity rather than a fault model.

Seismological Research Letters↗

USGS2026

Selenium and mercury tissue partitioning and trophodynamics in the Lake Koocanusa (USA–Canada) fish community

Mining-related contaminants such as selenium (Se) and mercury (Hg) accumulate in aquatic organisms and transfer through aquatic food webs, where they can exert toxic effect undermining the ecological health of aquatic resources. Yet, how Se and Hg co-distribute within food webs and within individual organisms remains poorly understood. We compiled muscle and ovary Se and Hg concentration data from fishes captured in Lake Koocanusa—a North American reservoir receiving elevated Se and Hg inputs from coal mining operations in the Elk River Valley, Canada—to provide insights into the co-processing of Se and Hg within fish and among fish species, including how ecological or seasonal factors shift these distribution patterns. Se and Hg concentrations (ranges: 0.21–38.7 μg Se g −1 dry weight and 0.01–0.84 μg Hg g −1 wet weight), as well as Se:Hg molar ratios, varied substantially between tissues and among species, reflecting biological and ecological differences. Our results suggest that the decoupling of Se or Hg deposition in fish muscle versus ovary may reflect different pathways of impairment, at the individual and population levels, and that interspecific and tissue-specific variability makes it challenging to set a universal Se:Hg threshold for the protection of aquatic organisms.

British Columbia, Montana↗

USGS2026

Integrating detrital magnetite geochemistry and (U-Th)/He chronometry as a sediment provenance tool in geologic and metallogenic terranes

Magnetite is ubiquitous in porphyry Cu systems and in sediment sourcing both barren and mineralized regions, with potential as an indicator mineral in concealed and coarsely-mapped terranes. We develop and test a workflow for integrated geochemistry and (U–Th)/He (He) dating for inferring detrital magnetite (DMt) provenance in these settings. The ca. 70 Ma Taurus porphyry Cu–Mo(–Au) district in eastern interior Alaska serves as a test case. DMt from streams draining porphyry-related mineralization was characterized by geochemistry and mineral inclusion and microstructure observations, complemented by similar data for potential porphyry and host rock sources. Principal component analysis and clustering of DMt geochemical data resolve multiple populations in our samples geochemically and texturally compatible with derivation from metamorphic, porphyry-related hydrothermal, and igneous sources. Hydrothermal magnetite comprises ∼16–50% of DMt nearest porphyry mineralization but diminishes to ∼4% ∼15 km downstream. Subsampled grains within populations yield ∼160–110 Ma, ∼70 Ma, ∼55 Ma, and ∼20 Ma magnetite He date modes. Combined with provenance, He dates capture Early Cretaceous regional exhumation of metamorphic host rock and Late Cretaceous porphyry Cu mineralization. DMt grains showing partial hematite replacement yield ca. 55–20 Ma dates regardless of source, overlapping regional warm/wet climatic intervals. We interpret Cenozoic dates to reflect exhumation to near-surface oxidizing conditions and(or) supergene weathering. Magnetite is thus a promising target phase for (1) tracking the spatiotemporal distribution of porphyry systems, and (2) linking the formation and exhumation of these systems to a regional geologic history, both in Alaska and globally.

Alaska, Yukon↗

USGS2026

Evaluating the use of uncrewed surface vessels to enhance Lake Erie acoustic prey-fish surveys

Incorporation of autonomous uncrewed surface vessels (USVs) into large-scale acoustic surveys may enhance spatiotemporal extent and quality of fish density estimates. Lake Erie is currently surveyed by three motorized research vessels (RVs), which annually collect acoustic data and estimate prey-fish abundances. To evaluate the feasibility of incorporating a USV into the existing survey to increase spatial coverage, we compared paired acoustic measurements of target strength (TS), area backscattering coefficient (ABC), and areal fish density from four motorized RVs (three currently and one historically used) and one USV (Saildrone Explorer). Acoustic data were collected along 2-km transects during five sampling events distributed throughout Lake Erie. Despite observing event-specific differences that were likely impacted by sampling conditions, survey-level estimates of areal density between RVs and the USV were comparable (i.e., RV 6% lower than USV). RVs and the USV appear to react differently (speed and stability) to variable environmental conditions (wind and waves), which impacted data quality and must be mitigated in future applications. However, similar to previous comparisons in marine and freshwater environments, incorporating a USV into an acoustic survey could enhance annual fish density estimates by increasing effort, spatial coverage, logistical flexibility, and biological data collection opportunities from RVs.

Michigan, New York, Ohio, Pennsylvania↗

USGS2026

Edible baits for systemic flea control, plague mitigation, and wildlife conservation: Evaluation of four active ingredients with three rodent species in western North America

The flea-borne agent of plague, Yersinia pestis , is lethal to endangered black-footed ferrets ( Mustela nigripes , BFFs) and the prairie dogs ( Cynomys spp., PDs) on which BFFs depend for habitat and prey. We developed bait pellets containing insecticides for flea control with PDs. Individual baits contained 0.46, 0.91, 1.21, or 1.52 mg fipronil, 5.40 mg afoxolaner, 50.62 mg fluralaner, or 85.20 mg spinosad. From 2023 to 2025, we tested the baits with black-tailed PDs ( C. ludovicianus , BTPDs), Gunnison's PDs ( C. gunnisoni , GPDs), and Richardson's ground squirrels ( Urocitellus richardsonii , RGSs). We sampled hosts 2810 times and detected 8825 fleas across 2 U.S. States, 1 Canadian Province, 6 sites, 9 PD colonies, and 41 sampling plots. Over ∼12 mo across 5 replicates in South Dakota, USA, bait pellets with 0.91 or 1.52 mg fipronil, applied at a rate of 125 baits/ha, were more effective in reducing the abundance of fleas on BTPDs than 0.46 mg fipronil or the 3 other active ingredients; on 2 South Dakota replicates with data from 24 mo posttreatment, the effects of fipronil pellets on flea abundance had waned after ∼24 mo. Similarly, over ∼12 mo on 2 replicates in Arizona, USA, pellets with 1.52 mg fipronil were more effective in reducing the abundance of fleas on GPDs than pellets with 0.46 mg fipronil; on 1 replicate with available data from ∼2 yr posttreatment, the effects of fipronil pellets had waned after ∼24 mo. Over ∼8-11 mo across 2 replicates in Saskatchewan, Canada, baits with 1.21 mg fipronil/pellet were more effective in suppressing the abundance of fleas on BTPDs and RGSs when applied at 250 pellets/ha than 62 pellets/ha; flea control had waned after ∼20-23 mo. When applied annually at 125-250/ha, baits with 0.84-1.52 mg fipronil (FipBits) provided an effective, efficient, and affordable tool for flea control on PD colonies.

Arizona, Saskatchewan, South Dakota↗

USGS2026

Unexpected appetites: Metabarcoding reveals grass carp (Ctenopharyngodon idella) foraging behaviors in the Great Lakes

Grass carp ( Ctenopharyngodon idella ) are herbivorous fish introduced to North America in the 1960s, and they are now established throughout the Mississippi River basin and Laurentian Great Lakes. Despite increasingly intensified management efforts, limited information exists on their foraging ecology. We used DNA metabarcoding to characterize the gut contents of grass carp captured from 2019 to 2022 to evaluate spatial, temporal, and environmental patterns in diet composition across Lake Erie and Lake Michigan. Contrary to long-standing assumptions that grass carp primarily consume submerged aquatic vegetation (SAV), results from Lake Erie’s western and central basins revealed a diet dominated by terrestrial and terrestrial-wetland plant genera, including maples ( Acer ), willows ( Salix ), cottonwoods ( Populus ), and nightshades ( Solanum ). In contrast, fish harvested from Lake Erie’s eastern basin and Lake Michigan tributaries consumed more SAV, particularly pondweeds like Potamogeton and Stuckenia . Diet composition varied by basin, river, and year, but not by ploidy (diploid vs. triploid). Distance-based redundancy analyses identified environmental variables as drivers of diet variability. These findings reframe previous risk assessments which were based on diets from small artificial environments, suggesting greater dietary plasticity and revealing previously overlooked terrestrial-aquatic food web connections. Results presented here could inform management actions and sampling locations. Understanding grass carp foraging behavior in invaded systems can provide a critical tool for refining removal strategies, preventing further expansion, and improving future ecological risk assessments.

Great Lakes↗

USGS2026

Describing the seasonal abundance and growth rates of larval fishes across productivity gradients in Lake Huron in 2017

Several of the Laurentian Great Lakes, including Lake Huron, have undergone oligotrophication in the past decades and prey fish biomass has concomitantly declined. One potential mechanism to explain declines in prey fish is slower growth and lower survival at the larval stage. To determine whether reduced productivity affects the growth of larval fish, we sampled larval fishes and their environment approximately monthly from May through August 2017 at nine nearshore to offshore transects across Lake Huron that included North Channel, Georgian Bay, and the main basin. North Channel transects had the highest chlorophyll a concentrations and zooplankton densities. Rainbow smelt ( Osmerus mordax ), burbot ( Lota lota ), bloater ( Coregonus hoyi ), and shiners ( Notropis spp.) were the most abundant larval fish taxa, peaking in June and July. We aged rainbow smelt and bloater using otoliths, and estimates of growth rate revealed rainbow smelt always grew faster. For both species, we explained variation in total length by comparing 16 candidate linear mixed-effects models, with age, chlorophyll a , zooplankton, water temperature, larval fish density, and interactions with age as predictor variables. For rainbow smelt, the full model was best; zooplankton had the greatest effect, but it was negative and opposite from our hypothesis. For bloater, four candidate models were most parsimonious; water temperature had the greatest effect, and it was positive as predicted from our hypothesis. To more effectively evaluate whether zooplankton can limit larval fish growth and survival, we recommend that future designs conduct more frequently sampling within a year even at the expense of fewer transects.

Lake Huron↗

USGS2026

Seasonal space use and spatial overlap of lake sturgeon populations inhabiting Lake St. Clair

Multi-jurisdictional management of adult lake sturgeon ( Acipenser fulvescens ) requires characterizing seasonal dynamics of their spatial distributions. Despite decades of research into lake sturgeon movement ecology, system-wide spatiotemporal behavior remains poorly understood in large lakes, particularly those with metapopulations differentiated by spawning river or migratory phenotypes. This study described seasonal space use of lake sturgeon populations in Lake St. Clair, a large, shallow lake divided by the international border between the State of Michigan and Province of Ontario. Our objectives were to characterize spatial behavior of adult lake sturgeon by: 1) assessing U.S. and Canadian residency patterns and cross-boundary movements with relevance for interjurisdictional management; 2) identifying seasonally important habitats where sturgeon regularly congregate; and 3) comparing seasonal spatial distributions and behavioral metrics among spawning populations and migratory phenotypes. A large sample of acoustic-tagged adult lake sturgeon of known spawning river and migratory phenotype were detected with a high-density (∼5 km spacing), lake-wide receiver grid. Home ranges estimated via Brownian Bridge movement models indicated near lake-wide use and seasonal variation in areas occupied, total area used, and residency within and across jurisdictional boundaries. Lake sturgeon seasonally congregated in several distinct areas but were not completely segregated by spawning populations or migratory phenotypes. Instead, space use by the two spawning populations followed a seasonally dependent, north-south gradient associated with the location of spawning inlet and outlet rivers. These results suggest that managers consider internationally coordinated approaches, especially for population assessment, that account for seasonal habitat shifts and cross-population and phenotypic mixing.

Michigan, Ontario↗

USGS2026

Decreased water transparency of nearshore Laurentian Great Lakes habitats is driven by increased dissolved organic carbon.

Little is understood of lake browning (due to increased dissolved organic carbon; DOC) in large lakes such as the Laurentian Great Lakes. Lake browning can alter whole lake ecosystems, including decreasing exposure to damaging ultraviolet radiation (UV-B) which is strongly and selectively attenuated by DOC more so than photosynthetically active radiation (PAR). We compared the changes in UV-B and PAR transparency to DOC data collected during the ice-free seasons from 62 nearshore sites in four of the five Great Lakes from 2002 to 2022 using linear mixed effects regression models based on backwards selected Bayesian information criteria. Regionally, DOC significantly increased from 2002 to 2022 by 0.5% per year on average. DOC strongly and inversely explained the variability of UV-B and PAR transparencies, as did seasons and offshore influence on these habitats. We provide regional evidence of lake browning within the nearshore habitats of the Great Lakes as a strong contrast to the well-documented increased offshore water transparency associated with the spread of invasive dreissenid mussels.

Great Lakes↗

USGS2026

Detecting occurrence and timing of grizzly bear parturition based on anomalies in accelerometer data

Documenting natality of brown (grizzly) bears ( Ursus arctos ) is an important component of many population monitoring and research programs. Brown bears give birth during hibernation, so observation of litters is generally not feasible until females exit dens, and detection of litters can be compromised by poor observability. Using triaxial accelerometer activity data stored on radiocollars, we developed a technique that predicts births by the presence of brief upsurges in activity likely associated with postnatal maternal behaviors. We developed presence criteria with a training sample of known parturient females ( n = 22) to detect anomalies within time-series of daily motion-counts (i.e., activity readings >0 measured at 10-min intervals) during 25 December–7 March. To test performance, we applied criteria to a blinded sample of activity data obtained from female grizzly bears (captured and collared during 2012–2022) in 4 populations in interior North America ( n = 295). We assigned predicted status and compared assignments to reproductive status at first visual observation. The true positive rate was 91% ( n = 47 females observed with cubs of the year) and the false-positive rate was 17% ( n = 65 females observed with older offspring). Births were predicted for 50% of females with unknown reproductive status ( n = 48), 21% of females observed without offspring ( n = 114), and 10% of subadult females considered too young to reproduce ( n = 21). Dates of predicted births varied from 27 December to 28 February. Our anomaly detection technique was successful at estimating parturition events, and despite some error, indicated that a number of litters were born but not observed, presumably due to mortality in or shortly after den emergence. This technique provides an additional tool for supplementing visual observations for natality estimation and population modeling, provided that potential biases stemming from increased detection rates are considered.

Alaska, British Columbia, Idaho, Montana↗

USGS2026

Bottom trawl assessment of Lake Ontario’s benthic prey fish community, 2025

Since 1978, bottom trawl surveys in Lake Ontario have provided information on the status and trends of the benthic prey fish community related to Fish Community Objectives that include understanding prey fish population dynamics and community diversity. Beginning in 2015, the benthic prey fish survey expanded from only U.S. sites to incorporate Canadian sites, increasing the survey’s spatial coverage to a lake-wide scale. Additionally, sampling in the eastern U.S. embayments (Black River, Chaumont, Guffin, and Henderson Bays), that were historically sampled during a September bottom trawl survey to index Yellow Perch ( Perca flavescens ; 1978-2007), resumed in 2015. The current survey provides abundance indices for sculpins, Round Goby ( Neogobius melanostomus ) and Bloater ( Coregonus hoy i) using techniques, gear, and timing comparable to surveys on Lake Michigan. This alignment provides a necessary biological reference point for evaluating Lake Ontario Bloater reintroduction. In 2025, the benthic prey fish survey completed 100 bottom trawl sites across main lake and embayment habitats at depths from 6 to 168 m. Sampling in US waters was limited in 2025 compared to previous years. In total, the 2025 survey sampled 59,870 fish from 23 species. No Bloater were detected in the 2025 survey. Round Goby was the most common species comprising 46% of the total catch by number, followed by Deepwater Sculpin ( Myoxocephalus thompsonii ), White Perch ( Morone americana ), and Alewife ( Alosa pseudoharengus ) at 23%, 9%, and 9% respectively. Slimy Sculpin ( Cottus cognatus ) lake-wide biomass density continues to be lower than when lakewide sampling began in 2015; zero Slimy Sculpin were detected in US waters, however sampling in the main lake within US waters was limited to the southeastern area of Lake Ontario. Deepwater Sculpin biomass has remained high since population recovery began in 2010. Embayment sampling in 2025 was limited to only Chaumont Bay.

Lake Ontario↗

USGS2026

Lake Ontario August gillnet survey and lake trout assessment, 2025

Lake Ontario Lake Trout ( Salvelinus namaycush ) rehabilitation has been assessed with fishery dependent and independent surveys to evaluate program benchmarks and compare observations with management objectives since 1983. These surveys provide information on the abundance, strain composition, and performance of stocked Lake Trout, as well as information on levels of natural recruitment, and Sea Lamprey ( Petromyzon marinus ) wounding rates. Lake Trout catch per unit effort (CPUE) in the August gillnet survey was notably lower in 2025. Percentage of naturally produced Lake Trout in US waters continued to be relatively low for mature and immature fish. Sea Lamprey wounding rates on Lake Trout > 432 mm in 2025 were below management target in US waters with zero A1 wounds observed. Overall, the 2025 survey results suggest that Lake Trout indicators continue to meet some of the management objectives but are not showing signs of meaningful recruitment to the adult stock.

Lake Ontario↗

USGS2026

Status and trends of the Lake Huron prey fish community, 1976-2025

The U. S. Geological Survey-Great Lakes Science Center has monitored annual changes in the offshore (depth > 9m) prey fish community of Lake Huron since 1976. Assessment of prey fish populations in Lake Huron is based on a bottom trawl survey that targets demersal species (i.e., those predominantly or intermittently associated with the lake bottom) and an acoustic-midwater trawl survey that targets pelagic species and life stages. Prey fish abundance and species composition in 2025 was generally consistent with trends observed over the past decade. Overall status of main basin prey fish community was rated as ‘fair.’ Bloater ( Coregonus hoyi ) and Rainbow Smelt ( Osmerus mordax ) remain the first and second most abundant species in the main basin followed by Alewife ( Alosa pseudoharengus ), whose populations consist mainly of low numbers of age-0 individuals. Abundance of Rainbow Smelt is higher, and abundance of Bloater lower, in Georgian Bay and the North Channel than in the main basin, which suggests dynamics of these species vary by basin. Native sculpin communities consist primarily of Deepwater Sculpin ( Myoxocephalus thompsonii ) due to the reduced abundance and distribution of Slimy Sculpin ( Cottus cognatus ). In contrast, biomass of the exotic Round Goby ( Neogobius melanostomus ) in 2025 was the second highest observed in the bottom trawl time series. Evidence of strong Bloater and Rainbow Smelt year classes in 2025 and continued recovery by Cisco ( Coregonus artedi ) in the North Channel were interpreted as positive community trends, whereas growth and expansion of Round Goby populations and low species diversity of pelagic prey fish communities merit concern. Use of complementary surveys (bottom trawl, acoustics) remains important for evaluating prey fish status in Lake Huron, where prey fish community dynamics vary by basin and prey fish responses to changing environmental conditions depend on species and/or habitat.

Lake Huron↗

USGS2025

An analysis of the linked decisions in the confiscation of illegally traded turtles

Over the last few decades, freshwater turtles have become more common in the illegal wildlife trade because of growing global demand. Illegally traded turtles may be intercepted by several different agencies with separate jurisdictions. When turtles are confiscated, uncertainties may make releasing them back to the wild difficult. We used tools from decision analysis to achieve the following three objectives: (1) map elements of the decision process and their relationships in the illegal turtle trade using conceptual models, (2) outline the linked decisions for turtle confiscation and repatriation using decision trees, and (3) evaluate the decision trees for two example scenarios, one with moderate uncertainty and one with high uncertainty. We used the wood turtle ( Glyptemys insculpta ) as a case study, which is a species of conservation concern in part due to illegal wildlife trafficking. We conducted 23 semi-structured interviews of decision makers in law enforcement, biologists, land managers, and zoo staff. Interviews revealed that decisions regarding the disposition of confiscated turtles are complicated by uncertainty in disease status and origin. Decision makers that handle confiscated turtles also recognize that their decisions are often made in sequence and dependent on the outcome of antecedent decisions. In evaluating our decision trees, we found that the optimal decisions for example scenarios were similar and insensitive to uncertainty. Future applications of the decision trees by decision makers would involve a decision analyst to parameterize and interpret the choices and consequences involved in working through these decision trees. Collectively, our work shows how the use of decision trees can help structure and evaluate risky decisions for repatriating confiscated wildlife.

Conservation Science and Practice↗

USGS2025

Aggregating three sources of long-term trends of swallows and martins to identify priority conservation areas in the Great Lakes region

1. Long-term monitoring of bird populations across scales is important in evaluating conservation targets and creating effective conservation strategies. For nearly six decades, the Breeding Bird Survey (BBS) has served as the primary broad-scaled source of relative abundance trends of swallows and martins in North America. Recently, however, it has become possible to obtain breeding population trends using semi-structured eBird community science data. Moreover, weather surveil-lance radar data of swallow and martin roosting populations yield a third complementary source of trend information. 2. Using results from these three approaches, we propose a novel method of spatially combining estimates of percent change per year into a probability of directional agreement and/or disagreement that describes (1) the direction of the trend within a given region, (2) the amount of evidence associated with the estimate and (3) how much uncertainty surrounds it. We focus our efforts on an area of high Hirundinidae concentration in the North American Great Lakes region and predict trends from 2012 to 2022. 3. We found a high probability of agreement between all three sources about ob-served declines in swallow and martin trends in the region surrounding Lake Ontario and to the west of Lake Michigan. Focusing future research on these regions could improve our understanding of these declines and help build more targeted conservation initiatives. 4. Synthesis and applications. Our data integration methodology allows managers to identify regions that accumulate evidence of concerning trends across multiple wildlife monitoring schemes. These regions can thus be prioritized in conservation and management efforts. This approach can be generalized to other sources of long-term monitoring data of different species, at different stages of their annual cycle, in any geographic location.

Great Lakes region↗

USGS2025

Larval fish export in response to altered discharge in the St. Marys river rapids

The St. Marys River (SMR) forms the border between Michigan, USA, and Ontario, Canada, connecting lakes Superior and Huron. Discharge is controlled by a 16-gate water control structure upstream of the SMR rapids. The SMR rapids are a critical spawning habitat in the Great Lakes, yet the influence of regulated discharge on larval fish export remains poorly understood. From 2018 to 2021, larval fish were sampled across four locations to assess community composition and export dynamics under varying discharge releases. Rainbow smelt ( Osmerus mordax ) dominated catches (87.9 %), followed by species in the family Leuciscidae (i.e., native minnows) and burbot ( Lota lota ). Larval densities were strongly influenced by water temperature and, to a lesser extent, discharge. Bayesian state-space models estimated a total export of ∼ 41.3 million larvae from the rapids across 3 years, with the highest export in 2019. Rainbow smelt larvae exhibited peak densities at intermediate flows (300–600 m 3 s −1 ) and temperatures (∼18–19 °C), while non-rainbow smelt taxa showed species-specific, less consistent responses. Nighttime sampling consistently yielded higher larval densities. Export estimates varied by analysis but both manual and Bayesian approaches captured similar interannual and taxonomic trends. Despite past expectations, the larval community was largely composed of prey species, with limited representation of lake sturgeon ( Acipenser fulvescens ), lake whitefish ( Coregonus clupeaformis ), or walleye ( Sander vitreus ). These results suggest the SMR rapids currently support significant forage fish production and highlight the importance of discharge and temperature in structuring larval export.

St Mary's River rapids↗

USGS2025

Predictors of mercury and pesticide fluxes by emerging adult aquatic insects from prairie pothole wetlands

Aquatic and terrestrial food webs are linked by movements of aquatic insects during their development from larvae to adults. Contaminants can affect these linkages by reducing insect survival and increasing tissue contaminant concentrations through adult metamorphosis, thus changing contaminant flux from water to land. Most anthropogenically influenced freshwater ecosystems are exposed to multiple contaminants. To better understand the combined effects of contaminants on aquatic–terrestrial linkages, we investigated how adult aquatic insect emergence and tissue contaminant concentrations affect insect-mediated contaminant flux of mercury and pesticides from wetlands. In a field survey of 15 wetlands in the Prairie Pothole Region, an important agricultural region of North America, we found that insect-mediated mercury flux was 3.5 times more strongly predicted by emergence biomass than tissue mercury concentration. Thus, factors that were previously found to influence aquatic insect emergence biomass in this system—including insecticide tissue concentrations in adult insects, open water surface area, and agricultural land use—were the most likely to drive insect-mediated mercury flux. Pesticide flux, however, was 3.3 times more strongly predicted by the tissue pesticide concentration than by emergence. Thus, factors that influence pesticide exposure and, to a smaller extent, emergence biomass were the most likely to drive pesticide flux. Our results show how factors driving contaminant fluxes by adult aquatic insects differ by contaminant class, and they suggest one mechanism by which toxic effects of one contaminant (pesticides) could influence the flux of another (mercury). Predicting contaminant fluxes in areas where different mixtures of contaminants are present can aid in identifying risk to insectivores.

Prairie Pothole Region↗

USGS2025

Assessing fish growth changes under an ecosystem regime shift: The approach of linear mixed-effects modeling with application to Lake Huron lake trout

Linear mixed-effects modeling has been used to characterize fish growth changes over time, but early studies did not fully consider the implicit relationship among the three major factors of fish age, year-class, and sampling year in model development. Our objective is to resolve this issue and develop a linear mixed-effects model to clearly assess how lake trout ( Salvelinus namaycush ) growth has responded to the ecosystem regime shift in Lake Huron. We found that, from the late 1970s through the early 2000s, lake trout weight-at-age in northern Lake Huron had large variation with no apparent temporal trend, whereas the weight-at-age in southern Lake Huron steadily declined but remained larger than that in northern Lake Huron. The difference between northern and southern Lake Huron almost disappeared prior to the 2003 collapse of alewives, which accelerated the weight-at-age declines during the 2000s in both regions. By 2010, lake trout growth had a modest recovery and then stabilized. Our model fitted and explained variation in lake trout weight-at-age between years, regions, and recruitment origins, with the fixed age effect representing the general growth trajectory, the fixed year effect as the year-specific growth index, and the random year-class effect as the cohort-specific growth index.

Lake Huron↗