Mining can cause environmental damage if managed improperly. Environmental impact assessments are designed to evaluate the risks of mining; however, these evaluations are hindered when mines expand their operational scope beyond activities considered in the original assessment. Our study focuses on the regulatory process of mine expansion and the National Environmental Policy Act (NEPA). Our multiple case study approach analyzed expansion projects for five hardrock mines in Alaska, USA. A media review identified expansion issues for each mine that received significant public attention. For each case, we examined government documents, media, and other literature to explore research questions related to variability in the application of environmental impact assessment procedures, the breadth and depth of public process, and issues raised during public comment periods. Across case studies, we synthesized the common themes and context dependence regarding the regulatory process of mining expansion. We found wide variation in the implementation of NEPA based on different institutional and geographic contexts, which led to unique sets of public concerns. We summarized differing levels of public engagement, varying approaches to cumulative effects analyses, and difficulties accessing public documents. These results demonstrate the challenges that mine expansions pose to conducting consistent and transparent environmental impact assessments.

In Canada, at least 200 active mines and 6500 quarries produce 60 commodities. Many proposed mines and quarries undergo impact assessment (IA) to predict potential impacts and inform final decision-making, alongside conditions for mitigating risk. We (1) present the first complete list of IA laws that apply to mining in Canada; (2) provide an open-source database of mine and quarry projects subject to IA; (3) quantify mining and IA trends; and (4) assess availability of information by jurisdiction. Our database includes 266 assessments of 227 projects under 13 jurisdictions proposed from 1974 to 2023. Over time, target commodities shifted from coal, oil sands, and peat, to metals (e.g., gold, copper, nickel) and production sizes increased. For many projects assessed across multiple jurisdictions, we could not explain differences in reported key metrics (production size, lifespan, footprint). Our database's comprehensiveness is limited by a lack of publicly available data. We recommend regulators adopt the findable, accessible, interoperable, and reusable principles for information sharing by standardizing key metrics, publishing project documentation, and improving registry functionality. We encourage enhanced inter-jurisdictional IA cooperation to ensure the public and decision-makers have access to fulsome information about new projects during a modern mineral rush in Canada.

River floodplains are dynamic mosaics of aquatic and riparian habitats maintained by flow regimes and sediment processes, but these floodplains may be rapidly shifting with climate change. Specifically, previous work has highlighted that glacier retreat can be associated with river channel and floodplain change. Within a large and glacially influenced watershed, the Taku Watershed of northwestern British Columbia and southeastern Alaska, we used remote sensing and Geographic Information System (GIS) to quantify four decades of annual floodplain habitat composition and river channel patterns in 16 subwatersheds that naturally varied in their glacier coverage and other landscape (e.g., floodplain elevation, slope) and climate variables (e.g., temperature, precipitation). We discovered rapid development of floodplain vegetation and increased habitat stability in subwatersheds with higher glacial coverage, and a lack of directional change in other subwatersheds. Floodplain vegetation coverage almost doubled over 38 years in subwatersheds with the highest glacier coverage. Focal analyses revealed that river channel structure also shifted in glacierized subwatersheds, with decreases in habitat turnover rate, water occupancy and some evidence for decreasing levels of channel braiding. A large landslide (1.5 km runout, 130 ha) during the study period caused a local disturbance to one of the floodplains, but with little immediate broader impacts at the scale of the entire floodplain. Collectively, climate change and associated glacier retreat are leading to the rapid transformation of floodplain ecosystems, with major implications for the habitat of important species such as migratory salmon.

The boreal ecosystem has experienced significant changes over recent decades as wildfires become more frequent, intense, and severe. As streams are highly prevalent and ecologically relevant, understanding interactions among wildfire and hydrologic patterns is important for effective aquatic ecosystem management. This study used a Bayesian mixture model to classify streamflow regimes from modeled streamflow data for 32,730 stream reaches (totaling 295,880 km) across the Yukon and Kuskokwim basins and the Northwestern Boreal Ecosystem in Alaska, USA, and Yukon Territory, Canada. We assessed time since burn and calculated the total length of stream (km) within burn perimeters for each streamflow class from 1985 to 2015. Additionally, we used field observations (2018-2022) to compare streamflow regimes in four burned and four unburned headwater streams (drainage basins ≤150 km2) in interior Alaska. Modeled stream reaches were grouped into twenty-two classes and reduced to eleven metaclasses based on similarities in streamflow statistics. These metaclasses formed two broad groups: 1) large rivers with lower variability and strong seasonal signals, and 2) mid- to small-sized tributaries with high variability, frequent high flow events, and weaker seasonal signals. The stream length burned analysis indicated an average increase of 47 km per year with first- and second-order streams experiencing more frequent fire. Empirical streamflow metrics from headwater stream gages revealed additional differences in streamflow patterns between burned and unburned streams. This streamflow classification establishes a baseline for understanding boreal stream responses to wildfire, detecting climate-induced regime shifts, and facilitating management and conservation of important boreal aquatic species.

Future ecological value of emerging habitats must be considered as climate change transforms the planet.

Glacier retreat is rapidly transforming some watersheds, with ramifications for water supply, ecological succession, important species such as Pacific salmon (Oncorhynchus spp.), and cultural uses of landscapes. To advance a more holistic understanding of the evolution of proglacial landscapes, we integrate multiple lines of knowledge starting in the early 1900s with contemporary data from the Taaltsux̱éi (Tulsequah) Watershed in British Columbia, Canada. Our objectives were to: 1) synthesize recent historical geography and Indigenous Knowledge, including glacier dynamics, and hydrology; 2) describe the limnology of a proglacial lake; 3) quantify decadal-scale downstream physical floodplain change; and 4) characterize riverine physical, chemical, and biological differences relative to distance from the proglacial lake. Since 1982, the Tulsequah Glacier has receded 0.07 km/yr, exposing a cold, deep, and growing proglacial lake. The downstream floodplain is rapidly changing; satellite imagery analysis revealed a 14 % increase in vegetation from 2003 to 2017 and Indigenous Knowledge described increases in vegetation and wildlife habitat over the last century. Contemporary measurements of physical-chemical water properties differed across sites representing the upper and lower watershed, and mainstem and off-channel habitats. Catches of juvenile salmonids in the upper watershed (closer to the glacier) were mostly limited to warmer, clearer groundwater-fed channels, whereas in the lower watershed there were salmonids in both groundwater-fed and mainstem habitats. There was limited zooplankton taxa diversity from the proglacial lake and benthic macroinvertebrates in the river. Collectively, our synthesis suggests that the transformation of proglacial landscapes experiencing rapid ice loss can be influenced by interlinked abiotic processes of glacier retreat, lake formation, and altered hydrology, as well as corresponding biological processes such as beaver repopulation, wetland formation, and riparian vegetation growth. These factors, along with expected increases to proglacial lake productivity and salmon habitat suitability, are an important consideration for forward-looking watershed management of glacier-fed rivers.

The frequency of dissolved oxygen depletion events (hypoxia) in coastal aquatic ecosystems has risen dramatically since the late 20th century, yet the causes and consequences of hypoxia for some culturally and economically important species remain poorly understood. In rivers, oxygen depletion can be caused by high densities of spawning Pacific salmon (Oncorhynchus spp.) consuming oxygen faster than can be replaced by reaeration. This process may be exacerbated when salmon densities are artificially inflated, such as when hatchery-origin salmon stray into rivers instead of returning to hatcheries. In Southeast Alaska, hatchery salmon production has increased rapidly since the 1970s, with over 553 million chum salmon (O. keta) and 64 million pink salmon (O. gorbuscha) released in 2021 alone. Straying is pervasive in streams with outlets <25 km from nearshore marine hatchery release sites. Using a previously ground-truthed mechanistic model of dissolved oxygen dynamics, we examined how water temperature and low-flow channel hydraulics contribute to hypoxia vulnerability. We then applied the model to predict hypoxia vulnerability for watersheds within 25 km of hatchery salmon release points, where straying salmon spawner densities are expected to be higher and promote dissolved oxygen depletion. Our model predicted that low-gradient stream reaches, regardless of water temperature, are the most prone to hypoxia due to low reaeration rates. Our spatial analysis determined that nearly 17,000 km of anadromous-accessible stream reaches are vulnerable to high densities of hatchery-origin salmon based on 2021 release sites. To our knowledge, this study is the first to map the spatial variation of hypoxia vulnerability in anadromous watersheds, identify habitat conditions most likely to promote hypoxia, and provide a repeatable analytical approach to identify hypoxia-prone stream reaches that can be updated as empirical data sets improve.

Models that assess the vulnerability of freshwater species to shifting environmental conditions do not always account for short-duration extremes, which are increasingly common. Life cycle models for Pacific salmon ( Oncorhynchus spp.) generally focus on average conditions that fish experience during each life stage, yet many floods, low flows, and elevated water temperatures only last days to weeks. We developed a process-based life cycle model that links coho salmon ( Oncorhynchus kisutch) abundance to daily streamflow and thermal regimes to assess: (1) “How does salmon abundance respond to short-duration floods, low flows, and high temperatures in glacier-, snow-, and rain-fed streams?” and (2) “How does the temporal resolution of flow and temperature data influence these responses?”. Our simulations indicate that short-duration extremes can reduce salmon abundance in some contexts. However, after daily flow and temperature data were aggregated into weekly and monthly averages, the impact of extreme events on populations declined. Our analysis demonstrates that novel modeling frameworks that capture daily variability in flow and temperature are needed to examine impacts of extreme events on Pacific salmon.

Mining provides resources for people but can pose risks to ecosystems that support cultural keystone species. Our synthesis reviews relevant aspects of mining operations, describes the ecology of salmonid-bearing watersheds in northwestern North America, and compiles the impacts of metal and coal extraction on salmonids and their habitat. We conservatively estimate that this region encompasses nearly 4000 past producing mines, with present-day operations ranging from small placer sites to massive open-pit projects that annually mine more than 118 million metric tons of earth. Despite impact assessments that are intended to evaluate risk and inform mitigation, mines continue to harm salmonid-bearing watersheds via pathways such as toxic contaminants, stream channel burial, and flow regime alteration. To better maintain watershed processes that benefit salmonids, we highlight key windows during the mining governance life cycle for science to guide policy by more accurately accounting for stressor complexity, cumulative effects, and future environmental change.

Widespread mortality of Pacific salmon Oncorhynchus spp. returning to spawn in Alaska coincided with record-breaking air temperatures and prolonged drought in summer 2019. Extreme environmental conditions are expected to happen more frequently with rapid climate change and challenge the notion that Alaska could indefinitely provide abundant, cool freshwater habitat for Pacific salmon. A total of 110 geographically widespread opportunistic observations of premature mortality (carcasses) were collected from a variety of sources. Premature mortalities were documented for Pink Salmon Oncorhynchus gorbuscha, Sockeye Salmon O. nerka, Chum Salmon O. keta, Chinook Salmon O. tshawytscha, and Coho Salmon O. kisutch. Additionally, observations of Pink Salmon returning to spawn in Prince William Sound streams in 2019, obtained from systematic aerial surveys conducted annually, revealed low migration success in 87% of rain-driven streams (n = 30), 52% of snow-driven streams (n = 65), and only 18% of glacier-driven streams (n = 11). Salmon mortality observations were consistent with death due to heat stress resulting from high water temperatures or drought caused hypoxia and stranding. Developing a better understanding of how broad-scale climate patterns manifest at the stream scale can help us determine whether a major shift in Pacific salmon productivity is underway and inform fisheries management plans to better mitigate future risks.

Downscaling coarse global and regional climate models allows researchers to access weather and climate data at finer temporal and spatial resolution, but there remains a need to compare these models with empirical data sources to assess model accuracy. Here, we validate a widely used software for generating North American downscaled climate data, ClimateNA, with a novel empirical data source, 20th century weather journals kept by Admiralty Island, Alaska homesteader, Allen Hasselborg. Using Hasselborg’s journals, we calculated monthly precipitation and monthly mean of the maximum daily air temperature across the years 1926 to 1954 and compared these to ClimateNA data generated from the Hasselborg homestead location and adjacent areas. To demonstrate the utility and potential implications of this validation for other disciplines such as hydrology, we used an established regression equation to generate time series of 95% low duration flow estimates for the month of August using mean annual precipitation from ClimateNA predictions and Hasselborg data. Across 279 months, we found strong correlation between modeled and observed measurements of monthly precipitation (ρ = 0.74) and monthly mean of the maximum daily air temperature (ρ = 0.98). Monthly precipitation residuals (calculated as ClimateNA data - Hasselborg data) generally demonstrated heteroscedasticity around zero, but a negative trend in residual values starting during the last decade of observations may have been due to a shift to the cold-phase Pacific Decadal Oscillation. Air temperature residuals demonstrated a consistent but small positive bias, with ClimateNA tending to overestimate air temperature relative to Hasselborg’s journals. The degree of correlation between weather patterns observed at the Hasselborg homestead site and ClimateNA data extracted from spatial grid cells across the region varied by wet and dry climate years. Monthly precipitation from both data sources tended to be more similar across a larger area during wet years (mean ρ across grid cells = 0.73) compared to dry years (mean ρ across grid cells = 0.65). The time series of annual 95% low duration flow estimates for the month of August generated using ClimateNA and Hasselborg data were moderately correlated (ρ = 0.55). Our analysis supports previous research in other regions which also found ClimateNA to be a robust source for past climate data estimates.

Streamflow controls many freshwater and marine processes, including salinity profiles, sediment composition, fluxes of nutrients, and the timing of animal migrations. Watersheds that border the Gulf of Alaska (GOA) comprise over 400,000 km(2) of largely pristine freshwater habitats and provide ecosystem services such as reliable fisheries for local and global food production. Yet no comprehensive watershed-scale description of current temporal and spatial patterns of streamflow exists within the coastal GOA. This is an immediate need because the spatial distribution of future streamflow patterns may shift dramatically due to warming air temperature, increased rainfall, diminishing snowpack, and rapid glacial recession. Our primary goal was to describe variation in streamflow patterns across the coastal GOA using an objective set of descriptors derived from flow predictions at the downstream-most point within each watershed. We leveraged an existing hydrologic runoff model and Bayesian mixture model to classify 4,140 watersheds into 13 classes based on seven streamflow statistics. Maximum discharge timing (annual phase shift) and magnitude relative to mean discharge (amplitude) were the most influential attributes. Seventy-six percent of watersheds by number showed patterns consistent with rain or snow as dominant runoff sources, while the remaining watersheds were driven by rain-snow, glacier, or low-elevation wetland runoff. Streamflow classes exhibited clear mechanistic links to elevation, ice coverage, and other landscape features. Our classification identifies watersheds that might shift streamflow patterns in the near future and, importantly, will help guide the design of studies that evaluate how hydrologic change will influence coastal GOA ecosystems. Plain Language Summary Streams provide society with many benefits, but they are being dramatically altered by climate change and human development. The volume of flowing water and the timing of high and low flows are important to monitor because we depend on reliable streamflow for drinking water, hydroelectric power, and healthy fish populations. Organizations that manage water supplies need extensive information on streamflow to make decisions. Yet directly measuring flow is cost-prohibitive in remote regions like the Gulf of Alaska, which drains freshwater from an area greater than 400,000 km(2), roughly the size of California. To overcome these challenges, a series of previous studies developed a tool to predict historical river flows across the entire region. In this study, we used 33 years of those predictions to categorize different types of streams based on the amount, variability, and timing of streamflow throughout the year. We identified 13 unique streamflow patterns among 4,140 coastal streams, reflecting different contributions of rain, snow, and glacial ice. This new catalog of streamflow patterns will allow scientists to assess changes in streamflow over time and their impact to humans and other organisms that depend on freshwater.

Abstract Organizations tasked with implementing long‐term ecological monitoring programs often struggle to stay funded. Government agencies are typically the only entities with sufficient capacity and motivation to support long‐term scientific programs that generate data for environmental management and conservation. Taxpayers bear this funding burden, yet we know of no studies assessing public perception of government‐led long‐term monitoring. We present the results of a survey designed to assess willingness to pay (WTP) for the benefits resulting from long‐term ecological monitoring in Southeast Alaska for residents and visitors. We hypothesized that four factors have the potential to influence preferences for long‐term ecological monitoring: (1) type of ecosystem service monitored (intermediate vs. final); (2) place of residence; (3) prior knowledge of monitoring; and (4) sociodemographic characteristics. We defined final ecosystem services as ecosystem attributes that have clear relevance to human well‐being and intermediate ecosystem services as those required to produce final services. We found a greater WTP for programs monitoring intermediate ecosystem services, longer‐running programs, and programs covering a larger spatial extent. Respondents with higher income and conservative political preferences were more likely to choose no monitoring program at all (status quo), whereas respondents with previous knowledge of monitoring were generally more supportive of long‐term monitoring programs.

Abstract Dissolved oxygen (DO) is essential to the survival of almost all aquatic organisms. Here, we examine the possibility that abundant Pacific salmon (Oncorhynchus spp.) and low streamflow combine to create hypoxic events in coastal rivers. Using high‐frequency DO time series from two similar watersheds in southeastern Alaska, we summarize DO regimes and the frequency of hypoxia in relationship to salmon density and stream discharge. We also employ a simulation model that links salmon oxygen respiration to DO dynamics and predicts combinations of salmon abundance, discharge, and water temperature that may result in hypoxia. In the Indian River, where DO was monitored hourly during the ice‐free season from 2010 to 2015, DO levels decreased when salmon were present. In 2013, a year with extremely high spawning salmon densities, DO dropped to 1.7 mg/L and 16% saturation, well below lethal limits. In Sawmill Creek, where DO was monitored every six minutes across an upstream–downstream gradient during the 2015 spawning season, DO remained fully saturated upstream of spawning reaches, but declined markedly downstream to 2.9 mg/L and 26% saturation during spawning. Modeled DO dynamics in the Indian River closely tracked field observations. Model sensitivity analysis illustrates that low summertime river discharge is a precursor to salmon‐induced oxygen depletion in our study systems. Our results provide compelling evidence that dense salmon populations and low discharge can trigger hypoxia, even in rivers with relatively cold thermal regimes. Although climate change modeling for southeastern Alaska predicts an increase in annual precipitation, snowfall in the winter and rainfall in the summer are likely to decrease, which would in turn decrease summertime discharge in rain‐ and snow‐fed streams and potentially increase the frequency of hypoxia. Our model template can be adapted by resource managers and watershed stakeholders to create real‐time predictive models of DO trends for individual streams. While preserving thermally suitable stream habitat for cold‐water taxa facing climate change has become a land management priority, managers should also consider that some protected watersheds may still be at risk of increasingly frequent hypoxia due to human impacts such as water diversion and artificially abundant salmon populations caused by hatchery straying.

Assimilation of mercury (Hg) into food webs is directly influenced by ecological factors such as local habitat characteristics, species feeding behavior, and movement patterns. Total Hg concentrations ([THg]) in biota from Subarctic latitudes are driven both by broad spatial processes such as long-range atmospheric transport and more local influences such as biovectors and geology. Thus, even relatively pristine protected lands such as national parks are experiencing Hg accumulation. We analyzed [THg] and stable isotopes of carbon (δ13C) and nitrogen (δ15N) in 104 Dolly Varden (Salvelinus malma) collected from two rivers in southeastern Alaska, upstream and downstream of apparent anadromous migration barriers in watersheds with and without glacial coverage. To assess the potential magnitude of marine-derived THg returning to freshwater, we analyzed [THg] in ten adult pink salmon from each study system. There were no differences in Dolly Varden mean [THg] between sites after the data were standardized for fork length, but unadjusted [THg] varied relative to fish size and δ15N values. While previous studies generally show that [THg] increases with higher δ15N values, we found that Dolly Varden below migration barriers and foraging on salmon eggs had the highest δ15N values among all sampled individuals, but the lowest [THg]. Dolly Varden residing below anadromous barriers had δ13C values consistent with marine influence. Since salmon eggs typically have low [Hg], our results suggest that abundant salmon populations and the dietary subsidy they provide may reduce the annual exposure to [Hg] in egg-eating stream fishes such as Dolly Varden. In addition to identifying a suitable species for freshwater Hg monitoring in southeastern Alaska, our study more broadly implies that river characteristics, location within a river, fish size, and feeding ecology are important factors influencing Hg accumulation.

Abstract In this Special Feature, we celebrate 100 years of National Park Service science by highlighting contributions from the agency's Inventory and Monitoring Division. This broad body of work coalesces into several themes, including the role of protected areas in understanding rapid global change and the growing interest in place‐based ecological insights that contextualize scientific information from protected areas across broader scales. Finally, we illustrate progress on the long‐sought integration of science into the resource management strategies implemented within “America's Best Idea,” now more important than ever given the many challenges our nation's parks face.

To design sustainable water quality monitoring programs, practitioners must choose meaningful variables, justify the temporal and spatial extent of measurements, and demonstrate that program objectives are successfully achieved after implementation. Consequently, data must be analyzed across several variables and often from multiple sites and seasons. Multivariate techniques such as ordination are common throughout the water quality literature, but methods vary widely and could benefit from greater standardization. We have found little clear guidance and open source code for efficiently conducting ordination to explore water quality patterns. Practitioners unfamiliar with techniques such as principal components analysis (PCA) are faced with a steep learning curve to summarize expansive data sets in periodic reports and manuscripts. Here, we present a seven-step framework for conducting PCA and associated tests. The last step is dedicated to conducting Procrustes analysis, a valuable but rarely used test within the water quality field that describes the degree of concordance between separate multivariate data matrices and provides residual values for similar points across each matrix. We illustrate the utility of these tools using three increasingly complex water quality case studies in US parklands. The case studies demonstrate how PCA and Procrustes analysis answer common applied monitoring questions such as (1) do data from separate monitoring locations describe similar water quality regimes, and (2) what time periods exhibit the greatest water quality regime variability? We provide data sets and annotated R code for recreating case study results and as a base for crafting new code for similar monitoring applications.