Christian M. Erikson and Jens M. Turowski of the GFZ Helmholtz Centre for Geosciences in Potsdam, Germany, publish their analysis in the journal Earth Surface Dynamics as a highlight letter. Their central claim is that step-pool spacing occupies a continuum between regularity and randomness, with the full range of possible configurations realized in nature and no single formation mechanism dominating. The finding, drawn from a compilation of 131 step-pool sequences spanning field sites, laboratory flume experiments, and numerical simulations, resolves a long-standing tension between competing models that had produced contradictory expectations about what a healthy mountain stream should look like.

The stakes are considerable. Mountain streams account for an estimated 60 to 80 percent of total global river length, and the transport of floodwaters and sediment through them is a costly natural hazard in populated mountainous regions. Step-pools are prominent in rivers with slopes exceeding roughly 3 percent, and their ability to provide flow resistance makes them a favored tool in hazard management. They are also used as a benchmark of channel recovery in river restoration, particularly in the growing number of dam-removal projects worldwide. Without a clear, mechanism-independent expectation for step spacing, practitioners have had no reliable target: one scientific camp predicted regular spacing tied to channel hydraulics, another predicted random spacing tied to the size and location of large boulders, and restoration designs inherited the confusion.

The roots of the dispute run deep. Mechanisms linked to hydraulics, such as the antidune mechanism, associate steps with regular spacing. Antidunes are bedforms that organize under rapidly flowing water into roughly periodic crests, and the idea, first proposed from flume experiments in 1982, was that these precursory bedforms act as nucleation points for developing steps. The pool-scour mechanism offers another hydraulic route to regularity: high-energy flow over a step scours a pool downstream, and the excavated material builds the next step, propagating a rhythmically spaced sequence. In contrast, mechanisms tied to channel properties and particle interactions predict randomness. In particle jamming, grains chain together across the channel, often in narrow sections; in keystone clustering, sediment accumulates around large immobile boulders. Because the underlying boulders and rough patches are themselves randomly distributed, the resulting steps inherit that randomness.

The scientific literature has swung back and forth between these camps, and the antidune mechanism is the emblematic case. Once a commonly invoked explanation, it fell from prominence as random-interaction models gained ground, was at one point called on to be abandoned entirely, and has recently been resurrected and again put forward as the dominant mechanism. Erikson and Turowski argue that this vacillation reflects a structural problem: without a comparative framework transferable across mechanisms, interpretations of step spacing have been constrained by prior assumptions about the formative process. A researcher who assumes antidunes will find regularity; one who assumes jamming will find randomness. Both may be partly right, and neither can settle the debate alone.

To break the deadlock, the researchers built a diagnostic framework from two statistical measures of spacing variability that can be calculated from readily obtainable measurements. The first is the coefficient of variation, the standard deviation of step spacing divided by the mean spacing, a standard measure of scatter. The second is a new metric they call the relative minimum: the smallest observed gap between steps divided by the mean spacing. The relative minimum exists to capture the effect of exclusion zones, the stretches of channel immediately downstream of a step where the hydraulic influence of that step prevents a new one from forming. The longer the exclusion zone, the less room remains for new steps, and the lower the maximum achievable coefficient of variation. Because no general method exists to measure exclusion-zone length directly, the minimum spacing serves as a practical proxy.

With these two metrics defining a two-axis plotting space, the team established two reference lines using Monte Carlo simulations repeated 100,000 times. A regular reference line was generated by taking a perfectly regular step sequence, adding Gaussian noise to the spacing, and adjusting positions until all steps respected the minimum-spacing constraint. A random reference line came from a modified Poisson process, in which spacings were drawn from an exponential distribution and any spacing below the minimum constraint was rejected, mimicking the way an exclusion zone limits pure randomness. A range-normalized coefficient of variation then places any real sequence between the two lines: values below 0.5 indicate a sequence closer to regular, values above 0.5 closer to random.

The compiled dataset of 131 sequences, drawn from channels with slopes spanning an order of magnitude from about 3 to 35 percent, revealed that natural step-pool sequences span nearly the full range of possible relative minimum spacing, from 0.07 to 0.84 against a possible range of 0 to 1. The observed coefficients of variation fell almost entirely within the bounds set by the two reference lines, with only three exceptions. Crucially, most sequences sat somewhere between the lines rather than clustering near either one. Of 27 averaged data sources, 18 were closer to the random reference line and 9 closer to the regular line, but the dominant impression was of a continuum fully occupied rather than two distinct populations. Sequences explicitly tied to roughness, keystone, and jamming mechanisms plotted nearest the random line, as expected, while pool-scour sequences and true antidunes plotted nearest the regular line. Channel slope showed no strong correlation with spacing variability.

The framework also produced surprises that cut against cherished assumptions. The flume experiments of Whittaker and Jaeggi, from which the antidune mechanism was first proposed, plotted closer to the random reference line than to the regular one, in an opposite corner of the diagram from genuine antidunes, suggesting that a roughness-based mechanism better explains their observations. The three outliers beyond the random reference line proved diagnostic in their own right: wood-constructed steps in the Vogelbach in Switzerland and Shatford Creek in Canada, and newly developed steps in Charles Brown Brook in the United States after a dam removal, where steps clustered around rough patches with large gaps between clusters. Artificially close spacing or isolated clustering can push a sequence past what pure randomness allows, turning the random reference line into a practical tool for spotting reaches where spacing has been forced by wood, engineering, or disturbance.

The implications reach directly into stream management. Because irreducible natural variability prevents full regularity and hydraulic exclusion zones prevent full randomness, any isolated set of observations will fail to match a truly regular or truly random ideal, meaning that restoration designs built on either assumption are fundamentally misguided. The authors suggest that channel equilibrium, a central concept in restoration, may need redefinition away from a static spacing target toward objectives that accommodate a range of configurations and multiple simultaneous processes. Moreover, because the random reference line is explicitly tied to channel hydraulics, it offers a testable prediction for how spacing evolves in channels that are not in equilibrium, potentially serving as an indicator of river adjustment. In the context of accelerating dam removals, where recovery is currently gauged by metrics tied to assumptions of regularity, such a mechanism-independent yardstick could eventually define concrete, physically grounded targets for restoring the staircases of the world’s mountain streams.

Subject of Research: Spacing regularity and randomness of step-pool sequences in steep mountain streams

Article Title: From regular to random: a unifying framework for step-pool spacing

Article References: Erikson, C. M., & Turowski, J. M. (2026). From regular to random: a unifying framework for step-pool spacing. Earth Surface Dynamics, 14(4), 653-659. https://doi.org/10.5194/esurf-14-653-2026

Image Credits: AI Generated

DOI: 10.5194/esurf-14-653-2026

Keywords: step-pools, mountain streams, geomorphology, fluvial processes, stream restoration, hydraulics, antidunes, particle jamming, sediment transport, dam removal, channel equilibrium, Earth Surface Dynamics

The research, conducted by Bethany Blakey of Utah State University and Natalie Bursztyn of James Madison University, examined citizen science data collected by the Watershed Education Network, a Missoula-based nonprofit whose Stream Team program has monitored local creeks for over two decades. Hundreds of volunteers contributed more than 4,000 hours of fieldwork between 2017 and 2024, measuring streambed sediments and tallying aquatic macroinvertebrates at ten sites—two upstream of the former dam as reference locations and eight downstream as impact sites. The dam, built in 1901, stood 18 meters wide and 3 meters tall, blocking 95 percent of the 210-square-kilometer watershed. It once supplied Missoula’s drinking water, but by the time of its removal it had been slated for demolition over safety and conservation concerns, with the project costing 1.1 million dollars and requiring the reconstruction of more than 300 meters of channel.

The scientific logic of the study rests on a well-established framework known as before-after-control-impact, or BACI. The idea is elegant: if a disturbance causes a real change, the difference between control sites and impacted sites should shift after the event. Upstream reaches, unaffected by the dam removal, serve as the control; downstream reaches are the impact zone. The researchers compared grain size distributions from Wolman pebble counts—a technique in which at least 100 stones are measured along their intermediate axis across the channel—and a macroinvertebrate biotic index adapted from the Hilsenhoff Biotic Index, which scores stream health based on the pollution tolerance of the insects living there. Because the number of observations was small, particularly at the upstream reference sites, the team relied on descriptive statistics rather than formal hypothesis tests, calculating the magnitude of change alongside its standard error.

The results were strikingly uneventful. Before the removal, median grain sizes upstream averaged 105.9 millimeters, while downstream sites averaged 100.1 millimeters—essentially indistinguishable given natural variability. After the removal, the upstream mean was 92.9 millimeters and the downstream mean 93.3 millimeters, still nearly identical. Every BACI value for every grain size percentile fell below its own standard error, meaning no detectable difference could be attributed to the dam coming down. The macroinvertebrate data told the same story. Biotic index values hovered within the good water quality range both before and after removal, upstream and downstream alike, with an overall post-removal difference of minus 0.13, well within the margin of error. For a stream that had been dammed since 1901, the absence of ecological upheaval demanded an explanation.

The authors point to two factors. First, the dam’s sluice gates had been permanently opened in 2012, eight years before the full removal, allowing water, fish, and sediment to pass freely during low to moderate flows. In effect, the creek had already undergone a staged removal—a strategy known from previous research to dramatically reduce erosion and sediment pulses compared with instantaneous breaching. By the time the concrete came out, the river had largely adjusted to a free-flowing condition. Second, no major flood occurred during the study period. Dam removal science describes a two-phase response: an initial rapid flush of reservoir sediment, followed by a slower, event-driven phase in which further erosion requires high flows. The first phase may have played out during the sluice gate opening, and without significant floods afterward, the second phase never really began. Peak flows in the two years after removal, around 21 to 25 cubic meters per second, were lower than the roughly 29 to 32 cubic meters per second peaks recorded before removal.

That null result is scientifically valuable in itself. Most dam removal studies capture only short-term post-removal impacts, and many collect no pre-removal data at all. Research on small historic dams has concentrated heavily on the eastern United States, even though the majority of the estimated 2.5 million dams in the country are under 1.83 meters tall and removals of these small structures are far more common than headline-grabbing demolitions of large dams. Montana alone has hundreds of small dams. The Rattlesnake Creek findings suggest that when a small dam has been effectively decommissioned through a staged opening, its physical removal may cause minimal detectable harm—or benefit—to sediment transport and aquatic life on a timescale of years. That insight matters directly for the nine remaining wilderness dams upstream in the Rattlesnake watershed, built between 1911 and 1923, whose potential removal is now under discussion.

Just as significant is what the study says about the volunteers who gathered the data. Skepticism about citizen science data quality has long shadowed the field, with some researchers finding volunteer datasets more variable than professional ones and others arguing that direct comparisons are inherently unfair. Yet the pebble count and macroinvertebrate datasets proved complete and analytically viable across all eight years. The authors attribute this success to field verification of data, well-designed paper datasheets, and the relative simplicity of the collection protocols—volunteers worked in teams, cross-checked tallies, and followed procedures rehearsed at the start of every outing. One volunteer described the experience as fulfilling childhood dreams of looking at bugs and counting rocks, adding that the work would matter for something. Another reflected that the program revealed science is not all organic chemistry; it can be fun things in the stream.

The study is equally candid about failure. The cross-section profiles, which would have revealed changes in channel shape and depth, proved unusable because of systematic data gaps. Before 2021, volunteers recorded numeric intervals without noting the measurement increments across the stream, and datasheets frequently failed to identify which of two required cross-sections was upstream and which was downstream. Without in-situ verification before leaving the field, the errors went unnoticed until analysis. From these shortcomings, the authors distilled four best practices: ensure every required measurement has a designated place on the datasheet and verify completeness before leaving the site; design digital datasheets that make data entry unambiguous; keep each data type in a single column or row; and create an easily accessible summary page that analysis software can read directly. The Watershed Education Network is now developing a tablet app with required entry fields to address exactly these vulnerabilities.

Beyond the data, the project illustrates the quieter power of community science. Stream Team outings became social events in a heavily recreated corridor, where hikers stopped to ask what bugs the volunteers had found and were invited to join the next outing. Participation in such programs has been shown to improve understanding of the scientific process and give voice to people otherwise excluded from environmental decisions. The study’s authors emphasize that citizen science can achieve spatial and temporal coverage that would be prohibitively expensive for professional researchers alone, provided that meticulous data management underpins the enthusiasm. As dam removals accelerate across Europe and North America, the Rattlesnake Creek experiment offers a dual lesson: staged decommissioning can defuse the ecological drama of removing a small dam, and a committed community of volunteers, given good protocols and honest accounting of their mistakes, can document the outcome with rigor that would make any professional monitoring team take notice.

Subject of Research: Citizen science monitoring of stream sediment and macroinvertebrate responses to a small dam removal on Rattlesnake Creek, Montana

Article Title: Citizen science as a long-term environmental baseline: assessing impacts of a small dam removal in Montana, USA

Article References: Blakey, B., & Bursztyn, N. (2026). Citizen science as a long-term environmental baseline: assessing impacts of a small dam removal in Montana, USA. Geoscience Communication, 9(3), 401-413. https://doi.org/10.5194/gc-9-401-2026

Image Credits: AI Generated

DOI: 10.5194/gc-9-401-2026

Keywords: citizen science, dam removal, Rattlesnake Creek, Montana, stream ecology, macroinvertebrates, pebble counts, sediment transport, BACI design, river restoration, Watershed Education Network, long-term monitoring

The scale of the problem the study confronts is difficult to overstate. Over the past century, streams and lakes across the country have deteriorated under mounting human pressure. More than 150,000 dams now fragment river networks, severing the upstream and downstream connections that countless species depend on for migration, spawning and genetic exchange. Beyond the barriers themselves, changes to the landscape, from agriculture to urbanization, and the extraction of groundwater have altered how and where water flows through entire watersheds. Flow regimes that evolved over millennia have been reshaped within a few human generations, and the consequences are visible in the biological record. Many freshwater species are now in rapid decline, a trend that researchers warn is being exacerbated by the impacts of a changing climate, which shifts temperature and precipitation patterns faster than aquatic organisms can disperse or adapt.

To confront this crisis systematically, The Nature Conservancy assembled a collaboration of 66 freshwater conservationists and set out to map freshwater networks across the contiguous United States and evaluate how resilient each one is to degradation. The approach was deliberately multidimensional. Each watershed received scores based on four criteria: its connectivity, meaning how well its aquatic habitats link together into functioning networks; its condition, reflecting the ecological integrity of the stream or river; its water availability; and the naturalness of its flow, a measure of how closely the timing and magnitude of water movement still resemble historical patterns. These scores were then checked against local surveys of freshwater biodiversity, grounding the resilience assessment in observed biological reality rather than purely physical or chemical proxies.

The result of this effort is a spatial blueprint the researchers call the Freshwater Resilient and Connected Network. This patchwork of rivers and streams covers 35 percent of the lower 48 states, yet the analysis indicates it could preserve the nation’s freshwater biodiversity if conserved and, where necessary, restored. The logic behind such a network is rooted in conservation biology: rather than spreading limited resources thinly across every waterway, concentrating protection on the places where ecosystems are most intact, most connected and most likely to withstand climatic disruption offers a disproportionate return on investment. Resilient, connected networks give species room to move, access to diverse habitat types and the ecological redundancy needed to absorb disturbances such as droughts, floods and warming waters.

Realizing that vision, however, will be a formidable challenge, and the study is candid about the gap between ambition and current reality. Of the 35 percent of waterways identified in the network, only 6 percent of the area is both protected and resilient today. A further 14 percent needs both protection and restoration before it can fulfill its role in the network. In other words, the vast majority of the lands and waters that underpin the nation’s freshwater future currently lack formal safeguards, and many have already been degraded enough to require active intervention. The numbers underscore that identifying priority areas is only the first step; the harder work of securing durable protection and reversing damage on the ground remains ahead.

The broader statistical picture the analysis paints of the contiguous United States is equally revealing. Of the 5.2 million miles of rivers and streams in the lower 48 states, 33 percent rated as above average for resilience. Rivers in this category should continue to support similar patterns of biodiversity in the future, making them strong candidates for protection. The researchers note an important nuance, however: rivers that score just above average may still require restoration to maintain their ecological function, meaning that even some of the better-performing waterways cannot simply be left alone. The geography of resilience is uneven as well. The strongest networks are concentrated along the Pacific Coast, in the Northern Rocky Mountains, around the Great Lake areas of Wisconsin and Minnesota, in northern Maine, and along the coastal regions of the southeastern United States and the Gulf of Mexico, areas where relatively intact landscapes and healthier flow regimes persist.

At the other end of the spectrum, vulnerable or below-average river networks made up 15 percent of the nation’s river and stream miles, and their distribution tells a story about the cumulative weight of human land use and arid climates. These stressed networks cluster in the Southwest deserts, in lower New England, across the shortgrass prairie east of the Rocky Mountains, and throughout the agricultural lands of the midwestern states. In these regions, decades of water diversion, damming, row-crop cultivation and development have eroded the connectivity and natural flow patterns that freshwater communities need. The identification of these hotspots of vulnerability is not merely descriptive; it signals where restoration investment is most urgent if the country hopes to prevent further local extinctions and the loss of aquatic ecosystem services.

The practical value of the new maps is already being demonstrated, according to the research team. The analysis has been used to identify dams for removal, a critical step in reestablishing longitudinal connectivity in fragmented river systems. It has also guided the prioritization of land protection in key headwaters, where safeguarding the upper reaches of watersheds protects water quality and flow for everything downstream. In addition, the framework is being applied to improve conditions in river systems that need restoration, directing effort toward reaches where interventions are most likely to succeed. The authors acknowledge one important limitation: the maps do not take into account human needs, such as water supply, recreation and economic uses of rivers. They note, however, that data representing human dimensions could be combined with this analysis to identify where conservation goals and human priorities intersect or conflict.

The researchers emphasize that resilience to climate change adds essential context to biodiversity conservation that static protection alone cannot provide. A reserve that protects a species’ current habitat may fail within decades if warming, altered precipitation or shifting flow regimes render that habitat unsuitable. By scoring watersheds for the physical features that confer long-term resilience, such as connectedness, water availability and natural flow, the framework aims to identify places where biodiversity can persist not just today but across a range of future climate scenarios. The authors state the hope directly: resilience to climate changes adds important context to efforts to conserve freshwater biodiversity, and they hope the study will help state, federal, Tribal and other conservation partners make investments where they have the greatest chance to succeed into the future.

The study, authored by Mark G. Anderson, Arlene P. Olivero, Analie R. Barnett, Melissa L. Khoury and Erika H. Martin of The Nature Conservancy, was funded by an anonymous donor, the Volgenau Foundation, Kia America and the Enterprise Mobility Fund, none of which played a role in study design, data collection and analysis, decision to publish or manuscript preparation. The authors report no known competing interests. As an observational, nationwide assessment published in PLOS One, it offers conservation planners a rigorous, data-driven foundation for sustaining freshwater life across the United States, and a clear-eyed picture of the challenges ahead: a third of the nation’s waters hold the key, but most of that territory still awaits the protection and restoration it will need to do its job.

Subject of Research: Mapping resilient and connected freshwater networks to conserve biodiversity in United States rivers and streams under climate change

Article Title: Conserving just 35% of nation’s waterways could sustain freshwater biodiversity

Article References: Conserving just 35% of nation’s waterways could sustain freshwater biodiversity. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: freshwater biodiversity, river conservation, climate resilience, PLOS One, The Nature Conservancy, watershed connectivity, dam removal, stream restoration, United States rivers, habitat protection, flow regime, conservation planning

The grant was first secured in 2023 by Andrea Dávalos, associate professor of biological sciences at SUNY Cortland, and Li Jin, professor of geology, with Mary Beth Voltura, associate professor of biological sciences, joining them to help develop the project. What began as a component of the Coregonine Restoration Framework, a binational plan representing eight U.S. states, three U.S. intertribal organizations and the Canadian province of Ontario to restore and conserve the coregonine subfamily of freshwater fish, has since expanded into wider opportunities for students, while keeping its focus firmly on aquatic life and the ecosystems that sustain it.

This year, the Cortland portion of the grant totaled 73,315 dollars, enough to support five Cortland students and two Oswego students in research placements across the state. Although the budget is modest by the standards of large research programs, the faculty behind the initiative argue that its impact is disproportionate to its size. Jin emphasized that the paid structure of the internships matters as much as the science itself, because it allows students to pursue valuable professional opportunities without the burden of financial stress that often forces undergraduates to choose between earning money and gaining research experience.

The internships are designed to immerse students in the full workflow of professional fisheries science. According to Dávalos, participants engage in original research, hone their communication skills and learn a variety of field and laboratory techniques used in fisheries work. Just as importantly, they interact daily with professionals, graduate students and professors, building the kind of networks that frequently shape career trajectories long before graduation. She described networking as one of the great aspects of the internship, noting that these relationships expose undergraduates to career paths they might never otherwise encounter.

Among this year’s participants, the placements spanned some of New York’s most important aquatic research institutions. Jonathan Hall worked at the Cornell Biological Field Station at Shackelton Point, Isabella Impellizzeri was based at SUNY Oswego, Minju Kim conducted her research at the New York State Water Resources Institute at Cornell University, Vinoj Ramachandran worked with the Department of Environmental Conservation in Cortland, and Ava Schiff was placed at the SUNY College of Environmental Science and Forestry’s Thousand Islands Biological Station. Each site offered a distinct window into the practice of fisheries and water-resources science.

Kim, a senior chemistry major with a minor in geographic information systems, spent her summer studying the effects of dam removal, a topic of growing importance as managers weigh the ecological benefits of restoring free-flowing rivers against the practical realities of aging infrastructure. Her work combined fieldwork, laboratory analysis and data processing, including bioindicator sampling, a technique that uses living organisms to assess environmental conditions over time. She said that participating in an active field research project provided invaluable insight into professional workflows and project execution, giving her a realistic picture of how environmental science is conducted outside the classroom.

The experience has already shaped Kim’s plans for life after graduation. She intends to pursue a career in environmental chemistry that applies environmental monitoring and sustainable ecosystem management, with a particular focus on water quality. Reflecting on the summer, she noted that the internship provided practical, professional skills in fieldwork and laboratory analysis that go beyond standard classroom theory, a distinction that many undergraduates only encounter for the first time in graduate school or their first job.

For Impellizzeri, a senior conservation biology major, the eight weeks at SUNY Oswego delivered a different but equally valuable set of skills centered on boat-based fieldwork. Her research contributed to weekly tows for larval fish at four sites, with the collected samples subsequently tested and identified in the laboratory. Along the way she completed New York boater safety training and drove a boat for the first time, and learned how to manage sample collection and water profile measurements on the water. She described the hands-on experience as invaluable, particularly the multitude of skills she acquired regarding boat procedures and safety.

The internship has also helped Impellizzeri clarify her next steps. Still weighing her career options after graduation, she said that working near the water proved highly interesting, and that she is now considering a job at one of the Great Lakes, whether conservation based or nature based in general. Her trajectory illustrates one of the central aims of the program: to give undergraduates enough direct exposure to fisheries science that they can make informed decisions about graduate study and employment in the field.

Faculty involved in the program say the combination of paid positions, covered housing costs and credit-earning placements has been central to its success, removing financial barriers while ensuring the experience carries formal academic weight. Applications for the Summer 2027 internships, the final year currently funded under the USGS grant, will open in the spring semester. As the Coregonine Restoration Framework continues its multi-state, multi-national effort to conserve a vulnerable subfamily of freshwater fish, the program’s graduates carry with them the field techniques, laboratory skills and professional connections that the next generation of fisheries scientists will need.

Subject of Research: Paid undergraduate fisheries research internships in New York funded by a USGS grant tied to the Coregonine Restoration Framework

Article Title: Students land research internships at fisheries across New York

Article References: Students land research internships at fisheries across New York. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: USGS grant, SUNY Cortland, SUNY Oswego, fisheries internships, undergraduate research, Coregonine Restoration Framework, dam removal, larval fish, water quality, New York State, aquatic science, fieldwork