Geology topics

Jeffrey Muehlbauer

Publications and source records attributed to Jeffrey Muehlbauer.

15 recordsLinked to original sources

USGS2026

DRIFteRS: A dataset of drift invertebrate densities in streams and rivers across western North America, 1997–2024

Prey availability is among the most influential and highly variable determinants of fish growth and freshwater habitat carrying capacity, yet it remains understudied compared to physical habitat variables (Ouellet et al., 2025; Rosenfeld et al., 2014; Weber et al., 2017). We often lack a clear understanding of how much food is available to fishes, how it varies spatially and temporally, and how it influences responses to restoration (Ouellet et al., 2025; Rossi et al., 2024; Wipfli et al., 2010). Drift invertebrates—the primary food source for juvenile salmonids and other drift-foraging fishes—play a pivotal role in these dynamics. To better understand the spatiotemporal variability of drift invertebrate abundance and biomass across the freshwater range of drift-feeding salmonids in western North America, we compiled the DRift Invertebrates For salmonids in River Systems (DRIFteRS) dataset. The dataset encompasses 6125 samples of drift invertebrates, and, for a subset of drift samples, associated benthic invertebrate density data, collected from 1360 reaches on 459 unique rivers and streams spanning 55 river basins considered hydrologically independent (i.e., not nested within the same larger watershed) across British Columbia, Canada, and the U.S. states of Alaska, Arizona, California, Colorado, Idaho, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming. Sample sites represent a diverse array of river and stream habitats (e.g., headwater, mainstem, side channel), in watersheds with diverse land uses (e.g., urban, wilderness, agricultural), and disturbance histories (e.g., fire, restoration). Collected between 1997 and 2024, the data span the full calendar year and capture daily and seasonal patterns in drift abundance and biomass densities. When paired with water quality and quantity data as well as remotely sensed environmental landscape data, such as land use/land cover, climate, and disturbance history, channel morphology, and riparian vegetation composition, the DRIFteRS dataset can aid in identifying key drivers of drift invertebrate densities and mean body size and support predictive modeling in unsampled locations and times. The dataset may also be used to analyze aquatic-terrestrial resource flows, derive prey-encounter rates and profitability (mean prey size), and inform broader investigations of sit-and-wait foraging ecology, especially when paired with data on drift-foraging predators. For salmonid-focused applications, the dataset can be integrated into habitat evaluation models, including bioenergetic (e.g., Naman et al., 2019) and life cycle models (e.g., Beechie et al., 2023), to improve estimates of habitat capacity and population dynamics for river- and stream-rearing salmonids. Understanding prey availability dynamics is increasingly important, because rising water temperatures increase salmonid metabolic demands (Crozier et al., 2010). Flow regime transitions (i.e., snow or glacier dominated to rain dominated; Beechie et al., 2013), wildfire frequency and intensity (Hessburg et al., 2021), as well as plant community and phenology shifts (Cleland et al., 2007; Franklin et al., 2016) are all predicted to change with rising temperatures and are potential drivers of terrestrial and aquatic invertebrate prey quality and availability in lotic systems. These insights can ultimately inform restoration prioritization and design, helping managers consider food resource implications when evaluating restoration priorities and match habitat improvement to food supply. The data are released under the Creative Commons Attribution 4.0 International license and may be reused with attribution.

Alaska, Arizona, British Columbia, California, Col↗

USGS2026

Monitoring for the future of Central Alaska streams

Streams are good indicators of change and the health of watersheds. By monitoring stream chemical composition and the kinds of life they support, we can learn about how they are being stressed (by activities such as mining or climate change) or recovering from a stress (after restoration efforts). But Central Alaska watersheds and the natural stream conditions they produce are diverse. From long-term monitoring, and repeat measurements, we can start to understand the related baselines and fine-tune our understanding of changes.

Alaska↗

USGS2026

Using monitoring data to understand lake water quality trends in southwest Alaskan National Parks

Lakes are vital ecosystems in southwest Alaska, supporting Pacific salmon, wildlife, and people. In Katmai and Lake Clark National Parks and Preserves, lakes span diverse landscapes containing volcanic uplands, glacier-fed valleys, and tundra all of which combine to influence their temperature, water quality, and ability to support critical uses. As the regional climate shifts, our understanding of lake responses requires more than just measurements of the lake surface water. Through long-term sampling of lakes from the surface to deep waters, we track how the environment —shaped by weather, geology, and land cover—governs lake water quality, including temperature, dissolved oxygen, specific conductance, pH, and turbidity. These data help us understand and predict how lake water quality will change across seasons and landscapes, and what this will mean for lake ecology and the habitats fish and wildlife depend on. This work builds a foundation for predicting how Alaska’s lakes are changing and what that means for the ecosystems and communities they support.

Alaska↗

USGS2024

U.S. Geological Survey Grand Canyon Monitoring and Research Center: Proceedings of the fiscal year 2023 annual reporting meeting to the Glen Canyon Dam Adaptive Management Program

This proceedings is prepared for the USBR and Glen Canyon Dam Adaptive Management Program (GCDAMP) to account for work conducted and products delivered in FY 2023 by SBSC's Grand Canyon Monitoring and Research Center (GCMRC) and to inform the Technical Work Group of science conducted by GCMRC and its cooperators in support of the GCDAMP. It includes a summary of accomplishments, modifications to work plans, and results related to projects included in GCMRC’s FY 2021-23 Triennial Work Plan. This work was done to support the 11 resource goals identified in the Glen Canyon Dam Long-Term Experimental and Management Plan (LTEMP) Environmental Impact Statement and Record of Decision.

Arizona, Nevada, Utah↗

USGS2023

Reimagining large river management using the Resist–Accept–Direct (RAD) framework in the Upper Mississippi River

Background Large-river decision-makers are charged with maintaining diverse ecosystem services through unprecedented social-ecological transformations as climate change and other global stressors intensify. The interconnected, dendritic habitats of rivers, which often demarcate jurisdictional boundaries, generate complex management challenges. Here, we explore how the Resist–Accept–Direct (RAD) framework may enhance large-river management by promoting coordinated and deliberate responses to social-ecological trajectories of change. The RAD framework identifies the full decision space of potential management approaches, wherein managers may resist change to maintain historical conditions, accept change toward different conditions, or direct change to a specified future with novel conditions. In the Upper Mississippi River System, managers are facing social-ecological transformations from more frequent and extreme high-water events. We illustrate how RAD-informed basin-, reach-, and site-scale decisions could: (1) provide cross-spatial scale framing; (2) open the entire decision space of potential management approaches; and (3) enhance coordinated inter-jurisdictional management in response to the trajectory of the Upper Mississippi River hydrograph. Results The RAD framework helps identify plausible long-term trajectories in different reaches (or subbasins) of the river and how the associated social-ecological transformations could be managed by altering site-scale conditions. Strategic reach-scale objectives may reprioritize how, where, and when site conditions could be altered to contribute to the basin goal, given the basin’s plausible trajectories of change (e.g., by coordinating action across sites to alter habitat connectivity, diversity, and redundancy in the river mosaic). Conclusions When faced with long-term systemic transformations (e.g., > 50 years), the RAD framework helps explicitly consider whether or when the basin vision or goals may no longer be achievable, and direct options may open yet unconsidered potential for the basin. Embedding the RAD framework in hierarchical decision-making clarifies that the selection of actions in space and time should be derived from basin-wide goals and reach-scale objectives to ensure that site-scale actions contribute effectively to the larger river habitat mosaic. Embedding the RAD framework in large-river decisions can provide the necessary conduit to link flexibility and innovation at the site scale with stability at larger scales for adaptive governance of changing social-ecological systems.

Upper Mississippi River↗

USGS2023

Insectivorous bat foraging tracks the availability of aquatic flies (Diptera)

Rivers and their adjacent riparian zones are model ecosystems for observing cross-ecosystem energy transfers. Aquatic insects emerging from streams, for example, are resource subsidies that support riparian consumers such as birds, spiders, lizards, and bats. We collaborated with recreational river runners in Grand Canyon, Arizona, USA, to record acoustic bat activity and sample riparian insects using light traps at dusk from April through October 2017–2020. River runners collected these data on 1,428 events over 611 sampling nights at 410 sites throughout a 470-km segment of the Colorado River. We documented 71 insect taxa in light traps and recorded 19 bat species with acoustic detectors. We hypothesized that bat activity along this highly regulated river segment would be influenced primarily by variation in prey availability, as compared to other habitat descriptors. We predicted that bat activity would be positively related to aquatic insect catch rates and unrelated to terrestrial insect abundance. We fit Bayesian regression models to test these hypotheses and to quantify the relationship between bat activity and a suite of environmental variables: time of year, time of day, distance from perennial tributaries, distance from rapids, channel width, geomorphic reach, tall vegetation cover, air temperature, and lunar phase. Bat activity was positively related to the abundance of aquatic flies (Diptera), which outcompeted all other prey categories and structural habitat descriptors in our models. Within our dusk sampling period, activity of small myotis (California myotis [ Myotis californicus ] and Yuma myotis [ M. yumanensis ]) was high late in the evening and canyon bats ( Parastrellus hesperus ), conversely, were more active early in the evening. Activity of canyon bats varied seasonally, with peak activity in August. Our results support the hypothesis that aquatic prey, specifically aquatic flies, are key predictors of bat activity along a large, regulated river corridor and demonstrate the power of community science as a tool for ecosystem monitoring.

Journal of Wildlife Management↗

USGS2023

Colorado River Basin

The Colorado River is often referred to as “the lifeblood of the west.” The basin supplies municipal water to nearly 40 million people and irrigates approximately 22,000 km 2 of agricultural lands. Twenty-two major rivers converge with the Colorado after it begins its descent from the Rocky Mountains and winds through the plateaus of Colorado, Utah, and Arizona, onto the deserts of southwestern Arizona, and finally into the Gulf of California, where inflows from the Río Hardy and Río Sonoyta in Mexico complete the drainage. The mainstem Colorado, Green, Yampa, Little Colorado, and Yampa Rivers are described in further detail in the 2005 edition (Blinn and Poff, 2005) of this book. In this edition, we discuss seven other major tributaries in the Colorado River basin: the Gunnison, San Juan, Virgin, Bill Williams, Verde, Black, and Salt Rivers. The water quality and quantity, flora and fauna, and sediment and organic loads of each of these tributaries uniquely alter the mainstem Colorado River and the habitat it provides. Thus, understanding the hydrology, ecology, and human use of these tributaries is critical toward understanding both the complex history and present-day management of the Colorado River Basin as a whole.

Arizona, Baja California, California, Colorado, Ne↗

USGS2022

Experimental reductions in sub-daily flow fluctuations increased gross primary productivity for 425 river kilometers downstream

Aquatic primary production is the foundation of many river food webs. Dams change the physical template of rivers, often driving food webs toward greater reliance on aquatic primary production. Nonetheless, the effects of regulated flow regimes on primary production are poorly understood. Load following is a common dam flow management strategy that involves sub-daily changes in water releases proportional to fluctuations in electrical power demand. This flow regime causes an artificial tide, wetting and drying channel margins and altering river depth and water clarity, all processes that are likely to affect primary production. In collaboration with dam operators, we designed an experimental flow regime whose goal was to mitigate negative effects of load following on ecosystem processes. The experimental flow contrasted steady-low flows on weekends with load following flows on weekdays. Here, we quantify the effect of this experimental flow on springtime gross primary production (GPP) 90-to-425 km downstream of Glen Canyon Dam on the Colorado River, AZ, USA. GPP during steady-low flows was 41% higher than during load following flows, mostly owing to non-linear reductions in sediment-driven turbidity. The experimental flow increased weekly GPP even after controlling for variation in weekly mean discharge, demonstrating a negative effect of load following on GPP. We estimate that this environmental flow increased springtime carbon fixation by 0.27 g C m –2 d –1 , which is ecologically meaningful considering median C fixation in 356 U.S. rivers of 0.44 g C m –2 d –1 and the fact that native fish populations in this river are food-limited.

PNAS Nexus↗

USGS2022

Population connectivity of aquatic insects in a dam-regulated, desert river

Humans have exaggerated natural habitat fragmentation, negatively impacting species dispersal and reducing population connectivity. Habitat fragmentation can be especially detrimental in freshwater populations, whose dispersal is already constrained by the river network structure. Aquatic insects, for instance, are generally limited to two primary modes of dispersal: downstream drift in the aquatic juvenile life stages and flight during the terrestrial winged adult stage. Yet the impacts of large hydropower dams can make rivers uninhabitable for incoming (drifting) juvenile insects, with remaining refugia found only in tributaries. The ability of adult aquatic insects to traverse such river stretches in search of suitable tributary habitat likely depends on factors such as species-specific dispersal ability and distance between tributaries. To explore the intersection of natural and human-induced habitat fragmentation on aquatic insect dispersal ability, we quantified population genetics of three taxa with varying dispersal abilities, a caddisfly (Hydropsychidae, Hydropsyche oslari ), a mayfly (Baetidae: Fallceon quilleri ), and a water strider (Veliidae: Rhagovelia distincta ), throughout tributaries of the Colorado River in the Grand Canyon, Arizona, USA. Using 2bRAD reduced genome sequencing and landscape genetics analyses, we revealed a strong pattern of isolation by distance among mayfly populations. This contrasts with caddisfly and water strider populations, which were largely panmictic. Analysis of thousands of informative single nucleotide polymorphisms showed that realized dispersal ability may not be accurately predicted by species traits for these widespread species. Principal components analysis revealed a strong division between caddisfly populations upstream and downstream of Havasu Creek (279 km through the 390 km study reach), suggesting that the geography of the Grand Canyon imposes a dispersal barrier for this species. Our use of genetic tools in the Grand Canyon to understand population structure has enabled us to elucidate dispersal barriers for aquatic insects. Ultimately, these data may be useful in informing effective conservation management plans for understudied organisms of conservation interest.

River Research and Applications↗

USGS2022

Little bugs, big data, and Colorado River adaptive management: Preliminary findings from the ongoing bug flow experiment at Glen Canyon Dam

The undammed Colorado River in Grand Canyon was characterized by spring snow-melt floods that sometimes exceeded 100,000 cubic feet per second (cfs). These were followed by occasional flash floods during summer monsoons, then by low flows from fall through early spring (Figure 1; Topping and others, 2003). This seasonally variable flow regime carried huge loads of sediment and was an important driver of natural processes that sustained the Colorado River ecosystem. For instance, high turbidity associated with this flow regime likely restricted algal growth to the river’s edge or shallow cobble habitats, similar to other desert rivers. Aquatic invertebrate assemblages were probably diverse and adapted to these variable conditions (Vinson, 2001; Haden and others, 2003). Native fishes were likely opportunistic feeders, consuming ants, seeds, and other terrestrial resources during times of flooding and switching to aquatic-derived resources like algae and aquatic invertebrates at other times (Minckley, 1991; Behn and Baxter, 2019). Regulation of the Colorado River by Glen Canyon Dam in 1963 eliminated the annual snowmelt floods, it sharply increased base flows by more than 50 percent, and dramatically increased within-day fluctuations in discharge for hydropower production (the ‘daily tides’ of the river, Figure 1 and 2; Topping and others, 2003). Glen Canyon Dam also changed other aspects of the river’s physical template, particularly temperature, sediment, and nutrient regimes. These changes to the physical template of the river led to fundamental changes in the natural processes that the sustain Colorado River ecosystem. For example, algae are common throughout the river during periods of clear water and represent the foundation of aquatic food webs (Stevens and others, 1997; Cross and others 2013). Many types of aquatic insects have disappeared or become rare, particularly sensitive groups such as mayflies, stoneflies, and caddisflies (Kennedy and others, 2016). Because aquatic insect assemblages in the Colorado River in Grand Canyon are neither diverse nor productive, food webs are simplified and inherently unstable, limiting populations of hungry fish (Cross and others 2013; Korman and others 2021).

Arizona↗

USGS2021

Hydropeaking intensity and dam proximity limit aquatic invertebrate diversity in the Colorado River Basin

River biodiversity is threatened globally by hydropower dams, and there is a need to understand how dam management favors certain species while filtering out others. We examined aquatic invertebrate communities within the tailwaters 0–24 km downstream of seven large hydropower dams in the Colorado River Basin of the western United States. We quantified aquatic invertebrate dominance, richness, abundance, and biomass at multiple locations within individual tailwaters and across the basin and identified biological community responses associated with dam operations and distance from dam. We found that each tailwater was dominated by 3–7 invertebrate taxa, accounting for 95% of total abundance. Half of these dominant taxa were non-insect, non-flying species and thus were unavailable to terrestrial consumers. Consistent with previous studies, aquatic insects and sensitive taxa were negatively associated with hydropeaking intensity (magnitude of daily flow fluctuations associated with hydropower generation), which limits the composition and potentially the quality of the invertebrate food base. While total invertebrate abundance and biomass did not change with increasing distance downstream from dams, insect and sensitive taxa richness, abundance, and biomass all increased, suggesting that impacts of hydropeaking are most acute immediately downstream of dams. Our results demonstrate that tailwaters experiencing hydropeaking support high abundances of aquatic invertebrate, but the diversity of these communities is low.

Arizona, California, Colorado, Nevada, New Mexico,↗

USGS2020

Variables affecting resource subsidies from streams and rivers to land and their susceptibility to global change stressors

Stream and river ecosystems provide subsidies of emergent adult aquatic insects and other resources to terrestrial food webs, and this lotic–land subsidy has garnered much attention in recent research. Here, we critically examine a list of biotic and abiotic variables—including productivity, dominant taxa, geomorphology, and weather—that should be important in affecting the nature of these subsidy dynamics between lotic and terrestrial ecosystems, especially the pathway from emergent aquatic insects to terrestrial predators. We also explore how interactions between these variables can lead to otherwise unexpected patterns in the importance of aquatic subsidies to terrestrial food webs. Utilizing a match-mismatch framework developed previously, we identify how these variables and interactions may be affected by a broad suite of stressors in addition to contaminants: climate change, land-use conversion, damming and water abstraction, and species invasions and extinctions. These stressors may all act to modify and potentially exacerbate the effects of contaminants on subsidies. The available literature on many variables is sparse, despite strong theoretical underpinnings supporting their importance for lotic–land subsidies. Notably, these understudied variables include those related to physical geomorphology and the structure of the stream/river and floodplain/riparian zone as well as species-specific interactions between aquatic and terrestrial organisms. We suggest that more explicit characterization of these variables and more research directly linking broad-scale stressors to subsidy resource–consumer interactions can help provide a more mechanistic understanding to lotic–land subsidy dynamics within a changing environment.

Book chapter↗

USGS2020

Net-spinning caddisfly distribution in large regulated rivers

Most of the world's large rivers are dammed for the purposes of water storage, flood control, and power production. Damming rivers fundamentally alters water temperature and flows in tailwater ecosystems, which in turn affects the presence and abundance of downstream biota. We collaborated with more than 200 citizen scientists to collect 2,194 light trap samples across 2 years and more than 2,000 river km. Samples contained 16,222 net‐spinning caddisfly ( Hydropsyche ) individuals across six species. We used these data to model the distribution of Hydropsyche throughout the Colorado River Basin in the western U.S.A. to identify the roles of water temperature, flows, and species‐specific morphology in determining aquatic species distributions throughout a large arid watershed that has been heavily altered by damming. We predicted that water temperatures would determine Hydropsyche presence and abundance to a greater extent than diel variation in river stage associated with hydropower production. Among many species, adult female Hydropsychids are morphologically adapted to swim to deep‐water oviposition sites. We predicted that the presence of this ability would negate the otherwise deleterious effects of high stage change on caddisfly egg mortality. We found that distributions of the two most widespread species, Hydropsyche occidentalis and Hydropsyche oslari (92% of total Hydropsyche captured), were both predicted by water temperatures. However, we also found that the abundance of H. oslari decreased by as much as 10‐fold as diel stage change increased, despite the presence of female morphological adaptations for deep‐water oviposition. We found sexual dimorphism and evidence for deep‐water swimming adaptations in 5/6 species. Our results show that net‐spinning caddisflies have species‐specific responses to environmental variation and suggest that environmental flows designed to reduce diel stage change and destabilise water temperatures may improve habitat quality for these ubiquitous and important aquatic insects.

Arizona, Colorado, New Mexico, Utah, Wyoming↗

USGS2020

Bug flows: Don’t count your midges until they hatch

Usually when people hear about a “bug problem” it’s due to an undesirable overabundance of insects (think plague of locusts). In the Colorado River in Grand Canyon, however, we are faced with the opposite predicament: the river is essentially devoid of bugs. Aquatic insects are a fundamental component of a healthy river ecosystem. Most aquatic insects spend their juvenile life stages (egg, larva, pupa) in the river and their winged adult life stage flying along the riparian corridor. Throughout these metamorphoses one thing is for certain: aquatic insects are prey for fish, birds, bats, lizards, and even other invertebrates. In Grand Canyon, food web studies conducted by the US Geological Survey (USGS) have demonstrated that populations of both native and sport fish are food limited (Cross et al. 2013, Kennedy et al. 2013). In other words, fish in Grand Canyon are consistently facing a calorie deficit. Indeed, the US Fish and Wildlife Service has cited the inadequate and unreliable food supply as the single greatest problem facing endangered Humpback Chub populations in the Grand Canyon (USFWS 2019).

Boatman's Quarterly Review↗

USGS2019

Aquatic–terrestrial linkages provide novel opportunities for freshwater ecologists to engage stakeholders and inform riparian management

Studies of aquatic–terrestrial ecosystem linkages explore the mechanisms by which components of one ecosystem, such as the aquatic insect community in a stream, directly affect components of an adjacent ecosystem, such as the density and diversity of riparian predators. On a human level, research into these linkages allows freshwater ecologists to form novel collaborations with stakeholders and other interest groups by emphasizing shared interests. To highlight this point, we use 3 case studies as examples of how aquatic–terrestrial linkages research can be leveraged to achieve multifaceted goals of improving riparian and freshwater management, engaging stakeholders, and advancing ecological understanding. In the 1 st case study, we describe a project in which consideration of the complex life histories of aquatic insects could have led to more effective outcomes for riparian bird restoration. The 2 nd case study provides an example of how studying contaminant transport through ecological subsidies has been incorporated into programs for contaminant management. In the 3 rd case, we use a study of terrestrial vertebrates feeding on adult aquatic insects to show how research into aquatic–terrestrial subsidies connects freshwater ecologists, youth groups, and commercial river guides. By focusing on how in-stream processes propagate onto land through ecological subsidies, we argue that freshwater ecologists also gain a platform for communicating their science to riparian managers and the public, which can improve the potential for stream and riparian co-management and restoration success.

Freshwater Science↗