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Mountain streams play an important role in the global carbon cycle by transporting, metabolizing, and exchanging carbon they receive from the terrestrial environment. The rates at which these processes occur remain highly uncertain because of a paucity of observations and the difficulty of measuring gas exchange rates in steep, turbulent mountain streams. This uncertainty is compounded by large temporal and spatial variability in stream carbon dioxide (CO2) concentrations in mountain environments. In this study, we measured diel, seasonal, and annual variations in CO2 partial pressure (pCO2) in seven headwater streams and a groundwater spring in the Colorado Rocky Mountains to determine how CO2 exchange fluxes (FCO2) vary with time, annual precipitation, and landscape characteristics. Our results show that temporal variability in pCO2 and FCO2 in mountain streams is large and is strongly influenced by solar radiation, the accumulation and melting of seasonal snowpacks, and interannual variations in precipitation. Spatial variations in pCO2 and FCO2 were related to landscape characteristics, with soil organic matter, wetlands, and likely groundwater discharge zones having a positive influence. Periglacial features, such as ice and rock glaciers, had a negative influence on stream pCO2 and FCO2. Estimated FCO2 from streams in an alpine/subalpine region of Colorado was 3.4 kg C m−2 yr−1 normalized to stream surface area (95% CI: 2.1–5.0 kg C m−2 yr−1), consistent with recent work on CO2 exchange from mountain streams in the Swiss Alps. Our results highlight the importance of mountain streams as substantial contributors in the global carbon cycle. Plain Language Summary: Mountain landscapes are a key component of the global carbon cycle. Mountain vegetation consumes atmospheric CO2 and produces organic matter, which can be stored in the soil. This organic matter decays over time and may be flushed into mountain streams and lakes during snowmelt or rain events, where it may be further processed and emitted back to the atmosphere as CO2 (or methane), completing the cycle. The rates at which these processes occur and the magnitude of aquatic carbon fluxes in mountain landscapes are poorly known; the goal of this study is to provide insight into their importance. We show that in the Rocky Mountains of Colorado, groundwater and soil water can be important sources of carbon to mountain streams. Photosynthesis imparts a daily cycle on stream CO2 concentrations, and the seasonal accumulation and melt of deep snowpacks causes a strong seasonal cycle in stream CO2. Annual variations in precipitation (primarily snowfall) can lead to large interannual variability in stream CO2 concentrations and the amount of CO2 exchanged with the atmosphere. Thus, increases or decreases in precipitation could have an important influence on future rates of carbon cycling in mountain environments. Key Points: Strong seasonal variability in pCO2 is related to accumulation and melt of seasonal snowAnnual CO2 gas exchange fluxes were positively related to annual precipitation, indicating climate may influence aquatic carbon cyclingCO2 exchange fluxes from mountain streams are comparable to exchange fluxes from boreal‐Arctic, temperate, and tropical landscapes [ABSTRACT FROM AUTHOR]

The article explores best solution that balances the rights of the public and the recreation economy with the rights of private landowners in the U.S. Topics discussed include economic impact of river-related recreation in Colorado to underline the importance of a clear definition of navigability in the state, history of public access to navigable waterways in the U.S., and legal void created by Colorado's lack of a clear navigability definition.

Stream habitat fragmentation caused by manmade structures is ubiquitous in Colorado, creating a need for passage solutions that accommodate multiple fish species. This study tested the effectiveness of a rock‐ramp fishway for passing nine fish species with a range of swimming abilities. The target species for the fishway design included Brassy Minnow Hybognathus hankinsoni (weakest swimming), Longnose Dace Rhinichthys cataractae, Longnose Sucker Catostomus catostomus, and Brown Trout Salmo trutta (strongest swimming). Testing included a 46‐h enclosure study and 3‐month extended study, during which fish passage was evaluated using PIT tags. All of the species exhibited successful passage through the fishway during the enclosure study, but movement probabilities varied by species. Five species were not detected at the fishway during the extended study, possibly due to issues with attraction flows, entrance conditions, or motivation. Hydraulic conditions within the fishway were also evaluated. Roughness elements maintained a benthic, low‐velocity zone across a range of flows, even when surface and depth‐averaged velocities surpassed the design criteria for the weakest swimming species. The methods from this study could be replicated at other locations to evaluate design criteria (e.g., slope, capacity, roughness, and configuration) and performance for a variety of fish species and fishway types. [ABSTRACT FROM AUTHOR]

Knickpoints in longitudinal river profiles are proxies for the climatic and tectonic history of active mountains. The analysis of river profiles commonly relies on the assumption that drainage network configurations are stable. Here, we show that this assumption must be made cautiously if changes in contributing area are fast relative to knickpoint migration rates. We studied the Parachute Creek basin in the Roan Plateau, Colorado, United States, where knickpoint retreat occurs in horizontally uniform lithology so that drainage area is the sole governing variable. In this basin, we identified an anomalous catchment in the degree to which a stream power-based model predicted knickpoint locations. The catchment is experiencing area loss as the plateau edge is eroded by cliff migration in proximity to the Colorado River. Model predictions improve if the plateau edge is assumed to have migrated over the time scale of knickpoint retreat. Finally, a Lagrangian model of knickpoint migration enabled us to study the kinematic links between drainage area loss and knickpoint migration and offered constraints on the temporal aspects of area loss. Modeled onset and amount of area loss are consistent with cliff retreat rates along the margin of the Roan Plateau inferred from the incisional history of the upper Colorado River. [ABSTRACT FROM AUTHOR]

Traditional methods of collecting, sorting, and identifying benthic macroinvertebrate samples are useful for stream biomonitoring and ecological studies, however, these methods are time consuming, expensive, and require taxonomic expertise. Estimating larval densities through collection of post-emergent exuvia can be a practical and time efficient alternative. We evaluated the use of multiple pass depletion techniques of the post-emergent exuvia of Pteronarcys californica to estimate larval densities at ten sites in three Colorado rivers. Exuvia density was highly correlated with both final-instar larval density (R2 = 0.90) and total larval density (R2 = 0.88) and the multiple pass removal technique performed well. Exuvia surveys found P. californica at three low density sites where benthic sampling failed to detect it. At moderate and high density sites the exuvia surveys always produced lower density estimates than benthic surveys. Multiple pass depletion estimates of exuvia proved to be an accurate and efficient technique at estimating larval densities and provided an effective alternative for traditional benthic sampling when objectives are detecting and monitoring P. californica, especially at low density sites. [ABSTRACT FROM AUTHOR]

An ancient drainage, named Crooked Ridge river, is unique on the Colorado Plateau in extent, physiography, and preservation of its alluvium. This river is important for deciphering the generally obscure evolution of rivers in this region. The ancient course of the river is well preserved in inverted relief and in a large valley for a distance of several tens of kilometers on the Kaibito Plateau-White Mesa areas of northern Arizona. The prominent landform ends ~45 km downstream from White Mesa at a remarkable wind gap carved in the Echo Cliffs. The Crooked Ridge river alluvium contains clasts of all lithologies exposed upstream from the Kaibito Plateau to the San Juan Mountains in Colorado, so we agree with earlier workers that Crooked Ridge river was a regional river that originated in these mountains. The age of Crooked Ridge river cannot be determined in a satisfactory manner. The alluvium now present in the channel is the last deposit of the river before it died, but it says nothing about when it was born and lived. Previous research attempted to date this alluvium, mostly indirectly by applying a sanidine age obtained ~50 km away, and directly from six sanidine grains (but no zircon grains), and concluded that Crooked Ridge river was a small river of local significance, because the exotic clasts were interpreted to have been derived from recycling of nearby preexisting piedmont gravels; that its valley was not large; and that it only existed ca. 2 Ma. Our proposition in 2013 was that Crooked Ridge river came into being in Miocene and possibly Oligocene time, which is when the very high San Juan Mountains were formed, thus giving rise to abundant new precipitation and runoff. To address some of this ambiguity, we examined all available evidence, which led us to conclude that several of the interpretations by previous researchers are not tenable. We found no evidence for a preexisting piedmont from which the Crooked Ridge river exotic clasts could be recycled. Furthermore, the principal advocate of the piedmont discounted it in a later publication. Tributaries to Crooked Ridge river in the White Mesa area contain no exotic clasts that could have been derived from a local clast-rich piedmont; only the Crooked Ridge river channel contains exotic clasts. So, we conclude that Crooked Ridge river was the principal stream, that it was of regional significance, that it was headed in the San Juan Mountains, and that it existed long before it died, perhaps as early as Oligocene time, until it was captured by the San Juan River, maybe ca. 2 Ma. West and downstream from The Gap, no deposits or geomorphic features attributable to the Crooked Ridge river have been preserved, but we infer that the river joined the Colorado and Little Colorado paleorivers somewhere on the east side of the Kaibab Plateau, and then crossed the plateau along a paleovalley that approximated the present alignment of the eastern Grand Canyon. West of the Kaibab Plateau, the combined rivers perhaps flowed in a northwest-trending strike valley to an as-yet-unknown destination. [ABSTRACT FROM AUTHOR]

The thermophilic microbial mat communities at hot springs in the Black Canyon of the Colorado River, thought to harbor the protistan human pathogen Naegleria fowleri, were surveyed using both culture-independent and -dependent methods to further understand the ecology of these hot spring microbiomes. Originating from Lake Mead source water, seven spring sites were sampled, varying in temperature from 25 to 55 °C. Amplicon-based high-throughput sequencing of twelve samples using 16S rRNA primers (hypervariable V4 region) revealed that most mats are dominated by cyanobacterial taxa, some but not all similar to those dominating the mats at other studied hot spring systems. 18S rRNA amplicon sequencing (V9 region) demonstrated a diverse community of protists and other eukaryotes including a highly abundant amoebal sequence related to Echinamoeba thermarum. Additional taxonomic and diversity metric analyses using near full-length 16S and 18S rRNA gene sequencing allowed a higher sequence-based resolution of the community. The mat sequence data suggest a major diversification of the cyanobacterial orders Leptolyngbyales, as well as microdiversity among several cyanobacterial taxa. Cyanobacterial isolates included some representatives of ecologically abundant taxa. A Spearman correlation analysis of short-read amplicon sequencing data supported the co-occurrences of populations of cyanobacteria, chloroflexi, and bacteroidetes providing evidence of common microbial co-occurrences across the Black Canyon hot springs., (© 2023. The Author(s).)

Detailed study of the response of step-pool mountain channels to wildfire is rare despite increasing vulnerability of these systems. This paper reports the initial biogeomorphic response of step-pool streams to storms following the 2012 Waldo Canyon Fire, Colorado, USA. Field surveys, benthic macroinvertebrate sampling, and light detection and ranging (LiDAR) terrestrial laser scanning through 2014 generated a substantial data set comparing changes within seven channels burned by a range of severity with three unburned reference reaches. Results showed that wildfire increased the susceptibility of step-pool channels to destabilize according to the severity of burn. Whereas the step-pool morphology (step height H, step length L, and H/L) remained relatively unchanged in unburned and low-severity burned channels--even through an extreme rainfall event with recurrence intervals up to 500-1000 years--study sites affected by high burn severity altered significantly following the first comparatively minor storms. Study channels burned by moderate severity exhibited variable responses ranging from minor to substantial morphological changes, suggesting that additional factors, including slope, local topography, and proximity to other highly disturbed sites may play explanatory roles. The ecological response corroborated the geomorphic findings, with data for benthic macroinvertebrates varying according to burn severity along with the changing post-fire step-pool morphology. Ordination analysis enabled data synthesis and showed that precipitation intensity (r = 0.59) and the severity of burn (r = 0.60) together influenced the interacting morphologic and ecological responses after the Waldo Canyon Fire. Variations in H (r = 0.72), L (r = 0.56), and thalweg elevation (r = 0.75) correlated the most with the types of benthic macroinvertebrates present. Following the Waldo Canyon Fire, the highest rainfall intensities coincidentally occurred over study sites in high-severity burn areas. Although disentangling the effects of rainfall intensity and burn severity proved difficult given this scenario, the interacting and complementary roles of burn severity and rainfall intensity likely led to the greatest morphologic and ecological impacts at those sites. Findings offer insights for the post-fire management of step-pool streams that characterize frequently burned mountain areas. As wildfires grow in frequency and magnitude under warming regimes, management becomes increasingly important for anticipating future changes in burned river landscapes, mitigating potential floods and hazards, and promoting sustainable river ecosystems. [ABSTRACT FROM AUTHOR]

In 1936, the completion of Hoover Dam on the Colorado River in Nevada and Arizona created Lake Mead, the largest reservoir in the United States. When the lake reached capacity in 1941 several canyons and valleys were flooded, along with two towns, several mines, farm fields, and roads. The area had not been surveyed archaeologically and little detailed information exists about the vegetation and geology of this region. The map reconstructions the geography of the area in 1930 before Lake Mead was constructed, showing roads, towns, mines, physical features, and private property, and was created using a range of historical United States Geological Survey (USGS) maps, a digital elevation model (DEM) providing underwater elevations, and other historical sources. The map includes portions of southern Nevada and northwest Arizona, United States, and is at a scale of 1:210,000. It is hoped that the map may draw attention to the lost geographies of other localities across the United States due to the more than 84,000 dams and reservoirs in the country. [ABSTRACT FROM AUTHOR]

Agricultural land retirement is increasingly used to manage water resources. This study uses well-level enrollment data to explore the factors that influence landowner participation in the Colorado Republican River Conservation Reserve Enhancement Program. An empirical model of enrollment is informed by a theoretical model of participation that incorporates aquifer and soil characteristics in addition to financial incentives. Our results reveal that enrollment is predicted to increase by 0.087 percentage points with a $10 increase in the incentives offered. The probability of enrollment is also influenced by the aquifer's saturated thickness and the soil characteristics that impact land productivity. [ABSTRACT FROM AUTHOR]

Sediment budgets are an important tool for understanding how riverine ecosystems respond to perturbations. Changes in the quantity and grain size distribution of sediment within river systems affect the channel morphology and related habitat resources. It is therefore important for resource managers to know if a river reach is in a state of sediment accumulation, deficit or stasis. Many sediment-budget studies have estimated the sediment loads of ungaged tributaries using regional sediment-yield equations or other similar techniques. While these approaches may be valid in regions where rainfall and geology are uniform over large areas, use of sediment-yield equations may lead to poor estimations of loads in regions where rainfall events, contributing geology, and vegetation have large spatial and/or temporal variability. Previous estimates of the combined mean-annual sediment load of all ungaged tributaries to the Colorado River downstream from Glen Canyon Dam vary by over a factor of three; this range in estimated sediment loads has resulted in different researchers reaching opposite conclusions on the sign (accumulation or deficit) of the sediment budget for particular reaches of the Colorado River. To better evaluate the supply of fine sediment (sand, silt, and clay) from these tributaries to the Colorado River, eight gages were established on previously ungaged tributaries in Glen, Marble, and Grand canyons. Results from this sediment-monitoring network show that previous estimates of the annual sediment loads of these tributaries were too high and that the sediment budget for the Colorado River below Glen Canyon Dam is more negative than previously calculated by most researchers. As a result of locally intense rainfall events with footprints smaller than the receiving basin, floods from a single tributary in semi-arid regions can have large (≥ 10 ×) differences in sediment concentrations between equal magnitude flows. Because sediment loads do not necessarily correlate with drainage size, and may vary by two orders of magnitude on an annual basis, using techniques such as sediment-yield equations to estimate the sediment loads of ungaged tributaries may lead to large errors in sediment budgets. [ABSTRACT FROM AUTHOR]

Aim To examine how the distributions of fishes in three rivers changed over four decades of rising air temperatures. Location Colorado, USA. Methods We used fish sampling over more than four decades in three rivers in Colorado, USA, to examine changes in the upper and lower distribution limits of fishes. Results There was a divergent pattern of range shifts among species. One coldwater fish species showed the expected pattern of retraction at its lower limit and expansion at its upper limit. However, warmwater fishes, on average, did not shift their upper distribution limit. Main conclusions All three rivers displayed a strong habitat transition from upstream, high-gradient reaches to downstream, low-gradient reaches, suggesting that habitat conditions associated with high channel slope may limit the ability of some fish species to track warming water temperatures. In addition, potential anthropogenic barriers to fish movement occurred near species distribution limits, and these may prevent or delay range shifts in river fishes. The overall pattern of range shifts was consistent across the three rivers, suggesting a coherent influence of species' traits, physiological tolerances and habitat requirements on fish species distributions. [ABSTRACT FROM AUTHOR]

Assessing spatial variation in hydrologic processes can help to inform freshwater management and advance ecological understanding, yet many areas lack sufficient flow records on which to base classifications. Seeking to address this challenge, we apply concepts developed in data-rich settings to public, global data in order to demonstrate a broadly replicable approach to characterizing hydrologic variation. The proposed approach groups the basins associated with reaches in a river network according to key environmental drivers of hydrologic conditions. This initial study examines Colorado (USA), where long-term streamflow records permit comparison with previously distinguished flow regime types, and Ecuador, where data limitations preclude such analysis. The flow regime types assigned to gages in Colorado corresponded reasonably well to the classes distinguished from environmental features. The divisions in Ecuador reflected major known biophysical gradients while also providing a higher resolution supplement to an existing depiction of freshwater ecoregions. Although freshwater policy and management decisions occur amidst uncertainty and imperfect knowledge, this classification framework offers a rigorous and transferrable means to distinguish catchments in data-scarce regions. The maps and attributes of the resulting ecohydrologic classes offer a departure point for additional study and data collection programmes such as the placement of stations in under-monitored classes, and the divisions may serve as a preliminary template with which to structure conservation efforts such as environmental flow assessments. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A 1240-year-long record of reconstructed annual flows of the Colorado River at Lees Ferry is analysed using singular spectrum analysis and multi-taper method of spectral analysis. Spectral analysis of the 100-year-long recent record of annual flows of Colorado River in the measured and reconstructed forms shows similar oscillations in high- and low-frequency bands. Therefore, the oscillatory components and trends extracted from the reconstructed data are a good representative of inter-annual, multi-decadal, and multi-centennial variability of natural flow in the river. In Colorado River the length of flow data is 1240 years and multi-centennial and multi-decadal oscillatory components can be extracted at a high confidence level. In this research we attempt to find whether the changes in streamflow in the twentieth century are due to an external cause such as climate change or whether they are part of the natural variability of flow observed in the past. The results suggest that there is only a part of the linear trend, caused by climate change or man-made effects, and an important part of that is due to climate variability which is believed to be totally natural. The same line of climate variability is still acting on our planet, and it may have gained new aspects due to the change in atmospheric composition and circulation as a result of anthropogenic effects. This may cause serious limitations to the water sustainability and water availability on the earth. [ABSTRACT FROM PUBLISHER]

Total mercury (THg) and selenium (Se) were analyzed by Inductively Coupled Plasma Mass Spectrometry in 11 internal and external tissues and stomach contents from 23 brown trout, Salmo trutta, of a 22.9-km reach of a high-gradient stream (upper Fountain Creek) in Colorado, USA, impacted by coal-fired power plants, shale deposits, and urbanization. Trout and water were sampled from four sites ranging from 2335 to 1818 m elevation. Lengths, weights, and ages of fish between pairs of the four sites were not significantly different. The dry weight (dw) to wet weight (ww) conversion factor for each tissue was calculated with egg-ovary highest at 0.379 and epaxial muscle fourth highest at 0.223. THg and Se in stomach contents indicated diet and not ambient water was the major source of Hg and Se bioaccumulated. Mean THg ww in kidney was 40.33 µg/kg, and epaxial muscle second highest at 36.76 µg/kg. None of the tissues exceeded the human critical threshold for Hg. However, all 23 trout had at least one tissue type that exceeded 0.02 mg/kg THg ww for birds, and four trout tissues exceeded 0.1 mg/kg THg ww for mammals, indicating that piscivorous mammals and birds should be monitored. Se concentrations in tissues varied depending on ww or dw listing. Mean Se dw in liver was higher than ovary at the uppermost site and the two lower sites. Liver tissue, in addition to egg-ovary, should be utilized as an indicator tissue for Se toxicity. [ABSTRACT FROM AUTHOR]

The lack of watershed-scale estimates of floodplain carbon stocks limits recognition of the important role of floodplains and river corridor restoration in efforts to enhance carbon sequestration. We use the South Platte River watershed of Colorado, USA as a case study to illustrate spatial patterns of, and controls on, floodplain carbon stocks at the watershed scale. This case study illustrates the disproportionate importance of floodplains for soil carbon stocks relative to adjacent uplands and provides an example of how spatially explicit data can be used to prioritize floodplain restoration with regard to carbon sequestration. We use the hydrogeomorphic floodplain tool GFPLAIN to delineate the extent of 100-year floodplains in the South Platte River watershed. We distinguish elevation bands for the steppe, montane, subalpine, and alpine zones. We also differentiate bead (floodplain width/channel width ≥ 5) and string (floodplain width/channel width < 5) reaches within the montane and subalpine zones. Drawing on prior, field-based measurements of organic carbon stock in downed, dead wood and soil in these floodplain types, we estimate total floodplain organic carbon stock based on median values of stock in different floodplain types and the spatial extent of these floodplain types. This estimate includes organic carbon stocks in lake and reservoir sediments in the watershed. Soil constitutes the greatest reservoir of floodplain carbon. The total estimated area of floodplain is 2916 km 2 , which is 4.3 % of the total watershed area of the South Platte River. Our preferred estimate is 42.7 Tg C stock (likely range of 39.1-42.7 Tg). This equates to 11.1 % of a previously estimated overall carbon stock (above and belowground biomass and soil organic carbon) in the entire watershed of 384 Tg C. Floodplains are thus disproportionately important, relative to their surface area, in storing organic carbon in this semiarid watershed. Field measurements of floodplain soil organic carbon stocks from across the globe indicate that this finding is not unique to this watershed, with implications for prioritizing floodplain management and restoration as a means of enhancing carbon sequestration., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Increasing demand for river water now conflicts with an increasing desire to maintain riparian ecosystems. Efficiently managing river flows for riparian vegetation requires an understanding of the time scale of flow effects, but this information is limited by the absence of long-term studies of vegetation change in response to flow variation. To investigate the influence of short- and long-term flow variability and dam operation on riparian vegetation, we determined the occurrence of 107 plant species in 133 permanent plots of known inundating discharge along the Gunnison River in Colorado on five different occasions between 1990 and 2013. Individual species moved up and down the gradient of inundating discharge coincident with increases and decreases in mean annual flow, and the correlations between flow and species occurrence were strongest when flows were weighted by time before vegetation sampling with a median half-life of 1.5 years. Some tall, rhizomatous, perennial species, however, responded to flows on a longer time scale. Logistic regression of species occurrence showed a significant relation with inundation duration for 70 out of 107 species. Plot species richness and total vegetative cover decreased in association with desiccation at low inundation durations and with fluvial disturbance at high inundation durations. Within-plot similarity in species occurrence between years decreased strongly with increasing inundation duration. Moderate inundation durations were dominated by tall, rhizomatous, perennial herbs, including invasive Phalaris arundinacea (reed canary grass). Over the 23-year study period, species richness declined, and the proportion of rhizomatous perennials increased, consistent with the hypothesis that decreases in flow peaks and increases in low flows caused by flow regulation have decreased establishment opportunities for disturbance-dependent species. In summary, annual-scale changes in vegetation were strongly influenced by flow variation, and decadal-scale changes were influenced by decreases in fluvial disturbance from upstream flow regulation beginning decades prior to the onset of this study., (Published 2022. This article is a U.S. Government work and is in the public domain in the USA. Ecological Applications published by Wiley Periodicals LLC on behalf of The Ecological Society of America.)

Biodegradation of [A-ring 14C] Estrone (E1), 17 β-estradiol (E2), and 17 α-ethinylestradiol ( EE2) to 14 CO2 was investigated under light and dark conditions in microcosms containing epilithon or sediment collected from Boulder Creek, Colorado. Mineralization of the estrogen A-ring was observed in all sediment treatments, but not epilithon treatments. No difference in net mineralization between light and dark treatments was observed for 14C-E2. Net mineralization of 14C-E1 and 14C- EE2 was enhanced in light treatments. Extents of 14 CO2 accumulation and rates of mineralization were significantly greater for E2 than E1 under dark conditions, but were comparable under light conditions. These results indicate substantial differences in the uptake and metabolism of E1 and E2 in the environment and suggest biorecalcitrance of E1 relative to E2 in light-limited environments. The extent of 14 CO2 accumulation and rate of mineralization for EE2 in dark treatments were less than half of that observed for E2 and generally lower than for E1, consistent with previous reports of EE2 biorecalcitrance. However, 14 CO2 accumulation and rates of mineralization were comparable for EE2, E2, and E1 under light conditions. These results indicate photoactivation and/or phototransformation/photodegradation processes can substantially enhance heterotrophic biodegradation of estrogens in sunlit environments and may play an important role in estrogen transport and attenuation. [ABSTRACT FROM AUTHOR]

Urbanization and elevated selenium can negatively affect aquatic macroinvertebrate communities. These factors are often highly correlated in streams along the Front Range of the Rocky Mountains, USA. Understanding which factor is the primary driver of macroinvertebrate community health would aid in the development of appropriate management actions to mitigate their influence. Data collected from three sites in the Big Thompson River, Colorado, in seven different years from 2006 to 2016 were used to develop a random forest model to determine the relative importance of an index of urbanization and dissolved selenium levels in predicting the relative status of macroinvertebrate communities as measured by Colorado multi-metric index (MMI) scores. Based on the percent increase in mean square error (%incMSE) variable importance measure, dissolved selenium has a greater influence on MMI scores than a development index (19.5% vs 15.2%). There is a significantly negative relationship between MMI scores and dissolved selenium levels. This relationship predicts a MMI score of 29.2 under the current dissolved selenium standard of 4.6 µg/L and 38.6 under the suggested lower standard of 3.1 µg/L. Although improvements in MMI score may result with any reduction in dissolved selenium, other factors may limit the maximum expected MMI scores in the absence of selenium as the intercept of the relationship is 57.9 on a scale of 0-100., (© 2022. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

A continuation of the current 23-year-long drought will require difficult decisions to prevent further decline.

Burrhead ChubMacrhybopsis marconisis a species of special concern endemic to subtropical streams in south Texas. We documented life history attributes and historical patterns in abundance and distribution to aid in understanding range-wide declines of the species among the Colorado and Guadalupe-San Antonio River systems. Life history results suggest Burrhead Chub lives for 2 years, reaches sexual maturity at age-1, and spawns multiple clutches during March–September. Review of museum vouchers revealed Burrhead Chub is now missing from 26% of its historical range, including most impounded stream segments. There was a significant difference in the size of stream fragments for which Burrhead Chub is missing or still persists. Timing of many extirpations occurred after fragmentation and coincided with a record drought (1949–1959) when range-wide stream flows were exceedingly low during the Burrhead Chub reproductive season. Furthermore, extensive historical collections taken during 1950–1961 in the Guadalupe River revealed a decline in relative abundance in upstream reaches as the drought continued. Based on these data, we hypothesize that Burrhead Chub experienced range-wide declines associated with historical drought conditions in desiccated stream fragments. Following the drought, stream flows recovered but recolonization by Burrhead Chub was blocked by impoundments in many fragments. These findings support previous linkages between stream connectivity, flow magnitude, and the persistence of fish populations while providing insight into the mechanisms driving freshwater fish declines in the plains of North America. Received January 20, 2013; accepted May 13, 2013 [ABSTRACT FROM AUTHOR]

Water resource management agencies have traditionally relied upon past observations of historical hydrologic records for long-term planning. This assumption of stationarity, that the past is representative of the future, may no longer be valid under changing climate conditions. The Gunnison River Basin contributes approximately 16% of the annual natural streamflow within the Upper Colorado River Basin, affecting water supply availability over the entire Colorado River Basin. Recent studies indicate that streamflow over the Gunnison River Basin, a subbasin within the Colorado River Basin, may decrease on the order of 15% through 2099. Further study has developed a methodology to statistically characterize the risk of regime shifts using observations of past streamflow through the use of a two-parameter gamma distribution. In this study, regime characteristics derived using a paleoreconstruction of streamflow over the Gunnison River Basin are compared regime characteristics developed using 112 projections of future hydrology to better understand how the frequency and duration of persistent dry and wet periods may change as the impacts of climate change are realized over the subbasin. Results indicate that under changing climate conditions, similar regime characteristics may be expected through 2039. However, between 2040 and 2099, more frequent and persistent dry regimes increase on the order of 50%. Conversely, wet regimes are expected to be shorter and less frequent than observed over the paleoclimatic record, decreasing in frequency by as much as 50%. [ABSTRACT FROM AUTHOR]

In Yellow Jacket Canyon, a small tributary stream in the San Juan River basin, Montezuma County, Colorado, we collected 11 subadult Colorado pikeminnows Ptychocheilus lucius during 2007-2010. Collection of these fish within this small tributary is significant given the distance of the sampling location to the mainstem San Juan River, sizes of Colorado pikeminnows collected, and documented association with mainstem river habitats. Subadults appear to be using Yellow Jacket Canyon on a regular basis. [ABSTRACT FROM AUTHOR]

The article discusses the establishment and perpetuation of historical myths. According to the article, historians sometimes assign false narratives to historical occurrences in order to promote a chauvinistic point of view, an urgency to provide answers to difficult historical questions, or from simple mistakes. The article examines the historical myths surrounding the expeditions of the late explorers Álvar Núñez Cabeza de Vaca, Francisco Vázquez de Coronado, and Luis Moscoso Alvarado in what would become Texas. The article compares those myths with the historical record left behind by Cabeza de Vaca in his work "Relaciíon," the mistranslation of the Spanish words Llano Estacado as "Staked Plains," and the misidentification and confusion of the Río Grande with the Río de las Palmas.

Abstract: The Río Colorado dryland river system in the southeast of the endorheic Altiplano Basin (Bolivia) terminates on a very flat coastal plain at the edge of the Salar de Uyuni, the world''s largest salt pan with an area of ca. 12,500km2. Since the Pleistocene the basin has experienced several lake expansion and contraction cycles in response to wetter and drier climate periods, respectively. At present the basin is in a dry climate period which results in a lake level lowstand and progradation of fluvial systems such as the Río Colorado onto the former lake bottom. The present field study of the terminus of the Río Colorado shows that the river experiences a gradual downstream decrease of bankfull width and depth. This bankfull decrease is caused by the combined effects of: (1) extremely low gradient of the lake bottom and, hence, loss of flow energy, and (2) downstream transmission losses due to high evaporation potential and river water percolation through the channel floor. Peak water discharge in seasonal, short-duration rain periods causes massive overbank flooding and floodplain inundation. On satellite images the morphology of the river terminus has a divergent pattern and resembles a network of coeval sinuous distributary channels. However, field observations show that only one channel is active at low flow stage, and at high-flow stage an abandoned, partially infilled channel may be active as well. The active channel at its termination splits into narrow and shallow anastomosing streams before its demise on the lacustrine coastal plain. The rest of the channels which form the divergent network are older sediment-filled abandoned sinuous river courses with multiple random avulsion points. These channel deposits, together with extensive amalgamated crevasse-splay deposits, form an intricate network of fluvial sand deposits. Successive stages of progressively deeper crevasse-channel incision into the floodplain are the result of waning-stage return flow of floodwaters towards the main channel. This results in increased crevasse-channel width, depth and length, and redeposition of eroded lacustrine coastal-plain sediment at the junction of the crevasse channel with the present-day river. A sedimentary model is proposed in which deep river bank incision by return flow in crevasse-channels creates the preferential locus for river avulsion. In a Lowstand Systems Tract with little vertical accommodation increase, the recurring avulsed-river paths result in a thin but laterally extensive network of amalgamated channel-fill, point-bar, crevasse-channel and crevasse-splay deposits. The resulting sedimentary architecture could easily be mistaken as produced by a distributary system of simultaneously active fluvial channels. [Copyright &y& Elsevier]

The understanding of nutrient uptake in streams is impeded by a limited understanding of how geomorphic setting and flow regime interact with biogeochemical processing. This study investigated these interactions as they relate to transient storage and nitrate uptake in small agricultural and urban streams. Sites were selected across a gradient of channel conditions and management modifications and included three 180-m long geomorphically distinct reaches on each of two streams in north-central Colorado. The agricultural stream has been subject to historically variable cattle-grazing practices, and the urban stream exhibits various levels of stabilisation and planform alteration. Reach-scale geomorphic complexity was characterised using highly detailed surveys of channel morphology, substrate, hydraulics and habitat units. Breakthrough-curve modelling of conservative bromide (Br−) and nonconservative nitrate (NO3−) tracer injections characterised transient storage and nitrate uptake along each reach. Longitudinal roughness and flow depth were positively associated with transient storage, which was related to nitrate uptake, thus underscoring the importance of geomorphic influences on stream biogeochemical processes. In addition, changes in geomorphic characteristics due to temporal discharge variation led to complex responses in nitrate uptake. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT Effective river management strategies require an understanding of how fluvial processes vary both spatially and temporally. Here, we examine the natural range of variability in the Conejos River Valley, southern Colorado, through documentation of terrace morphostratigraphic and sedimentological characteristics as well as through investigation of sediment contributions from headwaters, hillslopes and tributary streams. Additionally, soil development and radiocarbon ages, together with local and regional paleoclimate reconstructions, were used to infer the range of processes acting in this system. Since de-glaciation, the Conejos River has fluctuated between episodes of bedrock strath formation, aggradation and vertical incision. Morphostratigraphic relationships, soil development and radiocarbon ages enable us to propose a chronology for periods of alluvial deposition (around 8·9-7·6 ka, 5·5 ka and from 3·5 to 1·1 ka), separated by intervals of fluvial incision. We infer potential forcing mechanisms by utilizing multiple working hypotheses. Specifically, we discuss the potential for increases in sediment supply during periods of (1) para-glacial adjustment, (2) climatic cooling, (3) increased frequency of climate change and (4) increased fire frequency or severity. We also consider the effects of changes in stream discharge and extreme storm occurrence. We conclude that combinations of these processes, operating at different times, have contributed to sediment mobilization since de-glaciation. Stream and landform morphology also varies longitudinally due to the influence of remnant glacial topography. In particular, valley bottom overdeepening at tributary junctions has resulted in incision and strath formation into unlithified glacial deposits (i.e. fill-cut terraces) rather than bedrock in some reaches. Overall, the Conejos fluvial system has varied significantly both temporally and spatially since de-glaciation and appears to be sensitive to changes in sediment supply related to Holocene scale climate fluctuations. This natural range of variability must therefore be a key consideration in any future stream management policies. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

1. Research in forest and grassland ecosystems indicates that terrestrial invertebrates that fall into streams can be an important prey resource for fish, providing about 50% of their annual energy and having strong effects on growth and abundance. However, the indirect effects of land uses like cattle grazing on this important prey subsidy for stream salmonids are unclear. 2. During summer 2007, we compared the effects of three commonly used grazing systems on terrestrial invertebrate inputs to streams in northern Colorado and their use by trout. Cattle graze individual pastures for about 120 days under traditional season-long grazing (SLG), about 35-45 days under simple rotational grazing and 10-20 days under intensive rotational grazing in this region. We also compared these effects to a fourth group of sites grazed only by wildlife (i.e. no livestock use). 3. Overall, rotational grazing management (either simple or intensive), resulted in more riparian vegetation, greater inputs of terrestrial invertebrates, greater biomass of terrestrial invertebrate prey in trout diets, a higher input compared to trout metabolic demand and more trout biomass than SLG. However, these differences were frequently not statistically significant owing to high variability, especially for trout diets and biomass. 4. Despite the inherent variability, riparian vegetation and terrestrial invertebrates entering streams and in trout diets at sites managed for rotational grazing were similar to sites managed for wildlife grazing only. 5. These results indicate that rotational grazing systems can be effective for maintaining levels of terrestrial invertebrate subsidies to streams necessary to support robust trout populations. However, factors influencing the effect of riparian grazing on stream subsidies are both spatially variable and complex, owing to differences in microclimate, invertebrate and plant populations and the efforts of ranchers to tailor grazing systems to specific riparian pastures. [ABSTRACT FROM AUTHOR]

Stochastic simulation of multivariate hydrologic variables has a key role in evaluating alternative designs and operation rules of hydrologic facilities. The recently developed decomposition analysis, Independent Component Analysis (ICA), allows us to apply the simple univariate time series model to each extracted component by: (1) decomposing multivariate time series into independent components with ICA; (2) modelling and generating each component independently; and (3) mixing the generated components to come back to observational domain. However, we illustrate in the current study that fitting a univariate time series model to each extracted component might end up with the underestimation of the serial dependence that the observation data might contain. A alternative for parameter estimation is suggested to preserve the serial dependence of the observation variable using the relationship between the observation variable and the decomposed variable. The case study of the Upper Colorado River basin shows that some improvement is made through the suggested alternative. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Membrane scaling constrains the operation of Reverse Osmosis (RO) forcing low water recovery, increasing brine amount and disposal cost. A high water recovery hybrid system (without antiscalants) was designed and simulated for desalination of Colorado River (CR) water (TDS=941mg/L) at the same capacity as the Yuma plant (96 Mgpd). The hybrid system incorporates ion exchange (IEX) water softening of Primary RO (PRO) retentate before the water is sent to Secondary RO (SRO). pH adjustment and heating of the concentrate from SRO is done before it is sent to an optional Tertiary RO (TRO). IEX treatment helped remove the scale causing precursors like Ba2+, Ca2+ and Mg2+ while pH adjustment and heating partially alleviated the problem of silica scaling allowing a maximum recovery of 96.4% with the PRO-IEX-SRO-Heat-TRO sequence. Use of concentrate from the last RO for IEX regeneration eliminates need for regeneration chemicals. Optimal RO configurations that minimize total annualized cost were determined by formulating the design as a mixed-integer nonlinear programming (MINLP) problem. Optimal process schemes were identified for different brine disposal costs. Reductions in product water cost of 75% and 50% were attained at high and low brine disposal costs, respectively. [Copyright &y& Elsevier]

Tympanal ears in insects are important for both intraspecific communication and for the detection of nocturnal predators. Ears are thought, based on modern forms, to have originated independently multiple times within insects and can be found on multiple regions of the body. Here we describe and document the exceptionally well preserved tympanal ears found in crickets and katydids from the Eocene Green River Formation of Colorado, which are virtually identical to those seen in modern representatives of these groups. These specimens are among the best preserved insect ears in the fossil record and establish the presence of ears in two major clades of Orthoptera 50 million years ago. Also discussed and evaluated are previously described insect ears from the Mesozoic and the implications of the findings of the present study for studying the evolution of ears within insects. [ABSTRACT FROM AUTHOR]

BSTRACT [ABSTRACT FROM AUTHOR]

Total flow resistance can be partitioned into its components of grain (ff grain), form (ff step), wood (ff wood) and spill (ff spill) resistance. Methods for partitioning flow resistance developed for low-gradient streams are commonly applied to high-gradient systems. We examined the most widely used methods for calculating each component of resistance, along with the limitations of these methods, using data gathered from 15 high-gradient (0.02 < S0 < 0.195) step-pool, cascade, and plane-bed reaches in Fraser Experimental Forest. We calculated grain resistance using three equations that relate relative submergence (R/Dm,) to ff grain as well as using an additive drag approach. The drag approach was also used for calculating ff wood and ff step. The ff grain, contributed the smallest amount toward all reaches at all flows, although the value varied with the method used. The Parker and Peterson (1980) equation using D90 best represented ff grain at high flows, whereas the Keulegan (1938) equation using D50 best characterized ff grain at base flows, giving a lower bound for grain resistance. This suggests that ff grain, may be better represented if two grain sizes are used to calculate this component of resistance. The drag approach, which is used to calculate wood resistance, overestimated the significance of individual logs in the channel. The contribution of ff spell was reduced at higher flows when form drag around the step is accounted for at higher flows. We propose a method for evaluating the contribution of ff step that accounts for form drag around the steps once they are submerged at higher flows. We evaluated the potential sources of error for the estimation of each component of resistance. Determination of the drag coefficient was one of the major sources of error when calculating drag around wood, steps, or boulders. [ABSTRACT FROM AUTHOR]

The effects of channel bed disturbance on benthic chlorophyll a accrual were examined in three reaches of the Williams Fork River, CO, USA. A field calibrated multidimensional hydraulic model was used for estimation of shear-stress distributions. Sediment grain size was used to determine the critical shear stress for bed movement. Disturbance at a given location is defined as the percentage of time during the growing season that the bed sediment is in motion. This metric was compared with periphyton biomass accrual. Growth control factors including temperature, grazing intensity, nutrient concentrations, and irradiance also were measured. Disturbance mapping showed that the common concept of bed disturbance as a byproduct of high-flow events is overly simplistic. In the Williams Fork, bed movement occurs constantly over certain portions of the bed, even at low flows. There is a continuum of bed movement, expressed as percentage of the bed in motion, extending from low to high flows. Periphyton biomass accumulated exponentially in all study reaches but accumulation rates were inversely proportional to local disturbance. Periphyton biomass increased by approximately three orders of magnitude across the three reaches, but failed to reach a plateau. A combination of moderate grazing rates, low-nutrient concentrations, moderately impaired solar irradiance, and, most importantly, low temperatures explains the failure of periphyton biomass to reach a plateau. This study shows that the control of periphyton biomass may be explained in streams by bed disturbance over the growing season plus the separate, superimposed on influence of population growth rate control factors. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

pplication of optimization techniques for determining the optimal operating policy of reservoirs is a major issue in water resources planning and management. As an optimization Genetic Algorithm, ruled by evolution techniques, have become popular in diversified fields of science. The main aim of this study is to explore the efficiency and effectiveness of genetic algorithm in optimization of multi-reservoirs. A computer code has been constructed for this purpose and verified by means of a reference problem with a known global optimum. Three reservoirs in the Colorado River Storage Project were optimized for maximization of energy production. Besides, a real-time approach utilizing a blend of online and a posteriori data was proposed. The results obtained were compared to the real operational data and genetic algorithm was found to be effective and can be utilized as an alternative technique to other traditional optimization techniques. [ABSTRACT FROM AUTHOR]

Groundwater and surface water are hydraulically connected in some regions of the world. This type of aquifer system is called a tributary aquifer and can affect flows of adjacent streams. These accretions occur when slowly moving groundwater enters the bottom or side slopes of a stream, providing base flow. In this situation, groundwater becomes surface water. Groundwater that is hydraulically connected to surface water in this manner is called tributary groundwater. Colorado state law requires all water users???of both surface and tributary groundwater???to follow a strict water-right priority system of ???first in time, first in right.??? This Doctrine of Prior Appropriation, adopted in Colorado in 1876, is rigidly followed today. Since 2003, thousands of tributary groundwater irrigation wells have been curtailed from pumping (legally shut off) due to pumping depletions that reduce stream flow. The impacts to these groundwater users have been serious. Approximately 2,000 wells have been curtailed and will never pump again, and tens of thousands of acres of productive agricultural lands have been reverted to dryland crops or weeds. Surface and tributary groundwater use conflicts are inevitable in locations where rigid water-allocation systems are followed. Nobel Prize winner Eleanor Ostrom points out that common-pool resource management requires collective-choice arrangements if resource users???in this case, surface water and groundwater users???are to develop a stable management plan. This article will show that the Colorado Constitution prohibits such an arrangement and is the reason thousands of tributary groundwater wells have been permanently shut off in the state. By contrast, other states and regions of the world may be able to avoid drastic well curtailments if state or federal laws allow for common-pool resource management.Environmental Practice 12:304???315 (2010) [ABSTRACT FROM AUTHOR]

The article offers information on the town and county seat Walsenburg in Huerfano County, Colorado that are of interest to birders. The town and county seat has about 4,000 residents and it was named after Fred Walsen, who opened the first coal mine in the area in 1876. The recommended places for birding are the Masonic Cemetery, the Cucharas River and the Lathrop State Park. The dining establishments in the area include the La Plaza Inn, the Mexican restaurant Corine's and Grandpa & Grandma's (G&G).