Southwest Biological Science Center
Glen Canyon Dam Adaptive Management (GCMRC Science)
Aquatic insects are commonly used to gauge the health of stream and river ecosystems, yet collecting enough samples to adequately characterize a river segment as long as the Colorado River through Grand Canyon (> 250 miles) would be essentially impossible using traditional sampling methods. Since 2012, our group has been collaborating with river guides, private boaters, and educational groups to deploy light traps to collect adult aquatic insects in this river segment. These citizen scientists have generated an impressive quantity of samples and data, which are yielding fundamentally new insights into the Colorado River ecosystem.
Algae, phytoplankton, and rooted macrophytes represent the base of many aquatic food webs and are known as primary producers. Through photosynthesis, these organisms convert sunlight energy into chemical energy (i.e., carbon) that in turn fuels the growth of animals such as macroinvertebrates and fish. This project uses high frequency measurements of dissolved oxygen, which is a by-product of photosynthesis, to estimate rates of primary production at six locations in the Colorado River downstream of Glen Canyon Dam. Quantifying time series of primary production is used to identify the environmental factors that control primary production. Additionally, trends in primary production may be a leading indicator of changes in fish populations and the ecosystem as a whole.
Sediment controls the physical habitat of river ecosystems. Changes in the amount and areal distribution of different sediment types cause changes in river-channel form and river habitat. The amount and type of sediment suspended in the water column determines water clarity. Understanding sediment transport and the conditions under which sediment is deposited or eroded from the various environments in a river is therefore critical to understanding and managing sediment and sediment-related habitat in rivers. This project conducts and provides the science required to better understand the physics of sediment transport and channel change in rivers. All data collected by this project and user-interactive web tools to analyze these data are provided at either: https://www.gcmrc.gov/discharge_qw_sediment/ or https://cida.usgs.gov/gcmrc/discharge_qw_sediment/.
Construction of Glen Canyon Dam has led to large changes in environmental conditions of the downriver Colorado River. Whereas the pre-dam Colorado River experienced large seasonal variation in temperature and discharge and was highly turbid, the post-dam Colorado River is far less variable in terms of temperature and discharge and is frequently clear. Many nonnative fish species had already been introduced to the Colorado River or its tributary prior to dam completion, and some thrive in this altered environment. The federally endangered humpback chub is a native fish of the Colorado River that evolved in the pre-dam environment over millions of years and has been able to persist for a half-century in the post-dam environment, alongside introduced non-native species including rainbow trout. The goal of this project is to monitor all life stages of humpback chub (juvenile, subadult, and adult), estimate survival, growth, movement and abundances for various life stages and develop population models to predict responses to potential management strategies focused on either controlling non-native invasive species or restoring aspects of the physical environment.
Rainbow trout is a desirable sport fish that has been introduced in many locations around the world. Although introductions of rainbow trout and other nonnative fishes provide recreational fishing opportunities, they also pose threats to native fish populations. The Glen Canyon Dam Adaptive Management Program has tasked scientists and managers with identifying management options that allow rainbow trout to thrive from Glen Canyon Dam downstream to Lees Ferry, while minimizing impacts to downstream populations of native fish, especially the endangered humpback chub. This project aims to identify factors that drive rainbow trout growth through a combination of approaches. A synthesis of tailwaters (river segments just downstream of dams) across the Western US has elucidated larger scale patterns, relating river flows to the size of adult rainbow trout. Ultimately, this project aims to guide adaptive management of rainbow trout, balancing recreational interests within the tailwater with downstream native fish conservation.
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We study the links among different geomorphic processes that affect river valley landscapes in the Colorado River downstream from Glen Canyon Dam, Arizona. Dam-released flows affect the deposition and retention of sandbars that serve as sources for other sand resources, such as windblown sand dunes, throughout the Colorado River ecosystem. The degree to which the landscapes are differentially affected by river, wind, rainfall, or gravity-driven redistribution of river-derived sand is called sediment “connectivity”. Connectivity is affected by several factors including the amount of sand supplied as well as physical and vegetative barriers to sand transport. Connectivity affects the condition of natural and cultural resources – such as archaeological sites – in the ecosystem. In particular, we assess the potential for Colorado River sand to enhance the preservation of river-corridor archeological resources through burial by wind deposition and/or mitigation of gully erosion.
Introduced rainbow trout and brown trout are considered a threat to the endangered humpback chub in the Colorado River in Grand Canyon. These introduced species eat native fish, but impacts are difficult to assess because predation vulnerability depends on the physical conditions under which predation takes place. We studied how predation vulnerability of juvenile humpback chub changes in response to turbidity. We exposed hatchery-reared juvenile humpback chub and bonytail (a surrogate for humpback chub) to adult rainbow and brown trout at turbidities ranging from 0 (clear water) to 1,000 formazin nephlometric units (FNU). Turbidity as low as 25 FNU reduced predation of bonytail to rainbow trout and led to a 36% increase in survival compared to trials conducted in clear water. Predation vulnerability of bonytail to brown trout at 25 FNU also decreased with increasing turbidity and resulted in a 25% increase in survival. This research suggests that relatively small changes in turbidity may be sufficient to alter predation dynamics of trout on humpback chub in the Colorado River, and that turbidity manipulation may warrant further investigation as a fisheries management tool.
Riparian vegetation has increased dramatically along the Colorado River downstream of Glen Canyon Dam since the closure of the dam in 1963. The spatial patterns and temporal rates of vegetation increase occur due to changes in river hydrology, dam operations, and climate. The increase in vegetation, particularly onto otherwise bare sandbars, has impacted recreational, geomorphological, biological, and cultural resources along the river. Some of the riparian vegetation is non-native, invasive Tamarix that has recently been subject to herbivory and defoliation by the northern tamarisk beetle which has been in the Grand Canyon region since approximately 2009. We use remote sensing of very high resolution multispectral imagery and lidar acquired from fixed-wind airplanes and helicopters to monitor and research the short- and long-term dynamics of riparian vegetation and associated environmental science issues in the region.
Economic research at Grand Canyon Monitoring and Research Center is used to determine economic benefits of outdoor recreation in Glen Canyon National Recreation Area below Glen Canyon Dam and in Grand Canyon National Park, as affected by operation of Glen Canyon Dam. This research identifies recreationists’ preferences for attributes associated with their trips, spending that occurs regionally, and the net economic benefit to recreationists. To accomplish this research objective, surveys of recreationists are used to collect information. This material is necessary for the Glen Canyon Dam Adaptive Management Program, federal, and state decision-makers to make informed choices about the economic tradeoffs that occur, with regard to recreation, when evaluating resource management actions in Glen Canyon National Recreation Area and Grand Canyon National Park.
All aquatic invertebrates drift downstream at some point in their life cycle. Invertebrates may drift to find more preferable habitats, to leave the water during their transition from aquatic larvae to terrestrial adults, or accidentally such as when swept off the river bed by a flood. Regardless, when they enter the drift, invertebrates become particularly susceptible to predation by several groups of drift-feeding fish. In Glen, Marble, and Grand Canyons, these fish include rainbow trout (Oncorhynchus mykiss) that sustain the Lees Ferry a Blue Ribbon trout fishery, and the native, federally-endangered humpback chub (Gila cypha). By researching and monitoring invertebrate drift, our group can better understand the health of these fish populations, and how they interact with one another.
Since the completion of Glen Canyon Dam in 1963, the amount of sand supplied to Grand Canyon National Park has been reduced by more than 90 percent. The Paria River, a tributary to the Colorado River 15 miles downstream from the dam, is now the single most important supplier of sand to the Colorado River within the Park. This large reduction in sand supply has resulted in substantial decrease in the number and size of sandbars. Sandbars are important because they serve as campsites for river runner and hikers, provide important aquatic and riparian habitats, and are the source of sand that may help protect archaeological sites. The information collected by this project will be used to determine whether dam operations, including short-duration artificial floods, cause increases or decreases in sandbars and associated campsites in Grand Canyon National Park. More information can be found on the Grand Canyon Monitoring and Research Center website: https://www.gcmrc.gov/research_areas/sediment_geomorphology/sed/Sed_Geomorph_Home_Page.aspx.