Lower Colorado River Research Articles

Bedrock And Boulder Mortars, Basins, Slicks, And Cupules In The Southern Southwest

This article describes mortars, basins, slicks, and cupules created in bedrock and boulders in the Southern Southwest, and discusses the distribution and possible functions of these features. It defines the Southern Southwest as the region of the U.S. south of 34 degrees north latitude that includes the Califor­nia portion of the Lower Colorado River valley and southern portions of Arizona and New Mexico, and the portion of western Texas that includes El Paso, Hudspeth, Culber­son, Loving, Winkler, Ward, Reeves, and Jeff Davis counties (roughly the part of Texas from El Paso eastward just past the south­eastern corner of New Mexico, then south and south­westward to a point south of Fort Davis, then westward to the Río Grande).

How a strong low-angle normal fault formed: The Whipple detachment, southeastern California

AbstractMany low-angle normal faults (dip ≤30°) accommodate tens of kilometers of crustal extension, but their mechanics remain contentious. Most models for low-angle normal fault slip assume vertical maximum principal stress σ1, leading many authors to conclude that low-angle normal faults are poorly oriented in the stress field (≥60° from σ1) and weak (low friction). In contrast, models for low-angle normal fault formation in isotropic rocks typically assume Coulomb failure and require inclined σ1 (no misorientation). Here, a data-based, mechanical-tectonic model is presented for formation of the Whipple detachment fault, southeastern California. The model honors local and regional geologic and tectonic history and laboratory friction measurements. The Whipple detachment fault formed progressively in the brittle-plastic transition by linking of “minidetachments,” which are small-scale analogs (meters to kilometers in length) in the upper footwall.Minidetachments followed mylonitic anisotropy along planes of maximum shear stress (45° from the maximum principal stress), not Coulomb fractures. They evolved from mylonitic flow to cataclasis and frictional slip at 300–400 °C and ∼9.5 km depth, while fluid pressure fell from lithostatic to hydrostatic levels. Minidetachment friction was presumably high (0.6–0.85), based upon formation of quartzofeldspathic cataclasite and pseudotachylyte. Similar mechanics are inferred for both the minidetachments and the Whipple detachment fault, driven by high differential stress (∼150–160 MPa). A Mohr construction is presented with the fault dip as the main free parameter. Using “Byerlee friction” (0.6–0.85) on the minidetachments and the Whipple detachment fault, and internal friction (1.0–1.7) on newly formed Reidel shears, the initial fault dips are calculated at 16°–26°, with σ1 plunging ∼61°–71° northeast. Linked minidetachments probably were not well aligned, and slip on the evolving Whipple detachment fault probably contributed to fault smoothing, by off-fault fracturing and cataclasis, and to formation of the fault core and fractured damage zone.Stress rotation may have occurred only within the mylonitic shear zone, but asymmetric tectonic forces applied to the brittle crust probably caused gradual rotation of σ1 above it as a result of: (1) the upward force applied to the base of marginal North America by buoyant asthenosphere upwelling into an opening slab-free window and/or (2) basal, top-to-the-NE shear traction due to midcrustal mylonitic flow during tectonic exhumation of the Orocopia Schist. The mechanical-tectonic model probably applies directly to low-angle normal faults of the lower Colorado River extensional corridor, and aspects of the model (e.g., significance of anisotropy, stress rotation) likely apply to formation of other strong low-angle normal faults.

Post–12 Ma deformation in the lower Colorado River corridor, southwestern USA: Implications for diffuse transtension and the Bouse Formation

AbstractStructural evidence presented here documents that deformation was ongoing within the lower Colorado River corridor (southwestern USA) during and after the latest Miocene Epoch, postdating large-magnitude extension and metamorphic core complex formation. Geometric and kinematic data collected on faults in key geologic units constrain the timing of deformation in relation to the age of the Bouse Formation, a unit that records the first arrival and integration of the Colorado River. North-south–striking extensional, NW-SE–striking oblique dextral, NE-SW–striking oblique sinistral, and east-west–striking contractional faults and related structures are observed to deform pre– (>6 Ma), syn– (6–4.8 Ma), and post–Bouse Formation (<4.8 Ma) strata. Fault displacements are typically at the centimeter to meter scale, and locally exhibit 10-m-scale displacements. Bouse Formation basalt carbonate locally exhibits outcrop-scale (tens of meters) syndepositional dips of 30°–90°, draped over and encrusted upon paleotopography, and has a basin-wide vertical distribution of as much as 500 m. We argue that part of this vertical distribution of Bouse Formation deposits represents syn- and post-Bouse deformation that enhanced north-south–trending depocenters due to combined tectonic and isostatic subsidence in a regional fault kinematic framework of east-west diffuse extension within an overall strain field of dextral transtension. Here we (1) characterize post-detachment tectonism within the corridor, (2) show that diffuse tectonism is cumulatively significant and likely modified original elevations of Bouse Formation outcrops, and (3) demonstrate that this tectonism may have played a role in the integration history of the lower Colorado River. We suggest a model whereby intracontinental transtension took place in a several hundred kilometers-wide area inboard of the San Andreas fault within a diffuse Pacific–North America plate margin since the latest Miocene.

The Bouse Formation, a controversial Neogene archive of the evolving Colorado River: a scientific drilling workshop report (28 February–3 March 2019 – BlueWater Resort & Casino, Parker, AZ, USA)

Abstract. Neogene deposits of the lower Colorado River valley, especially the Miocene(?) and early Pliocene Bouse Formation, have been the focus of intense debate regarding the early paleoenvironmental history of this important continental-scale river system in southwestern North America and its integration with the proto-Gulf of California. Fine-grained units within these Neogene deposits also hold a promising archive of Pliocene paleoclimate history for this part of the world. Because the depocenter deposits of the Bouse Formation and the deposits that overlie and underlie it are poorly exposed and highly weathered, the formation is ripe for study through collection of drill cores. A workshop was held 28 February–3 March 2019 in Parker, AZ, USA, to discuss how scientific drilling might be employed to help resolve the Bouse controversies and improve our understanding of paleoclimate history in the region.

Using Ostracode Amino Acid D/L Ratios and Microfossil Analysis to Correlate Alluvial Packages along the Lower Colorado River Corridor, with Insight into the Early Pliocene Integration of the Colorado River and the Gulf of California

The lower Colorado River corridor below Grand Canyon developed sometime between ∼5.3 Ma and ∼4.8 Ma, as evidenced by the first appearance of Colorado River-derived sediments of the Bouse Formation in basins along its modern course and the abrupt appearance of distinctive hematite-stained “C-suite” Colorado River sand grains near the base of the Wind Caves member of the Latrania Formation in the Salton Trough. The oldest recognized evidence for a through-flowing Colorado River is the ∼4.5 Ma to ∼3.5 Ma Bullhead Alluvium. Interest and debate focuses on whether a “pre-Bullhead” Colorado River might have first reached the Salton Trough at 5.3 Ma, prior to deposition of some of the Bouse Formation. Fine-grained but undated Colorado River sediments have been recognized on the Yuma Proving Grounds, Arizona, since the 1970s. These sediments have been correlated by some to the Bouse Formation, and thus, would pre-date the Bullhead Alluvium and might provide evidence for the existence of a “pre-Bullhead” Colorado River. In this study, I use the extent of amino acid racemization in ostracode valves and microfossil assemblages to test correlations between the fine-grained sediments on the Yuma Proving Grounds with other independently dated lower Colorado River corridor alluvial packages that were deposited at ∼5 Ma (Bouse Formation) and at ∼75 ka to ∼60 ka (Chemehuevi Formation). The results of this study confidently demonstrate that the fine-grained sediments on the Yuma Proving Grounds are not late Miocene or early Pliocene in age but instead are correlative with the late Pleistocene Chemehuevi Formation. Evidence for a “pre-Bullhead” Colorado River remains elusive.

Insights into post-Miocene uplift of the western margin of the Colorado Plateau from the stratigraphic record of the lower Colorado River

AbstractThe spatial and temporal distribution of Pliocene to Holocene Colorado River deposits (southwestern USA and northwestern Mexico) form a primary data set that records the evolution of a continental-scale river system and helps to delineate and quantify the magnitude of regional deformation. We focus in particular on the age and distribution of ancestral Colorado River deposits from field observations, geologic mapping, and subsurface studies in the area downstream from Grand Canyon (Arizona, USA). A new 4.73 ± 0.17 Ma age is reported for a basalt that flowed down Grand Wash to near its confluence with the Colorado River at the eastern end of what is now Lake Mead (Arizona and Nevada). That basalt flow, which caps tributary gravels, another previously dated 4.49 ± 0.46 Ma basalt flow that caps Colorado River gravel nearby, and previously dated speleothems (2.17 ± 0.34 and 3.87 ± 0.1 Ma) in western Grand Canyon allow for the calculation of long-term incision rates. Those rates are ∼90 m/Ma in western Grand Canyon and ∼18–64 m/Ma in the eastern Lake Mead area. In western Lake Mead and downstream, the base of 4.5–3.5 Ma ancestral Colorado River deposits, called the Bullhead Alluvium, is generally preserved below river level, suggesting little if any bedrock incision since deposition. Paleoprofiles reconstructed using ancestral river deposits indicate that the lower Colorado River established a smooth profile that has been graded to near sea level since ca. 4.5 Ma. Steady incision rates in western Grand Canyon over the past 0.6–4 Ma also suggest that the lower Colorado River has remained in a quasi–steady state for millions of years with respect to bedrock incision. Differential incision between the lower Colorado River corridor and western Grand Canyon is best explained by differential uplift across the Lake Mead region, as the overall 4.5 Ma profile of the Colorado River remains graded to Pliocene sea level, suggesting little regional subsidence or uplift. Cumulative estimates of ca. 4 Ma offsets across faults in the Lake Mead region are similar in magnitude to the differential incision across the area during the same approximate time frame. This suggests that in the past ∼4 Ma, vertical deformation in the Lake Mead area has been localized along faults, which may be a surficial response to more deep-seated processes. Together these data sets suggest ∼140–370 m of uplift in the past 2–4 Ma across the Lake Mead region.

A legacy of geo‐climatic complexity and genetic divergence along the lower Colorado River: Insights from the geological record and 33 desert‐adapted animals

AbstractAimTo review the histories of the Colorado River and North American monsoon system to ascertain their effects on the genetic divergence of desert‐adapted animals.LocationLower Colorado River region, including Mojave and Sonoran deserts, United States.MethodsWe synthesized recent geological literature to summarize initiation phases of lower Colorado River evolution, their discrepancies, and potential for post‐vicariance dispersal of animals across the river. We simulated data under geological models and performed a meta‐analysis of published and unpublished genetic data including population diversity metrics, relatedness and historical migration rates to assess alternative divergence hypotheses.ResultsThe two models for arrival of the Colorado River into the Gulf of California impose east‐west divergence ages of 5.3 and 4.8 Ma, respectively. We found quantifiable river‐associated differentiation in the lower Colorado River region in reptiles, arachnids and mammals relative to flying insects. However, topological statistics, historical migration rates and cross‐river extralimital populations suggest that the river should be considered a leaky barrier that filters, rather than prevents, gene flow. Most markers violated neutrality tests. Differential adaptation to monsoon‐based precipitation differences may contribute to divergence between Mojave and Sonoran populations and should be tested.Main ConclusionsRivers are dynamic features that can both limit and facilitate gene flow through time, the impacts of which are mitigated by species‐specific life history and dispersal traits. The Southwest is a geo‐climatically complex region with the potential to produce pseudocongruent patterns of genetic divergence, offering a good setting to evaluate intermediate levels of geological‐biological (geobiological) complexity.

Distributed Neogene faulting across the western to central Arizona metamorphic core complex belt: Synextensional constriction and superposition of the Pacific–North America plate boundary on the southern Basin and Range

Abstract We present fault data from a belt of Miocene metamorphic core complexes in western and central Arizona (USA) to determine patterns of brittle strain during and after large-magnitude extension, and to evaluate the magnitude of postextensional dextral shear across the region. In the White Tank Mountains, coeval WNW- to NW-striking dextral, normal, and oblique dextral-normal faults accommodated constrictional strain with extension subparallel to the direction of ductile stretching during core complex development. Northwest-striking oblique dextral-normal faults locally accommodated similar strain in the Harquahala Mountains, whereas in the South Mountains, constriction was primarily partitioned on NE-dipping normal faults and conjugate NW- and north-striking strike-slip faults. We interpret brittle constrictional strain to have developed during the late stages of large-magnitude extension associated with core complex development and folding of detachment fault corrugations. The oblique orientation of the Arizona core complex belt with respect to the extension direction likely resulted in a minor component of dextral transtension, accounting for much of the constrictional strain. In addition, far-field stresses associated with the transtensional Pacific–North America plate boundary may have contributed to constriction, which characterizes most Neogene detachment fault systems in the southwest Cordillera. Following cessation of detachment fault slip across the Arizona core complex belt (ca. 14–12 Ma), distributed NW-striking dextral and oblique dextral–NE-side-up (reverse) faults modified the topographic envelope of corrugations to an orientation clockwise of the core complex extension direction. Based on our analysis of this misalignment, we interpret the postdetachment fault dextral shear strain to increase northwestward from 0.03 across the South Mountains (0.5–0.6 km total slip across 18 km) to >0.03–0.07 across the Harquahala and Harcuvar Mountains (1.2–2.5 km of total slip across ∼35 km) and ∼0.2 across the Buckskin-Rawhide Mountains (7–8 km across 36 km). This along-strike variation in dextral shear is consistent with the regional pattern of distributed strain associated with the Pacific–North America plate boundary, as cumulative dextral offset in the lower Colorado River region increases toward the eastern Mojave Desert region to the northwest.

The Upper Basin, Lower Basin, and Mexico: Coexisting on the Post-2026 Colorado River

Misuse of science in the apportionment of the Colorado River’s water in the 20th century led to an overallocation problem that must be addressed. Rules based on overestimation of the available water supply have allowed overuse in the Lower Colorado River Basin and left uncertainty about the obligation of various basin water users to contribute water toward meeting U.S. treaty obligations to Mexico. With a number of key water management agreements expiring in 2026, basin managers have an opportunity to correct the overallocation problems with negotiated agreements that reflect the reality of the river’s hydrology and reduce risks associated with winner-take-all litigation.

Size Sorting in Bonytail Skews the Sex Ratio of Stocked Fish

AbstractFor sexually dimorphic species, size‐based management can cause changes in the sex ratio of the target population. Bonytail Gila elegans populations in the Colorado River basin are augmented annually in an effort to re‐establish wild populations. To increase survival rates of stocked individuals, the Lower Colorado River Multi‐Species Conservation Program's Habitat Conservation Plan implemented a minimum stocking size. Anecdotal reports on hatchery populations suggest that females grow at a faster rate and reach larger sizes than males. If this observation is correct, a minimum stocking size may cause skewed sex ratios of stocked populations. To test this prediction, we compared average male and female lengths in 3‐year‐old fish from two cohorts before and after they were sorted by size. Our data support the observation that size in Bonytail is sexually dimorphic by age 3, with females being the larger sex. This is also the age at which fish begin to reach the minimum size to meet stocking requirements. As predicted, size‐grading produced a significantly skewed sex ratio in the animals slated for release. The consequences of augmenting wild populations with groups of animals having skewed sex ratios are largely unknown but could include increased mate competition, inadvertent artificial selection, or a reduction in genetic diversity.

Novel ectoparasite infestation on yuma ridgway's rails (Rallus obsoletus yumanensis)

Yuma Ridgway's Rails (Rallus obsoletus yumanensis) are federally endangered birds endemic to wetlands throughout the Lower Colorado River Basin in Nevada, California, Arizona, and Mexico. The U.S. population has declined in recent years for unknown reasons. We documented a novel and severe chigger mite infestation in the Yuma Ridgway's Rails in southwestern Arizona in 2017. Prevalence of the infestation was spatially heterogeneous: 92% (48 of 52) of the Yuma Ridgway's Rails that we captured at Imperial National Wildlife Refuge were infested, whereas only 11% (2 of 18) of the Yuma Ridgway's Rails at Cibola National Wildlife Refuge were chigger infested. We know little about the origin of this infestation or the impacts of the parasites on the behavior and fitness of Yuma Ridgway's Rails. However, ectoparasite infestations in other species have caused population declines and the intensity and novelty of this ectoparasite infestation, combined with population status of this species, warrants immediate attention to this issue and further study of these ectoparasites.

Endangered species managing endangered species: Polyculture of piscivorous Colorado Pikeminnow (Ptychocheilus lucius) with production Bonytail (Gila elegans) to control recruitment and increase growth rates

The decline and endangerment of native fish has led to an increase in hatcheries that sustain and augment threatened and endangered species. In an effort to restore self-sustaining populations, hatchery-reared Bonytail (Gila elegans) are released into the lower Colorado River annually. Current augmentation protocols for Bonytail require a minimum stocking size of 300 mm total length due to greater apparent survival of larger individuals. The fish culture process of reaching this desired target size requires multiple years of growth, during which precocious individuals regularly spawn. Recruitment in production ponds increases densities, potentially reducing growth rates and adversely affecting culture conditions. Polyculture techniques have been shown to have synergistic effects and under proper conditions effectively control unwanted biota. In an effort to address the management implications of Bonytail recruitment on adult growth and survival, we tested the use of a historically co-occurring piscivore, Colorado Pikeminnow (Ptychocheilus lucius), as a biological control agent. Colorado Pikeminnow effectively controlled Bonytail recruitment and had a positive effect on adult growth rates. Our results suggest polyculture of these two species can aid management actions by increasing augmentation efforts.

Investigation of recent decadal-scale cyclical fluctuations in salinity in the lower Colorado River

Beginning in the late 1970s, 10- to 15-year cyclical oscillations in salinity were observed at lower Colorado River monitoring sites, moving upstream from the international border with Mexico, above Imperial Dam, below Hoover Dam, and at Lees Ferry. The cause of these cyclical trends in salinity was unknown. These salinity cycles complicate the U.S. Bureau of Reclamation's (Reclamation) responsibility for managing salinity in the river for delivery of water to Mexico to meet treaty obligations. This study develops a conceptual model of the salinity cycles from time-series water quality, streamflow, and precipitation data in both the lower and upper Colorado River Basins in order to provide Reclamation the ability to understand, anticipate, and manage future salinity cycles in the lower river. Compared with the Lees Ferry record, both maximum and minimum salinity levels increase downstream by about 25% at Hoover Dam, by about 49% at Imperial Dam, and by about 69% at the northern international boundary with Mexico. In the upper basin, cyclical salinity trends are evident at the outflow of three major tributaries, where salinity is also noted to be inversely related to streamflow. Time series trends in precipitation within the catchments of the three upper basin tributaries indicate cyclical periods with above normal precipitation and periods with below normal precipitation. Periods of greater than normal precipitation in the contributing areas correspond with declines in salinity at the catchment monitoring sites and periods of less than normal precipitation correspond with rising salinity at the sites. Based on the conceptual model developed in this investigation, a multiple linear regression model was developed using a stepwise variable selection procedure to simulate salinity in Lake Powell inflow. Important variables in the explanation of salinity entering Lake Powell include flow from the three upper basin tributaries, seasonality, and mean precipitation in the upper basin, among others. The root mean square error of prediction for the MLR model was 31.48 mg/L (5.7%).

Identifying the migratory strategy of the Lower Colorado River Valley population of Greater Sandhill Cranes

Conring, C. M., K. Brautigam, B. A. Grisham, D. P. Collins, and W. C. Conway. 2019. Identifying the migratory strategy of the Lower Colorado River Valley population of Greater Sandhill Cranes. Avian Conservation and Ecology 14(1):11. https://doi.org/10.5751/ACE-01352-140111

Charles Bowden, Historian of the Future

Charles Bowden, Historian of the Future Bill Broyles (bio) and Bruce J. Dinges (bio) He bolted upright up in his sleeping bag as his fellow paddlers on the lower Colorado River canoe trip were already making breakfast. It was unusual for Chuck Bowden not to wake first, light the camp stove, and make coffee. For four days he had regaled his companions with details of a scandal that was about to hit the national headlines. Charles Keating and his Lincoln Savings and Loan had mishandled enough money ($3.4 billion) to shake U.S. financial markets and cause a cascade of bank failures. Bowden and his co-author, Michael Binstein, had dredged the records, staked out the courtrooms, stalked witnesses and attorneys, and interviewed the principals, including Keating—Chuck portrayed him as a fine fellow with whom to have dinner, but who would rob your bank blind if you let him. It was a story that Bowden had been living with for at least a year, sniffing through ledgers and shell companies like a bloodhound with a typewriter. Chuck wasn't one for typical greetings, like "Good morning" or "How did you sleep?" Instead, he launched into a monologue about whatever was on his mind. This morning's topic was a pre-dawn dream he had involving a nightclub, a band, and a lady wearing a black velvet evening gown who asked, "Do you want to touch my dress?" Chuck wanted to meet her. "Maybe tonight, if I'm lucky," he mused, before reaching for a cigarette. ________ Charles Clyde Bowden was born on the family's small farm near Joliet, Illinois, on July 20, 1945, and he died on August 31, 2014, in Las Cruces, New Mexico. In between, he led a full life, mostly following his own guide-star. At age three, the family moved to Chicago, where [End Page 7] Click for larger view View full resolution Charles Bowden as a graduate student at University of Wisconsin, about 1970. (Charles Bowden Papers, Wittliff Collections, Texas State University, San Marcos, box 101, folder 3. © Charles Clyde Bowden Literary Trust, Mary Martha Miles, Trustee.) [End Page 8] Chuck's father, Jude, worked for the Internal Revenue Service. His mother, Bernina "Bo," managed the household that included Chuck's older siblings George and Peggy (Peg). In 1957, when Chuck was twelve, the family relocated to Tucson, Arizona. Chuck attended Tucson High School and graduated from the University of Arizona, with a BA in history, in 1966. He enrolled in the graduate program at University of Wisconsin at Madison on a Woodrow Wilson Fellowship, earning a master's degree in American intellectual history in 1967. He went on Click for larger view View full resolution Charles Bowden's parents, Bo and Jude, with his brother George and sister Peggy, about 1944, Joliet, Illinois. (Charles Bowden Papers, Wittliff Collections, Texas State University, San Marcos, box 101, folder 3. © Charles Clyde Bowden Literary Trust, Mary Martha Miles, Trustee.) [End Page 9] Click for larger view View full resolution Charles Bowden, high school, Tucson, Arizona. (Charles Bowden Papers, Wittliff Collections, Texas State University, San Marcos, to be catalogued. © Charles Clyde Bowden Literary Trust, Mary Martha Miles, Trustee.) [End Page 10] to complete the course requirements for the PhD and worked on his doctoral dissertation, "Broke Bodies: A Look at 19th Century Notions about Health." In the meantime, he supplemented his income with a gig doing field research for the university archive before taking a job in 1970 as an American history instructor at the University of Illinois, Chicago Circle. He discovered that he hated classroom teaching and left before his contract expired. With few viable options Chuck and his wife, Zada Edgar, his high school sweetheart whom he married in 1968, returned to Tucson. Zada had earned her BA at Wisconsin and her MA at Smith College when the couple had lived in Ashfield, Massachusetts. Back in Tucson, Chuck took odd jobs while Zada obtained a JD at the University of Arizona before joining the Pima County Attorney's Office in 1976. He had submitted his dissertation to the University of Wisconsin history department, but the process dragged on with committee members coming and...

A History of Date Palms in the Lower Colorado River Valley

A History of Date Palms in the Lower Colorado River Valley

Remote sensing vegetation index methods to evaluate changes in greenness and evapotranspiration in riparian vegetation in response to the Minute 319 environmental pulse flow to Mexico

Abstract. During the spring of 2014, 130 million m3 of water were released from the United States' Morelos Dam on the lower Colorado River to Mexico, allowing water to reach the Gulf of California for the first time in 13 years. Our study assessed the effects of water transfer or ecological environmental flows from one nation to another, using remote sensing. Spatial applications for water resource evaluation are important for binational, integrated water resources management and planning for the Colorado River, which includes seven basin states in the US plus two states in Mexico. Our study examined the effects of the historic binational experiment (the Minute 319 agreement) on vegetative response along the riparian corridor. We used 250 m Moderate Resolution Imaging Spectroradiometer (MODIS), Enhanced Vegetation Index (EVI) and 30 m Landsat 8 satellite imagery to track evapotranspiration (ET) and the normalized difference vegetation index (NDVI). Our analysis showed an overall increase in NDVI and evapotranspiration (ET) in the year following the 2014 pulse, which reversed a decline in those metrics since the last major flood in 2000. NDVI and ET levels decreased in 2015, but were still significantly higher (P < 0.001) than pre-pulse (2013) levels. Preliminary findings show that the decline in 2015 persisted into 2016 and 2017. We continue to analyse results for 2018 in comparison to short-term (2013–2018) and long-term (2000–2018) trends. Our results support the conclusion that these environmental flows from the US to Mexico via the Minute 319 “pulse” had a positive, but short-lived (1 year), impact on vegetation growth in the delta.

Constraints to implementing the food-energy-water nexus concept: Governance in the Lower Colorado River Basin

The food-energy-water (FEW) nexus concept has emerged as a powerful approach to address the social and environmental challenges created by land and climate change. We present an analysis of the impact of the governance structure of the Lower Colorado River Basin (LCRB) on the implementation of the FEW nexus concept. Specifically, we quantified the linkages between food, energy, and water systems and then used two different future scenarios: (1) drought and (2) increased demand for alfalfa to look for the emergence of resource scarcity and/or vulnerabilities. Our results indicate that fluctuations in food production are not controlled by water availability but by the governance structure. Additionally, there is proportionally more water used for food than energy, and more energy used to move water to cities than water for agricultural production. Analysis of the production scenarios indicate tipping points of food, energy, and water resources based on climatic and consumptive trends that are not yet addressed by the rigid water laws in the LCRB. These results highlight the need for resource governance to play a strong formative role in the analysis and implementation of FEW nexus management strategies.

Comparisons of Reptile Assemblages in Two Subdivisions of the Sonoran Desertscrub Biotic Community

Anthropogenic disturbances can have negative effects on species assemblages. This study was established to form baseline data on the environmental structure and reptile assemblages within a planned energy corridor in Pinal County, Arizona, prior to construction. We emphasized evaluating the differences in reptile assemblages in two subdivisions of the Sonoran Desertscrub, the Lower Colorado River Valley (LCV) and Arizona Uplands (AZU). Surveys were conducted on 50 sites (LCV = 15; AZU = 35) along the proposed 67.1-km long energy corridor through environmental surveys and 50 drift-fence trapping arrays with 400 box funnel traps. Vegetation height, number of burrows, and percent rock, ground cover, and coarse woody debris were significantly higher in the AZU than in LCV. Eighteen reptile species (n = 995 captures) were detected on the energy corridor including 8 lizard species (n = 952 captures) and 10 snake species (n = 43 captures). Species richness, evenness, and capture rates were not significantly different between the LCV and AZU; however, species diversity was significantly higher in the LCV. Reptile abundance (LCV = 281; AZU = 714) differed in the two subdivisions, yet rank-abundance curves revealed no difference in dominance of species. Post hoc examination revealed that the geographic separation of sites within the LCV and the location of the study area (along the ecotone) may have contributed to our results. We conclude that both subdivisions are equally important to the maintenance of local biotic diversity and recommend that any future land set-asides consider both subdivisions.

Designing collaborative governance: Insights from the drought contingency planning process for the lower Colorado River basin

Agriculture, environment, industry, and millions of households in the western US and northern Mexico depend on the Colorado River, which is facing increasing water shortages due to climate change and rising demand. Collaborative governance will likely be key to solving allocation issues and achieving sustainable water use but has recently faced multiple challenges. This research integrates concepts from institutional, adaptive governance, and bargaining theories to analyze barriers and facilitators to collaborative governance in the drought contingency plan (DCP) process for the lower Colorado River basin from an Arizona stakeholder’s perspective. The DCP is ultimately an effort to create a set of rules to prevent and address shortages in the basin. Through a content analysis of public meetings of the Central Arizona Project’s governing board, we find a collective DCP or future related policy may be possible. But barriers to collaborative governance have intensified over time, hindering the process and making an agreement increasingly unlikely. The process is a perfect example of the interplay between rules and norms, and the issues that arise when norms underlying rules are interpreted differently. Our analysis provides insights for the design of collaborative water governance, including that conducting an analysis of power dynamics among the stakeholders would advance the DCP process. We ultimately argue that the Colorado River basin would benefit from a transition towards adaptive governance, and that our recommendations to improve collaboration are an important initial step. Additionally, our results reveal areas that require more empirical research, including understanding how to prepare for policy windows, rapid trust building among stakeholders, and theory building related to equity and marginalization in collaborative governance processes.