Lake Mead National Recreation Area Research Articles

Archival Collections at Lake Mead National Recreation Area

Abstract: The National Park Service administers from its offices in Boulder City, Nevada what was designated as the Lake Mead National Recreational Area in 1936. The NPS manages approximately 1.5 million acres of land and water making up the Recreational Area created by the 120-mile-long reservoir behind Hoover Dam named Lake Mead. The Lake and its environs present multiple recreational resources, including natural, cultural, archaeological, and historical sites. Professionally archived records at the Recreational Area's headquarters offer researchers in multiple fields of inquiry photographs, maps, planning documents, drawings, information on relations with indigenous peoples, and land records. Researchers will find convenient finding aids and trained archivists to assist.

Human dimensions of aquatic invasive species transport at Lake Mead National Recreation Area

Human dimensions of aquatic invasive species transport at Lake Mead National Recreation Area

Microplastics in Lake Mead National Recreation Area, USA: Occurrence and biological uptake.

Microplastics are an environmental contaminant of growing concern, but there is a lack of information about microplastic distribution, persistence, availability, and biological uptake in freshwater systems. This is especially true for large river systems like the Colorado River that spans multiple states through mostly rural and agricultural land use. This study characterized the quantity and morphology of microplastics in different environmental compartments in two large reservoirs along the Colorado River: Lakes Mead and Mohave, within Lake Mead National Recreation Area. To assess microplastic occurrence, surface water and surficial sediment were sampled at a total of nine locations. Sampling locations targeted different sub-basins with varying levels of anthropogenic impact. Las Vegas Wash, a tributary which delivers treated wastewater to Lake Mead, was also sampled. A sediment core (33 cm long, representing approximately 19 years) was extracted from Las Vegas Bay to assess changes in microplastic deposition over time. Striped bass (Morone saxatilis), common carp (Cyprinus carpio), quagga mussels (Dreissena bugensis), and Asian clams (Corbicula fluminea) were sampled at a subset of locations to assess biological uptake of microplastics. Microplastic concentrations were 0.44–9.7 particles/cubic meter at the water surface and 87.5–1,010 particles/kilogram dry weight (kg dw) at the sediment surface. Sediment core concentrations were 220–2,040 particles/kg dw, with no clear increasing or decreasing trend over time. Shellfish microplastic concentrations ranged from 2.7–105 particles/organism, and fish concentrations ranged from 0–19 particles/organism. Fibers were the most abundant particle type found in all sample types. Although sample numbers are small, microplastic concentrations appear to be higher in areas of greater anthropogenic impact. Results from this study improve our understanding of the occurrence and biological uptake of microplastics in Lake Mead National Recreation Area, and help fill existing knowledge gaps on microplastics in freshwater environments in the southwestern U.S.

Review: Lake Mead National Recreation Area: A History of America’s First National Playground by Jonathan Foster

Review: Lake Mead National Recreation Area: A History of America’s First National Playground by Jonathan Foster

Sperm quality biomarkers complement reproductive and endocrine parameters in investigating environmental contaminants in common carp (Cyprinus carpio) from the Lake Mead National Recreation Area

Lake Mead National Recreational Area (LMNRA) serves as critical habitat for several federally listed species and supplies water for municipal, domestic, and agricultural use in the Southwestern U.S. Contaminant sources and concentrations vary among the sub-basins within LMNRA. To investigate whether exposure to environmental contaminants is associated with alterations in male common carp (Cyprinus carpio) gamete quality and endocrine- and reproductive parameters, data were collected among sub-basins over 7 years (1999–2006). Endpoints included sperm quality parameters of motility, viability, mitochondrial membrane potential, count, morphology, and DNA fragmentation; plasma components were vitellogenin (VTG), 17ß-estradiol, 11-keto-testosterone, triiodothyronine, and thyroxine. Fish condition factor, gonadosomatic index, and gonadal histology parameters were also measured. Diminished biomarker effects were noted in 2006, and sub-basin differences were indicated by the irregular occurrences of contaminants and by several associations between chemicals (e.g., polychlorinated biphenyls, hexachlorobenzene, galaxolide, and methyl triclosan) and biomarkers (e.g., plasma thyroxine, sperm motility and DNA fragmentation). By 2006, sex steroid hormone and VTG levels decreased with subsequent reduced endocrine disrupting effects. The sperm quality bioassays developed and applied with carp complemented endocrine and reproductive data, and can be adapted for use with other species.

Fisher's exact approach for post hoc analysis of a chi-squared test.

This research is motivated by one of our survey studies to assess the potential influence of introducing zebra mussels to the Lake Mead National Recreation Area, Nevada. One research question in this study is to investigate the association between the boating activity type and the awareness of zebra mussels. A chi-squared test is often used for testing independence between two factors with nominal levels. When the null hypothesis of independence between two factors is rejected, we are often left wondering where does the significance come from. Cell residuals, including standardized residuals and adjusted residuals, are traditionally used in testing for cell significance, which is often known as a post hoc test after a statistically significant chi-squared test. In practice, the limiting distributions of these residuals are utilized for statistical inference. However, they may lead to different conclusions based on the calculated p-values, and their p-values could be over- o6r under-estimated due to the unsatisfactory performance of asymptotic approaches with regards to type I error control. In this article, we propose new exact p-values by using Fisher’s approach based on three commonly used test statistics to order the sample space. We theoretically prove that the proposed new exact p-values based on these test statistics are the same. Based on our extensive simulation studies, we show that the existing asymptotic approach based on adjusted residual is often more likely to reject the null hypothesis as compared to the exact approach due to the inflated family-wise error rates as observed. We would recommend the proposed exact p-value for use in practice as a valuable post hoc analysis technique for chi-squared analysis.

Lake Mead National Recreation Area: A History of America’s First National Playground. America’s National Park Series. By Jonathan Foster

Lake Mead National Recreation Area: A History of America’s First National Playground. America’s National Park Series. By Jonathan Foster

Lake Mead National Recreation Area: A History of America’s First National Playground

Lake Mead National Recreation Area: A History of America’s First National Playground

Attributes of a Breeding Population of Peregrine Falcons Associated with Reservoirs on the Colorado River

Abstract We describe results from a comprehensive effort to survey and monitor Peregrine Falcons (Falco peregrinus) breeding in Lake Mead National Recreation Area (LMNRA) from 2006–2010. We identified 37 breeding territories, and the annual occupancy rate averaged 94%. Pooled over time, breeding success was 72%, and average reproductive output was 1.8 young per nesting attempt. The closest distance between eyries from neighboring territories was 1.2 km; the lowest annual mean nearest-neighbor distance (NND) was 6.3 km. No relationship was apparent between NND and breeding success or reproductive output. Nesting attempts occurred twice as often in eyries with a north-facing (68%) aspect than in eyries with a south-facing (32%) aspect. Pairs using south-facing eyries began incubating 5 d earlier than those using north-facing eyries, although the difference was not statistically significant. On a finer scale, pairs most commonly selected northwest-facing eyries (45% of nesting attempts), despite experiencing...

Status and management of non-native plant invasion in three of the largest national parks in the United States

Globally, invasion by non-native plants threatens resources that nature reserves are designated to protect. We assessed the status of non-native plant invasion on 1,662, 0.1-ha plots in Death Valley National Park, Mojave National Preserve, and Lake Mead National Recreation Area. These parks comprise 2.5 million ha, 23% of the national park land in the contiguous USA. At least one non-native species inhabited 82% of plots. Thirty-one percent of plots contained one non-native species, 30% two, 17% three, and 4% four to ten non-native species. Red brome (Bromus rubens), an ‘ecosystem engineer’ that alters fire regimes, was most widespread, infesting 60% of plots. By identifying frequency of species through this assessment, early detection and treatment can target infrequent species or minimally invaded sites, while containment strategies could focus on established invaders. We further compared two existing systems for prioritizing species for management and found that a third of species on plots had no rankings available. Moreover, rankings did not always agree between ranking systems for species that were ranked. Presence of multiple non-native species complicates treatment, and while we found that 40% of plots contained both forb and grass invaders, exploiting accelerated phenology of non-natives (compared to native annuals) might help manage multi-species invasions. Large sizes of these parks and scale of invasion are formidable challenges for management. Yet, precisely because of their size, these reserves represent opportunities to conserve large landscapes of native species by managing non-native plant invasions.

Using Feathers to Determine Mercury Contamination in Peregrine Falcons and Their Prey

Abstract We document concentrations of total mercury (Hg) in feathers of Peregrine Falcons (Falco peregrinus) from 12 territories in Lake Mead National Recreation Area (LMNRA) and five territories in an adjacent southern Nevada (SNV) study area during 2012 and 2013. We also report total Hg concentrations in feathers of 94 species (337 individuals) collected as prey remains from peregrine nesting areas from 2008–2013. All peregrine feathers contained total Hg (range = 0.12–42.54 µg/g), and adults had a significantly higher mean total Hg concentration (12.19 µg/g) than hatch-year peregrines (3.76 µg/g). Mean total Hg concentrations in peregrines in LMNRA (adult = 17.24 µg/g, brood = 5.82 µg/g) were significantly greater than in SNV (adult = 2.7 µg/g, brood = 0.67 µg/g) for both age classes. Among peregrine territories, mean total Hg in prey was positively correlated with the proportion of aquatic birds taken as prey (biomass), and negatively correlated with distance of eyries to water. Among avian...

Novel associations between contaminant body burdens and biomarkers of reproductive condition in male Common Carp along multiple gradients of contaminant exposure in Lake Mead National Recreation Area, USA

Adult male Common Carp were sampled in 2007/08 over a full reproductive cycle at Lake Mead National Recreation Area. Sites sampled included a stream dominated by treated wastewater effluent, a lake basin receiving the streamflow, an upstream lake basin (reference), and a site below Hoover Dam. Individual body burdens for 252 contaminants were measured, and biological variables assessed included physiological [plasma vitellogenin (VTG), estradiol-17β (E2), 11-ketotestosterone (11KT)] and organ [gonadosomatic index (GSI)] endpoints. Patterns in contaminant composition and biological condition were determined by Principal Component Analysis, and their associations modeled by Principal Component Regression. Three spatially distinct but temporally stable gradients of contaminant distribution were recognized: a contaminant mixture typical of wastewaters (PBDEs, methyl triclosan, galaxolide), PCBs, and DDTs. Two spatiotemporally variable patterns of biological condition were recognized: a primary pattern consisting of reproductive condition variables (11KT, E2, GSI), and a secondary pattern including general condition traits (condition factor, hematocrit, fork length). VTG was low in all fish, indicating low estrogenic activity of water at all sites. Wastewater contaminants associated negatively with GSI, 11KT and E2; PCBs associated negatively with GSI and 11KT; and DDTs associated positively with GSI and 11KT. Regression of GSI on sex steroids revealed a novel, nonlinear association between these variables. Inclusion of sex steroids in the GSI regression on contaminants rendered wastewater contaminants nonsignificant in the model and reduced the influence of PCBs and DDTs. Thus, the influence of contaminants on GSI may have been partially driven by organismal modes-of-action that include changes in sex steroid production. The positive association of DDTs with 11KT and GSI suggests that lifetime, sub-lethal exposures to DDTs have effects on male carp opposite of those reported by studies where exposure concentrations were relatively high. Lastly, this study highlighted advantages of multivariate/multiple regression approaches for exploring associations between complex contaminant mixtures and gradients and reproductive condition in wild fishes.

Helicopter Emergency Medical Service (HEMS) Utilization Patterns by the National Park Service in Lake Mead National Recreation Area from 2008–2011

Helicopter Emergency Medical Service (HEMS) Utilization Patterns by the National Park Service in Lake Mead National Recreation Area from 2008–2011

Patterns of metal composition and biological condition and their association in male common carp across an environmental contaminant gradient in Lake Mead National Recreation Area, Nevada and Arizona, USA

There is a contaminant gradient in Lake Mead National Recreation Area (LMNRA) that is partly driven by municipal and industrial runoff and wastewater inputs via Las Vegas Wash (LVW). Adult male common carp (Cyprinus carpio; 10 fish/site) were collected from LVW, Las Vegas Bay (receiving LVW flow), Overton Arm (OA, upstream reference), and Willow Beach (WB, downstream) in March 2008. Discriminant function analysis was used to describe differences in metal concentrations and biological condition of fish collected from the four study sites, and canonical correlation analysis was used to evaluate the association between metal and biological traits. Metal concentrations were determined in whole-body extracts. Of 63 metals screened, those initially used in the statistical analysis were Ag, As, Ba, Cd, Co, Fe, Hg, Pb, Se, Zn. Biological variables analyzed included total length (TL), Fulton's condition factor, gonadosomatic index (GSI), hematocrit (Hct), and plasma estradiol-17β and 11-ketotestosterone (11kt) concentrations. Analysis of metal composition and biological condition both yielded strong discrimination of fish by site (respective canonical model, p<0.0001). Compared to OA, pairwise Mahalanobis distances between group means were WB<LVB<LVW for metal concentrations and LVB<WB<LVW for biological traits. Respective primary drivers for these separations were Ag, As, Ba, Hg, Pb, Se and Zn; and TL, GSI, 11kt, and Hct. Canonical correlation analysis using the latter variable sets showed they are significantly associated (p<0.0003); with As, Ba, Hg, and Zn, and TL, 11kt, and Hct being the primary contributors to the association. In conclusion, male carp collected along a contaminant gradient in LMNRA have distinct, collection site-dependent metal and morpho-physiological profiles that are significantly associated with each other. These associations suggest that fish health and reproductive condition (as measured by the biological variables evaluated in this study) are influenced by levels of certain metals in the Lake Mead environment.

The 100th Meridian Initiative at the Lake Mead National Recreation Area, NV, USA: Differences between boater behaviors before and after a quagga mussel, Driessena rostiformis bugensis, invasion

The 100 th Meridian Initiative was developed to help prevent the spread of aquatic nuisance species (ANS) through boater education and research on boater movement patterns and behaviors. Surveys employing these elements were conducted at Lake Mead National Recreation Area (LMNRA) in 2002-2003 before the discovery of the quagga mussel (Dreissena rostiformis bugensis Andrusov 1897) and in 2007-2008 after an established population of quagga mussels was found in the Lake. Boaters were asked questions in a personal interview or a mail-in survey regarding what body of water they had previously launched their watercraft in, where they were planning to launch next, if they cleaned their watercraft between each launch, and if they were aware of quagga mussels or other ANS. Results from the personal interviews and mail-in surveys indicated a significant increase in mussel awareness between the pre- and post- mussel invasion groups. Cleaning habits between the study periods for both interviews and mail-in surveys did not differ significantly. Boat trailer states of registration were also documented in both study periods in the parking lots of LMNRA. In 2002-2003, 0.6% of the trailers documented were from states with known zebra or quagga mussel populations, whereas in 2007-2008, 98.2% of states documented had known zebra or quagga mussel populations. Increased boater awareness will help prevent the spread of aquatic invasive species and the 100 th Meridian Initiative is a helpful way to educate boaters and collect relevant data on future mussel invasions. The preservation of natural waters is vital for the conservation of native species and the prevention of zebra and quagga mussel invasions will assist in this preservation. Further efforts should be directed toward educating boaters on effective cleaning methods.

The Quagga Mussel Crisis at Lake Mead National Recreation Area, Nevada (U.S.A.)

Parks are cornerstones of conservation; and non-native invasive species drive extensive changes to biological diversity in parks. Knowing this, national park staff at Lake Mead National Recreation Area in the southwestern United States had a program in place for early detection of the non-native, invasive quagga mussel (Dreissena rostriformis bugensis). Upon finding the mussel in January 2007, managers moved quickly to access funding and the best available science to implement a response. Managers considered four options--doing nothing, closing the park, restricting movement on the lakes, and educating and enforcing park visitors--and decided to focus on education and enforcing existing laws. Nonetheless, quagga spread throughout the park and soon began to appear throughout the western United States. I examined why efforts to control the expansion failed and determined the general lessons to be learned from this case. Concentrating human visitation on the lakes through land-use zoning opened a pathway for invasion, reduced management options, and led to the rapid spread of quagga. To reconcile competing mandates to protect nature and provide recreation, zoning in parks has become a common practice worldwide. It reduces stress on some areas of a park by restricting and thus concentrating human activity in particular areas. Concentrating the human activity in one area does three things: cements pathways that repeatedly import and export vectors of non-native invasive species; creates the disturbed area necessary to enable non-native invasive species to gain a foothold; and, establishes a source of invasions that, without appropriate controls, can quickly spread to a park's wilderness areas.

Sources and Distribution of Organic Compounds Using Passive Samplers in Lake Mead National Recreation Area, Nevada and Arizona, and Their Implications for Potential Effects on Aquatic Biota

The delineation of lateral and vertical gradients of organic contaminants in lakes is hampered by low concentrationsand nondetection of many organic compounds in water. Passive samplers (semipermeable membrane devices [SPMDs] and polar organic chemical integrative samplers [POCIS]) are well suited for assessing gradients because they can detect synthetic organic compounds (SOCs) at pg L(-1) concentrations. Semi-permeable membrane devices and POCIS were deployed in Lake Mead, at two sites in Las Vegas Wash, at four sites across Lake Mead, and in the Colorado River downstream from Hoover Dam. Concentrations of hydrophobic SOCs were highest in Las Vegas Wash downstream from waste water and urban inputs and at 8 m depth in Las Vegas Bay (LVB) where Las Vegas Wash enters Lake Mead. The distribution of hydrophobic SOCs showed a lateral distribution across 10 km of Lake Mead from LVB to Boulder Basin. To assess possible vertical gradient SOCs, SPMDs were deployed at 4-m intervals in 18 m of water in LVB. Fragrances and legacy SOCs were found at the greatest concentrations at the deepest depth. The vertical gradient of SOCs indicated that contaminants were generally confined to within 6 m of the lake bottom during the deployment interval. The high SOC concentrations, warmer water temperatures, and higher total dissolved solids concentrations at depth are indicative of a plume of Las Vegas Wash water moving along the lake bottom. The lateral and vertical distribution of SOCs is discussed in the context of other studies that have shown impaired health of fish exposed to SOCs.

Recreational Travel Fatalities in US National Parks

Injuries are a public health problem affecting traveling populations such as tourists visiting National Parks. This study investigates the distribution of visitor fatalities in US National Park Service (NPS) units and identifies the predeath activities and contributing factors associated with them. A retrospective study was conducted of visitor fatalities from all NPS units during 2003 and 2004. There were 356 reported fatalities during 2003 and 2004. Fatalities were most common during the summer months and on weekends. Males accounted for 75% of the reported fatalities, and visitors aged 20 to 29 and 50 to 59 years accounted for 51% of all deaths. Only 99 of 388 (26%) NPS units reported at least 1 fatality, and only 10 units reported 10 or more fatalities. However, these 10 units were responsible for 36% of all fatalities. Lake Mead National Recreation Area, Blue Ridge Parkway, Grand Canyon National Park, Great Smoky Mountains National Park, and Yosemite National Park reported the highest number of fatalities. Domestic visitors accounted for 73% of the fatalities, and European visitors accounted for 13%. Transportation and water-based activities recorded the highest number of fatalities. Motor vehicle crashes accounted for 20% of fatalities and was followed by suicide (17%), swimming (11%), hiking (10%), plane crashes (9%), climbing (6%), and boating (5%) incidents. Fatalities in NPS units are not widespread and are related to more common events such as motor vehicle crashes, suicide, swimming, and hiking rather than exotic causes such as bears or other wildlife. It is recommended that preventive techniques first be developed in the 10 NPS units responsible for 36% of the total NPS-wide fatalities.

TAMARIX APHYLLA: A NEWLY INVASIVE TREE IN SOUTHERN NEVADA

In the southwestern United States, the nonnative athel pine (Tamarix aphylla) was presumed to be sterile and therefore not as likely to spread as its widely distributed, nonnative congener, T. ramosissima. However, at Lake Mead National Recreation Area (LMNRA) in southern Nevada, populations of T. aphylla have recently spread beyond their limited pre-1990 distribution and now form extensive monospecific stands. Over a 3-year period, we quantified seed production and germination from 60 T. aphylla trees at LMNRA. The annual mean seed production period was 50.6 days, and the mean potential germination (under laboratory conditions) was 22%, indicating that T. aphylla trees at LMNRA are capable of sexual reproduction in southern Nevada. No seeds germinated in field experiments, apparently because of high soil salt levels. However, seedling regeneration is becoming increasingly common at LMNRA. Tamarix aphylla trees occupied a distinct zone along the shoreline of Lake Mead, above T. ramosissima in elevation and below native Larrea tridentata communities, suggesting either competitive exclusion or differential resource utilization. The T. aphylla zone tended to have the highest mean values for total vegetation cover, leaf litter depth, soil salinity, soil moisture, pH, total Kjeldahl nitrogen, and soil organic matter. The capacity for sexual reproduction of this alien plant, combined with a suite of characteristics shared with the invasive T. ramosissima (e.g., drought tolerance and copious saline leaf litter), makes T. aphylla a potentially invasive species along the shores of LMNRA and other mesic areas in the desert Southwest.

Regaining a water resource for communities along the Lake Mead shoreline

This report discusses a project to upgrade four small water treatment plants on the shores of Lake Mead National Recreation Area. Construction involved replacing the old dual‐media gravity filtration systems with new plants using the latest in filtration technology. The project also addressed the efficiency of irrigation systems by replacing existing flood irrigation systems with a more efficient drip system and by reducing the use of membrane filtration reject into the irrigation system to reduce potable water use. A combination microfiltration/nanofiltration treatment processes was selected for the replacement treatment plants. The article discusses the creation of a desert water team by the contractor to manage all four projects as one program with project oversight being provided from one central office where all documentation and data control were conducted. The article also describes how trouble‐shooting in the desert required creative solutions, and the problems that were encountered when the treatment plants were due to start‐up.