Las Vegas Wash Research Articles

Bird Community Responses to Restoration along Las Vegas Wash, Nevada

In a 12-year study of seasonal bird use along Las Vegas Wash (Clark County, Nevada), an area undergoing intensive channel stabilization and riparian and wetland restoration, we found that total bird abundance and species richness significantly increased. In the late phase of the project, total bird abundance was greatest during the nonbreeding season and winter transition, and species richness was greatest during the fall transition. Species associated with riparian shrubs decreased, likely as a response to large-scale removal of non-native shrubs and the lag in recovery of a native shrub understory. Species associated with trees and the mid-story had a mixed response, with detections of those species previously most closely associated with non-native trees showing a negative trend, while those associated with native overstory plants showing an increasing or mixed trend. Detections of wetland and aquatic species increased significantly throughout the project. This study shows differential restoration responses of species based on their natural history, seasons of primary use of the site, and the lag time in recovery of particular vegetation elements that are used by various species assemblages.

Sources of per- and polyfluoroalkyl substances in an arid, urban, wastewater-dominated watershed

Per- and polyfluoroalkyl substances (PFAS) enter surface waters from various sources such as wastewater treatment plants, fire-fighting sites, and PFAS-producing and PFAS-using industries. The Las Vegas Wash in Southern Nevada of the United States (U.S.) conveys wastewater effluent from the Las Vegas metropolitan area to Lake Mead, a drinking water source for millions of people in the U.S. Southwest. PFAS have previously been detected in the Las Vegas Wash, but PFAS sources were not identified. In this study, upstream wash tributaries, wastewater treatment effluents, and shallow groundwater wells were sampled in multiple campaigns during dry-weather conditions to investigate possible PFAS sources. Out of 19 PFAS, two short-chain PFAS—perfluoropentanoic acid (48 % of the total molar concentration) and perfluorohexanoic acid (32 %)—comprised the majority of PFAS loading measured in the Las Vegas Wash, followed by perfluorooctanoic acid (9 %). On a mass loading basis, the majority of total measured PFAS (approximately 90 %) and at least 48 % of each specific PFAS in the Las Vegas Wash likely entered via municipal wastewater effluents, of which the main source was likely residential wastewater. One of the drainage areas with a major civilian airport was identified as a potential source of relatively enriched perfluorosulfonic acids to a small wash tributary and shallow groundwater samples. Nonetheless, that tributary contributed at most 15 % of any specific PFAS to the mainstem of the Las Vegas Wash. Total PFAS concentrations were relatively low for the small tributary associated with an urban smaller airport and the lack of flow in the tributary channel immediately downgradient of an Air Force base indicates the smaller airport and base were unlikely significant PFAS sources to the Las Vegas Wash. Overall, this study demonstrated effective PFAS source investigation methodology and the importance of wastewater effluent as a PFAS environmental pathway.

Spatial and Temporal Dynamics of Key Water Quality Parameters in a Thermal Stratified Lake Ecosystem: The Case Study of Lake Mead

Lake Mead located in the Arizona–Nevada region of the Mohave Dessert is a unique and complex water system whose flow follows that of a warm monomictic lake. Although monomictic lakes experience thermal stratification for almost the entire year with a period of complete mixing, the lake on occasion deviates from this phenomenon, undergoing incomplete turnovers categorized with light stratifications every other year. The prolonged drought and growing anthropogenic activities have the potential to considerably impact the quality of the lake. Lake Mead and by extension the Boulder Basin receive cooler flow from the Colorado River and flow with varying temperatures from the Las Vegas Wash (LVW), which impacts its stratification and complete turnovers. This study analyzes four key water quality parameters (WQPs), namely, total dissolved solids (TDS), total suspended solids (TSS), temperature, and dissolved oxygen (DO), using statistical and spatial analyses to understand their variations in light of the lake stratifications and turnovers to further maintain its overall quality and sustainability. The study also evaluates the impacts of hydrological variables including in and out flows, storage, evaporation, and water surface elevation on the WQPs. The results produced from the analysis show significant levels of TDS, TSS, and temperature from the LVW and Las Vegas Bay regions compared with the Boulder Basin. LVW is the main channel for conveying effluents from several wastewater treatment facilities into the lake. We observed an increase in the levels of TDS, TSS, and temperature water quality in the epilimnion compared with the other layers of the lake. The metalimnion and the hypolimnion layer, however, showed reduced DO due to depletion by algal blooms. We observed statistically significant differences in the WQPs throughout various months, but not in the case for season and year, an indication of relatively consistent variability throughout each season and year. We also observed a no clear trend of influence of outflows and inflows on TDS, temperature, and DO. TSS concentrations in the lake, however, remained constant, irrespective of the inflows and outflows, possibly due to the settling of the sediments and the reservoir capacity.

The Nonstationary Flood Hydrology of an Urbanizing Arid Watershed

Abstract The Las Vegas metropolitan area in Nevada has experienced extensive urban growth since 1950 coincident with regional and local climate change. This study explores the nonstationary flood history of the Las Vegas Wash (LVW) watershed by deconstructing it into its constituent physical drivers. Observations and reanalysis products are used to examine the hydroclimatology, hydrometeorology, and hydrology of flash flooding in the watershed. Annual peak flows have increased nonlinearly over the past seven decades, with an abrupt changepoint detected in the mid-1990s, which is attributed to the implementation of flood conveyance systems rather than changes in land use. The LVW watershed exhibits two pronounced flood seasons, associated with distinct synoptic atmospheric circulations: winter floods linked to inland-penetrating atmospheric rivers and summer floods linked to the North American monsoon. El Niño–Southern Oscillation also plays a role in modulating extreme rainfall and the resultant floods because annual maximum daily rainfall totals positively correlate with El Niño, with Spearman’s correlation coefficient of 0.36 (p value < 0.05). Winter maximum daily rainfall totals have increased since 1950, whereas summer daily rainfall maxima have decreased. The trends in hydrometeorological drivers interact with urbanization to shift flood seasonality toward more frequent winter floods in the LVW watershed. A process-based understanding of the flood hydrology of the watershed also provides insights into flood frequency analysis and flood forecasting.

Butterfly Assemblages Associated with Restored Riparian Uplands: Las Vegas Wash, Nevada, USA

The butterfly assemblage found at riparian upland plant restoration areas (after removal of the invasive plant, tamarisk (Tamarix ramosissima Ledebour)) along Las Vegas Wash was examined over four different months. Upland areas were planted with a variety of plants, however, those with a mesquite (Prosopis spp. Linneaus) component contained additional butterfly species relative to other plots. Detrended correspondence analysis demonstrated a gradient of butterfly species that corresponded with mesquite, age of stand, and homogenous areas of tamarisk. Some potential butterfly species went undetected; perhaps because required herbaceous understory plants were absent, or the need for greater densities of the hemiparasitic mistletoe (Phoradendron) (Nutt.) which is utilized by certain butterfly species. A single plot of exotic tamarisk, the near-past dominant shrub of the Wash landscape, was examined. An incursion of the beetle Diorhabda carinulata (Desbrochers), a phytophagous tamarisk control agent, appeared to affect tamarisk nectar production along with butterfly abundance at the plot. Butterfly response to nectar at inadvertent seep areas suggests these features are important for butterfly directed landscape restoration activities. Use of a characteristic butterfly community for identifying goals for upland restoration was valuable in describing end-points that incorporated assets of natural mesquite bosques.

A Peristaltic Pump and Filter-Based Method for Aqueous Microplastic Sampling and Analysis

Sampling the aquatic environment for microplastic concentration is inherently difficult because of variations in microplastic concentration, shape, and density and the potential for contamination. We present an assessment of a method for microplastic sampling that uses a peristaltic pump to pump water through a series of in-line stainless-steel mesh filters. Following filtration, the stainless-steel filters were treated using previously published methods to isolate microplastics, adjusted for the stainless-steel mesh filters. Microplastics were identified using micro-Fourier transform infrared (μFTIR) spectroscopy in transmission mode. This method was tested in the laboratory using standard polyethylene beads and was applied to two sample sites at the Las Vegas Wash in Nevada. The results showed that 70% of the polyethylene beads were recovered after the peristaltic pump and laboratory steps with minimal blank contamination. The advantages of the peristaltic pump sampling method are it (1) supports a range of sample volumes, (2) reduces sample handling, (3) reduces the potential for contamination, (4) provides flexibility in sampling locations, and (5) supports a variety of filter types. Using stainless-steel mesh filters allows for (1) streamlined and direct field-to-laboratory sample processing, (2) μFTIR transmission mode analysis of filter-mounted microplastics, and (3) reduced filter and sample processing costs.

Wastewater discharge quality prediction using stratified sampling and wavelet de-noising ANFIS model

The monitoring of wastewater quality is vitally important for the stability of an ecosystem. Among many machine learning techniques proposed for predicting the quality of wastewater, the adaptive neuro-fuzzy inference system (ANFIS) can achieve the best accuracy. However, due to data size limitations, the uneven distribution of randomly sampled training data can cause out-of-range prediction errors in the ANFIS model. In this study, a general-purpose input parameter selection method is proposed, combined with an optimized wavelet de-noising ANFIS model, to predict salinity parameters in wastewater discharge samples from the Las Vegas Wash, Nevada, USA. A statistical, stratified sampling strategy is used to preprocess the wastewater quality dataset. Compared with existing artificial intelligence models, the experimental results prove that the proposed model has the best performance, in which the R2 testing value achieves 0.976, 0.975, 0.988, and 0.986 in predicting chloride, sulfate, electrical conductivity, and total dissolved solids, respectively.

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.

Association between degradation of pharmaceuticals and endocrine-disrupting compounds and microbial communities along a treated wastewater effluent gradient in Lake Mead

The role of microbial communities in the degradation of trace organic contaminants in the environment is little understood. In this study, the biotransformation potential of 27 pharmaceuticals and endocrine-disrupting compounds was examined in parallel with a characterization of the native microbial community in water samples from four sites variously impacted by urban run-off and wastewater discharge in Lake Mead, Nevada and Arizona, USA. Samples included relatively pristine Colorado River water at the upper end of the lake, nearly pure tertiary-treated municipal wastewater entering via the Las Vegas Wash, and waters of mixed influence (Las Vegas Bay and Boulder Basin), which represented a gradient of treated wastewater effluent impact. Microbial diversity analysis based on 16S rRNA gene censuses revealed the community at this site to be distinct from the less urban-impacted locations, although all sites were similar in overall diversity and richness. Similarly, Biolog EcoPlate assays demonstrated that the microbial community at Las Vegas Wash was the most metabolically versatile and active. Organic contaminants added as a mixture to laboratory microcosms were more rapidly and completely degraded in the most wastewater-impacted sites (Las Vegas Wash and Las Vegas Bay), with the majority exhibiting shorter half-lives than at the other sites or in a bacteriostatic control. Although the reasons for enhanced degradation capacity in the wastewater-impacted sites remain to be established, these data are consistent with the acclimatization of native microorganisms (either through changes in community structure or metabolic regulation) to effluent-derived trace contaminants. This study suggests that in urban, wastewater-impacted watersheds, prior exposure to organic contaminants fundamentally alters the structure and function of microbial communities, which in turn translates into greater potential for the natural attenuation of these compounds compared to more pristine sites.

Vertebrate paleontology, stratigraphy, and paleohydrology of Tule Springs Fossil Beds National Monument, Nevada (USA)

Tule Springs Fossil Beds National Monument (TUSK) preserves 22,650 acres of the upper Las Vegas Wash in the northern Las Vegas Valley (Nevada, USA). TUSK is home to extensive and stratigraphically complex groundwater discharge (GWD) deposits, called the Las Vegas Formation, which represent springs and desert wetlands that covered much of the valley during the late Quaternary. The GWD deposits record hydrologic changes that occurred here in a dynamic and temporally congruent response to abrupt climatic oscillations over the last ~300 ka (thousands of years). The deposits also entomb the Tule Springs Local Fauna (TSLF), one of the most significant late Pleistocene (Rancholabrean) vertebrate assemblages in the American Southwest. The TSLF is both prolific and diverse, and includes a large mammal assemblage dominated by Mammuthus columbi and Camelops hesternus. Two (and possibly three) distinct species of Equus, two species of Bison, Panthera atrox, Smilodon fatalis, Canis dirus, Megalonyx jeffersonii, and Nothrotheriops shastensis are also present, and newly recognized faunal components include micromammals, amphibians, snakes, and birds. Invertebrates, plant macrofossils, and pollen also occur in the deposits and provide important and complementary paleoenvironmental information. This field compendium highlights the faunal assemblage in the classic stratigraphic sequences of the Las Vegas Formation within TUSK, emphasizes the significant hydrologic changes that occurred in the area during the recent geologic past, and examines the subsequent and repeated effect of rapid climate change on the local desert wetland ecosystem.

Vertebrate paleontology, stratigraphy, and paleohydrology of Tule Springs Fossil Beds National Monument, Nevada (USA)

Tule Springs Fossil Beds National Monument (TUSK) preserves 22,650 acres of the upper Las Vegas Wash in the northern Las Vegas Valley (Nevada, USA). TUSK is home to extensive and stratigraphically complex groundwater discharge (GWD) deposits, called the Las Vegas Formation, which represent springs and desert wetlands that covered much of the valley during the late Quaternary. The GWD deposits record hydrologic changes that occurred here in a dynamic and temporally congruent response to abrupt climatic oscillations over the last ~300 ka (thousands of years). The deposits also entomb the Tule Springs Local Fauna (TSLF), one of the most significant late Pleistocene (Rancholabrean) vertebrate assemblages in the American Southwest. The TSLF is both prolific and diverse, and includes a large mammal assemblage dominated by Mammuthus columbi and Camelops hesternus. Two (and possibly three) distinct species of Equus, two species of Bison, Panthera atrox, Smilodon fatalis, Canis dirus, Megalonyx jeffersonii, and Nothrotheriops shastensis are also present, and newly recognized faunal components include micromammals, amphibians, snakes, and birds. Invertebrates, plant macrofossils, and pollen also occur in the deposits and provide important and complementary paleoenvironmental information. This field compendium highlights the faunal assemblage in the classic stratigraphic sequences of the Las Vegas Formation within TUSK, emphasizes the significant hydrologic changes that occurred in the area during the recent geologic past, and examines the subsequent and repeated effect of rapid climate change on the local desert wetland ecosystem.

An approach to measure parameter sensitivity in watershed hydrological modelling

ABSTRACTHydrological responses vary spatially and temporally according to watershed characteristics. In this study, the hydrological models that we developed earlier for the Little Miami River (LMR) and Las Vegas Wash (LVW) watersheds in the USA were used for detailed sensitivity analyses. To compare the relative sensitivities of the hydrological parameters of these two models, we used normalized root mean square error (NRMSE). By combining the NRMSE index with the flow duration curve analysis, we derived an approach to measure parameter sensitivities under different flow regimes. Results show that the parameters related to groundwater are highly sensitive in the LMR watershed, whereas the LVW watershed is primarily sensitive to near-surface and impervious parameters. The high and medium flows are more impacted by most of the parameters. The low flow regime was highly sensitive to groundwater-related parameters. Moreover, our approach is found to be useful in facilitating model development and calibration.EDITOR D. KoutsoyiannisASSOCIATE EDITOR S. Huang

Northern tamarisk beetle (Diorhabda carinulata) effects on established tamarisk-feeding invertebrate populations along the Las Vegas Wash, Clark County, Nevada

Abstract Biocontrol of tamarisk in the southwestern United States, in the form of species belonging to the genus Diorhabda, has been the subject of much research in the past few years in terms of efficacy and impact to native wildlife. This study documents the northern tamarisk beetle's (Diorhabda carinulata) arrival to the Las Vegas Wash in southern Nevada, and its impact on two other nonnative phytophagous invertebrate species that also feed on tamarisk. Our research indicates a negative correlation between the arrival of the northern tamarisk beetle and a population of tamarisk leafhoppers (Opsius stactogalus). There was no significant influence on a population of the splendid tamarisk weevil (Coniatus splendidulus). The arrival of the northern tamarisk beetle resulted in substantial defoliation of tamarisk whereas the two other species had minimal impacts on tamarisk foliage.

Wood decay in desert riverine environments

Floodplain forests and the woody debris they produce are major components of riverine ecosystems in many arid and semiarid regions (drylands). We monitored breakdown and nitrogen dynamics in wood and bark from a native riparian tree, Fremont cottonwood (Populus deltoides subsp. wislizeni), along four North American desert streams. We placed locally-obtained, fresh, coarse material [disks or cylinders (∼500–2000cm3)] along two cold-desert and two warm-desert rivers in the Colorado River Basin. Material was placed in both floodplain and aquatic environments, and left in situ for up to 12years. We tested the hypothesis that breakdown would be fastest in relatively warm and moist aerobic environments by comparing the time required for 50% loss of initial ash-free dry matter (T50) calculated using exponential decay models incorporating a lag term. In cold-desert sites (Green and Yampa rivers, Colorado), disks of wood with bark attached exposed for up to 12years in locations rarely inundated lost mass at a slower rate (T50=34yr) than in locations inundated during most spring floods (T50=12yr). At the latter locations, bark alone loss mass at a rate initially similar to whole disks (T50=13yr), but which subsequently slowed. In warm-desert sites monitored for 3years, cylinders of wood with bark removed lost mass very slowly (T50=60yr) at a location never inundated (Bill Williams River, Arizona), whereas decay rate varied among aquatic locations (T50=20yr in Bill Williams River; T50=3yr in Las Vegas Wash, an effluent-dominated stream warmed by treated wastewater inflows). Invertebrates had a minor role in wood breakdown except at in-stream locations in Las Vegas Wash. The presence and form of change in nitrogen content during exposure varied among riverine environments. Our results suggest woody debris breakdown in desert riverine ecosystems is primarily a microbial process with rates determined by landscape position, local weather, and especially the regional climate through its effect on the flow regime. The increased warmth and aridity expected to accompany climate change in the North American southwest will likely retard the already slow wood decay process on naturally functioning desert river floodplains. Our results have implications for designing environmental flows to manage floodplain forest wood budgets, carbon storage, and nutrient cycling along regulated dryland rivers.

Three-dimensional management model for Lake Mead, Nevada, Part 2: Findings and applications

A 3-dimensional numerical hydrodynamic and water quality model of Lake Mead was used to improve understanding of the general limnology and aquatic ecology of Lake Mead and to assess the benefits and refine the designs of 2 large-scale capital improvement projects, with total project costs estimated to exceed $1.4 billion. The model, which was developed and validated as described in a companion paper (Preston et al. 2014), was utilized to illustrate the rapid advection of algae on the lake surface by wind, the variable insertion level and fate of inflows, the velocity fields within the lake, and the replenishment of dissolved oxygen in the hypolimnion through 2 different mechanisms. Water quality information from the model was critical in the selection of the final location for a new municipal drinking water intake, allowing designers to optimize the intake elevation and to identify the benefits of maintaining the existing intakes (such as enabling selective withdrawal). Alternative discharge scenarios were modeled and ultimately demonstrated that chlorophyll a concentrations could be reduced to lower levels than the water quality standards by discharging treated wastewater effluent to the hypolimnion of Lake Mead via a proposed diffuser, rather than discharging to the surface via the Las Vegas Wash. Model results were used to facilitate port design and operation planning for the deep-water effluent diffuser to increase dilution and manage effluent concentrations at key locations.

Development of a phosphorus budget for Lake Mead

Phosphorus is the growth-limiting nutrient for phytoplankton in Lake Mead. Multiple agencies have developed an extensive phosphorus dataset with low detection limit since 2007 by obtaining monthly or biweekly samples at 19 monitoring stations throughout the lake and at all the major inflows. Approximately 2000 phosphorus grab samples were collected and analyzed as part of this effort. We developed a phosphorus budget for Lake Mead during 2007–2008 using these measured phosphorus data and evaluated its accuracy using the water and bromide budget developed in this study. Based on the phosphorus budget, total phosphorus (TP) loading from the Colorado River dominated external TP loading to Lake Mead, accounting for 98% of total external loading. The orthophosphate (Ortho-P) portion that is soluble and bioavailable accounted for <2% of the TP loading from the Colorado River, indicating that a significant portion of the Colorado River TP loading was in particulate form. Our analysis showed that 88% of this TP loading settled within 8 km of the river confluence. Calculated annual retention coefficients for Ortho-P indicated that Lake Mead retained about three-fourths of the influent Ortho-P; thus, Lake Mead is a significant phosphorus sink for the Colorado River, limiting the transport of phosphorus to downstream reaches or attached systems. In Boulder Basin, the most downstream basin where major drinking water intakes are located, Las Vegas Wash was the largest Ortho-P contributor during 2007–2008, validating the recent management efforts to reduce phosphorus loading in the Las Vegas Wash.

Bacterial contamination due to point and nonpoint source pollution in a rapidly growing urban center in an arid region

The distribution of bacterial contaminants (Escherichia coli and total coliforms) and nutrients (nitrogen and phosphorus) in a rapidly growing metropolitan area, the Las Vegas Valley, were studied to assess the contributions of point and nonpoint pollution sources under dry weather flow (pre rainfall) and wet weather flow (post rainfall) events. Nonpoint sources emanating from urban centers and septic seepage were found to be a primary source of bacterial contamination in the Las Vegas Wash, a mainstream wash channel where the Las Vegas Valley watershed drains. Contribution of point sources (wastewater treatment plants) to E. coli and total coliforms were found to be negligible. However, data in the Tropicana/Flamingo Wash, a tributary of the Las Vegas Wash, showed high bacterial activities in the wet antecedent rainfall condition as compared to the pre-rain dry antecedent condition suggesting that the rainfall increased bacterial activities.

Fractional dispersion equation for sediment suspension

This study proposes a stochastic approach to simulate sediment vertical dispersion in turbulent solid-liquid flows by developing a fractional advection-diffusion equation (fADE) to characterize the dynamics of sediment suspension. The fADE is a generalization of the traditional advection-diffusion equation (ADE) where the first-order spatial derivative is replaced with a fractional derivative of order alpha (0 < alpha <= 1). Many previous investigations of sediment suspension in steady sediment-laden flows apply the classic or improved Rouse equation, which was derived from the traditional ADE by assuming Fick's first law for the sediment dispersive flux. Recent observations in field and laboratory studies, however, have indicated that large errors may arise from the traditional ADE when applied to flows with coarse sediments. Instead, the vertical dispersion of suspended sediment is most likely a space nonlocal transport process in flows with turbulent bursting because particle vertical jumps with ejection events are no longer constrained to a small distance defined by the representative elementary volume. In other words, the vertical random displacements of suspended particles follow Levy motion instead of Brownian motion. After validating against field measurements in the Las Vegas Wash as well as a set of published experimental data, we find that the proposed fractional model can describe the real-world vertical distribution of suspended sediment concentration in steady turbulent flows. (C) 2013 Elsevier B.V. All rights reserved.

Spatial analysis for identifying hotspots of EDC and PPCP sources for monitoring systems

This study utilized spatial analysis to identify hotspots for endocrine disrupting chemicals (EDCs), pharmaceuticals, and personal care products (PPCPs) using data from potential sources including wastewater treatment plants, National Pollutant Discharge Elimination System (NPDES)-permitted pollution sources, septic systems, and agricultural and grazing areas. The study area is Lake Mead, to which the return of treated effluent is one of the largest water reuse practices in the USA. Based on Getis-Ord's Gi* statistic, clusters of pollution sources were identified based on the values of each feature and its neighboring features. Spatial analysis was applied to evaluate the impact from point and nonpoint source pollution. The results of spatial statistical analyses were used to evaluate the existing sampling locations in Las Vegas Wash. The results indicated that sampling locations with highest concentrations of EDCs/PPCPs were close to the outlets of subbasins with high susceptibility to EDCs/PPCPs, which confirms the suitability of sampling locations.

Exploring the effects of population growth on future land use change in the Las Vegas Wash watershed: an integrated approach of geospatial modeling and analytics

The Las Vegas Valley metropolitan area is one of the fastest growing areas in the southwestern United States. The rapid urbanization has presented many environmental challenges. For instance, as population growth and urbanization continue, the supply of sufficient clean water will become a concern. In addition, the area is also experiencing the longest drought in history, and the volume of water storage in Lake Mead, the main fresh water supply for the entire region, has been reduced greatly. The water quality in the main stem of the Las Vegas Wash (LVW) and Lake Mead may also be significantly affected. In order to develop effective sustainable management plans, the very first step is to predict the plausible future urbanization and land use patterns. This paper presents an approach to predict the future land use pattern at the LVW watershed using a Markov cellular automata model. The multi-criteria evaluation was used to couple population density as a variable depicting the driving force of urbanization in the model. Moreover, landscape metrics were used to analyze land use changes in order to better understand the dynamics of urban development in the LVW watershed. The predicted future land use maps for the years 2030 and 2050 show substantial urban development in the area, much of which are located in areas sensitive to source water protections. The results of the analysis provide valuable information for local planners and policy makers, assisting their efforts in constructing alternative sustainable urban development schemes and environmental management strategies.