6

Informing Dust Control Decisions for Off-Lake Sources

Dust control measures (DCMs) on the Owens Lake bed and elsewhere have proven their effectiveness in reducing PM₁₀ emissions (O’Brian 2021; NASEM 2020). Prior to the implementation of DCMs in 2000, Owens Lake was North America’s largest single point source of PM₁₀, or particulate matter with an aerodynamic diameter of 10 micrometers or less (Reheis 1997). As detailed in Chapter 3, between 2001—the first year following the initiation of construction of the U.S. Environmental Protection Agency (EPA)-approved best available control measures (BACMs)—and 2023, significant declines in both the number of exceedance days and the average 24-hr PM₁₀ exceedance values have occurred (see Table 3-1). While PM₁₀ exceedances have steadily declined from on-lake sources since 2001, exceedances from off-lake sources have held relatively steady over time (Figures 3-6, 3-9, 3-12, 3-18, 3-22, and 3-24; Chapter 3). In the past 3 years, the number of exceedances at all monitors combined from off-lake sources has been greater than the number of exceedances attributed to on-lake sources (Figure 3-3). Chapter 3 identifies the many landforms within this area of the Owens Valley Planning Area (OVPA) that contribute to PM₁₀ exceedances, including flood deposits, dunes, and alluvial fans.

In this chapter, the panel examines potential PM₁₀ emission control strategies for sand dunes and associated sand sheets and flood deposits beyond the Owens Lake regulatory shoreline. The panel does not attempt to evaluate what controls are reasonable, given the costs and other impacts, as this is a policy decision that is dependent on more than just science. However, the panel recognizes that several of the BACMs approved for use on the lakebed that are discussed at length in NASEM (2020) may be inappropriate for off-lake conditions. For example, the shallow flooding BACM and its variations would not be feasible off-lake due to the greater depth to groundwater, permeability, and sloping topography. The following discussion focuses only on dust control measures suitable for off-lake sources.

It is important that the implementation of dust control measures also include monitoring to establish the reduction in PM₁₀ emissions, as well as changes in soil texture, organic content, nutrients, moisture, and vegetation density. Vegetation density may be monitored remotely by aerial photography and by satellite sensing in the near future. Monitoring of soil conditions will require periodic sampling and analyses. Monitoring of dust emissions may be accomplished by remote ground-based cameras, remote sensing using satellite-mounted spectrometers, or in-situ monitoring (see Chapter 3 for discussion of low- to medium-cost PM₁₀ monitors). This monitoring can be regularly analyzed to help assess the long-term effectiveness of different management approaches over space and time. It cannot be expected that dust management strategies will be effective in perpetuity, especially under a changing climate and in the face of extreme events (e.g., floods). If incorporated within an adaptive manage-

ment strategy, monitoring can be used to evaluate effectiveness and identify when changes may be needed in dust control management approaches.

POTENTIAL DUST CONTROL MEASURES ON SAND SHEETS AND DUNES

There are several sand sheets and dune fields in the OVPA that are associated with PM₁₀ exceedances, including Keeler and Olancha (Chapter 3). The only off-lake sand sheet or dune area with implemented DCMs is the Keeler Dunes Dust Control Project, which could serve as a potential model for future DCMs if they were deemed necessary.

Artificial Roughness

Artificial roughness elements placed on surfaces of sand sheets and active dunes increase aerodynamic roughness to reduce wind velocities at the surface and offer shelter that prevents sand cascading (Dong, Fryrear, and Gao 1999; Potter and Zobeck 1990). Roughness elements create downstream turbulence with eddy scales related to their size. Large roughness elements such as buildings can create eddies on the scale of several meters, while smaller roughness elements, such as surface clods and vegetation, tend to create much smaller eddies on the scales of millimeters to centimeters. The inter-molecular friction in a field of eddies dissipates the energy of the flow. Natural roughness elements that have been used to control dust at other sites include soil clods, straw checkerboard, standing and flat crop residues, baled crop residues, or woody residues of trees and shrubs (Dong, Fryrear, and Gao 1999; Qiu et al. 2004). Roughness elements constructed of engineered materials such as plastic and metal are termed engineered roughness elements. For the purposes of this report, artificial roughness as a dust control measure is divided into four types: solid natural, porous natural, solid engineered, and porous engineered.

Natural Roughness Elements

Solid natural roughness elements. The simplest natural solid roughness element is a straw bale. Straw is harvested and baled into rectangular or round bales as part of removal of crop residues from harvested land before seeding a subsequent crop. Straw bales are inexpensive ($3 to $6 per bale in the Midwest United States; Halopka 2022), typically have little feed value, and are high in lignin, adding to their longevity in the environment. Straw bales add roughness and reduce surface friction velocities of the wind. By simply placing rectangular straw bales on Keeler Dunes, the Great Basin Unified Air Pollution Control District (or District) reported an average reduction in sand flux of 85–94 percent (Box 6-1). However, the primary benefit of straw bales is that the bales reduce horizontal sand flux and create safe zones on the lee side of the bale that protect seedling shrubs from sandblasting. As the shrubs become established and grow larger, they augment the aerodynamic roughness provided by the bales, further reducing surface wind speeds, saltation, and dust emissions. Thus, the maximal benefit is provided by combining the straw bales with shrub planting, as described in Box 6-1 on the Keeler Dunes Dust Control Project. (Shrubs as a dust control measure are discussed later in this section.) Straw bales have also been used to control sand movement and dust emissions at the Oceano Dunes State Vehicular Recreation Area, where damage to dune vegetation from off-road vehicle use has resulted in destabilized dunes and enhanced dust emissions (Gillies and Lancaster 2013; Gillies, Furtak-Cole, and Etyemezian 2020). In this region, straw bales were shown to reduce shear stress within the roughness array and result in a decline of saltation downwind of the array by roughly 40 percent. Straw bales and other roughness elements including sand fences were only considered as temporary solutions for mitigating dust emissions at the Oceano Dunes and have since been replaced with permanent vegetation treatments (State of California Department of Parks and Recreation 2024).

Straw bales may enhance habitat by fostering the survival of seedlings. The straw offers little in the way of food for migratory wildlife, but the mechanical integrity of the bale does allow for burrowing animals to create hibernation and nesting sites in the unstable sand. This could provide ecological benefits as animal waste products and organisms carried on the feet of the wildlife would enrich the sand and enhance its ability to support plant growth. While the placement of straw bales offers no cultural value to the site, these projects may be somewhat beneficial to the local economy if the straw is grown on local land or installed by local community members.

Porous natural roughness elements. Porous natural roughness elements have not been tested in the OVPA but may offer sand drift and dust emission control. Porous natural elements include the woody skeletons of trees and shrubs laid on the surface and straw inserted into the sediment surface vertically in a checkerboard pattern (Figure 6-3). The woody skeletons may offer promise in off-lake areas with cultural and historical sensitivity since they do not require modification to the ground surface. However, some of the larger woody skeletons may require large equipment to transport them onto the site.

Natural porous surface roughness created with plant matter (e.g., straw) placed in checkerboard patterns (Figure 6-3) have been shown effective at controlling sand movement and dust emissions (Bo et al. 2015; Li et al. 2006; Wang, Qu, and Niu 2020; Zhang et al. 2004; Zhang et al. 2018; Zhao et al. 2008) and have been used for this purpose for over a half century in northwestern China (Qiu et al. 2004). The straw checkerboards are typically established in 1-m² grids with an optimal height of straw 20 cm above the ground (Bo et al. 2015; Qiu et al. 2004) These straw checkerboards reduce wind speed near the surface to steady-state velocities less than threshold—which is the wind speed value necessary to initiate soil erosion and dust emissions within about 66 ft (20 m) of the upwind edge (Xu et al. 2018). Narrow bands have been shown to be as effective as solid straw checkerboard arrays of much greater areal coverage (Bo et al. 2015). This design results in a reduction of horizontal sand flux by as much as 99.5 percent (Qiu et al. 2004). Straw checkerboards are adaptable to sloping and undulating land, making this a flexible method for complex landscapes (Dehkordi et al. 2023; Lihui et al. 2015).

Straw checkerboards also trap dust and encourage soil formation and the colonization of the stabilized sand by vegetation (Li et al. 2006). Soil components and plant macronutrients such as nitrogen, phosphorus, and potassium carried on dust have increased in straw-checkerboard-bounded soil (Dehkordi et al. 2022) and a 10-year study demonstrated increases in silt, clay, organic matter, water availability, nutrients, and pH (Wang and Wang 2019). Li et al. (2020) report that microbially induced carbonate precipitation from calcium ions carried on dust lessen the temporal limitations of straw checkerboards by accelerating sand fixation through crust formation, and this stabilization results in accelerated vegetation recovery. Narrow bands of vegetation watering might be highly beneficial immediately upwind of large areas with straw checkerboards to limit burial of the windward squares of the checkerboard and to provide an immediately adjacent source of plant litter and seeds for sand colonization and stabilization by native vegetation.

Straw checkerboards are historically built with manual labor in China, and a single laborer can create about 200 m² per day. Recently, machines have been developed that increase the efficiency of installation (Figure 6-3). In China, straw checkerboards are functional for up to 4 years, but the warm and dry season in California may

result in less microbial degradation and longer function, similar to what has been noted with the straw bales. If more time is needed to protect establishing vegetation, new or partial straw checkerboards could be implemented where needed.

The ecological value of the straw checkerboards is primarily related to potential soil quality improvements and enhanced plant colonization, which in turn improve habitat for local wildlife. Straw checkerboard barriers provide minimal cultural value but may provide machine operator jobs locally and opportunities for local farmers to sell wheat or barley straw.

Engineered Roughness Elements

Solid engineered roughness. Solid engineered roughness elements are built from materials such as metal, concrete, or plastic and placed in an array to reduce near-surface wind speed through added friction. For example, Gillies (2017; 2018b) investigated dust control effects of a staggered array of plastic boxes (2.4 ft x 1.5 ft x 1.2 ft [0.725 m x 0.45 m x 0.38 m]; Figure 6-4). Maximum sand control efficiency of 90 percent was achieved approximately 200 ft (60 m) from the upwind edge of the array. The authors maintained that the control efficiency and distance to achievement is a function of the density and distribution of the roughness elements (Gillies et al. 2017, 2018b).

Although solid engineered roughness elements could be arranged on a sand dune or sand sheet as needed to reduce PM₁₀ emissions, they do not blend well with the natural landscape, have no intrinsic value to wildlife, and depending on the material from which they are constructed, are susceptible to photodegradation and other forms of weathering. For instance, polyethylene would degrade in approximately 1 year and photodegradation of the plastic could lead to release of microplastics into the environment, while concrete might still be serviceable after 50 years.

Porous engineered roughness elements. Engineered roughness elements may be constructed to provide specific

amounts of porosity in order to optimize the sheltering and aerodynamic roughness effects. These include porous structures and sand fences constructed of porous polymer sheets.

Porous engineered roughness elements have been tested as a dust control method at Mono Lake, California. Gillies, Etyemezian, and Nickolich (2018a) found that the porous engineered roughness elements achieved maximum control efficiency at approximately half the distance from the upwind edge of the array when compared with solid roughness elements and resulted in less near-element scour. Like the solid engineered elements, porous engineered roughness elements offer low aesthetic and wildlife value and have similar longevity.

Another type of porous engineered roughness element used at Owens Lake that could be considered for the off-lake area is sand control fencing made of various composite and woven materials (Figure 6-5). Sand control fences work by offering a physical barrier to stop saltating sand cascades and by reducing the wind velocity at the surface in front of and behind the fence. The relative effectiveness of such fences at reducing wind velocity is a function of the material and density. For instance, barriers of vertically placed parallel plastic pipe with an optical density of 12.5 percent (2.8 cm diameter pipes placed 18.7 cm apart) only reduced wind velocities by an average of 4.3 percent in the 33 ft (10 m) upwind and 99 ft (30 m) downwind region. In contrast, a barrier of vertically placed parallel plastic pipe with 75 percent optical density (1.1 in [2.8 cm] diameter pipes placed 0.3 in [0.9 cm] apart) reduced wind velocity by an average of 32.5 percent (Bilbro and Stout 1999). Maximum wind velocity reduction is found near the barrier, and the barrier effect diminishes with distance from the barrier. The height of the barrier also influences the effectiveness of sand control. Computational fluid dynamics programs have been used to design sand control fence networks (Xin et al. 2021).

Sand control fences are most effective when they contact the ground surface, but sediment may need to be removed periodically. In the case of more porous sand control fences, sand removal may be necessary on both sides of the fence as eddies in the lee of the elements result in sand deposition. Sand fences provide no habitat value, and land-based wildlife may need occasional gaps in the fence to provide for migration. The process of

installing sand fences could damage cultural resources in the area. Sand control fences may favor vegetation by trapping finer particles, plant litter, and seeds in wind transport (Zhang et al. 2007).

Shrubs as Perennial Vegetative Cover

For dune and sand sheet settings, vegetative cover is widely considered the primary surface protection from the erosive force of winds. Shrub communities are commonly found in off-lake areas surrounding Owens Lake (Chapter 2). Vegetation reduces aeolian transport—and therefore PM₁₀ emission—by mechanisms that are similar to those described previously with regard to porous roughness elements. Shrub communities reduce PM₁₀ emissions by reducing the wind velocities near the surface, capturing airborne sediments within their canopies, and further stabilizing the surface with their root mass and shed biomass. Shrubs and larger grasses (as opposed to flat or very low vegetation) also have a wake area with reduced surface shear stress in their lee, which protects large areas from emission, more efficiently dissipates momentum from the wind, and captures more (and higher) airborne material (Raupach et al. 2001). Although not as effective as crop residues or native grass cover, shrubs affect the wind fields and, in desert environments, may offer the only natural, self-sustaining protection of the soil surface from wind. Shrubs also serve as rigid structures into which moving sediment may become trapped.

A shrub-based dust control measure, with shrub densities of 2 per ft² (approximately 0.2 per m²),¹ or roughly 10 percent cover, are expected to have >85 percent control efficiency within 82 ft (25 m) of the edge of the shrub area (Li et al. 2013; Mayaud, Bailey, and Wiggs 2017). It has not been tested whether >95 or 99 percent control efficiency can be attained, although preliminary simulations by the panel assuming porous vegetation estimate that >20 percent shrub cover may be required (see Box 6-2). Due to edge effects, relatively large areas (>10 hectares) are necessary to ensure that a majority of the area is within target control efficiencies.

Shrub-based dust control has the potential to provide habitat for native and migratory species. Of the habitats found at Owens Lake, shrublands support the most diverse species of lizards, snakes, birds, and mammals (LADWP, 2010). Shrubs may be more accepted as a way to reduce aeolian transport in culturally sensitive areas, though the impact of infrastructure for delivering water is a potential issue. Shrubs also have positive aesthetic value.

Two approaches for increasing vegetation density in sand dunes and sand sheets include shrub planting and using connectivity modifiers to support vegetation growth between existing shrubs.

Planting Shrubs

In dunes that have been affected by human activity, shrub planting efforts can provide a natural and sustainable approach to reduce PM₁₀ emissions. Initially, shrubs planted at the correct density will not be able to provide this control efficiency until they grow larger because nursery shrubs require 5 to 10 years to grow into mature plantings, depending on the species. Fertilization may help increase the rate of growth, but the resulting fast growth may also reduce the amount of lignin in plant cells, which could impact the ability of the shrubs to survive sandblast injury. Most natives are adapted to low nutrient availability, and thus if fertilizer is used, it may only be needed sparingly. Additional temporary dust control will likely also be needed to provide near-term PM₁₀ reduction. Densities that are too low have the potential to become unsustainable, as pedestaling and abrasion of shrubs by moving sand can cause dieback and mortality (Okin, Gillette, and Herrick 2006). Additional analysis would be necessary to determine the shrub density and species composition necessary to achieve the desired levels of PM₁₀ control in off-lake dunes and sand sheets that are still contributing to exceedances (Box 6-2).

The planting of shrubs and their subsequent reproduction and colonization in the Keeler Dunes Dust Control Project (Box 6-1) is a great success story. The introduction of straw bales as temporary natural solid roughness elements in the active sand sheets and foredunes of the Keeler dune field allowed for protection of shrub seed-

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¹ This density is assumed to estimate control efficiency from the Keeler Dune data, based on the fact that two shrubs are roughly equivalent to one hay bale. Shrubs are roughly the same height as the approximately 15-in (38-cm) high bales but approximately one-half the width of the 44-in [112-cm] wide bales. Thus, shrubs have a profile area of approximately one-half of the bales used on Keeler Dunes. See equation two in Gillies et al. (2015).

lings from sandblast injury. A limited water distribution system combined with hand watering provided irrigation (approximately 0.1 ft/yr) for the seedlings until their root systems were sufficiently established to maintain growth. After shrubs have been established and have grown to target sizes, watering is expected to be tapered to zero, because the shrubs will be able to survive on local rainfall. In the last few growing seasons, the planted shrubs have been reproducing, and their offspring are colonizing the open spaces where control was previously lacking (Grace Holder, GBUAPCD, personal communication, May 2024).

Connectivity Modifiers

Desertification has been attributed to changes in ecosystem connectivity (Okin et al. 2009). In the last couple decades, shrubland plant communities have been replacing grasslands in semiarid and arid landscapes. Although the reasons are not entirely clear, changes in precipitation patterns due to climate change favor deep rooted shrubs over more shallow rooted grasses (Li et al. 2022). By increasing the distance between growing plants, more bare soil is available to be eroded by wind, and the topsoil is less likely to be deposited in shrub-based fertility islands, making plant establishment in the nutrient-deficient soil between the shrubs less likely. In addition to the loss of nutrients in the eroded topsoil, organic carbon is also lost and preferentially deposited in the shrub canopies and the soil directly below, making water less available between rain events in the bare interspaces. Thus, in the absence of factors that would reverse the state changes in connectivity, there is little chance of reversal (Bestelmeyer et al. 2015).

In an effort of modify the scale of connectivity in degrading drylands and sand sheets, researchers have used porous engineered structures as connectivity modifiers or ConMods (Okin et al. 2015; Rachal et al. 2015). ConMods are constructed of two pieces of 0.2 in (6 mm) mesh galvanized hardware cloth—both 0.8 ft (20 cm) tall by 2.2 ft (55 cm) long—that are attached to steel rods at each end and arranged crossing perpendicularly in the center of each piece to form a cross with a fifth pin anchoring the intersection (Figure 6-7; Rachal et al. 2015). ConMods are installed flush with the soil surface and may be placed on the landscape at user-selected spacings to trap seeds and litter that would otherwise only be trapped by a downwind shrub canopy. ConMods have been proven effective at trapping litter and seeds and helping vegetation establish in the formerly bare inter-shrub soil surfaces (Okin et al. 2015; Peters et al. 2020), effectively promoting degradation state reversal and increasing connectivity in plant cover, protecting the soil from the erosive forces of wind. Although engineered and offering no direct benefit to wildlife, they are small and not highly noticeable on the landscape from a distance. More work needs to be done with ConMods in order to determine the optimal density of their installation. They are immediately effective, but the effectiveness increases as litter is trapped and vegetation starts to grow. They may be removed at some future time, but care is needed not to damage the plants that have established. It may also be possible to build ConMods with biodegradable materials such as burlap and wooden dowels.

Limitations on Recreational Activity

Research at the Oceano Dunes State Vehicular Recreation Area and the Imperial Sand Dunes Recreation Area shows clear associations between off-highway vehicle (OHV) activity, decreasing vegetation cover, and increased dust emissions (Cheung et al. 2021; Groom et al. 2007; Walker et al. 2023). Following implementation of over 400 acres of dust control treatments at Oceano Dunes, including restored vegetation cover, there have been appreciable declines in PM₁₀ emissions measured at receptor sites downwind of the mitigation treatments (State of California Department of Parks and Recreation 2024). In the Owens Valley, the Bureau of Land Management (BLM) manages an OHV recreation and primitive camping area of approximately 400 acres (1.6 km²) or 36 percent of the total area of the Olancha Dunes, which has been operational for decades. Limiting recreational activity in areas that are highly susceptible to PM₁₀ emission is one potential dust control measure at the Olancha Dunes.

POTENTIAL DUST CONTROL ON FLOOD DEPOSITS

As described in Chapter 2, episodic floodwaters following rain events carry fine-grained sediments that deposit in the off-lake areas. As these flood deposits dry, the clay particles at the surface are highly vulnerable to erosion from the wind, and even armored clay surfaces can be abraded when bombarded with sand. Although flood deposits are recurring events that regenerate emissive sediment surfaces, dust control measures are available that could be used to reduce PM₁₀ emissions, if deemed reasonable, as described below.

Cover by Gravel or Cobbles

Gravel coverage has been proven effective at controlling dust emissions on the lakebed where gravel (>0.4-in [1.25 cm] diameter) is laid in a 4-in (10 cm) layer over bare ground (GBUAPCD 2013) or in a 2-in (5 cm) layer over a geotextile (GBUAPCD 2013). The gravel not only shields the erodible soil surface from wind but

also functions to limit surface evaporation. Gravel coverage can be used on off-lake flood deposits with complex topographies. NASEM (2020) also recommended consideration of cobbles, which are larger than gravel and have a greater capacity for capture and storage of windborne material compared to the more-uniform gravel. The advantage of gravel and cobble coverage is that these dust control measures require no water and have a control efficiency of >99 percent if not buried by encroaching sand movement. While gravel and cobbles are probably not practical for the sand sheet or dune areas due to the ease with which saltating sand can bury them and render them useless to control sand movement, they could serve to bury the fine clays of flood deposits and prevent future PM₁₀ emissions.

The use of these sterile geological materials is often regarded as unsightly and offers little or no value to wildlife habitats other than potential protection of small rodents and insects. The machinery used to transport and spread the gravel could damage both natural and cultural resources in the area. Additionally, gravel and cobbles would likely only serve to reduce PM₁₀ emissions until the next flood event.

Vegetation Establishment

Fine-grained flood sediments are typically associated with higher nutrient levels and water holding capacities than the surrounding coarse-grained deposits on sand sheets and alluvial fans. Thus, flood deposits might be suitable for vegetation establishment as a means to reduce dust emissions. This plan may require manipulation of the flood deposits by covering them with unlined layers of gravel or cobbles to allow for rapid infiltration of rainfall while limiting surface evaporation, creating an augmented environment for shrub establishment. Due to the depth of gravel in the gravel blankets, shrubs would need to be nursery-grown and transplanted to allow canopy to emerge above the gravel blanket while having roots in the finer sediments. While this vegetation would provide more resilient stabilization than just gravel and cobbles, the shrubs would need to be resistant to temporal flooding episodes. There may be native vegetation along streams and near shorelines of terminal lakes in this region that have such adaptations. For example, Sacrobatus has been shown to be tolerant of flooding conditions for up to 40 days (Ganskopp 1986), but vegetation is also susceptible to death through scour and uprooting during extreme storms. Longevity of this dust control measure would depend on the interval between floods, and barring changes to infrastructure or local topography, measures would potentially need to be renewed following a major flood event. Improved resilience of shrubs in flood deposit areas could be promoted through modifications of existing infrastructure that concentrates stormwater flows.

Modified Highway-Associated Floodwater Infrastructure

As noted in Chapters 3 and 4, one off-lake source of PM₁₀ emissions to Dirty Socks appears to be a pooled flood deposit next to Highway 190 (Figure 4-19). Future extended flooding in this area following large precipitation events could be minimized by the construction of distributed culverts where the floodwaters are currently retained by the highway.

The California Department of Transportation (Caltrans) also built several chevron-shaped berms to protect Highways 136 and 190 by diverting the braided flow into channels for passage through culverts. The panel was unable to determine to what extent these berms affected PM₁₀ emissions and exceedances compared to what would have occurred from flood deposits in the absence of this infrastructure (see Chapter 4). For instance, the 2022 image in Figure 4-18 shows the water flows during the high-energy storm event associated with the remnants of Hurricane Kay in 2022, when water flowed and pooled against the roadway, ultimately overtopping the road and damaging the roadbed. Instead of using berms to concentrate the flow to pass under the highway in a few culverts, removing the berms and creating many smaller culverts would facilitate passage of floodwater over a wider area, facilitating patterns of flow and infiltration in the off-lake area more similar to what it would have been had Highway 190 not been built. Additional culverts would also decrease the likelihood that water pools or flows behind (upstream of) the road creating potentially emissive flood deposits. The cost of reconstructing the highways with additional culverts and benefits of such modifications are uncertain. Once completed, however, there would probably be minimal annual maintenance costs.

Upslope Runoff Management

An alternative to modifications of highway features that concentrate flood flows would be upslope runoff management to encourage water spreading. Berms placed perpendicular to the flow tend to spread the flow laterally along the slope, enlarging the surface area available for infiltration and removing energy from the flood flows. Such berms have been used to heal eroded land, prevent gully formation, and enhance water harvesting for vegetation. Water harvesting is a relatively mature science used in arid regions globally (Boers and Ben-Asher 1982; FAO 1991). Water harvesting techniques often involve creating surface contours for diverting water to trees and shrubs, surface dimpling to enhance local storage and infiltration, and constructing permeable dams and other stormwater spreading features (Figure 6-8) to control water flow, offering flexibility in either spreading or concentrating the surface water flow as necessary (Mekdaschi and Liniger 2013). Increased infiltration on the fan itself would, with the exception of the most intense events, possibly prevent damage to on-lake dust control measures. In the Salton Sea Management Project, stormwater is spread laterally across the landscape to enhance infiltration and support vegetative growth for dust control and to leach salts from the surface soil. These approaches include using rock

weirs on swales and berms and constructing ditches along contours and perpendicular to creeks (California Natural Resources Agency 2024).

Historically, tribes engaged in extensive spreading of water across the valley floor north of the Owens Lake using irrigation ditches to promote the growth of food crops and other plants important for cultural reasons, including meadow and riparian species (Lawton et al. 1976). This did not occur in the immediate proximity around Owens Lake, despite the presence of creeks that could support these practices, presumably because the lake already provided abundant food (Lawton et al. 1976), but this practice could be a promising approach to promote vegetation cover to control dust while providing important habitat. A notable concern with this approach is the initial disturbance of the land surface, typically accomplished by large machinery, which could impact cultural resources.

OTHER POTENTIAL DUST CONTROL MEASURES

A number of novel techniques have been employed in China to control sand movement and dust emissions. These include producing seedlings of drought-adapted native trees and shrubs and planting them in small basins imprinted to deliver rainfall to the base of the seedling, as well as spreading plastic mulch over irrigated farm fields (Lyu et al. 2020).

In other areas of Asia plagued with sand and dust storms, the biopolymer Acacia gum has been used in the laboratory to stabilize loose sand (Dagliya and Satyam 2024) and the authors also report on similar studies utilizing other natural plant products to bond sand grains together. Other non-plant-based sprays and surface applications have been investigated including emulsions of asphalt, polyvinyl alcohol, styrene-butadiene, latex, and water-miscible resins applied in water dilutions at the rate of 3,785 liters per hectare (Armbrust 1977). The author also reports that feedlot manure applied at the rate of 31.8 tons per hectare to the surface, or 52.3 tons per hectare plowed into the substrate will also effectively control wind erosion. Tatarko, Trujillo, and Schipansk (2019) found that such treatments are often costly and temporary due to degradation from irrigation, sunlight, rainfall, tillage, or abrasion from adjacent untreated areas. In addition, many of these treatments are phytotoxic and not compatible with all soil types (Presley and Tatarko 2009). The Salton Sea Management Project evaluated multiple soil stabilizers and concluded that most would be temporary because they are soluble in water, but that soil binders may be useful in limited locations. For example, binders can create a hardened surface that can withstand heavy vehicle traffic and can be chemically stable in desert conditions with various sized particles (Environmental Science Associates 2022). Although soil stabilizers on their own may not be promising, they can be an extremely useful tool for temporary stabilization of soils for biocrust restoration (Faist 2020a).

Biocrusts have been observed in the “barren” areas of Owens Lake Playa (LADWP and Ecosystem Sciences 2010). Biocrusts are a consortium of organisms (e.g., cyanobacteria, green algae, bacteria, microfungi, lichens, mosses) that live at or near the soil surface and stabilize soil directly through their above-surface cover (e.g., mosses and lichens), their filaments and hyphae, and their secretions that aggregate soil particles (Belnap 2006; Rodriguez-Caballero et al. 2022). Many types of biocrust are relatively resistant to water and wind erosion but can be very vulnerable to burial or compression (e.g., footsteps, vehicles; Faist et al. 2020a). In the Mojave Desert, which is adjacent to Owens Valley, biocrust cover is greatest on 20–7,000-year-old surfaces and negligible on very young surfaces (e.g., active washes and recent sediment deposits). But even moderately active sand sheets can host cyanobacterial crusts, suggesting they are tolerant of some levels of burial and sand deposition (Bowker et al. 2016).

Although biocrust restoration has previously been viewed as futile as a dust control measure at the Owens Lake bed because it can be vulnerable to burial and was assumed to have a very slow natural recovery rate (NASEM 2020), recent work has demonstrated that biocrust recovery is possible in years to decades, in some instances. Environmental improvements such as soil stabilization, decreased ultraviolet (UV) radiation, and micro-irrigation can assist with biocrust recovery (Antoninka et al. 2020b; Fick et al. 2020; Zhou et al. 2020). In areas with unstable soil, soil stabilizers can be effective in short-term surface stabilization, facilitating the establishment of biocrusts, which can provide long-term surface stabilization in many drylands (Antoninka et al. 2020b; Faist 2020a). In biocrust restoration, preferred soil stabilizing agents are bio- or UV-degradable. Polyacrylamides and plant-based

stabilizers (e.g., psyllium, jute [a woven cloth from plant-based materials]) have been shown to be effective (Faist 2020a; Fick et al. 2020). However, it may be important to repeat stabilization treatments for multiple years until biocrust is established (Faist et al. 2020b). In addition, straw checkerboards (discussed above), can be one of the most effective site preparations for biocrust recovery on unstable soils (Faist et al. 2020b; Zhou et al. 2020). Care is required when implementing soil stabilization practices because soil stabilizers and straw checkerboards can decrease biofilm establishment when soil is already stable (Antoninka et al. 2020a). Other effective methods of decreasing sand movement onto developing biocrusts include tree shelterbelts, shrubs, and sand fences (Zhou et al. 2020). Detailed manuals exist to guide biofilm restoration (Faist 2020a), and cyanobacterial crust restoration has been seen to be successful at the scale of hundreds of hectares (Zhou et al. 2020). Research is currently being conducted in the Salton Sea to determine the potential for biocrusts to stabilize emissive surfaces (Salton Sea Management Program 2024).

APPLICATION OF TRIBAL KNOWLEDGE FOR DUST CONTROL

If dust control measures are determined to be necessary and feasible on off-lake sources, Tribal input into the evaluation of potential control mechanisms, starting at the very initial stages of project conceptualization and design, could support collaborative planning, successful implementation, and community engagement. For example, in similar projects, collaboration with indigenous communities improved community investment in restoration efforts and outcomes (Gann et al. 2019). If parties liable for managing off-lake dust control measures engage with Tribal communities even before any federally mandated environmental review, they will learn from Tribal knowledge and build trust amongst the Tribal Nations in the OVPA.

As described previously, tribes historically engaged in extensive spreading of water across the valley floor north of the Owens Lake using irrigation ditches (Cheyenne Stone, Big Pine Paiute Tribe of the Owens Valley, personal communication, November 2024; Lawton et al. 1976). This practice could be a promising approach to promote vegetation cover and reduce dust emission. Additional Tribal input to the panel for mitigating PM₁₀ emissions included mapping and clearing Russian thistle from ditches and roadways, as they can create dust once they become tumbleweeds. Limiting new excavations and new roadways east of Owens River and as well as limiting vehicle recreation on dry backwater lakes was also proposed as dust control methods (Mel Joseph, Lone Pine Paiute Shoshone Tribe, personal communication, August 2024).

CONCLUSIONS

If dust control measures are determined to be necessary and feasible for off-lake sources, implementation will require a systems-level landscape approach that considers cultural resources. Collaboration with local Tribal Nations will improve community investment in restoration efforts and outcomes.

Many areas around the OVPA are extremely dynamic settings, requiring different approaches over space, and possible re-treatment over time (e.g., in flood deposits). Nevertheless, the panel found that the establishment and maintenance of vegetation offers the best chance for natural, self-sustaining protection of the soil surface from wind. Additional methods that will support the eventual establishment of vegetation are expanded upon below.

A number of sand sheets and dune fields (e.g., Keeler and Olancha) are distributed along the eastern and southern side of the shoreline. Efforts to partially stabilize Keeler Dunes using solid natural roughness elements

of straw bales has resulted in the successful establishment of native shrub seedlings, which are providing seed for additional colonization of the sand. Porous naturally sourced roughness elements of straw checkerboards have also been used with great success in China to protect highways, rail lines, and villages from encroaching sand. These barriers are inexpensive to build and, although relatively short-lived, may be repaired or renewed as necessary until vegetation has successfully colonized the area.

Fine-grained flood deposits are scattered in topographic lows along the shoreline and within the sand sheets and dunes. These fine-grained deposits are extremely emissive and efforts to control these dust sources could reduce exceedances. Where current deposits of fine-grained material are small in size, they could be covered with unlined layers of gravel or cobbles. This system would allow for rapid infiltration of water into the flood deposits that hold water very effectively. Thus, plants could find a hospitable root zone that would provide water and nutrients for growth and reproduction, further stabilizing the surface. Longevity of this dust control measure would depend on the interval between floods and would potentially need to be renewed following a major flood event barring changes to infrastructure or local topography.

Flood deposits around Owens Lake have been affected by both the construction of the highway and a number of upgradient berms. Drainage improvements along the highway with the addition of culverts or the elevation of roadways would reduce future accumulation of material behind highways leading to PM₁₀ emissions. Highway berms concentrate flow toward a limited number of culverts under the highway, which may contribute to large deposits of fine-grained material after major precipitation events (e.g., the remnants of Hurricane Kay in 2022). Modification of the berm structures, highway culverts, and water harvesting and spreading are large, intensive dust management options, but they have the potential to reduce floodwater velocity, reduce the concentration of fine-grained sediment, and enhance water storage for vegetation establishment. Water harvesting from surface runoff and water spreading from drainage features could be used to encourage shrub growth in the future when climate change may make rainfall less predictable. Increased infiltration along the upper positions of the slope might also augment groundwater elevations such that the capillary fringe might be contacted by established shrub roots. Such a system may also limit erosion of gullies and ravines by reducing the velocity of floodwater.

Off-highway vehicle recreation is known to be associated with landscape changes that lead to PM₁₀ exceedances. In the Owens Valley, the Bureau of Land Management manages an off-highway vehicle recreation

and primitive camping area of approximately 400 acres (1.6 km²) or 36 percent of the total area of the Olancha Dunes. Additionally, there have been reports of vehicle recreation on dry backwater lakes causing dust emissions.