Ecoregion of the Nearactic Biome Number 1308 on map.
Extent of Mojave Desert: 33 to 38 degrees North; 113 to 119 degrees West
Country (State): United States (Arizona, California, Nevada, Utah).
I. Overview
Located adjacent to the crowded southern California Mediterranean ecosystems, the Mojave Desert is filled with military bases and is the site for new construction of renewable energy installations. It is also filled with recreation lands, including national parks and wilderness areas. It is not a barren desert, but is covered with typical vegetation of creosote bush, desert sage, and Joshua tree. Native wildflowers provide displays in the spring. Prior to the current renewable energy boom, the desert was home to mining operations in many areas. After these areas were abandoned in the early 20th century, the area was left alone and not grazed, providing a natural experiment in ecosystem recovery. As expected, soils that are severely disturbed and older soils take a long time to recover, and disturbances in these areas are essentially permanent, especially if the soil is compacted such as through use as a road. Younger soils such as those created from debris flows recover relatively fast and the vegetation returns within 80 to 100 years (Brown 2000a).
Soils in the Mojave Desert have been found to absorb carbon dioxide at night. The magnitude is as much as a temperate forest. If other deserts also exhibit this phenomenon, the effect could be huge, since 35 percent of the Earth’s land surface is desert or semiarid. However, these findings have not explained where the carbon is going. Some possibilities are to biotic crusts and expanded shrub cover. In addition, it is possible that it is an ephemeral effect, and the carbon could be released during the day, for example (Stone 2008). All of this indicates the many uncertainties in the understanding of the carbon cycle.
One native plant of the Mojave, Nicotiana attenuata, produces a floral nectar high in nicotine. It is pollinated by hawkmoths and hummingbirds. The combination of nicotine and floral scent does not make the plants more attractive to the pollinators, and in fact reduces the time a pollinator spends at each plant. However, this promotes the plant’s interest because pollinators visit more plants and thus pollinate more. In addition, nicotine deters caterpillars and carpenter bees, which would otherwise reduce reproductive success. Thus, the best strategy is to attract a pollinator but then prevent them from loitering (Raguso 2008).
Another plant in the Mojave, Linanthus parryae, tends to flower in blue and white patches across the landscape. For example, one side of a desert wash might be all blue while the other side might be all white. This is currently attributed to natural selection due to local environmental differences; however, in the past, it was attributed to genetic drift, where blue flower seeds happened to land in one place and spread (Pennisi 2007).
Characteristic of the Mojave are dry lakes in the valleys. In wetter years, these areas are briny, supporting microbes that can live in exceptionally high salinity. Most microbes live by reducing sulfur or carbon. However, at Searles Lake and the Trona Pinnacles National Natural Landmark in the northwestern Mojave, the brine is rich in the toxic element arsenic. Microbes have been found to use this element for biological processes in the briny sediments. Under aerobic conditions, arsenic III is oxidized. Under anaerobic conditions in deeper sediments, arsenic V is reduced. This takes the place of sulfate or carbonate reduction in other environments (Oremland et al. 2005).
At the Coso Mountains Wilderness, the Mojave Desert includes a group of volcanoes that last erupted more than 10,000 years ago but overlie large magma chambers. These volcanoes are considered potentially dangerous, but not as immediate a threat as the cascade volcanoes further north (Kerr 1983). Outside of volcanic areas, the desert has been relatively stable and sites such as Devils Hole,Nevada, have precipitated calcium carbonate for the last 500,000 years. There are no apparent depositional hiatuses. This can provide a unique climate record spanning several glacial cycles during the Pleistocene. Evidence from Devils Hole indicates that there are relatively rapid shifts from full-glacial to interglacial climates followed by a gradual return to full glacial conditions. Interglacial climates lasted about 20,000 years (Winograd et al. 1992).
In 1990, the desert tortoise was listed as a threatened species under the Endangered Species Act, causing virtually every project in theMojave Desertto consult with the US Fish and Wildlife Service prior to construction. From the beginning, there were disputes over population counts of the tortoises, which hibernate underground during droughts (Brown 2000b). In the Ivanpah Valley, California, in the Mojave Desert, an ideal site for generating solar power also turned out to be an ideal site for desert tortoises, which are an endangered species. Tortoises occur primarily on flats and alluvial fans adjacent to the mountains with soils ranging from sand to sandy-gravel, characterized by scattered shrubs and abundant interspace for growth of herbaceous plants. They occur in creosote bush, alkali sink, and tree yucca (Joshua tree) areas, places that are also ideal for new renewable power plant sites. Desert washes and other areas with deep soil provide sites for the tortoises to burrow and escape the desert heat. The 3,572-acre Ivanpah site, located on federal land to the east of Mojave National Preserve and to the south of Stateline Wilderness Area, was the subject of a Final Environmental Impact Statement (EIS) issued in August 2010. During the EIS process, the expected power output of the project was reduced ten percent due to a redesign that reduced the project footprint by 12 percent and the number of 460-foot power towers from seven to three. A Biological Opinion was issued by the US Fish and Wildlife Service onOctober 1, 2010, and the Bureau of Land Management (BLM) issued its Record of Decision onOctober 7, 2010. A 30-year right-of-way grant was issued to BrightSource Energy.
Consistent with the Biological Opinion, BrightSource proceeded to fence the construction area and remove tortoises for relocation to a nearby site on BLM property. The tortoises were placed in an on-site quarantine area for disease testing. However, construction monitoring of perimeter fence installation around Units 2 and 3 in the winter and spring of 2011 indicated that these portions of the project might contain more desert tortoises than anticipated in the 2010 biological opinion. The BLM requested revised consultation. The revised biological opinion, dated June 10, 2011, reiterated the need to fence the construction area, collect tortoises, and relocate elsewhere. It also required the rearing of young turtles and turtles from eggs until they were a size of 120 mm in length and five years of post-release monitoring. The company was also required to fence I-15 in the translocation area to a standard that would exclude turtles. As compensation for the 3,572 acres of public land lost to the solar facility, the California Energy Commission required BrightSource to acquire and restore good quality desert tortoise habitat at a ratio of 2:1, and to take actions on that newly acquired property to improve habitat quality, which could include restoration of closed roads, tortoise exclusion fencing along I-15 and US 95 and around the towns of Nipton, California, and Primm, Nevada, and elimination of invasive plant species. An interest-bearing account was also established to bankroll a management fund for the new properties.
The project was anticipated to increase the number of common ravens, a potential tortoise predator, at the project site. Brightsource was also therefore required to contribute to a management fund to reduce the numbers of common ravens in the area.
Another Mojave Desert solar project with tortoises present is the K Road Power project, a 350-MW photovoltaic generating station proposed for the Moapa Band of Paiute Indian Reservation on I-15 in Nevada. This is the subject of an EIS completed onMarch 16, 2012. The K Road project would be located on 2,153 acres of reservation land. During an October 2010 desert tortoise survey, up to 103 turtles were estimated to occur on the area to be disturbed. Similar to the Ivanpah project, the March 7, 2012, Biological Opinion requires the tortoises to be relocated and all construction activity to be monitored by desert tortoise biologists. The project includes a 6,000-acre desert tortoise relocation area to the north of the I-15 and an additional 5,000 acres south of I-15 for desert tortoise relocation if needed. The EIS looked at the impacts of an alternative site on the same reservation, but this site was estimated to have the same or greater effects on the desert tortoise
But these projects are not all that is underway in the desert tortoise habitat. To date, 13 solar projects have been approved inCaliforniaandNevada, and more are under development. Another one on I-10 in California, the Palen project, is awaiting a decision by BLM. Under development on the reservation to the south of K Road Project is a concentrating solar project, Moapa Solar. Also to the south of K Road, another concentrating solar plant is under development on BLM land by BrightSource as the Apex North East Las Vegas project. Power line projects and pipeline projects will also likely have cumulative effects on the tortoise habitat.
Another long-running environmental battle in the Mojave Desert was over the siting of a low level radioactive waste facility. It was proposed to be located at Ward Valley, on I-40 west of Needles, in 1988. However, due to opposition by environmental and tribal groups, the state signed legislation in 2002 preventing the use of the Ward Valley for a nuclear waste facility.
FurtherReading
Brown, Kathryn. 2000a. Ghost Towns Tell Tales of Ecological Boom and Bust. Science 290:35-37.
Brown, Kathryn. 2000b. Ecologists Spar Over Population Counts of Threatened Desert Tortoise. Science 290:36.
Ivanpah Solar Electric: http://www.blm.gov/ca/st/en/prog/energy/fasttrack/ivanpahsolar/fedstatus.html
K Road Power: http://projects2.pirnie.com/MoapaSolar/index.cfm?fuseaction=FEIS
Kerr, Richard A. 1983. Volcanoes to Keep an Eye on. Science 221:634-635.
Mohlenbrock, Robert H. 1984. The Field Guide to U.S.National Forests. Congdon and Weed, Inc.
O’Gara, Geoffrey. 2000. Guide to America’s Outdoors: Far West. National Geographic Society,Washington,DC.
Oremland, Ronald S., Thomas R. Kulp, Jodi Switzer Blum, Shelley E. Hoeft, Shaun Baesman, Laurence G. Miller, and John F. Stolz. 2005. A Microbial Arsenic Cycle in a Salt-Saturated, Extreme Environment. Science 308:1305-1308.
Palen Solar Power: http://www.blm.gov/ca/st/en/prog/energy/fasttrack/palen/fedstatus.html
Pennisi, Elizabeth. 2007. Natural Selection, Not Chance, Paints the Desert Landscape. Science 318:376.
Raguso, Robert A. 2008. The “Invisible Hand” of Floral Chemistry. Science 321:1163-1164.
Stone, Richard. 2008. Have Researchers Discovered a Hidden Loop in the Carbon Cycle? Science 320:1409-1410.
UNESCO-Man and the Biosphere Reserves Directory. http://www.unesco.org/mabdb/br/brdir/directory/database.asp (accessed5/30/11).
White, Mel. 2000. Guide to America’s Outdoors: Southwest. National Geographic Society.
Winograd, Isaac J., Tyler B. Coplen, Jurate M. Landwehr, Alan C. Riggs, Kenneth R. Ludwig, Barney J. Szabo, Peter T. Kolesar, and Kinga M. Revesz. 1992. Continuous 500,000-Year Climate Record from Vein Calcite in Devils Hole, Nevada. Science 258:255-260.
World Heritage List. http://whc.unesco.org/en/list
