Ecological Impacts

The total amount of water used by solar facilities across the landscape, how efficiently that water is used, and the source of the water have consequences for the hydrology of the California desert. Terrestrial, riparian, and aquatic habitats are likely to be affected.

Hydrology: Impacts to Terrestrial Habitats
The long-term sustainability of groundwater-dependent ecosystems in arid regions is sensitive to human activities that alter subterranean water systems.¹ Groundwater withdrawals for solar development that lower an already shallow water table may lead to reduction or even elimination of spring discharge. Some plant species in arid regions are more dependent on groundwater resources than precipitation because groundwater is less subject to annual variability than precipitation.² If pumping water for solar development reduces groundwater to a level below the root zones, these groundwater-dependent plants could be adversely affected.³ The result may include reduced plant species richness, reduction of plant cover, or shift in vegetation type.⁴ Additionally, water obtained for solar development could alter the ratio of surface water and groundwater availability, which could induce changes to vegetation community composition.⁵ Alteration in plant communities can, in turn, affect animal species through habitat loss or decreased habitat connectivity. Similar impacts to desert species may occur if solar development requires surface water diversions that decrease water supply to riverine systems and riparian corridors.⁶ In addition to habitat loss, decreased vegetation resulting from water extraction or diversion may result in increased erosion and sediment production since plant assemblages protect against wind and water scraping.⁷ Reduced soil moisture that may result from vegetation removal has the potential to cause localized and long-term increases in dust emission.

Habitat Connectivity: Impacts to Riparian Corridors
Riparian habitats, which are assemblages of plant communities characterized by their associations with surface or subsurface water, often function as migration corridors.⁸ Both the water and the plants associated with these corridors provide important resources for the species that rely on these riparian habitats. These habitats can be patchy, but they provide connectivity for species as they move across the landscape. If gaps between patches become too wide along the corridor, they may no longer be useful for migration. Solar development that limits water supply to these corridors, through either channel diversion or withdrawal, may impact the health of these habitats. Riparian habitats that suffer a loss of water may not be able to support as many plant communities, or water availability for animals may be depleted.

Hydrology: Impacts to Aquatic Habitats
Aquatic habitats, while relatively limited in arid regions, are susceptible to impacts from solar development if groundwater and surface water sources are affected. Desert springs are just one example of a rare aquatic habitat.⁹ Though they may occur as a single spring or a cluster of springs, distances between spring habitats are often too far to allow migration between them.¹⁰ If the vitality of a spring is compromised by groundwater extraction for solar development, species dependent on the spring may suffer loss of habitat that cannot be mitigated.¹¹

However, impacts to water supply as the result of groundwater extraction (for solar development or otherwise) can be difficult to predict both spatially and temporally; aquifers in the California desert are structurally complex, impacts may occur at great distances from extraction sites, and there may be a lag time between extraction and identifiable impacts.¹² This complexity also makes cumulative effects difficult to predict.

While impacts to groundwater- and surface water-dependent species and habitats from solar development may be difficult to predict or monitor, water extraction that exceeds groundwater recharge or replenishment from precipitation has potential long-term consequences. Additionally, impacts may be difficult to assign to specific projects, as they often occur at great distances from the extraction source and/or after significant time has passed.

Case Study: Water Extraction and Diversion in Owens Valley, CA
The depletion of surface and groundwater by solar development may have unexpected consequences, as illustrated by the impacts of both surface water diversion and groundwater pumping in Owens Valley, California. The Owens Valley, located in the Great Basin Desert in California’s Inyo County, provides a good example of terrestrial impacts that can result from reduced flows of surface and groundwater. In 1913, Los Angeles opened an aqueduct that diverted surface water from the Owens River, which runs through the Owens Valley, down to the city. Los Angeles began pumping groundwater in 1918, and opened a parallel aqueduct that pumped additional groundwater out of the valley in 1970.¹³ Surface water diversion and groundwater pumping have induced measurable changes in vegetation composition and cover of the Owens Valley, including increased shrub cover replacing grass cover.¹⁴ Preliminary evaluations of vegetation change found that from 1906 to 1968, major vegetation cover declined by 38 percent, and from 1968 to 1981, major vegetation cover declined by 67 percent.¹⁵ It has been estimated that approximately 25,000 acres of groundwater-dependent vegetation in the valley have been negatively affected by groundwater pumping.¹⁶

The water table served as a buffer for vegetation to adjust to annual fluctuations in precipitation, but diversion and pumping have resulted in fluctuations in the water supply that negatively affects native plants such as willow (Salix spp.), saltgrass (Distichlis spicata), greasewood (Sarcobatus vermiculatus), and favors weed species such as Russian thistle (Salsola spp.) and bassia (Bassia hysopifolia).¹⁷ Saltcedar (Tamarix ramosissima) has colonized riparian habitats below the aqueduct intake because intermittent surface water flow creates disturbance that harms native vegetation and favors saltcedar.¹⁸ Nevada saltbush scrub (Atriplex torreyi), saltgrass meadow, and alkali marsh communities around the Little Black Rock Spring have declined because of groundwater pumping.¹⁹

1 D.T. Patten, L. Rouse, J.C. Stromberg, “Isolated spring wetlands in the Great Basin and Mojave Deserts, USA: potential response of vegetation to groundwater withdrawal,” Environmental Management 41 (2008): 398-413.

2 A.J. Elmore, S.J. Manning, J.F. Mustard, J.M. Craine, “Decline in alkali meadow vegetation cover in California: the effects of groundwater extraction and drought,” Journal of Applied Ecology 43 (2006): 770-779.

3 A.J. Elmore, S.J. Manning, J.F. Mustard, J.M. Craine, “Decline in alkali meadow vegetation cover in California: the effects of groundwater extraction and drought,” Journal of Applied Ecology 43 (2006): 770-779.

4 D.T. Patten, L. Rouse, J.C. Stromberg, “Isolated spring wetlands in the Great Basin and Mojave Deserts, USA: potential response of vegetation to groundwater withdrawal,” Environmental Management 41 (2008): 398-413.

5 J.P. Brunel, “Sources of water used by natural mesquite vegetation in a semi-arid region of northern Mexico,” Hydrological Sciences Journal 54, no. 2 (2009): 375-381.

6 D.T. Patten, L. Rouse, J.C. Stromberg, “Isolated spring wetlands in the Great Basin and Mojave Deserts, USA: potential response of vegetation to groundwater withdrawal,” Environmental Management 41 (2008): 398-413.

7 J. Laity, “Aeolian destabilization along the Mojave River, Mojave Desert, California: Linkages among fluvial, groundwater, and aoelian systems,” Physical Geography 24, no. 3 (2003): 196-221.

8 K.L. Penrod, E.S. Rubin, C. Paulman, Mojave Desert Habitat Connectivity ~ Phase 1: A Brief Overview of the Mojave Desert’s Previously Identified Areas of Ecological Significance, (Fair Oaks, CA: SC Wildlands, 2009).

9 W.D. Shepard, “Desert springs – both rare and endangered,” Aquatic Conservation: Marine and Freshwater Ecosystems 3 (1993): 351-359.

10 W.D. Shepard, “Desert springs – both rare and endangered,” Aquatic Conservation: Marine and Freshwater Ecosystems 3 (1993): 351-359. 11 W.D. Shepard, “Desert springs – both rare and endangered,” Aquatic Conservation: Marine and Freshwater Ecosystems 3 (1993): 351-359.

12 Agency Hydrologist 1, Personal Communication, October 29, 2009.

13 Robert A. Sauder, The Lost Frontier: Water Diversion in the Growth and Destruction of Owens Valley Agriculture, (Tucson: The University of Arizona Press, 1994).

14 D.P. Groeneveld, “Owens Valley, California, Plant Ecology: Effects from Export Groundwater Pumping and Measures to Conserve the Local Environment,” in The History of Water: Eastern Sierra Nevada, Owens Valley, White-Inyo Mountains, ed. C.A. Hall Jr., V. Doyle-Jones, and B. Widawski, (CA: White Mountain Research Station Symposium, 1992), 128-155.

15 D. Jaques, “Preliminary Evaluation of Vegetation Changes from 1906 to 1968 to 1981 in the Southern Half of the Owens Valley, California,” in The History of Water: Eastern Sierra Nevada, Owens Valley, White-Inyo Mountains, ed. C.A. Hall Jr., V. Doyle- Jones, and B. Widawski, (CA: White Mountain Research Station Symposium, 1992), 444-445.

16 Robert A. Sauder, The Lost Frontier: Water Diversion in the Growth and Destruction of Owens Valley Agriculture, (Tucson: The University of Arizona Press, 1994).

17 D.P. Groeneveld, “Owens Valley, California, Plant Ecology: Effects from Export Groundwater Pumping and Measures to Conserve the Local Environment,” in The History of Water: Eastern Sierra Nevada, Owens Valley, White-Inyo Mountains, ed. C.A. Hall Jr., V. Doyle-Jones, and B. Widawski, (CA: White Mountain Research Station Symposium, 1992), 128-155.

18 D.P. Groeneveld, “Owens Valley, California, Plant Ecology: Effects from Export Groundwater Pumping and Measures to Conserve the Local Environment,” in The History of Water: Eastern Sierra Nevada, Owens Valley, White-Inyo Mountains, ed. C.A. Hall Jr., V. Doyle-Jones, and B. Widawski, (CA: White Mountain Research Station Symposium, 1992), 128-155.

19 M. DeDecker, “The Death of a Spring,” in The History of Water: Eastern Sierra Nevada, Owens Valley, White-Inyo Mountains, ed. C.A. Hall Jr., V. Doyle-Jones, and B. Widawski, (CA: White Mountain Research Station Symposium, 1992), 223-226.