Hydrologic response to climate change in the Las Vegas Valley

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This article is part of the Spring 2016 issue of the Earth Science Matters Newsletter

The city of Las Vegas was founded in the mid-19th century near a series of spring-fed meadows for which the city was named. These meadows, or “wetlands,” provided a continuous source of water to early residents, allowing them to survive and ultimately flourish in an otherwise harsh desert landscape. In prehistoric times, the wetlands were more extensive and covered much of the valley. Between ~100,000 and 10,000 years ago, for example, wetlands dotted the desert landscape throughout southern Nevada’s Las Vegas Valley, attracting a plethora of Ice Age animals, including mammoth, sloth, bison, camel, horse, dire wolf, and even American lion and sabre-toothed cat. Although the extent of the wetlands has decreased significantly since the end of the Pleistocene, the valley remains home to numerous species of water birds, reptiles, and mammals. New research examines the long-term history of these deposits to determine the sensitivity of desert wetlands to climate change, as well as to constrain the magnitude of hydrologic variability before 20th century urbanization and human alteration of the landscape.

fine-grained buff-colored sediment deposits in the Las Vegas Valley

In southern Nevada, fine-grained buff-colored deposits lie in the valley against the backdrop of the Las Vegas Range just outside the city limits of Las Vegas. Once thought to be remnants of a large lake, these deposits actually record the presence of extensive wetlands that responded dynamically to past episodes of abrupt climate change.

(Photo Credit: Eric Scott, Cogstone Resource Management, Inc.)

Desert wetlands coalesce where groundwater breaches the surface and provide otherwise dry and barren landscapes with stable water supplies that underpin unique ecosystems that support spring-dependent species. Within these settings, sediments transported by water and wind are trapped by a combination of wet ground conditions and dense plant cover. Over time, the sediments build up and are ultimately preserved in the geologic record as “paleowetland deposits.” These deposits contain information on the timing and magnitude of past changes in water table levels and, therefore are an important source of information on past variations of climate and hydrology.

Recently, scientists funded by the USGS Climate Research & Development Program, published the first in a planned series of scientific papers that utilized geological mapping, stratigraphic analysis, and radiocarbon dating to reconstruct a detailed history of ebb and flow for paleowetlands in the Las Vegas Valley. The results of the study reveal that the wetlands expanded and contracted in virtual lock step with climate variations recorded in Greenland ice cores and records from the western United States over the past 35,000 years or so. Most dramatically, the valley’s entire wetland system collapsed multiple times during this interval when conditions became too warm. Drought-like conditions in the valley, as recorded by widespread erosion and the formation of desert soils, typically lasted for a few centuries, illustrating the potential vulnerability of these fragile ecosystems to climate change.

Wetlands are an invaluable resource for flora and fauna in arid environments worldwide and serve as keystone ecosystems that support a high species biodiversity including endemic, threatened, and endangered biotas. The unique geological lens afforded by wetland deposits provides a valuable context when planning for the potential response of these fragile ecosystems to future climate warming.

The paper, Dynamic Response of Desert Wetlands to Abrupt Climate Change, was published in the Proceedings of the National Academy of Sciences USA. It is available at https://doi.org/10.1073/pnas.1513352112

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