NEWS NOTES ON SUSTAINABLE WATER RESOURCES  The Great Salt Lake  https://en.wikipedia.org/wiki/Great_Salt_Lake  “The Great S...

NEWS NOTES ON SUSTAINABLE WATER RESOURCES  The Great Salt Lake  https://en.wikipedia.org/wiki/Great_Salt_Lake ; “The Great Salt Lake , located in the northern part of the U.S. state of Utah, is the largest salt water lake in the Western Hemisphere, and the eighth-largest terminal lake in the world. In an average year the lake covers an area of around 1,700 square miles (4,400 km2), but the lake's size fluctuates substantially due to its shallowness. For instance, in 1963 it reached its lowest recorded size at 950 square miles (2,460 km²), but in 1988 the surface area was at the historic high of 3,300 square miles (8,500 km2). In terms of surface area, it is the largest lake in the United States that is not part of the Great Lakes region. “The lake is the largest remnant of Lake Bonneville, a prehistoric pluvial lake that once covered much of western Utah. The three major tributaries to the lake, the Jordan, Weber, and Bear rivers together deposit around 1.1 million tons of minerals in the lake each year. As it is endorheic (has no outlet besides evaporation), it has very high salinity (far saltier than seawater) and its mineral content is steadily increasing. Due to the high density resulting from its mineral content, swimming in the Great Salt Lake is similar to floating. Its shallow, warm waters cause frequent, sometimes heavy lake-effect snows from late fall through spring.” “Since 1847, the Great Salt Lake has steadily shrunk, reaching its lowest recorded level in 2016. Today, the lake is 3.6 meters below its 1847 level and just half its original volume. Previously, many researchers thought the decline—here and in other saltwater lakes—was caused by wet and dry cycles related to climate change, says Wayne Wurtsbaugh, a limnologist at Utah State University in Logan.  See https://www.sciencemag.org/news/2017/11/utah-s-great-salt-lake-has-lost-half-its-water-thanks-thirsty-humans ; “To test that notion, Wurtsbaugh and his colleagues recreated the climate around the Great Salt Lake for 170 years, based on historical precipitation, stream level records, and tree ring data. The records showed that precipitation and temperature patterns had hardly fluctuated during the period, meaning that the amount of water flowing into the lake from nearby streams is likely the same today as it was in 1847. Next, the team did some hydrological accounting, creating what’s known as a water balance. They compared the amount of water flowing into the lake from rivers, precipitation, and groundwater to the amount evaporating out of the lake; if the lake stayed the same size, the water in and out should balance. It didn’t.  “Why? Every year, people living in the region (which includes rapidly growing Salt Lake City) divert 3.3 trillion liters of water, not from the lake itself, but from the handful of streams feeding it. With climate staying relatively stable, the team concluded that humans are triggering the decline by consuming streamwater before it replenishes the lake, they reported last week in Nature Geoscience. Although some of that water returns to the lake (for example, by soaking into the ground after irrigation), Wurtsbaugh says the new calculations show that the overall amount fell 39% from 2003 to 2012. This, in addition to long-term stream records, suggests that climate change isn’t the culprit.  Wurtsbaugh says that the key to preserving saltwater lakes (including Iran’s Lake Urmia) is to strike a balance between human consumption and conservation. The team concludes that inflows to the Great Salt Lake will need to increase 24% to 29% to maintain its health and stability. Wurtsbaugh adds that with the population of Utah set to double by 2050, long-term conservation and planning is crucial. “We need to be thinking 50, 100, 200 years out.”