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FEATURE ARTICLE

Runaway Devils Lake

In the wake of climate change, a North Dakota lake swells without regard for people or property and with no easy fix in sight

Douglas Larson

Hydrological Cycles and Chemistry

As a terminal lake lacking a natural outlet below an elevation of between 444 and 445 meters, Devils Lake loses water mostly to evaporation, which amounts to 86 percent of total inflow in 1986 and 73 percent in 1987. In 1988, evaporation loss exceeded total inflow by more than 200 percent, resulting in a net lake-water loss of about 100,000 acre-feet. During dry periods, lake-water salts became increasingly concentrated as lake volume diminished. Salinity was first measured in 1899 and reported thereafter as total dissolved solids (TDS). Lake volume between 1899 and 1920 decreased from about 520,000 to 272,000 acre-feet, doubling the TDS concentration from about 8,500 to 16,000 milligrams per liter (mg/L). After 1923, salinity was not measured again until 1948 when the U.S. Geological Survey obtained a TDS reading of 25,000 mg/L, the highest on record for the lake. Salinity was probably higher around 1940, however, when lake levels were the lowest on record.

Salinity has decreased significantly over the past 20 years in response to the extraordinary increase in lake volume. Although most of the remnant lakes have merged, salinities are not uniform throughout the lake system. An upward-trending salinity gradient extends southeast from Pelican Lake to East Stump Lake, a distance of nearly 80 kilometers. In 1949, the USGS recorded TDS concentrations of 2,300, 13,000, 41,000 and 106,000 mg/L along a transect beginning near Pelican Lake and ending at East Stump Lake. By 2010, after the lakes had completely merged, average TDS concentrations along the same transect ranged from 987 mg/L at the Pelican Lake site to 1,418 mg/L at Devils Lake’s Main Bay to 2,245 mg/L at the former East Stump Lake basin.

Sulfate is the predominant constituent of the lake’s total ion composition. In 1949, sulfate concentrations in Devils Lake’s Main Bay averaged 7,490 mg/L, representing 51 percent of TDS. By 2010, dilution had reduced the average concentration to 630 mg/L (range 610-651 mg/L), or 44 percent of TDS. Total sulfate levels are regulated by North Dakota’s Department of Health to protect municipal and domestic sources of drinking water. Sulfate will become an environmental issue when efforts get underway to pump water from the lake and discharge it through man-made outlets.




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