Dust Sources at Mono Lake
Click on footnotes -- 1 -- to see the notes at the bottom of the profiles. Click on words in italics to see the definition in the glossary.
On windy days, particulate matter (mainly PM10, a particle size that lodges easily in the lungs) is carried into the air from around the shores of Mono Lake. Frequent source areas include a band in the relicted area around the northeast shore set back from the water's edge, the former land bridge, now an island near Negit Island, and the emerged western portion of Paoha Island that has sparse greasewood cover. Less frequent source areas include the east lakeshore between Warm Springs and Simons Springs, and lower areas of the former land bridge. Least frequent source areas are the wet areas near the lake from Black Point to Warm Springs.1
Other constituents are unvegetated or sparsely vegetated substrates, which encompass 6,900 acres, or a 39% greater area than efflorescent salts. These sources probably contribute substantially to emissions during high wind episodes, such as the diatomaceous particles which may contribute to Paoha Island's emissions.3
Efflorescent salt deposits are found mainly along the north and east shores generally below the 6,390 foot elevation, with small scattered deposits in other locations. As of 1989, efflorescent salts covered 65% of the relicted area, or 4,975 acres.4
Efflorescent salt deposits seldom develop where the groundwater is greater than 10 feet deep. Where they do develop, relatively shallow groundwater flows toward the lake,5 picking up salts from the lakebed sediments, or lakewater intrudes into low lying lakebed sediments. This saline groundwater rises to the surface through capillary action and evaporates or cools, leaving or precipitating the dissolved minerals on the surface,6 where they can be picked up by the wind.
This is the same process by which irrigation causes salt buildup in soils and drainage water.7 Up to three-quarters of irrigation water can evaporate or transpire, leaving the salts in the drainage water. If there is poor drainage, the salts build up in the soil.
These efflorescent salt deposits vary--both seasonally and diurnally--in their susceptibility to wind erosion, with wet conditions and warm and dry conditions causing high resistance to wind erosion. Warm and dry conditions favor the formation of a strongly cemented crust, which is prevalent through most of the summer.8
Cool salt deposit temperatures and low surface moisture levels favor the development of powdery noncrystalline salts highly susceptible to wind erosion. Powdery deposits usually form during spring or after fall rains. Daily fluctuations occur, especially in spring and fall, when deposits are wet at night and dry during the day.9
Once Mono Lake reaches 6392 feet above sea level, the Mono Basin is expected to be brought very close to and possibly into attainment of state and federal PM10 standards.10 Without this rise in the surface of the lake, groundwater draining the former lake sediments, extending up to 8 miles from the lake, might eventually reach a new equilibrium level with the lake surface. However, it would take at least hundreds of years for this to reduce or eliminate efflorescent salt formation.11 The Environmental Protection Agency and Great Basin Unified Air Pollution Control District halted further action on air quality violations because the lake level required by D1631 is expected to bring the Mono Basin into compliance.
(1)p. 3H-20, Mono
Basin EIR, 1993
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