Miller, Craig

Null, Sarah E.

Wurtsbaugh, Wayne A.

English

DigitalCommons@USU

Friends of Great Salt Lake Newsletter. Spring 2013 Vol 19 (No. 1 & 2): 14-15.Figure 1. Railroad causeway with Gunnison Bay onleft and Gilbert Bay on right, photo courtesy ofWayne Wurtsbaugh.Can the causeway in the Great Salt Lake be used to manage salinity?Sarah Null, USU, Logan, UTWayne Wurtsbaugh, USU, Logan, UTCraig Miller, Utah DWR, Salt Lake City, UTSouthern Pacific’s railroad causeway, converted to solid fill in 1959, divided the Great Salt Lake intoGunnison Bay to the north and Gilbert Bay to the south and changed the lake’s water and salt balance.Gilbert Bay has a higher surface elevation and a lower salinity (typically 8-17%) because it receivesnearly all of the fresh stream flow from the Bear, Weber, and Jordan/Provo watersheds. Bear River Bayis considered part of the south arm because the two are connected by an opening in the causeway. Withlittle fresh water, but plenty of evaporation, Gunnison Bay is often completely saturated with salt (~27%).Some water and salt flows through the causeway at breaches and culverts as well as through the fill of thecauseway, but this interflow is not enough to equalize salinity or the surface elevation between the northand south arms of the Great Salt Lake.There is an inverse relationship with lakeelevation and salinity, so that as elevation risesin wetter years, salinity decreases (Figure 2).The salt threshold for Great Salt Lake brineshrimp is not well documented, but probablyranges between about 8 – 20%.  Even less isknown about the salinity threshold for brineflies, but the two species occupy similarhabitats in the Great Salt Lake, and thus mayhave similar salt tolerances.We wondered how much the railroadcauseway alters natural conditions and whatthe salinity of the lake would be like had thecauseway not been built. To calculate thesalinity of the “whole” Great Salt Lake, weused lake elevations to estimate water volumeand a measured salt content of 4.9 billionmetric tons, until pumping to the west desert in the mid-1980s reduced it to 4.5 billion tons. Without thecauseway, we estimate that the “whole” Great Salt Lake salinity would have exceeded the tolerance ofbrine shrimp in 73% of the years between 1960-2011 (Figure 2B).  The fresher Farmington and BearRiver Bays would likely have supported brine shrimp during those years, but nevertheless, “whole” lakeproduction would likely have been lower than what actually occurred in Gilbert Bay with the causeway.During those drier years with the causeway, Gilbert Bay had acceptable salinities and supported brineshrimp, brine flies, and the bird community dependent on these prey species. In the very wet years of themid-1980s, Gilbert Bay became too fresh to support large populations of brine shrimp.  Then GunnisonBay, which at that time was less saline from heavy precipitation, supported brine flies and shrimp (as wellas brine shrimp cyst harvesters).Friends of Great Salt Lake Newsletter. Spring 2013 Vol 19 (No. 1 & 2): 14-15.Figure 2.  (A) Gilbert Bay elevation. (B) measured Gilbert Bay surfacesalinities (solid black line from http:// ut.water.usgs.gov/greatsaltlake),estimated "whole" Great Salt Lake salinity (thick blue line), and GunnisonBay salinities (dashed line).0510152025301840 1860 1880 1900 1920 1940 1960 1980 2000Salinity  (% )Approx. Salinity Rangefor  Brine ShrimpSalinity withoutrailroad causewayMeasuredWhole Lake SalinityRailroadCausewayGilbert Bay→SalinityB Gunnison BaySalinity4190419542004205421042151840 1860 1880 1900 1920 1940 1960 1980 2000Lake  Elevation  (feet) Lake ElevationAThis illustrates that the causeway provides some benefit by increasing the range of salinity levelsthroughout the lake during any given year.  While the causeway in the Great Salt Lake has certainlyaltered natural conditions, it has also increased the resiliency of life in the Great Salt Lake by raising thechances that tolerable salinity levels will exist somewhere despite hydrologic variability. But there aretradeoffs. Mineral extraction companies in the south are hurt by a divided and lake, whereas those innorth benefit by having saturated brine to utilize. In years when “whole” lake salinity would have beenwithin an acceptable range to support life, the divided lake had a much smaller area for brine shrimp andbrine fly production. Another negative is that the causeway causes a deep brine layer to form under abouthalf of Gilbert Bay where brine shrimp and brine flies cannot survive, and where toxic methyl mercury isproduced.If the railroad causeway separating Gilbert and Gunnison Bays were updated with a control structure tomanage the flow of water and salt, the causeway might be a management tool to maintain salinity, aquaticlife, and industry. Salt lakes worldwide are vulnerable to changes in salinity from hydrologic variabilityas well as human alteration from water regulation, land use, and climate change. A well-managedcauseway could provide some resiliency from these changes.

Can the Causeway in the Great Salt Lake be Used to Manage Salinity

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Can the Causeway in the Great Salt Lake be Used to Manage Salinity

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