Great Salt Lake

Overview

By: Floyd Nichols

The Great Salt Lake is located in Utah and is a highly saline Lake (Post, 1977). The Great Salt Lake is a remnant of a prehistoric freshwater lake, which has turned saline because of the blocked rainfall from the Sierra Nevada (Post, 1977). Furthermore, it is unique in that it the Lake shows an increasing salinity gradient from south to north, ranging from seawater concentrations to saturation, respectively (Weimer et al., 2009). Despite these high saline conditions, Great Salt Lake still shows high biodiversity, (Weimer et al., 2009; Tazi et al., 2014). Considering the extreme nature of this environment, many of the microorganisms are novel and uncultured; however, as the environment might suggest, the large majority of phyla that inhabit the Great Salt Lake are halotolerant and halophiles (Tazi et al., 2014). Interestingly, although living in highly saline environments such as the Great Salt Lake comes at an energetic cost, bacteria in this environment are less likely to be dormant (Aanderud et al., 2016). This suggests that saline environments act to filter structuring bacteria in lake ecosystems (Aanderud et al., 2016). Similarly, high primary productivity and high sulfate concentrations are associated with the Great Salt Lake as well as other hypersaline environments (Kjeldsen et al., 2007). Despite the information that has been obtained for microbial communities in the Great Salt Lake and other hypersaline environments, they still remain understudied.

Environment and Geology

The Great Salt Lake is a large Pleistocene lake that is a remnant of Lake Bonneville which was a fresh body of water (Spencer et al., 1984; Eardley, 1938; Post, 1977). The Great Basin, in which Lake Bonneville and other Pleistocene lakes formed, originated after the beginning of some extensive normal faulting (Eardley, 1938; Lindsay et al., 2016; Baskin, 2014; Gwynn, 1996). The Great Salt Lake is now a hypersaline body of water that is divided into a north-south end that is 300-miles long and an east-west end that is 180 miles long (Eardley, 1938). Due to evaporation, the north end is slightly more saline and with replacement of water only in the south (Post, 1977). The major source of freshwater inflow comes from three major rivers, the Bear, Weber, and Jordan rivers which enter the south arm (Lindsay et al., 2016; Baskin, 2014; Gwynn, 1996). Furthermore, due to the northward migration of water, the north arm is becoming increasingly enriched in minerals while the south-arm is slowly becoming depleted (Post, 1977, Lindsay et al., 2016). The geologic record indicates that the Great Salt Lake has gone through at least ten cycles in the last 100,000 years, and the present-day Great Salt Lake is at its lowest point in the most recent cycle (Post, 1977). Furthermore, the Great Salt Lake has no natural outlet to the sea and is thus a terminal lake (Post, 1977).

The land that surrounds the Great Salt Lake is primarily Mesozoic and Paleozoic sedimentary rock with the addition of some recent intrusive and extrusive rocks (Post, 1977). Within the lake, there are many small islands such as Gunnison, Dolphin, Black Rock, Antelope, and Fremont just to name a few (Earldey, 1938). The east of the lake is bounded by the Wasatch Mountain and the west is bounded by the Lakeside and Hogside Mountains (Eardley, 1938). The Wasatch Mountain and most of the east of the lake is primarily pre-Cambrian crystalline rock such as gneiss, schists, pegmatites, and granite (Eardley, 1938). The western side, however, is composed of Paleozoic and Algonkian limestone, shale, sandstone, and quartzite (Eardley, 1938).

The chemistry of both the north and south arm of the Great Salt Lake are markedly different. The south arm follows a composition that is more like the marine environment (thalassohaline) with the dominant ions being Na+ and Cl- (Post, 1977). The north arm, however, has an ionic composition that is dominated by Na+ and SO42- (Post, 1977). During the winter months in the north arm, when the temperature drops below 3°C NaSO4 will precipitate spontaneously out of solution to form an ~20 cm layer of hydrated NaSO4 at the bottom of the lake (Post, 1977). When the water temperature rises, the NaSO42- dissolves back into solution (Post, 1977).

Despite these harsh saline conditions, the Great Salt Lake has an extensive and diverse microbial community (Post, 1977; Lindsay et al., 2016; Weimer et al., 2009; Tazi et al., 2014). Due to the extensive microbial community and shallow conditions, microbialite structures are highly associated with the Great Salt Lake (Lindsay et al., 2016). Oolitic sands provide the base for much of the microbialite formation, and in addition microbialite structures will grow on lithified crusts of oolitic sands and lime muds resulting in reef like complexes (Lindsay et al., 2016; Riding, 2000).

Microbial Diversity

The microbial abundance and diversity in the Great Salt Lake is quite high despite its salinity and other extreme conditions (Post, 1977; Lindsay et al., 2016; Weimer et al., 2009; Tazi et al., 2014). Since the lake has a different ionic composition at the north arm and south arm, so too does the microbes differ (Post, 1977).

In general, the primary producers of the lake are from the genus Dunaliella (Post, 1977). The south arm has a lot of algae belonging to the cyanophyta; these consist of calcium carbonate precipitated around cells of Oscillatoria sp. and Coccochloris elegans (post, 1977). In the north arm, there are low levels of Duniella viridis, but it is highly populated with red algae with two flagella and sluggish motility (Post, 1977). The red algae are comparable morphologically to Dunaliella salina strains (Post, 1977). The red algae do not form uniform in the lake, but in huge patches (Post, 1977).

The bacteria of the north arm are very abundant and their numbers are so vast that the water becomes a rose wine color due to the carotenoid pigments (Post, 1977).

Key Microbial Players

South Arm

• Oscillatoria sp

• Coccochloris elegans