How Do Changes to the Railroad Causeway in Utah's Great Salt Lake Affect Water and Salt Flow?

40-years of Lake Urmia restoration research: Review, synthesis and next steps

Public concern over environmental issues such as ecosystem degradation is high. However, restoring coupled human-natural systems requires integration across many science, technology, engineering, management, and governance topics that are presently fragmented. Here, we synthesized 544 peer-reviewed articles published through September 2020 on the desiccation and nascent recovery of Lake Urmia in northwest Iran. We answered nine questions of scientific and popular interest about causes, impacts, stabilization, recovery, and next steps. We find: (1) Expansion of irrigated agriculture, dam construction, and mismanagement impacted the lake more than temperature increases and precipitation decreases. (2) Aerosols from Lake Urmia's exposed lakebed are negatively impacting human health. (3) Researchers disagree on how a new causeway breach will impact salinity, evaporation, and ecosystems in the lake's north and south arms. (4) Most researchers tried to restore to a single, uniform, government specified lake level of 1274.1 m intended to recover Artemia. (5) The Iranian government motivated and funded a large and growing body of lake research. (6) Ecological and limnological studies mostly focused on salinity, Artemia, and Flamingos. (7) Few studies shared data, and only three studies reported engagement with stakeholders or managers. (8) Researchers focused on an integration pathway of climate downscaling, reservoirs, agricultural water releases, and lake level. (9) Numerous suggestions to improve farmer livelihoods and governance require implementation. We see an overarching next step for lake recovery is to couple human and natural system components. Examples include: (a) describe and monitor the system food webs, hydrologic, and human components; (b) adapt management to monitored conditions such as lake level, lake evaporation, lake salinity, and migratory bird populations; (c) improve livelihoods for poor, chronically stressed farmers beyond agriculture; (d) manage for diverse ecosystem services and lake levels; (e) engage all segments of society; (f) integrate across restoration topics while building capacity to share data, models, and code; and (g) cultivate longer-term two-way exchanges and public support. These restoration steps apply in different degrees to other Iranian ecosystems and lakes worldwide.

Historic low stand of Great Salt Lake, Utah: I

Great Salt Lake of Utah is among the largest and most ecologically important water bodies in North America. Since the late 1950s, the lake has been divided into two hydrologically distinct water bodies by a rock-fill railroad causeway. Flux through the causeway is driven by two forces: differential surface elevation and differential density between the north and south arms. The south arm features episodic vertical stratification due to the influx of deep, dense brine from the north arm. The source of this brine (a breach, two culverts, or subsurface flow) has been investigated over the past 50 years. Quantification of subsurface water flux through the causeway has been problematic due to the heterogeneous and slowly compacting nature of the causeway fill over time. Between 2008 and 2015, enhanced gauging of various surface inflows and outflows and density measurements made throughout the lake permitted detailed water volume calculations of both lake arms. Results show that during high precipitation years, density-driven, north-to-south flow through the causeway predominates due to freshening of water in the south arm. At other times, south-to-north head gradient driven flow and north-to-south density-driven flow are approximately equal. The model suggests subsurface flux through the causeway is one important driver of the ecologically important deep brine layer in the south arm of the lake over the past 20 years.

Climatization—Negligent Attribution of Great Salt Lake Desiccation: A Comment on Meng (2019)

A recent article reviewed data on Great Salt Lake (Utah) and concluded falsely that climate changes, especially local warming and extreme precipitation events, are primarily responsible for lake elevation changes. Indeed climatically influenced variation of net inflows contribute to huge swings in the elevation of Great Salt Lake (GSL) and other endorheic lakes. Although droughts and wet cycles have caused lake elevation changes of over 4.5 m, they have not caused a significant long-term change in the GSL stage. This recent article also suggests that a 1.4 °C rise in air temperature and concomitant increase in the lake’s evaporative loss is an important reason for the lake’s decline. However, we calculate that a 1.4 °C rise may have caused only a 0.1 m decrease in lake level. However, since 1847, the lake has declined 3.6 m and the lake area has decreased by ≈50%, despite no significant change in precipitation (p = 0.52) and a slight increase, albeit insignificant, in river flows above irrigation diversions (p = 0.085). In contrast, persistent water extraction for agriculture and other uses beginning in 1847 now decrease water flows below diversions by 39%. Estimates of consumptive water use primarily for irrigated agriculture in the GSL watershed suggest that approximately 85% (2500 km2) of the reduced lake area can be attributed to human water consumption. The recent article’s failure to calculate a water budget for the lake that included extensive water withdrawals misled the author to focus instead on climate change as a causal factor for the decline. Stable stream flows in GSL’s headwaters, inadequate temperature increase to explain the extent of its observed desiccation, stable long-term precipitation, and the magnitude of increased water consumption from GSL together demonstrate conclusively that climatic factors are secondary to human alterations to GSL and its watershed. Climatization, in which primarily non-climatic processes are falsely attributed to climatic factors, is a threat to the credibility of hydrological science. Despite a recent suggestion to the contrary, pressure to support Earth’s rising human population—in the form of increasing consumption of water in water-limited regions, primarily to support irrigated agriculture—remains the leading driver of desiccation of inland waters within Earth’s water-limited regions.

The cost of addressing saline lake level decline and the potential for water conservation markets

The world's saline lakes are shrinking and human water diversions are a significant contributor. While there is increased interest in protecting the ecosystem services provided by these lakes, the cost of protecting water levels has not been estimated. To explore this question we consider the case of Great Salt Lake (Utah, USA) where human diversions from three rivers have caused the lake level to decline during the last century. Recent work has suggested the restoration of inflows is necessary to maintain a target elevation consistent with well-functioning ecosystems. We construct cost estimates of increasing water inflows using conservation cost curves for each river basin. We then compare the cost of uniform cutbacks to cap-and-trade systems which allow intra- and inter-basin trading. The cost of water to permanently implement uniform water right cutbacks to increase inflows by 20% above current levels is $37.4 million. Costs and cost-savings are sensitive to alternative allocation, inflow, and cost assumptions, and we estimate significant cost reductions from intra-basin water conservation markets (5-54% cost decrease) and inter-basin water conservation markets (22-57% cost decrease).

Effect of salinity on mercury methylating benthic microbes and their activities in Great Salt Lake, Utah

Surface water and biota from Great Salt Lake (GSL) contain some of the highest documented concentrations of total mercury (THg) and methylmercury (MeHg) in the United States. In order to identify potential biological sources of MeHg and controls on its production in this ecosystem, THg and MeHg concentrations, rates of Hg(II)-methylation and MeHg degradation, and abundances and compositions of archaeal and bacterial 16 rRNA gene transcripts were determined in sediment along a salinity gradient in GSL. Rates of Hg(II)-methylation were inversely correlated with salinity and were at or below the limits of detection in sediment sampled from areas with hypersaline surface water. The highest rates of Hg(II)-methylation were measured in sediment with low porewater salinity, suggesting that benthic microbial communities inhabiting less saline environments are supplying the majority of MeHg in the GSL ecosystem. The abundance of 16S rRNA gene transcripts affiliated with the sulfate reducer Desulfobacterium sp. was positively correlated with MeHg concentrations and Hg(II)-methylation rates in sediment, indicating a potential role for this taxon in Hg(II)-methylation in low salinity areas of GSL. Reactive inorganic Hg(II) (a proxy used for Hg(II) available for methylation) and MeHg concentrations were inversely correlated with salinity. Thus, constraints imposed by salinity on Hg(II)-methylating populations and the availability of Hg(II) for methylation are inferred to result in higher MeHg production potentials in lower salinity environments. Benthic microbial MeHg degradation was also most active in lower salinity environments. Collectively, these results suggest an important role for sediment anoxia and microbial sulfate reducers in the production of MeHg in low salinity GSL sub-habitats and may indicate a role for salinity in constraining Hg(II)-methylation and MeHg degradation activities by influencing the availability of Hg(II) for methylation.

Bacterial Dormancy Is More Prevalent in Freshwater than Hypersaline Lakes

Bacteria employ a diverse array of strategies to survive under extreme environmental conditions but maintaining these adaptations comes at an energetic cost. If energy reserves drop too low, extremophiles may enter a dormant state to persist. We estimated bacterial dormancy and identified the environmental variables influencing our activity proxy in 10 hypersaline and freshwater lakes across the Western United States. Using ribosomal RNA:DNA ratios as an indicator for bacterial activity, we found that the proportion of the community exhibiting dormancy was 16% lower in hypersaline than freshwater lakes. Based on our indicator variable multiple regression results, saltier conditions in both freshwater and hypersaline lakes increased activity, suggesting that salinity was a robust environmental filter structuring bacterial activity in lake ecosystems. To a lesser degree, higher total phosphorus concentrations reduced dormancy in all lakes. Thus, even under extreme conditions, the competition for resources exerted pressure on activity. Within the compositionally distinct and less diverse hypersaline communities, abundant taxa were disproportionately active and localized in families Microbacteriaceae (Actinobacteria), Nitriliruptoraceae (Actinobacteria), and Rhodobacteraceae (Alphaproteobacteria). Our results are consistent with the view that hypersaline communities are able to capitalize on a seemingly more extreme, yet highly selective, set of conditions and finds that extremophiles may need dormancy less often to thrive and survive.