Evaporation Cycle Research Articles

Marine Coastline Polygonal Ridges and Surface Roughness Development on a Salt-Crusted Playa: Recognition by Structure-from-Motion Photogrammetry

Salt crust is a normal landform in drying-out salt lake basins or marine regression coastlines, but the surface evolution processes over a decadal or even centenary period are not well understood due to poor data records. Microrelief characteristics control erodibility and erosivity, which will significantly influence wind erosion and dust emission. It is essential to classify the microrelief pattern of salt crust for mapping its spatial distribution and evaluating the environmental process. A desiccated inland tail-end lake would be an example of the coastline surface evolution after regression and represent a good case study of salt crust because of the fewer exogenic process interruptions. For this paper, field work was performed in the Lop Nur playa in China, about 90° E, 40° N, which used to be a salt lake half a century ago. Ground-based photos of the salt crust were acquired and imported into structure-from-motion (SfM) software to produce a fine centimeter-scale digital elevation model (DEM). Two indexes were introduced and extracted from the digital elevation model to classify various types of salt crust: roughness was calculated to evaluate the magnitude and the gray-level co-occurrence matrix (GLCM) score was derived to describe the structure pattern of the salt crust. Moreover, in this paper, sedimentary features during different parts of a playa evaporation cycle are reviewed and peculiar kinds of salt crust found on Lop Nur are further discussed.

Effects of heat source temperature and mixture composition on the combined superiority of dual-pressure evaporation organic Rankine cycle and zeotropic mixtures

Abstract Dual-pressure evaporation cycle is an emerging cycle type in the organic Rankine cycle (ORC) that can remarkably reduce the irreversible loss during heat absorption process and improve the adaptability to various heat sources. Introduction of zeotropic mixtures in dual-pressure evaporation ORC presents great potential to further increase the heat-power conversion efficiency due to the variable phase-change temperature. This study investigated the dual-pressure evaporation ORC using isobutane/isopentane mixtures for heat sources of 100–200 °C. Effects of heat source temperature and mixture composition on the system thermodynamic performance were analyzed. Application potential and applicable ranges of introducing isobutane/isopentane mixtures in dual-pressure evaporation ORC were evaluated. Results showed that the introduction of zeotropic mixtures in dual-pressure evaporation ORC substantially increased the power output. The maximum power output of dual-pressure evaporation ORC using isobutane/isopentane mixtures could increase by 11.9% and 15.2% at most compared with those of using isobutane and isopentane, respectively. It could increase by 25.7% at most compared with that of single-pressure evaporation ORC using isobutane/isopentane mixtures. In terms of being introduced into dual-pressure evaporation ORC, the zeotropic mixture with a high critical temperature can generally achieve larger range in applicable heat source temperature and larger increment in the power output.

Energy, Thermal, and Economic Analysis of Air Heat Pumps for Hot Water

AbstractOperation tests of an air heat pump used for domestic hot water (DHW) heating were performed. The influence of the supply air temperature in the evaporator cycle and the variable heat load of the condenser on the heating power of the heat pump and the coefficient of performance (COP) was evaluated and discussed. In order to ensure conditions for efficient compressor operation, it is advisable to gradate the heat load of the heat pump using a circulating pump with smooth capacity regulation. The economic analysis demonstrates that the usage of air heat pumps for DHW in comparison with installations equipped with solar collectors provides no measurable economic benefits.

The role of air-sea coupling in the downscaled hydroclimate projection over Peninsular Florida and the West Florida Shelf

A comparative analysis of two sets of downscaled simulations of the current climate and the future climate projections over Peninsular Florida (PF) and the West Florida Shelf (WFS) is presented to isolate the role of high-resolution air-sea coupling. In addition, the downscaled integrations are also compared with the much coarser, driving global model projection to examine the impact of grid resolution of the models. The WFS region is habitat for significant marine resources, which has both commercial and recreational value. Additionally, the hydroclimatic features of the WFS and PF contrast each other. For example, the seasonal cycle of surface evaporation in these two regions are opposite in phase to one another. In this study, we downscale the Community Climate System Model version 4 (CCSM4) simulations of the late twentieth century and the mid-twenty-first century (with reference concentration pathway 8.5 emission scenario) using an atmosphere only Regional Spectral Model (RSM) at 10 km grid resolution. In another set, we downscale the same set of CCSM4 simulations using the coupled RSM-Regional Ocean Model System (RSMROMS) at 10 km grid resolution. The comparison of the twentieth century simulations suggest significant changes to the SST simulation over WFS from RSMROMS relative to CCSM4, with the former reducing the systematic errors of the seasonal mean SST over all seasons except in the boreal summer season. It may be noted that owing to the coarse resolution of CCSM4, the comparatively shallow bathymetry of the WFS and the sharp coastline along PF is poorly defined, which is significantly rectified at 10 km grid spacing in RSMROMS. The seasonal hydroclimate over PF and the WFS in the twentieth century simulation show significant bias in all three models with CCSM4 showing the least for a majority of the seasons, except in the wet June-July-August (JJA) season. In the JJA season, the errors of the surface hydroclimate over PF is the least in RSMROMS. The systematic errors of surface precipitation and evaporation are more comparable between the simulations of CCSM4 and RSMROMS, while they differ the most in moisture flux convergence. However, there is considerable improvement in RSMROMS compared to RSM simulations in terms of the seasonal bias of the hydroclimate over WFS and PF in all seasons of the year. This suggests the potential rectification impact of air-sea coupling on dynamic downscaling of CCSM4 twentieth century simulations. In terms of the climate projection in the decades of 2041–2060, the RSMROMS simulation indicate significant drying of the wet season over PF compared to moderate drying in CCSM4 and insignificant changes in the RSM projection. This contrasting projection is also associated with projected warming of SSTs along the WFS in RSMROMS as opposed to warming patterns of SST that is more zonal and across the WFS in CCSM4.

Silica accumulation rates for siliceous sinter at Orakei Korako geothermal field, Taupo Volcanic Zone, New Zealand

The rate of silica accumulation on glass slides over 895 days (2 years 5 months and 12 days) was determined using in-situ experiments in the discharge channel of Map of Australia hot pool, located at Orakei Korako, Taupo Volcanic Zone (TVZ), New Zealand. The discharge channel consisted of constantly flowing alkali chloride water with a temperature of 75 °C, pH of 7, 269 ppm silica, a flow rate of 1.4 l/s and mass flow of 1.36 kg/s. One slide was placed parallel to the flow, while another slide was perpendicular to the flow direction. Amorphous silica (opal-A spheres) deposited on both slides to form abiotic, sub-aerial, lily-pad textures which grew on basal sub-aqueous sinter structures. Lily-pad sinter forms by capillary motion of the water reaching and wetting the sub-aerial sinter surface, where the silica accretes to previously formed sinter surfaces parallel to the pool water level. In our experiment, silica deposition was greater in the horizontal direction than the vertical direction. Silica accumulation was up to four times greater on the front face of each slide. The maximum vertical and horizontal growth rates of sinter observed in our experiment were 3.9 and 7.6 mm/year, respectively. The observation that very little sinter grows below the water line is consistent with most of the sinter precipitating as a result of cycles of wetting, evaporation and drying. Quantitative calculations show that the observed growth rates are within the maximum amount of sinter expected to be deposited by evaporation. These measurements provide a constraint on the mass flow and time required to form siliceous sinter deposits of a known thickness, at extinct hot spring sites. Better constraining siliceous sinter growth rates improves our understanding and reconstruction of paleo-hydrological hot spring conditions.

Design and performance analyses for a novel organic Rankine cycle with supercritical-subcritical heat absorption process coupling

Organic Rankine cycle (ORC) is a promising heat-power conversion technology for renewable energy development and waste heat recovery. This study proposes a novel ORC that can couple supercritical and subcritical heat absorption processes. The proposed dual-pressure (supercritical + subcritical) heat absorption cycle can potentially better enhance the heat-power conversion efficiency compared with the existing cycle types. For the dual-pressure (supercritical + subcritical) heat absorption cycle, the heat absorption pressures and vapor generator outlet temperature were optimized to achieve the maximum net power output, and its thermodynamic and exergy performance was studied for various heat source temperatures. The thermodynamic performance superiorities of the proposed novel cycle over those of other cycle types were also quantitatively analyzed. Results show that the dual-pressure (supercritical + subcritical) heat absorption cycle has advantages of substantially increasing the system efficiency compared to the conventional subcritical and dual-pressure evaporation cycles, and remarkably increasing the heat absorption capacity compared to the transcritical cycle. For R1234ze(E), the maximum net power output of the dual-pressure (supercritical + subcritical) heat absorption cycle is the largest for heat source temperatures above approximately 135 °C, and it can increase by 19.9%, 49.8%, and 20.4% at most compared with those of the conventional subcritical, transcritical, and dual-pressure evaporation cycles, respectively. The external exergy efficiency is 92.4–94.9% for heat source temperatures of 150–200 °C which indicates that the heat source fluid and working fluid can achieve an excellent temperature match. For other five working fluids, the maximum net power outputs of the dual-pressure (supercritical + subcritical) heat absorption cycle are also the largest.

Trade study of advanced ballast control systems for an extraterrestrial submarine

Saturn's largest moon, Titan, has seas of cryogenic liquid methane and ethane as well as dynamic geology and a cycle of methane evaporation and rain. NASA is evaluating concepts for an extraterrestrial submarine to explore these seas from surface to bottom to shoreline, representing an unprecedented design challenge. The Titan submarine ballast system that controls the vertical ascent and descent must operate autonomously for a minimum of 365 dives in cryogenic seas below 95 K and handle liquid density variations up to 30%. Further complicating the concept is the high solubility of nitrogen gas in the seas, which leads to potential phase change and boiling issues during ballast pressure control. This paper presents a trade study of 7 advanced concepts for an autonomous submarine ballast system for Titan; 4 were down-selected as viable concepts. For each concept, analytical system description and sizing, autonomous concept of operation, parts list, and pros and cons are given. Systems are traded using mass, power, and complexity in control as metrics.

Subsurface treatment of TiO2 nanoparticles for limestone: Prolonged surface photocatalytic biocidal activities

We report on a new subsurface deposition method for treating porous stone surfaces with titanium dioxide nanoparticles. Limestone samples were semi immersed in a TiO2 sol so that nanoparticles could be transported via capillary diffusion into pores and grains to accumulate in the near surface region where they aggregated and attached to the walls as water evaporated. The white glazing layer formed on the surface was wiped off to facilitate further diffusion. A few cycles of immersion, evaporation, and surface cleanup were repeated until the amount of TiO2 reached a saturation level. Lab tests showed that nanoparticles loaded with this method are more difficult to remove than in the case of direct coating of the surface. Even after accelerated washing and drying cycles by spraying water equivalent to 5000 mm rainfalls the sample surface still preserved good antifungal activity against P. chrysogenum and C. cladosporioides whereas such effects disappeared after the same washing process for specimens directly coated with similar amount of TiO2 nanoparticles.

Greenhouse- and orbital-forced climate extremes during the early Eocene.

The Palaeocene-Eocene Thermal Maximum (PETM) was a significant global warming event in Earth's deep past (56 Mya). The warming across the PETM boundary was driven by a rapid rise in greenhouse gases. The event also coincided with a time of maximum insolation in Northern Hemisphere summer. There is increased evidence that the mean warming was accompanied by enhanced seasonality and/or extremes in precipitation (and flooding) and drought. A high horizontal resolution (50 km) global climate model is used to explore changes in the seasonal cycle of surface temperature, precipitation, evaporation minus precipitation and river run-off for regions where proxy data are available. Comparison for the regions indicates the model accurately simulates the observed changes in these climatic characteristics with North American interior warming and drying, and warming and increased river run-off at other regions. The addition of maximum insolation in Northern Hemisphere summer leads to a drier North America, but wetter conditions at most other locations. Long-range transport of atmospheric moisture plays a critical role in explaining regional changes in the water cycle. Such high-frequency variations in precipitation might also help explain discrepancies or misinterpretation of some climate proxies from the same locations, especially where sampling is coarse, i.e. at or greater than the frequency of precession.This article is part of a discussion meeting issue 'Hyperthermals: rapid and extreme global warming in our geological past'.

Measurement and modeling of the spatiotemporal dynamics of beach surface moisture content

Abstract The spatiotemporal dynamics of surface moisture exert a significant influence on the operation of aeolian transport systems at many beaches. However, we currently lack the detailed understanding of variability in surface moisture required to incorporate it into aeolian models. This problem is addressed here through direct measurements and simulation modeling of beach surface moisture over a twelve-day period, and through quantification of the relative contributions of evaporation, condensation and groundwater inputs to surface moisture. It was found that the beach surface can be characterized spatially in terms of three moisture zones: a consistently dry zone ( 40%). The relative influence of groundwater inputs was found to decrease moving landward, as the depth of the water table increased and the amplitude of tidally-induced water table fluctuations decreased. The critical pressure head (groundwater depth) at which evaporation begins to impose a demonstrable influence on surface moisture variability was found to be 90–100 cm. Temporally, beach surface moisture is a function of the lunar tidal cycle at longer-term time scales (weekly), and diurnal tidal and evaporation cycles. A numerical model was used to simulate capillary transfers of moisture from the water table to the surface, and moisture losses due to evaporation. The model was found to reliably replicate the measured spatiotemporal variability in surface moisture. In the dry zone, where most aeolian transport would be expected to occur, simulated moisture contents were typically within ±0.2% of measured volumetric contents.

Experimental Study of the Air Heat Pump for Domestic Hot Water

The article contains the results of the experimental research of the air heat pump for the preparation of domestic hot water (DHW). An installation consisting of a modular heat pump for hot water connected to two storage tanks with a capacity of 130 dm3 each was the object of the research. The article presents the results of investigations on the influence of the supply air temperature in the evaporator cycle and the variable heat load of the condenser on the heating capacity of the heat pump and the coefficient of performance (COP). The tests were carried out for water heating cycles in the storage tank from room temperature to 50 °C. The research shows that heating water in a 130 dm3 storage tank with ventilation or external air at a temperature above 15 °C takes an average of 2 h, and the heat pump consumes approx. 2.2 kWh of energy per heating cycle. Pump operation in winter is possible with the use of ventilation air, but with the discharge of air cooled outside the building. In order to ensure conditions for effective compressor operation, it is advisable to gradate heat load of the heat pump. The optimal solution is to use a circulating pump with smooth regulation of performance. The air source heat pump for DHW heating is an ideal solution for heating systems equipped with solid fuel boilers. It is a maintenance-free and economical system for producing domestic hot water outside the heating season.

Seasonal evaporation cycle in oxbow lakes formed along the Tisza River in Hungary for flood control

AbstractAs a result of water regulation, dykes (i.e., embankments against floods) were constructed along the Tisza River and meanders were cut to control the floods in the region. These cut‐off meanders resulted in oxbow lakes that are important locations for nature conservation. We collected water samples over 5 years in 7 campaigns to measure the δ18O (‰) and δ2H (‰) ratios in 45 oxbow lakes from the Upper Tisza Region (NE‐Hungary). We applied Random Forest Regression involving climatic data to reveal the connection with the stable isotopes. We determined that isotope ratios changed as a function of time, due to evaporation and a varying water supply (precipitation and groundwater). The average difference in the isotopic ratios for the river and oxbows increased from spring to winter, but decreased between the oxbows on both sides of the dyke. We found that isotope ratios were determined by the maximum monthly temperature in the case of oxbows in the active floodplain, whereas in case of oxbows on the reclaimed side, this was also influenced by the maximum monthly temperature, and the cumulative evaporation. As direct measurement of evaporation is difficult to evaluate, stable isotope measurements provided an effective quantitative alternative to estimate evaporation. Measuring the seasonality of the δ18O and δ2H is important to interpret the results and these data are useful to water management experts to identify the lakes at risk of running dry.

Culture of Chondracanthus teedei and Gracilariopsis longissima in a traditional salina from southern Spain

The cultivation of two red macroalgal species, Chondracanthus teedei (Martens ex Roth) and Gracilariopsis longissima (S.G. Gmelin) Steentoft M, L.M. Irvine & W.F. Farnham, was assessed in a traditional salina, a system of earthen ponds used for marine salt extraction taking advantages of solar evaporation and tidal cycle. Vegetative thalli of both species were cultivated in rafts holding polypropylene ropes, from January to June 2015, when lock-gates were opened during the period of no salt production. The effects of three factors in the net growth rate were analysed: seedling density, water motion and seasonality. Water motion and seasonality showed a significant effect in the growth of both species. Seedling density only showed a significant effect in the growth of Gp. longissima, where the growth rates improved at high seedling densities. Values of tissue N were generally lower than critical quotas, suggesting that maximum growth was limited by the concentrations of dissolved nutrients. In addition, the high salinity and temperatures in late spring seemed to condition the values of net growth rate. The study suggested that macroalgal cultivation of these two valuable species could be a promising complementary activity in the integrated management of the salina during winter and early spring, when salinity is lower than 40 PSU, if nutrients in the water are increased with the semi-intensive fish cultivation and the hydrodynamic conditions along the rafts are enhanced.

Seasonal and diurnal evaporation from a deep hypersaline lake: The Dead Sea as a case study

Evaporation plays a major role in lake systems, as it affects the water, energy and solutes budgets. Water salinity reduces evaporation, and as a result affects the energy budget of the lake, including stored heat. In this study, we explore the seasonal and diurnal variations of evaporation and other energy fluxes over the Dead Sea, the deepest and saltiest hypersaline lake on Earth. We present two consecutive years observations using Eddy Covariance system, meteorological stations and a buoy station measuring the water column properties. These observations reveal the effects of synoptic and mesoscale atmospheric circulation on lake evaporation. The seasonal cycle of evaporation is characterized by two peaks. The summer evaporation peak is related to high radiation inputs. The winter peak stem from the high heat storage of the deep lake, with evaporation driven by high vapor pressure demand, combined with synoptic scale wind systems and thermal instability. In summer, the synoptic circulation is stable, providing a weak background wind velocity (Persian trough), hence, the dominant diurnal wind pattern is induced by the Mediterranean Sea Breeze (mesoscale circulation). The two years of eddy covariance measurements in the hypersaline Dead Sea, located in a hyperarid region, revealed annual evaporation rate of 1.13 ± 0.13 m yr−1. We explored several evaporation models versus the directly measured evaporation, and found that the most reliable is a mass transfer model, that was calibrated here for the Dead Sea.

Dead Sea evaporation by eddy covariance measurements vs. aerodynamic, energy budget, Priestley–Taylor, and Penman estimates

Abstract. The Dead Sea is a terminal lake, located in an arid environment. Evaporation is the key component of the Dead Sea water budget and accounts for the main loss of water. So far, lake evaporation has been determined by indirect methods only and not measured directly. Consequently, the governing factors of evaporation are unknown. For the first time, long-term eddy covariance measurements were performed at the western Dead Sea shore for a period of 1 year by implementing a new concept for onshore lake evaporation measurements. To account for lake evaporation during offshore wind conditions, a robust and reliable multiple regression model was developed using the identified governing factors wind velocity and water vapour pressure deficit. An overall regression coefficient of 0.8 is achieved. The measurements show that the diurnal evaporation cycle is governed by three local wind systems: a lake breeze during daytime, strong downslope winds in the evening, and strong northerly along-valley flows during the night. After sunset, the strong winds cause half-hourly evaporation rates which are up to 100 % higher than during daytime. The median daily evaporation is 4.3 mm d−1 in July and 1.1 mm d−1 in December. The annual evaporation of the water surface at the measurement location was 994±88 mm a−1 from March 2014 until March 2015. Furthermore, the performance of indirect evaporation approaches was tested and compared to the measurements. The aerodynamic approach is applicable for sub-daily and multi-day calculations and attains correlation coefficients between 0.85 and 0.99. For the application of the Bowen ratio energy budget method and the Priestley–Taylor method, measurements of the heat storage term are inevitable on timescales up to 1 month. Otherwise strong seasonal biases occur. The Penman equation was adapted to calculate realistic evaporation, by using an empirically gained linear function for the heat storage term, achieving correlation coefficients between 0.92 and 0.97. In summary, this study introduces a new approach to measure lake evaporation with a station located at the shoreline, which is also transferable to other lakes. It provides the first directly measured Dead Sea evaporation rates as well as applicable methods for evaporation calculation. The first one enables us to further close the Dead Sea water budget, and the latter one enables us to facilitate water management in the region.

Thermodynamic analysis of a condensing evaporator in an evaporative gas turbine cycle

Low efficiency is the main stumbling block preventing the widespread adoption of small-scale gas turbines in distributed energy production. The evaporative gas turbine cycle has been proposed as a way to improve efficiency, but the large number of components required make the configuration complex and expensive. The condensing evaporator is a component that simplifies the evaporative gas turbine cycle. The heat and mass exchanger device is designed for an externally fired application, which means that the flue gas stream is replaced by moist air. The air-water mixture condenses inside a tube bank, releasing heat to the evaporating water film on the other side of the tubes. Similar inventions include the tubular humidifier and the Maisotsenko compressed air saturator, which also aim to make the evaporative gas turbine cycle more economically feasible. Available theory focuses on either humidification towers or evaporative condensers in HVAC applications. The tubular humidifier has been analyzed in a similar manner as humidification tower since the flow configurations of the two components are similar. However, the theory of humidification towers is not directly applicaple to the condensing evaporator. This study proposes a method of analysis of the condensing evaporator in power generation.

Diurnal Course of Evaporation From the Dead Sea in Summer: A Distinct Double Peak Induced by Solar Radiation and Night Sea Breeze

AbstractPartitioning between the relative effects of the radiative and aerodynamic components of the atmospheric forcing on evaporation is challenging since diurnal distributions of wind speed and solar radiation typically overlap. The Dead Sea is located about a 100 km off the Eastern Mediterranean coast, where and the Mediterranean Sea breeze front reaches it after sunset. Therefore, in the Dead Sea the peaks of solar radiation and wind speed diurnal cycles in the Dead Sea are distinctly separated in time, offering a unique opportunity to distinguish between their relative impacts on evaporation. We present mid‐summer eddy covariance and meteorological measurements of evaporation rate and surface energy fluxes over the Dead Sea. The evaporation rate is characterized by a clear diurnal cycle with a daytime peak, few hours after solar radiation peak, and a nighttime peak coincident with wind speed peak. Evaporation rate is minimum during sunrise and sunset. Measurements of evaporation rate from two other water bodies that are closer to the Mediterranean coast, Eshkol Reservoir, and Lake Kinneret, present a single afternoon peak, synchronous with the sea breeze. The inland diurnal evaporation rate cycle varies with the distance from the Mediterranean coast, following the propagation of sea breeze front: near the coast, wind speed, and radiation peaks are close and consequently a single daily evaporation peak appears in the afternoon; at the Dead Sea, about a 100 km inland, the sea breeze front arrives at sunset, resulting in a diurnal evaporation cycle characterized by a distinct double peak.

Electricity production from black liquor: a novel integrated system

Energy recovery from black liquor (BL) can be performed through gasification process at temperatures above the melting point of the inorganic chemicals. Complementing the BL gasification experimental research, this study is conducted to simulate the thermodynamic modeling of integrated system for BL evaporation, gasification and combined cycle for power generation. BL evaporation system is initially proposed based on the concept of exergy recovery which can minimize the exergy loss, hence lower the required energy input for evaporation. In the proposed BL evaporation system, higher target solids content leads to lower total required energy for BL evaporation. The lowest required total energy for evaporation can be achieved at target solids content of 75 wt% wb. Furthermore, an integrated power generation adopting gasification and combined cycle is modeled and application of different BL evaporation technologies is also evaluated in terms of net energy efficiency. The integrated system with exergy recovery-based evaporation can achieve the net energy efficiency of 34.5%, which is significantly higher than adoption of multi-effect evaporators (24.5%) and conventional boiler-based evaporation (14.7%).

Tracing sulfate recycling in the hypersaline Pétrola Lake (SE Spain): A combined isotopic and microbiological approach

Sulfur (S) plays a significant role in saline environments, and sulfate (SO42−) is an important component of the biogeochemical S-cycle since it acts as the main electron acceptor in anoxic sediments. The purpose of this paper is to evaluate the fate of S, its origin, and processes affecting sulfate outcome in the hypersaline Pétrola Lake in the Castilla-La Mancha region (High Segura Basin, SE Spain). The lake is the terminal discharge zone of an endorheic basin with considerable anthropogenic pressures. Anthropogenic activities (mainly agricultural inputs and wastewater discharge), together with bedrock leaching of sulfate and sulfide-rich sediments, increase dissolved SO42− in surface and groundwater up to 123,000mg/L. The source and fate of sulfate in this environment was investigated coupling hydrochemistry, including hydrogen sulfide (H2S) microprofiles, isotopic analyses (δ34S, δ18OSO4, δ2HH2O, δ18OH2O, and tritium), mineralogical determinations, and molecular biology tools (16S rDNA amplification and sequencing). The origin of dissolved SO42− in water is related to pyrite oxidation from Lower Cretaceous sediments, and secondary gypsum dissolution. Under the lake, dissolved SO42− decreases with depth, controlled by three main processes: (1) seasonal evaporation cycles, (2) hydrodynamic instability caused by the different density-driven groundwater flow, and (3) sulfate-reduction processes, i.e. dissimilatory bacterial sulfate reduction (BSR). These processes control the continuous recycling of sulfur in the system. Lake water and groundwater are in hydraulic connection, and a density-driven flow (DDF) is able to transport reactive organic matter and dissolved SO42− towards the underlying aquifer. Hydrochemical evolution in depth, H2S production (up to 0.024nmol/cm3·s) and the presence of sulfate-reducing bacteria suggest the existence of BSR processes. However, isotope techniques are insufficient to elucidate BSR processes since their isotopic effect is masked by low isotope fractionation and high SO42− concentrations. The pattern here described may be found in other saline basins worldwide.

Temporal dynamics of flooding, evaporation, and desiccation cycles and observations of salt crust area change at the Bonneville Salt Flats, Utah

The Bonneville Salt Flats (BSF) in Utah is a dynamic saline playa environment responding to natural and anthropogenic forces. Over the last century, the saline groundwater from below BSF has been harvested to produce potash via evaporative mining, mostly used as agricultural fertilizers, while the surface halite crust has provided a significant recreational site for land speed racing. Perceptions of changes in the salt crust through time have spurred debates about land use and management; however, little is known about the timescales of natural change as the salt crust responds to climatic parameters that drive flooding, evaporation, and desiccation (FED) cycles that control surface salt growth and dissolution. Climate data over the last ~30years are examined to identify annual patterns in surface water balance at BSF to identify annual and seasonal climate constraints on FED cycles. Landsat satellite data from 1986 to the present are used to map the areal extent of the surface halite salt crust at BSF at the end of the desiccation season (between August 15 and October 30) annually. Overall, the observed area of the desiccation-stage BSF halite crust has varied from a maximum of 156km2 in 1993 to a minimum of 72km2 in 2014 with an overall trend of declining area of halite observed over the ~30years of analysis. Climatic variables that influence FED cycles and seasonal salt dissolution and precipitation have also varied through this time period; however, the relationship between surface water fluxes and salt crust area do not clearly correlate, suggesting that other processes are influencing the extent of the salt. Intra-annual analyses of salt area and weather illustrate the importance of ponded surface water, wind events, and microtopography in shaping a laterally extensive but thin and ephemeral halite crust. Examination of annual to decadal changes in salt crust extent and environmental parameters at BSF provides insights into the processes driving change and the sustainability of land use in this dynamic environment.