Origins And Processes of Groundwater Salinization Beneath Playa Lake Aquifers In Iran: A Chemical And Stable Isotope Approach

Groundwater salinization and interaction between Playa Lake and regional groundwater was investigated using multi-chemo-isotopic evidences. Forty groundwater and 26 Kashan Playa Lake (KPL) water samples collected and analyzed for their geochemical compositions. The evolution of hydrochemical facies in Kashan Plain Aquifer (KPA) to KPL is Ca-HCO3 (19%), Mix Ca-Cl (9%), Ca-Cl (17%), and Mix Na-Cl and Na-Cl (55%). Also, the Hydrochemical Facies Evolution Diagram (HFE-D) proposed cation exchange as the main process of salinization in KPA. Based on the binary hydrogeochemical diagrams of (Na+/ Cl-)/Cl-, (Ca2++Mg2+)/HCO3-+SO42-, and Cl/Br, dissolution of halite and gypsum in the Miocene marlstone in the KPA is the main source of salinity. The isotopic composition δ18O in aquifer and playa water samples varies from -10.03 to 7.03‰ (VSMOW) with an average of -6.95 ‰ and -60.73 to 25.08 ‰ with average of -45.82 ‰ for δ2H. Based on the result, the relation between δ18O and δ2H, and δ18O and Br, approve discharge of saline water from KPA to KPL. Likewise, the isotopic composition of δ34SO4, varies from 5.95 to 22.55 ‰ CDT in KPA, and 5.95 to 9.99 ‰ CDT in KPL. Also, the relation between δ18O- δ34SSO4 and Cl- δ34S were non-linear, indicating that sulphur concentration in KPA and KPL changed due to sulphide oxidation and sulphate reduction in the freshwater and deep brines in the aquifer and mixed during the over-pumping in the KPA. Oxidation of sulphide minerals such as galena (PbS), and Chalcopyrite (CuFeS2) may have been the source of sulfur in Dore mine in western part of the aquifer (recharge zone) leached by seasonal runoff. In general, water–rock interaction, ion exchange, and hydraulic gradient have been the dominating factors in changing the water chemistry between aquifer and playa leading to saline groundwater discharged to the playa.

Holocene lake water-aquifer interactions in La Ballestera Playa-lake (southern Spain) recorded by stable isotopes (δ18O and δD) of gypsum hydration water

<p>Oxygen and hydrogen stable isotopes (δ<sup>18</sup>O and δD) of lake water are sensitive to long-term changes in environmental conditions, including relative humidity, temperature and the evaporation/outflow ratio of the lake. Lacustrine gypsum (CaSO<sub>4</sub>·2H<sub>2</sub>O) forms in equilibrium with its parent fluid, so the isotopic composition of its structurally bonded hydration water (GHW) can reflect the δ<sup>18</sup>O and δD of lake water at the time of mineral formation, with insignificant effects of temperature and salinity on the water-GHW isotope fractionation factors. Using the stable isotope content of gypsum-rich sediment cores as a paleoclimatic proxy, the environmental conditions prevailing in the lake setting at the time of gypsum crystallization can be investigated.</p><p>Here we apply this method to reconstruct the δ<sup>18</sup>O and δD of paleo-water in La Ballestera Playa-lake (Seville, southern Spain) throughout the Holocene, from 11.2 cal kyr BP to the present. Gypsum crystallization took place punctually at 11.2 and 4.4 cal kyr BP, and did continuously from 2.9 cal kyr BP to the present. The δ<sup>18</sup>O and δD showed the lowest values at ~11.2 cal kyr BP (2.3‰ and -1.1‰, respectively) and were significantly higher at ~4.4 cal kyr BP (8.8‰ and 29.2‰, respectively). Likewise, relatively higher values (8.2‰ and 29.8‰, respectively) were recorded at ~2.9 cal kyr BP. Thereafter, the isotopic ratios increased until the present (11.4‰ and 37.1‰, respectively), suggesting increasing aridity and/or hydrological closeness of the lake. A relative minimum in δ<sup>18</sup>O and δD occurred at ~2.3 cal kyr BP, during the wetter stage of the Iberian Roman Humid Period, while a relative maximum at ~1.1 cal kyr BP was recorded during the Medieval Warm Period.</p><p>We use a steady-state Isotope Mass Balance to investigate the paleo-hydrological conditions in the lake setting at different stages of the Holocene. Our results suggest that at ~11.2 cal kyr BP La Ballestera Playa-lake was a flow-through lake closely connected to the aquifer with and evaporation/outflow ratio <0.5. At 4.4 cal kyr BP and from ~2.9 cal kyr BP until the present, the system behaved as a terminal lake (evaporation/outflow ratio close to 1), with less connection to the aquifer and the main water output occurred via evaporation. The studied system turned into a playa lake because of a regional water table lowering. This most likely resulted from increasing aridity in southern Iberia during the late Holocene, which has previously been suggested by other lake sediment records in this region. </p><p> </p><p><strong>Acknowledgement</strong></p><p>This study was supported by the Junta del Andalucía PY18-871 to FG, the project<strong> </strong>CGL2017-85415-R of the Ministerio de Economía y Competitividad of Spain and Fondo Europeo de Desarrollo Regional FEDER, the project B-RNM-144-UGR18, Proyectos I+D+i del Programa Operativo FEDER 2018 and the research groups RNM-189 y RNM-190 (Junta de Andalucía). Dr. Antonio García-Alix acknowledges the Ramón y Cajal fellowship, RYC-2015-18966. Fernando Gázquez acknowledges the postdoctoral “HIPATIA” program of University of Almería.</p>

Late Holocene Sedimentation Dynamics in the Lake Ulaan Basin, Southern Mongolia: A History of a Playa Lake

Sedimentation dynamics in the Lake Ulaan basin located in the northern margin of the Govi region, southern Mongolia show high sedimentation rates of 11.8–22.7 cm/ka in the eastern part of the basin and low rates of 3.3–5.8 cm/ka in the western part during the late Holocene. The eastern and western parts of the lake have been strongly influenced by fluvial and aeolian activities since the arid late Holocene. However, fluvial sediment input was more significantly recorded in the eastern part. Aeolian deflation has been prevailing throughout the lake bank recently. Lake Ulaan reached its maximum extent before the early Holocene (Sternberg and Paillou, 2015; Holguin and Sternberg, 2016) with a water depth of ~43 m (Lehmkuhl et al., 2018a). After the early Holocene, Lake Ulaan started to decrease its area, and the drop of the lake level intensified since the middle Holocene. In the late Holocene, the лйоупы western and eastern parts were initially exposed to wind deflation at 2.7–3.2 cal. ka BP and the aerial exposition continued at 0.6–1.3 cal. ka BP. In the Anthropocene, Lake Ulaan has rapidly shifted into a playa lake condition during the last five to six decades, and it has become an open-source area of dust generation blown out by the westerly winds.

Hydroclimatic fluctuation in Lake Yakhi, eastern Mongolia

<p>This study aims to reconstruct paleoclimate change in eastern Mongolia inferred from sedimentological and geochronological records from Lake Yakhi in the drainage basin of the Pacific Ocean. In a context of the study goal the hydroclimatic fluctuation in eastern Mongolia resulted from Lake Yakhi is presented here. Result from changes in lake area of Lake Yakhi shows it decreased from 79.72 km<sup>2</sup> in 1970 to 53.76 km<sup>2</sup> in 1986 and 35.03 km<sup>2</sup> in 2018. The hydraulic dynamics and field observation show that Lake Yakhi is shifting into a playa lake. For shrinking Lake Yakhi, shifting toward a playa lake is directly related to the global warming, i.e., it implies the lake is extremely sensitive to climate change in the late Holocene. This coincides with those conditions of large lakes in the Govi region in southern Mongolia (Orkhonselenge et al., 2018). The major element compositions of the lake sediments show that the core Y18-1 is dominated by SiO<sub>2</sub>, Al<sub>2</sub>O<sub>3</sub>, K<sub>2</sub>O and Na<sub>2</sub>O, while the cores Y18-2 and Y18-3 largely contain SiO<sub>2</sub>, Al<sub>2</sub>O<sub>3</sub>, CaO and Fe<sub>2</sub>O<sub>3</sub>. In addition to the dominant semimetal and transition metal, presence of oxides of alkali earth metals in the core Y18-1 and of alkaline earth metals in the cores Y18-2 and Y18-3 show a derivation of intermediate sedimentary and volcanic rocks in the drainage basin of Lake Yakhi. This coincides with the tectonostratigraphic terrane structure of the cratonal clastic sedimentary rocks (Badarch et al., 2002) in the Lake Yakhi area. Further detail geomorphological and geochronological records from Lake Yakhi would not review only the hydrogeochemical evolution, but the paleoclimate changes in eastern Mongolia. Leading the dates would precisely determine the paleohydroclimatic fluctuations in eastern Mongolia.</p>