Evaporation from the dried-up lake bed of Lake Urmia, Iran.

Lake Urmia in north-western Iran was once one of the world's largest hyper-saline lakes and represented a unique ecosystem for a number of endangered species. The lake's shrinking over the past decades has attracted considerable attention and several studies have addressed its water balance. Yet, evaporation of shallow groundwater from the dried-up lake bed has not been fully quantified - despite the appreciable size of these areas (approx. 4000 km2 in summer 2015). Here, we target this water cycle component by combining column experiments with upscaling and regionalisation techniques. In the experiments, we studied evaporation from two undisturbed soil cores from the exposed lake bed in a climate chamber, mimicking diurnal temperature and humidity variations in the three summer months of the study area. Despite the dropping water levels in the columns and the formation of salt crusts, evaporation rates remained remarkably constant (0.12 and 0.20 mm d-1). This suggests that the system is not driven by slow vapour diffusion, but controlled by capillary rise in the fine-grained sediments, ensuring steady water supply to the column surface. Thus, evaporation from the dried-up lake bed can be assumed to be largely independent from the unsaturated zone thickness (within the observed water level range) and evaporation rates can be simply upscaled and regionalised by considering the satellite-derived development of dried-up lake bed areas (1998-2020). In this time-period, estimated summer evaporation from the exposed lake bed reached maximum values of 0.04 and 0.07 km3 (summer 2015). While these absolute numbers are significant (comparable to the catchment's annual urban drinking water consumption), they correspond to only 4 and 7 % of the evaporation from the open lake surface (1.06 km3).

Processes controlling the extent of groundwater pollution with chromium from tanneries in the Hazaribagh area, Dhaka, Bangladesh.

The Hazaribagh industrial area in Dhaka city, the capital of Bangladesh, is considered one of the hotspots of chromium (Cr) pollution, due to excessive discharge of Cr contaminated waste over decades by approximately 150 tanneries. In 2000, elevated Cr concentrations were observed in the underlying Dupi Tila Aquifer (DTA), which is heavily deployed for drinking water supply of Dhaka city's population. In the following years, Cr concentrations in the DTA have dropped and apparently stayed low. In 2010, elevated Cr concentrations were found again in the DTA. This study aims to evaluate the status of the total Cr contamination in the surface waters, groundwater, and soils in the area, to clarify the temporal evolution of the total Cr contamination pattern in the DTA. For this, we collected water and soil samples in 2012, 2013, 2014, and 2019 for (hydro)chemical characterization and analyzed new groundwater level data on the development of the cone of depression below the city. Our study indicates that the temporal evolution of the total Cr contamination in the DTA is closely coupled to the groundwater dynamics. The rapid growth of the cone of depression due to excessive pumping resulted (i) in a disconnection of the groundwater table from the heavily contaminated Hazaribagh soils, and (ii) in an increased gradient between the contaminated surface waters and the groundwater, increasing infiltration into the groundwater. Finally, (iii) the further growth of the cone of depression resulted in an inflow of fresh groundwater from the west of Dhaka city, causing a dilution effect. Although in 2017 tanneries were moved out of the Hazaribagh area, the contaminated soils still pose a threat to groundwater quality when groundwater levels would recover.

Middle palaeolithic and neolithic occupations around Mundafan Palaeolake, Saudi Arabia: implications for climate change and human dispersals.

The Arabian Peninsula is a key region for understanding climate change and human occupation history in a marginal environment. The Mundafan palaeolake is situated in southern Saudi Arabia, in the Rub' al-Khali (the 'Empty Quarter'), the world's largest sand desert. Here we report the first discoveries of Middle Palaeolithic and Neolithic archaeological sites in association with the palaeolake. We associate the human occupations with new geochronological data, and suggest the archaeological sites date to the wet periods of Marine Isotope Stage 5 and the Early Holocene. The archaeological sites indicate that humans repeatedly penetrated the ameliorated environments of the Rub' al-Khali. The sites probably represent short-term occupations, with the Neolithic sites focused on hunting, as indicated by points and weaponry. Middle Palaeolithic assemblages at Mundafan support a lacustrine adaptive focus in Arabia. Provenancing of obsidian artifacts indicates that Neolithic groups at Mundafan had a wide wandering range, with transport of artifacts from distant sources.