Seasonal Intermittent Wetlands at the Desaguadero River. Argentine. Past, Present and Future Morphodynamics

The Desaguadero River comprises the upper section of a major hydrological system called Desaguadero-Salado-Chadileuvú-Curacó, located in the central-western sector of Argentina, on the eastern edge of the Diagonal Árida Sudamericana climatic belt. Within this basin, extensive wetlands have developed at the confluence of two main Andean rivers, the Mendoza and San Juan rivers, and from the surface flows generated during floods associated with the mountain ice and snow melts on the catchment area. The water from these rivers was channeled along the Desaguadero river, a north-south approximately 150 km long channel. This paper proposed the Desaguadero river wetlands as a product of co-development of ephemeral lakes and lunettes dunes, based on geomorphological surveying and field work supported by stratigraphical analyses of relict lake-shores and fluvial sedimentary deposits along with historical climatic data. The morphodynamic activity of these wetlands gradually decreased since the end of the 19th century until practically disappeared in the 20th century, due to both natural and anthropic causes.

High-resolution bathymetry mapping of shallow and ephemeral desert lakes using satellite imagery and altimetry

<p>Many of the world’s drylands are characterized by interior drainage systems that terminate at shallow desert lakes or playas. Except for episodic flooding these largely ephemeral water bodies, remain mostly dry. Surveying and mapping their respective floor topography in a suitable resolution for calculating water balance is a difficult and laborious task. As this is crucial for water resources management and reconstructing paleoenvironmental conditions, diverse methods and efforts were applied. However, detailed, high-quality bathymetric surveys in such environments are rare and have only been conducted in a few such lakes. This is primarily due to their shallow, low-relief, large areas, and often remote characteristics, which complicate application of conventional topographic surveying techniques.  Therefore, satellite-based remote sensing is an essential complementary approach for deriving bathymetry of such lakes.</p><p>Global digital elevation models, such as NASA’s Shuttle Radar Topography Mission (SRTM) or ASTER’s GDEM, are unsuitable for accurate measurements of these ephemeral lakes, mainly because of their impenetrability to water and their high signal-to-noise ratio in the low-relief environments. Recent studies addressed these complications by combining remote sensing data with local calibrations of in-situ measurements, or alternatively, by relating shoreline altitudes with precise altimetry. This approach requires a spatial interpolation of individual measurements. Therefore, it is prone to errors that demand intensive efforts to be reduced; even then the errors may remain larger than the actual depth of a flooded lake. Moreover, such methods are hard to apply in complex lakes with multiple sub-basins.</p><p>To tackle these problems, we developed a simple methodology to derive a high-resolution (30 m per pixel) bathymetry of shallow desert lakes. In this new method we combine two sources of data: a >30-yr record of Landsat-derived surface water occurrence data; and accurate high-resolution elevation data, acquired by the NASA’s recently launched ICESat-2 satellite (Ice, Cloud, and Land Elevation Satellite-2). We test the proposed new method over three ephemeral lakes around the world: Lake Eyre, Australia, with its complex shallow lake system, consisting of a few sub-basins; Sabkhat Al-Mellah, Algeria; Lago Coipasa, Bolivia. The accuracy of the resulted bathymetric maps was evaluated using cross-validation of ICESat-2 scans, yielding low RMSD values of ~0.3 m, versus ~2.5 m of the SRTM data (validated through other ICESat-2 scans). At Lago Coipasa, we show that bathymetry was effectively determined even when the lake was full of water (up to a few meters depth). This high-resolution, low-error bathymetry mapping complement other globally available topographic data.</p>

Seasonal and Diurnal Variations in the Priestley–Taylor Coefficient for a Large Ephemeral Lake

The Priestley–Taylor equation (PTE) is widely used with its sole parameter (α) set as 1.26 for estimating the evapotranspiration (ET) of water bodies. However, variations in α may be large for ephemeral lakes. Poyang Lake, which is the largest freshwater lake in China, is water-covered and wetland-covered during its high-water and low-water periods, respectively, over a year. This paper examines the seasonal and diurnal variations in α using eddy covariance observation data for Poyang Lake. The results show that α = 1.26 is overall feasible for both periods at daily and subdaily scales. No obvious seasonal trend was observed, although the standard deviation in α for the wetland was larger than that for the water surface. The mean bias in evaporation estimations using the PTE was less than 5 W·m−2 during both periods, and the root mean square errors were much smaller than the average evaporation measurements at daily scale. U-shaped diurnal patterns of α were found during both periods, due partly to the negative correlation between α and the available energy (A). Compared to the vapor pressure deficit (VPD), wind speed (u) exerts a larger contribution to these variations. In addition, u is positively correlated with α during both periods, however, VPD was positively and negatively correlated with α during the high-water and low-water periods, respectively. Subdaily α exhibited contrasting clusters in the (u, VPD) plane under the same available energy ranges. Our study highlights the seasonal and diurnal course of α and suggests the careful use of PTE at subdaily scales.

The carbonates of the post-Variscan basins of Sardinia: the evolution from Carboniferous–Permian humid-persistent to Permian arid-ephemeral lakes in a morphotectonic framework

Late to post-Variscan sedimentary basins of Sardinia were influenced during Pennsylvanian to Permian times by two main tectono-sedimentary cycles: a Pennsylvanian to Cisuralian cycle represented mainly by dark limnic deposits, overlain by a Guadalupian to a possibly Lopingian cycle, mostly characterized by red-bed deposits. Lacustrine waterbodies developed in some sedimentary basins that were filled with siliciclastic to frequently early silicified carbonate deposits, depending on the climate and environmental conditions, landscape morphology and tectonic regime. The limnic successions of the lower tectono-sedimentary cycle were deposited in permanent, tens of metres deep lakes in deep, narrow tectonic strike-slip basins under a temperate to warm-humid climate. They started as lakes with terrigenous sedimentary input and developed minor carbonate deposits mainly at the end of their story. Conversely, the red-bed successions of the upper cycle were deposited in ephemeral, shallow playa lakes related to wider basins in an extensive alluvial plain under a hot and arid climate. Here, the siliciclastic sediments are intercalated with thin carbonate beds that are typical of a high evaporation rate. The evolution of the lake type could be related not only to a major climatic shift, but also to the changing morphotectonic conditions of the Variscan chain influencing the local microclimate. Comparisons with coeval successions in the Provence Basin, the Massif Central Aumance basin (France) and the Saar–Nahe Basin (Germany) show both similarities and differences between the basins.

Assessment of the dust sources over Central and Southwest Asia with emphasis on the Sistan dust storms

Central and Southwest (SW) Asia are usually suffered by dust events of various intensity due to extended arid/desert regions and, therefore, the statistical evaluation of the dust activity and sources over the region has received an increasing interest. This study analyses the characteristics of the dust events and their sources over the Central and Southwest Asia from 2002 to 2018, based on meteorological observations at stations in Turkmenistan, Uzbekistan, Iran, Afghanistan and Pakistan, combined with Aerosol Optical Depth (AOD) at 10 km × 10 km derived from MODIS and a new 1-km high resolution algorithm. The dust events are classified based on visibility recordings and WMO codes, as dusty days (vis<10 km) and dust storms for visibility below 1 km. In general, the highest frequency of the dust storms is observed in the Sistan Basin, Iran and around the deserts of southern Afghanistan, while the dust-plume pathways have a distinct north-to-south pattern, from Central Asia to SW Asia and the Arabian Sea. Trend analysis in the Deep Blue MODIS AOD retrievals shows positive AOD trends over large parts of the Central Asia and negative over the Southwest Asia and Sistan. High resolution (1-km) AODs indicated that some parts of the Hamoun ephemeral lakes and the eastern part of the Sistan basin are the most active hotspot areas for dust emissions.

HOLOCENE EVOLUTION OF THE PEAT-BOG IN SŁUPIAŃSKA BAY (WIGRY LAKE, NE POLAND) IN THE LIGHT OF MALACOLOGICAL ANALYSIS

Three types of molluscan assemblages have been identified in a profile of calcareous gyttja and peat penetrated by drilling within the raised peat-bog of the Słupiańska Bay. Numerous shells of molluscs have been identified within the 5.35 m thick intervals of fine detritus of the calcareous gyttja. The shells belonged primarily to the bivalves and water snails. Terrigenous species appeared only rarely and have been more frequent in the upper part of the penetrated interval. The three distinguished molluscan assemblages have been described and interpreted in terms of representing different environmental conditions. Assemblage with Gyraulus laevis that occurs within the lower part of the interval consists of the cold-loving forms representing early Holocene. Assemblage with Gyraulus albus that occurs in the middle part of the interval consists of warm-loving species linked to the Atlantic Phase. Assemblage with terrigenous species, mainly snails, occurs in the upper part of the interval. The distinguished types of molluscan assemblages are composed of species characteristic of littoral habitat of ephemeral lakes and some of terrestrial habitats. Lake-level fluctuations are expressed by changing of molluscan fauna. Variable proportions of Bithynia tentaculata shells and opercula indicates low-level water stages of the Wigry Lake that took place during the Boreal Phase, the middle part of the Atlantic Phase and during the termination of the Sub Boreal and Sub Atlantic phases. The completion of gyttja accumulation and the beginning of peat deposition are associated with the latter period.

Non-marine palaeoenvironment associated to the earliest tetrapod tracks

Opinions differ on whether the evolution of tetrapods (limbed vertebrates) from lobe-finned fishes was directly linked to terrestrialization. The earliest known tetrapod fossils, from the Middle Devonian (approximately 390 million years old) of Zachełmie Quarry in Poland, are trackways made by limbs with digits; they document a direct environmental association and thus have the potential to help answer this question. However, the tetrapod identity of the tracks has recently been challenged, despite their well-preserved morphology, on account of their great age and supposedly shallow marine (intertidal or lagoonal) depositional environment. Here we present a new palaeoenvironmental interpretation of the track-bearing interval from Zachełmie, showing that it represents a succession of ephemeral lakes with a restricted and non-marine biota, rather than a marginal marine environment as originally thought. This context suggests that the trackmaker was capable of terrestrial locomotion, consistent with the appendage morphology recorded by the footprints, and thus provides additional support for a tetrapod identification.

Activation of a small ephemeral lake in southern Jordan during the last full glacial period and its paleoclimatic implications

Playas, or ephemeral lakes, are one of the most common depositional environments in arid and semiarid lands worldwide. Playa deposits, however, have mostly been avoided as paleoclimatic archives because they typically contain exceptionally low concentrations of organic material, making14C dating difficult. Here, we describe a technique for concentrating organic matter in sediments for radiocarbon dating and apply it to playa sediments recovered from a 2.35 m sediment core from a small playa in southern Jordan. Based on14C ages of the organic concentrate fraction, the playa was active from ~29 to 21 ka, coincident with the last major high stand of Paleolake Lisan and wet conditions recorded by other paleoclimatic proxies in the southernmost Levant during the last full glacial period (35–20 ka). The timing and spatial pattern of these records suggests that the increased moisture was likely derived from more frequent and deeper eastern Mediterranean (EM) cyclones associated with the intensification of the westerlies. The presence of full glacial pluvial deposits in southern Jordan (29°N), and the lack of similarly aged deposits in the northern Arabian Peninsula to the south, suggests that the southerly limit of the incursion of EM cyclones during last full glacial period was ~28°N.