Lake Level Variations Research Articles

A First Reliable Gravity Tidal Model for Lake Nasser Region (Egypt)

In the framework of the French–Egyptian Imhotep Project, two spring gravimeters have been installed in the area of Lake Nasser (Egypt) with the aim to establish a first reliable gravity tide model for the region. The two tidal gravity stations are located in Aswan, on the northern edge of the lake and in Abu Simbel in the south, respectively. This study was mainly aimed to obtain a reliable model of the crustal response to tidal forces and, consequently, to increase the accuracy of the geodetic observations, to be used in future geophysical studies in this region as well as to investigate the effect of the Lake level variations on the crustal deformation and related gravity changes. Nearly 3 years of gravity records (from May 2018 to April 2021) were collected. Since no scale factor was available for the two gravimeters, the first step of this study was to achieve a reliable calibration for each of the two collected gravity signals. After removing the instrumental drift, spikes, steps and tares, both gravimeters have been calibrated by fitting the output signal against a synthetic reference signal based on the body tidal gravity response due to Wahr-Dehant Earth model and FES2014 ocean tidal loading model. The calibrated signals have been analyzed with ET34-X-V80 software for tidal analyses. This enabled us to retrieve a set of frequency-dependent gravity factors (amplitude and phase) for the main tidal waves, as well as to obtain gravity residuals. It turns out that the accuracy of the amplitude estimates for the main tidal waves is 0.2 ÷ 1% for LCR_ET16 in Aswan and 1 ÷ 10% for the LCR_D-218 in Abu Simbel. To improve the tidal model at Abu Simbel, LCR_ET16 was stopped in Aswan and relocated there. The first 90 days of gravity recordings from ET16 at Abu Simbel provide promising results, with an accuracy of the order of 0.1% for the main tidal waves, even better than the results obtained in Aswan. The residual gravity signal after tidal subtraction at Aswan is in the range of ± 50 µGal. Further analyses of the instrumental contribution are however needed before to be able to interpret this gravity signal in terms of surface loading (i.e. changes in the water level of Lake Nasser) or underground hydrology.

Remote Sensing Application for Landslide Detection, Monitoring along Eastern Lake Michigan (Miami Park, MI)

We assessed the nature and spatial and temporal patterns of deformation over the Miami Park bluffs on the eastern margin of Lake Michigan and investigated the factors controlling its observed deformation. Our approach involved the following steps: (1) extracting bluff deformation rates (velocities along the line of sight of the satellite) using a stack of Sentinel-1A radar imagery in ascending acquisition geometry acquired between 2017 and 2021 and applying the Intermittent Small Baseline Subset (ISBAS) InSAR time series analysis method; (2) generating high-resolution (5 cm) elevation models and orthophotos from temporal unmanned aerial vehicle (UAV) surveys acquired in 2017, 2019, and 2021; and (3) comparing the temporal variations in mass wasting events to other relevant datasets including the ISBAS-based bluff deformation time series, lake level (LL) variations, and local glacial stratigraphy. We identified areas witnessing high line-of-sight (LOS) deformation rates (up to −21 mm/year) along the bluff from the ISBAS analysis and seasonal deformation patterns associated with freeze-thaw cycles, suggesting a causal effect. The acceleration of slope failures detected from field and UAV acquisitions correlated with high LLs and intensified onshore wave energy in 2020. The adopted methodology successfully predicts landslides caused by freezes and thaws of the slope face by identifying prolonged slow deformation preceding slope failures, but it does not predict the catastrophic landslides preceded by short-lived LOS deformation related to LL rise.

Machine-Learning Functional Zonation Approach for Characterizing Terrestrial–Aquatic Interfaces: Application to Lake Erie

Ecosystems at coastal terrestrial–aquatic interfaces play a significant role in global biogeochemical cycles. In this study, we aimed to characterize coastal wetlands with particular focus on the co-variability between plant dynamics, topography, soil, and other environmental factors. We proposed a functional zonation approach based on machine learning clustering to identify the spatial regions, i.e., zones that capture these co-varied properties. This approach was applied to publicly available datasets along Lake Erie, in the Great Lakes Region. We investigated the heterogeneity of coastal ecosystem structures as a function of along-shore distance and transverse distance, based on the spatial data layers, including topography, wetland vegetation cover, and the time series of Landsat’s enhanced vegetation index (EVI) between 1990 and 2020. Results showed that the topographic metrics (elevation and slope), soil texture, and plant productivity influence the spatial distribution of wetland land-covers (emergent and phragmites). These results highlight a natural organization along the transverse axis, where the elevation and the EVI increase further away from the coastline. In addition, the clustering analysis allowed us to identify regions with distinct environmental characteristics, as well as the ones that are more sensitive to interannual lake-level variations.

Sedimentary Characteristics of Lacustrine Beach-Bars and Their Formation in the Paleogene Weixinan Sag of Beibuwan Basin, Northern South China Sea

Beach-bar reservoirs have been promising hydrocarbon-bearing exploration advances in the Beibuwan Basin, especially in the WZ12-2 area within the Weixinan sag. The sedimentary characteristics, distribution and formation mechanisms of beach-bar sand bodies in Mbr2 (Member 2) of the Paleogene Liushagang Fm. in the WZ12-2 area within the Weixinan sag were analyzed based on well-log, seismic and core data on thin section and heavy mineral data. Mbr2 in the WZ12-2 area comprises a third-order sequence, which consists of three systems tracts (lowstand systems tract, transgressive systems tract and a locally developed highstand systems tract). Thick beach-bar sand bodies are developed in the WZ12-2 area during the lowstand systems tract stage. The formation of sandy beach-bar sand bodies can be divided into five stages. By integrating lithology, mineral composition, sedimentary structures and geophysical characteristics, it can be concluded that the beach-bar sand bodies in the study area were controlled by paleotopography, hydrodynamic environment, sediment provenance and lake-level variation. The gentle slope of the Qixi uplift and relatively stable passive tectonic background during the deposition of Mbr2 of the Liushagang Fm. laid a solid paleogeomorphological foundation for beach-bar deposition. Strong hydrodynamic forces and shallow water further contributed to beach-bar sand bodies formation. In addition, the sands in the fan delta in the northwestern part of the area served as point provenance and the deposits in the southeast acted as linear provenance in providing sediments to the beach-bars. High-frequency variations of the lake level drove vertical stacking of the beach-bar sand bodies and considerable lateral extension over a large area. The sedimentary characteristics and formation mechanism of lacustrine beach-bars in this study may provide a reference for hydrocarbon exploration in other similar basins in the world.

The persistent lake level decreasing induced Phragmites peatland development in the Bosten Lake (Northwest China) during the Medieval Warm Period

Northwest China (NW China) falls within Arid Central Asia (ACA) and has a climate dominated by westerly winds, a fragile ecosystem, and a high sensitivity to climate change. Paleoenvironmental reconstructions of this region can assist in understanding the general processes contributing to environmental variation in such arid areas. This study examined a dated sedimentary core containing both peat and lacustrine deposits obtained from the shore of the Bosten Lake, NW China. The study aimed to reconstruct paleoenvironmental variations over the last 3,000 years and to explore the possible drivers of peatland development over the last millennium. An examination of grain size and δ13C was conducted to investigate lake level variation. The results showed that the lake level of the Bosten Lake declined gradually between 2,905 and 480 cal yr BP and increased thereafter, consistent with other records of the Bosten Lake. At a centennial timescale, the lake level was high under a wet climate during the Dark Age Cold Period (DACP), whereas it decreased significantly during the Medieval Warm Period (MWP). The inferred “cold and wet” and “warm and dry” patterns indicated climatic characteristics of a “westerlies-dominated climatic regime”. In addition, the persistent decreasing lake level during the MWP resulted in Phragmites peatland initiation and development along the shores of the Bosten Lake.

Multi-variate regression analysis of lake level variability: A case of semi-closed, shallow rift valley lake in Northern Tanzania

Lakes are very important for domestic use, commercial purposes, and ecosystem sustenance; nevertheless, studies on how different stressors influence water resources are limited, posing challenges in the planning and managing of water resources. Lake Babati is one of the important lakes in the East African rift valley as a source of fish, drinking water, and hippopotamus habitat. The lake level has consistently declined, threatening the life of organisms depending on the lake. Nevertheless, no study postulated the reasons for its decline. Therefore, this study used statistical methods, regression analysis and HEC-HMS hydrological model to investigate the association and sensitivity of the hydrological components driving the lake level variability. Results showed that the Lake Babati level was significantly declining (p < 0.01) at a rate of 0.025 m yearly. The lake level variability was most sensitive to inflow, while outflow and evaporation had almost equivalent magnitude in driving the lake level variability and direct rainfall had the least influence. Although the lake level variability corresponded to changes in the basin supply components, the declining lake level trend was neither directly related to lake evaporation nor inflow as both parameters showed no significant trends. Furthermore, groundwater abstraction within the lakeshore is smaller than lake evaporation and is unlikely the main driver of the decline in lake level. Therefore, the declining lake level seemed related to the spillway outflow, which had been improved to avoid lake flooding resulting in large outflow during the peak seasons and probably the reason for the significant decline in the lake levels even in the rainy seasons. This study benchmarked the most sensitive hydrological drivers influencing lake level whose accurate monitoring and management could rescue the situation.

New ornithopod tracks from the Lower Cretaceous El Castellar Formation (Spain): Implications for track preservation and evolution of ornithopod footprints

Dinosaur tracks have been identified in several Upper Jurassic-Lower Cretaceous sedimentary units across the Maestrazgo Basin in eastern Iberia, which are preserved in a variety of transitional and continental paleoenvironments. Here, we described the lower Barremian San Benón tracksite with the first occurrence of clear dinosaur tracks in the El Castellar Formation within the Galve subbasin. This palustrine-lacustrine formation has yielded a rich osteological record although dinosaur tracks are notably scarce. The new footprints represent an uncommon case of dinosaur track preservation since the site has yielded several non contemporary tracks (part of different ichnoassemblages) preserved as carbonate casts at the base of a limestone bed forming a composite ichnofabric. The tracksite shows a complex history of sedimentation, track production and preservation linked to the lake level variations. The ornithopod tracks are identified to belong to the ornithopod ichnogenus Caririchnium , concretely to the ichnospecies C. magnificum. The studied tracks represent the oldest occurrence of this ichnotaxa in the Maestrazgo Basin and are coherent with other coeval (or almost coeval) occurrences in the Iberian Peninsula. The presence of C. magnificum in the El Castellar Formation fills a gap between the oldest (Tithonian-early Valanginian?) and younger (Barremian) occurrences of ornithopod tracks within the Maestrazgo Basin, being one of the most complete successions of ornithopod tracks in Europe. Interestingly, the underlaying formations have ichnoassemblages with Dinehichnus -like and Iguanodontipus -like tracks, whereas Caririchnium is mainly found in El Castellar Formation and other Barremian units. These changes in the ichnoassemblages reflect the ornithopod faunal changes shown by osteological data in the Iberian Peninsula recording a Late Jurassic-earliest Cretaceous stage dominated by basal iguanodontians followed by an Early Cretaceous stage with abundance of more derived and large-sized iguanodontians. • First occurrence of clear dinosaur tracks in the lacustrine El Castellar Fm in the Galve subbasin. • Uncommon case of dinosaur footprint preservation as casts in carbonates. • Complex history of sedimentation and track production linked to the lake level. • First occurrence of Caririchnium magnificum in the Maestrazgo Basin (Iberian Peninsula). • Ornithopod faunal changes during the Late Jurassic/Early Cretaceous.

Abrupt changes in the physical and biological structure of endorheic upland lakes due to 8‐m lake‐level variation during the 20th century

AbstractClimate‐induced variation in lake level can affect physicochemical properties of endorheic lakes, but its consequences for phototrophic production and regime shifts are not well understood. Here, we quantified changes in the abundance and community composition of phototrophs in Kenosee and White Bear lakes, two endorheic basins in the parkland Moose Mountain uplands of southeastern Saskatchewan, Canada, which have experienced &gt; 8 m declines in water level since ~ 1900. We hypothesized that lower water levels and warmer temperatures should manifest as increased abundance of phytoplankton, particularly cyanobacteria, and possibly trigger a regime shift to turbid conditions due to evaporative concentration of nutrients and solutes. High‐resolution analysis of sedimentary pigments revealed an increase in total phototrophic abundance (as β‐carotene) concurrent with lake‐level decline beginning ~ 1930, but demonstrated little directional change in cyanobacteria. Instead, significant increases in obligately anaerobic purple sulfur bacteria (as okenone) occurred in both lakes during ~ 1930–1950, coeval with alterations to light environments and declines in lake level. The presence of okenone suggests that climate‐induced increases in solute concentrations may have favored the formation of novel bacterial habitats where photic and anoxic zones overlapped. Generalized additive models showed that establishment of this unique habitat was likely preceded by increased temporal variance of sulfur bacteria, but not phytoplankton or cyanobacteria, suggesting that this abrupt change to physical lake structure was unique to deep‐water environments. Such climate‐induced shifts may become more frequent in the region due to hydrological stress on lake levels due to warming temperatures across the Northern Great Plains.

Characteristics and driving factors of lake level variations by climatic factors and groundwater level

Hongjiannao Lake (HL), the largest desert freshwater lake in China, has been undergoing quickly evolution of lake area during the past 30 years. The causes and driving mechanism of such changes, however, are still not well understood. The evolution process can be divided into three phases: the stationary phase, the shrinking phase, and the rising phase, which were affected by climate change and human activities, such as unreasonable utilization and water diversion. Here, wavelet coherence was used to analyze the relationship between the groundwater level and the lake level, and the results shown that groundwater levels in the lakeshore region were positively correlated to lake level within a short lag period of approximately 30 days. Then a gradient boosting decision tree-based regression model was applied to analyze the relative importance of climatic factors (model 1) and both of climatic factors and groundwater level (model 2) to the lake level. In model 1, the most important factor was the evaporation to the HL level, while in model 2, it was the groundwater level and the evaporation, which also achieved better prediction performance. Finally, using the 2021 meteorological data and groundwater level, model 2 was utilized to dynamically predict the daily water level of the HL, showing that the lake level fluctuated upward.

A multi-isotope and modelling approach for constraining hydro-connectivity in the East African Rift System, southern Ethiopia

During the last African Humid Period (AHP; 15–5 ka), many lakes in the East African Rift System (EARS) experienced pronounced lake-level variations that dramatically transformed the hydrological landscape. Currently dry, saline or marshy-wetland terminal lakes became vast waterbodies, interconnected via overflow sills resulting in the formation of a several thousand-kilometre-long chain of lakes in the EARS. A quantitative, process-based understanding of these hydrological systems can advance our interpretation of past hydroclimate variability from proxy records. Here, we provide a critical modern hydrological dataset for the data-sparse Lake Chew Bahir basin in southern Ethiopia. Driven by modern data, an isotope-enabled hydro-balance model was developed to assess how increases in rainfall modulate δ18O and 87Sr/86Sr variability. Considering a terminal Lake Chew Bahir scenario, humid conditions resulted in higher lake δ18O (∼+14‰) due to increased evaporation and longer water residence times. At the same time 87Sr/86Sr decreased from 0.7064 to 0.7061 due to an increased riverine Sr flux characterised by lower, unradiogenic 87Sr/86Sr ratios. In a modelling scenario where Lake Chew Bahir became a flow-through system with interconnectivity between lakes Abaya, Chamo, Chew Bahir and Turkana, higher lake δ18O (∼+12‰) relative to present was found, but δ18O was lower than in the terminal lake scenario. The lake water 87Sr/86Sr ratios (<0.7061) were also slightly lower. A moderate concomitant change in rainfall input δ18O of −1‰ in step with hydrological reorganisation resulted in the lowest lake δ18O (∼+5‰). Modelled δ18O values were similar to the δ18O range of endogenic carbonates from sedimentary cores from Lake Chew Bahir at the onset of the AHP, supporting the validity of our model, and suggesting that evaporation and the lake water residence time strongly influence lake water δ18O. However, the reported 87Sr/86Sr of fossil carbonates from Lake Chew Bahir during the AHP (0.7065–0.7060) could not be reproduced by our modelled scenarios without adjusting the surface-water-to-groundwater ratio, highlighting the potential role of groundwater as a water source in semi-arid regions. These results demonstrate the insights that can be gained from applying a process-based approach using O and Sr isotope hydro-balance modelling to aid interpretation of past hydro-balance and lake interconnectivity from lacustrine sedimentary records.

10Be chronology of deglaciation and ice-dammed lake regression in the vicinity of the Mylodon Cave (Cerro Benítez, Patagonia, Chile)

Located 51.5°S in the vicinity of the Southern Patagonian Ice Field, Cerro Benítez and the glacial valley of Lago Sofía host several caves and rock shelters that were occupied by megafauna and humans during the Late Pleistocene, including the Mylodon Cave and two of the oldest archaeological sites in Patagonia. During the last glaciation, Cerro Benítez was alternately covered by the Patagonian Ice Sheet and surrounded by an ice-dammed lake which restricted the access to the caves and rock shelters located under its uppermost level, 155 m a.s.l. This study aims to provide a detailed chronology of the deglaciation and lake regression in Cerro Benítez. The glacial fluctuations and the variations of lake level were reconstructed from multi-scale, remote-sensing data and field geomorphological mapping. In addition, we calculated the surface exposure age of 11 erratic blocks located above and on the lacustrine erosional platform using terrestrial cosmogenic 10Be in order to date ice downwasting and lake regression, respectively. Dates of ice downwasting and lake regression events were modelled from prior surface exposure ages using Bayesian statistics. The results suggest that the Patagonian Ice Sheet locally thinned by at least 300 m during MIS 3 in the aftermath of a major glacial advance. Following deglaciation, the ice-dammed lake experienced a slow local regression (ca. 2.5 mm. a−1) until 16.9 ka B2k, interpreted as the result of lake basin tilting due to differential post-glacial isostatic rebound. This initial phase of lake regression was followed by a faster regression caused by the reversal of the lake drainage between 16.9 and 15.4 ka B2k. We assess the chronological model by comparison with uplift and lakeshore erosion rates from the literature and eventually discuss the implications for megafaunal colonisation of the area.

The altitude of the depths: use of inland water archaeology for the reconstruction of inundated cultural landscapes in Lake Titicaca

ABSTRACT Andean societies have undergone abrupt climate changes that have affected their water resources and habitable or cultivable land. This is the case for Lake Titicaca, which has experienced fluctuations up to 20 metres during the last three millennia. Although paleoenvironmental reconstructions have provided valuable data on these lake level variations, their resolution is often not sufficient to assess their impact at the human time scale of land-use patterns. In this study, we provide a description of recent methodological developments in underwater archaeology that allows great advances in such reconstruction. Our results highlight that the level of the lake rose globally with multiple events of transgression and regression over the last two millennia. We also show that certain abrupt lake variation coincide with major transformations of the societies such as the emergence of the Tiwanaku state in the 6th century during a major transgression.

Astrochronology of a middle Eocene lacustrine sequence and sedimentary noise modeling of lake-level changes in Dongying Depression, Bohai Bay Basin

It has been demonstrated that the sedimentary deposits of Eocene succession in Bohai Bay Basin in China responded to astronomically forced climate changes. Several sections have been evaluated for cyclostratigraphy and many astronomical time scales (ATSs) have been constructed in Paleogene Bohai Bay Basin. However, the calibrations of age model and the constructed ATSs failed to reach an agreement and many of them relied on totally different orbital interpretations within the same section/borehole. In this work, we generated a new ATS for the middle Eocene lacustrine strata of middle to lower Member 3 (Es3m-l) and upper Member 4 (Es4u) of Shahejie Formation in Bohai Bay Basin. In this research, high resolution natural gamma-ray (GR) data were used for the cyclostratigraphy analysis of Es3m-l and Es4u Members of Well Fanye-1. We filtered ~11.11 m cycles of t Es3m-l and ~9.26 m cycles of Es4u which were directly correlated to the short eccentricity cycles (~100-kyr) of La2004 solution. The geomagnetic polarity ages of C18r/C19n, C19n/C19r and C19r/C20n in Geological Time Scale 2020 were adopted as age markers for the tuning in this study. This astrochronology provided astronomical time scale (ATS) in the range of 39.268 ± 0.050 Ma to 43.621 ± 0.050 Ma in Es3m-l and Es4u Member. The astrochronology of Well Fanye-1 of the same interval had been studied before. However, the ATS built in this paper used correlation coefficient (COCO) analysis and average spectral misfit (ASM) approach to provide quantitative measurement for fitting the observed sedimentary cycles to astronomical periods and given a range of plausible sedimentation rate. In this research, a sedimentary noise model was applied for the detection of high-resolution lake-level variations controlled by orbital forcing. The lake-level variations generated from the sedimentary noise model were supported by previous sequence stratigraphic interpretations. Variable sedimentation could be affected by lake-level changes which have been demonstrated by the evolutionary correlation coefficient analysis of GR series. In addition, from the ATS and thin section observations, it was concluded that carbonate-clay laminae in lacustrine shale were generated annually. Seasonal carbonate-clay laminated shale formations are controlled by orbital scale variability of monsoon and are always developed in a relatively high eccentricity amplitude under deep water environment conditions. Finally, the lake-level rise at ~40.500 Ma to ~40.050 Ma was demonstrated to be the response to Middle Eocene Climate Optimal (MECO) event in lacustrine records.

Sedimentary noise modeling of lake-level change in the Late Triassic Newark Basin of North America

Two different hypotheses, glacioeustasy and groundwater aquifer eustasy, have been proposed to explain short-term, high-amplitude sea-level oscillations during past greenhouse-dominated intervals. However, the veracity of aquifer eustasy on long-term, high amplitude sea level has never been rigorously tested. We evaluate these competing hypotheses using the objective approach of sedimentary noise modeling for lake-level reconstruction. Statistical tuning and astronomical calibration of paleoclimate and paleoenvironment proxies (depth rank, rock color, gamma ray, and sonic velocity) from the lacustrine Newark Basin enable the construction of a 31.55-Myr long astronomical time scale (ATS) for the Late Triassic that is comparable to the classic Newark ATS previously presented. Using this timescale, sedimentary noise modeling in the lacustrine Newark Basin is carried out through the Late Triassic. Lake level fluctuations reconstructed by sedimentary noise modeling and principal component analysis reveal that million-year scale lake-level variations were linked to astronomical forcing with periods of ~3.3 Myr, ~1.8 Myr, and ~1.2 Myr. Our results demonstrate that astronomical forcing, as a driver of groundwater dynamics, may have had an impact on global sea-level changes during the Late Triassic. This study thus emphasizes the importance of high-resolution, objective reconstruction of sea- and lake-levels for further testing the hypotheses of glacioeustasy and aquifer eustasy under warm conditions. • We reconstruct high-resolution lake-level changes in the Late Triassic. • Long-period astronomical forcing drove lake-level and sea-level variations. • Continental groundwater could have an impact on global sea-level fluctuations. • High-resolution, objective reconstruction of lake- and sea-levels is key to test aquifer eustasy versus glacioeustasy.

Composite microbialites: Thrombolite, dendrolite, and stromatolite associations in a modern environment, Pozo Bravo lake, Salar de Antofalla, Catamarca Puna, Argentina

ABSTRACT Pozo Bravo is a high-altitude Andean lake that harbors modern microbialites thriving in hypersaline conditions in the Salar de Antofalla, one of the driest sites on Earth and located in the Puna region of Catamarca, northwest Argentine. Due to the lake physiography, microbialites are restricted to a narrow belt following Pozo Bravo lake variations. Microbialites exhibit a wide range of external morphologies including domal, discoidal, tabular, and horseshoe-like bioherms which vary considerably in size, as well as large biostromal terraces. As documented by other studies on modern microbialites, external morphology appears to be mainly the product of the environmental setting. In Pozo Bravo lake, high evaporation rates and hypersalinity (driven by high temperature and strong winds), water-level fluctuations, and lake-bottom topography are major controlling factors. The distinctive feature of Pozo Bravo microbialites is their internal structure, showing a gradual transition from a thrombolitic core to dendrolitic structures and to a sharply overlying stromatolitic layer within a single microbialite. We suggest that these various microbialite textures represent a gradual change within an environmental gradient based on lake-level variations, and the influence of these environmental factors on biological activity, mainly by cyanobacteria and diatoms. The study of this site is particularly relevant given that it represents an active system where progressive changes in microbialite type (from thrombolites to dendrolites and stromatolites) are recorded, providing an excellent natural laboratory to study these textural changes from a mechanistic perspective, and it may provide insights for better understanding of the microbialite geological record. In addition, given that these systems are threatened by human activities (mining of lithium-rich brines), its study and preservation are necessary.

Integrating remote sensing of hydrological processes and dissolved organic carbon fluxes in long-term Lake Studies

Dissolved organic carbon (DOC) is an important fraction of organic carbon (OC) that together with colored dissolved organic matter (CDOM) plays a key role in the carbon cycling of lakes. Lake Võrtsjärv is a large and shallow eutrophic lake where water quality measurements have been carried out for a long time. The monthly characteristics of DOC and CDOM in Võrtsjärv and its input/output rivers were traced in 5-years observations. We attempted to link the hydro-morphological indices as lake area (A), water level (WL) and volume variations (Qc) with lake DOC fluxes and CDOM-DOC relationships to improve understanding of carbon fluxes in a very shallow, large and highly eutrophic lake, as well as of the possibility to estimate DOC fluxes by CDOM via remote sensing. The research questions were: how the properties and quantity of DOC, its fluxes and CDOM-DOC relationship in a very shallow, large and highly eutrophic lake are responding to 1) variable proportions of allochthonous and autochthonous processes and 2) changing hydrological conditions. The increased lake volume variation in spring caused the higher level of CDOM, signifying the terrestrial (allochthonous) DOC (DOCAlloch) domination in Lake Võrtsjärv. The proportion of DOCAlloch increased together with increasing WL, A and CDOM concentration. Although the generally high proportion of DOCAlloch in Võrtsjärv, the autochthonous DOC determines the water color (CDOM/DOC) in this highly productive ecosystem with short residence time (280–365 days). Our study on DOC flux revealed that the internal carbon sources, driven by hydrological factors, contribute significantly to the role of large and shallow lakes in global carbon cycling. The further development of water color remote sensing could provide novel directions for understanding the feedbacks of lake DOC flux and changing hydrology.

Monitoring Lake Levels From Space: Preliminary Analysis With SWOT

Lakes are an essential component of biogeochemical processes, and variations in lake level are regarded as indicators of climate change. For more than a decade, satellite altimetry has successfully monitored variation in water levels over inland seas, lakes, rivers, and wetlands. Through altimetry, the surface water levels are measured at varying temporal scales depending on the orbit cycle of the satellite. The futuristic mission of Surface Water and Ocean Topography (SWOT) scheduled to be launched in year 2022 shall offer the spatial coverage and resolution suitable for water level estimation and volume calculation in small water bodies like lakes worldwide. With a radar interferometer in Ka-band, SWOT proposes to provide two-dimensional maps of water heights 21 days repeat orbit configuration. Cycle average SWOT datasets for land will be developed with higher temporal resolution, with temporal resolution varying geographically. This work assesses the potential of SWOT for monitoring water volumes over a case study lake by analyzing SWOT like synthetic data produced using the SWOT simulator developed by the Centre National d'Etudes Spatiales (CNES). With SWOT relying on a novel technology, the initial 90 days of this mission after launch shall focus on an extensive calibration and validation. Firsthand results of SWOT-simulated water levels and volumes are presented over a case study region in the tropical band, namely, Pookode Lake, in the ecologically fragile district of Wayanad, Kerala, India. It is the second-largest freshwater lake in Kerala that is being affected by anthropogenic activities, causing huge depletion in lake water storage in the last four decades. Our analysis indicated that the lake region is subjected to a rise in temperature of 0.018°C per year. We further assess the potential of remote sensing and SWOT data to monitor water storage of Pookode Lake, which is undergoing a rapid change. Results show that the proxy water surface elevations have immense potential in scientific studies pertaining to lake monitoring across the world. Overall, the study shows the potential of SWOT for monitoring the variability of water levels and volumes in this region.

Astronomical constraints on the development of alkaline lake during the Carboniferous-Permian Period in North Pangea

Astronomical forcing associated with Earth's orbital and inclination exerts a major control on climate as recorded in the sedimentary rocks. Alkaline lake deposits in the second member (F 2 ) of the Fengcheng Formation provided a unique geological record to explore the paleoclimatic conditions during the Late Paleozoic Ice Age (LPIA) in northern Pangea. In this study, we utilize high-resolution downhole logs (GR, DEN and CAL) to conduct a comprehensive cyclostratigraphic analysis of the Fengcheng Formation. Time series analysis reveals evidences for 405-kyr long eccentricity cycles in logs series, which is also confirmed by objective statistical approaches by modeling of optimal sedimentation rates. Tuning of these downhole logging datasets to the interpreted 405-kyr eccentricity obtained a ~ 5.0-Myr-long astronomical time scale (ATS). Afterwards, by anchoring the U-Pb age at the first member (F 1 ) and second member (F 2 ) boundary, obtaining an absolute age framework for the Fengcheng Formation that extends from 297.0 to 301.98 Ma. Under the high-precision time framework, we performed sedimentary noise model to reconstruct the lake-level changes in terrestrial Junggar Basin. Notablely, modeling of the tuned CAL series reveals high-frequency lake-level changes at 10 5 –10 6 kyr orbital time scale (i.e., ~1.2 Ma, ~450 kyr, ~180 kyr, ~116 kyr). These high-frequency lake-level variations were possibly teleconnected with the high-latitude ice sheets periodic waxing and waning and/or low latitude monsoonal circulation. Moreover, the development of rhythmic evaporite-containing mudstone in the F 2 was tightly linked to the basin's hydrological cycles, which was ultimately paced by the astronomical forcing. Finally, we propose a simplified model for illustrating the formation of the rhythmic evaporite layers and emphasize that the favorable paleotectonic, paleogeographic and paleoclimatic conditions were necessary for development of the alkaline lake. • Comprehensive cyclostratigraphic analysis of the Fengcheng Formation • Reconstruct the lake-level changes by using DYNOT simulation approach. • A novel alkaline development model associated with orbital forcing was firstly proposed.

Middle Triassic lake deepening in the Ordos Basin of North China linked with global sea-level rise

The Yanchang Formation was deposited during the Middle Triassic in a vast lacustrine basin in the modern Ordos Basin and is a main target for hydrocarbon exploration in Central China. It is divided, based on sedimentary cycles and lithology , into the Chang 10 (the oldest) to Chang 1 (the youngest) members. During the deposition of the Chang 7 Member, the Ordos lake system reached its maximum depth and large volumes of organic-rich sediments were deposited. The evolution of the Ordos Basin sedimentary system during this phase is, however, not completely understood, and uncertainty still exists as for the chronostratigraphy of Chang 7 Member. We acquired palynological markers and palynofacies and a high-resolution δ 13 C org record through the entire Chang 7 Member, and a ID-TIMS 206 Pb/ 238 U date of 240.95 ± 0.033 Ma from a volcanic ash bed in the middle of this Member. These imply that the maximum deepening phase of the lacustrine system was during the earliest Ladinian . Evidence of marine influence in the Ordos Basin at that time and comparison to the sea-level oscillations observed in Western Tethys suggest that a global eustatic rise and highstand may have played a role in determining lake-level variations. • We report a zircon age of 240.950 ± 0.033 Ma from the middle portion of Chang 7 Member that indicates an early Ladinian. • The identified palynological assemblage also supports a late Middle Triassic age for Chang 7 Member. • The maximum expansion of the Ordos lake was probably influenced by the early Ladinian maximum in eustatic sea level.

Seasonal trends and cycles of lake-level variations over the Tibetan Plateau using multi-sensor altimetry data

The large number of lakes, little influenced by humans, on the Tibetan Plateau, form a natural laboratory for exploring cryosphere-hydrosphere-atmosphere processes under global warming. The water levels of these alpine lakes respond directly to water balance, but are mainly known only on the interannual scale. Seasonal variations are still poorly described due to limited gauge measurements. Here, the seasonal trends and cycles of lake-level changes on the Tibetan Plateau were examined using altimetry data from ICESat (132 available lakes), Cryosat-2 (244 lakes), Sentinel-3A (125 lakes), Sentinel-3B (120 lakes), and ICESat-2 (356 lakes). Bias between altimetry data sets was removed, and a validation against in-situ lake-level measurements from Qinghai Lake between 2003 and 2020 revealed a good performance (R2 > 0.80, RMSE < 0.12 m). The mean annual trend of lake level between 2003 and 2020 is 0.20 ± 0.01 m/yr, with similar rates (0.18–0.20 m/yr) in three different seasons. The rate was slightly greater (0.22 ± 0.02 m/yr) between 2010 and 2020, but seasonal trends were again similar in this period (0.21–0.25 m/yr). Declining water levels for lakes around Nam Co were identified, with a mean negative rate of −0.09 ± 0.02 m/yr. Furthermore, during 2016–2020, an accelerated lake-level rise was found, with a mean rate of 0.43 ± 0.05 m/yr (0.47–0.53 m/yr in four seasons). Lake levels in the southern TP are shown to have increased during 2016–2019: a reversal of the pre-2016 observations of declining levels. The seasonal cycles of lake-level variations show that the majority of lakes have a peak water level in August–September, followed by October–November. The features of the peaks vary distinctly in different climate regions, with the timing of the peak occurring gradually later as one moves from southwest to northeast. The seasonal cycles of water level and terrestrial water storage from GRACE data are highly consistent. The spatial pattern of lake-level changes during the seasonal period of rising lake levels also matches precipitation variations well, as does lake volume change with terrestrial water storage budget. The study reveals the tremendous potential of multi-sensor altimetry data for detecting seasonal features of lake-level variation, which is a great asset for understanding Earth's water dynamics and balance.