Mean Lake Surface Research Articles

Improving mean water lake surface elevation estimates using dense lidar measurements from the GEDI satellite mission

Lakes are an essential component of the global water cycle and are considered as sentinels of climate change. An accurate estimate of lake's water levels is necessary for reliable continuous monitoring of their water balance. Due to their huge number worldwide, satellite altimetry has been identified as an efficient tool for measuring their temporal variations of water level. This technique can reach an accuracy of a few centimeters for water level estimates over large lakes. Due to the coarse across-track spatial resolution of the radar altimetry missions, their spatial sampling only covers a small part of the lakes surface. To obtain an accurate estimate of the lake water level, it is necessary to apply a correction to account for the small-scale orthometric height undulations occurring on the lake area and not present in the current global geoid models. In this study, the high-density lidar measurements from GEDI are used to estimate the mean lake surface. From the 1,366,211 GEDI data over 1239 tracks acquired over more than 6000 km2 of the surface of Lake Issy-Kul (Kyrgyzstan, Central Asia) between May 2019 and mid-November 2021, 654,592 shots over 843 tracks were selected after a multi-step quality-check and processed to generate a mean lake surface of Lake Issyk-Kul. Comparison between the GEDI-based mean lake surface and GNSS kinematic surveys corrected from the lake level variations exhibit an RMSE of 0.065 m. The principal objective of performing such mean lake surface is to further use it in the framework of the calibration/validation of the Surface Water and Ocean Topography (SWOT) mission.

Bathymetric effect on geoid modeling over the Great Lakes area

Bathymetry data over lake areas are not included in the current and previous NGS (National Geodetic Survey) geoid models. Lake surfaces are simply treated as land surfaces during the modeling regardless of the apparent density difference between water and rock, resulting in artificial masses that distort the model from the actual gravity field and the corresponding geoid surface. In this study, compiled high-resolution bathymetry data provided by National Centers for Environmental Information are used to identify the real volume of water bodies. Under the mass conservation principle, two strategies are deployed to properly account the water body bounded by the mean lake surface and the bathymetry indicated lake floor into the current NGS geoid modeling scheme, where the residual terrain modeling method is used to account for topographic effects. The first strategy condenses water bodies into equivalent rock masses, with the cost of changing the geometrical shape of the water body. The second one keeps the shape of the water body unchanged but replaces the water and rock densities inside each topographical column bounded by the geoid surface and the mean lake surface by an averaged density. Both strategies show up to 1-cm geoid changes when compared with the previous geoid model that does not consider bathymetric information. All three geoid models are evaluated by local GNSS/Leveling benchmarks and multi-year-multi-mission altimetry indicated mean lake surface heights. The results show that both strategies can improve the geoid model precision. And the second strategy yields more realistic results.Graphical

Lake Heatwaves and Cold‐Spells Across Qinghai‐Tibet Plateau Under Climate Change

AbstractLake heatwaves (LHWs) and cold‐spells (LCSs), similar to marine heatwaves and cold‐spells, can have long‐term impacts on lake ecosystems and are vulnerable to climate change. Here we first comparatively assess LHW and LCS changes across the Qinghai‐Tibet Plateau (QTP) using satellite surface water temperature observations in 160 lakes over 1978–2017. Our findings reveal notable differences in the mean and trends of LHW and LCS metrics. Specifically, total days and frequency of LHW have been increasing at a rate of 8.82 ± 1.25 days per decade and 0.78 ± 0.10 counts per decade, respectively. Conversely, total days and frequency of LCS have decreased at −6.52 ± 1.46 days per decade and −0.51 ± 0.01 counts per decade, respectively. However, average duration and mean intensity show no significant difference. Additionally, the average duration of ice cover across the QTP has been decreasing (−2.60 ± 0.38 days per decade) due to the delayed freezing date (1.13 ± 0.18 days per decade) and earlier thawing date (−1.28 ± 0.27 days per decade) during 1978–2017. Furthermore, the annual mean lake surface water temperatures across the QTP exhibit a warming trend (0.00 ∼ 0.47°C per decade) from 1978 to 2017, with faster warming occurring in winter (0.00 ∼ 0.98°C per decade) compared to summer (−0.17 ∼ 0.47°C per decade). Accelerated lake warming will increase the frequency and mean intensity of LHWs while decreasing the number of LCSs. These results help to understand how QTP lakes respond to extreme temperatures under climate change.

Regional geoid determination in Tierra del Fuego including GPS levelling

A regional geoid model for the Argentine part of the Isla Grande de Tierra del Fuego, established in previous works on the basis of GPS levelling, suffers a lack of observation data in the remote south-western investigation area. In order to improve the data distribution in this region, the mean lake level of Lago Fagnano has been regarded as a natural indicator for the local geoid. Using a GPS buoy and pressure tide gauges, a method to determine the mean lake surface topography with respect to the ellipsoid has been developed. It is shown that the obtained lake level geometry is essentially controlled by the regional gravity field. The derived information on the mean lake level has been included in the geoid model, which results in a more detailed and plausible representation of the regional geoid.

Mapping mean lake surface from satellite altimetry and GPS kinematic surveys

Lake water height is a key variable in water cycle and climate change studies, which is achievable using satellite altimetry constellation. A method based on data processing of altimetry from several satellites has been developed to interpolate mean lake surface (MLS) over a set of 22 big lakes distributed on the Earth. It has been applied on nadir radar altimeters in Low Resolution Mode (LRM: Jason-3, Saral/AltiKa, CryoSat-2) in Synthetic Aperture Radar (SAR) mode (Sentinel-3A), and in SAR interferometric (SARin) mode (CryoSat-2), and on laser altimetry (ICESat). Validation of the method has been performed using a set of kinematic GPS height profiles from 18 field campaigns over the lake Issykkul, by comparison of altimetry’s height at crossover points for the other lakes and using the laser altimetry on ICESat-2 mission. The precision reached ranges from 3 to 7 cm RMS (Root Mean Square) depending on the lakes. Currently, lake water level inferred from satellite altimetry is provided with respect to an ellipsoid. Ellipsoidal heights are converted into orthométric heights using geoid models interpolated along the satellite tracks. These global geoid models were inferred from geodetic satellite missions coupled with absolute and regional anomaly gravity data sets spread over the Earth. However, the spatial resolution of the current geoid models does not allow capturing short wavelength undulations that may reach decimeters in mountaineering regions or for rift lakes (Baikal, Issykkul, Malawi, Tanganika). We interpolate in this work the geoid height anomalies with three recent geoid models, the EGM2008, XGM2016 and EIGEN-6C4d, and compare them with the Mean Surface of 22 lakes calculated using satellite altimetry. Assuming that MLS mimics the local undulations of the geoid, our study shows that over a large set of lakes (in East Africa, Andean mountain and Central Asia), short wavelength undulations of the geoid in poorly sampled areas can be derived using satellite altimetry. The models used in this study present very similar geographical patterns when compared to MLS. The precision of the models largely depends on the location of the lakes and is about 18 cm, in average over the Earth. MLS can serve as a validation dataset for any future geoid model. It will also be useful for validation of the future mission SWOT (Surface Water and Ocean Topography) which will measure and map water heights over the lakes with a high horizontal resolution of 250 by 250 m.

The Dynamic Change of Bosten Lake Area in Response to Climate in the Past 30 Years

The widely distributed lakes, as one of the major components of the inland water system, are the primary available freshwater resources on the earth and are sensitive to accelerated climate change and extensive human activities. Lakes play an important role in the terrestrial water cycle and biogeochemical cycle and substantially influence the health of humans living in the surrounding areas. Given the importance of lakes in the ecosystem, long-term monitoring of dynamic changes has important theoretical and practical significance. Here, we extracted water body information and monitored the long-term dynamics of Bosten Lake, which is the largest inland lake in China. We quantified the meteorological factors of the study area from the observation data of meteorological stations between 1988 and 2018. The characteristics of climate change and its correlation with the change of area in the Bosten Lake Basin in the past 30 years were analyzed. The major contributions of this study are as follows: (1) The initial water body was segmented based on the water index model Normalized Difference Water Index (NDWI) and Modified Normalized Difference Water Index (MNDWI) with a pre-assigned threshold value. The results were evaluated with the area extracted through artificial visual interpretation. Then we conducted mathematical morphology operators, opening and closing operations, and median filter to eliminate noise to ensure the accuracy of water body information extraction from the Bosten Lake. A long-term water surface area database of the Bosten Lake was established from high-resolution remote sensing images during 1988–2018. (2) Due to the seasonal difference of snow, ice content, and other objects on images, the areadynamics of Bosten Lake in the recent 30 years were analyzed separately in dry season and rainy season. The water surface area of Bosten Lake showed large inter-annual variations between 1988–2018. (3) Based on the assumption that climatic change has more direct effects on lake than human activities, six meteorological factors were selected to analyze the impacts of climate change on the annual mean lake surface area. The result indicated that in the past 30 years, climate conditions in the Bosten Lake Basin fluctuated greatly. We conducted correlations analysis between the areal dynamics of the Bosten Lake and the meteorological factors. Here, the annual average evaporation had the highest correlation with the areal dynamics of Bosten Lake followed by air temperature, precipitation, sunshine hours, and relative humidity, while the annual average wind speed had the weakest correlation.

The vertical distribution of Thaumarchaeota in the water column of Lake Malawi inferred from core and intact polar tetraether lipids

Several long paleoclimate records generated from Lake Malawi sediments rely on an assumption that the TEX86 paleothermometer reflects annual mean lake surface temperatures. Thaumarchaeota, the producers of the isoprenoid glycerol dialkyl glycerol tetraether (iGDGT) lipids that are the basis of the TEX86 proxy, can occupy a wide range of habitats in the upper water column of lacustrine systems, so it is crucial to specifically constrain the ecology of Thaumarchaeota in Lake Malawi to properly interpret its sedimentary TEX86 record. To investigate the spatial and vertical distribution of Thaumarchaeotal iGDGT production in Lake Malawi, suspended particulate matter (SPM) was collected from the upper water column (>300 m) at three sites spanning the north, central, and south basins of the lake and analyzed for intact polar (IPL) and core (CL) iGDGT lipid abundances. Samples were collected in January during the austral summer when the lake is strongly stratified. Concentrations of the most labile IPL, hexose-phosphohexose (HPH)-crenarchaeol, were greatest just below the deep chlorophyll maximum at ∼50 m water depth in the deeper north and central basins and ∼30 m in the shallow south basin. Maximum CL concentrations occur below the maximum HPH-crenarchaeol concentrations and therefore possibly reflect the accumulation of recently produced IPL GDGT degradation products. If the export of CLs to the sediments is dominated by this CL pool, sedimentary TEX86 would reflect Thaumarchaeota living within the thermocline during the stratified season and therefore may have a cool bias rather than reflecting true surface water temperatures. An increase in abundances of GDGT-2, crenarchaeol isomer, and monohexose (MH)-crenarchaeol at ∼150–200 m suggests that a secondary Thaumarchaeotal population, likely Group I.1b Thaumarchaeota, inhabits the subsurface water column near the anoxic-suboxic boundary. Total production of iGDGTs by this group appears to be much lower than the surface-dwelling clade, but its imprint on sedimentary TEX86 is unknown. An analysis of iGDGT production in the water column throughout the annual cycle is needed to resolve the timing and magnitude of export of CLs to the sediments from these two Thaumarchaeotal populations.

Thermal regimes of Rocky Mountain lakes warm with climate change.

Anthropogenic climate change is causing a wide range of stresses in aquatic ecosystems, primarily through warming thermal conditions. Lakes, in response to these changes, are experiencing increases in both summer temperatures and ice-free days. We used continuous records of lake surface temperature and air temperature to create statistical models of daily mean lake surface temperature to assess thermal changes in mountain lakes. These models were combined with downscaled climate projections to predict future thermal conditions for 27 high-elevation lakes in the southern Rocky Mountains. The models predict a 0.25°C·decade-1 increase in mean annual lake surface temperature through the 2080s, which is greater than warming rates of streams in this region. Most striking is that on average, ice-free days are predicted to increase by 5.9 days ·decade-1, and summer mean lake surface temperature is predicted to increase by 0.47°C·decade-1. Both could profoundly alter the length of the growing season and potentially change the structure and function of mountain lake ecosystems. These results highlight the changes expected of mountain lakes and stress the importance of incorporating climate-related adaptive strategies in the development of resource management plans.

A slab model of the Great Salt Lake for regional climate simulation

AbstractA slab lake model was developed for the Great Salt Lake (GSL) and coupled to a regional climate model to enable better evaluation of regional effects of projected climate change. The GSL is hypersaline with an area of approximately 4400 km2, and its notable shallowness (the deeper sections average 6.5–9 m at current lake levels) renders it highly sensitive to climate change. A time‐independent (constant) effective mixing depth of approximately 5 m was determined for the GSL by numerically optimizing model‐observation agreement, and improvement gained using a time‐dependent effective mixing depth assumption was smaller than the uncertainty in the satellite‐based observations. The slab model with constant effective mixing depth accounted for more than 97% of the variance in satellite‐based observations of GSL surface temperature for years 2001 through 2003. Using a lake surface temperature climatology in place of the lake model resulted in annual mean near‐surface air temperature differences that were small (∼10−2 K) away from the lake, but differences in annual precipitation downstream reached 3 cm (4.5%) mainly because of enhanced turbulent heat fluxes off the lake during spring. When subjected to a range of pseudo global warming scenarios, the annual mean lake surface temperature increased by 0.8°C per degree of air temperature increase.

Temporal variations in lake water temperature: Paleoenvironmental implications of lake carbonate δ18O and temperature records

δ18O and “clumped isotope” measurements of lacustrine carbonates provide important records of past terrestrial climate and paleoelevation. However, one of the primary challenges interpreting these data is constraining the relationship between mineral formation temperature and seasonal and mean annual climate. We examined surface water temperature records from 88 lakes across the globe to develop transfer functions that relate seasonal water surface temperature to mean annual air temperature. These transfer functions provide a means of reconciling proxy measures of water temperature with annual climatic conditions. Mean annual surface water temperature is related to mean annual air temperature (MAAT=−0.0318×TWater2+2.195×TWater−12.607; R2=0.96) independent of lake size, with consistently higher mean water temperatures than air. N. Hemisphere Spring (April–June) mean lake surface temperatures (MAAT=−0.0097×TWater2+1.379×TWater−8.227; R2=0.94) are only slightly warmer than MAAT for lakes in all climate zones, while summer water temperatures (JJA) (MAAT=−0.0055×TWater2+1.476×TWater−18.915; R2=0.90) may be 10–20°C warmer than MAAT for cold climate lakes. Comparison of carbonate stable isotopic data from sites with different timescales of carbonate formation, such as found along latitude or elevation gradients, can lead to large over- or underestimates of past temperature. Accurate paleoclimatic interpretation of isotopic proxies or use of temperature proxy constraints (i.e., fossil leaves) to estimate lake temperature and calculate water δ18O thus requires appropriate application of water temperature–air temperature transfer functions, particularly when considering ancient cool, high elevation lake systems.

A Landscape‐Based Classification of Fish Assemblages in Sampled and Unsampled Lakes

AbstractWe related fish species patterns and landscape‐scale environmental data from 216 Michigan lakes to identify repeatable types of fish assemblages, identify environmental factors related to assemblage types, and classify fish assemblages in unsampled lakes. Multivariate regression tree modeling of fish species abundances identified six assemblage types that were explained by degree‐days during the ice‐free period, lake surface area, and mean lake surface temperature. Warmwater species dominated southern lakes, while coolwater and coldwater species had higher abundances in northern lakes. Coolwater species were present in large southern lakes, whereas warmwater species were excluded from northern lakes that had low mean surface temperatures or low degree‐days. These results suggest that patterns of lake fish assemblages are shaped by differences in climate as well as lake‐specific differences in surface temperature regimes and in vertical availability of coldwater and coolwater habitats. Because we related fish patterns to readily available landscape‐level data, our approach can be used to characterize fish assemblages in all lakes across broad geographic extents.

Stable isotope composition of the Miocene Dinaride Lake System deduced from its endemic mollusc fauna

The aragonite shells of 55 mollusc specimens from the late Early and early Middle Miocene of two palaeolakes of the Dinaride Lake System (DLS) are analysed for their δ18O and δ13C signatures. The data set has a bimodal distribution with a prominent peak between −3 and −4‰ for both isotopes and a second much weaker peak at more depleted values of c. −9 to −7‰. Taxa with ‘heavy’ values are interpreted to represent the inhabitants of the shores or shallow areas of the lake. Depleted values are attributed to species preferring freshwater habitats of springs or small rivulets, thus representing the freshwater end-member. The overall rather high values in both stable isotopes result from a combination of evaporation effects and the influx of already isotopically heavy freshwater from the karstic catchment area. Thus, the DLS is interpreted as a closed freshwater system without marine influence but with enough contribution of freshwater to keep the oxygen values close to −5‰. Mean lake surface water temperatures, based on the δ18Oshell values, excluding the freshwater end-member taxa, range around roughly 19–21°C. Despite the problems in calculating these temperatures, the values are in agreement with mean annual air temperatures deduced from the palaeobotanic record by applying the Coexistence Approach method. The seasonal range was around 10–11°C and is mainly recorded in shells from lake settings. Taxa with freshwater end-member signatures lack this range due to the more stable temperature regime and less fluctuating dissolved inorganic carbon (DIC) pool. Congeneric species from the same stratigraphic horizon often display discrete but different isotope signatures. This fact suggests habitat segregation and might be a major factor for sympatric speciation and the endemic radiation within the mollusc fauna of the DLS.

Changing thermal dynamics of lakes in the Great Lakes region: Role of ice cover feedbacks

The impacts of climate variability and lake ice cover feedbacks on the seasonal thermal dynamics of inland lakes were evaluated for the period of 1916–2007. Analysis of regional scale impacts for the small inland lakes remains a major challenge in the Great Lakes region due to lack of observations at regional scale. Regional lakes were included into a land surface modeling perspective to understand the roles of climate variability on their open water season dynamics. The Variable Infiltration Capacity (VIC) model was applied with a physically based lake algorithm to simulate thermal conditions of lakes at regional scale during the open water period. Prior to its implementation, the VIC model was evaluated for lake surface water temperature in the selected lakes within the study domain. Results suggested that the cold (October–May) and spring (March–May) season air temperatures have increased by 1.38 and 1.54 °C, respectively during the period of 1916–2007. Increase in air temperature was statistically significant at the regional scale. Onset of the stratified season has occurred earlier by more than five days during the period of 1916–2007. Earlier onset of the stratified season was significantly related to the length of the stratified season, thermal storage in the lakes, and mean lake surface water temperatures. The combined impacts of increased air temperature and earlier onset of the stratified season led to increased heat storage in lakes by 82.5 × 10 16 J. Degree-days above 15 and 20 °C also increased by 97.5 and 33.0 degree-days during the period of 1916–2007. The lake ice cover was significantly related with the annual lake evaporation, timing of ice formation and break-up in lakes, and heat storage during the spring and summer. Results suggested the climate warming may lead to increased rate of evaporation that is driven by feedbacks of ice cover and snow storage.

Thermal Characteristics and Energy Balance of Various-Size Canadian Shield Lakes in the Mackenzie River Basin

This study addresses the thermal and energy budget characteristics of four different-size Canadian Shield lakes in the Mackenzie River basin during the ice-free season of 2000. The objectives are to characterize and compare the surface temperature and thermal structures, and to quantify the magnitudes and flux rates of the energy balance components of each lake. This study highlights the variability in thermal and energy balance characteristics arising from differences in mean lake depth and surface area. The lakes exhibit similar temporal patterns for air temperature, net radiation, wind speed, and wind direction. Net radiation and wind speed are highest over the largest lake, Great Slave Lake, due to colder surface temperatures and lengthy across-lake wind fetch, respectively. During the warming phase of the summer, surface temperature is inversely related to mean depth; however, during the cooling phase this relationship reverses. The shallowest of the four lakes remains isothermal during the entire ice-free period, while the three larger and deeper lakes are all dimictic. A lag in the onset of thermal stratification in the dimictic lakes is positively correlated with mean depth and surface area. Large evaporative water losses correspond to periods of low net radiation and cold dry air over Great Slave Lake. However, over the smaller, shallower lakes periods of high evaporation occur on days with high net radiation and warm, dry air. The capacity of larger lakes to store more heat results in longer ice-free periods and higher evaporation. Maximum heat content increases and occurs later for lakes of greater depth. Maximum evaporative rates occur later and cumulative evaporation is highest for lakes of greater depth and area. The ratios of total open water evaporation for the four lakes in order of size (smallest 5 1.0) are 1.0 : 1.2 : 1.3 : 1.4. Evaporation magnitudes are discussed in the context of other temperate and high-latitude lake studies.

Empirical modeling of summer lake surface temperatures in southwest Greenland

This work presents a method to estimate mean daily lake surface water temperatures using only air temperature, theoretical clear‐sky solar radiation, and lake size. Surface water temperatures were measured at a selection of lakes in southwest Greenland during the summers of 1998–2000. The lakes are small (surface area <150 ha) with maximum depths ranging from 3.5 to 47 m. An empirical model requiring only local air temperature and theoretical clear‐sky solar radiation is developed to predict daily mean lake surface temperatures in summer for each lake. The model approximates the slow integrated response of water temperature to meteorological forcing by applying an exponential smoothing filter to air temperature. Exponential smoothing results in a 35% improvement in model fit compared with a model using unsmoothed air temperatures. The smoothed air temperatures and clear‐sky solar radiation are linearly combined to estimate the daily mean lake surface temperatures. The smoothing parameters and the three linear coefficients of the model, obtained individually for each of 15 lakes, are found to relate to lake area and maximum depth, leading to the development of a general model. With this general model it is possible to predict the summer surface temperatures at any lake in this region where local air temperatures can be estimated. Cross‐validation of the general model at each lake in turn indicated a 90% forecast skill and average standard error of prediction of 1.0°C. Examination of the daily prediction errors over time suggests a relation to strong wind events.

Determination of gravity anomaly using satellite altimeter data in the Great Lakes

In this paper, the determination of gravity anomalies in the Great Lakes using satellite altimeter data of GEOSAT Geodetic Mission (GM) and TOPEX/Poseidon is discussed. The seasonal change of lake level was observed from TOPEX/Poseidon satellite altimeter data. This analysis of lake level change was made to determine the mean lake surface profiles along the TOPEX/Poseidon repeat tracks. The least squares collocation was used to predict gravity anomalies. The gravity anomalies are determined by using mean lake surface profiles derived from TOPEX altimeter data and along-track slopes and azimuth derived from lake surface heights measured by the GEOSAT altimeter. To remove influences of the cycle-to-cycle time variation of lake level, along-track slopes of altimeter height are used. These results are compared to the exisiting surface gravit data measured in the Great Lakes. The gravity anomaly in the Lake Huron derived from the altimeter data using the least squares collocation shows slightly better comparison with the surface gravity anomaly than that implied by the EGM-96 gravity model.

Eighty years of spatially coherent Austrian lake surface temperatures and their relationship to regional air temperature and the North Atlantic Oscillation

Eighty years of monthly mean lake surface temperature (LST) data from eight lakes in the northern perialpine area of Austria show a high degree of coherence among lakes in all seasons and reflect much of the temporal structure of the regional air temperature. Coherence is least in winter because of the distorting effect of varying periods of ice cover. In spring, regional coherence in meteorological driving forces that are essentially uncorrelated with air temperature (e.g., geostrophic wind speed) contribute to the coherence in LST, presumably by partially determining the timing of the onset of stratification. In summer, spatial coherence in LST appears to be related directly (via the radiation balance) and/or indirectly (via air temperature) to largeߚscale variations in highaltitude cloud cover. Correlations of the Austrian LSTs with (1) seasonal indices of the North Atlantic Oscillation (NAO), (2) the timing of spring ice breakߚup in Finland, and (3) air temperatures in northern and western Europe, suggest that from autumn to spring, spatial coherence of LST in central Europe is related to the dominance of the weather by largescale climatic processes occurring over the North Atlantic, whereas in summer the processes responsible are more regional in nature. The influence of the NAO on LST is greatest in lowߚlying lakes in which periods of ice cover are infrequent and short.