Tibetan Plateau Lakes Research Articles

Short- and medium-chain chlorinated paraffins in fish from an anthropized south-western Atlantic estuary, Bahía Blanca, Argentina

Chlorinated paraffins (CPs) are synthetic organic compounds of growing environmental and social concern. Short-chain chlorinated paraffins (SCCPs) were listed under the Stockholm Convention on Persistent Organic Pollutants (POPs) in 2017. Further, in 2021, medium-chain chlorinated paraffins (MCCPs) were proposed to be listed as POPs. We investigated SCCP and MCCP amounts and homolog profiles in four wild fish species from Bahía Blanca Estuary, a South Atlantic Ocean coastal habitat in Argentina. SCCPs and MCCPs were detected in 41% and 36% of the samples, respectively. SCCP amounts ranged from <12 to 29 ng g−1 wet weight and <750–5887 ng g−1 lipid weight, whereas MCCP amounts ranged from <7 to 19 ng g−1 wet weight and <440–2848 ng g−1 lipid weight. Amounts were equivalent to those found in fish from the Arctic and Antarctic Oceans and from some North American and Tibetan Plateau lakes. We performed a human health risk assessment and found no direct risks to human health for SCCP or MCCP ingestion, according to present knowledge. Regarding their environmental behavior, no significant differences were observed among SCCP amounts, sampling locations, species, sizes, lipid content, and age of the specimens. However, there were significant differences in MCCP amounts across species, which could be attributed to fish size and feeding habits. Homolog profiles in all fish were dominated by the medium-chlorinated (Cl6 and Cl7) CPs and shorter chain length CPs were the most abundant, with C10Cl6 (12.8%) and C11Cl6 (10.1%) being the predominant SCCPs and C14Cl6 (19.2%) and C14Cl7 (12.4%) the predominant MCCPs. To the best of our knowledge, this is the first study on the presence of CPs in the environment in Argentina and the South Atlantic Ocean. CP occurrence in the environment, particularly in the food chain, promotes the need for further research on their occurrence and behavior, and the impact of CPs in marine ecosystems in Argentina.

Simulation of Hydrologic Change of Linggo Co during 1979–2012 Using Hydrologic and Isotopic Mass Balance Model

The Tibetan Plateau (TP) and surrounding areas contain the largest number of glaciers outside the polar regions. The region affects downstream water supply and food security, thereby directly influencing one-third of the world’s population. The lakes in the central TP expanded rapidly in recent decades, which has attracted growing attention. Glacier meltwater was considered as a major component in the water balance of TP lakes, although few studies quantified its contribution. Stable isotope analysis is a powerful tool to trace hydrologic circulation, while its interpretation in paleoclimate records has been controversial. To bridge the gap between hydrologic and paleoclimatic studies, we performed a hydrologic and isotopic mass balance model to simulate the lake level change of Linggo Co in the central TP. The model was forced by the meteorological data, calibrated through observed lake level changes, and validated by oxygen isotope compositions (δ18O) of lake water. Our results indicated that glacier meltwater contributed 73.94% of the inflow water to Linggo Co before 1993 but decreased thereafter. Increasing glacier meltwater together with positive water balance (precipitation/evaporation) in the catchment contributed to the rapid expansion of Linggo Co after the mid-1990s. Lake water δ18O in Linggo Co was more sensitive to changes in the precipitation amount and precipitation δ18O than temperature. Our findings could shed light on the usage of δ18O proxy in future paleoclimate research on the TP.

Dataset of Comparative Observations for Land Surface Processes over the Semi-Arid Alpine Grassland against Alpine Lakes in the Source Region of the Yellow River

Thousands of lakes on the Tibetan Plateau (TP) play a critical role in the regional water cycle, weather, and climate. In recent years, the areas of TP lakes underwent drastic changes and have become a research hotspot. However, the characteristics of the lake-atmosphere interaction over the high-altitude lakes are still unclear, which inhibits model development and the accurate simulation of lake climate effects. The source region of the Yellow River (SRYR) has the largest outflow lake and freshwater lake on the TP and is one of the most densely distributed lakes on the TP. Since 2011, three observation sites have been set up in the Ngoring Lake basin in the SRYR to monitor the lake-atmosphere interaction and the differences among water-heat exchanges over the land and lake surfaces. This study presents an eight-year (2012–19), half-hourly, observation-based dataset related to lake–atmosphere interactions composed of three sites. The three sites represent the lake surface, the lakeside, and the land. The observations contain the basic meteorological elements, surface radiation, eddy covariance system, soil temperature, and moisture (for land). Information related to the sites and instruments, the continuity and completeness of data, and the differences among the observational results at different sites are described in this study. These data have been used in the previous study to reveal a few energy and water exchange characteristics of TP lakes and to validate and improve the lake and land surface model. The dataset is available at National Cryosphere Desert Data Center and Science Data Bank.

Occurrence, spatial distribution, and sources of PFASs in the water and sediment from lakes in the Tibetan Plateau.

Per-and polyfluoroalkyl substances (PFASs) are omnipresent globally and received increasing attention recently. However, there are limited data on PFASs in the Tibetan Plateau (TP), a remote high-altitude mountain region, which is regard as an important indicator region to study long-range transport behaviors of contaminants. This study investigates the occurrence, distribution, partitioning behavior, and sources of 26 PFASs in water and sediments from the four lakes of TP. The ΣPFAS concentrations ranged from 338 to 9766pgL-1 in water, and 12.2-414pgg-1 dry weight in sediments. Perfluorobutanonic acid (PFBA) and perfluorooctane sulfonate (PFOS) were detected in all samples. Qinghai Lake had the highest ΣPFAS concentrations in both water and sediments, while the Ranwu Lake had the lowest. The functional groups and CF2 moiety units were investigated as essential factors influencing the partition behavior. Principal component analysis (PCA) combined back-trajectory was used to infer possible sources of PFASs. The results suggested that the main source of PFASs in Yamdrok Lake, Namco Lake, and Ranwu Lake on southern TP were mainly originated from South Asia via long-range atmospheric transport (LRAT); while for the Qinghai Lake of northern TP, LRAT, local emissions, and tourism activities were the primary sources of PFASs.

Lake dynamics in Tibetan Plateau during 1990-2020 and exploratory factor analyses using Google Earth Engine.

Tibetan Plateau (TP) lakes are crucial water resources for many countries, and the region is sensitive to climate change, so the TP lakes' dynamics have always been the focus of TP research. Given the vastness of the TP, the diversity of topography, geomorphology, and meteorological features, and the significant disparities in precipitation between river basins, it is vital to examine lake dynamics and influencing variables from the basin's perspective. Based on Landsat imageries and supported by Google Earth Engine, lakes were mapped from 1990 to 2020. Results show that the TP lake's number and area have increased significantly in recent 30years except for a noticeable shrinkage from 1990 to 1995 and a slight decrease from 2013 to 2015. The lake area in the endorheic region basin area has grown obviously, with the most significant dynamics in the Qiangtang Basin, where the lake's number and total area have increased by about 30% over the 30years. In contrast, the lake areas in the outflow region basins were relatively stable. The dynamics were obviously affected by temperature, but the influencing factors and degree of influence on different river basins vary. The lake area in the Amu Dayra Basin and the Yellow Basin was more closely related to precipitation, and the lake area in the Hexi Basin was more related to temperature. The results provide a comprehensive understanding of lake spatial-temporal dynamics in the Tibetan Plateau and its river basins and a reference for studying lake long time series.

MSCANet: multiscale context information aggregation network for Tibetan Plateau lake extraction from remote sensing images

ABSTRACT Qinghai-Tibet Plateau lakes are important carriers of water resources in the ‘Asian’s Water Tower’, and it is of great significance to grasp the spatial distribution of plateau lakes for the climate, ecological environment, and regional water cycle. However, the differences in spatial-spectral characteristics of various types of plateau lakes, and the complex background information of plateau both influence the extraction effect of lakes. Therefore, it is a great challenge to completely and effectively extract plateau lakes. In this study, we proposed a multiscale contextual information aggregation network, termed MSCANet, to automatically extract Plateau lake regions. It consists of three main components: a multiscale lake feature encoder, a feature decoder, and a Multicore Pyramid Pooling Module (MPPM). The multiscale lake feature encoder suppressed noise interference to capture multiscale spatial-spectral information from heterogeneous scenes. The MPPM module aggregated the contextual information of various lakes globally. We applied the MSCANet to the lake extraction of the Qinghai-Tibet Plateau based on Google data; additionally, comparative experiments showed that the MSCANet proposed had obvious improvement in lake detection accuracy and morphological integrity. Finally, we transferred the pre-trained optimal model to the Landsat-8 and Sentinel-2A dataset to verify the generalization of the MSCANet.

Spatio-Temporal Evolution of Glacial Lakes in the Tibetan Plateau over the Past 30 Years

As the Third Pole of the Earth and the Water Tower of Asia, the Tibetan Plateau (TP) nurtures large numbers of glacial lakes, which are sensitive to global climate change. These lakes modulate the freshwater ecosystem in the region but concurrently pose severe threats to the valley population by means of sudden glacial lake outbursts and consequent floods (GLOFs). The lack of high-resolution multi-temporal inventory of glacial lakes in TP hampers a better understanding and prediction of the future trend and risk of glacial lakes. Here, we created a multi-temporal inventory of glacial lakes in TP using a 30-year record of 42,833 satellite images (1990–2019), and we discussed their characteristics and spatio-temporal evolution over the years. Results showed that their number and area had increased by 3285 and 258.82 km2 in the last 3 decades, respectively. We noticed that different regions of the TP exhibited varying change rates in glacial lake size; most regions show a trend of expansion and increase in glacial lakes, while some regions show a trend of decreasing such as the western Pamir and the eastern Hindu Kush. The mapping uncertainty is about 17.5%, which is lower than other available datasets, thus making our inventory reliable for the spatio-temporal evolution analysis of glacial lakes in the TP. Our lake inventory data are publicly published, it can help to study climate change–glacier–glacial lake–GLOF interactions in the Third Pole and serve as input to various hydro-climatic studies.

Comparison of Lake Extraction and Classification Methods for the Tibetan Plateau Based on Topographic-Spectral Information

Accurate identification and extraction of lake boundaries are the basis of the accurate assessment of lake changes and their responses to climate change. To reduce the effects of lake ice and snow cover, mountain shadows, cloud and fog shielding, alluvial and proluvial deposits, and shoals on the extraction of lake boundaries on the Tibetan Plateau, this study developed an RNSS water index to increase the contrast between the lake and similar surface objects of the spectral curve, and constructed a new method flow for lake extraction on the Tibetan Plateau based on image synthesis, topographic-spectral feature indexes, and machine learning algorithms. The lake extraction effects of three common machine learning classification algorithms were compared: the Cart decision tree, random forest (RF), and gradient boosting decision tree (GBDT). The results show that the new lake extraction method based on topographic-spectral characteristics and the GBDT classification method had the highest extraction accuracy for Tibetan Plateau lakes in 2016 and 2021. Its overall accuracy, Kappa coefficient, user’s accuracy, and producer’s accuracy for 2016 and 2021 were 99.81%, 0.887, 83.55%, 94.67% and 99.88%, 0.933, 89.18%, 98.24%, respectively, and the total area of lake extraction was the most consistent with the validation datasets. The three classification methods can effectively extract lakes covered by ice and snow, and the extraction effect was ranked as GBDT &gt; RF &gt; Cart. The lake extraction effect under mountain shadow was ranked as Cart &gt; GBDT &gt; RF, and the lake extraction effect under alluvial deposits and shoals was ranked as GBDT &gt; RF &gt; Cart. The results may provide technical support for extracting lakes from long time series and reveal the impact of climate change on Tibetan Plateau lakes.

Nonhomologous Black Carbon Decoupled Char and Soot Sequestration Based on Stable Carbon Isotopes in Tibetan Plateau Lake Sediment.

Combustion-derived black carbon (BC) is an important component of sedimentary carbon pool. Due to different physicochemical properties, determining the source of char and soot is crucial for BC cycling, especially for nonhomologous char and soot in the Tibetan Plateau (TP). This study analyzed the sequestration and source of BC, char, and soot in the Dagze Co (inner TP) sediment core via the content and δ13C, revealing the biomass and fossil fuel driving on nonsynchronous char and soot and their response to local anthropogenic activities and atmospheric transmission. The results showed that BC concentration increased from 1.19 ± 0.35 mg g-1 (pre-1956) to 2.03 ± 1.05 mg g-1 (after 1956). The variation of char was similar to BC, while nonhomologous growth was detected in char and soot (r = 0.29 and p > 0.05). The source apportionment showed that biomass burning for 71.52 ± 10.23% of char and promoted char sequestration. The contribution of fossil fuel combustion to soot (46.67 ± 14.07%) is much higher than char (28.48 ± 10.23%). Redundancy analysis confirmed that local anthropogenic activities significantly influenced BC burial and atmospheric transport from outside TP-regulated BC burial. The contribution of biomass and fossil fuels to nonsynchronous char and soot is conducive to understanding the anthropogenic effect on BC burial in the TP.

Water Environmental Characteristics and Water Quality Assessment of Lakes in Tibetan Plateau

Lakes are an important water resource and biological habitat in the Tibetan Plateau. Owing to the combined influence of climate, topography, and other natural factors as well as human factors, the water environment of the lakes on the Tibetan Plateau is facing more and more severe problems and challenges. To clarify the present status, distribution pattern, main characteristic factors of water quality, and important factors affecting the water quality of lakes on the Tibetan Plateau, the water environment of 12 typical lakes on the Tibet Plateau was investigated in summer (July-August) and autumn (October-November) in 2020. The field sampling and laboratory test data comprehensive analysis showed that:① several physical and chemical parameters of typical lakes on the Tibetan Plateau differed in spatiotemporal distribution. ② Salinity was the main characteristic of water quality in the typical lakes on the Tibetan Plateau. ③ The spatiotemporal distribution of lake eutrophication index showed little diversity and basically ranged from poor nutrition to moderate nutrition. The spatial and temporal distributions in the lake water quality index (WQI) were significantly different. The lake WQI grade decreased from "Moderate" to "Very poor" with the increase in salinity area, and the lake water quality in autumn was better than that in summer. ④ The spatiotemporal differences in lake water quality on the Tibetan Plateau were mainly controlled by precipitation, evapoconcentration, and human activities. This study will provide scientific basis for water environment protection and improvement of water ecosystems on the Tibetan Plateau.

Importance of Parameterizing Lake Surface and Internal Thermal Processes in WRF for Simulating Freeze Onset of an Alpine Deep Lake

AbstractThe alpine lakes widely distributed over the Tibetan Plateau (TP) are not only highly sensitive to climate but also regulate the regional climate. However, the lack of TP alpine lake observations limits the understanding of the lake‐atmosphere interactions. Here, we show the relative importance of parameterizing lake surface and internal thermal processes in describing the lake energy budget and lake‐atmosphere interactions. Based on the in situ observations at Lake Nam Co, a large and deep lake in the TP, we employed the coupled Weather Research and Forecasting with lake (WRF‐Lake) model to clarify their relative roles. Results show that the original model produces cold biases and too early timing of lake freeze onset. The adjustments of parameterizations of lake internal (temperature of maximum water density, extinction coefficient) and lake surface (roughness length) processes significantly improve the ability of the WRF‐Lake in simulating the lake thermal features and the freeze onset timing. The different parameterizations of lake internal thermal processes affect the onset timing of lake freeze mainly by altering the release of turbulent heat fluxes in summer, but the adjustments of lake surface roughness lengths change the turbulent heat fluxes during the unfrozen season from summer through early winter. Accordingly, the simulated lake freeze onset is much more sensitive to the surface roughness length schemes than to the internal thermal processes schemes. As the lake‐atmosphere interactions are very sensitive to the lake freeze onset, our results are critical for understanding and simulating the impact of TP lakes on the regional climate.

Widespread declines in water salinity of the endorheic Tibetan Plateau lakes

The Tibetan Plateau (TP) hosts more than one thousand lakes (>1km2) in its endorheic basins. The changing climate in recent decades has led to significant modifications in the endorheic hydrologic system. Most TP lakes experienced dramatically expanding areas, rising water levels, and increasing storage, which inevitably influenced the lake salinity. This study provides a regional-scale investigation of water salinity changes of the TP lakes (for 83 lakes with two-epoch salinity records, among the approximately 160 lakes >50km2) by synthesizing multi-source data around the 1970s and 2010s. Our results reveal lake salinity has considerably declined for most expanding lakes across the endorheic basins. The mean salinity of 62 terminal lakes dropped from 92.76 g l−1 to 42.00 g l−1 during the 1970s–2010s, in contrast to the slight variations (3.42 g l−1 to 1.48 g l−1) of the 21 exorheic or upstream lakes. As a result, many hypersaline lakes have become polysaline or oligosaline lakes, such as Cedo Caka, Norma Co, etc. In particular, some large lakes (e.g., Siling Co, ‘Twin Lakes’, and Ayakkum Lake) also experienced significant drops in water salinity, with the exceptional cases for Nam Co and Qinghai Lake probably due to the relatively low ratios of increased water mass to their net storages. The widespread declining water salinities could greatly influence bacterial richness, diversity, and evenness, and affect the aquatic carbon cycle and utilization in the high-altitude endorheic lakes. More attention should be paid on understanding the saline lake ecosystem evolution and the regional carbon cycle in response to changing water salinity of the TP lakes.

Drivers of Warming in Lake Nam Co on Tibetan Plateau Over the Past 40 Years

AbstractThe lake surface water temperature (LSWT) on Tibetan Plateau (TP) is sensitive to climate change. Based on a 1‐D lake model, we have investigated the interdecadal variation and long‐term trend of LSWT in Lake Nam Co (LNC) on TP during 1980–2018 and quantified the relative contributions of atmospheric factors to the LSWT trend. Results show LNC was warmed with a rate of 0.29°C decade−1, which is smaller than the warming of ambient air (0.45°C decade−1). The weakened wind speed, rising air temperature, increased downward longwave radiation, and decreased shortwave radiation contributed about 35%, 30%, 20%, and −15% of the estimated long‐term LSWT trend during 1980–2018, respectively. The contribution rate of 32.5% was from the interactions among all forcing variables. The primary warming was completed before 1997 (0.30°C decade−1) and was followed by a hiatus that the LSWT jumped to a warm level with a slightly negative trend (−0.08°C decade−1) after 1997. During this hiatus, the wind speed recovered from decrease and the deceleratingly increased downward longwave radiation slowed down the LNC warming. Particularly, the specific humidity shifted from increasing to decreasing trend played a key role in the hiatus of LNC warming after 1997, despite its slight contribution (−2.5%) to the LSWT trend during 1980–2018. The results showed the particularity of warming for a TP lake compared to the other ice‐covered lakes worldwide and provided a quantitative perspective for understanding the relative contributions of atmospheric factors to the long‐term trend of LSWT.

Sources and cycling of dissolved organic and inorganic carbon on the northern Qinghai-Tibetan Plateau: Radiocarbon results from Qinghai Lake

Tibetan Plateau lakes are sensitive to climate variabilities and affect regional temperature, precipitation and ecosystems. In this study, we investigated the concentrations and carbon isotope (14C and 13C) compositions of dissolved organic and inorganic carbon (DOC and DIC) along with the concentrations of major lithologic ions (Na+, Mg2+, K+, Ca2+) and dissolved silicate (DSi) in a large lake, namely, Qinghai Lake, and its seven inflowing rivers on the northeastern Qinghai-Tibetan Plateau of China. Our results revealed large differences in concentrations and isotopic compositions between DOC and DIC, as well as differences in the concentrations of major ions between the rivers and lake. The chemical weathering of carbonate and silicates in the catchments played important roles in controlling the fates of major ions in the rivers. In Qinghai Lake, evaporation resulted in 40–290 times the accumulation of Na+, Mg2+, and K+ observed in the rivers, while biological uptake and precipitation reduced the concentrations of Ca2+ and DSi in the lake by 4–17 times compared with those in the rivers. In addition, the concentrations of DOC and DIC in the lake were 6–7 times those in the rivers. The carbon isotope (δ13C and Δ14C) signatures of DOC and DIC revealed that the rivers transport millennium-aged DOC (1254 ± 316 years) and DIC (1513 ± 857 years), as influenced largely by the chemical weathering of rocks and preaged soil carbon on the plateau. In contrast, in Qinghai Lake, the ages of DOC are significantly younger (684 ± 378 years) than the ages of riverine DOC, as regulated by newly biologically produced modern DOC. Moreover, the DIC ages in Qinghai Lake are all modern, indicating that exchange with atmospheric CO2 is the dominant process controlling the lake DIC. The accumulation and removal of riverine-aged DIC in Qinghai Lake, however, are not well understood, and the unbalanced radiocarbon in lake DIC remains a mystery that needs further study.

Evolving phytoplankton primary productivity patterns in typical Tibetan Plateau lake systems and associated driving mechanisms since the 2000s

Phytoplankton primary productivity from the surface to the euphotic depth (PPeu) is an important indicator for estimating the carbon (C) sequestration capacity of a lake system. Approximately 50% of China's lake systems are distributed throughout the Tibetan Plateau (TP), playing an important C neutrality role in China and beyond. Over the past 20 years, the PPeu of TP lake systems may undergo dramatic spatial and temporal transformation under the significant influence of climate change and human activities. To reveal corresponding changing mechanisms, this study explored spatiotemporal PPeu patterns in typical TP lake systems with MODIS observations during 2002–2020. Since the 2000s, results reveal that the annual mean PPeu in TP lake systems ranges from 476.7 to 621.6 mg C/m2/d, with an average value of 553 ± 36.2 mg C/m2/d. Spatially, PPeu was much higher on the northeastern boundary and in the south of the TP compared to its remaining northern regions. PPeu trends in TP lake systems with higher salinity levels and those at higher altitudes were lower. Temporally, 48% of lakes on the TP exhibited a significant descending PPeu trend, while 31% of lakes exhibited a significant ascending trend. PPeu in TP lake systems may have mostly been influenced by day length (decimal hours), land surface temperature, and chlorophyll-a (Chl-a) content while being mainly limited by relative humidity (RHU). Additionally, PPeu also showed a significant positive relationship with total N and P imported from wastewater in TP (especially in Tibet), indicating that anthropogenic emissions could have an important influence on PPeu. Spatiotemporal pattern and driving mechanism results from this study can help us better understand the C sequestration capacity of TP lake systems.

Variation of satellite-derived total suspended matter in large lakes with four types of water storage across the Tibetan Plateau, China

Total suspended matter (TSM), as an indicator of the concentration of fine materials in the water column including particulate nutrients, pollutants, and heavy metals, is widely used to monitor aquatic ecosystems. However, the long-term spatiotemporal variations of TSM in lakes across the Tibetan Plateau (TP) and their response to environmental factors are rarely explored. Accordingly, taking advantage of the Landsat top-of-atmosphere reflectance and in-situ data, an empirical model (R2 = 0.83, RMSE = 1.08 mg/L, and MAPE = 19.49 %) was developed to estimate the average autumnal TSM in large TP lakes (≥50 km2) during the 1990–2020 period. For analyzing the spatiotemporal variability in TP lakes TSM, the examined lakes were classified into four types (Type A-D) based on their water storage changing in different periods. The results showed that the lakes in the southern and some northeastern parts of the TP exhibited lower TSM values than those situated in other regions. The assessment of TSM in each of these four lake types showed that more than half of them had a TSM value of <20 mg/L. Apart from Type D, the lakes with the TSM showing significantly decreasing trends were dominantly Types A-C. A relative contribution analysis involving five driving factors indicated that they contributed by >50 % to lake TSM interannual variation in 73 out of 114 watersheds, and the lakes area change demonstrated the greatest contribution (82.2 %), followed by wind speed (11.0 %). Further comparison between the entire lake and the non-expansive regions suggested that the expansive region played an indispensable role in determining the TSM value of the whole lake. This study can help to better understand the water quality condition and provide valuable information for policy-makers to maintain sustainable development in the TP region.

A Low-Cost Approach for Lake Volume Estimation on the Tibetan Plateau: Coupling the Lake Hypsometric Curve and Bottom Elevation

The widespread lakes on the Tibetan Plateau (TP) are key components of the water cycle, thus the knowledge of their spatial distribution and volume is crucial for understanding the hydrological processes under ongoing climate change. Many previous studies focus on investigating surface elevation, inundation area variations and water volume changes for these lakes. However, how much water is stored in lakes across the TP remains relatively unexplored. It is because of the incapacity of satellite remote sensing methods in lake depth measurements and the high cost of field bathymetric measurement. This study developed a low-cost approach by integrating remote sensing data and limited underwater surveys. The observed lake areas and surface elevations generated the elevation-area relationship. Underwater surveys were conducted to detect the potentially “maximum” lake depths using three optimized survey routes. With the constraint of lake-bottom elevation, the lake-bottom zone area could be estimated for calculating the lake volume. Experiments on nine TP lakes with different size and geometric characteristics demonstrate that the optimized survey line along the lake short axis is well balanced in efficiency and accuracy, with an overall volume bias of 15% approximately. The proposed hypsometric curve method coupled with the bottom elevation measurement is expected to provide a simplified but efficient solution for estimating the lake water volume on the TP, which could be applicable to ungauged lakes in other harsh environments.

Influence of salinity on glycerol dialkyl glycerol tetraether-based indicators in Tibetan Plateau lakes: Implications for paleotemperature and paleosalinity reconstructions

Glycerol dialkyl glycerol tetraethers (GDGTs) are powerful molecular tools that are suitable for paleoenvironmental reconstruction. The widely distributed lakes on the Tibetan Plateau (TP) are important terrestrial paleoenvironmental archives. However, studies on the distributions and environmental responses of branched GDGTs (brGDGTs; analyzed by a new method) are scarce, which makes their environmental response uncertain, further hindering the development of paleoclimate research and the reliability of reconstruction results for the TP region. Herein, we report the distribution of brGDGTs and archaeols in surface sediments from 83 lakes and 22 surrounding soils across the TP. The potential source, environmental response of sedimentary brGDGTs, and the implications for the application of GDGT-based indicators are further discussed. Our results indicate that the sedimentary brGDGTs in the TP lakes were mainly produced in-situ. Lake salinity had a noticeable effect on the brGDGT-based temperature indicators. Coupled with the global lake dataset, we found that the methylation index of 5-methyl brGDGTs (MBT'5ME) responded to temperature in freshwater lakes, while that of 6-methyl brGDGTs (MBT'6ME) showed a better correlation with temperature in saline lakes. However, both indices showed a poor correlation in brackish lakes. These varied responses implied that biological communities producing 5- and 6-methyl brGDGTs were likely to be different, and that 6-methyl brGDGTs might be predominantly synthesized in high-salinity environments. Furthermore, these responses will affect the reliability of paleotemperature records reconstructed by MBT'5ME or MBT'6ME paleothermometers. Therefore, it is essential to evaluate the applicability of these two proxies before using them for paleotemperature reconstruction. In addition, the applicability of GDGT-based salinity indicators on the TP was assessed. Both the archaeol and caldarchaeol ecometric (ACE) and its alternative approach ACE' showed good correlation with lake salinity on the TP, and their high response thresholds to salinity were also noted. It is therefore that these salinity proxies may only be applicable to large paleo-hydrological/salinity fluctuations. In contrast, the isomer ratio of 6- and 7-methyl brGDGTs (IR6 + 7ME and its revised form IR'6 + 7ME) was sensitive to salinity and covered different salinity ranges, which may represent novel salinity proxies. The integration of ACE and IR'6 + 7ME indicators could provide a basis for producing relatively reliable records of paleosalinity and palaeohydrological fluctuations. In conclusion, our work highlights the influence of salinity on GDGT-based indicators and can serve as a reference for paleotemperature and paleosalinity reconstructions in lakes.

Systematical δ13C investigations of TOC in aquatic plants, DIC and dissolved CO2 in lake water from three Tibetan Plateau lakes

The carbon isotope values (δ13C) of aquatic plants are of great significance for recognizing carbon cycles and tracing environmental changes in lakes. Yet, the influence of δ13C values of their utilizing carbon sources (especially in the case of CO2 separated from the HCO3– in water) on their δ13C differences have never been evaluated, which is mainly due to the lack of CO2 δ13C investigations in lake water. In this study, we used a newly developed fast-response automated gas equilibrator for real-time concentration and δ13C determination of dissolved CO2 in the surface and bottom lake water of Lake Tuosu, Lake Qinghai and Lake Keluke, China. Moreover, we determined the corresponding δ13C values of total organic carbon (TOC) of a submerged plant (Potamogeton) and an alga (Cladophora), as well as the δ13C values of dissolved inorganic carbon (DIC) in bottom lake water. The results showed that the CO2 δ13C values of bottom and surface water in these three lakes did not show significant differences and the δ13C values of CO2 at different water depths also did not show significant differences. However, Potamogeton had higher TOC δ13C values (average 14–16‰) than Cladophora in these lakes. Although Potamogeton and Cladophora could utilize HCO3– as an additional carbon source whose δ13C values were more positive (ca. 7–8‰) than CO2, this effect on their δ13C values was no >4‰ after evaluation. Thus, our results show that the δ13C values of carbon sources (including CO2 and HCO3–) are not the main factors in determining the TOC δ13C difference between Potamogeton and Cladophora, which could be primarily related to the biosynthetic fractionation for different aquatic plant species. Our results benefit further understanding and interpretations of δ13C variations in carbon cycles and paleoenvironment reconstructions for lakes.

Effects of climate change and nutrient concentrations on carbon sources for zooplankton in a Tibetan Plateau lake over the past millennium

Effects of climate change and nutrient concentrations on carbon sources for zooplankton in a Tibetan Plateau lake over the past millennium