Endorheic Research Articles

What Controls Lake Contraction and Then Expansion in Tibetan Plateau’s Endorheic Basin Over the Past Half Century?

AbstractThe evolutions of climate‐sensitive lakes on the Tibetan Plateau’s endorheic basin exhibited lake shrinkage before the mid‐1990s, but widespread and rapid lake expansions ever since. However, the quantitative contribution of glacier meltwater to lake changes, and the exact mechanisms behind its dominant drivers remain elusive. Here, a comprehensive examination of glacier mass balance since ∼1975 reveals that excess glacier meltwater compensated for net lake volume loss by 21% ± 5% during its contraction period 1975–1995, whereas promoted net volume gain by 9% ± 1% during expansion period 1995–2020 and by 17% ± 2% over the entire period 1975–2020. Further analyses reveal that the interdecadal variations of sea surface temperatures in the Atlantic, Pacific, and Indian Oceans favor a net moisture inflow to the Tibetan Plateau, leading to increased precipitation since 1995 relative to 1970s–1995, which effectively elucidates the climatic process causing rapid lake volume expansion in the endorheic basin.

Delineation of Hydrochemical Characteristics and Tracing Nitrate Contamination of Groundwater Based on Hydrochemical Methods and Isotope Techniques in the Northern Huangqihai Basin, China

Hydrochemical research and identification of nitrate contamination are of great significant for the endorheic basin, and the Northern Huangqihai Basin (a typical endorheic basin) was comprehensively researched. The results showed that the main hydrochemical facies were HCO3–Mg·Ca and HCO3–Ca·Mg. Spatial variation coefficients of most indices were greater than 60%, which was probably caused by human activities. The hydrochemical evolution was mainly affected by rock weathering and also by cation exchange. The D–18O relationship of groundwater was δD = 5.93δ18O − 19.18, and the d–excess range was −1.60–+6.01‰, indicating that groundwater was mainly derived from precipitation and that contaminants were very likely to enter groundwater along with precipitation infiltration. The NO3(N) contents in groundwater exceeded the standard. Hydrochemical analyses indicated that precipitation, industrial activities and synthetic NO3 were unlikely to be the main sources of nitrate contamination in the study area. No obvious denitrification occurred in the transformation process of nitrate. The δ15N(NO3) values ranged from +0.29‰ to +14.39‰, and the δ18O(NO3) values ranged from −6.47‰ to +1.24‰. Based on the δ15N(NO3) – δ18O(NO3) dual isotope technique and hydrochemical methods, manure, sewage and NH4 fertilizers were identified to be the main sources of nitrate contamination. This study highlights the effectiveness of the integration of hydrochemical and isotopic data for nitrate source identification, and is significant for fully understanding groundwater hydrochemistry in endorheic basins and scientifically managing and protecting groundwater.

Lake volume variation in the endorheic basin of the Tibetan Plateau from 1989 to 2019

Lake storage change serves as a unique indicator of natural climate change on the Tibetan Plateau (TP). However, comprehensive lake storage data, especially for lakes smaller than 10 km2, are still lacking in the region. In this dataset, we completed a census of annual relative lake volume (RLV) for 976 lakes, which are larger than 1 km2, on the endorheic basin of the Tibetan Plateau (EBTP) during 1989–2019 using Landsat imagery and digital terrain models. Our method first identifies individual lakes, determines their analysis extents and calculates annual lake area from Landsat imagery. It then derives lake area-elevation relationship, estimates lake surface elevation, and calculates RLV. Validation and comparison with several existing datasets indicate our data are more reliable and comprehensive. Our study complements existing lake datasets by providing a complete and long-term lake water volume change data for the region.

Exacerbated drought accelerates catastrophic transitions of groundwater-dependent ecosystems in arid endorheic basins

• Two Haloxylon species exhibited distinct water use strategies but analogous bistable transitions. • Drought accelerates catastrophic shifts in both Haloxylon ecosystems by reducing resilience. • Natural and anthropogenic forcings are aggravating drought in groundwater-dependent ecosystems. • Drought adaptation strategies for such ecosystems must account for maintaining resilience. Drought has become a major threat to regional sustainable development in drylands. Ecological drought, emphasizing the process of drought impacts on ecosystems in coupled human-natural systems, has been posing large risks to the stability of groundwater-dependent ecosystems (GDEs) in drylands. Yet, the interconnected avenues via which ecological drought drives vegetation transition, ecological resilience and ecosystem services in GDEs with species-specific traits remain elusive, especially in arid endorheic basins. Here, we combine comprehensive field measurements derived from representative groundwater depth transects in Central Asia and simulations obtained from the stochastic eco-hydrological models and the Langevin approach, we find that two groundwater-dependent species, the salt-tolerant Haloxylon ammodendron and salt-sensitive Haloxylon persicum , exhibit contrasting water use strategies being driven by variations in eco-physiological traits and environmental regimes. Nonetheless, both the low-resilient H. ammodendron and high-resilient H. persicum vegetation tend to show bistable transition corresponding to vegetated and bare soils under drought stress with stochastic noises and time delays. Alarmingly, ecological drought is accelerating catastrophic transitions in both Haloxylon ecosystems induced by diminishing ecological flows, depleting soil moisture, and aggravating salinization, together with climate forcing. In particular, exacerbated drought stress reduces ecological resilience, enhances the likelihood of catastrophic shifts, and reduces ecosystem services of GDEs in arid endorheic basins. Our results highlight that ecological drought adaptation strategies must account for resilience maintenance by balancing water scarcity, water overuse, and water/soil quality to avoid accelerating regime shifts in dryland ecosystems.

Implications From the Meteorological Data Effects on Water Level Fluctuations of the Lake Van (Eastern Anatolia/Türkiye)

Lake Van is located in the eastern part of Türkiye and forms the largest soda lake in the world. In this study, we present the relationship between instrumental data which belongs to Lake Van level changes and meteorological parameters by performing a multilevel analysis. The data set consists of monthly average levels of Lake Van and monthly meteorological parameters (temperature, precipitation and wind speed) between 1944-2019 years. Two different multilevel linear models; random intercept, random intercept and slope model were used. Unstructured (UN) covariance structure and Maximum Likelihood (ML) were used for repeated measurements and estimation, respectively. Log-likelihood (ll), Akaike Information Criteria (AIC), Bayesian Information Criteria (BIC) and AIC Corrected (AICC) were used for the selection of the best model. The random intercept and slope model (Model II) is explained as the best model for the lake level changes in this study. Statistical results in this study indicated that the temperature and wind speed are the key parameters controlling the Lake Van water level fluctuations, whereas the precipitation effect is minimal due to the type of precipitation (snowfall). For this reason, temperature, wind speed and also the type of precipitation (snowfall or rain) must be considered for disaster modelling in settlements of Lake Van and similarly closed basin lakes.

Atmospheric recycling of agricultural evapotranspiration in the Tarim Basin

Precipitation recycling, defined as that precipitation in a region is partially contributed by evapotranspiration from the same region, is the interaction between terrestrial hydrology and atmospheric processes, and plays a crucial role in forming water resources. For agricultural lands, the evapotranspiration of irrigation water alters local climate by reprecipitation in surrounding regions, which can also be analyzed from the viewpoint of precipitation recycling. As the largest endorheic basin in China, the Tarim Basin has strong precipitation recycling contributed by the surrounding mountains, as well as large irrigation areas producing high-quality cotton, which makes it an appropriate study case for the recycling of irrigation water. In this paper, we calculate the water vapor sources of precipitation (WSoP) and the reprecipitation of evapotranspiration (RPoET) in the Tarim Basin by using the Water Accounting Model—Two Layers, analyze their spatial distributions, and find the moisture recycling ratio of the basin as 15.4%. We set up comparative scenarios of evapotranspiration increase by irrigation areas in different locations of the Tarim Basin, and study their difference in reprecipitation and moisture recycling. Results show that the evapotranspiration increase in different locations has a marginal reprecipitation ratio ranging from 8% to 24%, and further boosts the whole basin’s moisture recycling ratio by 0.11%–0.29%. Significant difference among the scenarios proves that the location of irrigation areas affects the reprecipitation of its evapotranspiration, and the optimized moisture recycling can benefit water resource and ecosystem conditions inside the basin. In summary, this work would be useful to provide a practical basis for irrigation planning by considering the land-atmosphere interaction.

Ecological Assessment of Terminal Lake Basins in Central Asia under Changing Landscape Patterns

Climate change and anthropogenic activities drive the shrinkage of terminal lakes in arid areas to varying degrees. Ecological water conveyance (EWC) projects have emerged globally to restore the ecology of terminal lakes. However, there remains a lack of qualitative evaluation of the benefits of EWC on terminal lakes. This study compared the Taitema Lake Basin with the Aral Sea Basin in Central Asia, representative of terminal lake basins with and without EWC, respectively. The results show that the water area of Taitema Lake increased by 7.23 km2/year due to EWC (2000–2019), whereas that of the Aral Sea Basin decreased by 98.21% over the entire process of natural evolution (1972–2019). Land use changes before and after the EWC (1990–2019) included an increase and decrease in desert land and water bodies in the Aral Sea Basin, and a decrease and increase in desert land and arable land in the Tarim River Basin, respectively. The normalized difference vegetation index (NDVI) and actual evaporation (ETa) are the main factors influencing the change in the water area of the Aral Sea Basin with the changing environment, while EWC is the main factor influencing the change in the water area of Taitema Lake. The results confirm that EWC is a feasible measure for achieving ecological restoration of a terminal lake watershed in an arid area.

Potential impacts of reduced inflows to the Salton Sea: Forecasting non‐market damages

AbstractTerminal lakes throughout the American West provide important amenity and environmental values, but many are shrinking due to reduced inflows and warming temperatures. In California's Imperial Valley, agricultural water use reductions diminish inflows supporting the Salton Sea, a terminal desert lake and important environmental amenity for both the region and the state as a whole. The costs of these reduced inflows are difficult to monetize yet complicate management decisions. We assess the costs of potential future drought‐induced transfers by linking novel hydrologic scenarios to an economic framework for quantifying local and regional damages based on existing estimates of non‐market environmental values from the literature. The costs of lost wetland ecosystems, increases in particulate matter from exposed playa, and other local disamenities are substantial. For the scenarios considered, they range between approximately $500 million and $1 billion in present value (2019 USD). Estimated damages per acre‐foot (or thousand m3) of reallocated water exceed several thousand dollars. The majority arise from loss of wetland habitat; incremental particulate matter damages are relatively modest in our modeling but exacerbate salient air quality issues in the region. Interest in reallocating water from Imperial Valley, the largest user of Colorado River water, to other applications will increase over time. Our work highlights the importance of evaluating the impacts of such efforts.

Internal drainage system of Aldegondabreen, Spitsbergen, according to speleological studies

The systems of internal drainage of glaciers have been studied mainly by indirect methods. In order to reveal the structure of the internal drainage network inside Aldegondabreen, moulins and glacial caves were investigated by speleological methods in 2001–2021, which was accompanied by a semi-instrumental topographic survey in the cavities. This allowed us to see the change in the glacial cavities over time. There are three types of moulins in Aldegondadreen: active, dead and healed ones. We visited active and dead moulins. The depth of the entrance pits in the moulins varies from 52 to 65 m (moulin group No 1), from 70 to 75 (moulin group No 2) and from 45 to 60 m (moulin group No 3). The depth of moulins is equal to the thickness of the cold ice layer. Using the structure of the moulins, we show that the water from moulin group No 1 flows to the right marginal part of the glacier tongue. The water from moulin groups No 2 and No 3 flows to the left margin part of the glacier tongue, which is confirmed by the mapping of healed moulins locations. We find that the number of active and dead moulins has been decreasing since 2001, while the number of healed moulins has increased. We attribute this to a decrease in the thickness of the temperate ice layer at the base of the glacier due to climate change. Many moulins have narrow meanders at the lower part of the entrance pits, which usually finish by siphons. None of the moulins reaches the glacier bed, their lower parts are usually located in clean transparent ice. The lifetime of the moulins usually does not exceed 6 years. Our study of the caves on the glacier tongue revealed that they can be englacial or subglacial, and they originate along sub-horizontal thrusts located in the ice. We assume that the moulins reach the slip planes along thrusts close to the glacier bed. The water from the moulins flows along these slip planes as a film in early summer and turns into channels in mid- or late summer. The presence of thrusts in the ice depths can explain the development of internal drainage systems in glaciers (regardless of their size), outbursts of glacial lakes, surges and the formation of eskers. Clastic material for eskers formation can penetrate into a cave channel from the contact areas of the thrusts with uplifts on the bed. The results obtained can help in the interpretation of the available geophysical data for this glacier.

Possible formation pathways for zeolites in closed-basin lakes on noachian Mars: Insights from geochemical modeling

Zeolites are among the most common and widespread authigenic silicate minerals found in saline-alkaline paleolacustrine environments on Earth. Analcime, a Na-zeolite, has been detected on crustal outcrops on Mars using orbital spectral image data. Identifying other zeolite species is complicated by the lack of diagnostic absorption features in spectral data and spectral similarity to some polyhydrated sulfates. Therefore, analcime is the only zeolite species so far unambiguously identified as present on Mars. The presence of certain zeolite mineral species or assemblages in a closed basin paleolake can be used to track hydrological changes in that basin. This paper discusses the application of geochemical modeling to identify zeolite phases that could have formed in closed lake basins of late Noachian Mars. The composition of the high-silica Buckskin sample from Gale crater is used as a starting material because 1) most zeolite-rich assemblages in closed hydrologic systems on Earth originate from the decomposition of high-silica volcanic glass, and 2) geochemical modeling studies are already available for the more common lower silica basalts on Mars. This study, along with previous studies involving basaltic starting materials, allow a comparison between terrestrial and Martian data and an exploration of the differences in secondary mineral precipitation with substrates of different silica contents. The EQ3/6 geochemical modeling code was adopted, and Late Noachian Mars was assumed to be warm and semi-arid, with an atmosphere with 1.3 bars of PCO2 and current Mars PO2 (14.7 μbar). The Buckskin sample was reacted with three different starting solutions including two different rainfall chemistries and an acidic H2SO4 − HCl solution, which could have formed through volcanic degassing. The mineral formation and re-dissolution patterns under different Water/Rock (W/R) ratios are also explored.The results show that near neutral and acidic solutions in closed-basin lakes filled with high-silica volcaniclastic materials could eventually produce zeolite minerals like those in saline-alkaline lakes on Earth. Analcime forms only in water-limited environments (low W/R ratio), while chabazite is present even at relatively high W/R ratio. Clinoptilolite transforms to analcime with an increase in pH, with decreased W/R ratio, and with time. Analcime was found to be the most stable zeolite mineral over the greatest range of conditions in this environment, associated with increased pH, consistent with its presence as a very common constituent of saline-alkaline lake deposits on Earth. The study shows that the mineral precipitation patterns associated with the dissolution of high-silica materials through acid weathering are comparable to the mineral precipitation patterns following the dissolution of basaltic rocks by acid weathering under 0 − 25oC conditions or hydrothermal conditions as described in previous laboratory, field, and geochemical modeling studies.

Boron and lithium isotopic constraints on their origin, evolution, and enrichment processes in a river–groundwater–salt lake system in the Qaidam Basin, northeastern Tibetan Plateau

The Nalenggele River Catchment (NRC) is the largest river sourced from the northern slope of the Eastern Kunlun Mountains (EKM). The NRC terminates in the Qaidam Basin and feeds tail salt lakes. The river–groundwater system (freshwater) and the terminal salt lakes display high concentrations of B and Li, ranking the Qaidam Basin as a world–class mineral system. However, the source, pathway, and enrichment mechanism of these elements remain unclear. In this study, the B and Li isotopes from rivers and groundwater from mountain to basin were used to trace their origin and evolution processes. B and Li are found in high concentrations even in river and groundwater with low total dissolved solids (TDS), with average concentrations tens to hundreds times higher than those of natural freshwater systems. The observed B and Li isotopic footprints are significantly depleted in heavy isotopes in the NRC if compared to other geological systems dominated by natural weathering processes. Following the confluence of one of the main tributaries of the Hongshui River (HSR) sourced from the EKM, the B and Li concentrations increase sharply, while the δ11B and δ7Li values gradually decrease. This study indicates that the mechanism accounting for the B and Li endowment of the river–groundwater–salt lake system is mainly related to the Li–B fertility of the sources (deep fluids and country rocks), favorable tectonic conduits for water circulation, and high evaporation rates. Specifically, the deep fluids upwelling is responsible for the sourcing of B and Li. These fluids are then discharged to the river and groundwater through geothermal springs developing along deep faults or within volcanic craters. In this frame, the river and groundwaters act as carriers, and input B and Li into the lake basin. Ultimately, B and Li undergo an evaporation–mediated fractionation ending with the formation of brines and eventually accounting for the formation of the world–class Li–B salt lake deposits.

Numerical investigation of groundwater flow systems and their evolution due to climate change in the arid Golmud river watershed on the Tibetan Plateau

Climate warming is the greatest future challenge to the hydrosphere and the human community, especially in arid and semiarid regions. This study took the Golmud river watershed on the Tibetan Plateau as an example to numerically identify the development of groundwater flow systems in a large arid sedimentary basin and explore what would the dramatic climate warming pose on groundwater flow system. The numerical results show that the Golmud river watershed has developed three hierarchical groundwater flow systems. River seepage is the predominant recharge for the groundwater systems inside the basin. The local groundwater flow system discharges some 82.69% of all groundwater in the basin, followed by the intermediate system with 14.26% and the regional system with 3.05%. The local system is mainly distributed in the shallow area of the alluvial-pluvial fan at the piedmont and provides the dominant water resource for human exploitation and oasis ecological usages. Climate warming would increase about 30.78% of the quantity of the recharge water to the groundwater system inside the basin via river seepage due to the increasing precipitation and increased glacier melt in the headwater region of the watershed. These waters would pose disturbances to all groundwater flow systems but to different degrees. The local flow system exhibits the largest response to the climate warming with more than 90% of increased water cycled in and discharged through it. The significant groundwater level rising leads to the trailing edge of the overflow belt at the piedmont moving ∼5 km towards to the mountain pass, which would potentially pose a water disaster to the local region. The influences of climate warming on the intermediate and regional flow system are relatively limited. This study provides a preliminary understanding of the influences of climate warming on the groundwater flow systems in arid endorheic basins and is essential for tackling future climate change challenges faced by arid and semiarid regions.

Styrofoam Recycling: Relaxation-Densification of EPS by solar heat

The problem of Styrofoam waste is multifaceted. Not only do we need to properly handle the current and future stream of newly manufactured Styrofoam objects, we also have many decades of inert Styrofoam occupying a large fraction of both our active and full/decommissioned landfills, and floating in our oceans and waterways. Solutions are therefore required for recycling current waste streams as well as mitigating huge volumes of legacy Styrofoam waste, distributed globally wherever human populations, landfills, waterways, terminal lakes, reservoirs, or ocean gyres exist. Simply banning Styrofoam, aside from packing peanuts, has been of limited effect because Styrofoam is simply too useful and inexpensive. It is essentially a super-material that is hard to replace and difficult to do without. Every environmentalist who owns a modern television unpacked it from a Styrofoam shell inside a large cardboard box. 
 Polystyrene, the fundamental constituent of Styrofoam, is a common plastic that recycles well. The problem with recycling Styrofoam is that as a foam it is about 98% air by volume, so it must be densified before transport for recycling: the air has to be removed from the foam to return it to its original form as a solid plastic again. The shipment of un-densified Styrofoam for recycling is not economically viable, it would take about 50 trucks to transport only one truck load of fully densified plastic. This equates to un-densified Styrofoam costing more money for paying the costs of factors such as fuel for the vehicle, more drivers, etc. This means, waste Styrofoam must be densified at or near the point of its end-of-use.
 The focus of our experiments was to see how well zero-carbon, widely distributable methods of heat exposure could densify different types of expanded polystyrene packing peanuts. We show that this can readily be accomplished using the range of temperatures achievable by a typical solar oven (at or above 300°F) — well below the melting temperature of polystyrene (~ 500°F).
 
 Rather than using solar heat for this experiment, the proof of concept was demonstrated in a temperature-controlled laboratory oven to maintain well-controlled and stable temperatures to allow the generation of accurate temperature-time-densification curves.
 At the highest temperatures (~ 300°F) and the longest exposure time (10 minutes), the densification factor ranged from 50 to 53. This is very close to the theoretical limit. Lower temperatures result in partial densification with higher variability. Larger pieces would need longer heat exposure times.
 To achieve full densification, we suggest using a temperature of at least 300°F (149°C) for 10 or more minutes, for pieces of Styrofoam about the size of packing peanuts. This is easily achievable in solar ovens
 This process can be readily done in distributed locations at or near the location of end-of-use for Styrofoam products wherever solar ovens can achieve temperatures of about 300°F, thereby making the recycling and upcycling of Styrofoam economically viable for most inhabited regions of the globe, and especially in equatorial areas where plastic waste is especially troublesome.

Structural Characteristics of Endorheic Rivers in the Tarim Basin

Endorheic rivers as landlocked systems with no hydrological connections to marine environments are suffering from water and ecosystem crisis worldwide, yet little is known about their structural characteristics with complex geomorphic and climatic dependence. Based on the river networks identified from 30 m resolution digital elevation models and surface water dynamic information derived from Landsat images, we investigate the hierarchical characteristics of 60 sub-basins in the Tarim Basin, the largest endorheic river basin in China. In the Tarim River basin, endorheic rivers exhibit a self-similarity only in the range of stream-orders 1–4, compared to the range of stream-orders 1–5 observed in exorheic rivers, owning to the limited stream power to maintain the similar aggregation of rivers in the arid regions. Moreover, the Tarim River networks demonstrate lower bifurcation ratio (2.48), length ratio (2.03), fractal dimension (1.38), and drainage density (0.24 km−1) in representative sub-basins, with a significant decay in median values compared with those derived from exohreic rivers at similar scales, suggesting sparser and imperfect developed branching river networks in endorheic basins. Further analysis on the Tarim reveals that endorheic river structure is more related to glacier extent (r = 0.67~0.84), potential evapotranspiration (r = 0.63~0.81), and groundwater type index (r = 0.64~0.73), which is essentially different from the structure of exorheic river represented by the Yellow River largely controlled by surface runoff, precipitation, and vegetation coverage. This study stresses the differences in intrinsic structural characteristics and extrinsic drivers of endorheic and exorheic rivers and highlights the necessity of differentiated strategies for endorheic river management in fragile ecosystems.

Closing the irrigation water productivity gap to alleviate water shortage in an endorheic basin

Closing the irrigation water productivity (IWP) gap is an effective approach to alleviating water deficits and ensuring food security. However, few studies have attempted to quantify the IWP gap and the potential benefits of closing it. This study adopted the Heihe River Basin, the second-largest inland basin in China, as a typical study area. The aims of this study were to: (1) assess the positive achievements and potential risks triggered by the Heihe Ecological Water Diversion Project (EWDP) according to multi-source and multi-scale measured data; (2) analyze potential approaches to improve the IWP and quantify the potential benefits that can be achieved by closing its IWP gap. The results of this study indicated that the EWDP effectively reallocated surface water resources, replenished groundwater in the lower reaches, and facilitated the recovery of oases and economic development in the downstream regions. However, this project has indirectly led to an imbalance in the groundwater resource between the middle and lower reaches, resulting in decline in groundwater levels and degradation of local vegetation in the midstream regions. In addition, the expansion of cultivated land in the midstream and downstream oases has resulted in the deterioration of farmland environment. The water transfer resulted in a deceleration in the growth of IWP from 2.44 % to 1.15 %, and the existing IWP gap was 1.43 kg/m3 between 1984 and 2017. This study predicted a future increase in the IWP to 2.01 kg/m3 with a reduction in the gap to 0.45 kg/m3 while maintaining food production. The potential for conserving water in the Heihe agricultural region can reach 552 million m3 by reducing the planting area by 10 %, improving irrigation water use efficiency by 20 %, maintaining existing agricultural film inputs, and reducing fertilizer application by 10 %. Following the research recommendations can greatly alleviate the agricultural water shortage and over-extraction of groundwater in the middle reaches and ensure meeting ecological water demand in the lower reaches. This study can act as a reference for sustainable management of an endorheic basin.

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.

Ancient mining pollution in early to middle Holocene lake sediments from the Lake Superior region, USA

Determining the timing and transport mechanisms (i.e. fluvial and/or atmospheric) of pollution associated with ancient copper mining on Isle Royale in Lake Superior (United States) is important for understanding the current and future trajectory of ecosystems affected by human activity. This study reports metal concentrations in sediment from two small, closed-basin lakes located on Isle Royale (Lily Lake and Pond 2) as a measure of the extent of heavy metal emissions from Indigenous, precontact mining and annealing activities associated with one of the world’s oldest metal working industries. Lily Lake and Pond 2 are both located near known mines, but neither lake contains mines in its catchment and thus could not have received pollution via fluvial transport. Elevated concentrations of lead in sediments dating to ∼6000 years ago at both lakes provide evidence of atmospheric transport of pollution associated with mining emissions. The age of ∼6000 years before present is consistent with the timing of elevated lead concentrations in sediment from McCargoe Cove on the northern shore of Isle Royale. Collectively, the data indicate that the peak in Archaic Period mining occurred on southwestern Isle Royale ∼6000 years ago and was preceded by periods that varied in intensity and location across the area. The discovery of pollution signals in lake sediments from the Lake Superior region provides clues as to the timing, spatial patterns, and magnitude of one of the world’s earliest large-scale metal mining efforts. These findings provide a basis for determining the transport mechanisms of ancient mining pollution and are a step toward assessing the full environmental impact of mining and metal working efforts by early human civilizations. • Anthropogenic lead was detected in lakes near prehistoric mines on Isle Royale. • The presence of anthropogenic lead indicates airborne pollution transport • The peak of mining and associated pollution occurred ∼6000 years ago. • Findings are consistent with regional sediment records and copper artifact dates.

Topo-bathymetric and hydrological study of the water system "Lagoon La Picasa", Argentina

Knowledge of the water balance of lagoons, surface, and underground basins is essential not only to use water resources more rationally in space and time but also to improve their control and redistribution. The La Picasa lagoon basin is an inter-jurisdictional endorheic basin in the Argentine Republic at the intersection of Córdoba, Santa Fe, and Buenos Aires provinces. This basin has recently gone through recurrent floods caused by an increase in the level of the lagoon, which has affected infrastructure, transport, and agricultural activity. In the present work, a lagoon-scale approach is proposed. For the topo-bathymetric study, the lagoon's Digital Elevation Model (DEM) was defined using data collection, fieldwork, and data processing. In contrast, a 0D water balance model was developed in the hydrological study. Based on these two models, the rainfall excesses that impacted the lagoon were analyzed and quantified for evacuation through gravity discharge, a pumping system, or a combination of both systems. The main objective was to define a 0D water balance model that represents the La Picasa lagoon and then uses it as a tool to evaluate future hydrological situations that may occur.

Application of hydrological and hydraulic models to quantify surface runoff in the endorheic system of the La Picasa Lagoon basin

The basins in the plain present particularities from the approach of the hydrological processes that take place there. They are characterized by presenting a predominance of vertical water movements (evapotranspiration-infiltration) over horizontal movements (runoff), showing a strong interrelation between surface and underground water. The La Picasa Lagoon basin is defined as a naturally depressed humid pampa region with an undulating plain relief that has low sectors of temporary flooding and permanent lagoons without a defined drainage network. It is an inter-jurisdictional endorheic basin between the provinces of Córdoba, Santa Fe, and Buenos Aires (Argentina) that has suffered recurrent floods between 2014 and 2017 caused by an increase in the average level of the lagoon reaching historical maximums, producing floods, and affecting infrastructure, transport, and agricultural activity. Due to these problems, through the application of hydrological and hydraulic models, the behavior of La Picasa basin system is quantified and evaluated to avoid future floods. In the present work, a hydrological model is applied using the HEC-HMS free tool and a 1D/2D hydraulic model using the HEC-RAS free tool, where the system of channels and reservoirs that make up the system is considered. The flood marks in reservoirs and La Picasa Lagoon are analyzed, and it is defined as regulating the variation of levels in the different reservoirs within permitted ranges. These models are a useful tool for studying future hydrological situations that may occur around the study area.

Climate change and water security in the northern slope of the Tianshan Mountains

Water security is under threat worldwide from climate change. A warming climate would accelerate evaporation and cryosphere melting, leading to reduced water availability and unpredictable water supply. However, the water crisis in the Northern Slope of Tianshan Mountains (NSTM) faces dual challenges because water demands for fast-growing urban areas have put heavy pressure on water resources. The mountain-oasis-desert system features glacier-fed rivers that sustain intensive water use in the oasis and end in the desert as fragile terminal lakes. The complex balance between water conservation and economic development is subtle. This paper investigates changes in hydroclimatic variables and water security-related issues on the NSTM. The spatiotemporal variations in glaciers, climatic variables, rivers, lakes and reservoirs, groundwater, surface water, human water use, and streamflow were analyzed for the past four decades. The results show that temperature in the NSTM exhibited an apparent upward trend with a more significant warming rate in the higher altitude regions. Glacier mass loss and shrinkage was strong. The average annual streamflow increased from 1980-1989 to 2006–2011 at most hydrological stations. The monthly dynamics of surface water area showed notable variability at both inter-annual and seasonal scales, revealing the impacts of both natural and anthropogenic drivers on surface water availability in the region. The terrestrial water storage anomaly showed a decreasing trend, which might be related to groundwater pumping for irrigation. Human water use for agriculture and industry grew with the increase in cultivated land area and gross domestic product (GDP). The increased agricultural water use was strongly associated with the expansion of oases. It is unclear whether water availability would remain high under future climatic and hydrological uncertainties, posing challenges to water management. In the context of rapid urban growth and climate change, balancing water for humans and nature is vital in achieving the Sustainable Development Goals (SDGs) in NSTM. This study provides a baseline understanding of the interplay among water, climate change, and socio-economic development in NSTM. It would also shed light on wise water management under environmental changes for other rapidly developing mountain-oasis-desert systems worldwide.