Endorheic Research Articles

Climatic and hydrological variations on the southwestern Tibetan Plateau during the last 30,000 years inferred from a sediment core of Lake Zabuye

Climate change on the Tibetan Plateau (TP) is governed by the mid-latitude westerlies and Indian summer monsoon (ISM). However, the past hydrological changes on the TP induced by interactions between the westerlies and the ISM remain unclear. A sediment core from Lake Zabuye on the southwestern TP was analyzed to reconstruct climatic and hydrological variability over the last 30 kyr. Stable isotopic compositions (δ 13 C and δ 18 O) of authigenic carbonate act as an indicator of hydrological status for closed-basin lakes on the TP. Four major climatic and hydrological stages were identified: (1) last glacial maximum (29.8–18.9 cal kyr BP), the influence of the westerlies dominated, and a cold-wet climate prevailed; (2) last deglaciation (18.9–11.8 cal kyr BP), the influence of the westerlies receded, and a general trend of decreased wetness was interrupted by two pronounced glacial meltwater events recorded at 17.2 and 15.2 cal kyr BP, respectively; (3) early and middle Holocene (11.8–3.8 cal kyr BP), the Holocene climate optimum was attained and sustained under the dominance of ISM circulation; (4) late Holocene (from 3.8 cal kyr BP to the present), the ISM collapsed during the middle to late Holocene, and a hypersaline lacustrine environment was ultimately formed, as inferred from mirabilite deposition and isotopic signals. Our lake record demonstrates an anti-phase relationships between the westerlies and the ISM on the glacial-interglacial timescale over the southwestern TP. We suggest that both North Atlantic climate and tropical ocean temperature are major drivers of climatic variations on the TP.

Long-Term Water Level Fluctuations in Terminal Lakes of Central Asia

Long-Term Water Level Fluctuations in Terminal Lakes of Central Asia

30,000 Years of the southwestern Lake Urmia (Iran) paleoenvironmental evolution inferred from mineralogical indicators from lake and watershed sediments

• A robust chronology of sediments that matches the paleoclimate records from Lake Urmia (Iran) was established. • Continuous lake evolution was recorded based on grain size and XRD mineralogical analyses that include total sediment and specific clay and carbonate fractions of the catchment and lake sediments for the last 30 kyr. • Multi-proxy reconstructions suggest a humid Late Pleistocene , followed by frequent drier/wetter episodes, wet early Holocene and evaporative conditions during the Mid to Late Holocene transition. • A tentative reconstruction of lake levels from selected lakes surrounding Lake Urmia was performed at the regional Middle East scale. In order to understand the pattern and trends of the environmental evolution of Lake Urmia (Iran), one of the largest terminal lakes in Western Asia before its level drop over the past two decades, two sediment cores (Golman 6, 8.0 m; Golman 7, 12.5 m) were collected from the recently dried-out southwestern part of the lake. These sediment cores represent a continuous sedimentary sequence, composite core, that was extensively studied for grain size, total mineralogy including clay minerals, carbonates and their crystallinities, in comparison with the basin geological formations and within a reliable AMS- 14 C timescale. Lake Urmia deposits cover the time-span from 30 to ca 2 cal kyr BP. Grain-size of the siliclastic fractions from the lower part of the composite core consists of fine-silt and clay particles likely representing lacustrine deposits while the top sediments are characterized by variable composition of sand and silt. At about 30 cal kyr BP, our proxies indicate a low lake stand and even drying out at the coring site, which was followed by water level rise and the establishment of lacustrine conditions between 29.9 and 20.2 cal kyr BP. Since then, all our data suggest lake’s highly unstable conditions. Subsequently, clearly low lake levels to sometimes the drying out was recorded during the 20.2–15.3 cal kyr BP, 13.3–11.8 cal kyr BP and 5.6–4.1 cal kyr BP intervals. In contrast, lacustrine conditions were re-established between 15.3 and 13.3 cal kyr BP, between 11.8 and 5.6 cal kyr BP and between 4 0.1 and 2.3 cal kyr BP. High water level recorded between 15.3 and 13.3 cal kyr BP can be attributed to the Bölling/Alleröd warming, and the following regressive phase during the 13.3–11.8 cal kyr BP period corresponds to the Younger Dryas period. In the Early-Mid Holocene, the lacustrine environment from 11.8 to 5.6 cal kyr BP was characterized by high aragonite and salt contents, highlighting evaporative environment as like during the 29.9–20.2 cal kyr BP period. Our results allowed the Late Quaternary climate reconstruction at Lake Urmia basin scale and record the past climate change at a larger Western Asia scale.

Towards a Sustainable World: Diversity of Freshwater Gastropods in Relation to Environmental Factors—A Case in the Konya Closed Basin, Türkiye

The Konya Closed Basin (KCB) in Türkiye plays a key role in agricultural production and freshwater supply. However, the basin is impacted by humanly derived nitrogenous compounds and toxic metals. Keeping the water quality at a potable level in the basin is compulsory. This study was part of a project yielding monitoring of water quality in KCB in accordance with the Water Framework Directive (2000/60/EC). Eleven stations, except Beyşehir Lake and Mamasın Dam, were sampled for the first time for freshwater molluscs. Community structure indexes and multivariate statistical analyses were applied to determine the microhabitats of gastropods and their responses to environmental changes. The structure and distribution of gastropod assemblages differed depending on total phosphate, total nitrogen, dissolved oxygen, and pH. This study revealed that most of the gastropods in KCB are relatively tolerant to biodegradable pollution. However, there is a strong observed decline in population size requiring intensive future monitoring; measures have to be taken to preserve the remaining populations. Two endemic species need an urgent action plan to protect their habitats: Theodoxus anatolicus of Çeltik Canal and Bithynia pseudemmericia of Beyşehir Lake; a re-assessment of their extinction risk according to the IUCN rules is needed (2022). The results of this study will be useful for comparison with future studies to document potential improvements or continued ecological regression in the quality of aquatic ecosystems in the watershed.

The interactive feedback mechanisms between terrestrial water storage and vegetation in the Tibetan Plateau

A component of terrestrial water storage, vegetation is also an influential driver of changes in terrestrial water storage. In the context of warming on the Tibetan Plateau, it is essential to explore the relationship between changes in terrestrial water storage and vegetation in this region to understand further the role of vegetation in the changes of water systems in alpine mountains. Our study combines terrestrial water storage anomalies data and vegetation indices to determine how their interact. The results indicate a warming rate of 0.44°C/decade (p<0.01) over the Tibetan Plateau from 1980–2020, while evapotranspiration trended upward (12.9 mm/decade, p<0.01), which is slower than precipitation (15 mm/decade, p<0.01). On the Tibetan Plateau, spatial-temporal differences in temperature, precipitation, and evapotranspiration dominate the variations in terrestrial water storage. The change in terrestrial water storage was relatively stable from 2003 to 2011, but decreased from 2012 to 2016. Terrestrial water storage increased in endorheic basins while decreasing in exorheic basins. Partial correlation analysis indicates a negative correlation between the terrestrial water storage anomaly and the temperature. It is found that terrestrial water storage and net precipitation are positively correlated in the Yangtze River Basin and the northeast of the endorheic basins. However, the Qaidam Basin and the north part of the Yellow River Basin are negatively correlated. Under the current climate change state (the increased rate of precipitation is faster than actual evapotranspiration), vegetation change has an insignificant impact on the changes in terrestrial water storage. In contrast, changes in terrestrial water storage (surplus/deficit) significantly affect vegetation changes (greening/browning) in parts of the Tibetan Plateau. The study contributes to a deeper understanding of the relationship between water system changes and vegetation on the Tibetan Plateau.

Selection of the most suitable biogas facility location with the geographical information system and multi-criteria decision-making methods: a case study of Konya Closed Basin, Turkey

Selection of the most suitable biogas facility location with the geographical information system and multi-criteria decision-making methods: a case study of Konya Closed Basin, Turkey

Assessing the water security effectiveness of integrated river basin management: Comparative case study analysis for lesson-drawing

Climate change, population growth, over-abstraction and industrial pollution are impacting the security of water resources globally, raising policy relevant questions over the optimality of institutional arrangements for their management. This paper seeks to add to this debate by assessing the effectiveness of integrated river basin management for achieving water security, in two case studies: the Konya Closed Basin in Turkey, and the Kern County Subbasin in California. A modified Institutional Analysis and Development (IAD) framework is employed to compare biophysical, community and governance factors in these cases to show how they influence water security, measured through a dedicated set of indicators. Results show that differentials in water security outcomes between the cases is, in part, related to how organizational rules compel actor participation in planning processes and the degree of coherence between multi-level institutions, particularly inter-agency collaboration. On this basis, the paper then engages with the public policy theory literature on lesson-drawing to assess the potential for policy learning for these specific contexts and other countries. The significance of the study therefore relates to its holistic integration of governance analysis, comparative case design and lesson-drawing for informing future river basin institutional design in achieving effective water security.

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.

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

• River–groundwater–salt lake system is unusually enriched in B and Li elements. • B and Li isotopes are favorable to trace their origin and evolution processes. • Deep fluids with depleted B and Li isotopes upwell to supply main source. • Abundant sources and favorable tectonics govern enrichment of B and Li resources. 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 δ 11 B and δ 7 Li 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.