Dynamic changes in water resources and comprehensive assessment of water resource utilization efficiency in the Aral Sea basin, Central Asia.

The Aral Sea Basin in Central Asia faces significant challenges in improving water utilization and treatment because of frequent transboundary river water disputes and shortages of water resources. However, the traditional water resource utilization efficiency (WRUE) assessment models generally have the defect of over-validating evaluation results. To solve this problem, this study used the Coefficient of Variation method to constrain the self-contained weights in the traditional Data Envelopment Analysis (DEA) to construct an improved CV-DEA model, and assessed the WRUE of the Aral Sea Basin countries during 2000-2018 and compared the WRUE with that of the countries in the Mekong River Basin and Northeast Asia, then explored the factors influencing water utilization. The conclusions were drawn: since 1960, the runoff from the upper Amu Darya and Syr Darya rivers increased significantly, while the runoff from the lower Amu Darya River into the Aral Sea declined. Meanwhile, the water area of the Aral Sea shrank from 2.56 × 104 km2 to 0.70 × 104 km2 in 2000-2018, with the Northern Aral Sea remaining stable while the southern part shrinking sharply. The WRUE of the Aral Sea Basin (0.599, on average) was higher than that of the Mekong River Basin (0.547) and lower than that of Northeast Asia (0.885). Kazakhstan and Uzbekistan had the highest WRUE of 0.819 and 0.685 respectively, and the WRUE in both two countries improved from 2000 to 2018. Tajikistan (0.495) and Turkmenistan (0.402) experienced decreases in WRUEs. The high input redundancy of agricultural water consumption was the main driving force affecting WRUE in the basin.

Magnetic responses for heavy metal pollution recorded by the sediments from Bohai Sea, Eastern China.

The Bohai Sea is facing multidirectional pressure from economic development and pollutant emissions. Magnetic minerals and heavy metal concentrations in the sediments of core M5 from the Bohai Sea were performed. The results of concentration-related magnetic parameters, heavy metal contents, and PLI (Tomlinson pollution load index) illustrate there are essential linkages of the sources, migration, and deposition. The predominant magnetic mineral was magnetite. Based on the chronological data from 210Pb and 137Cs activities, the increasing magnetic parameters and heavy metal concentrations at a depth of 81 cm were dated to 1950 CE, which corresponded to the establishment of the People's Republic of China; the decrease at depths of 37-45 cm and 16-18 cm may be related to the decline in steel production in 1960 CE and the Tangshan earthquake in 1978 CE, respectively. This study enriches relevant theories of environmental magnetism via the ecological and environmental protection of the coastal zones.

Source and Quality of Groundwater Surrounding the Qinghai Lake, NE Qinghai-Tibet Plateau.

Comprehensive studies on the spatial distribution, water quality, recharge source, and hydrochemical evolution of regional groundwater form the foundation of rational utilization of groundwater resources. In this study, we investigated the water levels, hydrochemistry, and stable isotope composition of groundwater in the vicinity of the Qinghai Lake in China to reveal its recharge sources, hydrochemical evolution, and water quality. The level of groundwater relative to the level of water in the Qinghai Lake ranged from -1.27 to 122.91 m, indicating most of the groundwater to be flowing into the lake. The local evaporation line (LEL) of groundwater was simulated as δ2 H = 6.08 δ18 O-3.01. The groundwater surrounding the Qinghai Lake was primarily recharged through local precipitation at different altitudes. The hydrochemical type of most of the groundwater samples was Ca-Mg-HCO3 ; the hydrochemistry was primarily controlled by carbonate dissolution during runoff. At several locations, the ionic concentrations in groundwater exceeded the current drinking water standards making it unsuitable for drinking. The main source of nitrate in groundwater surrounding the Qinghai Lake was animal feces and sewage, suggesting that groundwater pollution should be mitigated in areas practicing animal husbandry in the Qinghai-Tibet Plateau, regardless of industrial and urbanization rates being relatively low in the region. The scientific planning, engineering, and management of livestock manure and wastewater discharge from animal husbandry practices is a crucial and is urgently required in the Tibetan Plateau.

Comparing watershed black locust afforestation and natural revegetation impacts on soil nitrogen on the Loess Plateau of China.

This study examined a pair of neighbouring small watersheds with contrasting vegetations: artificial forestland and natural grassland. Since 1954, afforestation which mainly planted with black locust has been conducted in one of these watersheds and natural revegetation in the other. The differences in soil total N, nitrate, ammonium, foliar litterfall δ(15)N and dual stable isotopes of δ(15)N and δ(18)O in soil nitrate were investigated in the two ecosystems. Results showed that there was no significant difference in soil total N storage between the two ecosystems, but the black locust forestland presented higher soil nitrate than the grassland. Moreover, the foliar litterfall N content and δ(15)N of the forestland were significant higher than the grassland. These results indicate that 60 years of watershed black locust afforestation have increased soil N availability. The higher nitrate in the forestland was attributed to the biological N fixation of black locust and difference in ecosystem hydrology. The dual stable isotopes of δ(15)N and δ(18)O revealed that the two ecosystems had different sources of soil nitrate. The soil nitrate in the forestland was likely derived from soil N nitrification, while the soil nitrate in the grassland was probably derived from the legacy of NO3(-) fertiliser.

Stable isotopes reveal sources of precipitation in the Qinghai Lake Basin of the northeastern Tibetan Plateau.

The use of isotopic tracers is an effective approach for characterizing the moisture sources of precipitation in cold and arid regions, especially in the Tibetan Plateau (TP), an area of sparse human habitation with few weather and hydrological stations. This study investigated stable isotope characteristics of precipitation in the Qinghai Lake Basin, analyzed moisture sources using data sets from NCEP-NCAR, and calculated vapor contributions from lake evaporation to the precipitation in the basin using a two-component mixing model. Results showed that the Local Meteoric Water Line (LMWL) was defined as δ(2)H=7.86 δ(18)O+15.01, with a slope of less than 8, indicating that some non-equilibrium evaporation processes occurred when the drops fell below the cloud base. Temperature effects controlled δ(18)O and δ(2)H in precipitation in the basin, with high values in summer season and low values in winter season. Moisture in the basin was derived predominantly from the Southeast Asian Monsoon (SEAM) from June to August and the Westerly Circulation (WC) from September through May. Meanwhile, the transition in atmospheric circulation took place in June and September. The SEAM strengthened gradually, while the WC weakened gradually in June, and inversely in September. However, the Southwest Asian Monsoon (SWAM) did not reach the Qinghai Lake Basin due to the barrier posed by Tanggula Mountain. High d-excess (>10 ‰) and significant altitude and lake effects of δ(18)O in precipitation suggested that the vapor evaporated from Qinghai Lake, strongly influenced annual precipitation, and affected the regional water cycle in the basin distinctly. The monthly contribution of lake evaporation to basin precipitation ranged from 3.03% to 37.93%, with an annual contribution of 23.42% or 90.54 mm, the majority of which occurred in the summer season. The findings demonstrate that the contribution of evaporation from lakes to atmospheric vapor is fundamental to water cycling on the TP.

Natural vegetation restoration is more beneficial to soil surface organic and inorganic carbon sequestration than tree plantation on the Loess Plateau of China.

Natural vegetation restoration and tree plantation are the two most important measures for ecosystem restoration on the Loess Plateau of China. However, few studies have compared the effects of the two contrasting measures on soil organic and inorganic carbon (SOC and SIC) sequestration or have further used SOC and SIC isotopes to analyze the inherent sequestration mechanism. This study examined a pair of neighboring small watersheds with similar topographical and geological backgrounds. Since 1954, natural vegetation restoration has been conducted in one of these watersheds, and tree plantation has been conducted in the other. The two watersheds have now formed completely different landscapes (naturally restored grassland and artificial forestland). Differences in soil bulk density, SOC and SIC content and storage, and SOC and SIC δ(13)C values were investigated in the two ecosystems in the upper 1m of the soil. We found that SOC storage was higher in the grassland than in the forestland, with a difference of 14.90 Mg ha(-1). The vertical changes in the δ(13)CSOC value demonstrated that the two ecosystems have different mechanisms of soil surface organic carbon accumulation. The SIC storage in the grassland was lower than that in the forestland, with a difference of 38.99 Mg ha(-1). The δ(13)CSIC values indicated that the grassland generates more secondary carbonate than the forestland and that SIC was most likely transported to the rivers from the grassland as dissolved inorganic carbon (DIC). The biogeochemical characteristics of the grassland were favorable for the formation of bicarbonate. Thus, more DIC derived from the dissolution of root and microbial respired CO2 into soil water could have been transported to the rivers through flood runoff. It is necessary to study further the transportation of DIC from the grassland because this process can produce a large potential carbon sink.