The hidden risk: Changes in functional potentials of microbial keystone taxa under global climate change jeopardizing soil carbon storage in alpine grasslands.

Climate change is endangering the soil carbon stock of alpine grasslands on the Qinghai-Tibetan Plateau (QTP), but the limited comprehension regarding the mechanisms that sustain carbon storage under hydrothermal changes increases the uncertainty associated with this finding. Here, we examined the relative abundance of soil microbial keystone taxa and their functional potentials, as well as their influence on soil carbon storage with increased precipitation across alpine grasslands on the QTP, China. The findings indicate that alterations in precipitation significantly decreased the relative abundance of the carbon degradation potentials of keystone taxa, such as chemoheterotrophs. The inclusion of keystone taxa and their internal functional potentials in the two best alternative models explained 70% and 63% of the variance in soil organic carbon (SOC) density, respectively. Moreover, we found that changes in chemoheterotrophs had negative effects on SOC density as indicated by a structural equation model, suggesting that some specialized functional potentials of keystone taxa are not conducive to the accumulation of carbon sink. Our study offers valuable insights into the intricate correlation between precipitation-induced alterations in soil microbial keystone taxa and SOC storage, highlighting a rough categorization is difficult to distinguish the hidden threats and the importance of incorporating functional potentials in SOC storage prediction models in response to changing climate.

Coupling strength of human-natural systems mediates the response of ecosystem services to land use change.

Addressing the dynamics of human-natural systems (HNS) driven by land use change (LC) is a key challenge for the sustainable development of ecosystem services (ES). However, how changes to the HNS coupling relationships affect ES is rarely reported. We used network analysis methods to construct an HNS correlation network in the Loess Plateau based on the correlation between the main components of HNS, such as ES, human factors, landscape pattern, vegetation cover, climate change and geomorphic characteristics, and quantitatively described the HNS coupling relationships through key network attributes. We analyzed the variation in HNS network attributes and their relationships with ES along an LC intensity gradient. The results show that carbon storage and soil conservation in the Loess Plateau increased by 0.56% and 0.26%, respectively, during the study period, while the habitat quality and water yield decreased by 0.11% and 0.18%, respectively. An increase in LC intensity reduces connectivity and density in the HNS network, which results in looser connections among HNS components. Importantly, we found that HNS network attributes explained 85% of ES variation across different LC intensity gradients and that connectivity and density had the strongest explanatory power. This means that LC mainly affects ES dynamics by changing the coupling strength of HNS. Our research offers a new perspective for linking LC-HNS-ES, which will help guide practitioners toward establishing and maintaining the sustainability of human well-being amidst changing HNS.

Dramatic shift in the drivers of ecosystem service trade-offs across an aridity gradient: Evidence from China's Loess Plateau.

Increased aridity creates challenges for sustainable ecosystem management due to the potential for trade-offs among ecosystem services. However, our understanding of how ecosystem service trade-offs (EST) respond to aridification remains limited. Here, generalized additive models and structural equation modeling were used to explore EST dynamics within an aridity gradient on the Loess Plateau, China. Trade-offs between water yield and both carbon storage and habitat quality showed nonlinear relationships with aridity, first increasing and then decreasing. Interestingly, climatic and human factors mostly indirectly influenced EST via effects on landscape characteristics. In regions with an Aridity Index (AI) value of <0.5, climatic and human factors strongly drove EST; in regions with AI > 0.5, landscape characteristics were most important. Therefore, landscape characteristics acted as the key regulators of EST. Importantly, AI values of ∼0.5 represented a transition point, after which dramatic shifts in EST-driver relationships were observed. As >22 % of the Earth's terrestrial surface is projected to reach this level of aridity by 2100, further research on this boundary (between sub-humid and semi-arid areas) is urgently needed to protect ecosystems from the effects of increasing aridity. This study may serve as a valuable reference for mitigating the potential negative effects of increased aridity on human well-being.

Network analysis reveals the regulatory effect of mixed stands on ecosystem structure and functions in the Loess Plateau, China.

Afforestation, an important measure for ecological restoration, has been implemented all over the world, but fragile ecosystem structures and climate change endanger its ecological functions. One major obstacle to optimizing ecological function has been quantifying and characterizing a complex ecosystem structure. Here, the structure and functions of six types of land-use restoration were investigated in the hilly-gully region of the Loess Plateau, China. In total, 44 ecological factors from canopy, understory and soil were determined. We constructed the related network of reforestation ecosystems, quantified the structure of ecosystem through network topology, and explored the relationships between structure and functions. The results showed that changes in plantation type altered the network hubs, but some nodes, such as species height, breast-height diameter and understory biomass, were often keystone hubs. Mixed plantations enhanced the connectivity among different modules. In addition, we found that closeness of network connectivity was an important factor influencing ecological functions, while soil erodibility was the main limiting factor for reforestation ecosystem structure in this region. Moreover, mixed plantations tended to have more balanced topological metrics and ecological functions. Overall, this study suggests that mixed plantations or monoculture plantations should be designed according to the characteristics and ecological demands of the regional ecological environment. Although monoculture plantations may support local ecosystems, mixed plantations offer more resilience to a landscape because they were help to achieve a balance among the ecological functions.

Waste-Printed Circuit Board Recycling: Focusing on Preparing Polymer Composites and Geopolymers.

The waste from end-of-life electrical and electronic equipment has become the fastest growing waste problem in the world. The difficult-to-treat waste-printed circuit boards (WPCBs), which are nearly 3-6 wt % of the total electronic waste, generate great environmental concern nowadays. For WPCB treatment and recycling, the mechanical-physical method has turned out to be more technologically and economically feasible. In this work, the mechanical-physical treatment and recycling technologies for WPCBs were investigated, and future research was directed as well. Removing electric and electronic components (EECs) from WPCBs is critical for their crushing and metal recovery; however, environmentally friendly and high-efficiency removal techniques need be developed. Concentrated metals rich in Cu, Al, Au, Pb, and Sn recovered from WPCBs need be further refined to add to their economic values. The low value-added nonmetallic fraction of waste-printed circuit boards (NMF-WPCBs) accounts for approximately 60 wt % of the WPCBs. From the perspective of environmental management, a zero-waste approach to recycling them should be developed to gain values. Preparing polymer composites and geopolymers offers many advantages and has potential applications in various fields, especially as construction and building materials. However, the mechanical and thermal properties of NMF-WPCBs composites should be further improved for preparing polymer composites. Surface modification or filler blending could be applied to improve the interfacial comparability between NMF-WPCBs and the polymer matrix. The NMF-WPCBs shows potential in preparing cement mortar and geological polymers, but the environmental safety resulting from metals needs to be taken into account. This study will provide a significant reference for the industrial recycling of NMF-WPCBs.

[Study on the leaching toxicity and disposal method of arsenic-bearing sludge].

OBJECTIVE: To study the leaching toxicity of the ferric salt and aluminum salt containing arsenic-bearing sludge coming from the high arsenic drinking water treated by coagulation/microfiltration process and its disposal method. METHODS: The Chinese standard method and TCLP method issued by USEPA were used to test the leaching toxicity of arsenic-bearing sludge and its Portland cement solidification tests were conducted. Minor ferric salt containing arsenic-bearing sludge was added into road-application concrete for its utilization. RESULTS: The arsenic concentrations in TCLP leaching solutions of ferric salt and aluminum sludge were 118 microg/L and 420 microg/L, respectively, which were higher than 9.5 microg/L and 11.8 microg/L of the Chinese standard method. However, all of them were less than identification standard for hazardous wastes of China. When arsenic-bearing sludge was solidified with cement, its leaching toxicity reduced about 90%. The unconfined compression strengths of solidification products were 3.25MPa and 0.76MPa which could meet the requirement for the landfill and sludge reclamation. The compression strengths of road-application concrete were upgraded about 12% when minor parts of ferric salt arsenic-bearing sludge was added. CONCLUSION: Ferric salt and aluminum salt arsenic-bearing sludge do not belong to the hazardous waste with leaching toxicity. Cement solidification is an efficient method for the disposal of arsenic-bearing sludge. The mix of arsenic-bearing sludge with road-application concrete could provide a method for the efficient utilization of arsenic-bearing sludge. At the same time, the possible environmental problems should be avoided.

[Application of pressure-driven membrane technologies for the removal of arsenic from drinking water].

Endemic arsenism caused by ingestion of arsenic-bearing drinking water has been an important public health problem in China. The experimental results of arsenic removal from drinking water by press-driven membrane technologies in recent years are introduced in this paper. Arsenic removal efficiencies and its influencing factors are mainly discussed. It is put forward the idea that coagulation/microfiltration process should be the hotspot in recent study in China due to its high arsenic removal efficiency, low energy consumption and high water recovery.