A system dynamics simulation-based strategic analysis of integrated water resources utilization and management in Shenzhen city.

As one of the most rapidly developing cities in China, Shenzhen grapples with an increasing challenge in managing water resources due to escalating conflicts with its soaring water demand. This study established a system dynamics (SD) model based on a causal loop diagram to explore the intricate interconnections within the urban water resources system. Through simulating water supply and demand in Shenzhen from 2021 to 2035, the model identified key sensitive factors and examined various utilization scenarios for multiple water resources. Results indicated that water scarcity posed a significant obstacle to Shenzhen's development. To tackle this challenge, several effective measures should be implemented, including enhancing water conservation capabilities, developing seawater resources, promoting water reuse, optimizing the economic structure, and managing population growth. Prioritizing water conservation efforts and maximizing the utilization of seawater resources were regarded as the most impactful strategies in alleviating the water crisis. Furthermore, the relationship between water conservation capabilities and seawater utilization scale was analyzed using the SD model, contributing to the development of a comprehensive water resources management strategy. The findings from this study would provide insights into robust methods for allocating water resources, thereby enhancing sustainable water management strategies applicable to regions facing similar challenges.

A novel method of identifying estuary high-nutrient zones for water quality management.

Coastal shallow waters are highly vulnerable to pollution, often leading to the development of intricate eutrophication zones. However, accurately determining these areas poses a significant challenge due to the complex interplay of estuarine hydrodynamics and nutrient transformation. To address such issue, a novel method was proposed to identify high-nutrient zones through calculating the continuous zonation of released tracers when their instantaneous concentrations declined to 1/e of their initial values. The method was well tested using idealized estuary models with varying shape parameters, water depths and river discharges. The results consistently revealed that the boundaries of high-nutrient zones fell within the mixed zone, characterized by salinity levels of 10- 20 psu. In Shenzhen Bay, a typical shallow bay, distinct differences were observed in the concentrations of dissolved inorganic nitrogen (DIN) and PO43-. Both the 20 psu isohaline and the proposed method effectively identified the partition boundary of high DIN and PO43- in 2001-2010, but only the newly proposed method demonstrated accuracy in delineating the actual high-nutrient zone during the continuous nutrient reduction period from 2010 to 2020. This study provides a practical and feasible approach that can serve as an auxiliary decision-making tool for managing estuarine water environments, and it has potential to facilitate the implementation of timely and effective measures for pollution control.

Toxic effects of lead (Pb), cadmium (Cd) and tetracycline (TC) on the growth and development of Triticum aestivum: A meta-analysis.

The environmental issue of lead (Pb), cadmium (Cd), and tetracycline (TC) contamination in cereal crops has become a growing concern worldwide. An in-depth understanding of this issue would be of importance to promote effective management strategies for heavy metals and antibiotics worldwide. The present study was conducted to assess the toxic effects of heavy metals (Cd, Pb) and antibiotics (TC) on Triticum aestivum (T. aestivum, common wheat) based on studies conducted in the past 22 years. Data pertaining to the growth and development of T. aestivum were extracted and analyzed from 89 publications spanning from 2000 to 2022. Our results showed that Pb, Cd and TC significantly reduced growth and development by 11 %, 9 %, and 5 %, respectively. Additionally, significant accumulation of Cd (42 %) and Pb (17 %) was observed in T. aestivum samples, although there was little change in TC accumulation, which showed limited absorption, accumulation, and translocation of TC in wheat plants. Pb had the greatest impact on the yield of T. aestivum, followed by Cd, while TC had no apparent effect. Furthermore, exposure to Cd, Pb and TC reduced the photosynthetic rate due to chlorophyll reduction, with Cd having the most pronounced effect (58 %), followed by Pb (37 %) and TC (8 %). Cd exposure also significantly enhanced gaseous exchange (37 %) compared to TC and Pb, which reduced gaseous exchange by 4 % and 10 %, respectively. However, the treatments with TC (>50-100 mgL-1), Pb (>1000-2000 mg L-1) and Cd (>500-1000 mg L-1) increased the defense system of T. aestivum samples by 38 %, 15 %, and 11 %, respectively. The obtained findings have significant implications for risk assessment, pollution prevention, and remediation strategies to address soil contamination from Pb, Cd and TC in farmland.

Development of biocatalytic microbial ecosystem (FPUS@RODMs@In-PAOREs) for rapid and sustainable degradation of various refractory organics.

The removal of diverse refractory organics from complex industrial wastewater continues to be a challenge. Although biological treatments are commonly employed, only partial degradation and increasing emergence of nitrogenous compounds, i.e., nitrate (NO3) and nitrite (NO2) would pose severe toxicity to the intact microbes. Herein, an efficient biocatalytic microbial ecosystem (BCME) was designed over a porous bio-carrier made of a functional polyurethane sponge (FPUS). The BCME comprised a unique set of organisms (RODMs) with novel metabolism, efficiently degrading highly-concentrated aromatics. Strategic enzyme immobilization was utilized to introduce in-situ production and aggregation of the oxidation and reduction enzymes (In-PAOREs) onto the FPUS, thereby ensuing sustained functions of the RODMs community. The developed FPUS@RODMs@In-PAOREs system was found to enhance the refractory organics removal rate to 4 kg/m3/day, and it would be attributed to the enzymatic catalysis of refractory organics (2000 mg/L) accompanied by the removal of COD (1200 mg/L) and nitrogenous compounds (200 mg/L). Besides, the fluctuating concentration of extra polymeric substances (EPS) played a dual role through enhancing adhesion, promoting the development of a functional microbial ecosystem, and creating an EPS gradient within the FPUS bio-carrier. This differential distribution of enzymes was established to significantly boost biocatalysis activity reaching 400 U/g VSS.

Strategic analysis on development of simultaneous adsorption and catalytic biodegradation over advanced bio-carriers for zero-liquid discharge of industrial wastewater.

With rapid industrial development, millions of tons of industrial wastewater are produced that contain highly toxic, carcinogenic, mutagenic compounds. These compounds may consist of high concentration of refractory organics with plentiful carbon and nitrogen. To date, a substantial proportion of industrial wastewater is discharged directly to precious water bodies due to the high operational costs associated with selective treatment methods. For example, many existing treatment processes rely on activated sludge-based treatments that only target readily available carbon using conventional microbes, with limited capacity for nitrogen and other nutrient removal. Therefore, an additional set-up is often required in the treatment chain to address residual nitrogen, but even after treatment, refractory organics persist in the effluents due to their low biodegradability. With the advancements in nanotechnology and biotechnology, novel processes such as adsorption and biodegradation have been developed, and one promising approach is integration of adsorption and biodegradation over porous substrates (bio-carriers). Regardless of recent focus in a few applied researches, the process assessment and critical analysis of this approach is still missing, and it highlights the urgency and importance of this review. This review paper discussed the development of the simultaneous adsorption and catalytic biodegradation (SACB) over a bio-carrier for the sustainable treatment of refractory organics. It provides insights into the physico-chemical characteristics of the bio-carrier, the development mechanism of SACB, stabilization techniques, and process optimization strategies. Furthermore, the most efficient treatment chain is proposed, and its technical aspects are critically analysed based on updated research. It is anticipated that this review will contribute to the knowledge of academia and industrialist for sustainable upgradation of existing industrial wastewater treatment plants.

Revisiting China's domestic greenhouse gas emission from wastewater treatment: A quantitative process life-cycle assessment.

The wastewater treatment industry could alleviate water pollution but consume a large amount of energy and resources. China has over 5000 centralized domestic wastewater treatment plants and produces an unignorable amount of greenhouse gases (GHG). By considering the wastewater treatment, wastewater discharge, and sludge disposal processes, and employing the modified process-based quantification method, this study quantifies wastewater treatment's on-site and off-site GHG emissions across China. Results showed that the total GHG emission was 67.07 Mt CO2-eq in 2017, with approximately 57% of on-site emissions. The top seven cosmopolis and metropolis (top 1%) emitted nearly 20% of the total GHG emission, while their emission intensity was relatively low due to the huge population. This means that a high urbanization rate may be a feasible way to mitigate GHG emissions in the wastewater treatment industry in the future. Furthermore, GHG reduction strategies can also focus on process optimization and improvement at WWTPs as well as the nationwide promotion of onsite thermal conversion technologies for sludge management.

Longitudinal changes in blood pressure are preceded by changes in albuminuria and accelerated by increasing dietary sodium intake.

BACKGROUND: Dietary sodium is a well-known risk factor for cardiovascular and renal disease; however, direct evidence of the longitudinal changes that occur with aging, and the influence of dietary sodium on the age-associated alterations are scarce. METHODS: C57BL/6 mice were maintained for 13 months on a low (LS, 0.02 % Na+), normal (NS, 0.3 % Na+) or high (HS, 1.6 % Na+) salt diet. We assessed 1) the longitudinal trajectories for two markers of cardiovascular and renal dysfunction (blood pressure (BP) and albuminuria), as well as hormonal changes, and 2) end-of-study cardiac and renal parameters. RESULTS: The effect of aging on BP and kidney damage did not reach significance levels in the LS group; however, relative to baseline, there were significant increases in these parameters for animals maintained on NS and HS diets, starting as early as month 7 and month 5, respectively. Furthermore, changes in albuminuria preceded the changes in BP relative to baseline, irrespective of the diet. Circulating aldosterone and plasma renin activity displayed the expected decreasing trends with age and dietary sodium loading. As compared to LS - higher dietary sodium consumption associated with increasing trends in left ventricular mass and volume indices, consistent with an eccentric dilated phenotype. Functional and molecular markers of kidney dysfunction displayed similar trends with increasing long-term sodium levels: higher renovascular resistance, increased glomerular volumes, as well as higher levels of renal angiotensin II type 1 and mineralocorticoid receptors, and lower renal Klotho levels. CONCLUSION: Our study provides a timeline for the development of cardiorenal dysfunction with aging, and documents that increasing dietary salt accelerates the age-induced phenotypes. In addition, we propose albuminuria as a prognostic biomarker for the future development of hypertension. Last, we identified functional and molecular markers of renal dysfunction that associate with long-term dietary salt loading.

Accumulation of high concentration fluoride in the Ulungur Lake water through weathering of fluoride containing rocks in Xinjiang, China.

Fluoride is a potential contaminant at high concentrations when used for drinking due to its adverse human health effects. The Ulungur Lake in Xinjiang, China has a long history of high fluoride concentration in lake water, but the mechanism leading to such high concentrations of fluoride is still unclear. In this study we evaluate the fluoride concentration in different water bodies and upstream rock formations in the Ulungur watershed. The result show that fluoride concentration in the Ulungur Lake water fluctuates around 3.0 mg L-1, although the fluoride concentrations in the feeding rivers and groundwater are all lower than 0.5 mg L-1. A mass balance model is developed for water, fluoride, and total dissolved solid in the lake, and the model explains why the concentration of fluoride in the lake water is higher than those in river and ground water. Bedrock compositions are measured from nearby formations which confirm the potential of these rocks to release fluoride into water bodies through water-rock interactions. The whole-rock concentrations of fluoride are in the range of 0.4-2.4 g kg-1 and the water-soluble concentrations of fluoride in the upstream rocks are 0.26-3.13 mg L-1. Biotite and hornblende are identified as the fluorine containing minerals in the Ulungur watershed. The concentration of fluoride in the Ulungur has been declining slowly in recent years due to increased water inflow fluxes, and our mass balance model predicts that the fluoride concentration will eventually reach 1.70 mg L-1 under a new steady state, but it requires about 25-50 years to reach the new steady state. The yearly fluctuation of fluoride concentration in the Ulungur Lake is likely due to changes in water-sediment interactions reflected in changes in lake water pH.

Flood risk assessment by using an interpretative structural modeling based Bayesian network approach (ISM-BN): An urban-level analysis of Shenzhen, China.

With increasingly uncertain environmental conditions under global change, it is rather important for water security management to evaluate the flood risk, which is influenced by the compound effect of severe weather events and strong anthropogenic activities. In this paper, a risk assessment model in the framework of Bayesian network (BN) was proposed through incorporating with the Interpretative Structural Modeling method (ISM), which would produce an integrated ISM-BN model for reliable flood assessments. The ISM is employed to identify the relations among multiple risk factors, and then helps to configure the BN structure to conduct a risk inference. The established model was further demonstrated in Shenzhen city of China to perform an urban-level risk analysis of the flood disaster, and the Enhanced Water Index (EWI) was introduced to derive model parameters for training and verification. The obtained results of risk assessment lead to an accuracy of 76% with the Area Under ROC Curve (AUC) of 0.82, and spatial distribution of risk levels also showed a satisfactory performance. In addition, it was found that the maximum daily rainfall among ten risk factors play a key part in flood occurrence, while the elevation and storm frequency are also sensitive indicators for the study area. Besides, the spatial flood risk map generated under various design rainfall scenarios would contribute to identifying potential areas that are worth paying particular attention. Thus, the developed assessment model would be a useful tool for supporting flood risk governance to achieve reliable urban water security.

Network evolution and risk assessment of the global phosphorus trade.

Phosphorus is an essential element for food production, but the distribution of its global reserve is highly uneven. With the increasing demand for products from all sectors of the phosphorus supply chain, the international phosphorus material trade is becoming increasingly intensive. However, the evolution of the global phosphorus trade network and potential supply risks caused by the trade structure and trade stability are rarely evaluated. By employing the complex network theory, a phosphorus material trade network and a quantitative evaluation index of the trade risk using the external supply risks are proposed to evaluate the supply risk in different countries from 2000 to 2020. According to the network analysis of global phosphorus trades for phosphate rock, phosphorus fertilizer and phosphoric acid, the number of trading countries and trading links has generally increased during the last twenty years. However, the trade structure was found to be significantly altered due to the stresses on the phosphorus reserve scarcity and trade restrictions from countries such as the United States and China. Correspondingly, Morocco has become the largest phosphorus-exporting country since 2016, while India was the world's largest phosphorus-importing country between 2008 and 2015. The topological network characteristics indicate that the phosphorus trade is well connected and more stable over time, but high supply risks were also identified, especially in developing countries in Africa within their phosphate rock and phosphorus fertilizer trade, which might threaten their food security. The obtained findings would be helpful for phosphorus trading countries to manage their trade risks in a timely manner.

Lysine-specific demethylase 1 deficiency modifies aldosterone synthesis in a sex-specific manner.

Biologic sex influences the development of cardiovascular disease and modifies aldosterone (ALDO) and blood pressure (BP) phenotypes: females secrete more ALDO, and their adrenal glomerulosa cell is more sensitive to stimulation. Lysine-specific demethylase 1 (LSD1) variants in Africans and LSD1 deficiency in mice are associated with BP and/or ALDO phenotypes. This study, in 18- and 40-week-old wild type (WT) and LSD1+/- mice, was designed to determine whether (1) sex modifies ALDO biosynthetic enzymes; (2) LSD1 deficiency disrupts the effect of sex on these enzymes; (3) within each genotype, there is a positive relationship between ALDO biosynthesis (proximate phenotype), plasma ALDO (intermediate phenotype) and BP levels (distant phenotype); and (4) sex and LSD1 genotype interact on these phenotypes. In WT mice, female sex increases the expression of early enzymes in ALDO biosynthesis but not ALDO levels or systolic blood pressure (SBP). However, enzyme expressions are shifted downward in LSD1+/- females vs males, so that early enzyme levels are similar but the late enzymes are substantially lower. In both age groups, LSD1 deficiency modifies the adrenal enzyme expressions, circulating ALDO levels, and SBP in a sex-specific manner. Finally, significant sex/LSD1 genotype interactions modulate the three phenotypes in mice. In conclusion, biologic sex in mice interacts with LSD1 deficiency to modify several phenotypes: (1) proximal (ALDO biosynthetic enzymes); (2) intermediate (circulating ALDO); and (3) distant (SBP). These results provide entry to better understand the roles of biological sex and LSD1 in (1) hypertension heterogeneity and (2) providing more personalized treatment.

Bacterial and Microeukaryotic Community Compositions and Their Assembly Processes in Lakes on the Eastern Qinghai-Tibet Plateau.

Bacterial and microeukaryotic community compositions and their assembly processes have remained challenging and remained unclear in lake ecosystems on the Qinghai-Tibet Plateau (QTP). We revealed the diversity and community compositions, driving factors, ecological assembly processes, and co-occurrence networks of bacterial and microeukaryotic communities in water bodies of the eight lake ecosystems across the Eastern QTP. The results demonstrated that the predominant bacteria in most samples were Proteobacteria, with an average relative abundance of 41.78%, whereas the most abundant of microeukaryotes differed among the sample sites. The redundancy analysis revealed that latitude and pH were the most important driving factors in shaping the bacterial and microeukaryotic community compositions. Homogeneous selection (56.40%) was the dominant process in assembling the bacterial communities, whereas dispersal limitation (67.24%) was the major process in governing the microeukaryotic communities. Furthermore, dissolved organic carbon and salinity were the major factors mediating the balance of deterministic and stochastic assembly processes in the bacterial and microeukaryotic communities. Both the bacterial and microeukaryotic community co-occurrence networks exhibited topological features of modularity and non-random topological features. The results offer insights into the mechanisms underpinning bacterial and microeukaryotic diversities and communities in the lake ecosystems on the QTP.

Nucleobase-Bonded Graphene Nanoribbon Junctions: Electron Transport from First Principles.

Carbon and hydrogen bonding constitute the backbone of life; in the form of graphene, possibly functionalized by DNA nucleobases, these hold promise for the programmable assembly of graphene-based nanoelectronic devices. It is still unknown how hydrogen-bonded junctions inherent in such devices will perform as electron transport media. Here, we design nucleobase-bonded graphene nanoribbons and quantify their quantum transport characteristics using first-principles calculations. Pronounced rectifying behavior and negative differential resistance are found, as well as high conductance of certain structures, with the guanine-cytosine junction in general being superior to the adenine-thymine junction. The identified sensitivity of the conductance to atomic details of the interfaces offers initial hints and guidance for experimental realization. The dependence of current on electrostatic gate doping, with an on/off ratio of ∼102, shows the potential of the junction as a field effect transistor.

A long-term reconstructed TROPOMI solar-induced fluorescence dataset using machine learning algorithms.

Photosynthesis is a key process linking carbon and water cycles, and satellite-retrieved solar-induced chlorophyll fluorescence (SIF) can be a valuable proxy for photosynthesis. The TROPOspheric Monitoring Instrument (TROPOMI) on the Copernicus Sentinel-5P mission enables significant improvements in providing high spatial and temporal resolution SIF observations, but the short temporal coverage of the data records has limited its applications in long-term studies. This study uses machine learning to reconstruct TROPOMI SIF (RTSIF) over the 2001-2020 period in clear-sky conditions with high spatio-temporal resolutions (0.05° 8-day). Our machine learning model achieves high accuracies on the training and testing datasets (R2 = 0.907, regression slope = 1.001). The RTSIF dataset is validated against TROPOMI SIF and tower-based SIF, and compared with other satellite-derived SIF (GOME-2 SIF and OCO-2 SIF). Comparing RTSIF with Gross Primary Production (GPP) illustrates the potential of RTSIF for estimating gross carbon fluxes. We anticipate that this new dataset will be valuable in assessing long-term terrestrial photosynthesis and constraining the global carbon budget and associated water fluxes.

Feasibility of using different hydrothermal processes for sewage sludge management in China.

Due to its tremendous volume and severe environmental concern, sewage sludge (SS) management and treatment are significant in China. The recent prohibition (June 2021) of reusing SS as organic fertilizers makes it urgent to develop alternative processes. However, there is currently little research analyzing the applicability of using HP for sewage SS treatment in China. The significant difference in SS composition and the much less land supply in urban areas might invalidate most previous localized suggestions. In this paper, the development of emerging hydrothermal processes (HPs) for SS treatment will be reviewed, focusing on their decomposition mechanisms and the benefits of HPs compared with current SS treatment technologies. The SS volume, composition, and regulatory regime in China will also be evaluated. Those efforts could address the potential SS treatment capacity shortage and provide an opportunity to recover nutrients, organics and energy embedded in SS. The results show that HPs' high investment cost is mainly limited by the process scale, while their operating costs are comparable to incineration. Minimizing equipment erosion, ensuring process safety, and designing a more efficient heat recovery system are recommended for the future commercialization of HPs in China.

Food waste and its embedded resources loss: A provincial level analysis of China.

Food waste is of great concern because it causes severe environmental pollution during disposal and contains many resources that should be well managed. Food waste quantification could clarify the resource value of wasted food and thus help to improve resource utilization efficiency, reduce water eutrophication potential, and reduce greenhouse gas emissions. By considering household food waste, out-of-home food waste, and food delivery waste in rural and urban regions, this paper quantifies the nitrogen, phosphorus, water, and carbon footprint embedded in China's food waste at the provincial level. The results indicate that food waste in China was 56.75 Mt. in 2018. Those wasted food cause 0.54 Mt. loss of phosphorus (5.12% of the phosphorus fertilizer consumption), 3.58 Mt. loss of nitrogen (10.43% of the nitrogen fertilizer consumption), and 120.25 billion tons loss of water (3.06 times of the storage capacity of the Three Gorges Reservoir). If ignoring the greenhouse gas emissions caused by land-use change, the carbon footprint caused by wasted food is 168.07 Mt. CO2eq, accounting for 1.44% of China's total GHG emission. Principal component analysis indicates that the per capita disposable income, urbanization rate, and personal consumption expenditure are critical factors for food waste volume variation in different provinces. Considering China's significant role in the global resource cycling, improving nutrient/resource utilization efficiency along the food supply chain, minimizing food waste volume, and developing economic-effective processes for food waste reuse and recycling are recommended to close the imbalanced resource cycle during the current food waste management.

Modeling the Simultaneous Effects of Particle Size and Porosity in Simulating Geo-Materials.

The particle discrete element method (PDEM) is widely used to simulate rock and soil materials to obtain stress and strain. However, there are three shortcomings: (1) Single sphere or ellipsoids directly replace the soil particles; (2) it treats the diameters of spheres or ellipsoids as the soil particle size; (3) the overlapping particle volume is not deducted in calculating the porosity. Hence, it is difficult for the simulation of the geological body to agree with reality. This research found a rotation calculation model and a pixel counting method to make joint soil particles more accurately simulate geological materials to solve the three shortcomings. The model successfully obtained the gradation curve and porosity of the simulated geological body with joint particles. This research will further enrich and broaden the application prospects of PDEM and provide a reference for scientific research and engineering fields in geological engineering, geotechnical engineering, and petroleum engineering.

Environmental risks of disposable face masks during the pandemic of COVID-19: Challenges and management.

Since the COVID-19 outbreak in early 2020, face mask (FM) has been recognized as an effective measure to reduce the infection, increasing its consumption across the world. However, the large amount of at-home FM usage changed traditional medical waste management practices, lack of improper management. Currently, few studies estimate FM consumption at a global scale, not to say a comprehensive investigation on the environmental risks of FM from a life cycle perspective. Therefore, global FM consumption and its associated environmental risks are clarified in the present study. Our result shows that 449.5 billion FMs were consumed from January 2020 to March 2021, with an average of 59.4 FMs per person worldwide. This review also provides a basis to understand the environmental risk of randomly disposed of FM and highlights the urgent requirement for the attention of FMs waste management to prevent pollution in the near future.

Response of vegetation carbon uptake to snow-induced phenological and physiological changes across temperate China.

Snow cover, which is undergoing significant change along with global climate change, has considerable impacts on the functioning of terrestrial ecosystems. However, how snow cover change affects the vegetation gross primary production (GPP) in temperate regions still requires in-depth exploration. In this study, we investigated how changes in the winter snow depth (WSD) and snowmelt date (SMD) affect spring GPP and summer GPP through their influences on the start date of the growing season (SGS) and the maximum daily GPP (GPPmax), respectively, across temperate China from 2001 to 2015, based on both in situ measurements and satellite products (i.e., GLASS GPP, WestDC snow depth and GLEAM soil moisture). Soil moisture is identified as an important factor in the snow-GPP relationship in temperate China. Since most of temperate China is water-limited, thicker snow cover along with later snowmelt generally resulted in earlier SGS via a significant increase in soil moisture (47% of the area), which lengthened the growth period and enhanced spring carbon uptake in these areas. However, in wetter regions (7% of the area), thicker snow cover with later snowmelt would be more likely to delay the SGS, thus reducing spring GPP. Moreover, although the direct impact mechanisms of snow cover dynamics on summer GPP have not been identified, the snow-induced SGS change was found to have delayed effects on summer photosynthesis capacity, as earlier SGS increased the GPPmax, and thus summer GPP. However, the photosynthesis enhanced by earlier SGS meanwhile increased the plant water consumption, which would bring water stress and reduce summer GPP if the subsequent precipitation is unable to compensate for the water consumption. Our findings on the effects of snow cover change on carbon uptake would provide the basic mechanisms for assessing how future climate change will affect ecosystem productivity.

Impact of physiological and phenological change on carbon uptake on the Tibetan Plateau revealed through GPP estimation based on spaceborne solar-induced fluorescence.

Although gross primary production (GPP) is an essential proxy for reflecting terrestrial ecosystem function, GPP estimation at regional scale on the Tibetan Plateau (TP) is constrained by the lack of ground observations. Moreover, how climate-induced phenological and physiological change further affects carbon uptake in this region remains unclear. In this study, we first estimated GPP at 8-day intervals and a 0.5° resolution from 2007 to 2015 over the TP based on an improved approach and GOME-2 sun-induced fluorescence (SIF) retrievals. The obtained SIF-based GPP coincided well with flux observations and two state of the art GPP products, with a regional carbon uptake of 0.62 ±â€¯0.04 PgC year-1 or 307 ±â€¯22 gC m-2 year-1. With the SIF-based GPP, two phenological indicators (start and end date of the growing season, i.e., SGS and EGS) and one physiological indicator (maximum photosynthesis capacity, GPPmax) were identified and their relative contributions to inter-annual GPP variability were further quantitatively separated using a multiple regression model. Advanced SGS, delayed EGS, and increasing GPPmax can all enhance carbon uptake and a combination of the three indicators can explain 72 ±â€¯20% of GPP inter-annual variability. The response of annual GPP to phenological and physiological variations has significant altitude dependence, as the decline of annual GPP in most of the area is dominated by the GPPmax decline, while the increase of annual GPP in the high-altitude area is dominated by the advanced SGS. The response of all three indicators to both temperature and precipitation variation has great spatial heterogeneity. Our study suggests that remote sensing of SIF can provide a unique opportunity to estimate GPP in regions with a lack of ground observations and that our enhanced understanding of the impact of the climate-induced phenological and physiological change on GPP variability in alpine ecosystems can improve GPP estimation in a changing climate.