Display omitted
•Nitrogen addition decreased DOC concentration across growing season.•Nitrogen addition altered DOM chemical composition in soil pore water.•Compositional transformations of DOM did ...not change its biogenic signals.•Seasonality of biotic/abiotic drivers constrained inner links of DOM characteristics.•Permafrost-induced retention reinforced edaphic DOC as a potential substrate.
Boreal peatlands, a crucial stock of dissolved organic matter (DOM), are susceptible to increased reactive nitrogen (N) inputs. However, the response of DOM characteristics to elevated N availability in these ecosystems is still obscure. Here, we investigated the seasonal variability of DOM quantity and characteristics in surface water and soil pore water after 5-year multi-level N addition (0, 3, 6, and 12 g N m−2 year−1) in a permafrost peatland of Northeast China. In this study, we used the excitation-emission matrix fluorescent spectroscopy combined with fluorescence regional integration, parallel factor analysis, and fluorescence parameters to decipher the effects of N addition on DOM composition, origin, and fate. Irrespective of N addition level, increased N availability reduced dissolved organic carbon concentrations in surface water and soil pore water. However, DOM characteristics are more responsive to N addition in soil pore water than in surface water. Nitrogen addition did not affect DOM composition in surface water, but altered the proportions of tyrosine-, tryptophan-, fulvic acid-, and humic-like DOM in soil pore water. Moreover, the changing trends of DOM composition were diverse during the growing season. In addition, compositional transformations of DOM did not change its biogenic signals, freshness, and humification in both surface water and soil pore water across the growing season. Our results suggest that increased N availability reduces DOM quantity and alters DOM chemical composition, which will improve our understanding of soil organic matter dynamics in boreal peatlands.
Display omitted
•Strong linkages were observed between lake pCO2 and TSI.•Groundwaters contributed an important CO2 source in the karst lake.•Biological mineralization of DOC deciphered the excess ...pCO2 in the drought.•Lake trophic state was converted from eutrophic to mesotrophic.•Over 58% of samples were supersaturated in CO2 in the karst lake.
Trophic state index (TSI) can assess lake trophic status and trace in-situ metabolism, exhibiting a high potential in explaining autochthonous carbon dioxide (CO2) in aquatic environments. However, there remains a knowledge gap in how TSI links to the partial pressure of CO2 (pCO2) generated and consumed in lakes. Here we explored the temporal variations of lake pCO2 and TSI, as well as their linkages in a karst plateau lake. Lake pCO2 ranged from 90.1 to 7169.3 μatm and was significantly high in the post-wet period (2534.3 ± 1637.9 μatm). Over 58% of samples were found to be supersaturated in CO2 with respect to the atmospheric equilibrium (410 μatm). Biological and hydrological processes regulated lake trophic status, resulting in mesotrophic state (30 < TSI < 50) in the post-wet period and eutrophic state (TSI > 50) in the drought and initial-wet periods. Coupled carbonate dissolution and photosynthesis consumed the pCO2, whereas groundwater and respiration contributed the pCO2 in the karst lake. Our results highlighted that lake TSI could decipher trophic status and further partially explain the pCO2 dynamics and sources.
Display omitted
•Contribution variations of various policies to PM2.5 deaths are quantified by period and region.•Carbon and pollution controls can enable 79% to reside in low PM2.5 areas by ...2060.•Population aging could double PM2.5 deaths by 2060 if other factors remain constant.•A joint effort for carbon and pollution could prevent 2.15 million PM2.5 deaths by 2060.•Pollution controls can greatly reduce PM2.5 before 2030, but climate policy becomes crucial after.
To confront the challenges posed by air pollution and climate change, China has undertaken significant initiatives to develop strategies that address both issues concurrently. However, the health benefits of these initiatives have not been clearly articulated. In this study, the dynamic changes in health impacts under air pollution and carbon reduction actions in China are evaluated by employing the latest concentration–response models and projected PM2.5 concentrations under future scenarios. From 2020 to 2060, the enforcement of clean air and climate mitigation policies is expected to increase the percentage of the population living with PM2.5 concentrations meeting the 10 μg/m3 standard by 79 %. Without the implementation of relevant mitigation measures, PM2.5-associated deaths are projected to double due to an aging population. In comparison to the 2060 reference scenario, the joint implementation of clean air and carbon neutrality measures is expected to reduce nationwide PM2.5-associated mortality by 62 %, equivalent to 2.15 (95 % CI: 1.80–2.48) million deaths. Stringent pollution controls are crucial for reducing PM2.5-associated deaths before 2030, after which carbon neutrality actions become increasingly significant from 2030 to 2060. The challenges of mitigating future PM2.5-associated deaths vary greatly across regions, showing a critical response to pollution control and carbon reduction. The research proves the effectiveness of China's future air pollution control and carbon reduction policies in mitigating PM2.5-associated deaths.
Land use pattern is increasingly regarded as an important determinant of environmental quality and regional ecosystems. Understanding the correlation between land use metrics and water quality is ...essential to improve water pollution prediction and provide guidance for land use planning. Here, we examined the land use metrics and water quality parameters (i.e., dissolved oxygen, DO; pH; ammonia nitrogen NH
4
+
-N; permanganate index, COD
Mn
), as well as their relationships in the Yangtze River basin. The DO and pH exhibited the notable spatio-temporal variability, suggesting that anthropogenic land uses (farmland and urban land) greatly impacted riverine water quality. The catchment and riparian scales respectively showed a high potential in explaining water quality in the dry and wet seasons. The land use metrics were tightly linked to water quality in the dry season, indicating that intensive farming activities led to high loadings of agriculture-related chemicals and thus water quality deterioration. Our results provided useful information regarding riverine water quality response to land use metrics at multi-spatial scales.
TiO₂ nanoparticles with surface porosity were prepared by a simple and efficient method and presented for the removal of malachite green (MG), a representative organic pollutant, from aqueous ...solution. Photocatalytic degradation experiments were systematically conducted to investigate the influence of TiO₂ dosage, pH value, and initial concentrations of MG. The kinetics of the reaction were monitored via UV spectroscopy and the kinetic process can be well predicted by the pseudo first-order model. The rate constants of the reaction kinetics were found to decrease as the initial MG concentration increased; increased via elevated pH value at a certain amount of TiO₂ dosage. The maximum efficiency of photocatalytic degradation was obtained when the TiO₂ dosage, pH value and initial concentrations of MG were 0.6 g/L, 8 and 10
mol/L (M), respectively. Results from this study provide a novel optimization and an efficient strategy for water pollutant treatment.
•Coupled carbonate dissolution with photosynthesis controls DIC temporal dynamics.•Carbon sequestration through karst process limits pCO2 levels and CO2 emissions.•Part of dissolved carbon is ...constantly in the cycling of inorganic-organic phases.•Biological metabolism establishes inner links between DIC and DOC components.
Dissolved carbon (DC) deciphers biotic and abiotic processes in aquatic ecosystems, representing a critical component of global carbon cycling. However, underlying drivers of riverine DC dynamics and internal links have yet to be studied. Here, we investigated fluvial physicochemical characteristics, dissolved inorganic carbon (DIC) species, carbon dioxide (CO2) exchange, dissolved organic carbon (DOC) compositions and properties in a karst river system Qijiang, Southwest China. Carbonate dissolution combined with photosynthetic uptake could explain dynamics of DIC species. Carbon sequestration caused low-magnitude of partial pressure of aqueous CO2 (pCO2, 620.3 ± 1028.7 μatm) and water-air CO2 flux (F, 154.3 ± 772.6 mmol/m2/d), yielding an annual CO2 emission of 0.079 Tg CO2/y. Relatively high biological index (BIX, 0.77–0.96 on average) but low humification index (HIX, 0.67–0.78 on average) indicated notable autochthonous processes. Humic-like component was the predominant DOC, accounting for 39.0%-75.2% with a mean of 57.2% ± 6.17%. Meanwhile, tryptophan-like component (5.84% ± 2.31%) was also identified as collective DOC by parallel factor analysis (PARAFAC) across samples. Biological metabolism established internal linkages between DIC and DOC in the karst river system. Our findings highlighted biological process as a determinant for DC cycling in karst aquatic ecosystems.
Display omitted
•Humic- and tryptophan-like are main DOM components, contributing 39-82% and 16-61% to %Fmax.•Partial recalcitrant compounds are degradable with UV humic-like DOM to amino acids.•Large amounts of ...tyrosine-like DOM generate after 56-day of aerobic incubation.•Elevated temperature enhances UV humic-like and labile DOM degradation to CO2.•Biological decomposition of riverine DOM follows a sequential evolution.
Biological degradation of dissolved organic matter (DOM) regulates its structure and fate in river ecosystems. Previous views suggested that labile components were dominantly consumed by microbial metabolism. Here we provide new observations that a part of recalcitrant compounds largely contribute to riverine DOM biodegradation. The excitation-emission matrix fluorescent spectroscopy combined with peak picking and parallel factor analysis are used to explore component variability during DOM incubation. Humic-like and tryptophan-like DOM are the primary components of riverine DOM, with proportion contributions of 39%–82% and 16%–61% for % of the maximum fluorescence intensity, respectively. After 56 days of aerobic incubation in the dark, large amounts of tyrosine-like DOM generation are observed. Elevated temperature enhances the decomposition of ultraviolet humic-like substance and further stimulates labile DOM bio-mineralization into carbon dioxide. Meanwhile, averaged proportions of amino acid compositions (peak B and T) markedly increase (p < 0.05) as the humic-like compositions (peak A, M and C) decrease after DOM incubation, suggesting incomplete degradation of refractory DOM from high-molecular to low-molecular weight compounds. The findings support the new notion of the continuous DOM biodegradation in a mode as “steps by steps”, contributing to a new understanding of carbon cycling for the UN Sustainable Development Goal.
Display omitted
Display omitted
•Labile DOC was rapidly depleted from the tributaries to the main stem.•Initial optical properties reflected the DOM bioavailability in rivers.•Recalcitrant DOMs were synchronously ...consumed and produced during incubations.•Optical properties traced the DOM biodegradation in the Longchuan River.•The %BDOC:DOC exhibited the tight linkages with the optical properties.
The optical properties can characterize the chemical composition, bioavailability and origins of dissolved organic matter (DOM), and thus indicate its biodegradability in natural waters. However, there remains a large gap in how DOM optical properties (UV–visible and fluorescence spectra) trace and predict the dissolved organic carbon biodegradation (%BDOC) in river systems. Over a 56-day laboratory incubation experiment, we examined the variations of %BDOC and DOM optical properties in a headwater tributary of the upper Yangtze River. We found that DOC biodegradability was significantly higher in the tributaries (20 °C: 38.9 ± 19.8%; 30 °C: 58.6 ± 19.5%) than that in the main stem (20 °C: 26.1 ± 18.2%: 30 °C: 41.8 ± 16.3%) (p < 0.001). The %BDOC, exhibiting coincident peaks in the agricultural regions and troughs in the ecologically fragile regions, increased by a factor of two-fold with a temperature gradient of 10℃. The optical properties SUVA254 and S275-295 decreased, while the S350-400, FI and BIX increased after the incubations, implying the synchronous biodegradation and production of young DOMs via microbial respiration. The %BDOC:DOC tightly linked to a254, S275-295, S350-400 and BIX, illustrating that optical properties could predict the riverine %BDOC. The findings demonstrated that optical properties could be regarded as the useful tracers of DOM biodegradation in river systems.
Display omitted
•High DOC biodegradation (51.6 ± 19.8%) was observed in the headwater rivers.•Riverine Q10 values (mean 2 ± 1.7) are highly variable in the Dry-hot Valley Region.•Aromatic and lignin ...fractions were incompletely degraded after 56-day incubations.•Elevated incubation temperature boosted the biodegradability of recalcitrant DOMs.•The DOC biodegradation was negatively correlated with the DOC:TDP ratio.
Aquatic carbon (C) loss is mostly driven by in-situ mineralization of dissolved organic carbon (DOC) and leads to autonomous carbon dioxide (CO2) emissions to the atmosphere. However, limited studies have examined the biodegradability of riverine DOC, especially for the initial trophic controls of DOC biodegradation (%BDOC) and variations in dissolved organic matter (DOM) chemical composition. In this study, we employed a laboratory incubation experiment to determine the riverine %BDOC, temperature sensitivity (Q10 value), nutrients and DOM optical properties in a subtropical river in the Dry-hot Valley Region. We observed the %BDOC at 30 °C (52 ± 19.8%) was significantly higher than that at 20 °C (34 ± 19.9%) with an average Q10 value of 2 ± 1.7. Decreases in a254, a350 values indicated that the aromatic and lignin fractions were decomposed, while increases in E2:E3 and decreases in E4:46 values suggested that large molecular DOMs were incompletely degraded and accumulated after 56-day incubations. The %BDOC was negatively correlated with the DOC:TDP ratio, which suggested that P availability was a dominant control in aquatic microbial respiration. Our results conclude that temperature and trophic status regulate biodegradability of DOC, and also stimulate the incomplete degradation of recalcitrant fraction in DOMs.
The impact of land use metrics on watershed water quality is scale-dependent on a seasonal - spatial basis. Exploring the associations between land use metrics and riverine water quality provides ...useful information for effective land use planning for water quality security, whilst, these relationships remain poorly understood. 94 water samples covering entire tributaries in the Three Gorges Reservoir Area were collected and analyzed over the time period of 2015–2016, and consequently, multivariate statistics and empirical models were used for understanding the associations between land use metrics and water quality across multi-scales. Analysis of variance (ANOVA) revealed significant spatial differences in water temperature (WT), potential of hydrogen (pH), dissolved oxygen (DO), total nitrogen (TN), total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), TDN/TDP, nitrate nitrogen (NO3−-N), ammoniacal nitrogen (NH4+ -N) and permanganate index (CODMn). Meanwhile, Oxidation-Reduction Potential (ORP), electrical conductivity (EC), DO, TN, TDN, TP, TDP, NO3−-N, NH4+-N and CODMn generally appeared higher values in the dry season. Redundancy analysis (RDA) showed that the total explained variation of land use metrics on overall water quality was slightly stronger at catchment scale than at 100 m and 500 m buffer scales. The influence of land use metrics on water quality was a little stronger in the dry season than the wet season, but there were multi-spatial scale effects of different land use metrics. Our results can provide important information in land use planning and making multiple scales measures for water quality conservation.
Display omitted
•Multi-scale land use effects on seasonal water quality in TGR Area are examined.•Water quality is better predicted by land use metrics in dry season than wet season.•Water quality is better predicted by land use metrics in catchment than in buffer.•Predictors of land use metrics are variable resulting from different scale effects.•Land use metrics on whole water quality show slightly multi-scale variations.
PDF
