Urbanization significantly increases greenhouse gas emissions from a subtropical headwater stream in Southeast China.

Streams are disproportionately significant contributors to increases in greenhouse gas (GHG) effluxes in river networks. In the context of global urbanization, a growing number of streams are affected by urbanization, which has been suggested to stimulate the water-air GHG emissions from fluvial systems. This study investigated the seasonal and longitudinal profiles of GHG (N2O, CH4, and CO2) concentrations of Jiuxianghe Stream, a headwater stream undergoing urbanization, and estimated its GHG diffusive fluxes and global warming potentials (GWPs) using the boundary layer method. The results showed that N2O, CH4, and CO2 concentrations in Jiuxianghe Stream were 0.45-7.19 µg L-1, 0.31-586.85 µg L-1, and 0.16-11.60 mg L-1, respectively. N2O, CH4, and CO2 concentrations in the stream showed 4.55-, 23.70-, and 7.68-fold increases from headwaters to downstream, respectively, corresponding to the forest-urban transition within the watershed. Multiple linear regression indicated that NO3--N, NH4+-N, and DOC:NO3--N accurately predicted N2O and CO2 concentrations, indicating that N nutrients were the driving factors. The Jiuxianghe Stream was a source of atmospheric GHGs with a daily GWP of 7.31 g CO2-eq m-2 d-1 on average and was significantly positively correlated with the ratio of construction land and forest in the sub-watershed. This study highlights the critical role of urbanization in amplifying GHG emissions from streams, thereby augmenting our understanding of GHG emissions from river networks. With global urbanization on the rise, streams experiencing urbanization are expected to make an unprecedentedly significant contribution to riverine GHG budgets in the future.

Anthropogenic Activities Generate High-Refractory Black Carbon along the Yangtze River Continuum.

Combustion-driven particulate black carbon (PBC) is a crucial slow-cycling pool in the organic carbon flux from rivers to oceans. Since the refractoriness of PBC stems from the association of non-homologous char and soot, the composition and source of char and soot must be considered when investigating riverine PBC. Samples along the Yangtze River continuum during different hydrological periods were collected in this study to investigate the association and asynchronous combustion drive of char and soot in PBC. The results revealed that PBC in the Yangtze River, with higher refractory nature, accounts for 13.73 ± 6.89% of particulate organic carbon, and soot occupies 37.53 ± 11.00% of PBC. The preponderant contribution of fossil fuel combustion to soot (92.57 ± 3.20%) compared to char (27.55 ± 5.92%), suggested that fossil fuel combustion is a crucial driver for PBC with high soot percentage. Redundancy analysis and structural equation modeling confirmed that the fossil fuel energy used by anthropogenic activities promoting soot is the crucial reason for high-refractory PBC. We estimated that the Yangtze River transported 0.15-0.23 Tg of soot and 0.15-0.25 Tg of char to the ocean annually, and the export of large higher refractory PBC to the ocean can form a long-term sink and prolong the residence time of terrigenous carbon.

Sediment record in pollution, toxicity risk, and source assignment of polycyclic aromatic hydrocarbons (PAHs) in Erhai Lake, Southwest China.

Surface sediments and sediment core had been collected from Erhai Lake, Southwest China to study the concentrations, toxicity risks, and sources of polycyclic aromatic hydrocarbons (PAHs). The average concentrations of Σ16PAHs, seven carcinogenic PAHs (carPAHs), and carcinogenic toxic equivalents (TEQcar) in the surface sediments and sediment core were 1634.50 ± 488.56 ng g-1 and 436.72 ± 128.17 ng g-1, 67.18-293.65 ng g-1 and 91.07-265.90 ng g-1, and 34.89 ± 13.17 ng g-1 and 36.99 ± 7.52 ng g-1, respectively. The Σ16PAHs and carPAHs concentrations in surface sediments were higher in the southern lake. The Σ16PAHs and TEQcar in the sediment core peaked in the 2010s and 1980s. The spatiotemporal variations in TEQcar and carPAHs were similar. Positive matrix factorization revealed that traffic emissions contributed 35.71 % of the TEQcar, whereas coal and biomass combustion contributed 12.89 % in the surface sediments. The contribution of gasoline and fossil fuel to TEQcar significantly increased from 19.2 % (1890s) to 66.5 % (1990s), that of benz[a]pyrene (coal combustion) decreased, and those of benz[b]fluoranthene and indeno[1,2,3-cd]pyrene (petroleum combustion and traffic emissions) increased from 1.92 % to 3.93 % and from 1.54 % to 2.52 % in the sediment cores, respectively, owing to changes in energy consumption.

Nonhomologous Black Carbon Decoupled Char and Soot Sequestration Based on Stable Carbon Isotopes in Tibetan Plateau Lake Sediment.

Combustion-derived black carbon (BC) is an important component of sedimentary carbon pool. Due to different physicochemical properties, determining the source of char and soot is crucial for BC cycling, especially for nonhomologous char and soot in the Tibetan Plateau (TP). This study analyzed the sequestration and source of BC, char, and soot in the Dagze Co (inner TP) sediment core via the content and δ13C, revealing the biomass and fossil fuel driving on nonsynchronous char and soot and their response to local anthropogenic activities and atmospheric transmission. The results showed that BC concentration increased from 1.19 ± 0.35 mg g-1 (pre-1956) to 2.03 ± 1.05 mg g-1 (after 1956). The variation of char was similar to BC, while nonhomologous growth was detected in char and soot (r = 0.29 and p > 0.05). The source apportionment showed that biomass burning for 71.52 ± 10.23% of char and promoted char sequestration. The contribution of fossil fuel combustion to soot (46.67 ± 14.07%) is much higher than char (28.48 ± 10.23%). Redundancy analysis confirmed that local anthropogenic activities significantly influenced BC burial and atmospheric transport from outside TP-regulated BC burial. The contribution of biomass and fossil fuels to nonsynchronous char and soot is conducive to understanding the anthropogenic effect on BC burial in the TP.

Polycyclic aromatic hydrocarbons in remote lakes from the Tibetan Plateau: Concentrations, source, ecological risk, and influencing factors.

Polycyclic aromatic hydrocarbons (PAHs) have received worldwide attention due to their potential teratogenic, persistent, and carcinogenic characteristics. In this study, the PAHs concentrations in two dated sediment cores taken from central Tibetan Plateau (TP) were analyzed to study the deposition history, potential sources, ecological risks, and influencing factors. Total concentration of PAHs (∑PAHs) ranged from 50.0 to 195 ng g-1 and 51.9-133 ng g-1 in sediments of Pung Co (PC) and Dagze Co (DZC), respectively. 2-3-ring PAHs were dominant in the two lake sediments, accounting for an average of 77.5% and 80.1%, respectively. The historical trends of ∑PAHs in the two lakes allowed to distinguish three periods, namely, relative stability before the 1950s, a gradual increase between the 1950s and the 1990s, and then a decline to the present-day. In addition, the trend in the concentration level of each PAH composition was consistent with ∑PAHs before the 1990s, while they exhibited different trends since the 1990s, which may be the result of a combination of anthropogenic activities and climate change in recent years, whereas before the 1990s the PAH profile was mainly influenced by atmospheric deposition. The results of source apportionment examined according to diagnostic ratios and positive matrix factorization were consistent and revealed that PAHs were primarily derived from biomass and coal combustion. Significant correlations between PAHs and organic carbon (OC) indicate that OC might be a key factor influencing the concentration of PAHs in sediments. The ecological risk assessment demonstrated that PAHs in TP sediments occurred at a low risk level. Results of this study could be helpful to develop a deeper insight into the deposition history of PAHs in remote lakes of the TP region and explore the response of these variations to climate change and human activities.

Coal combustion facilitating faster burial of char than soot in a plateau lake of southwest China.

Black carbon (BC) is a retarder in carbon cycle, and the proportion of char and soot in BC restricts the significance of BC as a sink in carbon cycle. Tracing the sources of char and soot is helpful for in-depth understanding the anthropogenic-driven burial and pattern of BC, and is crucial for regulating emissions of BC and impact of BC on carbon cycle/climate change. This study investigated source-driven BC via the concentration and δ13C of BC (char and soot) in a Plateau lake sediment. The burial rate of BC (mean: 6.42 ± 5.09 g m-2 yr-1) showed an increasing trend (3.7 times after 1977 compared with before), and the growth rate of char (4.1 times) was faster than soot (2.5 times). The source trace results, showing faster growth of coal combustion ratio in char (increased 21% after 1980 compared with before) than soot (13%), proved that coal combustion promoted faster growth of char in BC. Redundancy analysis confirmed that more low-temperature utilization of coal urged a stronger driving force for char than soot, which caused BC to have lower aromatic content and higher reactivity in organic carbon pool from the past to present, further impact the effects of BC on carbon cycle.

Stable carbon isotopes trace the effect of fossil fuels on fractions of particulate black carbon in a large urban lake in China.

Black carbon (BC), the highly recalcitrant aromatic carbonaceous from the incomplete combustion of fossil fuel and biomass, is an important carbon sink in carbon cycle. Char and soot, the main components of BC, have significantly different origin and physicochemical characteristics (particle sizes and resultant transportability). The limited understanding of char and soot sources leads to poor insight into the effect of BC on carbon cycle. Sources of char and soot were investigated in this study using stable carbon isotopes to study the effect of BC on the organic carbon pool in a lake, thereby improving the knowledge of lacustrine carbon cycling. The concentration of BC in Taihu Lake ranged from 0.0 to 0.7 mg·L-1and accounted for 10.9 ± 4.7% of the particulate organic carbon. The spatial-mean δ13C values of BC, char, and soot were -23.2 ± 2.0‰, -23.5 ± 2.2‰, and -22.9 ± 1.6‰, respectively. The BC in water was primarily derived from fossil fuels (66.0 ± 9.3%), with liquid fossil fuel accounting for 48.2 ± 13.2% of the BC. The contribution of liquid fossil fuel to soot (49.3%) was much higher than that to char (36.1%); correspondingly, the contributions of biomass and coal to soot (29.2% and 21.5%) were lower than those to char (38.1% and 25.8%). The contribution of liquid fossil fuel combustion to organic carbon (OC), char, and soot gradually increased from 31.9% to 49.3%. Biomass and coal combustion primarily contributed to char (38.1% and 25.8%) and OC (37.5% and 30.6%). The source apportionment of BC, char, and soot revealed the influence of anthropogenically driven BC, char, and soot on the lake and, by extension, to the global carbon cycle.

Spatial variation of particulate black carbon, and its sources in a large eutrophic urban lake in China.

Black carbon (BC), characterized by high aromaticity and stability, has been recognized as a substantial fraction of the carbon pool in soil and sediment. The effect of BC on the particulate organic carbon (POC) pool in lake water, which is an important medium of carbon transmission and transformation, has not been thoroughly studied. The investigations of BC composition and distribution, POC, polycyclic aromatic hydrocarbons (PAHs), and stable carbon and nitrogen isotopes were conducted in a eutrophic urban lake, Taihu Lake, which is the third largest freshwater lake in China. The results indicate that the BC is composed of 55 ± 12% char and 45 ± 12% soot and accounted for 12 ± 6% of POC (the maximum value is 31%). The comparatively high levels of BC and char are distributed in the northern Taihu Lake, especially in Meiliang Bay (0.72 ± 0.38 mg L-1 and 0.45 ± 0.24 mg L-1). The distribution of soot presents a declining trend from the lakeshore to the central lake, particularly in the northern, western, and southern lakes. Source apportionment results from positive matrix factorization of PAHs suggest that consumption of fossil fuel (79 ± 20%) is the dominant source of BC, which agrees with the low ratio of char/soot (1.41 ± 0.71) and relatively depleted δ13C. The covariation of BC and PAHs and terrestrial dissolved organic carbon indicate that the effect of terrestrial input significantly regulates the distribution of BC in Taihu Lake, which is reflected in the high BC value along the lakeshore.

Anthropogenic-Driven Alterations in Black Carbon Sequestration and the Structure in a Deep Plateau Lake.

The continuous flux of organic carbon (OC) from terrestrial ecosystems into inland water is an important component of the global carbon cycle. The buried OC pool in inland water sediments is considerable, and black carbon (BC) is a significant contributor to this OC pool because of the continuous growth in BC emissions. Therefore, determining the effect of BC on total OC burial and variations in the structure of BC during the burial process will contribute significantly to our understanding of lacustrine carbon cycling. This study investigated BC burial and its structural variations in response to anthropogenic drivers using four dated sedimentary cores from a deep plateau lake in China. The BC burial rate rose from 0.96 ± 0.64 g·m-2·y-1 (mean of sedimentary cores pre-1960s) to 4.83 ± 1.25 g·m-2·y-1 (after 2000), which is a 5.48 ± 2.12-fold rise. The increase of char was similar to those of BC. The growth rate of soot was 7.20 ± 4.30 times, which is higher than that of BC and char, increasing from 0.12 ± 0.08 to 0.64 ± 0.23 g·m-2·y-1. There was a decreasing trend in the ratio of char and soot at a mean rate of 62.8 ± 6.46% (excluding core 3) in relation to increased fossil fuel consumption. The contribution of BC to OC burial showed a significant increasing trend from the past to the present, particularly in cores 3 and 4, and the mean contribution of the four cores was 11.78 ± 2.84%. Source tracer results from positive matrix factorization confirmed that the substantial use of fossil fuels has promoted BC burial and altered the BC structure. This has resulted in BC with a higher aromatic content in the lake sediment, which exhibits reduced reactivity and increased stability. The strong correlation between BC and allochthonous total OC indicates that the input pathways of the buried BC in this plateau lake sediment were terrestrial surface processes and not atmospheric deposition.

Rapid photodegradation of terrestrial soil dissolved organic matter (DOM) with abundant humic-like substances under simulated ultraviolet radiation.

Solar ultraviolet (UV) radiation exhibits a significant degradation for dissolved organic matter (DOM) in natural water ecosystems. However, research on photodegradation process of terrestrial components (e.g., humic-like substances) of DOM are limited due to drastic water dilution and rapid degradation. Here, photochemical degradation of terrestrial soil DOM with abundant humic-like substances from different land use were investigated by utilizing spectral technologies. Simulated UV radiation caused obvious losses on concentration, component structures, and fluorescence characteristic of soil DOM samples. The correlations between absorption specific parameters (a280, SUVA254, and SR) and dissolved organic carbon (DOC) were especially pronounced (p < 0.05), which could be used as valid indicators to determine changes in DOM composition and molecular size during photobleaching process. The decreases of DOM fluorescence intensity were corresponded to first-order kinetic and half-life reactions. The greatest reduction on fluorescence intensity (31.56-81.97%) belonged to peak C (i.e., humic-like substances). Overall, DOM from forest and grass soil ecosystems was more easily photochemical degraded than anthropogenic soil DOM. Enhancive contribution of fresh DOM formed by photodegradation increased autochthonous characteristic and bioavailable nutrition by increasing biological index (BIX) values and ammonia nitrogen (NH4+-N) concentration. The slight microbial decomposition effects on DOM happened in unsterilized dark condition. Our findings provided insights for understanding the rapid photodegradation processes of composition and structure of terrestrial DOM. Graphical abstract.

[Determination of 9 residual acrylic monomers in acrylic resins by gas chromatography-mass spectrometry coupled with microwave assisted extraction].

A reliable gas chromatography-mass spectrometry (GC-MS) method was developed for the determination of 9 residual acrylic monomers (methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl acrylate, butyl methacrylate, styrene, acrylic acid and methacrylic acid) in acrylic resins. Solid resin was precipitated with methanol after microwave assisted extraction with ethyl acetate for 30 min, and liquid resin was diluted with methanol directly. The nine acrylic monomers got a good separation within 20 min on a DB-WAX column. The limits of quantification (LOQs, S/N = 10) of the method were in the range of 1-10 mg/kg for liquid resin and 3-50 mg/kg for solid resin. The calibration curves were linear within 1-500 mg/L range with correlation coefficients above 0. 995. The recoveries ranged from 84.4% to 108.6% at five spiked levels. The sensitivity, recovery and selectivity of the method can fully meet the requirements of practical work.